高分辨率WRF三维变分同化在北京地区降水预报中的应用

Application of WRF 3DVar to a High Resolution Model over Beijing Area

为迎接2008年北京奥运会,改进北京地区的天气预报,建立了一个基于三重嵌套区域(27/9/3 km)的WRF三维变分同化(WRFVar)和WRF模式的高分辨率快速更新循环同化预报(Rapid-Up-date Cycle)系统,并针对2006年8月1日发生在北京地区的强对流天气进行了一系列数值试验,结果表明:高分辨率的快速更新循环系统很好地预报出了此次强降水过程;在WRF三维变分同化里调节背景场误差和观测误差,提高了降水预报的效果;插值得出的3 km背景场误差可以作为一个合理的近似在3 km分辨率的WRFVar中使用,用户可以不必积累高分辨率的预报场去计算背景场误差,从而节省大量计算资源。3 h频次的RUC已经能满足预报要求,更高频次(1 h)的RUC并没有导致预报的进一步提高。

To improve the weather forecast over the Beijing area for the 2008 Olympic game, a triple nests （27/9/3 kin） WRFVar/WRF system with 3 h update cycle is established. Experiments have been done for a convective event occurred on August 1, 2006, the results showed that the high-resolution rapid update cycle gave good precipitation forecast; the tunings of background error statistics （BES） and observation error statistics in WRFVar improved the skill of the precipitation forecast; the BES for the fine domain （3 km） obtained by interpolatation from its parent domain （9 km） can be used in 3 km WRFVar as a reasonable approximation. User can now save much work related to the derivation of the fine mesh BES from the forecast over a period of time; rapid update cycle with 3 h frequencies has satisfied the forecast and update cycle wish 1 h frequency was not necessary.