Speakers
Description
High-speed streams (HSSs) and interplanetary coronal mass ejections (ICMEs) are two primary solar wind structures responsible for driving geomagnetic storms. These structures originate from distinct solar sources and differ in terms of plasma composition and dynamics. One important consequence of their interaction with the Earth's magnetosphere is the generation of plasma waves, including electromagnetic ion cyclotron (EMIC) waves. In the outer radiation belt region, EMIC waves can be excited by anisotropic distributions of ring current ions (H⁺, He⁺, and O⁺), often enhanced during geomagnetic storms due to ion injections from the plasma sheet. EMIC waves cause losses in the outer radiation belt by scattering relativistic electrons to lower pitch angles through cyclotron resonance, pushing them into the loss cone. This leads to their precipitation into the atmosphere. While EMIC wave occurrence during storms has been extensively investigated, the role of solar wind composition — particularly the ion abundances associated with HSSs and ICMEs — in modulating EMIC wave generation remains poorly constrained. This study investigates how differences in solar wind ion composition (H⁺, He⁺, and O⁺) influence EMIC wave generation mechanisms in the outer radiation belt during geomagnetic storms driven by HSSs and ICMEs. We analyzed multi-satellite observations from the Van Allen Probes, THEMIS, and ACE missions, focusing on events from the Van Allen era (October 2012 to June 2019) with Dst ≤ –30 nT and with apogees of THEMIS and Van Allen Probes located in the nightside magnetosphere. ACE data were used to characterize the upstream solar wind, including ion composition. THEMIS observations allowed identification of ion injections, and the Van Allen Probes provided detailed measurements of EMIC wave activity and ion flux variations (H⁺, He⁺, and O⁺) in the inner magnetosphere. The results show that ion injections are generally stronger during ICME-driven events than during those driven by HSSs. Moreover, EMIC wave activity — characterized by power spectral density — tends to be more intense during ICME-driven storms. Ongoing analysis includes the computation of the integrated EMIC wave power during both types of events and the classification of wave activity by ion band, aiming to determine whether different solar wind structures preferentially enhance certain EMIC wave bands. These results contribute to a better understanding of the relationship between solar wind composition and EMIC wave generation mechanisms, with implications for wave–particle interaction studies and the modeling of radiation belt responses under different solar wind driving conditions.
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