极端天气气候背景下两次降雪过程的对比分析

Contrastive Analysis of Two Snow Events under the Extreme Weather and Climate Background

利用常规观测资料、NCEP 1°×1°分析资料,从同期气候背景、影响系统特征、干侵入特征和影响等方面,对2008年1月28日20时—29日08时、2月1日20时—2日08时江西中、北部两次较强降雪过程进行了分析。结果发现,两次过程发生的气候背景主要与大气环流异常及拉尼娜事件有关。两次过程的系统配置具有相同的特点,中层700—500 hPa西南气流强盛,低层850 hPa到地面的冷空气垫深厚,700—850 hPa存在逆温层。两次过程都具有干侵入特征,干侵入所引起的对流层中低层垂直方向上的降温,使中低层0℃以上暖层明显减弱,700 hPa温度降为0℃以下,为混合云内雨转雪的发生提供了必要的温度条件。两次过程中,低层冷平流越强,雪区南界越偏南。江淮到黄淮的下沉气流为对流层高层干空气侵入提供了动力条件,高层干冷空气向南、向下侵入,导致对流层低层850 hPa偏北气流加强和维持,加大了中低层垂直风切变,使上升运动加强,为水汽凝结、冰晶和雪晶比含水量的增加提供了必要条件,从而使降雪得到发展。两次过程中,上升运动越强,降雪强度越大。

The convention al observation data and NCEP 1°×1° analyzed data were employed to analyze the climate backgrounds, the influencing systems, and the dry intrusion of the two snow events during January 28-29 and February 1-2, 2008 in the middle and north Jiangxi. The results showed that the climate backgrounds of the two cases were mainly correlated with atmospheric circulation anomalies and La nina events. The two events had the same synoptic configuration, such as strong southwest current from 700 to 500 hPa, deep cold air from 850 hPa to surface and inversion layer from 700 to 850 hPa. Dry intrusion occurred in the two events, which caused vertical temperature decrease at middle to low levels, and the warm level above 0 ℃ weakened obviously, the temperature at 700 hPa dropped to below 0 %. These provided the essential temperature condition for rain to snow in cloud. In the two events, the stronger the cold advection at low level was, the more southern the snow region was. The sinking air from Jiangsu and Anhui to the Yellow River area provided the dynamic condition for dry intrusion in the upper troposphere, then intensified and maintained the low-level northern air current, increased the middle-to-low level vertical wind shear, strengthened the ascending movement, thus provided the moisture condensation, the moisture content increases of the ice crystal and the snow crystal to snow. In the two events, the stronger the ascending movement was, the heavier the snow was.