沈阳降雪含水比变化特征及其大气影响因子

Snow-to-liquid ratio variation and its atmospheric influence factors in Shenyang

降雪含水比是新增积雪深度与融化后等量液体深度的比值，是冬季雪深预报中的一个重要参数，一般使用经验值10进行积雪深度换算．利用1981－2012年沈阳站降水量、积雪深度、气温和风速等观测资料及1999－2012年NCEP再分析资料（1°×1°），分析了沈阳站32 a降雪含水比的变化特征和大气影响因子．结果表明：沈阳站降雪含水比的平均值为11．4，主要集中在6～12区间变化，小于4和大于20的极值发生概率相对较低，极值都出现在12月份，11月和3月均值接近10，而其他月份在12左右．小雪的降雪含水比均值最大为13．3，其它为10点多．500 hPa上温度和550 hPa上的风速是沈阳站降水含水比的高空大气影响因子．

Defined as the ratio of the depth of new snowfall to the depth of melted liquid equivalent,snow-to-liquid ratio （SLR）is the most important parameter of forecasting winter snow depth;the empirical rule of 10 was applied to convert the snow depth.Using the observed data from 1981 to 2012 in Shenyang Station and NCEP reanalysis data （1°×1°）from 1999 to 2012,variations of 32-a SLRs and its possible atmospheric influ-ence factors in Shenyang were analyzed.The results show that the mean SLR for 153 snowfall events was 1 1 .4 in Shenyang,mainly changing from 6 to 12,the probability less than 4 or more than 20 was relatively lower,the extreme value occurred in December,and the monthly mean value in November or March closed to 10,while in other month it was about 12.The mean SLR of slight snow was the largest that was 13.3,and for other level snowfall it was more than 10.Diagnosing the relation between SLR of different levels and atmospheric condi-tions,air temperature and wind speed from 600 hPa to 450 hPa in the middle and upper atmosphere showed that air temperature at 500 hPa and wind speed at 550 hPa were the remarkable upper air influence factors on SLR in Shenyang.