一次江淮气旋暴雪的积雪特征及气象影响因子分析

Study on Snow Cover and Its Meteorological Influence Factors of Jianghuai Cyclone Snowstorm

利用自动站、人工加密观测及常规观测资料,通过对2017年2月21—22日一次江淮气旋暴雪过程积雪特征的分析,揭示了近地面气象要素对积雪深度的复杂影响。结果表明:(1)江淮气旋系统特有的空间结构导致山东南、北地区的降雪量和积雪深度不均衡分布。(2)积雪深度具有时效性,在降雪结束时达到峰值,因温度的变化导致峰值不一定维持到次日08时。(3)积雪深度是近地面多气象要素共同作用的结果,降水相态、降雪量、降雪强度、气温、地温和风速均有影响。主要表现为:雨夹雪在转为纯雪之前可产生不超过1 cm的积雪,如果不转雪则不会产生有量积雪;各地降雪含水比差异较大,全省平均为0. 5 cm·mm^(-1),低于全国平均值;在降雪不融化的情况下,降雪量、降雪强度越大则积雪越深,降雪强度大是气温和地温都高于0℃时产生积雪的必要条件;地温和气温越低对积雪形成越有利,积雪开始产生时的地温最高阈值多在0℃左右,地温先突降后缓升是积雪产生前后的共性特征,积雪产生后1～2 h内地温略有上升并逐渐趋于稳定;积雪产生时气温一般低于0℃,气温高于0℃时大部分降雪融化;有利于产生积雪的平均风力多不超过2级,极大风则在3～4级以下。

Based on automatic weather station, dense and routine observation data, this study analyzes the characteristics of snow cover and its meteorological impact factors on a case of Jianghuai cyclone snowstorm that occurred from 21 to 22 February 2017. The results show that the typical spatial structure of Jianghuai cyclone led to the different snowfall amounts and depths in Shandong. The snow cover peaked when the snow ended and its persistence depended on temperature, so snow depth was of timeliness. Commonly,snow depth is affected by multiple meteorological factors of surface, including precipitation type, snowfall amount, snowfall intensity, temperature, soil temperature and wind speed. Sleet can produce snow cover below 1 cm if it turns to pure snow. Average snow-to-liquid ratio in Shandong is 0. 5 cm · mm-1, lower than the value for the whole country. Large snowfall, strong snowfall intensity, low air and soil temperatures are beneficial to snow depth. Enough snow intensity is necessary for obvious snow cover when air and soil temperatures are both higher than 0℃. It’s common that soil temperature drops quickly before visible snow cover and rises stably within 1 to 2 hours. Air temperature is usually below 0℃ when snow cover forms. Weak wind speed under Grade 2 is good for snow cover to form.