VLF wave intensity in the plasmasphere due to tropospheric lightning

Abstract

AbstractA climatology of VLF (very low frequency) wave intensity from lightning in the plasmasphere is constructed. Starting from Optical Transient Detector/Lightning Imaging Sensor (OTD/LIS) lightning data representing 1995–2005, a climatology of strikes is assembled with 1° × 1° latitude‐longitude spatial resolution, averaged into 2 h bins for each month of the year. Assuming a linear relationship between optical flash rate and VLF power flux, and that the VLF amplitude drops off as one over distance, a proxy for VLF power is developed. A typical lightning spectrum is applied and the values are scaled by appropriate transionospheric absorptions for each time and place. These values are mapped along geomagnetic field lines in order to compare them to E‐field spectral densities measured by the DEMETER satellite between 2005 and 2009. An overview of the DEMETER survey mode data is presented which leads to the best scaling of the lightning VLF climatology in LEO (low earth orbit). The resulting data set represents a monthly, 2‐hour, solar minimum climatology of VLF wave intensity from lightning in LEO. Finally, the E‐field spectral densities are converted to Poynting flux, mapped to the plasmasphere, and converted to B‐field spectral densities. Good overall agreement is found with previous observations and estimates. This new climatology is expected to have a significant impact on calculations of pitch‐angle diffusion for relativistic electrons in the inner radiation belt.