Oceanic And Continental Differences In The Characteristics Of Red Sprites And Their Parent Thunderstorms In South China

Red sprites are one of the atmospheric transient luminous events(TLEs)occurring over thunderstorm clouds,which has received wide attention from researchers and scholars in recent years.At present,domestic research on red sprites is mainly focused on the northern part of China and Taiwan.However,there are no relevant studies or reports in South China,where thunderstorms and red sprites are highly prevalent.Therefore,it is important to carry out the study of red sprites in this region.In this paper,based on ground-based optical data from 2018-2021,combined with the electric field,lightning positioning,and meteorological data,a statistical analysis of the characteristics of red sprites and their parent thunderstorms in South China was conducted from the perspectives of morphological characteristics,spatial and temporal distribution,and the causative lightning.In addition,individual cases of oceanic and continental thunderstorms in the region were selected and analyzed to explore the causes of the sea-land differences in the polarity of red sprites.The main findings are as follows:(1)The morphology of red sprites in South China is complex and diverse,mainly column-shaped and carrot-shaped,which can be produced by negative cloud-to-ground strokes.Besides,the brightness of positive polarity red sprites is much higher than that of negative polarity,and their vertical development structure is more clearly defined.The number of positive red sprites is much more than negative sprites,and from the spatial distribution,there are obvious differences in the distribution of positive and negative red sprites between sea and land,with positive sprites dominating on land and negative sprites occurring mainly in the ocean.In terms of temporal distribution,red sprites occur mainly in summer,which has a good consistency with lightning activity.The red sprites mainly occur after the peak of daily lightning frequency,and there is no significant difference between the red sprites triggered by oceanic and continental thunderstorms over time.(2)According to the statistics of the causative lightning characteristics of red sprites in South China,it is found that the absolute value of peak current(-136 kA)of the negative red sprites parent lightning is generally larger than that of positive ones(+74 kA).Besides,positive cloud-to-ground strokes with peak currents lower than 20 kA are also likely to trigger red sprites.In addition,negative sprites are likely to occur above the convection region of thunderstorm clouds with the low bright temperature at the cloud top,while positive sprites are concentrated to trigger above the stratus clouds region.Since the negative sprites are mainly concentrated on the ocean,the peak current of the red sprite parent lightning on the ocean is significantly higher than that on the land area,and the cloud-top bright temperatures near the red sprites are significantly lower than that on the land.(3)The analysis of three individual cases of red sprite parent thunderstorms reveals that red sprites occur mainly in areas of high lightning density and at all stages of lightning activity.Therefore,the outbreak of red sprites may not serve as an indicator signal of weakening convective activity in thunderstorms,which is different from the existing understanding.Lightning activity during thunderstorms is dominated by negative ground cloud-to-ground strokes,and positive and negative red sprites can occur in different regions of the same thunderstorm.It is noteworthy that there is a shift in the polarity of strong cloud-to-ground strokes from ocean to land from predominantly negative to predominantly positive,explaining the cause of the sea-land difference in the polarity of red sprites.(4)This paper reports a case of a massive red sprite event with the largest number of ground-based observations in the mainland China region so far.Through the analysis of its parent thunderstorm and weather situation,it is pointed out that South China in May may be a high outbreak region for red sprites.This work enriches the understanding of the large-scale red sprite event in China and is of guiding significance for the arrangement of domestic red sprite observation experiments.