THERMOBARIC CONVECTION

Roland W. GARWOOD, Jr.*, Shirley M. Isakari, and Patrick C. Gallacher

In The Polar Oceans and Their Role in Shaping the Global Environment
O. Johansen, R. Muench, and J. Overland, Eds.,
Vol. 85 of Geophysical Monograph Series,
American Geophysical Union,
Washington, D. C., pp.199-209

* Dept of Oceanography, NPS, MONTEREY CA 93943, USA

Abstract:

Large-eddy simulation of two cases of free convection in the polar seas reveal the three-dimensional structure of thermobaric-enhanced turbulence, with and without salinity stratification. In the first case, with no initial stratification, 3.6 km-deep free thermal convection produces anticyclonic cells of rising warmer water at the surface, with largest cell diameters of about 1 km. Narrow linear shear zones of colder near-surface water between these warm cells are the source of sinking cyclonic thermobaric plumes that provide the energy to power the convective system. The prediction of a mid-depth maximum in the turbulent kinetic energy caused by thermobaricity is corroborated numerically. In the second case, thermal convection in a mixed layer overlying salinity-stratified warmer water may generate two kinds of conditional instabilities. In a thermobaric parcel instability, detraining parcels of mixed-layer water may penetrate the pycnocline without significant mixing of the stable surrounding water. In a thermobaric layer instability, a nonturbulent layer may become statically unstable and turbulent if advected below a predicted critical depth. For either kind of instability, the thermobaric increase in density of a parcel or layer of cold water may cause plumes of near-surface water to penetrate deep into the pycnocline and possibly to the bottom as "cumulus towers" of the polar seas.

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Last review: February 2003
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