Solar cycle

Sunspot Numbers

Solar Cycle Prediction

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Solar Cycle

The Solar Cycle, also known as the sunspot cycle, is a nearly periodic 11-year change in the Sun's activity measured in terms of variations in the number of observed sunspots on the solar surface. Sunspots are regions of reduced surface temperature caused by concentrations of magnetic field flux that inhibit convection. The cycle is produced by the solar magnetic activity cycle and is the most prominent aspect of the Sun's larger 22-year magnetic cycle known as the Hale cycle.

Overview

The Solar Cycle affects all layers of the solar atmosphere, influencing space weather and geomagnetic activities through the emission of solar flares, the ejection of coronal mass ejections (CMEs), and variations in solar wind and solar irradiance. These in turn can affect satellite operations, communication systems, and even power grids on Earth.

History

The existence of the solar cycle was first observed in 1843 by Samuel Heinrich Schwabe, who after 17 years of observations noticed a periodic variation in the number of sunspots. Rudolf Wolf later compiled and studied these observations, formalizing the method to calculate the sunspot number to monitor the solar cycle's progress.

Phases of the Solar Cycle

The solar cycle can be divided into several phases, primarily characterized by the rise to a maximum and then a decline to a minimum in sunspot numbers. These phases are:

1. Minimum Solar Activity: Characterized by few to no sunspots, this phase marks the beginning of a new solar cycle. 2. Ascending Phase: Sunspot numbers increase, leading to more frequent solar flares and CMEs. 3. Solar Maximum: The peak phase of the cycle, with the highest number of sunspots and solar activity. 4. Descending Phase: Sunspot numbers and solar activity decrease. 5. Minimum Solar Activity: The cycle ends as it returns to a period of minimal sunspots, before beginning anew.

Impact on Earth

The Solar Cycle has significant effects on Earth's climate and space environment. During solar maximum, the increased solar activity can lead to more intense Northern Lights (aurora borealis) and Southern Lights (aurora australis). However, it can also pose risks to satellite integrity, increase radiation exposure to astronauts, and affect power grid operations.

Predicting the Solar Cycle

Predicting the characteristics of future solar cycles is an area of ongoing research. Various models and methods are used, including statistical analysis and dynamo theory, but predicting the exact timing and strength of solar cycles remains challenging.

Solar Cycle 25

The current cycle, Solar Cycle 25, began in December 2019, as announced by the Solar Cycle 25 Prediction Panel, an international group of experts. Early predictions suggest that Solar Cycle 25 will be similar in strength to its predecessor, Solar Cycle 24, which was below average in activity compared to previous cycles.