Three‐dimensional ozone transport during the ozone hole breakup in December 1987

Abstract

Since the onset of springtime ozone depletion in the Antarctic lower stratosphere, the question has arisen as to the extent to which transport of ozone hole material out into the surrounding regions might influence ozone levels at midlatitudes through a so‐called ozone hole dilution effect. One such event was previously identified which followed the vortex breakup during early December 1987, but the extent to which it was attributable to the presence of an Antarctic ozone deficit, rather than being the result of ozone transports which would have occurred anyway in the absence of an ozone hole, was not quantified at the time. Here we describe the results of a more detailed study of the December 1987 event, in which we have addressed this issue. A quasi‐conservative coordinate transformation technique is used on ozone data from the second stratospheric aerosol and gas experiment (SAGE II) to obtain a three‐dimensional description of the hemispheric ozone distribution immediately prior to the event. A contour advection technique is used to describe the stratospheric material evolution during the period, and this provides a detailed depiction of the quasi‐horizontal ozone transports which occurred at the time. The calculated dynamically induced total ozone changes during the period are then separated into contributions arising from “vertical” and “horizontal” advection. The potential vorticity tendency form of the quasi‐geostrophic omega equation is solved to provide insight into the horizontal scales and vertical domain of the dynamical “forcing” primarily responsible for the vertical advection component. Finally, by imposing a “no ozone hole” ozone distribution during the period, and comparing the resulting ozone distribution with that obtained with the unmodified reconstruction, we then isolate a significant component of the observed midlatitude total ozone changes which was attributable solely to the presence of Antarctic ozone depletion.