Variation of vertical stability parameter in the surface layers of the Arabian Sea off Cochin

Abstract

In the ocean, the vertical stratification of a water column mainly depends on the vertical stability parameter. The latter has been found to be dependent upon the change of density (represented as Sigma-T) in the vertical direction. Potential temperature is to be used for accurate determination of Sigma-T when stability is to be computed. But the effect of compressibility on temperature need be taken into consideration below 100 m. only and in general the effect of changes in salinity is mostly small. Hence in the upper layers (mostly the ones constituting the mixed and top thermocline layers) the stability can be accurately represented by E = 10* —raz according to Hesselberg and Sverdrup (1914-15). For positive values of E the stratification is stable and is not altered by vertical displacements of small quanta of water. For negative values of E the stratification is unstable and the slightest disturbance is sufficient to cause a readjustment in the stratification. Between layers with positive and negative stability there is always a surface with E=0. A small mass of water on displacement to the side where E is positive is always driven back to the surface, but a displacement to the side where E is negative removes it more and more from that surface. Thus the vertical stability, instability, or neutrality can be judged as E = O.