We present Van Allen Probe observations of electromagnetic ion cyclotron (EMIC) waves triggered solely due to individual substorm-injected ions in the absence of storms or compressions of the magnetosphere during 9 August 2015. The time at which the injected ions are observed directly corresponds to the onset of EMIC waves at the location of Van Allen Probe A (L = 5.5 and 18:06 magnetic local time). The injection was also seen at geosynchronous orbit by the Geostationary Operational Environmental Satellite and Los Alamos National Laboratory spacecraft, and the westward(eastward) drift of ions(electrons) was monitored by Los Alamos National Laboratory spacecraft at different local times. The azimuthal location of the injection was determined by tracing the injection signatures backward in time to their origin assuming a dipolar magnetic field of Earth. The center of this injection location was determined to be close to ∼20:00 magnetic local time. Geostationary Operational Environmental Satellite and ground magnetometer responses confirm substorm onset at approximately the same local time. The observed EMIC wave onsets at Van Allen Probe were also associated with a magnetic field decrease. The arrival of anisotropic ions along with the decrease in the magnetic field favors the growth of the EMIC wave instability based on linear theory analysis.
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The Van Allen Probes EMFISIS data are available at http://emfisis.physics. uiowa.edu/, EFW data at http://www.space.umn.edu/ rbspefw-data/, and HOPE and MagEIS data at https://rbsp-ect.lanl.gov/. The authors thank Craig Kletzing for the EMFISIS data. The GOES satellite data are available at the website: https://satdat.ngdc.noaa.gov/sem/ goes/data/. The solar wind parameters and geomagnetic indices are available at OMNI/CDAWeb: https://omniweb.gsfc.nasa.gov/. The LANL satellite energetic particle data are provided by Geoff Reeves. The authors thank I. R. Mann, D. K. Milling, and the rest of the CARISMA team for the data. CARISMA is operated by the University of Alberta, funded by the Canadian Space Agency. Ground station SNKQ is part of the NRCan (Natural Resources Canada) network operated by Geological Survey of Canada. Portions of this research were funded by the Van Allen Probes mission. Work at the University of Minnesota was supported by JHU/APL contract UMN 922613 under NASA contract JHU/APL NAS5-01072.
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- EMIC waves
- Van Allen Probes
- ion injections
- magnetic dip