Numerical Simulation Study Of The Thunderstorm Charging Mechanism

In this paper, the one-dimensional time-varying model of thundercloudelectrification has been used for simulating two thunderstorm processes by usingobservations of CCOPE and STEPS primarily, and discussing the effect of surfacetemperature, surface pressure, cloud base height, cloud radius, reversal temperature,temperature lapse rate, charge transfer amount, upward flow speed and pellet flux onelectrical process of thundercloud from sensitivity tests.In model, Fletcher glaciation mechanism and Hallett-Mossop glaciationmechanism have been adopted as the ice glaciation mechanisms of crystal. Thenumerical simulation results show that, the site of the vertical field extremes in theresults simulated by using radiosonde observation data of CCOPE and STEPS hasgood consistency with surveyed results, but the simulated extremes are larger thansurveyed extremes, the result has been caused by the boundedness include thresholdbe set bigger and parameters are constant. Sensitivity tests results show that: withsurface temperature increasing, the vertical thickness of negative charge will bedecreased, the biggest density of positive charge and negative charge will be increased.When the surface pressure reduce, the charging altitude is lower, the time of the firstlightning flash decreased and the lightning flash frequency increased. With the cloudbase height decreasing, the charging altitude will be dropped and the dropped range isabout0.1km, and the time of the first lightning flash will be decreased, the lightningflash frequency will be increased. The lightning frequency will be increased with the cloud radius under the Fletcher glaciation mechanism and Hallett-Mossop glaciationmechanism, this is consistent with the previous research results. When reversaltemperature is lower, the range of negative charge carried by ice crystal is larger. Inmodel, when surface temperature is32℃and the reversal temperature is lower then-26℃, there will be a reversed-polarity charge structure in thundercloud. The effect oftemperature lapse rate on lightning frequency is different in the Fletcher glaciationmechanism and Hallett-Mossop glaciation mechanism, with the temperature lapse rateincreasing, the range of positive and negative charges and maximum value of positivecharge will be decreased, the maximum absolute value of negative charge will beincreased. The lightning frequency varies directly as the charge transfer amount, andthe charge transfer amount has no effect on first lightning time. With pellet fluxincreasing, the time of the first lightning flash will be decreased; the lightning flashfrequency will be increased. It is easer to occur C-G lightning in Fletcher glaciationmechanism in the simulation.The comparative analysis of the simulated result of the inland and coastalthunderstorm cases show that the first lightning time of inland case is smaller thancoastal case, the lightning frequency of inland is bigger and the electrical activity ismore powerful. The model can simulate the charge structure and spatiotemporaldistributions of electric field intuitively.