EMIC Waves in the Earth's Inner Magnetosphere as a Function of Solar Wind Structures During Solar Maximum

Abstract

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.

Low Frequency ULF Waves in the Earth's Inner Magnetosphere: Statistics During Coronal Mass Ejections and Seeding of EMIC Waves

“…They formulated criteria to identify the CME, HSS, and QSW conditions in the upstream SW and then categorized each EMIC wave event according to the upstream SW conditions preceding to the event. As expected, they reported that the majority of EMIC wave events were observed during CME conditions in the upstream SW, where the state of the upstream SW is identified as CME if an interplanetary shock, and/or ejecta, and/or a magnetic cloud are observed within the time interval of 18 h preceding the end of an analyzed EMIC wave event (see Gamayunov et al, 2020, for more details). For our analysis of the low frequency ULF waves here we will use those EMFISIS data that include the CME-driven EMIC wave events identified by Gamayunov et al (2020).…”

“…As expected, they reported that the majority of EMIC wave events were observed during CME conditions in the upstream SW, where the state of the upstream SW is identified as CME if an interplanetary shock, and/or ejecta, and/or a magnetic cloud are observed within the time interval of 18 h preceding the end of an analyzed EMIC wave event (see Gamayunov et al, 2020, for more details). For our analysis of the low frequency ULF waves here we will use those EMFISIS data that include the CME-driven EMIC wave events identified by Gamayunov et al (2020). (Note that EMIC waves do not affect the low frequency ULF waves, and so the statistics of low frequency ULF waves cannot depend on whether or not EMIC fluctuations exist in the data segments analyzed.)…”

“…The AE dependencies in Figures 6a and 6c are qualitatively similar to those for the Kp dependencies in Figures 5a and 5c 1.4 1.5 P     . A strong power increase takes place in the region around AE 400 nT  that separates the quiet and disturbed geomagnetic conditions (e.g., Gamayunov et al, 2020). The observed power increase is likely to be caused by unstable ion distributions that are developing during an increased ion injection in the nightside magnetosphere by both the substorm-associated inductive electric field and the large-scale electric field of convection.…”

“…Recently Gamayunov et al. (2020) analyzed the strongest EMIC wave events observed by the two Van Allen Probes during their first MLT revolution. They formulated criteria to identify the CME, HSS, and QSW conditions in the upstream SW and then categorized each EMIC wave event according to the upstream SW conditions preceding to the event.…”

“…For our analysis we use the magnetic field observations by the two Van Allen Probes (Kessel et al., 2013; Mauk et al., 2013) during the time period from October 1, 2012 through June 7, 2014. During this period both probes completed their first pass through all magnetic local times (MLTs), and this MLT revolution took place during solar maximum of the 24th solar cycle (Gamayunov et al., 2020, Figure 1). Because the CME occurrence rate maximizes during solar maximum (e.g., Borovsky & Denton, 2006), as a first step here we analyze the ULF waves only during CME conditions in the upstream SW. To our knowledge, such an analysis for ULF waves during CME conditions is done for the first time.…”