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
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.