Comparison of land skin temperature from a land model , remote 1 sensing , and in - situ measurement

39 40 Land skin temperature (Ts) is an important parameter in the energy exchange 41 between the land surface and atmosphere. Here hourly Ts from the Community Land 42 Model Version 4.0, MODIS satellite observations, and in-situ observations in 2003 43 were compared. Compared with the in-situ observations over four semi-arid stations, 44 both MODIS and modeled Ts show negative biases, but MODIS shows an overall 45 better performance. Global distribution of differences between MODIS and modeled 46 Ts shows diurnal, seasonal, and spatial variations. Over sparsely vegetated areas, the 47 model Ts is generally lower than the MODIS observed Ts during the daytime, while 48 the situation is opposite at nighttime. The revision of roughness length for heat and 49 the constraint of minimum friction velocity from Zeng et al. [2012] bring the modeled 50 Ts closer to MODIS during the day, and have little effect on Ts at night. Five factors 51 contributing to the Ts differences between the model and MODIS are identified, 52 including the difficulty in properly accounting for cloud cover information at the 53 appropriate temporal and spatial resolutions, and uncertainties in surface energy 54 balance computation, atmospheric forcing data, surface emissivity, and MODIS Ts 55 data. These findings have implications for the cross-evaluation of modeled and 56 remotely sensed Ts, as well as the data assimilation of Ts observations into Earth 57 system models.