Isentropic Cross-Tropopause Ozone Transport in the Northern Hemisphere

Abstract

This paper investigates isentropic ozone exchange between the extratropical lower stratosphere and the subtropical upper troposphere in the Northern Hemisphere. The quantification method is based on the potential vorticity (PV) mapping of Stratospheric Aerosol and Gas Experiment (SAGE)-II ozone measurements and contour advection calculations using the NASA Goddard Space Center Data Assimilation Office (DAO) analysis for the year 1990. The magnitude of the annual isentropic stratosphere-to-troposphere ozone flux is calculated to be approximately twice the flux that is directed from the troposphere into the stratosphere. The net effect is that 46 10 9 kg yr 1 of ozone are transferred quasi horizontally from the extratropical lower stratosphere into the subtropical upper troposphere between the isentropic surfaces of 330 and 370 K. The estimated monthly ozone fluxes show that the isentropic cross-tropopause ozone transport is stronger in summer/fall than in winter/ spring, and this seasonality is more obvious at the upper three levels (i.e., 345, 355, and 365 K) than at 335 K. The distributions of the estimated monthly ozone fluxes indicate that the isentropic stratosphere-to-troposphere ozone exchange is associated with wave breaking and occurs preferentially over the eastern Atlantic Ocean and northwest Africa in winter and over the Atlantic and Pacific Oceans in summer.

Stratosphere‐troposphere exchange of mass and ozone

“… Jing et al [2004] apply PV ozone mapping to the same contour advection method used by Dethof et al [2000] to investigate the isentropic cross‐tropopause transport of ozone. They find that the maximum net downward flux of ozone occurs in the summer months in agreement with the results shown in Figure 2c.…”

“… Dethof et al [2000] examine the isentropic cross‐tropopause mass transport using contour advection [ Norton , 1994; Waugh and Plumb , 1994]. Jing et al [2004] extend this method to examine the isentropic ozone flux. However, no prior studies have examined the net global ozone flux on the basis of both diabatic and adiabatic transport.…”

Influence of isentropic transport on seasonal ozone variations in the lower stratosphere and subtropical upper troposphere

“…Estimates of the global net diabatic cross‐tropopause ozone flux are between 400 ∼ 500 × 10 9 kg yr −1 . On the other hand, the isentropic ozone STE has not been well quantified until a recent study by Jing et al [2004]. On the basis of contour advection and the correlation between ozone mixing ratio and potential vorticity, Jing et al [2004] estimated the isentropic cross‐tropopause ozone fluxes between 330 and 370 K in the NH.…”

“…This indicates that from a global viewpoint, the isentropic ozone STE seems to be a smaller contributor to the total ozone budget in the troposphere than the diabatic exchange. However, the isentropic ozone transport from stratosphere to troposphere (S→T) in the NH mostly occurs around 30°–40°N latitude [ Jing et al , 2004] and the maximum diabatic S→T mass transport in the NH is located around 60°N latitude [ Schoeberl , 2004]. Therefore the isentropic STE could be significant in controlling regional ozone levels in the subtropical UT.…”

“…The purpose of the present study is to provide a global estimate of the isentropic ozone STE and to investigate its association with the seasonal ozone variations derived from ozonesonde observations in the LS/UT. As described by Jing et al [2004], PV is used to define the tropopause and to distinguish between stratospheric ozone and tropospheric ozone, because PV is conserved in isentropic transport and has larger absolute values in the stratosphere than in the troposphere. By applying contour advection, the development of filaments on PV contours during the isentropic transport is well depicted, and the cross‐tropopause transport ozone fluxes from troposphere to stratosphere (T→S) and from S→T are determined by calculating the amount of ozone within the filaments poleward and equatorward of the tropopause, respectively.…”