The Application Of Nudging Soil Moisture On Climate Prediction Improvement

Seasonal and sub-seasonal climate predictions are a challenging issue.In order to improve the ability of the climate model to predict climate on a seasonal scale,it is an effective way to assimilate the initial and boundary variables in the model.In this paper,using different atmospheric Nudging scheme and indirect soil Nudging scheme to improve short-term climate prediction,and discusses the important role of land surface state variable(soil moisture)in short-term climate.Based on the WRF Mesoscale numerical model,the simulation experiments of using different Nudging schemes in summer in China in 2009 are carried out.The performance of grid,spectral observation nudging atmospheric variable scheme and indirect soil nudging scheme in climate simulation is compared and the possible reasons for the improvement of each scheme are analyzed.On this basis,the prediction experiment of short-term precipitation in summer 2010 is conducted by using the indirect soil Nudging scheme in the Eastern China and Tibetan Plateau.The former is relatively flat and close to the ocean,and the latter is far away from the ocean and the terrain is complex.The effect and possible mechanism of assimilating soil moisture to improve climate prediction are explained.The main conclusions are as follows:1)There is a significant deviation of the "South Dry North Wet" in the regional seasonal precipitation simulation and a clear cold deviation in temperature simulation in the WRF model.The addition of the Grid and Spectral Nudging schemes can effectively correct the precipitation and temperature deviation,and the difference between the two Nudging schemes is small.After nudging atmospheric variable,the summer monsoon intensity in the southwest is weakened,and the summer monsoon begins to shift eastward at about 30°N.The diverangence center over land move to the ocean eastward and the fake dry tongue is removed.These are the main reason for the improvement of precipitation.2)The effect of the Indent Soil Nudging scheme on the improvement of temperature and precipitation is obvious,and the spatial distribution of precipitation in the north of the Yangtze River and South China is improved.The difference in spatial variation of temperature simulation is also reduced between observation and simulation in the whole area.ISN can improve the simulation results by updating the slow process variables(soil moisture),and can effectively dynamic adjust the surface temperature and relative humidity balance.The temperature and relative humidity RMSE are obviously reduced at 700 hPa and 850 hPa,respectively.And the scheme has slight effect on simultaneous geopotential height.3)In the prediction of precipitation in the Eastern China,the results of the assimilation experiment with ISN scheme with respect to control experiment and other atmospheric Nudging experiment have effectively reduced the wet deviation in the north and the dry deviation in the south,which indicates that the effect of atmospheric initial field on later precipitation is small,and the initial information of soil moisture plays a relatively important role in summer precipitation,and the duration of influence can span the whole summer.After the ISN scheme updates the spatial distribution of the soil initial field,the corresponding water vapor and heat conditions will change in the spatial distribution and temporal variation,and the vertical zonal and meridian circulation of whole troposphere effectively change the low-level water vapor polymerization,improve the model's ability to predict precipitation.4)In the numerical experiment of the Tibetan Plateau region,the spatial distribution of the precipitation of the plateau can be effectively reproduced by adding the ISN scheme.Through the updating of the soil initial field,the surface water vapor and heat flux will change accordingly.The vertical circulation is also obviously enhanced,especially in the zonal average on the plateau region has obvious north-south convergence,500 hPa subtropical high eastward,The anticyclone system on 300 hPa move westward.