Using Polarimetric Radar Observations to Characterize First Echoes of Thunderstorms and Nonthunderstorms: A Comparative Study.

This work compares the characteristics of the first echoes of thunderstorms and nonthunderstorms retrieved from S‐band polarimetric radar observations. Observations of 57 (39) isolated thunderstorm (nonthunderstorm) cells with roughly equivalent aerosol and water vapor conditions but different convective available potential energy were obtained with a S‐band polarimetric radar and three independent lightning location systems during 2016/2017 in southern China. Storms with the first echoes were divided into three types based on echo top heights, namely, type 1 (below 0°C layer), type 2 (0°C to −10°C), and type 3 (above −10°C layer). Our observations show median values of radar reflectivity (ZH) and differential reflectivity (ZDR) of type 1 and type 2 in warm phase layer (below 0°C layer) are obviously greater in nonthunderstorms than in thunderstorms, but this feature is not significant in type 3 storms. In the mixed 1 phase layer (0°C to −10°C), median ZH in type 2 is greater in nonthunderstorms while median ZDR in type 3 is slightly smaller. In the mixed 2 phase layer (−10°C to −38°C), median ZH is greater in thunderstorms while median ZDR is smaller, and ZDR values in nonthunderstorms are closer to zero. Although results of ZDR comparisons in the mixed phase are likely affected by random errors and/or residual bias errors, these different signatures suggest different characteristics of liquid or ice particles between thunderstorms and nonthunderstorms. This study is expected to advance our understanding of physical processes responsible for the generation of the first flash. Plain Language Summary: Thunderstorms generally show stronger convective activity than nonthunderstorms do. What are thunderstorms and nonthunderstorms like at the beginning of precipitation radar detection? Observations of 57 (39) isolated thunderstorm (nonthunderstorm) cells based on a S‐band polarimetric radar and three independent lightning location systems during 2016/2017 in southern China are investigated. We found that polarimetric radar parameters of the first echoes are different between thunderstorms and nonthunderstorms, especially, the larger echo intensity in nonthunderstorms below −10°C layer. Comparative results in different height layers suggest different characteristics of liquid/ice particles of the first echoes between thunderstorms and nonthunderstorms. This study would help us to understand the characteristics of microphysics in the formation of thunderstorms. Key Points: The first echoes of thunderstorms and nonthunderstorms determined using radar are manually retrievedThe parameters of polarimetric radar of the first echoes are different between thunderstorms and nonthunderstormsDifferent properties suggest different characteristics of liquid/ice particles of the first echoes between thunderstorms and nonthunderstorms [ABSTRACT FROM AUTHOR]