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Title: A SENSITIVITY STUDY OF CLIMATE OF ENERGY BALANCE SIMULATIONS WITH USE OF SATELLITE DRIVED EMISSIVITY DATA OVER THE NORTHERN AFRICA AND THE ARABIAN PENINSULA

Author
item ZHOU, L - GA INST OF TECH
item DICKINSON, R - GA INST OF TECH
item TIAN, Y - GA INST OF TECH
item JIN, M - UNIV OF MD
item OGAWA, K - HITACHI INC
item YU, H - GA INST OF TECH
item Schmugge, Thomas

Submitted to: Journal of Geophysical Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2003
Publication Date: 12/27/2003
Citation: Zhou, L., Dickinson, R.E., Tian, Y., Jin, M., Ogawa, K., Yu, H., Schmugge, T.J. 2003. A sensitivity study of climate of energy balance simulations with use of satellite derived emissivity data over the northern African and the Arabian Peninsula. Journal of Geophysical Research. 108(D24):4795-4851.

Interpretive Summary: This paper demonstrates the importance of surface emissivity measurements in climate models. These measurements are particularly important for the desert areas discussed in the paper because it is only for non-vegetated areas such as these for which there is significant variation in the surface emissivity. This study indicates that a decrease of soil emissivity by 0.1 will increase ground and air temperature by about 1.1°C and 0.8°C and decrease net and upward longwave radiation by about 6.6 W/m^2 and 8.1 W/m^2, respectively, at the ground surface. Changes of this magnitude will have a significant impact in climate models.

Technical Abstract: This paper analyzes the sensitivity of simulated climate and energy balance to changes in soil emissivity over Northern Africa and the Arabian Peninsula and considers how this information may be used to improve emissivity parameterizations in climate models. Analysis of satellite observations suggests that the soil emisivity in current models is too high over this region. Sensitivity tests based on the recently developed NCAR Community Land Model indicate that this bias could produce significant errors in the model simulated ground and air temperature, net and upward longwave radiation, and sensible heat flux. There is a linear relationship between changes in emissivity and changes in these variables. Statistical results show that, on average for the study region, a decrease of soil emissivity by 0.1 will increase ground and air temperature by about 1.1°C and 0.8°C and decrease net and upward longwave radiation by about 6.6 W/m^2 and 8.1 W/m^2, respectively, at the ground surface. The decreased net longwave radiation (more absorption) is mainly balanced by an increase of sensible heat flux of about 5.9 W/m^2. These relations vary seasonally and diurnally. The temperature increases are slightly higher in winter than in summer and twice as large during nighttime as during daytime, while the other variables show more change in summer/daytime than in winter/nighttime. Our experimental results are consistent with our theoretical energy balance analyses. When a more realistic emissivity value is used, the model cold bias over the Sahara in comparison with land surface air temperature observations could be partially reduced. These results indicate that the simple representations of the land surface emissivity in climate models, especially for bare soil, need improvements based on satellite and in situ observations.