| In order to fully understand the effect of artificial hail suppression on the concentration and spatio-temporal changes of ice particles in cloud,as well as the microphysical process and discharge initiation of hail cloud,this paper uses a three-dimensional strong storm dynamic electric coupling numerical model including silver iodide catalytic scheme,and selects a hail suppression process during the hail cloud field observation experiment in Xunyi County,Shaanxi Province on July 28,1997 for simulation study.Several groups of simulation experiments were carried out with silver iodide as the only variable,and the characteristic changes of thunderstorm cloud microphysical process and discharge initiation process before and after silver iodide seeding were compared and analyzed,and the following conclusions were drawn:(1)After Ag I was scattered into the clouds,ice crystals were produced mainly by condensation,and the number of ice crystals produced by the propagation process of ice crystals increased as a whole.After catalysis,the process of source ice crystal coalescence and the process of snowflake colliding raindrop are obviously enhanced.As a result,the process of converting source ice crystals of graupel into graupel by touching frozen raindrops is enhanced by catalysis.As a result,the quantity conversion rate of automatic conversion of ice crystals into graupel increases 40 min before and then decreases.The formation and growth of hail mainly depend on the automatic conversion process of graupel to hail.After catalysis,the conversion rate of quantity and mass in this process is significantly reduced.(2)After catalysis,on the whole,the concentration and specific water content of ice crystals,snowflakes and graupel particles increase within the range of 0-40 ℃,and with the increase of catalytic dose.The seeding of Ag I reduces the average scale of graupel and greatly reduces the conversion ratio to hail.Therefore,the specific water content and concentration of hail decreases,achieving the purpose of hail suppression.With the increase of Ag I dose,the number concentration and specific content of ice crystals,snowflakes and graupel particles have the same overall trend of change,and the increasing and decreasing regions correspond to,but the change is more obvious.Hail suppression would be better,but rainfall would first increase and then decrease.(3)Seeding Ag I can cause the enhancement of charging from seeding to the late maturity stage of hail clouds.In the early stage,the positive non-inductive charging rate area in the lower part appears earlier,the center is enhanced,and the upper boundary is raised,while in the late stage,the negative non-inductive charging rate area in the upper part is enhanced.Therefore,the bottom secondary positive charge area was enhanced in the early stage after sowing,and the upper main positive charge area and the middle negative charge area were enhanced in the late stage.However,the inductive electrification rate also increases and expands after catalysis,especially the negative inductive electrification rate.The intensities of non-induced electrification and induced electrification increase with increasing catalytic dose of Ag I.(4)The characteristics of charge structure also changed after the catalysis.The main positive and negative charge zones on the top appeared in advance,and the bottom subpositive charge zone increased and became stronger with the increase of seeding amount.After seeding,the bottom subpositive charge zone was enhanced in the early stage,and the upper main positive charge zone and the middle negative charge zone were enhanced in the late stage.The intensity of charge region increased obviously after catalysis,and with the increase of catalytic dose,the intensity of charge region increased.(5)Seeding Ag I had a certain inhibitory effect on ground flash,but cloud flash and total flash increased slightly after catalysis,the peak time of first discharge and cloud flash was advanced,the discharge duration was stronger,and the lightning frequency decreased slightly in the lightning frequent period.However,catalysis had little effect on the electric initiation and discharge before hail and after the late maturity stage of hail cloud. |
