雷暴下近地面电特性及其对人工引雷的影响

ELECTROSTATIC CHARACTERISTICS NEAR GROUND UNDER THUNDERSTORM AND ITS EFFECT ON ARTIFICIAL TRIGGERING LIGHTNING

利用已建立的一维时变模式，对雷暴下近地面的电特性进行了计算。计算结果表明：由于地面的不规则性所产生的电晕电流密度可达２．０ｎＡ／ｍ２，由此而形成的空间电荷密度在１００ｍ高度以下可达１．１ｎＣ／ｍ３，传导电流可达３．５ｎＡ／ｍ２，并可延伸到１０００ｍ高度，形成０．１ｎＣ／ｍ３和１．０ｎＡ／ｍ２的电荷密度和电流密度。在雷暴的消散阶段，由于电晕离子的影响，可在地面形成３．０—４．０ｋＶ／ｍ与雷暴电场极性相反的电场。几百米高度上的空中电场有助于提高人工引发雷电的成功率。兰州地区，雷暴下部有大量正电荷存在，当低层空间电场达到７０．０ｋＶ／ｍ左右时。

Electrostatic characteristics near ground under thunderstorm have been studied by using a one-dimension model.Maximum corona current density produced due to ground irregularities is about 2.0nA/m 2 .Space charge density below 100m is about 1.1nC/m 3 ,the conduction current density,at same level,can is about 3.5nA/m 2 .Corona ions can reach up to 1 000m above ground level with a space charge density of 0.1nC/m 3 and conduction current density of 1.0nA/m 2 .During dissipating stage of storm,corona ions can produce an electric field of about 3 4kV/m that is similar in magnitude and opposite in polarity to that when storm is active.Effect of the space charge layer should be considered in artificially triggering lightning experiment.Electric field at several hundred metre level above ground would be a better criterion for triggering lightning.Triggering lightning experiment by using present small rocket would be successful when the electric field in low altitude reaches about 70kV/m in Lanzhou region where thunderclouds have a typical charge structure with a large amount of positive charge.