baroclinic

Baroclinic is a property of a fluid, especially the atmosphere or oceans, describing a state in which density is not a function of pressure alone and surfaces of constant density (isopycnals) are not parallel to surfaces of constant pressure (isobars). In a barotropic fluid, density depends only on pressure, and the isobar and isopycnal surfaces align, leading to zero baroclinicity. Mathematically, baroclinicity occurs when the cross product ∇ρ × ∇p is nonzero.

In meteorology, the atmosphere is considered baroclinic where horizontal temperature gradients exist, such as along fronts. This misalignment allows generation of vorticity and is a source of available potential energy that can be converted into kinetic energy through baroclinic instability. This instability helps amplify mid-latitude disturbances and forms cyclones and fronts. The degree of baroclinicity varies with latitude, season, and vertical structure, with the upper troposphere often displaying more baroclinic characteristics than the surface layer.

In oceanography, baroclinicity arises from vertical density stratification. Because density changes with depth, surfaces of equal density are tilted, producing vertical shear and complex current structures. Baroclinic effects influence the growth of instabilities and the distribution of heat and nutrients in the ocean.

Overall, baroclinicity describes the misalignment of pressure and density (or temperature) fields and is central to the development of weather systems in the midlatitudes and to the layered dynamics of the oceans.