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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

1. Introduction Land use/land cover change is increasingly being recognized as an important yet poorly quantified component of global climate change ( Houghton et al. 2001 ). Land use/land cover change mechanisms include both transformation of natural land surfaces to those serving human needs (i.e., direct anthropogenic change; e.g., conversion of tropical forest to agriculture) as well as changes in land cover on longer time scales that are due to biogeophysical feedbacks between atmosphere

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

1. Introduction Global mean surface temperature time series derived from in situ observations reveal the interdecadal global warming over the last several decades ( Houghton et al. 2001 ). Many studies reported that this upward trend is significantly a result of primary human impacts such as greenhouse gases ( Houghton et al. 2001 ) and land use ( Pielke et al. 2002 ). The anthropogenic land-use impact on surface warming may become more important as the surface vegetation changes in the form of

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

improve the atmospheric boundary layer (ABL) simulations using improved surface boundary conditions in atmospheric models. The surface fluxes, and to some extent the entrainment fluxes at the top of the ABL, determine ABL structure and evolution. Improved surface fluxes over land require, in addition to surface observations of temperature and humidity, detailed observations of soil moisture and soil temperature. Soil moisture (and soil temperature) is not available from most routine meteorological

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

conditions. The urban model is integrated with the Community Land Model, version 3 (CLM3; Oleson et al. 2004 ; Dickinson et al. 2006 ). Our model has been evaluated for two urban sites described in Part I , but further evaluation is needed before the model can be used to investigate global urban climate questions. Thus, the purpose of this paper is twofold. First, the robustness of the model is examined through sensitivity studies: the sensitivity of the model fluxes to morphological, radiative, and

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