集合均方根滤波同化地闪资料的试验研究

Assimilating Cloud-to-ground Lightning Data Using Ensemble Square Root Filter

闪电资料作为雷达资料的良好补充,可以弥补雷达资料时空与地域的限制。国内外大量研究发现,对流性天气中的地闪与雷达回波具有很强的相关性,这为同化闪电资料提供了一定的可能性。依照GSI云分析中的方法,将闪电资料转换为三维代理回波,运用三维变分方法加入随机扰动产生集合成员,再用集合均方根滤波方法进行同化。选取2009年6月5日发生于苏皖地区的一次强对流天气过程进行一系列同化预报试验。试验结果表明:闪电资料转换为三维代理回波后经集合均方根滤波同化后具有良好的适用性。预报回波能迅速得以改善,时效为3 h左右。同化多时次的闪电资料可以提供更好的预报结果,可提高3 h内短时临近降水预报精度。

Lightning network data can provide a useful supplement to radar observations,which are limited in temporal and spatial coverage. It has been previously found that in convective weather systems,the correlation between cloud- to- ground lightning and radar reflectivity is strong,which suggests the possibility of improving convection forecasting through assimilating lightning network data.Based on a simple assumed relationship between flash density and reflectivity in the Gridpoint Statistical Interpolation（ GSI） system,the lightning data were first converted into 3D lightning- proxy radar reflectivity,which was subsequently assimilated by ensemble square root filter. In the sampling procedure,the ensemble members are produced by WRF- 3DVAR. In this study,the benefits of assimilating lightning data are illustrated by a series of experiments using data from a strong convection event which occurred in Jiangsu and Anhui provinces,China,on 5 June 2009. For this case,the results show that convection forecasting is improved by assimilation of the lightning- proxy reflectivity using ensemble square root filter. There was a significant improvement in the prediction of reflectivity,and this was maintained for about 3 hours. The 3 hours precipitation forecast was also improved. Assimilating multi- time lightning data with assimilation cycles can further improve forecasting accuracy.