The more compact version is that for absolute vorticity, <math>\eta</math>, using the pressure system:
Here, <math>\rho</math> is density, u, v, and <math>\omega</math> are the components of wind velocity, and <math>\nabla_h</math> is the 2-dimensional (i.e. horizontal-component-only) del.
The terms on the RHS denote the positive or negative generation of absolute vorticity by divergence of air, twisting of the axis of rotation, and baroclinity, respectively.
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