摘要
The three-dimension spatiotemporal development characteristics of positive cloud-to- ground (CG) lightning discharges have been analyzed by using the data measured by the lightning mapping array system with high time and space resolution. The results indicate that a positive CG lightning discharge can be divided into three stages based on the characteristics of its development. The first stage is discharge process in cloud with a long duration preceding the return stroke. This process with an average of 370 ms propagated at velocity of 105 m/s and produced intensive radiation with a magnitude equal to that of the negative leader. During this stage, the lightning channels de-veloped horizontally in the positive charge region with few branches as the negative polarity break-down. During the stage after the return stroke of the positive CG lightning, the lightning channels propagated at velocity of 2 times faster than that before the return stroke. This stage involved lots of positive fast impulses and corresponded to the continuing current process producing less and dis-persed radiation points and more intensive radiation powers. During the final stage of the positive CG lightning, the lightning channels developed at velocity equal to that before the return stroke and the radiation points appeared mainly at the ends of channel. The spatiotemporal development character-istics of the positive CG lightning are very different from that of the negative CG lightning. All of the radiation points of the positive CG lightning appeared in the positive charge region of cloud. Little or no radiation was detected during the positive leader just before the return stroke. The duration of the positive CG lightning was an average of 730 ms. The positive CG lightning discharges with lasting time of 500―600 ms were 43%. 90% of the positive CG lightning discharges involved one return stroke, the most return stroke number being four. The current of the return stroke was an average of 36.5 kA with maximum and minimum values of 70 kA and 11.5 kA respectively. 40% of the return stroke currents were more than 40 kA.
The three-dimension spatiotemporal development characteristics of positivecloud-to-ground (CG) lightning discharges have been analyzed by using the data measured by thelightning mapping array system with high time and space resolution. The results indicate that apositive CG lightning discharge can be divided into three stages based on the characteristics of itsdevelopment. The first stage is discharge process in cloud with a long duration preceding thereturn stroke. This process with an average of 370 ms propagated at velocity of 10~5 m/s andproduced intensive radiation with a magnitude equal to that of the negative leader. During thisstage, the lightning channels developed horizontally in the positive charge region with few branchesas the negative polarity breakdown. During the stage after the return stroke of the positive CGlightning, the lightning channels propagated at velocity of 2 times faster than that before thereturn stroke. This stage involved lots of positive fast impulses and corresponded to the continuingcurrent process producing less and dispersed radiation points and more intensive radiation powers.During the final stage of the positive CG lightning, the lightning channels developed at velocityequal to that before the return stroke and the radiation points appeared mainly at the ends ofchannel. The spatiotemporal development characteristics of the positive CG lightning are verydifferent from that of the negative CG lightning. All of the radiation points of the positive CGlightning appeared in the positive charge region of cloud. Little or no radiation was detectedduring the positive leader just before the return stroke. The duration of the positive CG lightningwas an average of 730 ms. The positive CG lightning discharges with lasting time of 500-600 ms were43%. 90% of the positive CG lightning discharges involved one return stroke, the most return strokenumber being four. The current of the return stroke was an average of 36.5 kA with maximum andminimum values of 70 kA and 11.5 kA respectively. 40% of the return stroke currents were more than40 kA.
基金
supported by the National Natural Science Foundation of China(Grant No.40475002)
the Ministry of Science and Technology of China(Grant No.2003BA904B10).
