Open-ocean deep convection, which occurs in the Labrador Sea, the Greenland Sea, and the Mediterranean Sea in the current world climate, is an important phenomenon that strongly influences the thermohaline circulation governing the poleward transport of heat in the ocean. These basins with open-ocean convection are characterized by a small Rossby deformation radius compared with the basin scale so that rotational effects become important on comparatively small length scales. (see, e.g., Marshall & Schott, MIT Center for Global Change Science, 1998.)
One important aspect of this phenomena is the spreading phase of open-ocean convection in response to a strong surface cooling event (Legg & Marshall, JPO, 1993; Legg, Jones, & Visbeck, JPO, 1996). Based on recent work by the authors, we present a ``most probable state'' equilibrium statistical theory for the spreading phase of open-ocean convection, modeled by a random distribution of hetons in the context of a two-layer quasigeostrophic fluid in a closed basin. The statistical theory depends only on a few bulk conserved quantities such as energy, circulation and the range of values of potential vorticity in each layer. We find that, although the initial ensemble of hetons is homogeneous and purely baroclinic, the solutions that arise as the most probable state of the statistical theory usually possess a nonuniform distribution of hetons with a sizeable barotropic component. For the parameters typical of open-ocean convection sites, i.e., small deformation radius, these solutions have sharp temperature anomalies confined to the center of the basin, circumscribed by powerful barotropic rim currents that typically contain 90% of the energy. This strongly resembles the saturated states observed in the spreading phase of open-ocean convection.
Close window or click on previous window to return to the Conference Program.
12th Conference on Atmospheric and Oceanic Fluid Dynamics