Vortex-averaged ozone losses in the winter 2002/2003

A total ozone depletion of 67 Dobson units from December 1, 2002, to March 10, 2003, has been derived by the vortex average method taking into account both diabatic descent of the air masses and transport of air into the vortex. Defining the Vortex Edge Potential vorticity (PV) criteria are used to define the extent of the Arctic vortex: The PV value exhibiting the largest gradient in PV as a function of equivalent latitude is used as the edge of the vortex. In case of multiple maxima within 10% of each other the PV value closest to the previous day is used. If the PV gradient with respect to equivalent latitude is smaller than 1.0 × 10−6 Km2s−1kg−1/degree for an isolated point, the average PV value of the previous and the next day is used. If two or more points have a gradient below this limit, the vortex is considered broken down or not yet established. In such cases the PV value of the “edge” is determined such that the equivalent latitude is the same as for the level above. At 475 K and above the vortex was established by December 10, 2002, and did not break down before April. At 435 K the vortex was established on January 2, 2003. At 400 K and below no vortex existed at any time in the winter 2002/03.