Ionospheric Storms
An ionospheric storm is defined as turbulence in the F region of the ionosphere, usually due to a sudden burst of radiation from the Sun (WMO, 1992).
NB. The F region is the highest region of the ionosphere, at altitudes greater than 160 km (100 miles).
Primary reference(s)
WMO, 1992. International Meteorological Vocabulary. World Meteorological Organization (WMO), Report No. 182. Accessed 16 October 2020.
Additional scientific description
‘Ionospheric storm’ is the term used to denote the major changes that take place in the ionosphere as a result of geomagnetic activity. Ionospheric storms are closely associated with magnetic storms and can lead to severe disruptions of radio-wave propagation, particularly at high latitudes (AMS, 2012).
The Ionosphere is part of Earth’s upper atmosphere, between 80 and about 600 km where extreme ultraviolet (EUV) and x-ray solar radiation ionise the atoms and molecules. The ionosphere is important because it reflects and modifies radio waves used for communication, navigation and radar tracking of space objects. Other phenomena such as energetic charged particles and cosmic rays also have an ionising effect and can contribute to the ionosphere (NOAA, 2019a).
The atmospheric atoms and molecules are impacted by the high energy EUV and X-ray photons from the sun. The photon flux at these wavelengths varies by nearly a factor of ten over the 11-year solar cycle. The density of the ionosphere changes accordingly. Due to spectral variability of the solar radiation and the density of various constituents in the atmosphere, layers are created within the ionosphere, called the D, E, and F-layers. Other solar phenomena, such as flares, and changes in the solar wind and geomagnetic storms also affect the state of the ionosphere. Since the largest amount of ionisation is caused by solar irradiance, the night-side of the Earth, and the pole pointed away from the sun (depending on the season) have much less ionisation than the day-side of the Earth, and the pole pointing towards the sun (NOAA, 2019b).
In general, there are two phases of an ionospheric storm, an initial increase in electron density (the positive phase) lasting a few hours, followed by a decrease lasting a few days. During night-time this decrease can result in the effective disappearance of the ionosphere and hence is another process that can cause High-frequency (HF) blackout. At low latitudes only the positive phase is usually seen. Individual storms can vary, and their behaviour depends on geomagnetic latitude, season, and local time (NASA, 2019).
Metrics and numeric limits
The ionospheric storm scale called ‘I-scale’ [ái skéil] is used in ionospheric storm plots and for the classification of phenomena. See ISES (2019) for further details on the I-scale.
Key relevant UN convention / multilateral treaty
None identified.
Examples of drivers, outcomes and risk management
Ionospheric storms are caused by solar activity such as flares and coronal mass ejections, which result in large variations in the particle and electromagnetic radiation incident upon the Earth. Thus, it is important to monitor such storms, and if possible forecast their evolution (NASA, 2019).
References
AMS, 2012. Ionospheric storm. Glossary of Meteorology, American Meteoroidal Society (AMS). Accessed 25 November 2019.
ISES, 2019. Ionospheric storm scale. International Space Environment Service (ISES). Accessed 25 November 2019.
NASA, 2019. Ionospheric storms. National Aeronautics and Space Administration (NASA). Accessed 25 November 2019.
NASA, 2019a. Ionosphere. Space Weather Prediction Center, National Oceanic and Atmospheric Administration (NOAA). Accessed 25 November 2019.
NASA, 2019b. Space Weather Glossary. Space Weather Prediction Center, National Oceanic and Atmospheric Administration (NOAA). Accessed 25 November 2019.