降雪含水比研究进展

降雪深度预报与定量降水预报(QPF)一样是冬季天气预报最重要的业务之一,而降雪含水比是降雪深度预报中所必须的重要参数,国外一般多将其称为snow-to-liquid ratio(SLR)。本文回顾了过去几十年来国内外在SLR的变化特征、影响因素等方面的主要研究进展,并对其预报技术和方法进行了总结和比较。研究表明:SLR具有明显的时间变化,并且存在季节和空间分布差异;大气温度和相对湿度是影响SLR的两个最重要气象因子,气压、垂直运动等气象因素,以及地表风、积雪自重、太阳辐射和积雪融化也会不同程度地影响SLR;随着预报技术的发展,SLR的预报方法可概括为气候学的、统计学的和基于物理基础的三类预报方法,气候学方法过于简单化,统计学方法的应用提高了SLR的预报能力,但仍无法摆脱统计方法自身的缺陷,比较而言,基于数值模式的瞬时预报更符合未来雪深预报业务的精细化发展趋势;目前,国内降雪深度观测资料较少、观测频率较低,有效开展地面降雪和探空加密观测,解决观测资料不足是今后SLR研究中亟待解决的问题;基于数值天气预报业务模式,探索气象因子对SLR的影响机理,建立适合我国冬季天气预报业务需求的降雪预报系统是未来的发展方向。

Advances in Snow-to-Liquid Ratio

Same as with quantitative precipitation forecast (QPF), snowfall depth forecasting is one important operation of weather forecasting in winter, and the relationship between snowfall depth and precipitation which is called snow to liquid ratio (SLR) abroad is an important parameter required to forecast snowfall depth. In this paper, the main research progresses in variations of SLR and its impact factors at home and aboard in recent decades are reviewed, and the SLR forecast techniques and methods are summarized and compared. Studies indicate that SLR changes obviously in temporal scale, and has seasonal and spatial distribution differences. Air temperature and relative humidity are the two most important meteorological factors affecting SLR. In addition, other meteorological factors such as pressure, vertical motion, surface wind, snowfall weight, solar radiation and snow melting also affect SLR in different degrees. With the development of prediction technology, the methods of SLR forecasting can be summarized as three categories, including climatological, statistical and physical methods. The climatological method is too simple, the application of new statistical methods could improve the prediction ability of SLR, but this method still cannot get rid of the inherent deficiencies of statistics. Comparatively, the method based on the numerical model for predicting instantaneous SLR fits the developing trend toward refinement in snowfall depth forecast in future. At present, observation data of snowfall depth are less and the observation frequency is low in China, thus it is important to effectively carry out the surface snowfall and sounding observation densely, and solve the problem of lack of observation data in the research of SLR. Besides, based on the operational numerical weather prediction model exploring the influence mechanism of meteorological factors on SLR and establishing the forecast operation system suitable for winter snowfall are the developing trend in China.