Thursday, October 2, 2008

Journal Club MTG2: Urban Parameterization for CCSM

As part of the journal meetings we are reviewing "An Urban Parameterization for a Global Climate Model. Part 1: Formulation and Evaluation for Two Cities" by KW Oleson et al. The paper reviews efforts to capture land use change in urban areas and the effects this has on the atmosphere. The global models currently divides the world into a grid and each grid cell is further divided into various plant function types and wetland, urban etc. Each is dealt with separately however there is no scheme for urban areas. This paper presents an "urban canyon" solution that supposedly captures the urban climatology. There are separate energy balances and surface temperatures for each canyon facet. I really appreciate the added heat sources from waste (air conditioners) and traffic. A 1D heat conduction is solved numerically for fluxes in and out of surfaces. The paper then describes an experiment looking at two different cities areas, Mexico City and Vancouver. The results suggest an increased understanding of fluxes but says that the timing is off in the model, but note that no one has perfected the urban diurnal cycle. I want to note that the observations are rather sparse though. The paper also states that implementing this system globally might be problematic as no urban map yet exists categorising urban types. Something to look forward to in the future. Lastly a relevant question is, at what resolution does this actually matter? Perhaps a global view is not the answer but maybe regional is.

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