Wednesday 05 Mar 2014Baroclinic circulation regimes and heat transport- comparing laboratory and atmosphere-ocean models (Taylor and Francis sponsored)

Prof Peter Read - University of Oxford

Harrison 170 12:00-13:00

The range and diversity of baroclinic flow regimes in laboratory experiments, such as the “classical” rotating annulus, have been the subject of both experimental investigation and theoretical study for more than 60 years. Such experiments have long been regarded as useful analogues of circulation systems in planetary atmospheres and oceans, since they capture much of the essential Physics of the key instabilities and processes that dominate the large-scale circulations of rapidly rotating, terrestrial planetary atmospheres and (at least to some extent) oceans, including those of the Earth itself. But just how good an analogue can these experiments be, given they are energized in a very different way from real atmospheres and oceans, and are typically in cylindrical, rather than spherical, geometry?

Atmosphere and ocean modelers have been relatively reluctant until recently to explore the full range of circulation regimes across wide stretches of parameter space in fully spherical, radiatively-driven models of atmospheric or oceanic flow, partly because of the relative computational expense of such models, but also because such remote regions of parameter space were not apparently populated by known planetary objects. But this situation is changing rapidly now because of the burgeoning discoveries of many planets around other stars, that may densely populate very wide ranges of parameter space in their
atmospheric circulations and climate.

In this presentation, we will present and review a range of simulations using a simplified, radiatively-driven, 3D, time-dependent numerical model of atmospheric flow in a spherical domain that explores a wide stretch of the key parameter space, for comparison with the results of laboratory experiments on baroclinic flows. Many previously unremarked similarities, both qualitative and quantitative, are apparent, including the ordering of circulation regimes by a suitably-defined Thermal Rossby Number, although planetary vorticity gradients (or the “beta-effect”) need to be carefully taken into account. The efficiency of heat transport in such regime studies is of particular interest. In the latter part of this presentation, therefore, we will present some new analyses of heat transport measurements in rotating annulus experiments and discuss their implications for “macroturbulent” theories of heat and tracer transport in atmospheres and oceans.

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