A HETON PERSPECTIVE OF BAROCLINIC EDDY TRANSFER IN LOCALIZED OPEN-OCEAN CONVECTION

A simple point-vortex ''heton'' model is used to study localized ocean convection. In particular, the statistically steady state that is est ablished when lateral buoyancy transfer, effected by baroclinic instab ility, offsets the localized surface buoyancy loss is investigated. Pr operties of the steady state, such as the statistically steady density anomaly of the convection region, are predicted using the hypothesis of a balance between baroclinic eddy transfer and the localized surfac e buoyancy loss. These predictions compare favorably with the values o btained through numerical integration of the heton model. The steady s tate of the heton model can be related to that in other convection sce narios considered in several recent studies by means of a generalized description of the localized convection. This leads to predictions of the equilibrium density anomalies in these scenarios, which concur wit h those obtained by other authors. Advantages of the heton model inclu de its inviscid nature, emphasizing the independence of the fluxes aff ected by the baroclinic eddies from molecular processes, and its extre me economy, allowing a very large parameter space to be covered. This economy allows us to examine more complicated forcing scenarios: for e xample, forcing regions of varying shape. By increasing the ellipticit y of the forcing region, the instability is modified by the shape and, as a result, no increase in lateral fluxes occurs despite the increas ed perimeter length. The parameterization of convective mixing by a re distribution of potential vorticity, implicit in the heton model. is c orroborated: the heton model equilibrium state has analogous quantitat ive scaling behavior to that in models or laboratory experiments that resolve the vertical motions. The simplified dynamics of the heton mod el therefore allows the adiabatic advection resulting from baroclinic instability to be examined in isolation from vertical mixing and diffu sive processes. These results demonstrate the importance of baroclinic instability in controlling the properties of a water mass generated b y localized ocean convection. A complete parameterization of this proc ess must therefore account for the fluxes induced by horizontal variat ions in surface buoyancy loss and affected by baroclinic instability.