Analyses on Lightning Feature and Formation Condition for a Thunderstorm Process in Yunnan

Using NCEP/NCAP data and new generation monitoring detection data of radar echo,satellite cloud image and lightning position system,the thunderstorm process in Yunnan from 21 to 23 September 2010 is analyzed.The results show that westward moving of tropical depression 'FANAPI' provided the advantageous circulation background conditions of easterly convergence,warm between 300 K and 302 K on the low level and wet(relativity is above 80%) on the upper level.Negative lightning plays a role in the whole lifetime of a thunderstorm cloud cluster.The cloud top brightness temperature decreases and all lightning is negative and its frequency reaches up to 1 245 times·(30 min)-1 at the development stage.The cloud top brightness temperature gradually increases,the negative lightning decreases,a small amount of positive lightning emerge and rise gradually from mature to disappear stages.In addition,the spatial distributions of thunderstorm cloud cluster structure and lightning are asymmetric.The structure feature is that the front is main convective zone and the rearward is plume or high cloud.The cloud top brightness temperature in the front is lower than that the rearward,and its gradient larger.Dense negative lightning mainly located in the region with cloud top brightness temperature≤-60 ℃ and its big gradient in the front.Sparse positive lightning disperse in the rearward of dense negative lightning and the cloud center.From Doppler weather radar,it is found that the cloud zone in the front of thunderstorm cloud cluster appears the mesoscale band echo of nonuniform structure,and echo free space in the rearward.The dense negative lightning mainly locate at the severe echo with intensity≥40 dBz and ET≥10 km,and nearby the nonuniform wind field of mesoscale.And the more the echo intensity,the higher the ET and the denser the negative lightning.Sparse positive lightning disperse in the rearward of severe or weak convective echoes or sheet echo at the later stage of development.