The Application Research Of Radar Data For The Lightning Warning Of Isolated Storm Cells In Beijing

With the application of electronic devices, the loss caused by the devices'sensibility to lightning is now becoming more and more serious. So, it is very important to predicate which storm cell will become a thunderstorm or what time the lightning in a thunderstorm will initiate. More attention have been paid on the development of lightning prediction method.A lightning warning method is given in this thesis using the data of radar, lightning detection and air sounding for 20 isolated storm cells in Beijing from July to August in 2005. According to this method, the warning process should be following these two steps as follow.The first step is to judge whether an isolated cell has a potential power to become a thunderstorm or not. If the 40 dBz echo top of a cell has risen beyond the 0℃stratification level and stayed above this height, this cell might develop to be a thunderstorm.The second step is to conclude that a cell will be a thunderstorm or not, and predicts the occurring time of the first lightning in this thunderstorm. To do this, there are two factors needed to be focused orderly after the foregoing condition was met: 1) if the 40 dBz echo top keeps going up to the -10℃stratification level, the conclusion will be drawn that the cell will become a thunderstorm and the first lightning in it will occur in the next 15 minutes. 2) if the 40 dBz echo top can not reach the -10℃stratification level, the additional factor of P value, which is a percentage of the volumes of the echo with greater than 40 dBz to that of the echo with greater than 25 dBz (all these echoes must exist above the 0℃stratification level), should be considered. If the P value exceeded 5%, the first lightning in the cell will also occur in the next 15 minutes.A prediction test of this method was carried out using the data of the other isolated cells in Beijing in the same period. The test result shows that the method is effective in judging whether a normal cell will become a thunderstorm cell and predicting the time of the first lightning in the cell.In addition, a linear relation was found between two time intervals. One interval is between the occurring time of the first interacloud flash (IC) and the first cloud-to-groud (CG) in a cell. Another is between the appearing of first 25 dBz in the cell and the V value ( change rate of 35 dBz echo thickness in the cell ) reaching its maximum. It further gives a chance for the CG prediction.At last, a two-dimensional electrification and discharging numerical model was used to discuss the foundation of the warning method. It indicates that: 1 ) the raindrop don't have effect on the formation of dominating negative charge center; 2 ) there is a charge zone in a cell, and the greater charge region always lies on the upper level; 3 ) the height of the main quality of the graupel and the hail must correspond with the height of the charge zone fully or partially, so that the graupel and the hail can charge more, then the strong dominating negative charge center will emerge finally.