Density ratio

The density ratio of a column of seawater is a measure of the relative contributions of temperature and salinity in determining the density gradient. At a density ratio of 1, temperature and salinity are said to be compensated: their density signatures cancel, leaving a density gradient of zero. The formula for the density ratio, R, is: The density ratio of a column of seawater is a measure of the relative contributions of temperature and salinity in determining the density gradient. At a density ratio of 1, temperature and salinity are said to be compensated: their density signatures cancel, leaving a density gradient of zero. The formula for the density ratio, R, is: R = αθz/βSz, where When a water column is 'doubly stable'--both temperature and salinity contribute to the stable density gradient--the density ratio is negative (a doubly unstable water column would also have a negative density ratio, but does not commonly occur). A statically stable water column with a density ratio between 0 and 1 (cool fresh overlying warm salty) can support diffusive convection, and a statically stable water column with a density ratio larger than 1 can support salt fingering. Density ratio may also be used to describe thermohaline variability over a non-vertical spatial interval, such as across a front in the mixed layer. If the signs of both the numerator and denominator are reversed, the density ratio remains unchanged. A related quantity which avoids this ambiguity as well as the infinite values possible when the denominator vanishes is the Turner angle, Tu.