Effects of the land-surface heterogeneities in temperature and moisture from the “combined approach” on regional climate: a sensitivity study

In order to better understand the land–atmosphere interactions and increase the predictability of climate models, it is very important to investigate the effects of land-surface heterogeneities, in which the temperature and moisture heterogeneities are very significant. In this paper, the land-surface scheme BATS [Dickinson, R.E., Henderson-Sellers, A., Kennedy, P.J., Wilson, M.F., 1993. Biosphere /Atmosphere Transfer Scheme (BATS) Version 1e as Coupled to the NCAR Community Climate Model. NCAR Tech. Note TN-387+STR, National Center for Atmospheric Research, Boulder, CO], in the NCAR regional climate model RegCM2, was treated with a “combined approach” that is computationally effective to represent land-surface heterogeneities in temperature and moisture, and was tested by using real data of China during the summer monsoon in 1991 as initial and boundary conditions. Different from the results of the off-line simulations for warm season in Giorgi [Mon. Weather Rev. 125 (1997a) 1900], as for temperature, we used a cosine probability density function (PDF), which is more effective in computation and different from the linear PDF applied by Giorgi [Mon. Weather Rev. 125 (1997b) 1885]; we can see that the summer monsoon climate is generally sensitive to the temperature heterogeneity (e.g., precipitation is sensitive to the temperature heterogeneity). Similar to the results in Giorgi [Mon. Weather Rev. 125 (1997b) 1900], the regional climate seems to be very sensitive to the moisture heterogeneity, which shows a regularity as changing with the heterogeneity, i.e., with the heterogeneity increasing, the mean sensible heat flux is generally increased, while the mean latent heat flux is generally decreased. So, the capability of simulation for summer monsoon climate may be improved via the appropriate representation of the heterogeneities in temperature and moisture. In addition, other results reveal the limitations of off-line experiments, and therefore the coupling of the land-surface scheme (with the inclusion of heterogeneity representation) to the atmospheric model is necessary for the study on land–atmosphere interactions.