Glossary of space

ACRIMSAT The Active Cavity Radiometer Irradiance Monitor (ACRIM) Satellite Mission is a NASA mission to measure Total Solar Irradiance (TSI) over a five-year period. The instrument, third in a series of long-term solar-monitoring tools built for NASA by the Jet Propulsion Laboratory, will continue to extend the database first created by ACRIM I, which was launched in 1980 on the Solar Maximum Mission (SMM) spacecraft. ACRIM II followed on the Upper Atmosphere Research Satellite (UARS) in 1991. See ACRIMSAT Fact Sheet
Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) ASTER is an imaging instrument that will fly on Terra as part of NASA's Earth Observing System (EOS). ASTER will be used to obtain detailed maps of land surface temperature, emissivity, reflectance and elevation. See ASTER Web Site.
Advanced Very High Resolution Radiometer (AVHRR) A five-channel scanning instrument that quantitatively measures electromagnetic radiation, flown on NOAA environmental satellites. AVHRR remotely determines cloud cover and surface temperature. Visible and infrared detectors observe vegetation, clouds, lakes, shorelines, snow, and ice. See TIROS.
Ames Research Center (ARC) Located at Moffett Field, California, ARC is active in aeronautical research, life sciences, space science, and technology research. The Center houses the world's largest wind tunnel and the world's most powerful supercomputer system. ARC Web Site
Arctic circle The parallel of latitude that is approximately 66.5 degrees north of the equator and that circumscribes the northern frigid zone.
Astronomical Unit (AU) The distance from the Earth to the sun. On average, the sun is 149,599,000 kilometers from Earth.
Atmospheric Radiation Measurements Program (ARM) U.S. Department of energy program for the continual, ground-based measurements of atmospheric and meteorological parameters over approximately a ten-year period. The program will study radiative forcing and feedbacks, particularly the role of clouds. The general program goal is to improve the performance of climate models, particularly general circulation models of the atmosphere.
Boreal Ecosystem-Atmosphere Study (BOREAS) A global change project to study and understand the interaction between the boreal forest biome and the atmosphere. See also: Introduction to BOREAS BOREAS Web Site
Clarke Belt A belt 22,245 miles (35,800 kilometers) directly above the equator where a satellite orbits the Earth at the same speed the Earth is rotating. Science fiction writer and scientist Arthur C. Clarke wrote about this belt in 1945, hence the name.
Clouds and the Earth's Radiant Energy System (CERES) CERES measures both solar-reflected and Earth-emitted radiation from the top of the atmosphere to the surface. It also determines cloud properties including the amount, height, thickness, particle size, and phase of clouds using simultaneous measurements by other instruments. These measurements are critical for understanding cloud-radiation climate change and improving the prediction of global warming using climate models. CERES is flying, or will fly, on the Tropical Rainfall Monitoring Mission (TRMM), Terra, and EOS-PM. See CERES Web Site.
Coastal Zone Color Scanner (CZCS) The first spacecraft instrument devoted to measurement of ocean color. Although instruments on other satellites have sensed ocean color, their spectral bands, spatial resolution, and dynamic range were optimized for geographical or meteorological use. In the CZCS, every parameter is optimized for use over water to the exclusion of any other type of sensing. The CZCS flew on the Nimbus-7 spacecraft.
Defense Meteorological Satellite Program (DMSP) A U.S. Air Force meteorological satellite program with satellites circling in sun-synchronous orbit. Imagery is collected in the visible- to near-infrared band (0.4 to 1.1 micrometers) and in the thermal-infrared band (about 8 to 13 micrometers) at a resolution of about three kilometers. While some of the data is classified, most unclassified data is available to civilian users.
Distributed Active Archive Center (DAAC) There are eight DAACs located around the United States that are tasked with processing, storing, and distributing satellite remote sensing data for NASA and other agencies. See NASA DAACs web site
Doppler radar The weather radar system that uses the Doppler shift of radio waves to detect air motion that can result in tornadoes and precipitation, as previously-developed weather radar systems do. It can also measure the speed and direction of rain and ice, as well as detect the formation of tornadoes sooner than older radars.
EPA (Environmental Protection Agency) U.S. agency that ensures: Federal environmental laws are implemented and enforced effectively; U.S. policy--both foreign and domestic--fosters the integration of economic development and environmental protection so that economic growth can be sustained over the long term; public and private decisions affecting energy, transportation, agriculture, industry, international trade, and natural resources fully integrate considerations of environmental quality; national efforts to reduce environmental risk are based on the best available scientific information communicated clearly to the public; everyone in our society recognizes the value of preventing pollution before it is created; people have the information and incentives they need to make environmentally-responsible choices in their daily lives; and schools and community institutions promote environmental stewardship as a national ethic.
ESA European Space Agency.
Earth Probes Discipline-specific satellites and instruments that will be used by NASA to obtain observations before the launch of EOS spacecraft. Generally smaller than the EOS satellites and instruments, Earth Probes are planned to complement the broad environmental measurements from EOS with highly focused studies in areas such as tropical rainfall (TRMM), ocean productivity (SeaWiFS), atmospheric ozone (TOMS), and ocean surface winds (NSCAT).
Earth Radiation Budget Experiment (ERBE) An experiment to obtain data to study the average radiation budget of the Earth and determine the energy transport gradient from the equator to the poles. Three satellites were flown in different orbits to obtain the data: the Earth Radiation Budget Satellite, ERBS (launched in October 1984), NOAA-9 (launched in December 1984), and NOAA-10 (launched in September 1986). See Television and Infrared Observation (TIROS).
Earth Science Data and Information System (ESDIS) A project that is responsible for providing scientific and other users access to data from NASA's Earth Science Enterprise. The ESDIS Project provides this access through the development and operation of the Earth Observing System (EOS) Data and Information System (EOSDIS).
Earth system science An integrated approach to the study of the Earth that stresses investigations of the interactions among the Earth's components in order to explain Earth dynamics, evolution, and global change.
Earth system The Earth regarded as a unified system of interacting components, including geosphere (land), atmosphere (air), hydrosphere (water and ice), and biosphere (life).
Enhanced Thematic Mapper Plus (ETM +) An eight-band multispectral scanning radiometer onboard the Landsat 7 satellite that is capable of providing high-resolution imaging information of the Earth's surface.
FEMA U.S. Federal Emergency Management Agency.
Fahrenheit Temperature scale designed by the German scientist Gabriel Fahrenheit in 1709, based upon water freezing at 32 degrees Fahrenheit and water boiling at 212 degrees Fahrenheit under standard atmospheric pressure. Compare with centigrade.
Fraction of Photosynthetically Active Radiation (FPAR) Radiation between 400 and 700 nm used by the green canopy in the photosynthetic process.
Gaia hypothesis The hypothesis that the Earth's atmosphere, biosphere, and its living organisms behave as a single system striving to maintain a stability that is conductive to the existence of life.
General Circulation Model (GCM) A global, three-dimensional computer model of the climate system which can be used to simulate human-induced climate change. GCMs are highly complex and they represent the effects of such factors as reflective and absorptive properties of atmospheric water vapor, greenhouse gas concentrations, clouds, annual and daily solar heating, ocean temperatures and ice boundaries. The most recent GCMs include global representations of the atmosphere, oceans, and land surface.
Geographic Information System (GIS) A system for archiving, retrieving, and manipulating data that has been stored and indexed according to the geographic coordinates of its elements. The system generally can utilize a variety of data types, such as imagery, maps. table, etc.
Geostationary Meteorological Satellite (GMS) Japan's geostationary weather satellite.
Glenn Research Center at Lewis Field (GRC) The John H. Glenn Research Center at Lewis Field (formerly known as the Lewis Research Center), located outside Cleveland, Ohio, conducts a varied program of research in aeronautics and space technology. Aeronautical research includes work on advanced materials and structures for aircraft. Space-related research focuses primarily on power and propulsion. Another significant area of research is in energy and power sources for spacecraft, including the Space Station, for which GRC is developing the largest space power system ever designed. GRC Web Site
Gross National Product The total value of all goods and services produced by the people of a given country over a year.
High-Resolution Infrared Radiation Sounder (HIRS) Instrument carried by NOAA polar-orbiting satellites that detects and measures energy emitted by the atmosphere to construct a vertical temperature profile from the Earth's surface to an altitude of about 40 km. Measurements are made in 20 spectral regions in the infrared band.
International Geosphere-Biosphere Programme (IGBP) The International Geosphere-Biosphere Programme (IGBP) is an interdisciplinary scientific activity established and sponsored by the International Council for Science (ICSU). The program was instituted by ICSU in 1986, and the IGBP Secretariat was established at the Royal Swedish Academy of Sciences in 1987 and is focused on acquiring basic scientific knowledge about the interactive processes of biology and chemistry of the earth as they relate to Global Change. See IGBP web site
International System of Units (SI) The International System of Units prescribes the symbols and prefixes shown in the table to form decimal multiples and submultiples of SI units. The following examples illustrate the use of these prefixes: 0.000,001 meters = 1 micrometer = 1°m 1000 meters = 1 kilometer = 1 km 1,000,000 cycles per second = 1,000,000 hertz = 1 megahertz =1 MHz
Intertropical Convergence Zone (ITCZ) A discontinuous belt of thunderstorms paralleling the equator and marking the convergence of the northern and southern hemisphere surface trade winds. See El Niño's Extended Family
Japanese National Space Development Agency (NASDA) The agency reports to the Japanese Ministry of Science and Technology.
Jason-1 Jason-1 is an oceanography mission to monitor global ocean circulation, discover the tie between the oceans and atmosphere, improve global climate predictions, measure sea level rise and monitor events such as El Nino conditions and the Pacific Decadal Oscillation. The Jason-1 satellite carries a radar altimeter and it is a follow-on mission to the highly successful TOPEX/Poseidon mission. It is joint mission between France and USA.The satellite will be launched in late 2000. Jason web site
Jet Propulsion Laboratory (JPL) Located in Pasadena, California, JPL is operated under contract to NASA by the California Institute of Technology. Its primary focus is the scientific study of the solar system, including exploration of the planets with automated probes. Most of the lunar and planetary spacecraft of the 1960s and 1970s were developed at JPL. JPL also is the control center for the worldwide Deep Space Network, which tracks all planetary spacecraft. JPL Web Site
Joint Education Initiative (JEI) The JEI project was developed by USGS, NOAA, NASA, industry, and teachers to enable teachers and students to explore the massive quantities of Earth science data published by the U.S. Government on CD-ROM. JEI encourages a research and analysis approach to science education.
Kelvin The standard unit of thermodynamic temperature. It is defined as 1/273.16 of the temperature of the triple point of water above absolute zero. The symbol for this is K. Kelvin is measured by the same temperature steps as Celsius but is shifted downwards so that 0 degrees K is absolute zero; water freezes at 273 K and boils at 373 K.
Ku-band Radar and microwave band in which the wavelengths vary from 1.67-2.4 cm.
La Niña A period of stronger-than-normal trade winds and unusually low sea-surface temperatures in the central and eastern tropical Pacific Ocean; the opposite of El Niño. See La Niña fact sheet.
Langley Research Center (LaRC) Oldest of NASA's field centers, LaRC is located in Hampton, Virginia, and focuses primarily on aeronautical research. Established in 1917 by the National Advisory Committee for Aeronautics, the Center currently devotes two-thirds of its programs to aeronautics, and the rest to space. LaRC researchers use more than 40 wind tunnels to study improved aircraft and spacecraft safety, performance, and efficiency. LaRC Web Site
Little Ice Age A cold period that lasted from about A.D. 1550 to about A.D. 1850 in Europe, North America, and Asia. This period was marked by rapid expansion of mountain glaciers, especially in the Alps, Norway, and Alaska. There were three maxima, beginning about 1650, about 1770, and 1850, each separated by slight warming intervals.
METEOSAT (METEOrological SATellite) Europe's geostationary weather satellite, launched by the European Space Agency and now operated by an organization called Eumetsat.
Madden-Julian Oscillation A "wave" of disturbed tropical weather that spreads eastward around the globe on a 30-to-60-day cycle, usually beginning in the Indian Ocean. The disturbance brings periods of enhanced tropical rainfall followed by periods of suppressed rainfall, and it also influences cloudiness and sea surface temperature. Although the Madden-Julian Oscillation originates in the tropics, it influences weather in the subtropics and mid-latitudes as well.
Measurements of Pollution in the Troposphere (MOPITT) MOPITT will fly aboard Terra as part of NASA's Earth Observing System(EOS). It is an instrument designed to enhance our knowledge of the lower atmosphere and to particularly observe how it interacts with the land and ocean biospheres. MOPITT is a scanning radiometer employing gas correlation spectroscopy to measure upwelling and reflected infrared radiance in three absorption bands of carbon monoxide and methane.
Meteor The former Soviet Union's series of polar orbiting weather satellites. The Meteor satellites transmit images in a system compatible with the NOAA polar-orbiting satellites.
Methane (CH4) A hydrocarbon that is a greenhouse gas. Methane is produced through anaerobic (without oxygen) decomposition of waste in landfills, animal digestion, decomposition of animal wastes, production and distribution of natural gas and oil, coal production , and incomplete fossil fuel combustion. The atmospheric concentration of methane has been shown to be increasing at a rate of about 0.6% per year and the concentration of about 1.7 parts per million by volume (ppmv) is more than twice its preindustrial value. However, the rate of increase of methane in the atmosphere may be stabilizing.
Moderate-resolution Imaging Spectroradiometer (MODIS) MODIS will fly aboard Terra as part of NASA's Earth Observing System (EOS). It will view the entire surface of the Earth every 1-2 days, making observations in 36 co-registered spectral bands, at moderate resolution (0.25 - 1 km), of land and ocean surface temperature, primary productivity, land surface cover, clouds, aerosols, water vapor, temperature profiles, and fires. See MODIS Web Site.
Montreal Protocol An international agreement to drastically reduce CFC production, the Protocol was adopted in Montreal in 1987. It was significantly strengthened at a subsequent meeting in London in 1990 that called for a complete elimination of CFCs by the year 2000. The agreement was again amended by a Meeting of the Parties in Copenhagen in November 1992. Consumption of controlled substances--such as CFCs and halons--was greatly reduced or eliminated, and many accountability dates were moved forward, often from 1 January 2000 to 1 January 1996.
Mount Pinatubo A volcano in the Philippine Islands that erupted in 1991. The eruption of Mount Pinatubo ejected enough particulate and sulfate aerosol matter into the atmosphere to block some of the incoming solar radiation from reaching Earth's atmosphere. This effectively cooled the planet from 1992 to 1994, masking the warming that had been occurring for most of the 1980s and 1990s.
Multi-angle Imaging Spectro-Radiometer (MISR) MISR will fly aboard Terra as part of NASA's Earth Observing System. It will monitor the monthly, seasonal, and long-term trends in the amount and type of atmospheric aerosol particles, including those formed by natural sources and by human activities; the amount, types, and heights of clouds; and the distribution of land surface cover, including vegetation canopy structure. See MISR Web Site.
Multispectral Scanner (MSS) A line-scanning instrument flown on Landsat satellites that continually scans the Earth in a 185 km. (100 nautical miles) swath. On Landsats 1, 2, 4, and 5, the MSS had four spectral bands in the visible and near-infrared with an IFOV of 80 meters. Landsat-3 had a fifth band in the thermal infrared with an IFOV of 240 meters.
NCDC National Climatic Data Center, located in Asheville, North Carolina. See National Oceanic and Atmospheric Administration.
NESDIS National Environmental Satellite Data and Information Service. See National Oceanic and Atmospheric Administration.
NGDC National Geophysical Data Center, located in Boulder, Colorado. See National Oceanic and Atmospheric Administration.
NODC National Oceanographic Data Center, located in Washington, D.C. See National Oceanic and Atmospheric Administration.
NRA NASA Research Announcement.
NSFNET National Science Foundation NETwork.
NSF National Science Foundation.
National Center for Atmospheric Research (NCAR) Located in Boulder, Colorado, NCAR's mission is to plan, organize, and conduct atmospheric and related research programs in collaboration with universities, to provide state-of-the-art research tools and facilities to the entire atmospheric sciences community, to support and enhance university atmospheric research education, and to facilitate the transfer of technology to both the public and private sectors. See NCAR web site
National Snow and Ice Data Center (NSIDC) The National Snow and Ice Data Center (NSIDC) is an information and referral center supporting polar and cryospheric research. They distribute data and maintain information about snow cover, avalanches, glaciers, ice sheets, freshwater ice, sea ice, ground ice, permafrost, atmospheric ice, paleoglaciology, and ice cores, and also publish reports and a quarterly newsletter and maintain a collection of monographs, technical reports, and journals. See NSIDC web site
National Weather Service (NWS) See National Oceanic and Atmospheric Administration.
Newton's laws of motion Newton's three laws of motion are: 1. Every body continues in a state of uniform motion in a straight line unless acted upon by some external force. 2. The time rate of change of momentum (mass x velocity) is proportional to the impressed force. In the usual case where the mass does not change, this law can be expressed in the familiar form: force = mass x acceleration or F = ma. 3. To every force or action, there is always an equal and opposite reaction.
North Atlantic Oscillation (NAO) A large see-saw in atmospheric mass between the subtropical high located near the Azores and the sub-polar low near Icealand. See Atlantic Rhythms
POES (Polar-orbiting Operational Environmental Satellite) Operated by the National Oceanic and Atmospheric Administration, they are designated 'NOAA satellites.' Included in this group are the current series of TIROS-N satellites, the third-generation polar-orbiting environmental spacecraft operated by NOAA.
R&D Research and Development.
S-band A nominal frequency range from 4 to 2 GHz (7 to 20 cm wavelength) within the microwave (radar) portion of the electromagnetic spectrum. S-band radars are used for medium-range meteorological applications, for example rainfall measurements, as well as airport surveillance and specialized tracking tasks.
SPOT Systeme Pour l'Observation de la Terre. French, polar-orbiting Earth observation satellite(s) with ground resolution of 10 meters. SPOT images are available commercially and are intended for such purposes as environmental research and monitoring, ecology management, and for use by the media, environmentalists, legislators, etc.
Sea-viewing Wide Field-of-View Sensor (SeaWiFS) SeaWiFS is an ocean color sensor to study ocean productivity and interactions between the ocean ecosystems and the atmosphere. See SeaWIFS Web Site.
Shuttle Radar Topography Mission (SRTM) A NASA Space Shuttle mission that used C-band and X-band interferometric synthetic aperture radars (IFSARs) to acquire topographic data over 80% of Earth's land mass (between 60degN and 56degS) between February 11-22, 2000. SRTM web site
Stennis Space Center (SSC) The John C. Stennis Space Center (SSC), located on Mississippi's Gulf Coast, is NASA's prime test facility for large liquid propellant rocket engines and propulsion systems. The main mission of the Center is to support testing, on a regular basis, of the Space Shuttle's main propulsion system. SSC is responsible for a variety of research programs in the environmental sciences and the remote-sensing of Earth resources, weather, and oceans, and is the lead NASA Center for the commercialization of space remote sensing. SSC Web Site
Stratospheric Aerosol & Gas Experiment (SAGE) A NASA experiment to determine the vertical distribution of stratospheric aerosols, ozone, nitrogen oxide, and water vapor on a global scale and to develop a viable, satellite-based, remote sensing technique to measure these gases. SAGE III web site
TOVS TIROS Operational Vertical Sounder. See Television Infrared Operational Satellite (TIROS).
Terra The flagship of the Earth Observing System, a series of spacecraft that represent the next landmark steps in NASA's leadership role to observe the Earth from the unique vantage point of space. Focused on key measurements identified by a consensus of U.S. and international scientists, Terra will enable new research into the ways that Earth's lands, oceans, air, ice, and life function as a total environmental system. See Terra website.
Tracking and Data Relay Satellite System (TDRSS) Tracking and Data Relay Satellite System (TDRSS) An orbiting communications satellite, developed by NASA, used to relay data from satellite sensors to ground stations and to track the satellites in orbit.
Tropospheric Emission Spectrometer A high-resolution infrared spectrometer for monitoring the minor components of the lower atmosphere.
United States Geological Survey (USGS) A bureau of the Department of the Interior. USGS was established in 1879 following several Federally sponsored independent natural resource surveys of the West and Midwest. The Department of the Interior has responsibility for most of our nationally owned public lands and natural resources. The USGS monitors resources such as energy, minerals, water, land, agriculture, and irrigation. The resulting scientific information contributes to environmental-policy decision making and public safety. For example, USGS identifies flood- and landslide-prone areas and maintains maps of the United States.
United States Global Change Research Program (USGCRP) The USGCRP addresses significant uncertainties concerning the natural and human-induced changes to Earth's environment. The USGCRP has a comprehensive and multidisciplinary scientific research agenda. See Global Change Research Program.
Van Allen belts or Van Allen Radiation belts Doughnut-shaped regions encircling Earth and containing high energy electrons and ions trapped in the Earth's magnetic field (the magnetic field has definite boundaries, and is distorted into a tear-drop shape by the solar wind). Explorer I, launched by NASA in 1958, discovered this intense radiation zone. These regions are called the inner and outer Van Allen radiation belts, named after the scientist who first observed them. See magnetosphere.
Vegetation Canopy Lidar (VCL) The first satellite mission of NASA's Earth System Science Pathfinder project that will create the first maps of the three-dimensional structure of vegetation in the world's forests. The VCL lidar holds five lasers that each send 242 pulses per second at the Earth's surface. Each beam covers an area 75 feet across. By spacing the five beams a little over a mile apart, each VCL orbit will sample an area 5 miles across. See VCL fact sheet.
Visible/Infrared Spin Scan Radiometer (VISSR) High-resolution, multi-spectral imaging system flown on the pre-GOES-8 geostationary GOES spacecraft. Similar systems are flown on the METEOSAT and GMS spacecraft.
Walker cell A zonal circulation of the atmosphere confined to equatorial regions and driven principally by the oceanic temperature gradient. In the Pacific, air flows westward from the colder, eastern area to the warm, western ocean, where it acquires warmth and moisture and subsequently rises. A return flow aloft and subsidence over the eastern ocean complete the cell.
X-band A nominal frequency range from 12.5 to 8 GHz (2.4 to 3.75 cm wavelength) within the microwave (radar) portion of the electromagnetic spectrum. X-band is a suitable frequency for several high-resolution radar applications and has often been used for both experimental and operational airborne systems.
absolute zero The temperature at which significant molecular activity stops. Absolute zero is commonly used by scientists who study what happens to things when they become very cold and is measured as 0 degrees Kelvin -- equal to -459 degrees Fahrenheit or -273 degrees Celsius.
absorption The process in which radiant energy is retained by a substance. A further process always results from absorption, that is, the irreversible conversion of the absorbed radiation into some other form of energy within and according to the nature of the absorbing medium. The absorbing medium itself may emit radiation, but only after an energy conversion has occurred.
acceleration Science: in general, any increase in the speed or rate at which some process occur; in technical use acceleration and speed are not synonymous. Mechanics: the vector representing the rate of change in velocity vector over time. It is expressed in meters (or feet) per second per second, and it involves an increase or decrease in speed and a change in direction.
active system (active sensor) A remote-sensing system that transmits its own radiation to detect an object or area for observation and receives the reflected or transmitted radiation. Radar is an example of an active system. Compare with passive system.
advect A horizontal movement of a mass of fluid, such as ocean or air currents. Can also refer to the horizontal transport of something (e.g., pollution, phytoplankton, ice, or even heat) by such movement.
aerosol Particles of liquid or solid dispersed as a suspension in gas.
air mass Large body of air, often hundreds or thousands of miles across, containing air of a similar temperature and humidity. Sometimes the differences between air masses are hardly noticeable, but if colliding air masses have very different temperatures and humidity values, storms can erupt. See front.
air pollution The existence in the air of substances in concentrations that are determined unacceptable. Contaminants in the air we breathe come mainly from manufacturing industries, electric power plants, automobiles, buses, and trucks.
air pressure The weight of the atmosphere over a particular point, also called barometric pressure. Average air exerts approximately 14.7 pounds (6.8 kg) of force on every square inch (or 101,325 newtons on every square meter) at sea level.
albedo The ratio of the outgoing solar radiation reflected by an object to the incoming solar radiation incident upon it.
algae Simple rootless plants that grow in sunlit waters in relative proportion to the amounts of nutrients available. They are food for fish and small aquatic animals, and a factor in eutrophication.
algal blooms Sudden spurts of algal growth due to greatly increased amounts of phosphorus entering the aquatic ecosystem from sewage systems and agricultural fertilizers. Excessive growth of the algae causes destruction of many of the higher links of the food web. Algae that die and sink to the bottom at the end of the growing season stimulate massive growth of bacteria the following year, resulting in depletion of oxygen in the deeper water layers. This may result in fish kills and replacement with less valuable species who may be more tolerant of increased phosphorus levels. Deoxygenation also may cause chemical changes in the mud on the bottom, producing increased quantities of chemicals and toxic gases. All these changes further accelerate the eutrophication (aging) of the aquatic ecosystem.
algorithm A mathematical relation between an observed quantity and a variable used in a step-by-step mathematical process to calculate a quantity. In the context of remote sensing, algorithms generally specify how to determine higher-level data products from lower-level source data. For example, algorithms prescribe how atmospheric temperature and moisture profiles are determined from a set of radiation observations originally sensed by satellite sounding instruments.
alkaline Substance capable of neutralizing acid, with a pH greater than 7.0. See pH.
altimeter An active instrument (see active system) used to measure the altitude of an object above a fixed level. For example, a laser altimeter can measure height from a spacecraft to an ice-sheet. That measurement, coupled with radial orbit knowledge, will enable determination of the topography.
amplitude The magnitude of the displacement of a wave from a mean value. For a simple harmonic wave, it is the maximum displacement from the mean. For more complex wave motion, amplitude is usually taken as one-half of the mean distance (or difference) between maxima and minima.
anaglyph images of the same scene in contrasting colors or from different viewing angles that look three-dimensional when they are superimposed
anemometer Instrument used to measure wind speed, usually measured either from the rotation of wind-driven cups or from wind pressure through a tube pointed into the wind.
anomaly The deviation of (usually) temperature or precipitation in a given region over a specified period from the normal value for the same region. The angular distance of an Earth satellite (or planet) from its perigee (or perihelion) as seen from the center of the Earth (sun).
anthropogenic Made by people or resulting from human activities. Usually used in the context of emissions that are produced as a result of human activities.
anticyclone A high pressure area where winds blow clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. See cyclone, wind.
aphelion The point in its orbit when a planet is farthest from the sun. For more information, see Milutin Milankovitch
apogee On an elliptical orbit path, the point at which a satellite is farthest from the Earth.
aquifer Layer of water-bearing permeable rock, sand, or gravel capable of providing significant amounts of water.
ascending node The point in an orbit (longitude) at which a satellite crosses the equatorial plane from south to north.
atmospheric pressure The amount of force exerted over a surface area, caused by the weight of air molecules above it. As elevation increases, fewer air molecules are present. Therefore, atmospheric pressure always decreases with increasing height. A column of air, 1 square inch in cross section, measured from sea level to the top of the atmosphere would weigh approximately 14.7 lb/in2. The standard value for atmospheric pressure at sea level is: 29.92 inches or 760 mm of mercury 1013.25 millibars (mb) or 101,325 pascals (pa).
atmospheric response variables Variables that reflect the response of the atmosphere to external forcing (e.g., temperature, pressure, circulation, and precipitation).
atmospheric windows The range of wavelengths at which water vapor, carbon dioxide, or other atmospheric gases only slightly absorb radiation. Atmospheric windows allow the Earth's radiation to escape into space unless clouds absorb the radiation. See greenhouse effect.
atoll A coral island consisting of a ring of coral surrounding a central lagoon. Atolls are common in the Indian and Pacific Oceans.
attenuation The decrease in the magnitude of current, voltage, or power of a signal in transmission between points. Attenuation may be expressed in decibels, and can be caused by interference?s such as rain, clouds, or radio frequency signals.
azimuth The direction, in degrees referenced to true north, that an antenna must be pointed to receive a satellite signal (compass direction). The angular distance is measured in a clockwise direction.
backscatter Process by which up to 25% of radiant energy from the sun is reflected or scattered away from the surface by clouds.
band In radio, a continuous sequence of broadcasting frequencies within given limits. In radiometry, a relatively narrow region of the electromagnetic spectrum to which a remote sensor responds; a multispectral sensor makes measurements in a number of spectral bands. In spectroscopy, spectral regions where atmospheric gases absorb (and emit) radiation, e.g., the 15 µm carbon dioxide absorption band, the 6.3 µm water vapor absorption band, and the 9.6 µm ozone absorption band.
bandwidth The total range of frequency required to pass a specific modulated signal without distortion or loss of data. The ideal bandwidth allows the signal to pass under conditions of maximum AM or FM adjustment. (Too narrow a bandwidth will result in loss of data during modulation peaks. Too wide a bandwidth will pass excessive noise along with the signal.) In FM, radio frequency signal bandwidth is determined by the frequency deviation of the signal.
base A substance that forms a salt when it reacts with acid. A base is a substance that removes hydrogen ions (protons) from an acid and combines with them in a chemical reaction.
beamwidth The measure of the 'width' of an antenna pattern, measured in degrees of arc. Generally an antenna with low gain has a wide pattern, receiving signals well from a number of different directions.
bearing The combination of antenna azimuth and elevation required to point (aim) an antenna at a spacecraft. The bearing for geostationary (i.e., GOES) satellites is constant. The bearing for polar-orbiting satellites varies continuously.
berm A platform of wave-deposited sediment that is flat or slopes slightly landward.
bioassay A measurement of the effects of a substance on living organisms.
biodegradation Decomposition of material by microorganisms.
biodiversity The totality of genes, species, and ecosystems in a region or the world.
biogenic Produced by natural processes. Usually used in the context of emissions that are produced by plants and animals.
biogeochemical cycles Movements through the Earth system of key chemical constituents essential to life, such as carbon, nitrogen, oxygen, and phosphorus.
biomass Organic nonfossil material of biological origin. For example, trees and plants are biomass.
biome Well-defined terrestrial environment (e.g., desert, tundra, or tropical forest). The complex of living organisms found in an ecological region.
biosphere Part of the Earth system in which life can exist, between the outer portion of the geosphere and the inner portion of the atmosphere.
biota The plant and animal life of a region or area.
blackbody An ideal emitter which radiates energy at the maximum possible rate per unit area at each wavelength for any given temperature. A blackbody also absorbs all the radiant energy incident on it; i.e., no energy is reflected or transmitted.
blizzard A severe weather condition characterized by low temperatures and strong winds (greater than 35 mph) bearing a great amount of snow, either falling or blowing. When these conditions persist after snow has stopped falling, it is called a ground blizzard.
boreal Northern; from the Greek name for the Goddess of the North Wind. A boreal forest is the set of forest ecosystems than can survive in the north.
brightness temperature A measure of the intensity of radiation thermally emitted by an object, given in units of temperature because there is a proportional correlation between the intensity of the radiation emitted and physical temperature of the radiating body.
broadleaf The leaves of trees associated with deciduous forests.
bus The basic frame of a satellite system that includes the propulsion and stabilization systems but not the instruments or data systems.
calibration Act of comparing an instrument's measuring accuracy to a known standard.
calorie The amount of heat needed to raise the temperature of one gram of water at 15 degrees centigrade one degree centigrade. Compare with British Thermal Unit.
canopy The layer formed naturally by the leaves and branches of trees and plants.
carbohydrate an organic compound present in the cells of all living organisms and a major organic nutrient for human beings; consists of carbon, hydrogen, and oxygen, and makes up sugar, starch, and cellulose.
carbon cycle All parts (reservoirs) and fluxes of carbon. The cycle is usually thought of as four main reservoirs of carbon interconnected by pathways of exchange. The reservoirs are the atmosphere, terrestrial biosphere (usually includes freshwater systems), oceans, and sediments (includes fossil fuels). The annual movements of carbon, the carbon exchanges between reservoirs, occur because of various chemical, physical, geological, and biological processes. The ocean contains the largest pool of carbon near the surface of the Earth, but most of that pool is not involved with rapid exchange with the atmosphere.
carbon dioxide A minor but very important component of the atmosphere, carbon dioxide traps infrared radiation. Atmospheric CO2 has increased about 25 percent since the early 1800s, with an estimated increase of 10 percent since 1958 (burning fossil fuels is the leading cause of increased CO2, deforestation the second major cause). The increased amounts of CO2 in the atmosphere enhance the greenhouse effect, blocking heat from escaping into space and contributing to the warming of Earth's lower atmosphere.
carbon sequestration The uptake and storage of carbon. Trees and plants, for example, absorb carbon dioxide, release the oxygen and store the carbon. Fossil fuels were at one time biomass and continue to store the carbon until burned.
carbonates chemical compounds derived from carbonic acid or carbon dioxide
carrying capacity The steady-state density of a given species that a particular habitat can support.
cartography The science of mapmaking.
celsius Temperature scale proposed by Swedish astronomer Anders Celsius in 1742. A mixture of ice and water is zero on the scale; boiling water is designated as 100 degrees. A degree is defined as one hundredth of the difference between the two reference points, resulting in the original term, "centigrade" (100th part). To convert celsius to Fahrenheit: multiply the celsius temperature by 1.8 and add 32 degrees. F = 9/5 C + 32 To convert Fahrenheit to celsius: subtract 32 degrees from the Fahrenheit temperature and divide the quantity by 1.8. C = (F -32) / 1.8.
chlorophyll Chlorophyll is a green compound found in leaves and green stems of plants. The intense green color of chlorophyll is due to its strong absorbencies in the red and blue regions of the spectrum, and because of these absorbencies the light it reflects and transmits appears green. It is capable of channeling the energy of sunlight into chemical energy through the process of photosynthesis. In this process the energy absorbed by chlorophyll transforms carbon dioxide and water into carbohydrates and oxygen.
cirrus A type of cloud composed of ice crystals and shaped in the form of hairlike filaments. It is formed at an altitude of approximately 29,000 feet.
climate change The term 'climate change' is sometimes used to refer to all forms of climatic inconsistency, but because the Earth's climate is never static, the term is more properly used to imply a significant change from one climatic condition to another. In some cases, 'climate change' has been used synonymously with the term, 'global warming'; scientists however, tend to use the term in the wider sense to also include natural changes in climate.
climate model A quantitative way of representing the interactions of the atmosphere, oceans, land surface, and ice. Models can range from relatively simple to quite comprehensive. Also see General Circulation Model.
climate system The five physical components (atmosphere, hydrosphere, cryosphere, lithosphere, and biosphere) that are responsible for the climate and its variations.
climatology Science dealing with climate and climate phenomena.
cloud albedo Reflectivity that varies from less than 10% to more than 90% of the insolation and depends on drop sizes, liquid water content, water vapor content, thickness of the cloud, and the sun's zenith angle. The smaller the drops and the greater the liquid water content, the greater the cloud albedo, if all other factors are the same.
cloud forcing The difference between the radiation budget components for average cloud conditions and cloud-free conditions. Roughly speaking, clouds increase the albedo from 15 to 30%, which results in a reduction of absorbed solar radiation of about 50 W/m^2. This cooling is offset somewhat by the greenhouse effect of clouds which reduces the OLR by about 30 W/m^2, so the net cloud forcing of the radiation budget is a loss of about 20 W/m^2. Were the clouds to be removed with all else remaining the same, the Earth would gain this last amount in net radiation and begin to warm up.
coccolithophore A single-celled marine plant that lives in large numbers throughout the upper layers of the ocean. See Coccolithophore fact sheet.
condensation Change of a substance to a denser form, such as gas to a liquid. The opposite of evaporation.
conduction The transfer of heat from one substance to another by direct contact. Denser substances are better conductors; the transfer is always from warmer to colder substances.
conifer An evergreen, cone-bearing tree, as a fir or pine.
contrails Condensation trails. Artificial clouds made by the exhaust of jet aircraft.
convection The rising of warm air and the sinking of cool air. Heat mixes and moves air. When a layer of air receives enough heat from the Earth's surface, it expands and moves upward. Colder, heavier air flows under it which is then warmed, expands, and rises. The warm rising air cools as it reaches higher, cooler regions of the atmosphere and begins to sink. Convection causes local breezes, winds, and thunderstorms.
coriolis force The apparent tendency of a freely moving particle to swing to one side when its motion is referred to a set of axes that is itself rotating in space, such as Earth. The acceleration is perpendicular to the direction of the speed of the article relative to the Earth's surface and is directed to the right in the northern hemisphere. Winds are affected by rotation of the Earth so that instead of a wind blowing in the direction it starts, it turns to the right of that direction in the northern hemisphere; left in the southern hemisphere.
coupled system Two or more processes that affect one another.
cryosphere One of the interrelated components of the Earth's system, the cryosphere is frozen water in the form of snow, permanently frozen ground (permafrost), floating ice, and glaciers. Fluctuations in the volume of the cryosphere cause changes in ocean sea-level, which directly impact the atmosphere and biosphere.
culmination The point at which a satellite reaches its highest position or elevation in the sky, relative to an observer (aka the closest point of approach).
cumulonimbus A cloud type that is dense and vertically developed and is associated with rain (particularly of a convective nature). It is heavy and dense with a flat base and a high, fluffy outline, and can be tall enough to occupy middle as well as low latitudes. This type of cloud is formed from about 10,000 to 12,000 feet of altitude.
cumulus Clouds forming in the troposphere which are vertically formed with flat bases and fluffy, rounded tops. They have often been described as cauliflower-like in structure. They occur at heights of 500-6000 meters in elevation from the earth and most often occur scattered or in dense heaped packs. They are formed due to buoyant upward convection during warm, anti-cyclonic summer weather.
cyclone An area of low pressure where winds blow counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. See anticyclone, wind.
data set A logically meaningful grouping or collection of similar or related data. Data having mostly similar characteristics (source or class of source, processing level and algorithms, etc.)
data A collection of facts, concepts or instructions in a formalized manner suitable for communication or processing by human beings or by computer.
deciduous Shedding leaves at the end of the growing season.
declination The angular distance from the equator to the satellite, measured as positive north and negative south.
decomposition The breakdown of matter by bacteria and fungi. It changes the chemical makeup and physical appearance of materials.
deforestation Those practices or processes that result in the change of forested lands to non-forest uses. This is often cited as one of the major causes of the enhanced greenhouse effect for two reasons: 1) the burning or decomposition of the wood releases carbon dioxide; and 2) trees that once removed carbon dioxide from the atmosphere in the process of photosynthesis are no longer present and contributing to carbon storage.
degree A unit of angular measure represented by the symbol o. The circumference of a circle contains 360 degrees. When applied to the roughly spherical shape of the Earth for geographic and cartographic purposes, degrees are each divided into 60 minutes.
delta The fan-shaped area at the mouth or lower end of a river, formed by eroded material that has been carried downstream and dropped in quantities larger than can be carried off by tides or currents.
demodulation The process of retrieving information (data) from a modulated carrier wave, the reverse of modulation.
deposition Process by which water changes phase directly from vapor into a solid without first becoming a liquid.
descending node The point in a satellite's orbit at which it crosses the equatorial plane from north to south.
desert A land area so dry that little or no plant or animal life can survive.
desertification The man-made or natural formation of desert from usable land.
detector A device in a radiometer that senses the presence and intensity of radiation. The incoming radiation is usually modified by filters or other optical components that restrict the radiation to a specific spectral band. The information can either be transmitted immediately or recorded for transmittal at a later time.
detritus Accumulated organic debris from dead organisms, often an important source of nutrients in a food web.
dew point The temperature to which air must be cooled for saturation to occur, exclusive of air pressure or moisture content change. At that temperature dew begins to form, and water vapor condenses into liquid.
dew Atmospheric moisture that condenses after a warm day and appears during the night on cool surfaces as small drops. The cool surfaces cause the water vapor in the air to cool to the point where the water vapor condenses.
diatom A class of unicellular algae more formally known as Bacillariophyceae that live in cold waters of relatively low salinity.
digital elevation model (DEM) A representation of the topography of the Earth in digital format, that is, by coordinates and numerical descriptions of altitude.
digital In signal processing this refers to the representation of quantities in discrete units. The information is contained and manipulated as a series of discrete numbers as opposed to an analog representation where the information is represented as a continuous signal. In practice, even analog signals are usually processed digitally in that the analog signal is sampled to create a digital signal that can be processed by inherently digital computers.
diurnal Performed in twenty-four hours, such as the diurnal rotation of the Earth.
doldrums Region near the equator characterized by low pressure and light shifting winds. See Wind.
doppler effect (aka Doppler shift) The apparent change in frequency of sound or light waves, varying with the relative velocity of the source and the observer. If the source and observer draw closer together, the frequency is increased. Named for Christian Doppler, Austrian mathematician and physicist (1803-1853).
downwelling The process of accumulation and sinking of warm surface waters along a coastline. A change of air flow of the atmosphere can result in the sinking or downwelling of warm surface water. The resulting reduced nutrient supply near the surface affects the ocean productivity and meteorological conditions of the coastal regions in the downwelling area.
dynamics The study of the action of forces on bodies and the changes in motion they produce.
dynamo A physical system that converts mechanical energy (energy of motion) into magnetic energy. In the Sun, the mechanical energy results from the movement of the plasma at the Sun’s core.
easterly wave A migratory wavelike atmospheric disturbance in the tropical easterlies. Easterly waves occasionally intensify into tropical cyclones. They are also called tropical waves.
eccentricity (aka ecce or E0 or e) One of six Keplerian elements, it describes the shape of an orbit. In the Keplerian orbit model, the satellite orbit is an ellipse, with eccentricity defining the 'shape' of the ellipse. When e=0, the ellipse is a circle. When e is very near 1, the ellipse is very long and skinny.
eclipse The partial or total apparent darkening of the sun when the moon comes between the sun and the Earth (solar eclipse), or the darkening of the moon when the full moon is in the Earth's shadow (lunar eclipse).
ecology Science dealing with the interrelationships between living organisms and their environments.
ecosystem Any natural unit or entity including living and non-living parts that interact to produce a stable system through cyclic exchange of materials.
electrical resonance An effect in which the resistance to the flow of an electrical current becomes very small over a narrow frequency range.
electromagnetic radiation Energy propagated as time-varying electric and magnetic fields. These two fields are inextricably linked as a single entity since time-varying electric fields produce time-varying magnetic fields and vice versa. Light and radar are examples of electromagnetic radiation differing only in their wavelengths (or frequency). Electric and magnetic fields propagate through space at the speed of light.
electromagnetic spectrum The entire range of radiant energies or wave frequencies from the longest to the shortest wavelengths--the categorization of solar radiation. Satellite sensors collect this energy, but what the detectors capture is only a small portion of the entire electromagnetic spectrum. The spectrum usually is divided into seven sections: radio, microwave, infrared, visible, ultraviolet, x-ray, and gamma-ray radiation.
electromagnetic wave Method of travel for radiant energy (all energy is both particles and waves), so called because radiant energy has both magnetic and electrical properties. electromagnetic waves are produced when electric charges change their motion. Whether the frequency is high or low, all electromagnetic waves travel at 300,000,000 meters per second.
elevation The angle at which an antenna must be pointed above the horizon for optimal reception from a spacecraft.
elliptical orbits Bodies in space orbit in elliptical rather than circular orbits because of factors such as gravity and drag. The point where the orbiting satellite is closest to Earth is the perigee, sometimes called peri-apsis or perifocus. The point where the satellite is farthest from Earth is called apogee, apoapsis, or apifocus. A line drawn from perigee to apogee is the line-of-apsides, sometimes called the major-axis of the ellipse. It's simply a line drawn through the ellipse the long way.
emissivity The ratio of the radiation emitted by a surface to that emitted by a black body at the same temperature.
energy budget A quantitative description of the energy exchange for a physical or ecological system. The budget includes terms for radiation, conduction, convection, latent heat, and for sources and sinks of energy.
enhanced greenhouse effect The natural greenhouse effect has been enhanced by anthropogenic emissions of greenhouse gases. Increased concentrations of carbon dioxide, methane, and nitrous oxide, CFCs, HFCs, PFCs, SF6, NF3, and other photochemically important gases caused by human activities such as fossil fuel consumption and adding waste to landfills, trap more infra-red radiation, thereby exerting a warming influence on the climate. See Climate Change and Global Warming.
environment The complex of physical, chemical, and biological factors in which a living organism or community exists.
estuary A bay that formed when a broad river valley was submerged by rising sea level or a sinking coast.
eutrophication The process whereby a body of water becomes rich in dissolved nutrients through natural or man-made processes. This often results in a deficiency of dissolved oxygen, producing an environment that favors plant over animal life.
evaporation Change from a liquid (more dense) to a vapor or gas (less dense) from. When water is heated it becomes a vapor that increases humidity. Evaporation is the opposite of condensation.
evapotranspiration The sum of evaporation and plant transpiration. Potential evapotranspiration is the amount of water that could be evaporated or transpired at a given temperature and humidity, if there was plenty of water available. Actual evapotranspiration can not be any greater than precipitation, and will usually be less because some water will run off in rivers and flow to the oceans. If potential evapotranspiration is greater than actual precipitation, then soils are extremely dry during at least a major part of the year.
exosphere The uppermost layer of the atmosphere, its lower boundary is estimated at 500 km to 1000 km above the Earth's surface. It is only from the exosphere that atmospheric gases can, to any appreciable extent, escape into outer space.
external forcing Influence on the Earth system (or one of its components) by an external agent such as solar radiation or the impact of extraterrestrial bodies such as meteorites.
false color A color imaging process which produces an image of a color that does not correspond to the true or natural color of the scene (as seen by our eyes).
far infrared Electromagnetic radiation, longer than the thermal infrared, with wavelengths between about 25 and 1000 micrometers. See electromagnetic spectrum.
fault line A fracture in rock along which one side has moved with respect to the other. See Putting Earthquakes in Their Place
feedback mechanisms Factors which increase or amplify (positive feedback) or decrease (negative feedback) the rate of a process. An example of positive climatic feedback is the ice-albedo feedback.
field of view The range of angles that are scanned or sensed by a system or instrument, measured in degrees of arc.
field The set of influences (electricity, magnetism, gravity) that extend throughout space.
flood plain The nearly flat portion of a river (stream) valley adjacent to the river (stream) channel; it is built by sediment deposited during floods and is covered by water during a flood.
fluorocarbons Carbon-fluorine compounds that often contain other elements such as hydrogen, chlorine, or bromine. Common fluorocarbons include chlorofluorocarbons and related compounds (also know as ozone depleting substances).
flux the measure of the flow of some quantity per unit area per unit time
fog A cloud on the ground.
food chain A sequence of organisms, each of which uses the next lower member of the sequence as a food source.
force Any external agent that causes a change in the motion of a free body, or that causes stress in a fixed body.
fossil fuel Any hydrocarbon deposit that can be burned for heat or power, such as petroleum, coal, and natural gas.
fossil Hardened remains or traces of plant or animal life from a previous geological period preserved in the Earth's crust.
free radicals Atomic or molecular species with unpaired electrons or an otherwise open shell configuration, usually very reactive. Specific to atmospheric chemistry, free radicals are: short-lived, highly reactive, intermediate species produced by dissociation of the source molecules by solar ultraviolet radiation or by reactions with other stratospheric constituents. Free radicals are the key to intermediate species in many important stratosphericchain reactions in which an ozone molecule is destroyed and the radical is regenerated. See ozone
frequency (F) Number of cycles and parts of cycles completed per second. F=1/T, where T is the length of one cycle in seconds.
frost Ice crystals formed by deposition of water vapor on a relatively cold surface.
gamma ray A high energy photon, especially as emitted by a nucleus in a transition between two energy levels.
geodesy A branch of applied mathematics concerned with measuring the shape of the Earth and describing variations in the Earth's gravity field.
geodynamics The study of the Earth's motions, including rotation, tectonics, ocean tides, and structure (i.e., core, mantle). See Putting Earthquakes in Their Place
geoid A surface of constant gravitational potential around the Earth--an averaged surface perpendicular to the force of gravity.
geomorphology The study of present-day landforms, including their classification, description, nature, origin, development, and relationships to underlying structures. Also the history of geologic changes as recorded by these surface features. The term is sometimes restricted to features produced only by erosion and deposition.
geophysical Relating to the study of the physical characteristics and properties of the solid earth, its air and waters, and its relationship to space phenomena.
geosphere The physical elements of the Earth's surface crust, and interior.
geostationary Describes an orbit in which a satellite is always in the same position (appears stationary) with respect to the rotating Earth. The satellite travels around the Earth in the same direction, at an altitude of approximately 35,790 km (22,240 statute miles) because that produces an orbital period equal to the period of rotation of the Earth (actually 23 hours, 56 minutes, 04.09 seconds). A worldwide network of operational geostationary meteorological satellites provides visible and infrared images of Earth's surface and atmosphere. The satellite systems include the U.S. GOES, METEOSAT(launched by the European Space Agency and operated by the European Weather Satellite Organization-EUMETSAT), the Japanese GMS and most commercial, telecommunications satellites.
geosynchronous (aka GEO) Synchronous with respect to the rotation of the Earth. See geostationary.
gigabit One billion (1,073,741,824) bits.
glacier A multi-year surplus accumulation of snowfall in excess of snowmelt on land and resulting in a mass of ice at least 0.1 km2 in area that shows some evidence of movement in response to gravity. A glacier may terminate on land or in water. Glacier ice is the largest reservoir of fresh water on Earth, and second only to the oceans as the largest reservoir of total water. Glaciers are found on every continent except Australia.
global carbon budget The balance of the exchanges (incomes and losses) of carbon between the carbon reservoirs or between one specific loop (e.g., atmosphere - biosphere) of the carbon cycle. An examination of the carbon budget of a pool or reservoir can provide information about whether the pool or reservoir is functioning as a source or sink for CO2.
global climate change The long-term fluctuations in temperature, precipitation, wind, and all other aspects of the Earth's climate. External processes, such as solar-irradiance variations, variations of the Earth's orbital parameters (eccentricity, precession, and inclination), lithosphere motions, and volcanic activity, are factors in climatic variation. Internal variations of the climate system also produce fluctuations of sufficient magnitude and variability to explain observed climate change through the feedback processes interrelating the components of the climate system.
global measurement All of the activities required to specify a global variable, such as ozone. These activities range from data acquisition to the generation of a data-analysis product, and include estimates of the uncertainties in that product. A global measurement often will consist of a combination of observations from a spacecraft instrument (required for global coverage) and measurements in situ (needed to provide reference points for long-term accuracy).
global positioning system (GPS) A system consisting of 25 satellites in 6 orbital planes at 20,000 km altitude with 12 hr periods, used to provide highly precise position, velocity and time information to users anywhere on Earth or in its neighborhood at any time.
global variables Functions of space and time that describe the large scale state and evolution of the Earth system. The Earth system's geosphere, hydrosphere, atmosphere, and biosphere and their components are, or potentially are, global variables.
global warming An increase in the near surface temperature of the Earth. Global warming has occurred in the distant past as the result of natural influences, but the term is most often used to refer to the warming predicted to occur as a result of increased emissions of greenhouse gases. Scientists generally agree that the Earth's surface has warmed by about 1 degree Fahrenheit in the past 140 years. The Intergovernmental Panel on Climate Change (IPCC) recently concluded that increased concentrations of greenhouse gases are causing an increase in the Earth's surface temperature and that increased concentrations of sulfate aerosols have led to relative cooling in some regions, generally over and downwind of heavily industrialized areas. Also see Climate Change and Enhanced Greenhouse Effect.
grassland Region in which the climate is dry for long periods of the summer, and freezes in the winter. Grasslands are characterized by grasses and other erect herbs, usually without trees or shrubs. Grasslands occur in the dry temperate interiors of continents.
gulf stream A warm, swift ocean current that flows along the coast of the Eastern United States and makes Ireland, Great Britain, and the Scandinavian countries warmer than they would be otherwise.
habitat The area or region where a particular type of plant or animal lives and grows.
hail Precipitation composed of balls or irregular lumps of ice. Hail is produced when large frozen raindrops, or almost any particles, in cumulonimbus clouds act as embryos that grow by accumulating supercooled liquid droplets. Violent updrafts in the cloud carry the particles in freezing air, allowing the frozen core to accumulate more ice. When the piece of hail becomes too heavy to be carried by upsurging air currents it falls to the ground.
haze Fine dry or wet particles of dust, salt, or other impurities that can concentrate in a layer next to the Earth when air is stable.
heat balance The equilibrium existing between the radiation received and emitted by a planetary system.
heat island effect A dome of elevated temperatures over an urban area caused by the heat absorbed by structures and pavement.
hemisphere Half of the Earth, usually conceived as resulting from the division of the globe into two equal parts, north and south or east and west.
herbaceous Green and leaf-like.
horse latitudes The subtropical latitudes (30-35 degrees), where winds are light and weather is hot and dry. According to legend, ships traveling to the New World often stagnated in this region and had to throw dead horses overboard or eat them to survive, hence the name horse latitudes.
humus Humus is dark, organic material that forms in soil when plant and animal matter decays.
hurricanes Severe tropical storms whose winds exceed 74 mph. Hurricanes originate over the tropical and subtropical North Atlantic and North Pacific oceans, where there is high humidity and light wind. These conditions prevail mostly in the summer and early fall. Since hurricanes can take days or even weeks to form, time is usually available for preventive or protective measures. From space, hurricanes look like giant pinwheels, their winds circulating around an eye that is between 5 and 25 miles in diameter. The eye remains calm with light winds and often a clear sky. Hurricanes may move as fast as 50 mph, and can become incredibly destructive when they hit land. Although hurricanes lose power rapidly as soon as they leave the ocean, they can cause high waves and tides up to 25 feet above normal. Waves and heavy flooding cause the most deaths during a hurricane. The strongest hurricanes can cause tornadoes.
hydrocarbon A chemical containing only carbon and hydrogen. Hydrocarbons are of prime economic importance because they encompass the constituents of the major fossil fuels, petroleum and natural gas, as well as plastics, waxes, and oils. In urban pollution, these components--along with NOx and sunlight--contribute to the formation of tropospheric ozone.
hydrochlorofluorocarbon (HCFC) One of a class of compounds used primarily as a CFC substitute. Work on CFC alternatives began in the late 1970s after the first warnings of CFC damage to stratospheric ozone. By adding hydrogen to the chemical formulation, chemists made CFCs less stable in the lower atmosphere enabling them to break down before reaching the ozone layer. However, HCFCs do release chlorine and have contributed more to atmospheric chlorine buildup than originally predicted. Development of non-chlorine based chemical compounds as a substitute for CFCs and HCFCs continues.
hydrodynamics The study of fluid motion and fluid-boundary interaction.
hydrologic cycle The process of evaporation, vertical and horizontal transport of vapor, condensation, precipitation, and the flow of water from continents to oceans. It is a major factor in determining climate through its influence on surface vegetation, the clouds, snow and ice, and soil moisture. The hydrologic cycle is responsible for 25 to 30 percent of the mid-latitudes' heat transport from the equatorial to polar regions. See The Water Cycle
hydrology The science that deals with global water (both liquid and solid), its properties, circulation, and distribution, on and under the Earth's surface and in the atmosphere through evapotranspiration or is discharged into oceans.
hydrosphere The totality of water encompassing the Earth, comprising all the bodies of water, ice, and water vapor in the atmosphere.
hyperspectral describes a sensor that observes hundreds or thousands of virtually continuous wavelengths of electromagnetic energy, or imagery from such a sensor
ice age A glacial epoch or time of extensive glacial activity
ice core A cylindrical section of ice removed from a glacier or an ice sheet in order to study climate patterns of the past. By performing chemical analyses on the air trapped in the ice, scientists can estimate the percentage of carbon dioxide and other trace gases in the atmosphere at that time.
ice sheet (continental glacier) A glacier of considerable thickness and more than 50,000 sq km in area. It forms a continuous cover of ice and snow over a land surface. An ice sheet is not confined by the underlying topography but spreads outward in all directions. During the Pleistocene Epoch, ice sheets covered large parts of North America and northern Europe but they are now confined to polar regions (e.g., Greenland and Antarctica).
ice shelf A thick mass of ice extending from a polar shore. The seaward edge is afloat and sometimes extends hundreds of kilometers over the sea. Ice shelves generally fall into three categories: those fed by glaciers, those created by sea ice, and composite shelves incorporating both glacier- and sea-ice-supplied ice.
imager A satellite instrument that measures and maps the Earth and its atmosphere. Imager data are converted by computer into pictures.
in situ Latin for 'in original place.' Refers to measurements made at the actual location of the object or material measured. Compare remote sensing.
information system All of the means and mechanisms for data receipt, processing, storage, retrieval, and analysis. Information Systems can be designed for storage and dissemination of a variety of data products--including primary data sets and both intermediate and final analyses--and for an interface providing connections to external computers, external data banks, and system users. To be effective, the design and operation of an information system must be carried out in close association with the primary producers of the data sets, as well as other groups producing integrated analyses or intermediate products.
insolation Solar radiation incident upon a unit horizontal surface on or above the Earth's surface.
ion Atom or molecule that has acquired an electric charge by the loss or gain of one or more electrons.
isobars Lines drawn on a weather map joining places of equal barometric pressure.
isothermal Of or indicating equality of temperature.
isotherms Lines connecting points of equal temperature on a weather map.
isthmus Narrow strip of land located between two bodies of water, connecting two larger land areas.
jet stream Rivers of high-speed air in the atmosphere. Jet streams form along the boundaries of global air masses where there is a significant difference in atmospheric temperature. The jet streams may be several hundred miles across and 1-2 miles deep at an altitude of 8-12 miles. They generally move west to east, and are strongest in the winter with core wind speeds as high as 250 mph. Changes in the jet stream indicate changes in the motion of the atmosphere and weather.
kilobit 1024 bits. Also represented as Kb.
kilometer (km) Metric unit of distance equal to 3,280.8 feet or .621 statute miles.
knot Unit of speed of one nautical mile (6,076.1 feet) an hour.
lahar A flood of mud and rocks from the slopes of a volcano. May be triggered by earthquakes, landslides, or when the rim of a caldera lake is breached. See When Rivers of Rock Flow
lake A body of fresh or salt water entirely surrounded by land.
land breeze A nocturnal coastal breeze that blows from land to sea. In the evening the water may be warmer than the land, causing pressure differences. The land breeze is the flow of air from land to sea equalizing these pressure differences. See sea breeze.
land cover The characteristics of a land surface as determined by its spectral signature (the unique way in which a given type of land cover reflects and absorbs light).
laser (light amplification by stimulated emission of radiation) Active instrument that produces discretely coherent pulses of light (light waves with no phase differences, or with predictable phases differences, are said to be coherent).
laser ranging The use of lasers to measure distances.
latent heat The heat that is either released or absorbed by a unit mass of a substance when it undergoes a change of state, such as during evaporation, condensation, or sublimation.
latitude (aka the geodetic latitude) The angle between a perpendicular at a location, and the equatorial plane of the Earth.
lava dome lava that piles up over a volcanic vent, usually in a rounded mass
leaf area index (LAI) The area of foliage per unit area of ground. Conventionally this refers to the ratio of the area of the upper side of the leaves in a canopy projected onto a flat surface to the area of the surface under the canopy. Occasionally this has been used in reference to both sides of the leaves.
legend A listing that contains symbols and other information about a map.
lidar Acronym for 'Light Detection and Ranging,' a technique for performing accurate remote measurements of atmospheric trace gas concentration over ranges of several meters to tens of kilometers. This is done by probing the absorption lines of the gases with narrow spectral laser radiation using the differential absorption lidar technique.
light 1. Form of radiant energy that acts upon the retina of the eye, optic nerve, etc., making sight possible. This energy is transmitted at a velocity of about 186,000 miles per second by wavelike or vibrational motion. 2. A form of radiant energy similar to this, but not acting on the normal retina, such as ultraviolet and infrared radiation. Interplay between light rays and the atmosphere cause us to see the sky as blue, and can result in such phenomena as glows, halos, arcs, flashes, and streamers.
lithosphere The component of the Earth's surface comprising the rock, soil, and sediments. It is a relatively passive component of the climate system, and its physical characteristics are treated as fixed elements in the determination of climate.
longitude The angular distance from the Greenwich meridian (0 degree), along the equator. This can be measured either east or west to the 180th meridian (180 degrees) or 0 degree to 360 degrees W.
longwave radiation The radiation emitted in the spectral wavelength greater than 4 micrometers corresponding to the radiation emitted from the Earth and atmosphere. It is sometimes referred to as 'terrestrial radiation' or 'infrared radiation,' although somewhat imprecisely.
magnetosphere The region surrounding a celestial body where its magnetic field controls the motions of charged particles. The Earth's magnetic field is dipolar in nature. That is, it behaves as if produced by a giant bar magnet located near the center of the planet with its north pole tilted several degrees from Earth's geographic north pole. The Earth's magnetic field presents an obstacle to the solar wind, as a rock in a running stream of water. This obstacle is called a bow shock. The bow shock slows down, heats, and compresses the solar wind, which then flows around the rest of Earth's magnetic field. See Van Allen belts.
mass balance The term ‘mass balance’ is often used by glaciologists to describe the difference between all of the ice that is added to a glacier, and all of the ice the glacier loses over a period of time. Ice sheets and glaciers can lose mass due to melting, calving, evaporation, etc. They can gain mass from direct precipitation, avalanching, and windblown snow. The net result of all these outputs and inputs of ice are then the glacier’s mass balance.
mean sea level The average height of the sea surface, based upon hourly observation of the tide height on the open coast or in adjacent waters that have free access to the sea. In the United States, it is defined as the average height of the sea surface for all stages of the tide over a nineteen year period. Mean sea level, commonly abbreviated as MSL and referred to simply as 'sea level,' serves as the reference surface for all altitudes in upper atmospheric studies.
megabit (mbps) Millions of bits per second. A unit of information transfer rate -- e.g. Ethernet can carry 10 mbps.
mesopause The upper boundary of the mesosphere where the temperature of the atmosphere reaches its lowest point.
mesosphere The atmospheric layer above the stratosphere, extending from about 50 to 85 kilometers altitude. The temperature generally decreases with altitude.
metabolism the sum of all the chemical and physical processes within a living organism, including anabolism and catabolism
metadata Information describing the content or utility of a data set. For example, the dates on which data were procured are metadata.
meteorite a solid mass of mineral or rock matter that has fallen to the earth's surface from outer space without being completely vaporized in the atmosphere.
meteorology Study of the atmosphere and its phenomena.
microbe any microorganism
micrometer One millionth of a meter, used to measure wavelengths in the electromagnetic spectrum. Also known as a "micron" or µm
microwave Electromagnetic radiation with wavelengths between about 1000 micrometers and one meter.
middle infrared Electromagnetic radiation between the near infrared and the thermal infrared, about 2-5 micrometers.
millibar (mb) One thousandth of a bar, a unit of atmospheric pressure. The average atmospheric pressure at sea level is 1.01325 bars or 1013.25 mb. See pascal (Pa), atmospheric pressure.
model (noun) A mathematical representation of a process, system, or object developed to understand its behavior or to make predictions. The representation always involves certain simplifications and assumptions.
mountain and valley breezes System of winds that blow downhill during the night (mountain breeze) and uphill during the day (valley breeze).
nadir Point on Earth directly beneath a satellite, the opposite of zenith. Compare with subsatellite point.
nanometer (nm) One billionth of a meter. Nanometers are used to measure wavelengths in the electromagnetic spectrum.
nautical mile A nautical mile is a unit of distance equal to 1,852 meters. The length of the nautical mile is very close to the mean value of the length of 1 minute of latitude, which varies from approximately 1,843 meters at the equator to 1,861.6 meters at the pole.
near infrared Electromagnetic radiation with wavelengths from just longer than the visible (about 0.7 micrometers) to about two micrometers. See electromagnetic spectrum.
negative feedback An interaction that reduces or dampens the response of the system in which it is incorporated.
nitrogen dioxide A gas consisting of one atom of nitrogen and two atoms of oxygen.
nitrogen fixation the process by which nitrogen gas in the atmosphere is converted into biologically useful, nitrogen-containing compounds, usually ammonium. Most nitrogen fixation is done by bacteria.
nitrogen oxides (NOx) Gases consisting of one molecule of nitrogen and varying numbers of oxygen molecules. Nitrogen oxides are produced in the emissions of vehicle exhausts and from power stations. In the atmosphere, nitrogen oxides can contribute to formation of photochemical ozone (smog), can impair visibility, and have health consequences; they are thus considered pollutants.
nitrous oxide (N2O) A powerful greenhouse gas with a global warming potential of 320. Major sources of nitrous oxide include soil cultivation practices, especially the use of commercial and organic fertilizers, fossil fuel combustion, nitric acid production, and biomass burning.
obliquity The angle between the plane of the Earth's orbit and the plane of the Earth's equator; the "tilt" of the Earth.
occluded front (occlusion) A composite of two fronts formed as a cold front overtakes a warm front. A cold occlusion results when the coldest air is behind the cold front. The cold front undercuts the warm front and, at the Earth's surface, coldest air replaces less-cold air. A warm occlusion occurs when the coldest air lies ahead of the warm front. Because the cold front can not lift the colder air mass, it rides piggyback up on the warm front over the coldest air.
ocean color a change in the color of the ocean surface as a result of sediment, organic matter, or phytoplankton, all of which can change how the ocean surface reflects and absorbs sunlight. In a natural-color (photo-like) image from space, the clear waters of the open ocean look dark blue. Chlorophyll and other pigments in phytoplankton can color the water bright blue, green, and even reddish-brownish. Sediment can turn the water milky blue. Organic matter can turn the water tea-colored.
ocean The salt water surrounding the great land masses. The land masses divide the ocean into several distinct portions, each of which also is called an ocean. The oceans include the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, and the Arctic Ocean.
optical thickness (optical depth) In calculating the transfer of radiant energy, the mass of an absorbing or emitting material lying in a vertical column of unit cross-sectional area and extending between two specified levels. Also, the degree to which a cloud prevents light from passing through it; the optical thickness then depends on the physical constitution (crystals, drops, and/or droplets), the form, the concentration, and the vertical extent of the cloud.
orbit The path described by a heavenly body in its periodic revolution. Earth satellite orbits with inclinations near 0 degree are called equatorial orbits because the satellite stays nearly over the equator. Orbits with inclinations near 90 degrees are called polar orbits because the satellite crosses over (or nearly over) the north and south poles. See orbital inclination.
orbital plane An imaginary gigantic flat plate containing an Earth satellite's orbit. The orbital plane passes through the center of the Earth.
organic Chemistry: of or relating to any covalently bonded compound containing carbon atoms. Biology: relating to or involving an organism or organisms.
ozone layer The layer of ozone that begins approximately 15 km above Earth and thins to an almost negligible amount at about 50 km, shields the Earth from harmful ultraviolet radiation from the sun. The highest natural concentration of ozone (approximately 10 parts per million by volume) occurs in the stratosphere at approximately 25 km above Earth. The stratospheric ozone concentration changes throughout the year as stratospheric circulation changes with the seasons. Natural events such as volcanoes and solar flares can produce changes in ozone concentration, but man-made changes are of the greatest concern.
ozone mini-hole(s) Rapid, transient, polar-ozone depletion. These depletions, which take place over a 50-kilometer squared area, are caused by weather patterns in the upper troposphere. The decrease in ozone during a mini-hole event is caused by transport, with no chemical depletion of ozone. However, the cold stratospheric temperatures associated with weather systems can cause clouds to form that can lead to the conversion of chlorine compound from inert to reactive forms. These chlorine compounds can then produce longer-term ozone reductions after the mini-hole has passed.
pH A symbol for the degree of acidity or alkalinity of a solution. Expressed as a negative logarithm of the hydrogen ion concentration in a solution, pH = -log10[H+]. If the hydrogen ion concentration of a solution increases, the pH will decrease, and vice versa. The value for pure distilled water is regarded as neutral, pH values from 0 to 7 indicate acidity, and from 7 to 14 indicate alkalinity.
paleoclimate Climate as it existed in the distant past, particularly before historical records.
paleoclimatology The study of past climates, throughout geological history, and the causes of the variations among.
paleogeography The study of ancient or prehistoric geography.
panchromatic Sensitive to all or most of the visible spectrum.
parameter A constant whose values determine the specific form or characteristics of an expression.
particulates Very small pieces of solid or liquid matter such as particles of soot, dust, fumes, mists or aerosols. The physical characteristics of particles, and how they combine with other particles, are part of the feedback mechanisms of the atmosphere.
parts per billion A unit of measure used for very small quantities, it is equal to the ratio of the weight or volume of one component of a mixture to a billion weights or volumes of the mixture. When based on weight (ppbw), it is equal to the weight or mass of the component divided by the total weight or mass in a given volume, multiplied by one billion. When based on volume (ppbv) it is equal to the volume of the component divided by the total volume of the mixture, multiplied by one billion.
pascal (Pa) Unit of atmospheric pressure named in honor of Blaise Pascal (1632-1662), whose experiments greatly increased knowledge of the atmosphere. A pascal is the force of one newton acting on a surface area of one square meter. It is the unit of pressure designated by the International System. 100,000 Pa = 1000 mb = 1 bar. See atmospheric pressure, millibar.
passive microwave A system sensing only microwave radiation emitted by the object being viewed or reflected by the object from a source other than the system.
passive system A system sensing only radiation emitted by the object being viewed or reflected by the object from a source other than the system. See active system.
payload The instruments that are accommodated on a spacecraft.
perigee (aka periapsis or perifocus) On an elliptical orbit path, the point where a satellite is closest to the Earth.
perihelion The point in the orbit of a planet or comet which is nearest the Sun (as opposed to the aphelion, which is the point in the orbit farthest from the Sun).
period decay (aka decay) The tendency of a satellite to lose orbital velocity due to the influence of atmospheric drag and gravitational forces. A decaying object eventually impacts the surface of the Earth or burns up in the atmosphere. This parameter directly affects the satellite's mean motion.
period Time required for a satellite to make one complete orbit. A division of geologic time, delimited by full-scale withdrawal of the sea from land masses and by limited crustal, climatic, and volcanic upheaval in a localized area. Two or more periods are required to make up a geologic era, and each period is comprised of two or more geologic epochs.
permafrost Perennially frozen ground that occurs wherever the temperature remains below 0° C for several years.
perturbations Minor corrections to the Keplerian model of a satellite orbit as an ellipse of constant shape and orientation. Since satellite orbits are affected by Earth's gravity and drag caused by the Earth's atmosphere (causing satellites to spiral downward), minor adjustments must be made to the orbit.
photochemical smog A type of smog that forms in large cities when chemical reactions take place in the presence of sunlight, its principal component is ozone. Ozone and other oxidants are not emitted into the air directly but form from reactions involving nitrogen oxides and hydrocarbons. Because of its smog-making ability, ozone in the lower atmosphere (troposphere) is often referred to as 'bad' ozone.
photochemistry The study of the impact of light on certain chemical molecules.
photodissociation A chemical reaction involving sunlight in which molecules are split into their constituent atoms. Also known as photolysis.
photon A quantum (smallest unit in which waves may be emitted or absorbed) of light.
photoreceptor A sensor sensitive to light.
photosynthesis The process by which green plants use light to synthesize organic compounds from carbon dioxide and water. In the process oxygen and water are released. Increased levels of carbon dioxide can increase net photosynthesis in some plants. Plants create a very important reservoir for carbon dioxide.
photosynthetically active radiation Electromagnetic radiation in the part of the spectrum used by plants for photosynthesis.
physical climate system The system of processes that regulate climate, including atmospheric and ocean circulation, evaporation, and precipitation.
physics The scientific study of matter, energy, motion, and force. (From a Greek term meaning "the science of nature.")
phytoplankton Microscopic, plant-like marine organisms (mostly algae and diatoms), which are responsible for most of the photosynthetic activity in the oceans. Phytoplankton are the base of the ocean food web, and they absorb about as much carbon dioxide from the atmosphere each year as plants on land do.
pixel Pixel, short for picture element, is the ground area corresponding to a single element of a digital image data set.
planetary albedo The fraction of incident solar radiation that is reflected by a planet and returned to space. The planetary albedo of the Earth-atmosphere system is approximately 30 percent, most of which is due to backscatter from clouds in the atmosphere.
planetary boundary layer the turbulent layer of atmosphere occupying the lowest few hundred meters of the atmosphere.
planetesimals small bodies that formed from the solar nebula
plasma A fourth state of matter (in addition to solid, liquid, and gas) that exists in space. In this state, atoms are positively charged and share space with free negatively charged electrons. Plasma can conduct electricity and interact strongly with electric and magnetic fields. The solar wind is actually hot plasma blowing from the sun. See magnetosphere.
plate tectonics Concept that the Earth's crust is composed of rigid plates that move over a less rigid interior.
platforms A satellite that can carry instruments. See bus. The same term is applied to automatic weather data transmitters installed on buoys, balloons, ships, and planes, and mounted in remote areas.
polar orbit An orbit with an orbital inclination of near 90 degrees where the satellite ground track will cross both polar regions once during each orbit. The term is used to describe the near-polar orbits of spacecraft such as the USA's NOAA/TIROS and Landsat satellites.
polar stratospheric clouds (PSCs) High altitude clouds that form in the stratosphere above Antarctica during the Southern Hemisphere winter. Their presence seems to initiate the ozone loss experienced during the ensuing Southern Hemisphere spring.
polar vortex A circumpolar wind circulation which isolates the Antarctic continent during the cold Southern Hemisphere winter, heightening ozone depletion.
pollutant Strictly, too much of any substance in the wrong place or at the wrong time is a pollutant. More specifically, atmospheric pollution may be defined as the presence of substances in the atmosphere, resulting from man-made activities or from natural processes that cause adverse effects to human health, property, and the environment.
polynya An area of open sea surrounded by ice.
positive feedback An interaction that amplifies the response of the system in which it is incorporated.
precession The comparatively slow torquing of the orbital planes of all satellites with respect to the Earth's axis, due to the bulge of the Earth at the equator which distorts the Earth's gravitational field. Precession is manifest by the slow rotation of the line of nodes of the orbit (westward for inclinations less than 90 degrees and eastward for inclinations greater than 90 degrees).
prevailing westerlies Winds in the middle latitudes (approximately 30 degrees to 60 degrees) that generally blow from west to east. The subtropical high pressure regions at the horse latitudes (30 degrees) forces surface air poleward, and the rotation of the Earth causes these winds to bear to the right (east) in the Northern Hemisphere and to the left (east) in the Southern Hemisphere (see Coriolis force). This is, to some extent, an idealized picture of the atmospheric circulation. The actual circulation on individual days includes modifications and variations due to the migratory cyclones and anticyclones of middle latitudes, causing rapid and often violent weather changes, as warm semi-tropical air from the horse latitudes meets cold polar air from the high latitudes.
primary productivity The rate at which new plant biomass is formed by photosynthesis. Gross primary productivity is the total rate of photosynthetic production of biomass; net primary productivity is gross primary productivity minus the respiration rate.
process study An organized, systematic investigation of a particular process designed to identify all of the state variables involved and to establish the relationships among them. Process studies yield numerical algorithms that connect the state variables and determine their rates of change; such algorithms are essential ingredients of Earth system models.
process An association of phenomena governed by physical, chemical, or biological laws. An example of a process is the vertical mixing of ocean waters in the so-called surface-mixed layer; the state variables for this process include temperature, salinity in the water on a vertical scale of tens of meters, and heat flow and wind stress at the sea surface. Other examples include the volcanic deposition of dust and gases into the atmosphere, eddy formation in the atmosphere and oceans, and soil development.
prograde orbit Orbits of the Earth in the same direction as the rotation of the Earth (west-to-east).
psychrometer An instrument designed to measure dew point and relative humidity, consisting of two thermometers (one dry bulb and one wet bulb). The dew point and humidity levels are determined by drying the wet bulb (either by fanning or whirling the instrument) and comparing the difference between the wet and dry bulbs with preexisting calculations. See hygrometer.
pycnocline In the ocean, a region where the water density increases rapidly with depth.
pyroclastic flow a fast-moving, fluid-like cloud of hot ash, pumice, rock fragments, and gas that occurs during explosive volcanic eruptions or the collapse of a lava dome
pyroclastic materials of volcanic origin, including rock fragments, volcanic ash, and volcanic gases. Aside from gases, volcanic materials can linger on the land surface, sometimes flattening and welding together.
pyrogenic Resulting from fire activities. Usually used in the context of emissions that are produced by fires -- e.g., smoke from fires.
radar interferometry The study of interference patterns caused by radar signals; a technique that enables scientists to generate three dimensional images of the Earth's surface.
radiant 1. In optics, the point or object from which light proceeds. 2. In geometry, a straight line proceeding from a given point, or fixed pole, about which it is conceived to revolve. 3. In astronomy, the point in the heavens from which a shower of meteors seems to proceed.
radiation budget A measure of all the inputs and outputs of radiative energy relative to a system, such as Earth. See Earth Radiation Budget Experiment.
radiation Energy transfer in the form of electromagnetic waves or particles that release energy when absorbed by an object.
radiative cooling Cooling process of the Earth's surface and adjacent air, which occurs when infrared (heat) energy radiates from the surface of the Earth upward through the atmosphere into space. Air near the surface transfers its thermal energy to the nearby ground through conduction, so that radiative cooling lowers the temperature of both the surface and the lowest part of the atmosphere.
radiative forcing A change in the balance between incoming solar radiation and outgoing infra-red radiation. Without any radiative forcing, solar radiation coming to the Earth would continue to be approximately equal to the infra-red radiation emitted from the Earth. The addition of greenhouse gases traps and increased fraction of the infra-red radiation, reradiating it back toward the surface and creating a warming influence (i.e., positive radiative forcing because incoming solar radiation will exceed outgoing infra-red radiation).
radiative transfer Theory dealing with the propagation of electromagnetic radiation through a medium.
radio spectrum The complete range of frequencies or wave lengths of electromagnetic waves, specifically those used in radio and television.
radio wave An electrical impulse sent through the atmosphere at radio frequency.
radioactive Giving off or capable of giving off radiant energy in the form of particles or rays, as in alpha, beta, and gamma rays.
radiometer An instrument that quantitatively measures electromagnetic radiation. Weather satellites carry radiometers to measure radiation from snow, ice, clouds, bodies of water, the Earth's surface, and the sun.
rain gauge Calibrated container that measures the amount of rainfall during a specific period of time.
real time As it happens.
reflection The return of light or sound waves from a surface. If a reflecting surface is plane, the angle of reflection of a light ray is the same as the angle of incidence.
relative humidity The ratio of the amount of water vapor in the air compared to the amount required for saturation (at a particular temperature and pressure).
resolution A measure of the ability to separate observable quantities. In the case of imagery, it describes the area represented by each pixel of an image. The smaller the area represented by a pixel, the more accurate and detailed the image.
respiration The process by which animals use up stored foods (by combustion with oxygen) to produce energy.
retrograde orbit An east-to-west orbit of Earth (Earth spins west to east). See prograde orbit.
revolution Process of the Earth circling the sun in its orbit. Revolution determines the seasons, and the length of the year. In addition, differences in seasons occur because of Earth's inclination (tilt on its axis) of about 23.5 degrees as it revolves around the sun. Compare with rotation.
rotation Process of the Earth turning on its axis. Rotation determines day and night, and the length of the day. Compare with revolution.
sahel The transition zone in Africa between the Sahara Desert to the north and tropical forests to the south. This dryland belt stretches across Africa and is under stress from land use and climate variability.
salinity The degree of salt in water. The rise in sea level due to global warming would result in increased salinity of rivers, bays and aquifers. This would affect drinking water, agriculture and wildlife.
sampling The process of obtaining a sequence of discrete digital values from a continuous sequence of analog data.
satellite revolution The time from one perigee (the point of an elliptical orbit path where a satellite is closest to Earth) to the next.
satellite A free-flying object that orbits the Earth, another planet, or the sun.
savanna One of the Earth's biomes characterized by an extensive cover of grasses with scattered trees. The savanna biome is a transitional biome between those dominated by forests and those dominated by grasses and is associated with climates having seasonal precipitation accompanied with a seasonal drought.
scanning radiometer An imaging system consisting of lenses, moving mirrors, and solid-state image sensors used to obtain observations of the Earth and its atmosphere. Scanning radiometers, which are the sole imaging systems on all current operational weather satellites, have far better long-term performance than the vidicon TV camera tubes used with earlier spacecraft.
scattering The process by which electromagnetic radiation interacts with and is redirected by the molecules of the atmosphere, ocean, or land surface. The term is frequently applied to the interaction of the atmosphere on sunlight, which causes the sky to appear blue (since light near the blue end of the spectrum is scattered much more than light near the red end).
scatterometer A high-frequency radar instrument that transmits pulses of energy towards the ocean and measures the backscatter from the ocean surface. It detects wind speed and direction over the oceans by analyzing the backscatter from the small wind-induced ripples on the surface of the water.
scene Object space illuminated by a sensor.
sea breeze Local coastal wind that blows from the ocean to land. Sea breezes usually occur during the day, because the heating differences of land and sea cause pressure differences. Cooler, heavier air from the sea moves in to replace rising warm air on the coastline. See land breeze
sea ice draft The height of sea ice from the keel (the lowest point underwater) to the water surface.
sea ice thickness The height of sea ice from the keel (the lowest point underwater) to the ridge (the highest point above water).
sea level The datum against which land elevation and sea depth are measured. Mean sea level is the average of high and low tides.
sea surface temperature (SST) The temperature of the layer of seawater (approximately 0.5 m deep) nearest the atmosphere.
sea surface temperature anomaly Temperature of emitted energy from the sea surface. SST anomaly = (SST - SST mean), where SST = sea surface temperature.
sensible heat The excess radiative energy that has passed from the Earth's surface to the atmosphere through advection, conduction, and convection processes.
sensor calibration The relationship between input and output for a given measurement.
shield volcano a low, broad volcano named for its resemblance to an ancient warrior shield.
shortwave radiation The radiation received from the sun and emitted in the spectral wavelengths less than 4 microns. It is also called 'solar radiation'.
sine wave A smoothly varying wave that repeats itself; its frequency is the rate at which the fundamental shape repeats itself. Any waveform can be distilled into a combination of pure sine waves of varying frequencies and amplitudes.
sink The process of providing storage for a substance. For example, plants--through photosynthesis--transform carbon dioxide in the air into organic matter, which either stays in the plants or is stored in the soils. The plants are a sink for carbon dioxide.
smog This is a term used to describe a mixture of smoke and fog. Smog occurs when high concentrations of moisture is combined with smoke (often containing oxides of sulfur and nitrogen) in the presence of high temperatures or thermal inversions and the absence of wind. These conditions cause polluted air to stagnate over industrial areas and can create a respiratory health hazard. Large coastal industrial centers with surrounding high ground are more prone to smog. There is often a diurnal (over a day) variation in the process of smog formation because one of the necessary components for its formation is sunlight.
solar backscatter ultraviolet radiometer (SBUV) Instrument that measures the vertical distribution and total ozone in the Earth's atmosphere. Data is used for the continuous monitoring of ozone distribution to estimate long-term trends. SBUV instruments are flown on NOAA polar-orbiting satellites.
solar constant Aka total solar irradiance. The constant expressing the amount of solar radiation reaching the Earth from the sun, approximately 1370 watts per square meter. It is not, in fact, truly constant and variations are detectable.
solar cycle Eleven-year cycle of sunspots and solar flares that affects other solar indexes such as the solar output of ultraviolet radiation and the solar wind. The Earth's magnetic field, temperature, and ozone levels are affected by this cycle.
solar maximum The point in the 11-year solar cycle at which sunspot activity is highest.
solar minimum The point in the 11-year solar cycle at which sunspot activity is lowest.
solar radiation Energy received from the sun is solar radiation. The energy comes in many forms, such as visible light (that which we can see with our eyes). Other forms of radiation include radio waves, heat (infrared), ultraviolet waves, and x-rays. These forms are categorized within the electromagnetic spectrum.
sounder A special kind of radiometer that measures changes in atmospheric temperature with height, as well as the content of various chemical species in the atmosphere at various levels. The High Resolution Infrared Radiation Sounder (HIRS), found on NOAA polar-orbiting satellites, is a passive instrument. See passive system.
southern oscillation A large-scale atmospheric and hydrospheric fluctuation centered in the equatorial Pacific Ocean. It exhibits a nearly annual pressure anomaly, alternatively high over the Indian Ocean and high over the South Pacific. Its period is slightly variable, averaging 2.33 years. The variation in pressure is accompanied by variations in wind strengths, ocean currents, sea-surface temperatures, and precipitation in the surrounding areas. El Niño and La Niña occurrences are associated with the phenomenon.
spatial A characteristic that refers to a location (which may be a specific location on the Earth's surface, or relative to an arbitrary point).
spectral band A finite segment of wavelengths in the electromagnetic spectrum.
spectral signature This refers to the particular form or shape evinced by the power spectrum calculated from the data comprising the time series of a process.
spectrophotometer A device for measuring the relative amounts of radiant energy or radiant flux as a function of wavelength.
spectrum 1. The series of colored bands diffracted and arranged in the order of their respective wave lengths by the passage of white light through a prism or other diffracting medium and shading continuously from red (produced by the longest visible wave) to violet (produced by the shortest visible wave). 2. Any of various arrangements of colored bands or lines, together with invisible components at both ends of the spectrum, similarly formed by light from incandescent gases or other sources of radiant energy, which can be studied by a spectrograph. 3. In radio, the range of wave lengths of radio waves, from 3 centimeters to 30,000 meters, or of frequencies of radio waves, from 10 to 10,000,000 kilocycles. Also radio spectrum. 4. The entire range of radiant energies. See electromagnetic spectrum.
stratification The formation of distinct layers with different temperatures, salinity, or oxygen content in the ocean or another body of water. When the water column becomes stratified with a layer of warm, buoyant water at the surface and a layer of colder, denser water below, vertical mixing (upwelling) slows down or stops. The lack of mixing can cause deeper water to become oxygen depleted, while surface waters become nutrient depleted.
stratocumulus Low altitude gray colored clouds composed of water droplets that have a patchy appearance. Each cloud patch consists of a rounded mass. This cloud has a somewhat uniform base and normally covers the entire sky. Between the patches blue sky can be seen.
stratosphere Region of the atmosphere between the troposphere and mesosphere, having a lower boundary of approximately 8 km at the poles to 15 km at the equator and an upper boundary of approximately 50 km. Depending upon latitude and season, the temperature in the lower stratosphere can increase, be isothermal, or even decrease with altitude, but the temperature in the upper stratosphere generally increases with height due to absorption of solar radiation by ozone.
stratovolcano a volcano composed of alternating layers of volcanic ash, lava, and rocks ejected by previous eruptions. Stratovolcanoes are typically steep-sloped and conical.
subduction a process in which one lithospheric plate descends beneath another, often as a result of folding or faulting
subsatellite point Point where a straight line drawn from a satellite to the center of the Earth intersects the Earth's surface.
subsidence In weather forecasting terminology, this term refers to sinking motions of air masses. It could also refer to sinking motions within fluids or bodies of water.
subtropical Generally the part of the Earth's surface between the tropics and the temperate regions, or between about 40 degrees N. and S.
sulfate aerosol Particulate matter that consists of compounds of sulfur formed by the interaction of sulfur dioxide and sulfur trioxide with other compounds in the atmosphere. Sulfate aerosols are injected into the atmosphere from the combustion of fossil fuels and the eruption of volcanoes like Mt. Pinatubo. Recent theory suggests that sulfate aerosols may lower the Earth's temperature by reflecting away solar radiation (negative radiative forcing). Global Climate Models which incorporate the effects of sulfate aerosols more accurately predict global temperature variations.
sulfur dioxide (SO2) A compound composed of one sulfur and two oxygen molecules. Sulfur dioxide emitted into the atmosphere through natural and anthropogenic processes is changed in a complex series of chemical reactions in the atmosphere to sulfate aerosols. These aerosols result in negative radiative forcing (i.e., tending to cool the Earth's surface).
sun-synchronous Describes the orbit of a satellite that provides consistent lighting of the Earth-scan view. The satellite passes the equator and each latitude at the same time each day. For example, a satellite's sun-synchronous orbit might cross the equator twelve times a day, each time at 3:00 p.m. local time. The orbital plane of a sun-synchronous orbit must also precess (rotate) approximately one degree each day, eastward, to keep pace with the Earth's revolution around the sun.
sunglint The mirror-like reflection of the Sun off a water surface in a satellite image. If the ocean were as smooth as a mirror, a sequence of nearly perfect reflections of the Sun would appear in a line along the track of the satelliteâ€™s orbit. Because the ocean is never perfectly smooth or calm, however, the Sunâ€™s reflection gets blurred as the light is scattered in all directions by waves. The blurred reflection gives the ocean surface a washed out appearance—the sunglint region.
sunphotometer A device that measures the properties of light emanating from the sun.
sunspot A region on the surface (photosphere) of the sun that is temporarily cool and dark compared to surrounding areas. See Sunspots and the Solar Max and ACRIMSAT fact sheet
surface air temperature The temperature of the air near the surface of the Earth, usually determined by a thermometer in an instrument shelter about 2 m above the ground. The true daily mean, obtained from a thermograph, is approximated by the mean of 24 hourly readings and may differ by 1.0 degrees C from the average based on minimum and maximum readings. The global average surface air temperature is 15 degrees C.
swath The area observed by a satellite as it orbits the Earth.
synoptic chart Chart showing meteorological conditions over a region at a given time; weather map.
synoptic view The ability to see large areas at the same time.
synthetic aperture radar (SAR) A high-resolution ground-mapping technique that effectively synthesizes a large receiving antenna by processing the phase of the reflected radar return. The along-track resolution is obtained by timing the radar return (time-gating) as for ordinary radar. The cross-track (azimuthal) resolution is obtained by processing the Doppler phase of the radar return. The cross-track 'dimension' of the antenna is a function of the length of time over which the Doppler phase is collected. See Doppler effect.
taiga The open northern part of the boreal forest. It consists of open woodland of coniferous trees growing in a rich floor of lichen, and is generally cold and swampy.
tectonic Corresponding with the broad architecture of the outer part of the Earth
telemetry A space-to-ground data stream of measured values (including instrument science data, instrument engineering data, and spacecraft engineering data) that does not include command, tracking, computer memory transfer, audio, or video signals.
temperate Region in which the climate undergoes seasonal change in temperature and moisture. Temperate regions of the earth lie primarily between 30 and 60 degrees latitude in both hemispheres.
temperature A measure of the energy in a substance. The more heat energy in the substance, the higher the temperature. The Earth receives only one two-billionth of the energy the sun produces. Much of the energy that hits the Earth is reflected back into space. Most of the energy that isn't reflected is absorbed by the Earth's surface. As the surface warms, it also warms the air above it.
temporal A characteristic that refers to the time at which a given data set was acquired.
terminus (of a glacier) The end, or foot, of a glacier.
terrestrial radiation The total infrared radiation emitted by the Earth and its atmosphere in the temperature range of approximately 200-300K. Because the Earth is nearly a perfect radiator, the radiation from its surface varies as the fourth power of the surface's absolute temperature. Terrestrial radiation provides a major part of the potential energy changes necessary to drive the atmospheric wind system and is responsible for maintaining the surface air temperature within limits for livability.
thematic mapper (TM) A Landsat multispectral scanner designed to acquire data to categorize the Earth's surface. Particular emphasis was placed on agricultural applications and identification of land use. The scanner continuously scans the surface of the Earth, simultaneously acquiring data in seven spectral channels. Overlaying two or more bands produces a false color image. The ground resolution of the six visible and shortwave bands of the Thematic Mapper is 30 meters, and the resolution of the thermal infrared band is 120 meters. Thematic mappers have been flown on Landsats-4 and -5.
theorem The last statement of a formal proof; a mathematical assertion that can be proven.
theory An explanation for some phenomenon that is based on observation, experimentation, and reasoning.
thermal infrared Electromagnetic radiation with wavelengths between about 3 and 25 micrometers.
thermal Of, making use of, producing, or caused by heat.
thermocline A transition layer of water in the ocean, with a steeper vertical temperature gradient than that found in the layers of ocean above and below. The permanent thermocline separates the warm mixed surface layer of the ocean from the cold deep ocean water, and is found between 100- and 1000-m depths. The thermocline first appears at the 55(em60° N and S latitudes, where it forms a horizontal separation between temperate and polar waters. The thermocline reaches its maximum depth at mid-latitudes and is shallowest at the equator and at its northern and southern limits. The thermocline is stably stratified, and transfer of water and carbon dioxide across this zone occurs very slowly. Thus, the thermocline acts as a barrier to the downward mixing of carbon dioxide.
thermodynamic The science of heat and temperature and of the laws governing the conversion of heat into mechanical, electrical, or chemical energy.
thermohaline Refers to the combined effects of temperature and salinity that contribute to density variations in the oceans.
thermosphere The outermost shell of the atmosphere, between the mesosphere and outer space; where temperatures increase steadily with altitude.
thunder The sound that results from lightning. Lightning bolts (static electricity) produce intense heat. This burst of heat makes the air around the bolt expand explosively, producing the sound we hear as thunder. Since light travels faster than sound, we see the lightning before we hear the thunder.
thunderstorm Local storm resulting from warm humid air rising in an unstable environment. Air may start moving upward because of unequal surface heating, the lifting of warm air along a frontal zone, or diverging upper-level winds (these diverging winds draw air up beneath them). The scattered thunderstorms that develop in the summer are called air-mass thunderstorms because they form in warm, maritime tropical air masses away from other weather fronts. More violent severe thunderstorms form in areas with a strong vertical wind shear that forces the updraft into the mature stage, the most intense stage of the thunderstorm. Severe thunderstorms can produce large hail, forceful winds, flash floods, and tornadoes.
topography The technique of graphically representing the exact physical features of a place or region on a map. The physical features of a place or region.
total solar irradiance The amount of solar energy hitting the top of the Earth’s atmosphere, currently accepted to be about 1,368 watts per square meter.
trace gas Any one of the less common gases found in the Earth's atmosphere. Nitrogen, oxygen, and argon make up more than 99 percent of the Earth's atmosphere. Other gases, such as carbon dioxide, water vapor, methane, oxides of nitrogen, ozone, and ammonia, are considered trace gases. Although relatively unimportant in terms of their absolute volume, they have significant effects on the Earth's weather and climate.
trade winds Surface air from the horse latitudes that moves back toward the equator and is deflected by the Coriolis Force, causing the winds to blow from the Northeast in the Northern Hemisphere and from the Southeast in the Southern Hemisphere. These steady winds are called trade winds because they provided trade ships with an ocean route to the New World.
transpiration The process in plants by which water is taken up by the roots and released as water vapor by the leaves. The term can also be applied to the quantity of water thus dissipated.
tropical The area between 23.5 degrees north and south of the equator. This region has small daily and seasonal changes in temperature, but great seasonal changes in precipitation.
tropopause The boundary between the troposphere and the stratosphere (about 8 km in polar regions and about 15 km in tropical regions), usually characterized by an abrupt change of lapse rate. The regions above the troposphere have increased atmospheric stability than those below. The tropopause marks the vertical limit of most clouds and storms.
troposphere The lower atmosphere, to a height of 8-15 km above Earth, where temperature generally decreases with altitude, clouds form, precipitation occurs, and convection currents are active. See atmosphere.
tropospheric ozone (O3) Ozone that is located in the troposphere and plays a significant role in the greenhouse gas effect and urban smog. See Ozone for more details.
trough Elongated area of low atmospheric pressure, either at the surface or in the upper atmosphere.
tundra A type of ecosystem dominated by lichens, mosses, grasses, and woody plants. It is found at high latitudes (arctic tundra) and high altitudes (alpine tundra). Arctic tundra is underlain by permafrost and usually very wet.
typhoon Hurricanes in the Western Pacific Ocean.
ultraviolet radiation The energy range just beyond the violet end of the visible spectrum. Although ultraviolet radiation constitutes only about 5 percent of the total energy emitted from the sun, it is the major energy source for the stratosphere and mesosphere, playing a dominant role in both energy balance and chemical composition. Most ultraviolet radiation is blocked by Earth's atmosphere, but some solar ultraviolet penetrates and aids in plant photosynthesis and helps produce vitamin D in humans. Too much ultraviolet radiation can burn the skin, cause skin cancer and cataracts, and damage vegetation.
updraft A relatively small-scale current of air with marked upward vertical motion.
upwelling The rising of colder, denser water from deep in the ocean or other body of water to the surface, often as a result of wind-driven surface currents. Upwelling can occur anywhere, but is most common in coastal areas and along the equator. Because nutrients accumulate in deeper ocean water through the remains and waste of marine life, upwelling fertilizes surface waters and increases productivity.
validation Comparing a climate model's predictions with observations of the real climate, in order to test the reliability and accuracy of the model. The most obvious way to test a climate model is to use it to analyze past events, and then see whether its simulated prediction 'came true,' or how close it was to being correct.
vector A physical quantity that has both a magnitude and a direction and that adds like displacement; velocity, acceleration, and force are prime examples.
velocity The time rate at which a body changes its position vector; velocity is a vector quantity whose magnitude is expressed in units of distance over time, such as miles per hour. (From the Latin word for "speed.")
vernal equinox The beginning of spring in the Northern Hemisphere. The time/day that the sun crosses the equatorial plane going from south to north.
visible That part of the electromagnetic spectrum to which the human eye is sensitive, between about 0.4 and 0.7 micrometers. See spectrum.
vog volcanic smog that results from the mixing of sulfur dioxide and other volcanic pollutants with oxygen and water vapor in the presence of sunlight.
vortex A mass of fluid rotating about an axis, i.e., whirlpool or whirlwind.
water cycle The process by which water is transpired and evaporated from the land and water, condensed in the clouds, and precipitated out onto the earth once again to replenish the water in the bodies of water on the earth. See The Water Cycle
water vapor The most abundant greenhouse gas, it is the water present in the atmosphere in gaseous form. Water vapor is an important part of the natural greenhouse effect. While humans are not significantly increasing its concentration, it contributes to the enhanced greenhouse effect because the warming influence of greenhouse gases leads to a positive water vapor feedback. In addition to its role as a natural greenhouse gas, water vapor plays an important role in regulating the temperature of the planet because clouds form when excess water vapor in the atmosphere condenses to form ice and water droplets and precipitation.
wave cyclone A cyclone that forms and moves along a front, producing by its circulation a wavelike deformation of the front.
wave 1. In electricity, a periodic variation of an electric current or voltage. 2. In physics, any of the series of advancing impulses set up by a vibration, pulsation, or disturbance in air or some other medium, as in the transmission of heat, light, sound, etc.
wavelength Physical distance of one period (wave repeat).
weather Atmospheric condition at any given time or place. Compare with climate.
weathering the natural processes by which the actions of atmospheric and other environmental agents, such as wind, rain, and temperture changes, result in the physical disintegration and chemical decomposition of rocks and earth materials in place, with little or no transport of the loosened or altered material.
wind chill The wind can reduce significantly the amount of heat your body retains. The following wind chill chart does not take into account such variables as type of clothing worn, amount of exposed flesh, and physical condition, all of which would alter body heat.
wind velocity Vector term that includes both wind speed and wind direction.
wind A natural motion of the air, especially a noticeable current of air moving in the atmosphere parallel to the Earth's surface. Winds are caused by unequal heating and cooling of the Earth and atmosphere due to absorbed, incoming solar radiation and infrared radiation lost to space--as modified by such effects as the Coriolis force, the condensation of water vapor, the formation of clouds, the interaction of air masses and frontal systems, friction over land and water, etc.
window Term used to denote a region of the electromagnetic spectrum where the atmosphere does not absorb radiation strongly.
x-ray Short electromagnetic waves whose wavelengths range from .00001 to 3000 angstroms.
xenolith Rock fragment or mineral found in igneous rock that is not of igneous origins.
xeric An environment or habitat containing little moisture.
zooplankton Animal plankton. Small herbivores that float or drift near the surface of aquatic systems and that feed on plant plankton (phytoplankton and nanoplankton).

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