Beijing Strong Thunderstorm Cloud Flash Characteristics And Cloud Physics And Precipitation Evolution Study Of The Relationship

The observational characteristics of cloud-to-ground lightning, radar echo, and precipitation for 8 severe storms occurred in Beijing area during 2000-2001 are investigated. More detailed analyse in cloud vertical velocities , microphsical distribution and evolution characteristic associated with lightning using MM5 model.The results show that there is a close relationship between cloud lightning features and the precipitation types, intensity as well as the evolution of storms. There are apparent differences of lightning features between the heavy-rain and hail-producing weather. The proportion of negative lightning is higher, the precipitation is more. Positive lightning frequency has apparent relationship with hail-producing , strong wind The hail-producing weather has more positive lightning especially at the time just before hailfall at which the positive lightning frequency increase rapidly. The portion of positive lightning is clearly increasing ,which often ahead of hail-producing weather several minutes or one hour time. This can provide reference of prew -arning of severe storms weather. In addition, it is found that no flash occurs with radar echo over 30-45dBZ and flash often occurs with radar echo more than 45 dBZ in the studied case, which is a little high from the previous studies .Numerical simulation research indicates, the positive lightning emerges at the top and bottom of cloud, and negative lightning emerges at the middle layer about -10°C. Negative cloud-to-ground lightning occurrence has good relationship with graupel content and position. With the maximum center of graupel water content descending, the negative cloud-to-ground lightning frequercy inceases. There is a good relationship between positive lightning at the top of cloud and the amount of ice crystal. A large amount of ice crystal fromed in cloud is a primary reason for sudden increase of positive lightning. There is a time phase difference between lightning occurring time and strong updrafts occurring time, powerful lightning lags stong updrafts by 1-3 hours.