Electron Scattering by Electrostatic Electron Cyclotron Harmonic Waves and Time Domain Structures During Storm-Time

Kurzfassung

Recent studies have shown that existing ring current models overestimate the electron flux of 10-50 keV during storm-time, which is due to a missing loss process operating in the pre-midnight sector. At the same time, there are several studies which suggest that wave-particle interactions with electrostatic electron cyclotron harmonic (ECH) waves or time domain structures (TDS) can efficiently scatter electrons at energies of several hundred eV to a few keV, depending on the observed wave amplitude. These resonant interactions between electrons and ECH waves or TDS have an impact on electron phase space density evolution, but typical quasi-linear studies of ring current dynamics do not currently incorporate them. Since the scattering rates due to wave-particle interactions with both ECH waves and TDS increase with increasing geomagnetic activity, they are possible candidates to explain part of the missing loss process during storm-time. In this study, we perform a detailed analysis of the efficiency of ECH wave scattering for a wave event that occurred during the geomagnetic storm on 17 March 2013, by calculating quasi-linear bounce-averaged scattering rates. Furthermore, we estimate the diffusion coefficients due to TDS in the inner magnetosphere. The resulting lifetimes from both ECH waves and TDS are incorporated into simulations conducted using the 4-dimensional Versatile Electron Radiation Belt (VERB-4D) code. The results demonstrate that for the considered event, ECH waves can scatter electrons over a wide range of energies up to several keV, but the resulting lifetimes are too long to significantly alter the resulting pitch angle distribution. However, first results indicate that TDS are able to efficiently scatter electrons up to tens of keV, removing a substantial part of the overestimated flux in the model. This strengthens the assumption that they are a possible candidate to explain part of the missing loss process in ring current models.