华北地区一次中尺度对流系统上方的Sprite放电现象及其对应的雷达回波和闪电特征

利用低光度相机首次观测到了2013年7月31日华北地区一次中尺度对流系统(MCS)上空产生的中高层Sprite放电现象。结合闪电定位、天气雷达等同步观测, 对一次MCS诱发的Sprite的形态学特征及其对应的母体闪电和雷暴系统的雷达回波特征等进行了详细分析。研究除发现了2例圆柱型、3例胡萝卜型和1例舞蹈型 Sprite外, 还发现了2例发光主体发育不完全的Y字型Sprite。估算的Sprite的底部平均高度低于61.8±3.5 km, 顶部平均高度为84.3±6.8 km。Sprite持续时间算术平均值为25.7±9.8 ms, 几何平均值为24.4 ms。Sprite的母体闪电均为正地闪, 峰值电流在+62.5～+106.2 kA之间, 算术平均值为+77.1±22.2 kA, 是本次MCS所有正地闪平均峰值电流的1.4倍。Sprite母体闪电的脉冲电荷矩变化(iCMC)在+475～+922 C km之间, 几何平均值为+571.0 C km。Sprite母体闪电发生在MCS雷达回波25～35 dBZ的层状云降水区, 弱回波(<30 dBZ)面积的突然增加对Sprite的产生有重要指示作用。Sprite易发生在MCS成熟—消散阶段正地闪比例(POP)显著增加的时段。在本次MCS消散阶段中, 有两个时间段可能有利于产生Sprite。在Sprite集中发生时间段, 北京闪电综合探测网(BLNET)探测到的正地闪比例为54.2%, 正地闪连续电流比例70.24%, 连续电流持续时间为58.17±50.31 ms, 有利于Sprite的产生。

Sprites over a Mesoscale Convective System in North China and the Corresponding Characteristics of Radar Echo and Lightning

Sprites were observed over a mesoscale convective system (MCS) on 31 July 2013 in North China using a low-light video camera. The characteristics of sprite morphology, sprite parent lightning, and the corresponding radar echo in the MCS were analyzed based on coordinated Beijing Lightning NETwork (BLNET) data and weather radar data. Among the eight sprites produced in this MCS, two were columnar sprites, three were carrot sprites, one was a dancing sprite, and two were wishbone sprites (underdeveloped carrot sprites). The estimated channel bottom of the sprites was lower than 61.8±3.5 km, and the channel top was at 84.3±6.8 km on average. The arithmetic mean (AM) and geometric mean (GM) of sprite duration were 25.7±9.8 ms and 32.7 ms, respectively. All of the parent lightning strokes of these sprites were positive cloud-to-ground (+CG) strokes, with an AM peak current of +77.1 kA, ranging from +62.5 kA to +106.2 kA, which was 1.4 times larger than that of the total +CGs in this MCS. The estimated GM value of impulse charge moment change was +571.0 C km, ranging from +475 to +922 C km. In this MCS, sprites were produced above the trailing stratiform region of the MCS, where the radar echo was between 25 and 35 dBZ, and the burst of weak radar echo (<30 dBZ) was a key indicator of sprite production. Sprites tended to be produced early in the dissipation stage of the MCS, with an increasing percentage of the +CG flash (POP) rate. During the dissipation stage of the MCS, there were actually two stages that tended to produce sprites with increasing POP rates. During the period of sprite production, BLNET detected a POP rate as high as 54.2%. Meanwhile, 70.24% of the +CG strokes contained continuing currents, with an AM value of 58.17±50.31 ms, making +CG strokes in this MCS favorable for sprite production.