Planetary scale land-ocean contrast of near-surface air temperature and precipitation forced by present and future SSTs

Abstract

The land-ocean contrasts of near-surface temperature and precipitation averaged over tropics (40 S-40 N) and extra tropics in the Northern Hemisphere (40 N-70 N) were studied using the global version of the Experimental Climate Prediction Center (ECPC) global to regional forecast system (G-RSM) under current and projected sea surface temperatures (SSTs) with four different stratiform cloud parameterizations. As common features of the simulations, we found that there is a large land-ocean contrast in surface downward longwave radiation flux (LWd), downward shortwave flux (SWd), upward shortwave flux (SWu), latent heat flux (LHF) and sensible heat flux (SHF). Since smaller LWd is compensated by larger SWd, and larger SWu is compensated by smaller LHF, there is a tendency toward the reduction of the land-ocean contrast of the total surface fluxes. There were significant differences in near-surface air temperature and precipitation among the four simulations. The main cause is due to clear-sky LWd. The second largest term is the SWd, which works in the opposite direction of the difference in LWd. The difference in the near-surface temperature among the schemes is mostly determined by the sum of the LWd and SWd. The variability of precipitation among the four cloud schemes is large everywhere except in tropical oceans. In general, the difference in evaporation explains the precipitation difference among the schemes everywhere except tropical oceans where moisture convergence is negative. When the simulations are performed with warmer SST, the differences among the cloud schemes are very similar to those in present-day simulations. However, the magnitude of the response to warm SST depends on the cloud scheme. Those sensitivities are connected to that of the effect of cloudiness on SWd and surface albedo. © 2009, Meteorological Society of Japan.