On the Occurrence of Lightning-Induced Electron Precipitation (LEP) Events

Lightning-induced electron precipitation (LEP) is a well-established contributor to the loss of trapped radiation belt electrons at mid-to-low latitudes. Previous calculations of global losses of electron radiation due to LEP estimated the precipitating flux and energy spectra of a `typical' LEP event, and based occurrence rates of LEP events on global lightning occurrence data. Recent work has demonstrated that the amount of LEP, as recorded on several VLF/LF signals, is highly variable and dependent on additional factors. The duration, spatial extent, and energy spectra of the precipitation is likely influenced by such parameters as: 1) causative lightning flash current; 2) trapped radiation belt flux levels and magnetospheric conditions; 3) loss cone angle of the trapped flux (a function of the earth's magnetic field strength); and 4) causative lightning flash location. The relative contribution of these parameters is not yet fully understood, and additional parameters such as an equinoctial dependence are likely to play a role. Using case studies of LEP events associated with thunderstorms in Texas, we develop empirical relationships to describe the temporal profile and energy spectra of electron precipitation induced by lightning-generated whistlers given the lightning flash characteristics, satellite measurements of trapped energetic electron flux in the slot region, and measurements of VLF subionospheric signal perturbations associated with the precipitation of energetic electrons. We also discuss extension of our analysis to regions outside the central United States, as means to develop quantitative rationale for the estimation of global loss of radiation belt electrons caused by LEP.