The storm that wasn't: A look at multiple loss processes occurring simultaneously and how they interact with each other.

Abstract:

One of the long outstanding challenges of understanding the inner magnetosphere is accurately describing and forecasting radiation belt dynamics. Although much progress has been made, there is still ongoing debate about the relative importance of different loss and source mechanisms. Here we will closely examine one relatively simple event where radiation belt electrons (~ 30 eV to MeV) were lost to the upper atmosphere and endeavor to identify the relative importance of the responsible loss mechanisms.

Although the size of the solar wind compression on 9 January 2014 was modest, it has given us an opportunity to observe clearly how multiple different loss mechanisms can occur simultaneously and interact with each other. The observed magnetospheric compression led to some radiation belt electrons being lost, but it also led to the simultaneous generation of EMIC, chorus, and hiss waves. The ICME generated shock encountered the Earth’s magnetosphere on 9 January 2014 at ~20:11 UT and the Van Allen Probes observe the coincident excitation of EMIC and Chorus waves outside the plasmasphere and hiss waves inside the plasmasphere. As the shock encountered the magnetosphere, an electric field impulse was observed to generate an increase in temperature anisotropy for both ions and electrons. This increased temperature anisotropy led to increased wave growth on both the ion and electron cyclotron branches. The simultaneous generation of multiple types of waves simultaneously may lead to significant impacts on the acceleration and loss of radiation belt electrons during different types of geomagnetic activity. During this relatively small event BARREL had three payloads in conjunction with the Van Allen Probes, two of the payloads inferred electron precipitation within the energy range typically associated with chorus wave pitch angle scattering. One can hypothesize that with larger and/or longer lasting ICME-shocks, or with a larger initial population of radiation belt electrons, more electron precipitation, and a larger range of energies, may be observed to precipitate to the upper atmosphere.