PENETRATIVE CONVECTION INDUCED BY THE FREEZING OF SEAWATER

Thermosolutal convection induced by freezing a layer of seawater from above is studied in a series of numerical experiments. The model equat ions take into account the dependence of the density and the temperatu re of maximum density on salt content, the possible presence of penetr ative convection and supercooling effects. The threshold Values for th e onset of convection are determined over a wide range of parameter sp ace. Two types of cell pattern are predicted by the linear theory: (1) convection of the entire fluid cell and (2) multi-layer convection. A n attempt is made at quantifying the cabbeling instability associated with the onset of the latter. Only multi-layer convection prevails for supercritical Rayleigh numbers. For a specific parameter range, a flo w pattern consisting of a strongly convecting layer floating between t wo relatively stable layers is found. The numerical experiments seem t o imply that penetrative convection delays the release of heat to the atmosphere during the formation of polynyas. Copyright (C) 1996 Elsevi er Science Ltd.