由大尺度观测提取中尺度信息的可能性研究

利用浅水方程模式和变分四维同化方法对由大尺度观测提取中尺度信息的可能性进行了模拟试验研究。试验的初始场是在平直气流上叠加一个半径为 5倍格距的圆形涡旋。分别设定观测点的间距是 5 ,7和 9倍格距 ,观测的时间间隔分别是 1,2和 3h ,同化时间为 6h或 12h ,考察同化产生的初始场。试验结果是 :观测点的间距是 5倍格距时 ,由观测给出的分析场不能反映涡旋的基本特征 ,而在同化产生的初始场中 ,涡旋的基本结构清楚 ,但强度有所削弱。增加观测次数或者延长同化时间 ,可以改善同化的结果。对于移动较快的系统 ,同化的结果较好。当观测点的间距是 9倍格距时 ,同化的结果与分析场相比已无明显改进。

A STUDY OF POSSIBILITY OF EXTRACTING THE MESOSCALE INFORMATION FROM LARGE-SCALE OBSERVATIONS

The possibility of extracting the mesoscale information from large-scale observations is evaluated with numerical simulation experiments by using the shallow water model and the method of four-dimensional variational data assimilation. The initial field for the simulation is set to a circular vortex with radius of 5 times mesh scale added to a straight flow. The distances between the observation stations are 5,7 or 9 times mesh scale separately. The observation is available every 1, 2 or 3 hours. The data assimilation period is defined to be 6 or 12 hours. The initial fields resulting from the assimilation are evaluated The conclusions are: When the distance between the observation stations is 5 times mesh scale, the basic properties of the vortex can not be represented by the analysis fields from the observations; The basic structure of the vortex is well defined in the initial fields from the assimilation, but the intensity is slightly weakened; The assimilation results can be improved by increasing the observation frequency or lengthening assimilation time; The assimilation results are better for the fast moving system; When the distance between the observation stations is 9 times mesh scale, there is no obvious improvement from the assimilation results compared with analysis fields.