Analysis of a Rare Cryogenic Freezing Rain and Snow Event in Cold Wave Weather over Guangdong Province in 2016
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Abstract:
Based on the routine observations and NCEP reanalysis data (4 times a day), the circulation background, the characteristics of cold air activity, dynamical and water vapor conditions, especially the features of precipitation phase state, and the vertical structure of atmospheric temperature using wetbulb temperature (WBT) are analyzed for the rare cryogenic freezing rain and snow event over Guangdong province in late January 2016. The results show that the primary reason of temperature sudden drop in the north and centralsouth parts of Guangdong Province during this cold wave event is that strong cold air outbroke when the transverse trough swinged southward and the severe cold air moved southward with abnormally strong cold high, frontal zone, cold temperature center and advection in the atmospheric circulation pattern of the transverse trough turning into vertical. The favorable dynamical conditions for the convergence of warm and cold air at 700 hPa and water vapor conditions for the convergence in South China of southwesterly of 700 hPa carrying water vapor from the Bay of Bengal across the north of the IndoChina Peninsula and Beibu Gulf resulted in this weather process. The precipitation phase state was closely related to the intensity of the warm layer (temperature above 0 ℃) and WBT under the favorable circulation, dynamical and water vapor conditions. The warm layer weakened significantly and the subfreezing layer with WBT below 0 ℃ underneath strengthened, leading to the transition of precipitation phase state from rain to solidstate, i.e. snow, sleet and graupel. When the solidstate precipitation appeared, there was no melting effect because of the WBT below 0 ℃ in the middle and lower atmosphere; thus snow or sleet was more likely to be present in the north of Guangdong Province, whereas sleet or graupel was mainly present in the Pearl River Delta, which locates further south due to the existence of a weak warm layer. Therefore, the use of upperair sounding and model forecast sounding data, particularly WBT in the analysis of the vertical structure of atmospheric temperature should be paid more attention during cold wave weather involving precipitation phase state prediction.
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Supported by:Beijing E-Tiller Technology Development Co., Ltd.
Supported by:Beijing E-Tiller Technology Development Co., Ltd.