3-DIMENSIONAL OZONE TRANSPORT DURING THE OZONE HOLE BREAKUP IN DECEMBER 1987

Since the onset of springtime ozone depletion in the Antarctic lower s tratosphere, the question has arisen as to the extent to which transpo rt of ozone hole material out into the surrounding regions might influ ence ozone levels at midlatitudes through a so-called ozone hole dilut ion effect. One such event was previously identified which followed th e vortex breakup during early December 1987, but the extent to which i t was attributable to the presence of an Antarctic ozone deficit, rath er than being the result of ozone transports which would have occurred anyway in the absence of an ozone hole, was not quantified at the tim e. Here we describe the results of a more detailed study of the Decemb er 1987 event, in which we have addressed this issue. A quasi-conserva tive coordinate transformation technique is used on ozone data from th e 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, an d this provides a detailed depiction of the quasi-horizontal ozone tra nsports which occurred at the time. The calculated dynamically induced total ozone changes during the period are then separated into contrib utions arising from ''vertical'' and ''horizontal'' advection. The pot ential 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 vert ical advection component. Finally, by imposing a ''no ozone hole'' ozo ne distribution during the period, and comparing the resulting ozone d istribution 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 Antarc tic ozone depletion.