Observation at Moshiri(L=1.6)of Whistler-Triggered VLF Emissions in the Electron Slot and Inner Radiation Belt Regions.

Abstract

The morphological characteristics of whistler-triggered VLF emissions including diurnal, seasonal variations, Kp dependence, latitudinal distribution and spectral shape, were investigated based on the VLF data obtained at Moshiri (L=1.6) in Japan during a ten year span (1976 to 1985). The following results emerged; (1) There is no clear tendency for whistler-triggered emissions to occur at a particular local time, (2) an equinoctial maximum in occurrence probability is recognized, (3) the occurrence probability increases with increasing Kp in the range from 3 to 7, (4) the occurrence L shell is localized in two regions; one is L=2.1 to 3.4 (the electron slot region) and the other is just around L=1.6 (the inner radiation belt), and (5) a whistler-triggered emission is characterized by an initial component quasi-constant frequency and a subsequent large frequency drift with df/dt=10-20kHz/s. These characteristics are satisfactorily interpreted in terms of the gyroresonance interaction between lightning-generated whistlers and energetic electrons, with reference to previous results on lightning-induced particle precipitation.