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Alumni ProjectImproving the Processes of Land-Atmosphere Interaction in CCSM 2.0 at High ResolutionRobert E. Dickinson, Professor, SummaryWe focus on the physical and computational issues of including heterogeneities in the climate treatment of land atmosphere coupling. Such heterogeneities come from either atmospheric or surface details. We consider three approaches to such heterogeneity: a) run the full atmosphere+land climate model components at higher resolution; using either a regional or global model; b) integrate the land elements at higher resolution; c) parameterize the most significant heterogeneities. Our research has largely focused on use of the Community Land MODEL (CLM) as described by Co-I Dai et al. (2003).1. Introduction A widespread recognition of the importance of climate change for human activities is one of the major drivers for growth of terascale computing. Some improvements are immediately realized through introduction of higher resolution of the atmospheric and ocean models. However, more dramatic improvements are likely through development of improved descriptions of physical processes treated by the models, especially those that can be observationally characterized in much finer details than are conventionally included in the climate models. This project has advanced the treatment of land with much improved details in the climatically most important processes. We have also carried out high resolution simulations to examine the further consequences of such. 2. Recent Advances Our most recent progress has been in the development of a comprehensive approach to downscaling between NCAR CCSM and its underlying land model . This current land model was developed through earlier efforts of our project (Dai et al, 2003). We have done an extensive reformulation of the requirements for scaling between the land model and the atmospheric resolution elements and tested key elements involving the application of moist convective precipitation to the land model. The underlying concept is to introduce a PDF (histogram) of land properties in place of the current tiling system that is designed only to handle land cover heterogeneity. This is essentially the same concept we have been working with as a subgrid with Co-I Hahmann. However, the tile elements are only required to be approximately of equal area. The main point is to formulate the treatment of the heterogeneous properties as accurately as possible, and relaxing the requirement of equal area may accommodate land cover information with greater accuracy. The details of what should be included in this framework are given at http://climate.eas.gatech.edu/dickinson . This approach improves the inclusion of precipitation and runoff in the climate model and allows an appropriate treatment of the sub-grid scale effects of topography. We have been especially testing the implementation of this approach for precipitation in simulations of CCSM 2.2. For that, we assume an exponential distribution of precipitation with a prescribed expected value for intensity over the areas of rain. These tests and tests of higher resolution simulations are reported on the web site of Shaikh, ( http://climate.eas.gatech.edu/shaikh ) As part of the development of subgrid disaggregation parameterizations of the fine-mesh model, Andrea Hahmann has developed an off-line interface with subgrid resolutions of 1/2, 1/4 and 1/8 degree to make use of recently released ISLSCP II forcing data. model. Her graduate student, Ana Mosor is currently using hourly precipitation and Eta-model analysis fields to study the relationship between elevation and precipitation and environmental controls in order to find parameters to be used in the fine-mesh disaggregation of precipitation over complex terrain. 3. Completion of earlier work Several other research components of this project have yielded published materials. They include Hahmann (2003) who demonstrates the importance of a sub-grid treatment of precipitation on a climate model, the work of Dai et al (2004) that improves the treatment of leaf photosynthesis through doing separate energy balance computation for sun versus shade leaves, the work of Yu et al. (2003, 2004) that provides a basis for testing the impacts of global aerosol on land processes, the study of Wu et al. (2003) that examines numerically the feedbacks between soil moisture and climate in CLM2 integrated for 50 years with CAM2, and the paper of Steiner et al (2004) from her dissertation that incorporates the CLM into the RegGCM regional model . Recent Publications Supported by SciDAC • Dai, Y., X. Zeng, R.E. Dickinson, I. Baker, G.B. Bonan, M.G. Bosilovich, A.S. Denning, P.A. Dirmeyer, P.R. Houser, G.-Y. Niu, K.W. Oleson, C.A. Schlosser and Z.-L. Yang: The Common Land Model (CLM). BAMS. Vol. 84, No. 8 pp. 1013-1023, 2003. • Dai, Y. and R.E. Dickinson: A Two- Big-Leaf Model for Canopy Temperature, Photosynthesis and Stomatal Conductance. Submitted to Journal of Climate, 2003. • Hahmann, A.N: Representing spatial sub-grid scale precipitation variability in a GCM. J. Hydrometeorology. • Steiner, A., J. Pal, F. Giorgi, R. E.Dickinson and W. L. Chameides: The coupling of the Common Land Model (CLM0) to a regional Climate Model (RegCM2). •Wu, Wanru, and R. E. Dickinson: Time scales of layered soil moisture memory in the context of land-atmosphere interaction. Journal of Climate. Revised, 2003. • Yu, Hongbin, R.E. Dickinson, M. Chin, Y.J. • Yu, Hongbin, R.E. Dickinson, M. Chin, M. Zhou, Y.J. Kaufman, L. Zhou, Y. Tian, O. Dubovik, and B.N. Holben: The direct radiative effect of aerosols as determined from a combination of MODIS retrievals and GOCART model simulations. Journal of Geophysical Research. In press, 2004.
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