摘要
利用常规气象观测资料、NCEP/NCAR再分析资料,分析了2016年1月下旬广东罕见大范围雨雪冰冻天气过程的大尺度环流和冷空气活动特征、动力和水汽条件,采用湿球温度讨论了降水相态和大气温度垂直结构特征。结果表明:此次寒潮过程环流形势为横槽转竖型,横槽下摆引导强冷空气向南迅猛爆发,以及伴随着异常强的冷高压、锋区、冷温度中心和冷温度平流的冷空气主力南侵,是本次寒潮过程粤北和广东中南部温度陡降的主要原因;700hPa冷暖空气的辐合,以及700hPa西南气流从孟加拉湾输送水汽经中南半岛北部到北部湾至华南地区加强并辐合,是造成雨雪冰冻天气产生的重要动力和水汽条件;在有利的大尺度环流、动力和水汽条件配合下,降水相态的变化与暖层强度及湿球温度密切相关,暖层的明显减弱及暖层下方湿球温度低于0℃冷冻层的强度增强,导致降水相态由雨向雪、雨夹雪、霰等固态降水转变;在发生固态降水的平均时段内,粤北地区中低层湿球温度均低于0℃,无明显融化作用,产生纯雪或雨夹雪的可能性大;而位置偏南的珠江三角洲地区仍存在浅薄的暖层,因此主要出现雨夹雪或霰。当寒潮入侵涉及华南降水相态预报时,需要注重实况探空和模式预报探空的大气温湿垂直结构的分析,更应重视湿球温度的研究和应用。
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 wet-bulb 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 central-south 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 Indo-China 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 solid-state,i.e.snow,sleet and graupel.When the solid-state 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 upper-air 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.
引文
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