Numerical Simulation Of Lightning Charge Structure Characteristic And Attributions Over Tibet Plateau

To further recognize the particularity of thunderstorm over Tibet Plateau,this paper has analyzed the primary attribution of charge distribution,and also predicted the microphysics and electrification occurring on Aug,13,2003 and Aug,11,2003 in Tibet Plateau,using a three-dimensional dynamics-electrification coupled model.The charging parameterization included both the graupel/hail-cloud/ice inductive charging mechanism and the graupel/hail-ice non-inductive charging mechanism.The charging processes between other large and small particles are small,so they were ignored in this study.The main results are as following:(1)The characteristics of thunderstorms in Tibet Plateau are unique.The life period of the thunderstorm is short,and the positive cloud-to-ground flashes occur frequently.The updraft and downdraft is weaker,and solid precipitation is more than liquid precipitation.Cloud top of thunderstorms are low and warm cloud area is small.Meanwhile,the height of solid small particles(ice crystals,snow)is low.The solid large particles(gravel,hail)distributed widely and mainly grounded.(2)The thunderstorms in Tibet Plateau mainly divided into two groups in the stage of development,a kind of group displays the weaker negative dipolar structure,another displays a vertical tripole charge structure.The lower positive charge center occupies widely and it lasts a long time.And then the first group transforms into a vertical tripole charge structure.Finally,the charge structure transforms into dipole distribution in dissipation stage.(3)When the convection is weak,the thunderstorm displays a negative dipole polarity charge structure.At that time,the upper negative area formed by ice crystals are negatively charged,and the lower positive area formed from graupel positively charged particles.In the mature stage,the upper main positive charge center is formed by the ice crystal,and the main negative charge center is formed by graupel particles and ice crystals.When the convection is strong,the main positive charge center is mainly formed by ice crystals,and the main negative charge center is mainly formed by ice and graupel.The lower positive charge center are mainly formed by snow and graupel.When the charge structure is dipolar,the negative charge center is formed by graupel particles.(4)There are less electric charge in the lower positive charge center whose occupies widely and it lasts a long time,but this is the special features of the thunderstorms on the plateau.Plateau thunderstorms have relatively weak convection,and rising wind speed is small.Because of the low ambient temperature,the thunderstorm warm cloud area is less thick,and high effective liquid water content in the mixed phase region.This is the reason why the charge structure is formed.The positive charge center are mainly formed by graupel.In addition,snow particles also contribute to a certain degree.The range,duration time and strength of the lower positive charge center are determined by the solid-state precipitation intensity and the region of solid particle.