Mixed Layer Density Ratio from the Levitus Data

Abstract

An analysis of the Levitus data is employed to examine Stommel's mixed layer density ratio regulator hypothesis. Three different methods of computing the lateral density ratio (Rl≡α?T/??S) are used and the least squares method was found to have the least variance in the density ratio over the temperature range of 7°?17°C. Seasonal mean and annual mean density ratios in the North Pacific Ocean are calculated. The spring season has the highest density ratio of 2.1, and the fall season has the lowest of 1.64. The vertical variation in the lateral density ratio is small, in the upper 50 m, especially during the winter season. Overall, in the world's ocean, the mixed layer annual mean density ratios in the 7°?17°C range show remarkably consistent values, in support of Stommel's hypothesis. However, our estimate shows a systematically lower density ratio than that of Stommel in each ocean. Only the South Pacific and South Atlantic have density ratios equal to or slightly over 2. The North Pacific, North Atlantic, and Indian Oceans have density ratios around 1.7.