THERMALS WITH BACKGROUND ROTATION AND STRATIFICATION

Scaling analysis and experiments are used to study the evolution of th ermals in the presence of background rotation. When the ambient enviro nment is homogeneous, the thermal rises and expands until it reaches a critical height where the Rossby number becomes approximately 1. The thermal then stops expanding and rises in a column. Both the critical height and column radius scale with (F0f-2)1/2. F0 is the initial ther mal buoyancy and f is the Coriolis frequency. The thermal vertical vel ocity is independent off. When the background is stratified with buoya ncy frequency N, the thermal rises to a neutral buoyancy level which s cales with (F0N-2)1/4. For N/f < 0.6 column formation occurs before th e thermal reaches the neutral level. For N/f > 0.6 the thermal reaches the neutral level before rotation is important. In both regimes, geos trophic adjustment eventually causes the formation of a baroclinic vor tex consisting of an anticyclonic lens of thermal fluid at the neutral level and cyclonic circulation below. The lens has Nh/fl is similar t o 1. The lens thickness 2h and the radius l obey relations of the form (F0N-2)1/4(N/f)m. However, the exponents m are different in the two r egimes. The relevance of these results to deep-ocean convection and hy drothermal venting is discussed.