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Abstract
Abstract. It has been suggested that whistler-induced electron precipitation (WEP) may be the most significant inner radiation belt loss process for some electron energy ranges. One area of uncertainty lies in identifying a typical estimate of the precipitating fluxes from the examples given in the literature to date. Here we aim to solve this difficulty through modelling satellite and ground-based observations of onset and decay of the precipitation and its effects in the ionosphere by examining WEP-produced Trimpi perturbations in subionospheric VLF transmissions. In this study we find that typical Trimpi are well described by the effects of WEP spectra derived from the AE-5 inner radiation belt model for typical precipitating energy fluxes. This confirms the validity of the radiation belt lifetimes determined in previous studies using these flux parameters. We find that the large variation in observed Trimpi perturbation size occurring over time scales of minutes to hours is primarily due to differing precipitation flux levels rather than changing WEP spectra. Finally, we show that high-time resolution measurements during the onset of Trimpi perturbations should provide a useful signature for discriminating WEP Trimpi from non-WEP Trimpi, due to the pulsed nature of the WEP arrival.
Highlights
It has been suggested that whistler-induced electron precipitation (WEP) may be the most significant inner radiation belt loss process for some electron energy ranges (e.g. Dungey, 1963; Rodger et al, 2003)
It has been argued that the WEP fluxes derived from the AE-5 Electron Model should be more typical than those described by an e-folding energy of E0=120 keV, as the latter is based on a single measurement (Rodger et al, 2003)
Combining these results with the calculations presented in Clilverd et al (Fig. 5, 2002) it appears that variations in the Lightning Induced Enhancement (LIE) patch size will lead to relatively small changes in Trimpi, and that the large variation in observed Trimpi is primarily due to changing WEP spectra and precipitation flux
Summary
It has been suggested that whistler-induced electron precipitation (WEP) may be the most significant inner radiation belt loss process for some electron energy ranges (e.g. Dungey, 1963; Rodger et al, 2003). Large D-region patch dimensions have been explained through a quasi-trapped whistler propagation theory in which ducted energy spreads at the magnetic equator (Strangeways, 1999), resulting in whistler-mode signals which have leaked outside their whistler duct still contributing to the horizontal lateral extent of WEP Such leakage would give a significantly larger precipitation footprint than the actual dimensions of the whistler duct. A different mechanism leading to large WEP patch dimensions comes through the precipitation caused by obliquely (nonducted) propagating whistlers, creating an ionospheric disturbance of ∼1000 km spatial extent (Johnson et al, 1999) At this stage there is no clear experimental evidence to indicate whether quasi-ducted or nonducted whistler propagation dominates the overall WEP losses (Rodger et al, 2003). In this paper we closely examine the onset and decay of Trimpi perturbations so as to better understand the WEP fluxes producing the ionospheric modification, characterized through experimental WEP observations, and investigate the estimates of the likely impact of the WEP on the radiation belts
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