Potential temperature

The potential temperature of a parcel of fluid at pressure P {displaystyle P} is the temperature that the parcel would attain if adiabatically brought to a standard reference pressure P 0 {displaystyle P_{0}} , usually 1,000 hPa (1,000 mb). The potential temperature is denoted θ {displaystyle heta } and, for a gas well-approximated as ideal, is given by The potential temperature of a parcel of fluid at pressure P {displaystyle P} is the temperature that the parcel would attain if adiabatically brought to a standard reference pressure P 0 {displaystyle P_{0}} , usually 1,000 hPa (1,000 mb). The potential temperature is denoted θ {displaystyle heta } and, for a gas well-approximated as ideal, is given by where T {displaystyle T} is the current absolute temperature (in K) of the parcel, R {displaystyle R} is the gas constant of air, and c p {displaystyle c_{p}} is the specific heat capacity at a constant pressure. R / c p = 0.286 {displaystyle R/c_{p}=0.286} for air (meteorology). The concept of potential temperature applies to any stratified fluid. It is most frequently used in the atmospheric sciences and oceanography. The reason that it is usedin both fluids is that changes in pressure can result in warmer fluid residing under colder fluid – examples being dropping air temperature with altitude and increasing water temperature with depth in very deep ocean trenches and within the ocean mixed layer. When potential temperature is used instead, these apparently unstable conditions vanish as a parcel of fluid is invariant along its isolines.