Improved Tropospheric Ozone Residual and Comparisons to the GMI Model

Our tropospheric ozone residual (TOR) is produced by subtracting the stratospheric ozone column measured by MLS and the tropospheric ozone column measured by OMI. In our approach we use backward and forward trajectories from four days of MLS V2.2 measurements to boost the horizontal resolution of the stratospheric ozone field. The MLS stratospheric column is then subtracted from the OMI Col. 3 total ozone column. High reflectivity scenes (clouds) are no longer discarded - the OMI cloud pressure and radiative cloud fraction is used to adjust the surface pressure to the cloud centroid pressure. The subsequent TOR fields are validated by comparing them to ozonesondes. Our TOR fields show a 0.8 correlation to sonde columns; a clear improvement over earlier calculations. OMI-MLS TOR from 2005 and 2006 are compared with the Global Modeling Initiative (GMI) derived tropospheric column. The results show that the OMI-MLS TOR underestimates the tropospheric column. GMI tropospheric column and OMI-MLS TOR compare better if the lowest 1.5 km of the GMI column is excluded. This is consistent with a global -7 DU low offset from the sonde columns that is probably due to lack of OMI boundary layer ozone sensitivity. The GMI model zonal distribution also shows relatively higher tropospheric columns at mid latitudes and lower column amounts at high latitudes compared to the OMI-MLS TOR.