Van Allen Probe Observations of Chorus Wave Activity, Source and Seed electrons, and the Radiation Belt Response During ICME and CIR Storms

Bingham, Sam

Van Allen Probe Observations of Chorus Wave Activity, Source and Seed electrons, and the Radiation Belt Response During ICME and CIR Storms

Tuesday, 6 March 2018

Lakehouse (Hotel Quinta da Marinha)

Sam Bingham, University of New Hampshire Main Campus, Durham, NH, United States, Christopher Mouikis, UNH, New Hampshire, United States, Lynn M Kistler, Univ New Hampshire, Durham, NH, United States, Kristoff W Paulson, University of New Hampshire, Chelmsford, MA, United States, Alex J Boyd, New Mexico Consortium, Los Alamos, NM, United States, Chia-Lin Huang, University of New Hampshire, Durham, NH, United States, Charles J Farrugia, New hampshire university, Durham, NH, United States, Harlan E. Spence, Solar System Exploration Research Virtual Institute, NASA Ames Research Center, Moffett Field, CA, United States and Craig Kletzing, University of Iowa, Department of Physics and Astronomy, Iowa City, IA, United States

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Abstract:

A superposed storm-phase epoch analysis, using Van Allen Probes observations, is used to examine the chorus wave activity, plasma conditions associated with the wave activity, development of the seed population, and the outer radiation belt response for 25 ICME and 35 CIR storms. Gyroresonant wave particle interactions with whistler mode chorus have been shown to be a major contributor to enhancements in the outer radiation belt during geomagnetic storms. The anisotropy of source electrons (10s of keV) provides the free energy for chorus waves, which can accelerate sub-relativistic seed electrons (100s of keV) to relativistic energies.

Plasma data from the Helium Oxygen Proton Electron (HOPE) instrument and magnetic field measurements from the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) are used to identify chorus wave activity and to model a linear theory based proxy for chorus wave growth. The observed chorus wave power shows a progression of peak power on the dawnside during the storm main phase that weakens while spreading across the dayside during the storm recovery period. According to the linear theory results, this wave activity is driven by the enhanced convection driving plasma sheet electrons across the dayside of the inner magnetosphere. Both ICME and CIR storms show comparable levels of wave activity.

Data from the Magnetic Electron Ion Spectrometer (MagEIS) and the Relativistic Electron Proton Telescope (REPT) are used to observe the storm-phase development of the seed and relativistic electrons. A superposed epoch analysis of seed and relativistic electrons vs. L shows a stronger and earlier occurring seed electron enhancement in the ICME storms, compared to the CIR storms, along with a greater average radiation belt enhancement in the ICME storms.

These results highlight the importance of the presence of the seed population in radiation belt dynamics while also giving evidence that the greater seed population in ICME storms, possibly driven by greater convection and substorm activity, can lead to a greater propensity for radiation belt enhancements.