The role of land surface schemes on land-atmosphere coupling strength in weather and climate models

Wide disparities of land-atmosphere coupling strength have been found among many general circulation models (GCM) in the GEWEX Global Land-Atmosphere Coupling Experiment (GLACE). One potential reason may be the different implementations of the land surface schemes (LSS) that GCMs use to simulate the terrestrial branch of the hydrologic cycle. Preliminary studies show that an evaporation rate that varies strongly and consistently with soil moisture tends to lead to a higher coupling strength in the GCM, thus a strong relationship between local surface properties and fluxes in the land surface scheme more likely results in a strong dependency of precipitation on soil moisture. In this study, the multi-model intercomparison in the relationship between surface properties and fluxes is conducted using data sets from the Second Global Soil Wetness Project (GSWP-2), and is discussed in the context of land-atmosphere coupling strength. Note that more than half of the GLACE GCMSs have LSSs that participated in GSWP-2. All LSSs participating in GSWP-2 were integrated in an offline mode from 1986 through 1995, forced with the same meteorological data. The complications in the relationship between local surface properties and fluxes that exist in the fully coupled GLACE experiment are reduced since the land surface states have no ability to affect the atmosphere in GSWP-2 datasets. This helps us to isolate the role of LSS behavior in the GLACE results.