Thermal wind

The thermal wind is not actually a wind, but a vector difference in the geostrophic wind between two pressure levels  and , with . It is a wind shear. It is only present in an atmosphere with horizontal gradients of temperature (or in an ocean with horizontal gradients of density), i.e. baroclinicity. In a barotropic atmosphere the geostrophic wind is independent of height. The name stems from the fact that this wind flows around areas of low (and high) temperature in the same manner as the geostrophic wind flows around areas of low (and high) pressure.
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