粤东一次罕见持续性大雾天气过程的分析

Analysis of a Rare,Persistent Heavy Fog in Eastern Guangdong

采用高分辨率的探空、地面实测资料以及NCEP/NCAR再分析资料,对2010年2月23日—3月6日粤东地区一次罕见的持续性大雾天气过程进行了分析,结果表明:此次连续性大雾天气过程是由辐射雾和平流雾组成;探空资料的分析表明,大雾期间大气层结呈现对流稳定或弱的不稳定特性,同时近地面层存在明显的逆温结构;大雾期间850 hPa华南沿海西南方向气流的存在为这次过程提供了充足的水汽条件;地面不断有弱冷空气的入侵,使低层大气变得弱不稳定,并维持了冷的下垫面,但没有完全破坏近地面层的逆温;在深厚逆温条件下,持续的低空西南支暖湿水汽输送和适量的水汽辐合,导致水汽凝结,使得粤东地区的大雾和毛毛雨维持;持续强劲的暖湿气流和弱冷空气的不断入侵维持冷的下垫面,使雾雨天气在华南沿海长时间维持;大雾后期,强冷空气入侵破坏了大气的层结和逆温条件,大雾天气消散。同时,当Δθse 850～1 000<0时,将出现雾雨天气。

With high-resolution sounding and surface observations and NCEP/NCAR reanalysis data, this work studies a rare, persistent heavy fog that took place from February 23 to March 6, 2010 in eastern Guangdong. The results show that the process was composed of radiation and advection fog. It is also shown by the sounding data that the atmospheric stratiform during the fog was convectively stable or mildly unstable while a significant inversion existed in the layer near the surface. At 850 hPa, a southwesterly airflow over the coastal part of South China supplied the fog with abundant amount of water vapor. Together with the in- trusion of moderate cold air over the surface, the low-level atmosphere was made mildly unstable and the un- derlying surface was kept at relatively cold temperatures without complete destruction of the near-surface-lev- el inversion. Under the condition of deep inversion and with the transportation of warm and humid airflow by the low-level southwest branch of the Westerlies and the convergence of adequate amount of water vapor, condensation resulted, maintaining the heavy fog and light rain over eastern Guangdong. Persistent and pow- erful warm and humid airflows were also responsible for the long duration of fog and rain in South China. To- wards the end of the foggy weather, cold air became stronger and destroyed the atmospheric stratification and the conditions for the inversion to exist, dissipating the fog. It is drawn that fog and rain will appear when △θse850-1000〈0.