GPS弯曲角资料在WRF模式中的同化试验——对台风“森拉克”的影响分析

ASSIMILATION EXPERIMENT OF GPS BENDING ANGLE USING WRF MODEL——Analysis of Impact on Typhoon “SinLaku”

实现了在WRF模式中GPS掩星弯曲角资料的三维变分同化,正演算子采用大气一维球对称假设条件下,Abel变换方法计算弯曲角。以2008年13号台风"森拉克"为例,研究了COSMIC弯曲角资料对台风预报路径、强度及降水等的影响。与控制试验及台风实况的对比结果表明,同化COSMIC弯曲角资料后,在24小时预报以后,对台风路径预报有较明显的改进效果,路径预报误差平均降低约67.5%;但台风强度预报整体偏弱。分析认为,同化弯曲角资料后,台风附近形势场的改进是提高路径预报的原因。由于弯曲角资料本身存在水平分辨率较低的问题,以及对流层底部信号质量不如中上部和平流层是台风强度预报偏弱的重要原因。

The 3D variational assimilation of bending angle data from GPS occultation was realized in WRF model. Under the assumption of atmospheric spherical symmetry, forward operators can be used to calculate the bending angle from the background information by using Abel transform method. The influence of COSMIC bending angle data on the prediction of typhoon paths, center pressure and precipitation were studied with the case of typhoon SinLaku, No. 13 in 2008. Compared with a control experiment and real typhoon observations, the prediction results of assimilating COSMIC bending angle data shows that important improvement of typhoon path was achieved after 24-h prediction. Average error of path prediction was reduced by 67.5%, but the typhoon strength forecasted was lower than the observation. By analyzing the result, we concluded that the reason for the improvement of path forecasting after assimilating bending angle data was the change of pressure situation. The horizontal resolution of bending angle data themselves is lower, and data quality at the lower troposphere is not as good as that in the higher troposphere and stratosphere, which are the main reason for the lower typhoon strength.