Ozone in the near-tropopause region: Comparison of NASA Global Modeling Initiative simulations with SAGE II and ozonesonde climatologies

We use monthly mean, tropopause-referenced ozone climatologies constructed from multiple years of ozonesonde and SAGE II satellite data to evaluate near-tropopause ozone mixing ratios and vertical gradients generated by the NASA Global Modeling Initiative (GMI) three-dimensional chemistry and transport model. Most of the sonde station data sets exceed 10 years in length, and the SAGE II climatology was constructed from observations made between December, 1984, and November, 2002. The model includes a full description of stratospheric and tropospheric physicochemical processes extending from the surface to above the stratopause with a vertical resolution near the tropopause of approximately1 km. This “combined” CTM can be driven with several sets of meteorological data; here we focus on results using meteorological data from the NASA GEOS-4 AGCM. The GEOS-4 AGCM has been shown to have good stratosphere-to-troposphere mass and ozone fluxes. Preliminary results indicate that tropical profiles of modeled and observed ozone mixing ratios and vertical gradients agree best, with larger discrepancies at higher latitudes. We investigate the various factors causing these discrepancies and compare results of simulations using other meteorological data sets to drive the CTM.