How are Solar Flares Classified and Why?


The classification of solar flares is important for space weather forecasting and its potential impacts on Earth. Solar flares can cause a variety of effects on the Earth's upper atmosphere, such as ionization, radio blackouts, and geomagnetic storms. Geomagnetic storms, in turn, can cause power outages, communication disruptions, and damage to satellites and other space-based infrastructure.

Solar flares that are classified as X-class are the most powerful and can have a more significant impact on space weather than smaller flares. For example, an X-class flare could produce a severe geomagnetic storm that disrupts power grids, communication networks, and satellite operations. Therefore, understanding the classification of solar flares and their potential impacts is crucial for space weather forecasting and taking appropriate measures to mitigate any potential negative effects.

Solar Flare Classification System

Solar flares are classified based on their intensity, which is measured by the amount of X-ray radiation they emit at the peak of the flare. The classification system was established by the National Oceanic and Atmospheric Administration (NOAA) and is divided into three main categories: C, M, and X. Each category is ten times more intense than the one below it. Within each category, flares are assigned a number from 1 to 9 (except for X-class flares, which can go beyond 9), indicating their relative intensity within that category.

  • C-Class Flares: These are the smallest and most common solar flares, with intensities between 10^-6 and 10^-5 Watts per square meter (W/m^2). C-class flares typically have minimal impact on Earth and spacecraft, but they can cause minor radio blackouts in the polar regions.
  • M-Class Flares: M-class flares are medium-sized flares, with intensities between 10^-5 and 10^-4 W/m^2. These flares can cause brief radio blackouts that affect Earth's polar regions and can generate minor radiation storms. They may also cause small-scale geomagnetic storms, which can affect power grids, satellite operations, and GPS signals.
  • X-Class Flares: These are the most powerful and least frequent solar flares, with intensities greater than 10^-4 W/m^2. X-class flares can have significant effects on Earth and spacecraft, depending on their intensity:
    • Radio blackouts: X-class flares can cause widespread high-frequency (HF) radio blackouts, disrupting communications and navigation systems, especially near the Earth's poles.
    • Geomagnetic storms: Intense solar flares can trigger strong geomagnetic storms, which can affect power grids, induce electrical currents in pipelines, disrupt GPS signals, and cause auroras at lower latitudes than usual.
    • Radiation storms: High-energy particles released during powerful solar flares can cause radiation storms that pose a risk to astronauts, especially those on extravehicular activities or traveling to the Moon or Mars. These storms can also damage satellites, affecting their electronics and solar panels, as well as degrade the performance of other spacecraft systems.
    • Satellite drag: Increased geomagnetic activity can cause the Earth's upper atmosphere to expand, increasing the drag on low-Earth orbit satellites. This can lead to a decrease in their orbital altitude, shortening their operational lifetimes or even causing them to re-enter the atmosphere.

It's worth noting that solar flares can also be classified based on their location on the solar disk, their duration, and other characteristics. However, the GOES classification system is the most commonly used method for classifying solar flares based on their energy output.

The video below is of the M1 Solar Flare and Eruption, February 7, 2023 which is an example of a Sun event which can cause space weather.

Source: NASA