Pc5 wave storms in near-Earth space

Ultra low frequency (ULF) waves occur in the Earth’s magnetosphere due to various drivers. For example, large-scale structures originating from the Sun, such as high-speed streams (HSS) and interplanetary coronal mass ejections (ICME), are associated with elevated wave activity. ULF waves, especially the Pc5 frequency range (2-7 mHz), cause electron acceleration in the radiation belts. These high-energy electrons can damage satellites in orbits near the radiation belts. This is one of the main motivations of researching why and when ULF wave activity occurs.

In this work we define a “wave storm” to describe time periods of higher Pc5 wave power, by using a Pc5 index calculated from ground-based magnetometer measurements from the Earth's dayside. We investigate which structures drive the most wave activity and which cause the most intense wave storms. The number of wave storms is observed to have variation along the solar cycle. Similarly to geomagnetic storms, ICMEs drive the majority of the most intense wave storms. Sheath regions on ICMEs increase the probability of a wave storm. We compare the values of solar wind parameters during and outside of wave storms. The clearest differences are found in solar wind velocity, as expected. To investigate the effect on radiation belts, we do a similar comparison to geostationary electron flux indices. Radiation belt electron flux is observed to increase in relation to wave storms, but with a time lag.