Influid dynamics, abarotropic fluid is a fluid whose density is a function of pressure only.[1] The barotropic fluid is a useful model of fluid behavior in a wide variety of scientific fields, from meteorology to astrophysics.
The density of most liquids is nearly constant (isopycnic), so it can be stated that their densities vary only weakly with pressure and temperature. Water, which varies only a few percent with temperature and salinity, may be approximated as barotropic. In general, air is not barotropic, as it is a function of temperature and pressure; but, under certain circumstances, the barotropic assumption can be useful.
Inastrophysics, barotropic fluids are important in the study of stellar interiors or of the interstellar medium. One common class of barotropic model used in astrophysics is apolytropic fluid. Typically, the barotropic assumption is not very realistic.
Inmeteorology, abarotropic atmosphere is one that for which the density of the air depends only on pressure, as a resultisobaric surfaces (constant-pressure surfaces) are also constant-density surfaces. Such isobaric surfaces will also beisothermal surfaces, hence (from thethermal wind equation) thegeostrophic wind will not vary with depth. Hence, the motions of a rotating barotropic air mass is strongly constrained. The tropics are more nearly barotropic than mid-latitudes because temperature is more nearly horizontally uniform in the tropics.
Abarotropic flow is a generalization of a barotropic atmosphere. It is a flow in which the pressure is a function of the density only and vice versa. In other words, it is a flow in which isobaric surfaces are isopycnic surfaces and vice versa. One may have a barotropic flow of a non-barotropic fluid, but a barotropic fluid will always follow a barotropic flow. Examples include barotropic layers of the oceans, an isothermal ideal gas or anisentropic ideal gas.
A fluid which is not barotropic isbaroclinic, i. e., pressure is not the only factor to determine density. For a barotropic fluid or a barotropic flow (such as a barotropic atmosphere), thebaroclinic vector is zero.
If is expressible as a function of only, that is,, the in Eq. 5-66 is integrable. Fluids having this characteristic are calledbarotropic fluids.