Convection in Small Basins

Abstract

Convection in the world's oceans often occurs in small, semienclosed basins where bottom slopes and nearby continental shelf breaks are commonplace. The evolution of convectively generated heat anomalies in such settings is studied using quasigeostrophic finite-difference and point vortex models. The displayed behaviors divide essentially into two categories: whole fluid column convection, in which bottom-slope effects are felt immediately, and partial fluid column convection, in which the topographic effects can be delayed. In both cases, topography significantly modifies the evolution of convective patches from that occurring over flat bottoms. Vertical walls induce strong self-propagation mechanisms that accelerate alongslope heat transport, while the continental shelf slope is repulsive and rejects lower-layer anticyclones. These anomalies are then ?stranded,? being too far offshore to interact with the shelf break and having lost their heton partner in the interaction. Weaker deep ocean topographic slopes disrupt heton formation and disperse convective patches by topographic mechanisms. Partial fluid column convection, with stratification under the mixed layer, proceeds through a cascade from small to large length scales. In oceanically relevant regimes, smaller scales are shielded from bottom slopes and can disperse as small hetons. Larger-scale structures are prevented by the topography from forming into hetons and instead evolve as if in a sloping-bottom two-layer system. The small hetons, when encountering shelf breaks, can experience topographic repulsion and stranding. Comparisons with the Mediterranean Sea suggest alternative interpretations for some observations, and several observed Labrador Sea mesoscale convective characteristics can be ascribed to topographic effects.