18.2. Vorticity

Another variable that meteorologists commonly use is the amount of local spin in the atmosphere or vorticity. There are two primary components of vorticity: relative vorticity and Earth’s vorticity. Earth’s vorticity we have already talked about in terms of the Coriolis parameter. The relative vorticity is calculated using the following equation in algebraic form:

\[ \text{vorticity} = \zeta = \frac{\Delta v}{\Delta x} - \frac{\Delta u}{\Delta y} \]

Absolute vorticity is the relative vorticity plus Earth’s vorticity.

\[ \text{Absolute Vorticity} = \eta = \zeta + f \]

Earth’s vorticity, \(f\), is simply the Coriolis parameter (\(f = 2\Omega\sin{\phi)}\), where \(\phi\) is the latitude.

Displaying the relative or absolute vorticity helps to identify troughs and ridges and will be important to diagnosing vertical motions in dynamic and synoptic meteorology. Many meteorological phenomena are rotating systems, which will all have varying degrees of vorticity.