宁夏降雪日数的气候特征和环流结构

Climate Characteristics of Snowfall Day Numbers in Ningxia and Structure of Atmospheric Circulation

选取常规气象观测资料和大气环流特征量,运用统计分析、最大熵谱法和相关分析方法,分析了1961—2010年50 a期间宁夏降雪日数的气候特征和影响的大气环流。结果表明:宁夏各等级降雪日数,在季节上均呈现双峰型分布,峰值点出现在春季和秋季,冬季时,降雪等级越高,出现的概率越低;地理分布型基本一致,自北向南明显增加,高发中心与地形特征关系密切;以非持续性1 d的出现频率较高,随降雪量级的增大,持续时间缩短;降雪总日数减少,小雪、大雪和暴雪的降雪贡献减少,中雪的降雪贡献增加;具有短中长不同时间尺度的周期变化。影响宁夏降雪日数的大气环流系统主要是北半球极涡、西藏高原指数、大西洋欧洲环流型和欧亚(亚洲)环流型。与宁夏降雪日数显著相关的大气环流特征量是随季节变化的,相应的大气环流特征也不同,但影响机制相同,均为宁夏降雪天气提供了冷空气条件和水汽条件。

Conventional observed data and the characteristic quantities of the atmospheric circulation wereused to analyze the climate characteristics of snowfall day numbers in Ningxia and the affecting atmospheric circulation during the period of 1961 to 2010 by the methods of the statistic analysis, correlation analysis, and maximum entropy spectrum. The results have shown that the snowfall day numbers of each grade occur- ring in Ningxia have two extreme values which appear in spring and autumn. In winter, the heavier the snowfall, the lower the frequency. The geographical distribution of snowfall day numbers in different seasons is relatively consistent and increases obviously from north to south in Ningxia. High frequency centers have a strong correlation with terrain features. The frequency of non-sustained 1 d snowfall is higher, and the lasted time decreases with the increasing of snowfall grades. The total day numbers of snowfall have decreased, the contributions of light snow, heavy snow and snowstorms have reduced, however, moderate snow has the opposite trend. Different grades of snowfall have different variations of short, medium and long period. Polar vortex in the Northern Hemisphere, index of the Tibetan Plateau, European-Atlantic pattern and Eurasian circulation （Asia circulation） are the main atmospheric circulation systems influencing snowfall day numbers in