Home > CSSS Seminars > David Randall   David Randall Department of Atmospheric Science Colorado State University http://diwi.atmos.colostate.edu/group/dave/dave.html A Breaking the Cloud-Parameterization Deadlock A key factor limiting the reliability of simulations of anthropogenic climate change is our inability to accurately represent the various effects of clouds on climate. Despite the best efforts of our community, the problem has resisted solution for several decades. We briefy review the many reasons for this, and argue that it will be many more decades before the problem can be solved through the approaches to cloud parameterization that have been used up to now. We then outline an alternative approach, called "super-parameterization," in which high-resolution cloud-system resolving models (CSRMs) are used in place of the conventional cloud parameterizations. Tests performed with the Community Atmosphere Model show that super-parameterizations can give more realistic simulations of the current climate, including greatly improved simulations of the Madden-Julian Oscillation and other tropical wave disturbances. Super-parameterizations increase the cost of climate simulation by a factor of several hundred, but can make efficient use of massively parallel computers. In addition, super-parameterizations make it possible for a climate model to converge to a global CSRM as the horizontal grid spacing of the climate model decreases to a few kilometers. No existing climate model has this convergence property. Superparameterizations have the potential to greatly increase the reliability of climate-change simulations.
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