Lapse rate

Lapse Rate is a term used in meteorology and climatology to describe the rate at which air temperature decreases with an increase in altitude. Understanding the lapse rate is crucial for various applications, including weather forecasting, aviation, and studying the Earth's atmosphere. The concept is also significant in environmental science and physical geography for understanding climate patterns and the distribution of plant and animal life.

Definition

The lapse rate is defined as the rate of decrease in temperature with elevation. It is usually expressed in degrees Celsius per kilometer (°C/km) or degrees Fahrenheit per thousand feet (°F/1000ft). The average global lapse rate is about 6.5°C/km (3.57°F/1000ft) in the troposphere, which is the lowest layer of the Earth's atmosphere.

Types of Lapse Rates

There are several types of lapse rates, each significant in the study of atmospheric processes:

• Dry Adiabatic Lapse Rate (DALR): The rate at which dry air cools as it rises or warms as it descends, assuming no heat exchange with the surroundings. The DALR is approximately 9.8°C/km (5.38°F/1000ft).
• Moist Adiabatic Lapse Rate (MALR): The rate at which saturated air (air at 100% humidity) cools as it rises. The MALR varies with temperature and pressure but is generally less than the DALR because of the heat released during condensation.
• Environmental Lapse Rate (ELR): The actual rate of temperature decrease with altitude in the atmosphere at a specific time and place. The ELR can vary widely depending on local weather conditions.

Importance

The lapse rate is a fundamental concept in understanding atmospheric stability and the development of weather patterns. For example, if the ELR is greater than the DALR, the atmosphere is considered unstable, which can lead to the formation of clouds, thunderstorms, and other weather phenomena. Conversely, if the ELR is less than the DALR, the atmosphere is stable, which tends to suppress cloud formation and precipitation.

In aviation, pilots must be aware of the lapse rate and atmospheric conditions to ensure safe flight operations, especially when flying over mountainous terrain where rapid changes in altitude can lead to significant temperature variations.

See Also

• Atmospheric pressure
• Troposphere
• Weather forecasting
• Climatology