The Influence Of Key Physical Parameters On The Streamer Discharge Triggered By The Particles Of Water

The initiation and triggering of lightning in thundercloud has always been the focus of atmospheric physical,at the same time,the formation of lightning is also concerned.It's important to understand lightning initiation so that could study lighting in thundercloud,coupling with other macro-meteorological conditions and to reduce disaster caused by lightning.So far,the mechanism how lightning is formed in thundercloud electric fields,and how lightning can be triggered frequently in thundercloud with field below conventional breakdown threshold field is still unclear.On this question,different theories have been proposed.A part of researchers consider that Hydrometeors are subject to ambient field will be significantly enhanced in their vicinity and finally streamer is triggered then lightning is initiated in thundercloud.Therefore,it's very important to study the effect of different size of hydrometeors on the triggering of streamer discharge in thundercloud,as so as to study new mechanism of streamer discharge and light initiation in thunderstorms in future.In this paper,at 7 km altitude,our simulation are conducted at lowest ambient field in which streamer can be initiated for hydrometeors with different radii as well as the hydrometeor with rigid interface and streamer discharge evolves steadily over time.Conducting sphere and dielectric sphere model were established,respectively.According to knowledge of electrodynamics,the initial potential distribution in uniform background electric field can be seen.Successive over relaxation(SOR)method is applied to solve the Poisson equation,a new approach based on the multiple image charge method is formulated to find the follow-up electric field distribution.The model also includes electron impact ionization,two-body and three-body electron attachments,electron-positive ion and negative-positive ion recombination,drift and diffusion of electrons.In addition,the photoionization effect is considered during the process of streamer discharges.The simulation results shown,when the radius of hydrometeors is 2mm,the streamer discharge can be triggered at lowest ambient field.095E_k,the radius of hydrometeors is 3mm,the streamer discharge can be triggered at lowest ambient field.084E_k,the radius of hydrometeors is 4mm,the streamer discharge can be triggered at lowest ambient field.0 8E_k,the radius of hydrometeors is 5mm,the streamer discharge can be triggered at lowest ambient field.07 6E_k,the radius of hydrometeors is 6mm,the streamer discharge can be triggered at lowest ambient field.072E_k,the radius of hydrometeors is 7mm,the streamer discharge can be triggered at lowest ambient field.071E_k,the radius of hydrometeors is 8mm,the streamer discharge can be triggered at lowest ambient field.069E_k,change the size of spherical hydrometeors from 2mm to 8mm,lowest ambient field in which positive streamer can be initiated for hydrometeors with different radius and no negative streamer be triggered for hydrometeors.However,there is no streamer discharge occurrence when radius is 1mm,unless the hydrometeors are charged or the hydrometeors are elongated,as well there is no streamer can be triggered from the upper end of the hydrometeors.In this paper lowest ambient field in which streamer can be initiated for hydrometeors with different radius,the Meek number's value calculated according to radius of hydrometeors and ambient field to meet the criteria for electron avalanche conversion to streamer discharge.compared with the simulation results of other researcher,lowest ambient field in which streamer can be initiated for column hydrometeors with different radius,the minimum ambient field required by spherical hydrometeors to trigger streamer discharge is obviously larger than that required by column hydrometeors to trigger streamer discharge.Moreover,lowest ambient field required to trigger streamer discharge decreases with the increase of the size of hydrometeors.There is a certain difference between the two models,which is related to the shape of hydrometeors.The results of this paper demonstrate that spherical hydrometeors of different size can trigger streamer in the corresponding lowest ambient field,and it evolves steadily over time,the relationship between the size of spherical hydrometeors and corresponding lowest ambient field was obtained.This research provides a new direction to research mechanism of streamer discharge and light initiation in thunderstorms in future.