Numerical Simulation Of Upward Lightning Trigger And Spread

There were two mainly parts in this thesis, firstly setting up stochastic upward lightning parameterization scheme, and producing different thunder cloud background of space charge through the establishment of different distributions of charge structure, were performed to quantitatively investigate the effect of building height on upward lightning trigger and spread, the LPC on the polarity of upward lightning. Then put upward lightning parameterization scheme in an existing 2-dimensional Thunderstorm Electrification and Lightning Model, by analyzing the force of ch on upward lightning. The main results are as follows.(1)Choose the dipolar charge structure was simulated, the both upward lightning were negative, the Upward lightning branch was less in initial stage, To about 2 km away from the ground, upward lightning began to appear a lot of branch, the lightning channel appeared obvious bifurcate. Building height was play key role in upward lightning trigger, it was more likely to trigger the upward lightning with the increase. Building height had certain adverse effect on upward lightning spread, with the increase of building height, the horizontal and vertical propagation distance of upward lightning, the fractal dimension and propagation length of lightning channel also decreased gradually.(2)Choose the three charge structure was simulated, to make some changes to the triggering condition of upward lightning, by a large number of simulation experiments, the article found out that the LPC has a shielding effect on the transmission of upward lightning. When the horizontal distance was less than 1600m between the LPC center and the main negative charge center, the upward lightning spread to the LPC. When the distance was between 1600～2700m, without a recoil leaders, the upward leaders also produced polarity reversal, and pass to the main negative zone, form the bipolar upward lightning. The vertical height of polarity reversal within a certain range, the vertical height increased with the positive charge increasing.(3)Put upward lightning parameterization scheme in an existing 2-dimensional Thunderstorm Electrification and Lightning Model. The conclusion follows as:1 Simulated three groups of discharge experiment, only a set appeared upward lightning. the time was 41.9min, occur in the mature stage of the lightning, appeared two minutes before intracloud lightning, the upward lightning was defined as triggered lightning.2 According to the charge pattern of different time, the development of thunderstorm and the function of intracloud lightning due to the increasing of LPC and the enhance of electric field intensity, and triggering the upward lightning.3 By the sensitivity experiments the article found that when the relative potential temperature disturbance (ch) value was higher, the convection of thunderstorm was more intense, the cloud-to-ground lightning and intracloud lightning were more, but upward lightning were not.