A comparison of outer electron radiation belt dropouts during solar wind stream interface and magnetic cloud driven storms

Abstract

Energetic electrons are trapped in the Earth's radiation belts which occupy a toroidal region between 3 and 7 R E above the Earth's surface. Rapid loss of electrons from the radiation belts is known as dropouts. The source and loss mechanisms regulating the radiation belts population are not yet understood entirely, particularly during geomagnetic storm times. Nevertheless, the dominant loss mechanism may require an event based study to be better observed. Utilizing multiple data sources from the year 1997-2007, this study identifies radiation belt electron dropouts which are ultimately triggered when solar wind stream interfaces (SI) arrived at Earth, or when magnetic clouds (MC) arrived. Using superposed epoch analysis (SEA) technique, a synthesis of multiple observations is performed to reveal loss mechanism which might, perhaps, be a major contributor to radiation belt losses under SI and MC driven storms. Results show an abrupt slower decaying precipitation of electron peak (about 3000 counts/sec) on SI arrival within 5.05 < L < 6.05, which persist till 0.5 day before gradual recovery. This pattern is interpreted as an indication of depleted electrons from bounce lost cone via precipitating mechanism known as relativistic electron microburst. On the other hand, MC shows a pancake precipitating peak extending to lower L (Plasmapause); indicating a combination of electron cyclotron harmonic (ECH) and whistler mode waves as the contributing mechanisms.

Contribution of ULF Wave Activity to the Global Recovery of the Outer Radiation Belt During the Passage of a High‐Speed Solar Wind Stream Observed in September 2014

“…Coupling between the solar wind and the Earth's magnetosphere depends on the global structure of the solar wind, including interplanetary coronal mass ejections. Previous studies have shown that there is a relationship between the properties of the solar wind during HSS and the dynamics of electron fluxes in the outer radiation belt (Hendry et al, ; MacDonald et al, ; Ogunjobi et al, ). Here we investigate the impact of the high‐speed and low‐density solar wind streams on the acceleration of high‐energy electrons trapped in the outer radiation belt (e.g., Li et al, ).…”