Using DAO Model Potential Vorticities for Estimating Isentropic Cross-Tropopause Ozone Fluxes

The GEOS-1 datasets for the year of 1990 from the Data Assimilation Office (DAO) at NASA's Goddard Space Flight Center (GSFC) are used to estimate the isentropic stratosphere-troposphere exchange of ozone using the Contour Advection technique. The procedure involves using DAO potential vorticities (PV) to define the dynamical tropopause and to generate the global distributions of ozone from the monthly relationships between the DAO PV and the SAGE version 6.1 ozone. It is demonstrated that the inferred PV-O₃ relationship produces ozone profiles which are in good agreement with ozonesonde measurements with a standard deviation of about 0.07 ppmv. According to Hoerling, et al (1991), 3.5 PVU (1 PVU=10^-6 K m² kg^-1 s^-1) represents an optimal definition of the tropopause outside the tropics for the ECWMF dataset in January, 1979. This study extends the analysis of the 3.5 PVU tropopause to all seasons and shows that the 3.5 PVU tropopause is generally consistent with the thermal tropopause in mid-latitudes. Using the 3.5 PVU tropopause and ozone produced by the PV-O₃ relationship, we calculate the ozone fluxes across the tropopause along four isentropic layers (335 K, 345 K, 355 K and 365 K) by applying Contour Advection. The total annual stratosphere-to-troposphere isentropic ozone flux for the four layers in the NH is 191 Tg/yr (1 Tg=10{^9} kg). It is approximately 60% of the total annual stratospheric-to-troposphere ozone transport (335 Tg/yr in the NH) calculated from 3-D general circulation models (Crutzen, et al, 1995). We conclude that the potential vorticities obtained from the DAO assimilation model results well represent the tropopause when the value of 3.5 PVU is used and they produce a robust relationship with ozone which makes it feasible to estimate the isentropic cross-tropopause transport of ozone globally.