不同背景场误差样本模拟方案对数值预报的影响——以“苏迪罗”台风为例

Impacts of different background error samples simulation schemes on numerical forecast-taking typhoon "Soudelor" as an example

利用天气研究和预报模式(Weather Research and Forecasting Model,WRF)、WRF三维变分同化(Weather Research and Forecasting-Three-Dimensional Variational Data Assimilation,WRF-3DVAR)及美国国家气象中心(National Meteorological Center,NMC)方法,采用热启动循环同化和冷启动两种不同初值方案开展数值试验,探讨不同初值方案模拟的背景场误差样本对背景误差协方差及其同化预报效果产生的影响。结果表明:由不同初值方案模拟的背景场误差样本统计得到的背景误差协方差,其单点同化试验均符合理论模型,但二者分析增量场的差异较显著。对2015年"苏迪罗"台风降水个例进行的数值试验表明,不同初值方案模拟的背景场误差样本统计得到的背景误差协方差对同化分析场具有一定影响,进而对台风移动路径和台风降水的模拟产生了较显著的影响,但对台风强度和台风中心附近最大风速的影响不显著。4个不同起报时刻数值试验进一步表明,采用热启动循环同化背景场误差样本模拟方案统计的背景误差协方差,对"苏迪罗"台风路径和降水预报效果较好,其中对台风路径的影响主要体现在数值预报模式积分24 h之后。

Based on the methods of WRF(Weather Research and Forecasting Model),WRF-3DVAR(Weather Research and Forecasting-Three-Dimensional Variational Data Assimilation)and the NMC(US National Meteorological Center),we investigated whether or not and how the statistical background error samples under different initialization schemes have non-neglected impacts upon the background error covariance and its related forecasting effects.Experiments with hot-start cycled assimilation and cold-start initialization schemes were carried out.It is seen that the results from single point observation idealized assimilation experiments with background error covariance calculated from statistical background error samples under different initialization schemes are consistent with those from theoretical models.The differences in analyzed incremental fields are obvious and should not be ignored.The experimental results of"Soudelor"typhoon rainfall event in 2015 indicate that the background error covariance calculated from background error samples under different initialization schemes has a certain effect on the assimilation fields,and exerts obvious effects on the forecasts of typhoon track and rainfall,but have little impacts on the typhoon intensity and maximum wind speed near the typhoon center.Numerical experiments with four different initial time indicate that the background error covariance calculated from background error samples under hot-start cycled assimilation schemes shows a much better forecast for"Soudelor"typhoon track and rainfall,and its impacts on typhoon track are mainly shown after 24-h integration of the numerical forecast model.