雷暴活动与MLT区域金属Na层变化特征的统计研究

结合WWLLN闪电定位资料、子午工程海口站激光雷达所测的中性金属钠原子密度数据,利用SEA时序叠加法对对流层雷暴活动与中间层及低热层(MLT)金属钠(Na)原子变化进行了分析,探究了金属钠原子层对雷暴活动的响应及变化特征。研究表明:在雷暴日,MLT区域Na原子在距地面90~95 km处的密度小于非雷暴日的值;利用总雷暴活动触发下的SEA统计得到,Na原子密度在触发后的24 h内出现了明显的减弱,在触发前则有微弱的增强;触发前Na原子密度的增强与闪电活动的发生距离和方位有关;在东北方高密度闪电活动的触发下,Na原子密度在距地面85~93 km的范围内、触发点前-12~0 h显著增强;Na原子密度峰值在91 km和87 km处的相对增强幅度最高,在96 km之上的高度未发现明显的峰值;Na原子柱密度分布特征在闪电触发前-12~0 h与其后0~24 h与之前-24~-12 h存在显著差异,最高相对变化量为36.1%。研究结果表明低纬上空MLT区的Na原子密度的变化应考虑雷暴电场及闪电活动的影响因素。

Statistics on the Characteristics of Metal Na Layer in MLT Region under the Condition of Thunderstorm Activities

The thunderstorm activities in tropospheric and metal Na layer in Mesosphere and Lower thermosphere(MLT)area were analyzed using superposed epoch analysis(SEA),combined with the lightning location data of WWLLN and Na density data of the radar metal of Haikou station. The response and variation characteristics of Na atoms density were analyzed under the trigger of lightning activities. The results are showed as following.(1)The density of Na atoms of the thunderstorm day in MLT region within 90~95 km above the ground was smaller than that of non-thunderstorm one.(2)Before and after the trigger time,the Na atoms density presented different activities. Using the SEA under the trigger of total lightning activities during the thunderstorm processes,density of Na atoms was decreasing obviously within 24 h after the trigger time,while it had only a bit augment before trigger. It had relation with the distance and position of lightning activities away from the station.(3)Under the control trigger of northeast lightning activities,density of Na atoms presented significantly enhancement. The density enhancement of Na atom occurred about-12~0 h before the trigger time,and it ranged from 85 km to 93 km above ground. The maximum of variation ratio of enhancement was at 87 km,and the peak of Na atoms density was at 91 km. Above the 96 km,there had no obvious augment in density.(4)The column density and median density of Na atoms presented obviously difference during the epoch-12~0 h with the epoch0~24 h and epoch-24~-12 h. The Maximum of variation ratio was 36. 1%. The results show that the factor of thunderstorm electric field or lightning activities should be considered for the change of Na atoms density in MLT region of low latitude.