Features Statistics and Warning of Flash Heavy Rains
Based on Doppler radar data, sounding data and precipitation data, 537 flash heavy rain processes in Puer and Xishuangbanna are analyzed. Three short time severe precipitation models are established, including the flash heavy rain into the low centroid and weak convergence type, the low centroid and convergence type and the high centroid type. In addition, comparative analysis is carried out on the features of intensity, velocity, life cycle, vertical wind shear and interrelationships of convergence and heavy rainfall duration, shear line in convergence zone and precipitation intensity, DVIL and precipitations of different types. Then the warning methods are derived as follows: if meeting the following conditions, it is a highly possible to see flash heavy rains. First, in the case of a lower centroid of echo in heavy precipitation, if echo intensity is 40-45 dBz and not inclined, echo intensity remains unchanged by vertical direction, H40 dBz≥H0, overall length by velocity of echo intensity about 40 dBz is more than or equal to 0.67 h in 0℃ layer, we can give warning time of 30-40 min before flash heavy rainfall. Second, in the case of a high centroid of echo in heavy precipitation, if the intensity of echo is uniform (40-45 dBz), the width of echo is greater than or equal to 3 km on the edge of strong echo, overall length by velocity of echo intensity about 40 dBz is more than or equal to 0.47 h in 0℃ layer, we can give warning time of about 28 min before flash heavy rainfall. Finally, the genesis for flash heavy rains is discussed.