ISSN 1006-9895

CN 11-1768/O4

Spatial Observation of Red Sprites over a Winter Mesoscale Convective System in North America and the Analysis of Its Parent Thunderstorm

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    Red sprites are large-scale transient luminous events (TLEs) that usually occur between about 40 and 90 km altitudes above thunderstorms, and they are caused by cloud-to-ground (CG) lightning strokes and subsequent continuous current. Compared with studies that focus on sprites that occur in summer, those focusing on winter sprites are fewer due to limited comprehensive synchronous observation data. Influenced by the upper trough and warm, moist airflow at low level, a thunderstorm occurred in Arkansas, North America, on December 27–28, 2008. The Imager for Sprites and Upper Atmospheric Lightning (ISUAL) aboard the FORMOSAT-2 satellite could record two red sprite events. Using the red sprites optical observation data obtained by ISUAL, Doppler weather radar data, National Lightning Location data, ultra-low frequency magnetic field data, and cloud-top brightness temperature data provided by the National Environmental Center/Climate Prediction Center of the United States and the sounding data, this paper presents a detailed study of the characteristics of the winter thunderstorm that produced the red sprites and the related lightning activity. The results show that ISUAL did not record the halo that accompanied the two red sprites. The first was a columnar sprite, and the specific morphology of the second could not be determined because of its dim light. The parent thunderstorm of the red sprites was a mesoscale convective system (MCS), which appeared around 1500 UTC on the 27th near northern Arkansas and moved from west to east. The thunderstorm became stronger at about 2359 UTC, and the area of maximum radar reflectivity (55–60 dBZ) reached 339 km2 and then began to weaken. At 0303 UTC, the thunderstorm intensity increased, then the cloud gradually spread, and the thunderstorm began to weaken and completely dissipated at 1100 UTC. The first recorded sprite occurred at 0446:05 UTC, and the second at 0447:17 UTC. They tended to be produced in the dissipation stage of the MCS, when the frequency of the positive and negative CG lightning was low and the Percentage Of Positive CG to total CG (POP) increased significantly, and they were mostly over the stratiform cloud area with a 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 the sprite production was the decay of the thunderstorm and that the area of the stratiform region developed, which is consistent with the results of previous studies on summer sprites. The parent CG flash of red sprites was positive and with a single return stroke, and it was located in the trailing stratiform region of the MCS, where the radar reflectivity ranged from 25 to 35 dBZ. The corresponding radar echo top heights were 2.5 km and 5 km, and the peak currents were +183 kA and +45 kA, respectively. Based on the ultra-low frequency magnetic field data, the impulse charge moment changes (iCMCs) of two parent lightning discharges were estimated to be +394 C km and +117 C km. The ultra-low frequency magnetic antenna recorded the internal current signal of the first red sprite, indicating that the red sprite was strongly discharged.

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  • Received:November 03,2019
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  • Online: September 27,2020
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