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Here we analyze the statistics of electromagnetic ion cyclotron (EMIC) waves observed in the Earth's inner magnetosphere during coronal mass ejection (CME), high-speed stream (HSS), and quiet solar wind (QSW) conditions in the upstream solar wind (SW). For our analysis we use the EMIC wave observations by the two Van Allen Probes during their first magnetic local time (MLT) revolution. The major results of our analysis are as follows: (1) Criteria to identify the HSS, CME, and QSW conditions in the SW are formulated. (2) 54%, 36%, and 10% of EMIC wave events are observed during CME, HSS, and QSW, respectively. (3) 12% of events are closely associated with the fast growth of magnetospheric compression, among which 76%, 24%, and 0% are observed during CME, HSS, and QSW, respectively. (4) A majority of the QSW, HSS-driven, and CME-driven events is observed in the 9–12, 12–24, and 8–24 hr MLT sectors, respectively. (5) CME-driven events are distributed along all L shells, whereas the majority of the HSS-driven and QSW events are confined to L > 3.5. (6) The fractions of events during CME and HSS have a maximum in the near-equatorial region, whereas the fractions of the QSW events have a minimum there. (7) Independent of the SW driver, no strong events are observed below the local O+ gyrofrequency, whereas 65–70% and 30–35% of events are observed between the O+ and He+ gyrofrequencies and above the He+ gyrofrequency, respectively.


Published in JGR Space Physics at 10.1029/2020JA027990

Available for download on Saturday, February 20, 2021

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