热带沿海地区一次局地雷暴消散阶段的云内电场

Vertical electrical field during decay stage of local thunderstorm near coastline in tropical island

利用球载电场探空仪于2019年8月12日在海南岛东北部海岸线附近获得的一次局地雷暴消散阶段的云内电场探空资料,结合S波段天气雷达、地面大气平均电场仪、地闪定位等观测资料,详细分析了该雷暴的演变过程和电学特征.由电晕电流反演的垂直电场廓线可知,云内正、负电场最大值分别位于大约6.3和8.3 km处,垂直方向上,云内分布着6个电荷区,最下部为负电荷区,往上依次改变极性,且所有电荷区都位于零度层以上的混合相区域.由于数据中断,无法准确判断上部负电荷区上部边界以及其上方的正电荷区信息,其余四个电荷区分别位于海拔高度6.0—6.3 km,6.3—6.6 km,6.9—7.3 km以及7.3—8.3 km之间,电荷密度分别为-1.84,1.80,-1.46和1.04 nC/m^(3).由已有数据推算,最上部负电荷区电荷密度应大于-0.51 nC/m^(3),其电荷区相对强度仅次于靠近其下部边界的正电荷区,两者电荷区厚度都超过1 km.

In order to directly observe the electric field characteristics and study the charge structure in thunderstorms occurring in tropical regions,a balloon-borne strong electric field sounding is used to measure the vertical component of the electric field,temperature within the cloud and real-time location information of the sounding.Based on the principle of corona discharge,two 1-m-long metal probes are used as the sensors to detect the vertical electric field.In the summer of 2019,a result of electric field sounding within a local thunderstorm was obtained in the northeastern coastal area of Hainan Island,China.With the combination of an S-band weather radar,atmospheric electric field instrument and lightning locating network,the charge structure of the thunderstorm is analyzed in detail.The results show that the thunderstorm is a small-scaled local thunderstorm occurring in the afternoon,the sounding starting to be observed at the decay stage of the thunderstorm.In this period,lightning activities is rare,and the variation of ground electric field is similar to that of conventional summer thunderstorms.The whole sounding process lasts 34 min,during which the vertical airflow in the cloud is relatively stable,basically keeping 4-6 m/s.It can be seen from the electric field profile that the charge distribution in the thunderstorm cloud shows a complex charge structure which is composed of six charge regions.A negative charge region is lowermost,and above this the polarity alternates successively from bottom to up,where all charge regions are located above the melting-layer.Due to data interruption,it is impossible to accurately judge the upper boundary of the upper negative charge region and the information about the positive charge region above.The remaining charge regions are located in an altitude range of 6.0-6.3 km,6.3-6.6 km,6.9-7.3 km and 7.3-8.3 km,respectively.The charge densities in these four regions are-1.84 nC/m^(3),1.80 nC/m^(3),-1.46 nC/m^(3),and 1.04 nC/m^(3),respectively.According to the existing data,the charge density of the uppermost negative charge area should be greater than-0.51 nC/m^(3).Moreover,the upper positive charge region(the fourth from bottom up)has the largest strength,followed by the negative charge region above it,both of which are more than 1 km in thickness.The electric field intensities in the other charge regions are relatively small.The pairs of positive and negative charge regions at the bottom are slightly different in strength and thickness.