Land-Surface Model Development for the GISS GCM

A land-surface model is linked to the Goddard Institute for Space Studies (GISS) GCM Model II to form Model II-LS. The land-surface model primarily influences the simulation of surface air temperature over land, both in monthly means and diurnal range, and affects the major components of the hydrologic cycle over land—evapotranspiration, runoff, and, more indirectly, precipitation. Comparisons of January and July results of Model II-LS to results generated from the GISS GCM Model II and to observations show that the new land surface primarily provides improvements in the simulation of global evaporation and diurnal surface temperature range. The interannual variability of June–August surface air temperature in the Northern Hemisphere is also improved. When the land-surface model is combined with new parameterizations for moist convection and the planetary boundary layer, the combined version of the GCM yields improvements in evaporation. Simulations of a grassland site from an off-line version of the land-surface model compared to observations provided by the Project for Intercomparison of Land-Surface Parameterization Schemes of the Global Energy and Water Cycle Experiment show that the land-surface model simulates the ground temperature lag with depth in a reasonable way. Thus, the land-surface parameterization provides a more realistic simulation of climate variables over land in conjunction with other improvements to the GISS GCM.