Numerical simulation of lightning-generated EM fields in the ionosphere

Intense lightning affects the atmosphere, ionosphere, and magnetosphere through a variety of processes. a complete evaluation of lightning-generated electromagnetic fields at different regions (from the ground to the magnetosphere) is necessary to explore the mechanisms and quantify the conditions to initiate these processes. We have developed a fully electromagnetic 2-D cylindrical simulation that treats the ionosphere as a true cold plasma by using finite-difference time domain method (FDTD) and a new PML technique to simulate the slowly varying fields in a large volume of space. This model is a powerful tool to simulate electromagnetic fields generated by both lightning currents and sprite currents at different locations. Sprite currents are modeled by defining a specific region with time varying mesospheric conductivity. Measured data is used to validate the model. The intensity and frequency spectra of ionospheric electromagnetic fields at high altitude show that sprite-generated waves suffer less attenuation before entering the magnetosphere. The signatures of electromagnetic fields radiated by intense lightning and sprites at different altitudes and over a wide range of distances from the source are compared to determine the different characteristics of the radiated fields at balloon, rocket, and satellite altitudes.