Comparison of land skin temperature from a land model, remote sensing, and in situ measurement

Land skin temperature (Ts) is an important parameter in the energy exchange between the land surface and atmosphere. Here hourly Ts from the Community Land Model version 4.0, Moderate Resolution Imaging Spectroradiometer (MODIS) satellite observations, and in situ observations from the Coordinated Energy and Water Cycle Observation Project in 2003 were compared. Both modeled and MODIS Ts were interpolated to the 12 station locations, and comparisons were performed under MODIS clear-sky condition. Over four semiarid stations, both MODIS and modeled Ts show negative biases compared to in situ data, but MODIS shows an overall better performance. Global distribution of differences between MODIS and modeled Ts shows diurnal, seasonal, and spatial variations. Over sparsely vegetated areas, the model Ts is generally lower than the MODIS-observed Ts during the daytime, while the situation is opposite at nighttime. The revision of roughness length for heat and the constraint of minimum friction velocity from Zeng et al. (2012) bring the modeled Ts closer to MODIS during the day and have little effect on Ts at night. Five factors contributing to the Ts differences between the model and MODIS are identified, including the difficulty in properly accounting for cloud cover information at the appropriate temporal and spatial resolutions, and uncertainties in surface energy balance computation, atmospheric forcing data, surface emissivity, and MODIS Ts data. These findings have implications for the cross evaluation of modeled and remotely sensed Ts, as well as the data assimilation of Ts observations into Earth system models.