Modelling the relaxation of red sprite plasma

Abstract

Red sprites consist of multiple ionised columns extending above a thunderstorm from ~30 km to ~90 km. Electron densities in these columns are very much larger than the ambient background, perhaps fives times at 70 km. These highly ionized structures cause observable perturbations in subionospheric VLF transmissions known as "VLF Sprites". Three models of initial sprite electron density are considered, and using a realistic ionization relaxation model the time dependence of electron density is derived. A 3-D Born propagation code of is used to compute the time profile of a VLF sprite. Two profiles show good agreement with the time signature experimentally observed, in that scattered amplitude and phase decrease linearly log(t). These simulations provide insight into the nature and structure of sprite columns, and indicate an additional constraint which should be applied to red sprite creation models.

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