OZONE AND POTENTIAL VORTICITY AT THE SUBTROPICAL TROPOPAUSE BREAK

Ozone measurements near 200 mbar from two flights between California a nd Tahiti are interpreted using maps of potential vorticity (PV) on is entropic surfaces. We focus on extremely abrupt changes in ozone mixin g ratio observed at latitudes of 13 degrees N and 23.5 degrees N. Thei r proximity to strong PV gradients on the 350 K isentropic surface sho ws that they are associated with crossings of tile subtropical tropopa use. Small-scale anticorrelations between ozone and carbon dioxide nea r one of the two ozone transitions indicate that some stratosphere-tro posphere exchange does occur in this region. Ozone mixing ratios on th e stratospheric side of the subtropical tropopause varied from 50 to 1 00 parts per billion by volume, a range that is more commonly associat ed with the midlatitude troposphere and is much less than seen on the stratospheric side of the midlatitude tropopause.