探空气球漂移及其对数值预报影响的研究

为了考察探空资料随高度的漂移对高分辨率数值预报模式的影响, 充分发掘探空资料的应用价值, 根据探空资料的探测原理, 设计定位方案, 计算出了各气压层上探空气球所处的实际位置。对位置订正前后的资料分别用3D-VAR系统进行同化, 将同化结果作为WRF模式的初始场进行数值预报并对预报效果进行对比分析。结果表明:探空气球在施放过程中的漂移距离远远超过目前数值模式可取的水平分辨率; 所设计的探空气球定位方案对水平分辨率为10 km ×10 km的数值预报模式基本是可用的; 总的来讲, 位置订正对分析增量场的改变与原分析增量场相比小一个量级。模式预报结果显示, 探空资料的定位使降水预报效果得到了改善。研究表明, 将各气压层上探空资料订正到实际位置对高分辨率数值预报模式的预报效果有一定程度的正面影响, 但仍需要更多的个例来验证。

Study on Sounding Balloon Drifting and Its Impact on Numerical Predictions

To investigate the impact of height-depending sounding balloon's drifting on numerical prediction and extract to the full utility of soundings, a positioning scheme is designed to locate the balloon's position at every pressure level, based on sounding principles. Data used before and after the position correcting are assimilated using the 3D-VAR system separately, with the assimilations applied as the initial field of the WRF model for predictions, which then undergo analysis for comparison. The main results are as follows: (1) the distance a sounding balloon drifts during operation is a lot longer than that is accepted as a horizontal resolution by present numerical models; (2) the positioning scheme presented for sounding balloons is basically applicable to a resolution of 10km×10km; (3) on the whole, the position correction leads to the fact that the resulting analytic increment field is one order of magnitude smaller than the original; (4) analysis of the model predictions shows that soundings, when positioned, would improve predictions. Moreover, the accurate position correction of leveled soundings will better the output of high-resolution numerical models to some extent but further case studies are needed.