Open AccessRadiation belt electron precipitation by man‐made VLF transmissions
Author(s) -
Gamble Rory J.,
Rodger Craig J.,
Clilverd Mark A.,
Sauvaud JeanAndré,
Thomson Neil R.,
Stewart S. L.,
McCormick Robert J.,
Parrot Michel,
Berthelier JeanJacques
Publication year - 2008
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2008ja013369
Subject(s) - ionosphere , electron precipitation , daytime , transmitter , physics , electron , van allen radiation belt , atmospheric sciences , very low frequency , local time , latitude , computational physics , geophysics , astronomy , magnetosphere , plasma , telecommunications , channel (broadcasting) , quantum mechanics , computer science , statistics , mathematics
Enhancements of drift‐loss cone fluxes in the inner radiation belt have been observed to coincide with the geographic location of the powerful VLF transmitter NWC. In this paper we expand upon the earlier study to examine the occurrence frequency of drift‐loss cone enhancements observed above transmitters and the intensity of the flux enhancements and to demonstrate the linkage to transmitter operation. Our study has confirmed the strong dependence that these enhancements have upon nighttime ionospheric conditions. No enhancements were observed during daytime periods, consistent with the increased ionospheric absorption. We have also confirmed the persistent occurrence of the wisp features east of the NWC transmitter. The enhancements are initially observed within a few degrees west of NWC and are present in 95% of the nighttime orbital data east of the transmitter for time periods when the transmitter is broadcasting. No enhancements are observed when NWC is not broadcasting. This provides conclusive evidence of the linkage between these drift‐loss cone electron flux enhancements and transmissions from NWC. When contrasted with periods when NWC is nonoperational, there are typically ∼430 times more 100–260 keV resonant electrons present in the drift‐loss cone across L = 1.67–1.9 owing to NWC transmissions. There are almost no wisp‐like enhancements produced by the transmitter NPM, despite its low‐latitude location and relatively high output power. The lack of any wisp enhancement for L < 1.6 suggests that nonducted propagation is an inefficient mechanism for scattering electrons, which explains the lower cutoff in L of the NWC‐generated wisps and the lack of NPM‐generated wisps.