The NCAR land surface model (LSM version 1.0) was coupled to a modified version of the NCAR Community Climate Model (CCM) - a greatly modified version of the CCM2 and precursor to the CCM3 (without the CCM3 convection scheme). LSM has interactive hydrology and replaces the prescribed surface wetness and prescribed snow cover in the CCM. It also replaces the land albedos and surface fluxes, using instead parameterizations that include hydrological and ecological processes (e.g., soil water, phenology, stomatal physiology, evaporation of intercepted water). Two ten-year simulations, one with LSMt and one without, were compared to determine the impact of LSM on the simulated climate. Major findings are: * Without LSM, the atmospheric model has extensive regions of colder than observed surface air temperatures. LSM improves the simulation of surface air temperature in January, April, July, and October, except in northern North America and Asia in July where the model introduces a cold bias. * The interactive hydrology - in which the latent heat flux decreases as the soil dries and the amount of water in the soil is a mass balance between precipitation input and evapotranspiration and runoff losses - improves the seasonality of the surface fluxes, resulting in reduced latent heat flux and increased sensible heat flux during periods of water depletion, and eliminates unrealistic annual water budgets in which evaporation exceeds precipitation. * LSM has little impact on vertical profiles of temperature and zonal wind, but dries the atmosphere up to 500 mb for many regions in July. * LSM simulates land-atmosphere exchange of CO2 with clearly defined growing seasons that depend on temperature and water availability. * LSM allows the coupled land-atmosphere model to be used for paleoclimate applications, future climate change scenarios, studies of land use effects on climate, and other experiments in which surface properties change greatly from extant conditions.
