Deriving tropospheric ozone from assimilated profiles

van Peet, Jacob C. A.; van der A, Ronald J.

We derived global tropospheric ozone (O3) columns from GOME-2A (Global Ozone Monitoring Experiment) and OMI (Ozone Monitoring Instrument) O3 profiles, which were simultaneously assimilated into the TM5 (Tracer Model, version 5) global chemistry transport model for the year 2008. The horizontal model resolution has been increased by a factor of 6 for more accurate results. To reduce computational cost, the number of model layers has been reduced from 44 to 31. The model ozone fields are used to derive tropospheric ozone, which is defined here as the partial column between mean sea level and 6km altitude. Two methods for calculating the tropospheric columns from the free model run and assimilated O3 fields are compared. In the first method, we calculate the residual between assimilated total columns and the partial model column between 6km and the top of atmosphere. In the second method, we perform a direct integration of the assimilated O3 fields between the surface and 6km. The results are validated against tropospheric columns derived from ozone sonde measurements. Our results show that the residual method has too large a variation to be used reliably for the determination of tropospheric ozone, so the direct integration method has been used instead. The median global bias is smaller for the assimilated O3 fields than for the free model run, but the large variation makes it difficult to make definitive statements on a regional or local scale. The monthly mean ozone fields show significant improvements and more detail when comparing the assimilated O3 fields with the free model run, especially for features such as biomass-burning-enhanced O3 concentrations and outflow of O3 rich air from Asia over the Pacific.

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Zitierform:

van Peet, Jacob C. A. / van der A, Ronald J.: Deriving tropospheric ozone from assimilated profiles. 2019. Copernicus Publications.

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Rechteinhaber: Jacob C. A. van Peet

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