西藏聂拉木县大到暴雪典型天气特征分析
Analysis of Typical Weather Characteristics of Heavy Snow in Nyalam County Tibet

利用聂拉木县2006~2015年降雪数据的分析，南支槽型和孟加拉湾风暴型特征分析，大到暴雪天气个例，对暴雪天气进行分类，分析其强度、频次及特点；分析聂拉木县冬季大到暴雪的气候特点、环流背景，对环流作分型，天气的特征分类、形成机制。结果表明：在2006~2015年的72次暴雪过程中，南支槽影响的暴雪过程达69次，占90%，2006~2015年聂拉木暴雪发生时段的高空资料发现，此类天气过程的500环流背景多数为两槽一脊型。南支槽影响的暴雪天气聂拉木一般受偏西南风控制，南支槽的强弱和位置与降雪强度关系密切。孟加拉湾风暴和南支槽结合引发的暴雪过程有3次；2次发生在10月，1次在5月，风暴最大风速10级以上；主要生成于15？N~25？N，85？E~90？E；移动路径偏西北；15？N以北、85？E~90？E是影响聂拉木暴雨雪天气的关键区，冬季后期和春季发生较少。暴雪过程主要影响系统为南支槽，南支槽东移上高原，而西太副高的位置和强度有利于南支槽的加强维持东移影响高原西部，即南支槽为此次聂拉木的暴风雪天气提供了稳定的环流背景；特大暴雪时560线基本会穿过高原，并且560线位置在高原上偏南的程度和降水强度有一定的关系，一般呈正比。暴雪提供水汽大多数来源于孟加拉湾。
Based on the analysis of the snowfall data in Nyalam County from 2006 to 2015, the analysis of the characteristics of the southern branch trough type and the Bay of Bengal storm type, and the case of heavy snow weather, the snowstorm weather is classified, and its intensity, frequency and characteristics are analyzed; We analyze the climate characteristics and circulation background of heavy snow in winter in Nyalam County, classify the circulation, weather characteristics and formation mechanism. The results show that in the 72 snowstorms in 2006~2015, the south branch channel affected 69 snowstorms, accounting for 90%. The high altitude data during the snowstorm in Nyalam in 2006~2015 found that the 500 circulation background of such weather processes was mostly of two troughs and one ridge type. The snowstorm weather in Nyalam affected by the South Branch is generally controlled by the southwest wind. The strength and location of the South Branch are closely related to the snowfall intensity. There are three snowstorms caused by the combination of the Bay of Bengal storm and the South Branch Trough; Two times in October and one time in May, the maximum wind speed of the storm is above 10; It is mainly generated at 15？N~25？N and 85？E~90？E; The moving path is northwest; The north of 15？N and 85？E~90？E are the key areas that affect the storm and snow weather in Nyalam, with less occurrence in late winter and spring. The main impact system of the snowstorm process is the South Branch, which moves eastward to the plateau, while the location and intensity of the West Pacific subtropical high are conducive to the strengthening of the South Branch and the eastward movement of the South Branch, which affects the western part of the plateau, that is, the South Branch provides a stable circulation background for the snowstorm in Nyalam; In case of heavy snow, the 560 line will basically pass through the plateau, and the degree of the position of the 560 line to