An Experimental Study Of The Impact Of Initial Conditions On Predictability Of Soil Moisture And Soil Temperature In BCC Model

Soil moisture has an important impact on weather and climate.Soil moisture has memory,so it is considered to be one of the most important sources of climate predictability in the sub-season forecast.However,the studies about the effect of soil moisture initialization in model and predictability of soil temperature and moisture are still relatively insufficient.BCC_CSM model is a climate model coupled with atmosphere,land,ocean and ice.The understanding of the soil moisture initial conditions and the predictability of the model soil temperature and humidity itself are a major requirement for evaluating and improving the performance of the business model.Based on BCC_CSM2.0,this article carry out three experiments to research the impact of soil moisture initialization condition.The results shows that:1)Due to the lack of soil moisture observation data and coordination between the observation and model,an initialization experiment(Obs_Forcing experiment),which forces the BCC_CSM model from 1994 to 2013 by using the NCEP atmospheric reanalysis data and the National Meteorological Information Center(NMIC)precipitation data is designed to produce a good model initial value.The soil moisture simulated by the Obs_Forcing experiment can describes the features that soil moisture is dryer in northern china and wetter in southern china.The soil moisture in Obs_Forcing experiment has a same distribution with the soil moisture provided by National Meteorological Information Center obtained by CLDAS(CMA Land Data Assimilation System).2)Taking two experiments by using a respectively true initial value of soil moisture(Obs_Hindcast experiment)and an ideal initial value of soil moisture climatology(Clim_Hindcast experiment).The result of Obs_Hindcast shows that the predictability of soil moisture in BCC_CSM model is about 3 pentads in surface layer(0.007m)and even reach 1–2 months in 0.619 m layer in some regions of China.3)Comparison between two experiments shows that initialization of soil moisture also has an impact on the prediction of soil moisture.The forecast skill of soil moisture in Obs_Hindcast experiment is higher than it in Clim_Hindcast experiment in early phase of prediction experiment.In the surface layer,the impact of soil moisture initialization continue for 2–3 pentads and 1–2 months in 0.619 m.4)The prediction skills of soil moisture in shallow layers(0.007–0.062m)strongly depend on the variations of rainfall,and there is a 1–2 days lag between the variations of soil moisture and rainfall,but about 5 days for that in the middle layers(0.366–0.619m).Based on the above relationship between soil moisture and rainfall,the time lag phenomenon occurs in the variations of the prediction skills in the shallow layers and the middle layers as well.5)The predictability of soil temperature in the BCC_CSM model is about 2 pentads in surface layer(0.007m).The predictability of soil temperature also increases with depth,it is about 5 in 0.619 m.The initialization of soil moisture has an impact on the prediction of soil temperature as well.