Computer simulations on sprite initiation for realistic lightning modelswith higher-frequency surges

摘要

Computer simulations on transient luminous emissions in the mesosphere and lowerionosphere have been performed for realistic lightning modelings with fast-varying currentsurges (M components) superimposed on the lightning continuing current (CC). Thealgorithm used here is an electromagnetic (EM) code, which enables us to estimateself-consistently the reduced electric field, electron density, conductivity, and luminosityas a function of space and time by solving the Maxwell equations. It is found that Mcomponents in the CC with small amplitudes, but with a fast-varying EM effect, caninitiate or enhance the occurrence of sprites. Even for a return stroke (RS) without CC,subsequent high-frequency current variations (like M components) are found to lead todramatic changes in the sprite occurrence. The physics underlying these changes isstudied by means of, e.g., temporal and spatial variations of luminosity, electron density,and conductivity. As the conclusion, the RS is a fundamental agency for spites, buthigh-frequency variations as EM effects exhibit an additional essential influence on spriteoccurrence. These computational results are used to offer some useful ideas concerning theunsolved problems of sprites and halos, including polarity asymmetry, long-delaycharacteristics, and morphological shapes of sprites.