Frontiers of Engineering Reports on Leading-Edge Engineering from the 2004 NAE Symposium on Frontiers of Engineering (2005) / Chapter Skim
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Small-Scale Processes and Large-Scale Simulations of the Climate System--Bjorn B. Stevens
Small-Scale Processes and Large-Scale Simulations of the Climate System--Bjorn B. Stevens
Pages 89-94
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From page 89... ...
Atmospheric and oceanic circulations operate on spatial scales ranging from micrometers or smaller to planetary scales and temporal scales ranging from microseconds to millennia and beyond. The representation of this range of scales is far beyond the capacity of any envisioned computational platform.
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From page 90... ...
Typically, small-scale processes are broken down into distinct classes of problems -- clouds, radiative transfer, hydrometeor interactions, surface interactions, small-scale turbulence, chemistry, and so on -- processes that can be thought of as the atoms. Although one may be interested only in the net effect of all of these processes, atomization facilitates idealization and subsequent study.
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From page 91... ...
A key aspect of the similarity approach is simplifying the problem to a point where it becomes empirically tractable and then hoping that the answers so derived are relevant to less idealized situations. For the surface flux problem, the similarity approach usually consists of first considering flow over a uniformly rough wall in the absence of temperature differences; the essence of the flow can only conceivably be retained if only two variables are considered, namely the distance, z, from the surface and a velocity scale that measures the momentum flux, e.g., u*
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From page 92... ...
To address these problems, a boot-strapping approach has been developed, wherein idealized fluid simulations designed to isolate particular processes, or collections of processes, are used to develop our intuition. Slowly, these simulations are refined to their essence, from which pseudo-empirical statements are extracted, and the parameter space is explored.
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From page 93... ...
Here fine-scale simulations are embedded in larger-scale simulations, in a sense performing the procedure outlined above "on the fly." For some processes, this approach has great potential -- particularly processes that resist simplification and in situations where myriad interactions among unresolved processes occur on a narrow range of scales that are clearly separated from the smallest of the resolved "large-scales." Although these qualifications appear onerous, they are satisfied by some elements of one of the more vexing parameterization problems in atmospheric sciences -- relating the statistics of deep convective clouds to the state of the large-scale circulations. Recent applications of this approach, called super-parameterization, or cloud-resolving-convective parameterization (Grabowski and Smolarkiewicz, 1999)
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From page 94... ...
2003. A cloud resolving model as a cloud parameterization in the NCAR Community Climate System Model: preliminary results.
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