GPSRO同化对天山暴雪影响的模拟研究

Simulation of the Influence of GPSRO Assimilation upon Snow-Storm over Tianshan Mountains

GPS掩星资料(GPSRO)业务同化的正效果已经在多个国家的数值预报中心得到证实,但在新疆数值预报业务中尚未应用。为验证GPSRO同化对天山暴雪预报的影响,以GFS数据为背景场,用WRFDA同化了GPS掩星事件反演的折射率和温湿廓线,并评估了其对2014年12月07日08时到09日08时(北京时)天山暴雪过程预报效果的影响。结果表明,GPS掩星温湿廓线和折射率同化对此次天山暴雪过程预报均有正效果,改善幅度前者劣于后者。同化后风场U、V分量沿风向方向的影响范围均大于垂直风向方向,其增量极值中心位置向下风方向偏移。温度、湿度场的分析增量分布均接近各向同性,增量极值中心位置与掩星事件位置相对应。同化后温度分析均以增暖为主,湿度分析以增湿为主,气压分析以减压为主。温湿廓线同化产生的资料影响范围平均大于折射率同化产生的影响范围。并且,在任何网格点,无论是温度场还是比湿场,温湿廓线同化产生的分析差的绝对值大于折射率同化。温湿廓线与折射率同化后风场的分析增量整体上均随着高度的增加先减后增,温度场分析增量整体上随高度升高而增大,气压分析增量随高度升高单调递增,比湿分析增量绝对值的大值区主要集中在500 h Pa以下的低空,其最大值位于700 h Pa附近。

The positive effect of GPSRO has been proved in a couple of national centers of numerical weather prediction. In order to test its contribution in improving the snowstorm forecasting precision over Tianshan Mountain, its inversed temperature-moisture profiler and refrectivity are assimilated with WRFDA using GFS as its background for prediction of the snowstorm occurred during Dec 7th till 8th, 2014, and their range of influence generated by DA are further compared. It is found that assimilation of each of these two types of datasets can induce a positive influence of the selected snowstorm simulation, while the refinement range of the latter is greater than the former. The range of influence of zonal and meridional components of wind field along the wind direction caused by assimilation of the temperature-moisture profiler or refractivity is greater than that along the perpendicular direction, and the location of maximum center is not at the observation sites but at its downstream zone, while the corresponding range of influence of temperature and pressure as well as humidity is almost all the same at all horizontal direction, with their maximum analysis increment located around the GPSRO observation. Their assimilation both are proved the initial field become warmer、dryer with lower pressure. The range of influence generated by assimilation of temperature-moisture profiler is greater than that of refrectivity for almost every levels, with the absolute value of analysis increment of the former lager than that of the later at all grid points. The wind analysis increments of assimilation of both temperature-moisture profiler and refractivity increase firstly and then decrease with altitude, the pressure of that increased monotonically, while the increment of humidity mainly concentrated under 500 hPa, with its maximum absolute value near 700 hPa.