The Improvement Of The Electrification And Discharge Parameterization And Comparative Study Of Three-dimensional Thunderstorm Model

In older to study the influence of ice crystal multiplication on noninductive electrification during the development of thunderstorm, this paper addition ice multiplication caused by fragmentation of relatively large individual cloud drops during freezing is induced in the three-dimensional thunderstorm model to evaluate the distribution of the variant particles, charge and the electric field in thunderstorm with an ideal environment. In addition, in order to get a more comprehensive and reasonable three-dimensional numerical model of thunderstorm, the electrification and discharge parameterization in the original program was modified by adding a new electrification and improving the discharge parameterization, especially introducing two different lightning channel selection schemes into the numerical model to simulate the thunderstorm clouds. The main results are as follows:(1) Ice crystal multiplication affects the concentration and the distribution of both the ice crystals and graupel particles in the thunderstorm during its development and mature stage. Ice crystal multiplication makes the concentration of ice crystals increase about10%-15%and the high value area become larger compared to the condition without multiplication. It also makes the numerical concentration of graupel particles increase about15%and the high value region become larger as well.And the non-inductive charge transfer rate is higher than that without adding multiplication process. The positive charge transfer rate always occurs nearby the area with high graupel concentration, while the negative one always appears in the overlap region with the high ice and graupel concentrations.(2) By the effect of ice multiplication the concentration of ice crystals and graupel particles become larger.The ice Graupel-ice collision probability increases and the number of collisions increased.All contribute to an increase in non-inductive charge transfer and the non-inductive electrification rate increases. Makes the value of vertical electric field in the thunderstorm is much higher and the moment of strong vertical electric field emergenced is about4-5min in advance, contrast to condition without multiplication.(3) It is found that the strong updraft is one of the important factors in a strong electric field generation within the thunderstorm cloud based on the simulation of the improved model. During the mature stage of the thunderstorm, because of the rapid decline of the updraft and the drag force produced by the falling larger water particles, the maximum value of the downdraft speed increases, leading to the decline of the vertical height of the positive and negative charge regions in thunderstorm and more cloud-to-ground (CG) lightning discharges.(4) The improved model presents the simulation of the bidirectional leaders and the forked structure of the lightning channels. In contrast with three-dimensional lightning channel expansion results of two different channel expansion schemes in discharge parameterization, it was found that both the "Pos" and "Ran " schemes present the bidirectional leaders and the forked structure of the lightning channels. The "Pos" scheme is based on the electric field intensity, sometimes makes the vertical development of the lightning channel inadequate and the branches of the lightning channel less than the"Ran" scheme. The "Ran" scheme chooses the next discharge point randomly from the points which meet the given conditions, causes a great vertical extension of the lightning channels and more complex branches.