大兴安岭林区负地闪电荷源的反演

Retrieval of the charge sources neutralized by negative cloud-to-ground lightning flashes in the Daxing'anling Forest region

在中国东北大兴安岭林区进行了基于全球定位系统(GPS)时间同步的闪电地面电场变化多站观测。利用2010年7月14日一次过境雷暴多站同步的闪电电场变化资料,采用非线性最小二乘拟合法对雷暴成熟阶段的15次负地闪(包含57次回击和8次连续电流过程)中和的电荷源进行了拟合。大兴安岭林区负地闪单次回击中和的电荷量平均为1.0 C(范围为0.1-5.0 C),20%的继后回击中和电荷量大于首次回击,继后回击与首次回击中和电荷量的比为0.1-6.1,平均为0.8±1.0。单次连续电流中和的电荷量平均为3.8 C(范围为0.4-7.3 C),连续电流期间通道中的平均电流估计为25.3 A(范围4.9-50.8 A),一次负地闪中和的总电荷量平均为6.4 C(范围为1.4-12.4 C)。负地闪回击和连续电流中和电荷源的高度分布与雷暴云的发展有关,对应的环境温度为-10—-25℃。在雷暴成熟阶段前期,负地闪回击和连续电流中和电荷源距地面的高度从5.0 km缓慢上升至10.5 km;在雷暴成熟阶段后期,负地闪回击和连续电流中和电荷源距地面的平均高度从9.0 km下降到6.0 km,单次回击中和的电荷量也较前期减小约一个量级。与雷达回波的叠加显示,负地闪回击和连续电流中和的电荷源主要位于大于40 dBz的强对流中心区,部分位于30—40 dBz的强回波区边缘或较弱的回波区。

Using the data from slow and fast antenna network of the 7 stations synchronized by UPS in the Daxing＇anling Forest region on July 14,2010,the magnitude and location of charge neutralized by return strokes and continuing currents of negative cloud-to-ground lightning flashes are fitted.The charge lowered by the discrete negative return stroke ranged from 0.1 to 5.0 C with an arithmetic mean of 1.0 C.The charge transported by continuing current processes was from 0.4 to 7.3 C with an arithmetic mean of 3.8 C,and the corresponding average current was from 4.9 to 50.8 A with an arithmetic mean of 25.3 A.The total charge neutralized by a negative flash was in a range from 1.4 to 12.4 C with an arithmetic mean of 6.4 C.The charge neutralized by return strokes and continuing currents gradually raised up from 5.0 km to 10.5 km during the early-mature stage of thunderstorm.When the thunderstorm evolved into the late-mature stage, the average height of charge sources desccndcd from 9.0 to 6.0 km,corresponding to the ambient temperature of about -10℃ to -25℃.The superposition of the neutralized charge and radar echo shows the charge sources of negative cloud-to-ground mainly concentrated inside the cloud region with radar reflectivity higher than 40 dBz.