Spectroscopic and thermal temperatures in the return stroke of lightning

Abstract

Two different models of the temperature and state of ionization in the return stroke of a cloud-ground lightning stroke are in use in the literature. In the model that has been adopted for interpretation of the spectroscopic data on lightning, the mechanism of capture of free electrons to form negative oxygen ions is disregarded, the ionization being assumed to exist in the form of free electrons and heavy positive ions. In this case the thermalization time of the channel is expected to be short, so that the optical and thermal temperatures are effectively equal. In the model that accepts negative ion formation as a fundamental process, the ionization behind the tip of the return stroke is considered to be rapidly interchangeable between free electrons and heavy atomic and molecular oxygen ions. It is expected on this model that there exists a distinct time lag of the thermal temperature behind the optical temperature.