A numerical investigation of slanted convection and subsurface anticyclone generation in an Arctic baroclinic current system

Abstract

A nonhydrostatic three‐dimensional numerical model is used to investigate convection along slanted isopycnal surfaces and subsurface anticyclone generation in a baroclinic jet system appropriate for the Beaufort Sea environment. The current is initially bounded to the left by a coastal wall and subsequently subject to surface friction exerted by sea ice and cooling at the sea surface. Despite spatially uniform cooling rates used in the model, convection favors limited areas with high cyclonic vorticity. In a meandering current system, rigorous convection occurs primarily in meander troughs where the current turns cyclonically. The cyclonic vorticity enhances convection, which in turn enhances cyclonic vorticity. The positive feedback mechanism, previously known in atmospheric literature as convective instability of the second kind, often strengthens convection and the consequent subsurface anticyclones by as much as 1 order of magnitude. Subsequent seaward detrainment in subsurface depths of interest moves anticyclones from the cyclonic side of the jet to the anticyclonic side. The subsurface anticyclones may be strengthened for the second time because of favorable changes of ambient vorticity. Thus downward convection along slanted isopycnal surfaces of a left‐bounded baroclinic jet (similar to segments of the Beaufort Sea anticyclonic gyre) is an efficient way to produce subsurface anticylcones and propel them seaward afterward.