The CCD_IUP tropospheric ozone dataset

Download link: IUP_CCD dataset (1996-2018) 

Figure caption. Seasonal tropospheric ozone trends in units of DU/decade from 1996 to 2015.

References

• Leventidou, E., Eichmann, K.-U., Weber, M., and Burrows, J. P.: Tropical tropospheric ozone columns from nadir retrievals of GOME-1/ERS-2, SCIAMACHY/Envisat, and GOME-2/MetOp-A (1996–2012), Atmos. Meas. Tech., 9, 3407-3427, doi:10.5194/amt-9-3407-2016, 2016.
• Leventidou, E., Weber, M., Eichmann, K.-U., Burrows, J. P., Heue, K.-P., Thompson, A. M., and Johnson, B. J.: Harmonisation and trends of 20-year tropical tropospheric ozone data, Atmos. Chem. Phys., 18, 9189-9205, https://doi.org/10.5194/acp-18-9189-2018, 2018.

Synopsis

Tropical Tropospheric Columns of Ozone (TTCO) can be retrieved from satellite data using the total column of ozone and cloud information from the same nadir viewing satellite instrument. The Convective Clouds Differential (CCD) is a statistical method of retrieving tropical tropical tropospheric ozone columns using monthly mean data. The technique assumes that ozone columns above deep convective clouds (ACCO), typically in the Pacific region, simulate stratospheric ozone, which is subtracted from the total ozone columns for cloud free conditions to obtain the tropospheric column as residual (Ziemke et al., 1998). Due to the basic assumption that the stratospheric ozone column is invariant as a function of longitude the method is only appropriate for the tropics.

The CCD_IUP dataset is based upon monthly tropical tropospheric columns of ozone (TTCO) retrieved in a 2.5° latitude by 5° longitude grid between 20°S and 20°N from GOME/ERS-2, SCIAMACHY/ENVISAT and GOME-2/MetopA data covering the period between 1996 and 2018. The CCD_IUP data were validated by comparisons with Southern Hemisphere ADditional OZonesondes (SHADOZ) data. Biases are within ±5 DU and root-mean-square (RMS) deviation of less than 10 DU are found for all instruments (Leventidou et al., 2016).

As small differences in TTCO between the individual instruments were evident, it was necessary to develop a scheme to harmonise the three datasets into one consistent time series starting from 1996 until 2017. Correction offsets (biases) between the instruments using SCIAMACHY as intermediate reference have been calculated in order to merge the TTCO data. No corrections were applied for GOME, and mean biases with respect to SCIAMACHY in the overlapping period (2007–2012) were calculated and applied to correct the GOME-2 data (Leventidou et al., 2018).

The merged CCD data are stored in monthly netcdf formatted files using the following naming convention: CCD_IUP-OZONE-L3C-TTOC-UBR_CCDV1merged-YYYYMM-fv0001.nc, where YYYY is the year and MM the month. The monthly mean tropical tropospheric ozone columns are given in unit of mole concentration mol/m² along with the uncertainties of the TTCO retrieved from the original data (1996-2002 GOME, 2003-2012 SCIAMACHY, and 2013-2017 GOME-2). In order to convert to DU and to molecules/cm² ozone columns have to by multiplied by 2241.15 and 6.022x10¹⁹, respectively. The data cover the longitudes from -180° to 180° and latitudes between -20° and 20°.