甘肃中川地区雷暴的地闪特征

CHARACTERISTICS OF LIGHTNING DISCHARGE TO GROUND IN ZHONGCHUAN AREA

利用在甘肃中川地区一次雷暴过程的５站电场变化同步观测资料，对１９９６年８月１２日的４次地闪过程分析发现甘肃中川地区负地闪回击所中和的负电荷离地高度为２．７４～５．４１ｋｍ（对应环境温度为－２．０～－１５．０℃），而正地闪回击所中和的正电荷离地高度低于２．０ｋｍ（对应环境温度为±５．０℃）。正地闪放电过程较负地闪中和的电荷量要大７倍左右。在雷暴初期及活跃期前期，地闪回击发生之前有持续１７０～３００ｍｓ的云内放电过程，它发生在云下部正电荷区和主负电荷区。与雷达回波的对比发现，负地闪发生在雷暴大于２０ｄＢｚ的强回波区或４０ｄＢｚ强回波边缘而正地闪却发生在相对较弱的回波区域。

Sources of charge structure for the individual strokes of four multiple stroke flashes to ground have been estimated by using measurements of the electrostatic field changes obtained at 5 sites on the ground beneath thunderstorm.The result shown that the altitude of neutralized negative charge is between 2.74～5.41 km above the ground (the corresponding ambient temperature is -2.0～-15.0℃),while that of neutralized positive charge is less than 2.0 km above the ground (the corresponding ambient temperature is +5℃).The charge neutralized by positive discharge is about 7 times larger than that neutralized by negative discharges.Positive and negative flashes usually follow cloud discharges which lasted 170～300 ms and occurred between lower positive charge region and main negative charge region during the developing stage and early active stage of thunderstorm.The comparison with radar echo has shown that the negative discharge initiates in the regiom greater than 20 dBz or near the edge of the region with severe echoes greater than 40 dBz,while positive discharge initiates in the weak echo region.