To understand the relationship between generation of electromagnetic ion cyclotron (EMIC) waves and energetic particle injections, we performed a statistical study of EMIC waves associated with and without injections based on the Van Allen Probes (Radiation Belt Storm Probes) and Geostationary Operational Environmental Satellite (GOES; GOES-13 and GOES-15) observations. Using 47 months of observations, we identified wave events seen by the Van Allen Probes relative to the plasmapause and to energetic particle injections seen by GOES-13 and GOES-15 on the nightside. We separated the events into four categories: EMIC waves with (without) injections inside (outside) the plasmasphere. We found that He + EMIC waves have higher occurrence rate inside the plasmasphere, while H + EMIC waves predominantly occur outside the plasmasphere. Meanwhile, the time duration and peak occurrence rate of EMIC waves associated with injections are shorter and limited to a narrower magnetic local time region than those without injections, indicating that these waves have localized source regions. He + EMIC waves inside the plasmasphere associated with injection are usually accompanied by an increase in H + flux within energies of 1–50 keV through all magnetic local time regions, while most wave events outside the plasmasphere show less relationship with H + flux increase. From these observations, we suggest that injected hot ions are the major driver of He + EMIC waves inside the plasmasphere during active time. Expanding plasmasphere during quiet times can provide broad wave source regions for He + EMIC waves on the dayside. However, H + EMIC waves outside the plasmasphere show different characteristics, suggesting that these waves are generated by other processes.
Bibliographical noteFunding Information:
C.-W. Jun and L. R. Lyons were supported by NASA grant NNX16AF76G. J. Bortnik would like to acknowledge the NASA LWS grant NNX14AN85G and NASA HTIDeS NNX16AG21G. The 1-min time resolution GOES magnetic field and energetic particles data were provided from GOES Space Environment Monitor Data describing the environment at geosynchronous orbit, https://www.ngdc.noaa.gov/stp/ satellite/goes/dataaccess.html. We acknowledge use of Van Allen Probes data of the Level 3 EMFISIS magnetometer data obtained from http://emfisis.physics.uiowa.edu/ data/index; the Level 3 HOPE unidimensional particle flux data were obtained from https://www.rbsp-ect. lanl.gov/data_pub/rbspa/hope/level3/. The geomagnetic indices (Kp, AE, and SYM-H index) data were obtained from the SPDF/Goddard Space Flight Center interface at http://omniweb.gsfc. nasa.gov/.
- EMIC waves associated with and without injections
- relationship between EMIC wave activity and energetic H flux variation
- simultaneous observations using the Van Allen Probes and GOES satellites
- spatial occurrence distributions of EMIC waves