Anticorrelation between whistler occurrence and MLR and QP emissions
Abstract
We investigate a possible influence of lightning-generated whistlers on the occurrence of selected whistler mode emissions in the inner magnetosphere. Specifically, we focus on Magnetospheric Line Radiation (MLR) and Quasiperiodic (QP) emissions, i.e., electromagnetic waves at frequencies of a few kHz with a clear frequency/time modulation of the wave intensity. We use the data from the low altitude satellite DEMETER (2004-2010) to demonstrate that the occurrence of both these emissions exhibits a clear seasonal dependence, with a minimum during the northern summer. We argue that this dependence follows the global distribution of lighting-generated whistlers. Further, we use the whistler occurrence rate data obtained by the neural network on board DEMETER to directly compare whistler occurrence in the presence and in the absence of MLR/QP emissions. It is shown that the whistler occurrence rate as detected by the neural network is significantly lower in the presence of MLR/QP emissions than normally. We discuss whether this is due to a lower efficiency of whistler identification in the presence of MLR/QP emissions or whether this is a real effect suggesting a possible controlling role of whistlers for the occurrence of other electromagnetic emissions.