Speaker
Description
We investigate operational anomalies on GOES spacecraft that are attributed to shallow internal charging driven by enhanced flux of 100 - 300 keV electrons. This population is not traditionally associated with either surface charging (dominated by electrons with energies 10s of keV) or deep dielectric charging (typically linked to MeV-range electrons). Using data from 2017-2021 during the recent solar minimum, we examine solar wind conditions and geomagnetic indices associated with these anomalies. All anomalies are divided into clustered anomalies (separated by less than two days) and background anomalies (separated by longer intervals). Clustered anomalies exhibit a strong dependence on magnetic local time (MLT), peaking prior to local noon, and are associated with elevated Kp values. In contrast, background anomalies are uniformly distributed in MLT and have a distinct Kp dependence. Superposed epoch analysis reveals that clustered anomalies predominantly occur during high-speed solar wind streams (HSS), under conditions of elevated solar wind velocity, reduced proton number density, and weakly southward IMF Bz. The observed MLT and Kp dependencies for clustered anomalies suggest a charging process involving dielectric materials with relaxation timescales shorter than one day, while background anomalies may reflect longer-term accumulation. To demonstrate the modeling capabilities, we employ the Comprehensive Inner Magnetosphere Ionosphere (CIMI) model to simulate the 100 - 300 keV electron fluxes at GEO. The model reproduces the observed MLT distributions and flux magnitudes with reasonable accuracy, supporting the identification of this electron population as a key contributor to shallow charging phenomena. This study highlights the role of the intermediate-energy electron population in spacecraft anomaly occurrence at GEO, particularly during periods of HSSs. Our findings call for a reevaluation of hazard assessments for spacecraft charging to incorporate this important electron energy range.
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