Ozone Hole Meteorology: 2008 Potential Vorticity
The Antarctic polar vortex acts as a barrier to the exchange of polar and midlatitude air. The potential vorticity (PV) is a conserved quantity that acts as a tracer for motion on an isentropic surface. Plotting contours of PV on an isentropic surface readily shows the extent of the polar vortex. In the Antarctic winter, the PV is more negative going from midlatitudes to the pole. The spacing of PV contours is very wide in the midlatitudes, very tight at the polar vortex edge, and then widens again inside of the vortex. The edge of the vortex is defined to be where the contours of PV are closest together. The area inside of this edge can be determined as the area of the polar vortex.
A useful quantity in analyzing PV and vortex behavior is the equivalent latitude. Since PV tends to decrease from the equator to the South Pole, we calculate the area under successive PV contours. The areas are rearranged so that they vary from 1 at the equator to 0 at the pole. The transformed contours of PV can be thought of as being symmetrically arranged around the pole and monotonically decreasing from the equator to the pole. The latitudes on this transformed map projection are called equivalent latitudes. Plotting PV vs. equivalent latitude shows an interesting shape: an "S" curve, where the upswing area of the "S" is located at the vortex edge. Finding the maximum in the first derivative of PV with respect to equivalent latitude determines the vortex edge.
Comparison to all years
The following figures show the daily progression through the ozone hole season, comparing the current year to the climatology of all other years.
-- click on a link for a PDF figure --