Slot region electron loss timescales due to plasmaspheric hiss and lightning‐generated whistlers

Abstract

[1] Energetic electrons (E > 100 keV) in the Earth's radiation belts undergo Dopplershifted cyclotron resonant interactions with a variety of whistler mode waves leading to pitch angle scattering and subsequent loss to the atmosphere. In this study we assess the relative importance of plasmaspheric hiss and lightning-generated whistlers in the slot region and beyond. Electron loss timescales are determined using the Pitch Angle and energy Diffusion of Ions and Electrons (PADIE) code with global models of the spectral distributions of the wave power based on CRRES observations. Our results show that plasmaspheric hiss propagating at small and intermediate wave normal angles is a significant scattering agent in the slot region and beyond. In contrast, plasmaspheric hiss propagating at large wave normal angles and lightning-generated whistlers do not contribute significantly to radiation belt loss. The loss timescale of 2 MeV electrons due to plasmaspheric hiss propagating at small and intermediate wave normal angles in the center of the slot region (L = 2.5) lies in the range 1-10 days, consistent with recent Solar Anomalous and Magnetospheric Particle Explorer (SAMPEX) observations. Wave turbulence in space, which is responsible for the generation plasmaspheric hiss, thus leads to the formation of the slot region. During active periods, losses due to plasmaspheric hiss may occur on a timescale of 1 day or less for a wide range of energies, 200 keV < E < 1 MeV, in the region 3.5 < L < 4.0. Plasmaspheric hiss may thus also be a significant loss process in the inner region of the outer radiation belt during magnetically disturbed periods.Citation: Meredith, N. P., R. B. Horne, S. A. Glauert, and R. R. Anderson (2007), Slot region electron loss timescales due to plasmaspheric hiss and lightning-generated whistlers,

Parametric validations of analytical lifetime estimates for radiation belt electron diffusion by whistler waves

“…This condition is generally satisfied for typical plasmaspheric whistler spectra (e.g., see Fig. 2 from Meredith et al, 2007). The filling of the trough in pitch-angle diffusion rate between the Landau and first cyclotron peaks from the i = 1 waves, which is provided by the i = 2 and 3 waves, can be written from Eqs.…”

“…We shall consider two cases at L = 2 and 2.5 in quiet conditions, as provided by Meredith et al (2007). For L = 2 and 2.5, one has pe / c0 = 5.6 and 7.3, respectively.…”

“…For L = 2 and 2.5, one has pe / c0 = 5.6 and 7.3, respectively. The G ω functions are obtained by roughly fitting the corresponding CRRES average spectra, and they will be compared with the different fits given by Meredith et al (2007) in Sect. 5.6.…”

Relativistic electron flux dropouts in the outer radiation belt associated with corotating interaction regions

“…Precipitation loss of electrons due to wave scattering is attributed to a number of wave scattering mechanisms-e.g., interaction with electromagnetic ion cyclotron waves Meredith et al, 2003;Loto'aniu et al, 2006;, plasmaspheric hiss [Abel and Thorne, 1998;Meredith et al, 2006Meredith et al, , 2007, whistler mode chorus waves Thorne et al, 2005;Shprits et al, 2007], and lightning-generated whistlers [Voss et al, 1998;Rodger et al, 2003;Bortnik et al, 2006]. Drift loss of electrons occurs when the magnetopause is compressed inward and intersects the drift path of electrons in the outer radiation belt [Shprits et al, 2006;Turner et al, 2012;Tu et al, 2013Tu et al, , 2014.…”

Impact of Solar Wind on the Earth Magnetosphere: Recent Progress in the Modeling of Ring Current and Radiation Belts

“…The energetic electrons reside in 2 distinct regions: the inner belt and the outer belt, which are usually separated by the slot region (1.8 < L < 3) of depleted particle populations. Pitch-angle diffusion loss of electrons by inter-acting with whistler mode plasmaspheric hiss is believed to be the cause of the slot region (Albert, 1994;Lyons et al, 1972;Meredith et al, 2007). The inner belt is relatively stable while the outer belt is highly variable with geomagnetic activity.…”