Effects Of Different Land Surface Processes On The Numerical Prediction Of Summer Precipitation In China

The summer heavy rainfall in Huaihe River basin is an important weather disaster in China and many researches have been done about its dynamic process or its forecast. But its forecast is still a big challenge in numerical weather prediction (NWP). This is closely associated with the poor understanding of the mechanisms of the heavy rainfall. The mesoscale convection system is severely influenced by the synoptic-scale forcing and the local inhomogeneities. The issues about the effects of the landscape inhomogeneities on the convection development and how to impact the convection system are still unclear and needed to be further explored. Numerical simulations are conducted using the high resolution GRAPES model to investigate the impact of the different land process on the prediction of mesoscale convection. Also, the land surface-planetary boundary layer (PBL) interactions responsible for the initiation of deep convection are discussed.In this study, sensitivity simulations are performed to assess the impact of land surface process by 1) replacing the Noah land surface model (LSM) with a simple slab soil model (Slab), 2) replacing the T213 initial soil data in Noah LSM with the global land data assimilation system (GLDAS) soil data. The results show that the local convective precipitation is sensitive to the land process, whereas the synoptics dictate on the location of the rain belts which are mainly dominated by the large scale forcing, however, a proper characterization of land surface process can be crucial in developing the associated convection. Furthermore, Slab convection is further delayed by 1-2 hours, indicating that detailed surface parameterization is necessary for a realistic model forecast. The soil moisture gradient affects the distribution of the surface fluxes for sensible and latent heat. The sensible heat is increasing form night to day, and Noah LSM has the rapid response but Slab not. The rapid increasing of sensible heat is critical for the growth of PBL, with the small-scale vertical motions of PBL themselves playing a major role in PBL growth. PBL growth and thermodynamic destabilization may be augmented when mesoscale ascent occurs in conjunction with the strong surface heating. Additionally, the continuous simulations of the heavy rainfall in July 2007 indicate that there are significant improvement of the location and intensity of heavy rainfall by the Noah LSM, which is close to the observation.