Establishment and Real-time Forecasting Verification of AREM-RUC 3 h Rapid Update Assimilation and Forecast System

The 3 h rapid update assimilation and prediction system called AREM-RUC is built up based on AREM model and LAPS system,and the real-time forecasting performance,during the period from June to December 2009,was compared among AREM-YW,AREM-SY and AREM-RUC which are the three model systems running in operation at Institute of Heavy Rain of CMA.The results show that(1) the TS score of light rain,moderate rain,heavy rain and torrential rain forecasted by AREM-RUC leading 24h is higher than that of AREM-YW and AREM-SY in the area of China,the middle-lower valley of Yangtze River,south China,north China,northeast China,and eastern part of southwest China.(2) As to prediction deviation,the area of heavy rain forecasted by AREM-RUC is larger than the observation,but those by AREM-YW and AREM-SY are smaller than the observations.(3) The real-time forecast of AREM-RUC for a local heavy rain process happened in Dangyang in Hubei province on June 17,2009 is much better than those of AREM-SY and AREM-YW,and the prediction about rainfall area and time is improved greatly with 3h updated forecasts.(4) The AREM-RUC gives a much better forecast for an extremely heavy rain event happened on June 29,2009 with the location and intensity of the heavy rain center close to the observation,while the heavy rain intensity forecasts by AREM-YW and AREM-SY are much weaker than the observation.The further study shows that the GRAPES-3DVAR assimilation scheme adopted in AREM-SY gives an analysis of a westward and stronger Western Pacific Subtropical High,a weaker water vapor and a weaker low-level shear,which is the main reason why the rain belt forecasted by AREM-SY is weaker and to the north.(5) The verification of 6h rainfall forecast for the extremely heavy rain event on June 29,2009 suggests that the 3h updated forecast makes an improvement in the prediction of 6h accumulated precipitation.