Differences in inner magnetospheric wave activity, outer Van Allen belt electron dynamics and atmospheric precipitation during CME sheaths and flux ropes

Coronal mass ejection (CME) driven sheath regions are one of the key structures driving strong magnetospheric disturbances, in particular at high latitudes. Sheaths are turbulent and compressed regions that exhibit large-amplitude magnetic field variations and high and variable dynamic pressure. They thus put the magnetosphere under particularly strong solar wind forcing. We show here the results of our recent studies that have investigated the response of inner magnetosphere plasma waves, energy and L-shell resolved outer belt electron variations and precipitation of high-energy electrons to the upper atmosphere during sheath regions. The data come primarily from Van Allen Probes and ground-based riometers. Our results reveal that sheaths drive intense “wave storms” in the inner magnetosphere (ULF, EMIC, chorus, hiss). Lower-energy electron fluxes (source and seed populations) are typically enhanced due to frequent and strong substorms injecting fresh electrons, while relativistic electrons are effectively depleted at wide L-ranges due to scattering by wave-particle interactions and magnetopause shadowing playing in concert. We found that even non-geoeffective sheaths can drive significant wave activity and dramatic changes in the outer belt electron fluxes. The “complex ejecta”, however, that consist of multiple sheaths and distorted CME ejecta can lead to sustained chorus and ULF waves, and as a consequence, effective electron acceleration to high energies. We also report some distinct characteristics in the intensity and Magnetic Local Time distribution of precipitation during sheaths when compared to other large-scale solar wind driver structures. The different precipitation responses likely stem from driver specific characteristics in their ability to excite inner magnetosphere plasma waves.