1.Key Laboratory of Middle Atmosphere and Global Environment Observation LAGEO,Institute of Atmospheric Physics,Chinese Academy of Sciences,Beijing;2.University of Science and Technology of China;3.Chengdu University of Information Technology;4.National Cheng Kung University
红色精灵是发生在雷暴云上空的一种大尺度瞬态放电发光现象,他们通常出现在地面上空40 ~ 90 km之间,是由地闪回击和随后可能存在的连续电流产生的。目前,由于综合同步观测资料较少,与夏季红色精灵相比,全世界对冬季红色精灵的研究屈指可数。2008年12月27日至28日,受高空槽及低层暖湿气流的影响,北美阿肯色州地区爆发了一次冬季雷暴天气过程,搭载于FORMOSAT-2卫星上的ISUAL(Imager of Sprites and Upper Atmospheric Lightning)探测器有幸在这次雷暴上空记录到了两例红色精灵事件。本文利用ISUAL获取的红色精灵观测资料、多普勒天气雷达资料、美国国家闪电定位资料、超低频磁场数据、美国国家环境中心/气候预测中心提供的云顶亮温和探空数据等综合观测数据,对产生红色精灵的这次冬季雷暴特征和相关闪电活动规律进行了详细研究。结果表明,在两例红色精灵中，IUSAL均未观测到伴随的“光晕（halo）”现象，第一例为“圆柱状”红色精灵,第二例红色精灵由于发光较暗,无法判断其具体形态。产生红色精灵的母体雷暴是一次中尺度对流系统,该系统于27日1500 UTC左右出现在阿肯色州北部附近,并自西向东移动。2359 UTC系统发展到最强,最大雷达反射率因子(55 ~ 60 dBZ)的面积达到339 km2,之后开始减弱。0303 UTC雷暴强度有所增加,随后云体便逐渐扩散,雷暴开始减弱,并在1100 UTC完全消散。两例红色精灵发生分别在04:46:05 UTC和04:47:14 UTC,此时雷暴处于消散阶段,正负地闪频数均处于一个较低水平且正地闪比例显著增加,并且多位于云顶亮温-40 ~ -50 ℃的层状云区上空。红色精灵的出现伴随着30 ~ 35 dBZ回波面积的增加。在红色精灵发生期间,雷达反射率大于40 dBZ的面积减少,10 ~ 40 dBZ的面积增加,表明红色精灵的产生与雷暴对流的减弱和层状云区的发展有关,这与已有的夏季红色精灵的研究结果类似。红色精灵的母体闪电为正地闪单回击,位于中尺度对流系统雷达反射率为25 ~ 35 dBZ的层状云降水区,对应的雷达回波顶高分别为2.5 km和5 km,峰值电流分别为+183 kA和+45 kA。根据超低频磁场数据估算两个母体闪电的iCMC分别为+394 C km和+117 C km。超低频磁天线记录到了第一例红色精灵内部的电流信号,表明这例红色精灵放电很强。
Red sprites are one type of large-scale transient luminous events (TLEs) that usually occur between about 40 ~ 90 km altitude above thunderstorms, which are caused by cloud-to-ground lightning strokes and subsequent continuous current. Compared with sprites in summer, there are fewer studies on the winter sprites in the world due to fewer comprehensive synchronous observation data. Influenced by the upper trough and warm-moist airflow in low level, a thunderstorm took place in in Arkansas, North America on 27 ~ 28 December 2008, the Imager of Sprites and Upper Atmospheric Lightning (ISUAL) aboard the FORMOSAT-2 satellite was lucky to record two red sprite events . Using red sprites optical observation data obtained by ISUAL, Doppler weather radar data, National Lightning Location data, ultra-low frequency magnetic field data, cloud top brightness temperature data provided by the National Environmental Center/Climate Prediction Center of the United States and the sounding data, this paper makes a detailed study of the characteristics of the winter thunderstorm that produced red sprites and related lightning activity.The results show that ISUAL did not recorded the halo that accompanied two red sprites. The first was columnar sprite, and the second was unable to determine its specific morphology because of its dim light. The parent thunderstorm of red sprites is a mesoscale convective system, which appeared around 1500 UTC on 27th near northern Arkansas and moved from west to east. The thunderstorm developed stronger at about 2359 UTC, and the area of maximum radar reflectivity (55 ~ 60 dBZ) reaches 339 km2, then began to weaken. At 0303 UTC, the intensity of thunderstorm increased, then the cloud gradually spread, and the thunderstorm began to weaken, and completely dissipated at 1100 UTC. Two sprites occurred at 04:46:05 UTC and 04:47:17 UTC, respectively . They tended to be produced in the dissipation stage of the MCS, when the frequency of positive and negative cloud-to-ground lightning is low and POP increases significantly, and they were mostly over the stratiform cloud area with brightness temperature of - 40 ~ 50 ℃. The sprite production was accompanied by an increase in the echo area of 30 ~ 35 dBZ. The area of radar reflectivity larger than 40 dBZ decreased, and the area of 10 ~ 40 dBZ increased during the sprite time window, suggesting that production of the sprite was the decay of the thunderstorm and the area of the stratiform region develops, which is consistent with previous studies on summer sprites. The parent CG of red sprites was positive with a single return stroke, and located in the trailing stratiform region of the MCS, where the radar reflectivity was range 25 from 35 dBZ. The corresponding radar echo top heights were 2.5 km and 5 km, and the peak currents are + 183 kA and + 45 kA, respectively.. Based on ultra-low frequency magnetic field data, the iCMC of two parent lightning is estimated to be + 394 C km and + 117 C km, respectively. Ultra-low frequency magnetic antenna recorded the internal current signal of the first red sprite, indicating that the red sprite discharged strongly.