The impact of land surface initialization on seasonal forecasts with CCSM

Series of seasonal forecast experiments investigate the impact of specifying the observed initial state of the land in conjunction with the observed states of the atmosphere and the ocean with the National Center for Atmospheric Research (NCAR) Community Climate System Model (CCSM). We are able to successfully initialize all components of the CCSM, and produce a good representation of the mean land surface climate in the first season's forecast. In comparison with a previous set of forecast experiments which had initialized only the observed ocean state, there is firm evidence that we produce a much better representation of the interannual variability of the soil surface. The seasonal forecast of soil moisture is far superior, due in part to the ability of the CCSM to persist large-scale anomalies present in the initial soil state. The superior land surface forecast leads to a superior seasonal forecast of surface temperature. There is little evidence of an improved forecast of precipitation over land; although there is a suggestion of an improvement in the forecast over ocean.