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:
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 statically stable water column with a density ratio between 0 and 1 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.