Impact of Initial Soil Temperature and Moisture on the Temperature and Relative Humidity at 2 m in the WRF Model over North China in Winter

The effects of initial soil temperature and moisture were explored by performing a series of 84-hour numerical simulations form 10 to 25 December 2023, using the WRF model with soil temperature and moisture initialized with CMA-GFS forecasts and the China Meteorological Administration Land Data Assimilation System (CLDAS) analysis respectively.It showed that the relative humidity (RH2m) and the temperature (T2m) at 2 m were poorly during the first 21-hour integration and getting better during the following time integration initialized with CLDAS than that with CMA-GFS, with a maximum root mean square error (RMSE) decrease of 8.3% and 10% respectively.Further diagonosis indicated that the first 21-hour integration usually a accompanied with more sensible and latent heat fluxes in case of the soil temperature and moisture initialized with CLDAS.It means that the model would take a longer spin-up time during which any satisfiable forecasted T2m and RH2m might not be gotten, due to the in consistanece in initial conditions which came from the different source datasets containing some more reliable variables although.Spatially, when the model was initialized with CLDAS, it represented much more favourable with smaller negative deviation of RH2m and positive deviation of the daily maximum T2m, which maximally decreased by 8% and 1.5 °C in Henan respectively, and unfavourable with larger positive deviation of the daily minimum T2m in the southern region of Shanxi and central Hebei.Whereas, it represented pretty well performance of daily maximum and minimum T2m and bad performance of RH2m with larger negative deviation in the northern region of northern Shanxi and northern Hebei.Among groups of initial soil conditions, the moister and colder initial soil group had the best forecasting performance of T2m which is tightly closed to the observation, and the moister and warmer initial soil group has the worst although the T2m difference between the simulations initialized with CLDAS and CMA-GFS is small.Compared with the initial soil temperature, the initial soil moisture has a greater impact on T2m.The drier initial soil would lead to a better forecasting performance of daily minimum T2m, accompanied with larger sensible heat flux and smaller latent heat flux in the integration.