Simulation of Earth‐Ionosphere Cavity Resonances With Lightning Flashes Reported by OTD/LIS

Abstract

AbstractLightning flashes cause a globally resonant electromagnetic wave field known as Earth‐ionosphere cavity resonances. This global wave field is simulated here by use of lightning flashes reported by the lightning imagers on board the Optical Transient Detector (OTD)/Lightning Imaging Sensor (LIS) space missions. The stochastic occurrence of global lightning flashes in time and space is described with a likelihood function composed of a series of delta functions. This likelihood function is generated by random variates calculated from inverse transform sampling of the global lightning distributions measured by OTD/LIS. The simulation uses spherical harmonic expansion coefficients, calculated from frequency and distance dependent magnetic field measurements, to describe the wave field around the Earth. The incoherent superposition of the waves at each location results in simulated time series and spectra. The simulations agree very well with actual measurements of magnetic fields with a radiometer at Arrival Heights in the Antarctic as part of the Stanford ELF/VLF Radio Noise Survey. The simulated relative radiant energy distributions are attributed to corresponding “Earth‐ionosphere cavity brightness temperatures” TEIC. The spherical harmonic expansion of these brightness temperatures exhibits a spectrum where the amplitudes of the spatial expansion coefficients decrease with increasing angular degree. The calculated Earth‐ionosphere cavity brightness temperatures can be used for comparison with atmospheric temperatures in future studies.