Application of WRF 3DVar to a high-resolution model over Beijing area

To improve the weather forecasting over the Beijing area for the 2008 Olympic Games,a triple-nested(27/9/3km) WRFVar/WRF system with 3-h update cycle was established.Experiments have been done for a convective event that occurred on August 1,2006.The results showed that the high-resolution rapid update cycle gave a 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 interpolation from its parent domain(9 km) can be used in 3 km WRFVar as a reasonable approximation.The user can now save a great deal of work related to the derivation of the fine mesh BES from the forecast over a period of time;the rapid update cycle with 3-h frequency has satisfied the forecast,and the update cycle with 1-h frequency was not necessary.

Development of 1km-Scale Operational Model in South China

To support short-range weather forecasts,a high-resolution model(1km)is developed and technically upgraded in the South China Regional Center,including the improvement of the 3D reference scheme and the predictor-corrector method for semi-implicit semi-Lagrangian(SISL)in model dynamical core,as well as the improvement of physical parameterization.Furthermore,the multi-process parallel I/O and parallel nudging techniques are developed and have facilitated rapid updating in the assimilation prediction system and fast-output post processing process.The experimental results show that the improved 3D reference scheme and upgraded physic schemes can effectively improve the prediction accuracy and stability with a longer integration time step.The batch test shows that the precipitation forecast performance of 1-km model is significantly better than that of 3-km model.The 1-km model is in operation with a rapidly updating cycle at 12-minute intervals,which can be applied to short-range forecasts and nowcasting.