Investigating radiation belt losses though numerical modelling of precipitating fluxes

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.

Lightning-driven inner radiation belt energy deposition into the atmosphere: implications for ionisation-levels and neutral chemistry

“…The spatially varying mean WEP energy fluxes shown in Fig. 1 are combined with WEP energy spectra, in both cases calculated following the approach outlined in Rodger et al (2003Rodger et al ( , 2004b. The parameters of the WEP burst were selected by comparison with the calculations of Faraday Trimpi produced by WEP with a mean precipitation energy flux at L=2.23 of 2×10 −3 ergs cm −2 s −1 (Rodger et al, 2004b), specifically the "normal" Faraday Trimpi spectral conditions (Clilverd et al, 2004).…”

“…1 are combined with WEP energy spectra, in both cases calculated following the approach outlined in Rodger et al (2003Rodger et al ( , 2004b. The parameters of the WEP burst were selected by comparison with the calculations of Faraday Trimpi produced by WEP with a mean precipitation energy flux at L=2.23 of 2×10 −3 ergs cm −2 s −1 (Rodger et al, 2004b), specifically the "normal" Faraday Trimpi spectral conditions (Clilverd et al, 2004). Following the approach outlined in the Rodger et al (2003Rodger et al ( , 2004bRodger et al ( , 2005 studies, this starting point is used to derive global variations.…”

Lightning driven inner radiation belt energy deposition into the atmosphere: regional and global estimates

“…Three of the four study days showed a high degree of consistency between the levels of lightning return stroke peak current required to produce any given perturbation scatter amplitude value, providing a link between the lightning currents and WEP energy flux (Clilverd et al, 2004). On the remaining day, the Trimpi signatures observed were 6-7 dB greater for a given lightning intensity than on the other study days, consistent with significantly harder radiation belt precipitation spectra (Rodger et al, 2004b), probably caused by post-geomagnetic storm acceleration processes of radiation belt electrons (Meredith et al, 2002).…”

“…We model the WEP burst following the approach outlined in Rodger et al ( , 2004b. The parameters of the WEP burst have been selected for comparison with the calculations of Faraday Trimpi produced by WEP with a mean precipitation energy flux at L=2.23 of 2×10 −3 ergs cm −2 s −1 (Rodger et al, 2004b), specifically the "normal" Faraday Trimpi spectral conditions (Clilverd et al, 2004).…”

“…Recent studies into the magnitude and time decay of Trimpi perturbations observed at Faraday, Antarctica, have clarified the relationships between WEP mean precipitation energy flux, WEP energy spectra, and VLF perturbation scattering of WEP produced modifications to the ionosphere (Rodger et al, 2004b). Building on this modelling, the dependence of WEP precipitation fluxes on the strength of the associated lightning's return stroke peak current has been identified (Clilverd et al, 2004).…”