Sensitive and Mechanism Study of Surface Data Assimilation to a Local Torrential Rain Forecast in Shandong Province
Using the WRF (Weather Research and Forecasting) model and it’s 3DVAR (3-Dimentional Variational) data assimilation (DA) system, sensitive experiments of data assimilation on a local torrential rain event in middle Shandong province on 8 May 2011 are carried out adopting data assimilation and rapid update cycle of 36 km, 12 km and 4 km nested grid at three-hour intervals. Assimilated data includes surface data, radiosonde data and the groud-based GPS/PW (precipitable water vapor) data in Shandong.
Results show that both surface data assimilation and rapid update cycle are playing key roles in the precipitation forecast. The model cannot forecast the rainfall in Shandong if assimilating no surface observational data or assimilating all data with cold start. The rainfall area forecast is significantly improved due to surface data assimilation, which can improve the initial atmosphere elements such as temperature, pressure, humidity and wind over 700 hPa. Therefore, the temperature and humidity structure of initial atmosphere condition is altered, the upper humidity and thermal instability are enhanced at around 700 hPa, the lower wind field becomes stronger. As a result, the upper unstable atmosphere is triggered by the dynamic effect of the lower wind field, precipitation appears in Shandong.
Dr. Chunyan Sheng Shandong Meteorological Bureau