Energy spectra and pitch angle distributions of lightning‐induced electron Precipitation: Analysis of an event observed on the S81‐1(SEEP) satellite

Abstract

Temporal and spectral signatures of a lightning‐induced electron precipitation (LEP) burst observed on the S81‐1 (SEEP) satellite are analyzed and compared with the predictions of a test particle model of the gyroresonant whistler‐particle interaction in the magnetosphere. The flux to be detected by specific detectors on the low altitude (∼220 km) satellite at L ≃ 2.24 is calculated in terms of the integral counting rate as a function of time and in terms of the dynamic energy spectra during the initial ∼300‐ms precipitation pulse. For a whistler wave packet with frequency range 500 Hz to 6 kHz the dynamic energy spectra are found to depend sensitively on the electron angular distribution in the vicinity of the loss cone. In the case of a whistler wave originating in northern hemisphere lightning the maximum whistler‐induced pitch angle scattering of electrons occurs near ∼10°S geomagnetic latitude. However, scattering occurring over the latitude range of ∼20°N to ∼20°S is found to be significant and contributes to the observed LEP pulse. The dynamic energy spectra of the LEP pulse and the temporal profile of the integral counting rate are consistent with the predictions of a test particle model of the gyroresonant scattering of the electrons by a whistler wave having an equatorial intensity at 6 kHz of ∼200 pT. The measured LEP pulse pitch angle distribution is wider than that estimated on the basis of the test particle model.

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

“…Intense geomagnetic disturbances can inject energetic electrons into the slot and inner radiation belt, leading to a harder energy spectrum for the trapped population. In these cases the WEP energy spectra will also harden, as has been experimentally observed (Inan et al, 1989;Clilverd et al, 2004). As injections into the inner radiation belt are quite rare, we are able to assume that the "quiet" WEP energy spectra are more indicative of typical conditions.…”

Investigating radiation belt losses though numerical modelling of precipitating fluxes

“…It has been argued that the WEP fluxes derived from the AE-5 Electron Model (case A) should be more typical than those described by an e-folding energy of E 0 =120 keV (case B) , as the latter is based on a single measurement, albeit an in-situ observation which has been subject to significant analysis (Inan et al, 1989;Voss et al, 1998). The Rodger study noted that the selection of WEP spectra and the value of typical precipitation magnitude lead to a significant source of uncertainty in the calculated lifetime of radiation belt electrons.…”

“…In the second case B the WEP energy spectrum is taken to be proportional to exp(−E/E 0 ), where E is the kinetic energy of a trapped electron and E 0 is the e-folding energy, with E 0 =120 keV. This value is taken from a detailed analysis of an experimentally observed WEP event (SEEP Event (D); Voss et al, 1998), which concluded that the differential energy spectrum of the trapped electrons for this event could be best described by E 0 =120±40 keV (Inan et al, 1989). Note that this e-folding energy is roughly two and a half times bigger than that found for case A, leading to a WEP burst (B) having a greater high-energy contribution, as seen in Fig.…”

Decay of whistler‐induced electron precipitation and cloud‐ionosphere electrical discharge Trimpis: Observations and analysis

“…For CID Trimpis, the delay (sferic to onset) may be as much as 100 ms if sprite plasma is so hot as to make it transparent to VLF. Although the hot electrons cool to almost ambient in <1 ms at 50 km, the cooling time is -100 ms at 85 km [Rodger et al, 1998c], so the rise time of CID Trimpis would be expected to be slower than 20 ms. One might expect the risetime of WEP Trimpis to be determined by the duration of the pulse of precipitating electrons, which is of the order of 300 ms [Inan et al, 1989]. However, the risetimes of WEP Trimpis that we consider in section 4 appear to be >1 s, suggesting precipitation over a range of latitudes due to multipath or non- The directions of arrival (DoA) of the NWC signal scattered off each CID (sprite plasma), deduced from both the difference in phase at spaced receivers and by PVDF at one or both sites, were within -6 ø of the NWC direction.…”