Research On The Meteorological Field And Thunderstorm Characteristics That Produce Huge Jets

Gigantic jets(GJs)are one type of the upward electrical discharges from thunderstorms,which belong to a larger group of electrical discharge phenomena in the middle and upper atmosphere termed transient luminous events(TLEs).In order to analyze the characteristics of meteorological environment and thunderstorm that produced GJs,we used optical observation data,reanalysis data and satellite data,sounding data,automatic weather station data,Doppler weather radar observation data,lightning positioning data,extremely low frequency magnetic field data,etc.,to carry out detailed research of three cases of GJ which occur in China.The main results are as follows:(1)Meteorological environments that produced GJ are tropical or tropical-like,but other environment can also produce GJ.The thunderstorms of Case 1 and Case 2 were in very humid and high convective available potential energy(CAPE)environments.The relevant environmental parameters were common in summer thunderstorms,which indicates tropical or tropical-like environment characteristics.However,the vertical wind speed shear in 0~6 km was weak in Case 1,and strong in Case 2.In Case 3,the vertical wind shear in 0~6 km was strong,precipitable water(PWAT)and CAPE were very low,and the relevant environmental parameters did not show tropical or tropicallike environment characteristics.(2)The existence of the wind speed shear layer above the parent thunderstorms is conducive to the ocurrence of GJ.In these three cases,there were wind speed shear layers at about 6~12 km above the parent thunderstorms,which may cause the mixing of the upper charge region of the thunderstorm and the shield charge region,or change the thunderstorm charge structure to make the upper charge relatively separated from the central charge zone;both of these conditions can destroy the charge balance of the upper charge zone of the thunderstorm,which is beneficial to producing GJ.(3)There is a diversity of GJ-producing thunderstorms.All three cases were ocuured in the development stage of thunderstorms.The thunderstorms of Case 1 and Case 2 are multi-cell thunderstorms,and the parent thunderstorm of Case 3 is a mesoscale convective systems(MCS).Two sprites were also captured in a time window of 15 minutes containing the Case 3 GJ,indicating that the MCS provides favorable conditions not only for the GJ but also for the sprites.(4)The production of GJ is related to the high cloud top,but low cloud top thunderstorm can also produce GJ.The locations of Case 1 and Case 2 were in the coldest cloud top brightness temperature(the highest cloud top),the corresponding cloud heights were 15.1 km and 16.1 km respectively;and area of the coldest temperature reached the maximum at the time of the two cases.While Case 3 was in the area where cloud top brightness temperature was about 10°C higher than the coldest temperature,the corresponding cloud height was 12.2 km;and the coldest temperature area was not the largest at the time of Case 3 occured.(5)Strong convection is conducive to the production of GJ,but weak convection conditions can also produce GJ.The observations suggest a link between overshooting top and the occurrence of GJ.Overshooting top could increase the probability of GJ occurrence,but is not a sufficient condition for GJ occurrence.Case 1 and Case 2 both occurred in the strong convection region with radar reflectivity greater than 45 dBZ,and the storms had overshooting tops before and after Case 1 and Case 2.Case 3 occurs in the MCS area where the radar relativelyless than 40 dBZ,and did not have overshooting top.(6)There is a diversity of lightning activity characteristics of GJ-producing thunderstorms.Before and after the occurrence of these three cases,lightning activities of parent thunderstorms were dominated by negative cloud-to-ground(CG)flashes.Before Case 1 and Case 3 occurred,the negative CG flash frequency decreased significantly,and no CG flash was detected 13 s before Case 3 occurred in the reasearch area.While Case 2 occurred in the negative CG flash frequency increasing stage.In addition,Case 1 located where the positive CG flashes concentrated.Case 2 occurred where the negative CG flashes clustered.While near the Case 3,the distribution of CG flashes were sporadic.