西藏南部暴雪气候特征及预报指标研究

Study on Climate Characteristics and Forecast Index of Heavy Snowfall in the Southern of Xizang

摘要: 利用1981~2014年降水、积雪、环流场和物理量资料对西藏南部暴雪的气候特征及预报指标进行分析。结果表明：西藏南部暴雪主要集中在初冬和春初，各地10月~次年5月均可出现暴雪；聂拉木、帕里和错那呈双峰分布，普兰和隆子呈单峰分布。在年变化方面，错那和帕里暴雪日数呈略微增多趋势，聂拉木和普兰呈减少趋势，隆子基本不变。影响西藏南部暴雪的天气系统为南支槽、孟湾风暴与南支槽配合两大类型。高空急流、水汽条件与西藏南部暴雪天气密切相关。暴雪落区一般位于湿中心或湿中心西侧比湿梯度大值区，且水汽通量梯度大值区一侧通常伴有低空西南急流带。暴雪落区通常垂直上升运动较强，400与200 hPa散度差值越大，降雪强度越大。能量大值区梯度增大(减弱)与暴雪过程开始(结束)有很好的对应关系。

Abstract: Based on the rainfall data, circulation field and physical variables from 1981 to 2014, the climatic characteristics and prediction indexes on heavy snowfall in the southern of Xizang are studied. The results show that heavy snowfall on southern Xizang can occur from October to May of the following year, and mainly in early winter and early spring, its monthly change of the snowstorm shows a significant twin-peak feature. Cuona and Pali increased slightly in the climate trend of snowstorm days, Nielamu and Pulan showed a decrease, Longzi basically unchanged. The weather system affecting the snowstorm in the southern Xizang is composed of South Trough and Bay of Bengal Storm. Heavy snow in southern Xizang is closely related to upper-level jet stream and water vapor conditions. The snowfall region is generally located in the moist center or the larger wet gradient in the west area and in the high value region of water vapor flux gradient with the southwest low-level rapids in 500 hPa. Generally, the vertical upward movement in the snowstorm falling area is strong, and there is a convergence in the lower layer and divergence in the lower layer. The greater the difference of divergence between 400 hPa and 200 hPa is, the heavier the snow is. The increase (weakening) of the gradient in the energy high value area corresponds well to the beginning (end) of the blizzard process.