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Young-Kwon Lim, Ming Cai, Eugenia Kalnay, and Liming Zhou

urbanization, agricultural activity, and deforestation. The impact of surface temperature changes forced by different regional vegetation types is not well documented. Only urban impact has been assessed by comparing observations in cities with those in rural areas ( Easterling et al. 1996 ; Hansen et al. 2001 ). But this approach is only applicable to urban effects, and the estimated signals vary with the criteria in classifying urban and rural areas. The present study is motivated by the difficulty in

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M. Baldi, G. A. Dalu, and R. A. Pielke Sr.

Rasmussen 1998 ). The development of thermally forced secondary circulations is favored by the absence of ambient flow, since they are suppressed by ambient flows with a wind speed exceeding 6 m s −1 for surface inhomogeneities larger than 50 km, or by weaker winds for smaller inhomogeneities ( Segal and Arritt 1992 ). From a climatic point of view, land-use changes have an impact on the regional and global scale, since spatially heterogeneous land-use effects may be at least as important in altering

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K. W. Oleson, G. B. Bonan, J. Feddema, M. Vertenstein, and C. S. B. Grimmond

and land (i.e., indirect change; Cramer et al. 2001 ; Foley et al. 2005 ). Global and regional models have been used extensively to investigate effects of direct and indirect land use/land cover change mechanisms on climate ( Copeland et al. 1996 ; Betts 2001 ; Eastman et al. 2001 ; Pielke et al. 2002 ; Feddema et al. 2005 ). However, all of these studies have focused on land use/land cover related to changes in vegetation types. Urbanization, or the expansion of built-up areas, is an

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Vinodkumar, A. Chandrasekar, K. Alapaty, and Dev Niyogi

*). When all of the effects due to data assimilation are allowed to occur at the surface only, the adjustment turbulent sensible heat flux H F S can be written as where Δ z is the thickness of the lowest model layer, and ρ and c P refer to density and specific heat at a constant air pressure, respectively. In the same way, if (∂ q F a /∂ t ) represents the rate of change of the surface layer mixing ratio to direct nudging, by the same argument the adjustment turbulent latent heat flux H F 1

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