Perturbations of subionospheric LF and MF signals due to whistler‐induced electron precipitation bursts

Abstract

First evidence of whistler‐induced burst precipitation effects on subionospherically propagating signals in the LF and MF ranges have been observed at Palmer (L ∼ 2.4) and Siple stations (L ∼ 4.3), Antarctica. The occurrence rate on a 37.2‐kHz LF signal originating in California was usually comparable to that on the more disturbed VLF paths. At Palmer, examples at 37.2 kHz were seen on 70% of the nights during a March‐April 1983 observing period. Perturbations on a ∼1800 km‐long 780‐kHz MF path to Palmer occurred on nights of high activity on VLF paths, but fewer than 10 MF events were usually detected as compared to >50 on the active VLF paths. The MF perturbations were of order 50% in amplitude and were not in general followed by a ∼30‐s decay toward a pre‐event level, as is usually the case for the VLF signals. Test particle modeling of the whistler‐particle interaction supports the idea that the MF signals are affected by ionization extending above the nominal ∼85‐km reflection height for VLF signals and also are consistent with the observed time delay between the 780‐kHz signal perturbation and the whistler‐generating lightning stroke. Fast phase advances correlated with the whistlers were regularly observed on a 12.9‐kHz Omega signal. The data provide a means of inferring the existence of multiple precipitation regions and offer new evidence that whistlers originating in the northern hemisphere can cause significant precipitation in the southern hemisphere, at least in the vicinity of the South Atlantic magnetic anomaly.