The GOME-type Tropical Tropospheric Ozone Essential Climate Variable (GTTO-ECV) satellite data record and an updated S5P-BASCOE dataset

A tropospheric ozone time series from 1995 until end 2022 has been generated within ESA’s Climate Change Initiative+ programme. The GOME-type Tropical Tropospheric Ozone Essential Climate Variable (GTTO-ECV) satellite data record combines data from GOME, SCIAMACHY, OMI and the three GOME-2 missions. The retrieval is based on the Convective Cloud Differential technique, which limits the coverage to the tropical belt (20°S to 20°N). We generated two monthly mean data sets at 1° x 1° resolution: one corresponds to a tropospheric column up to 200 hPa as in the previous CCI data release (Heue et al., 2016), while the other is limited to 270 hPa and includes the operational Sentinel-5P data as an additional sensor. An internal reprocessing of S5P CCD using 200 hPa is planned but might not be ready in time. Besides a consistent reprocessing of the CCD data for individual sensors, we also updated the harmonising scheme. The mean bias as well as the mean annual cycle relative to the reference instrument (OMI) are used to correct for the differences between the sensors.

Heue et al (2016) claimed a mean tropospheric ozone trend of +0.7 DU/decade (1995-2015). How did the trend change with the extended data set? The GTTO-ECV data record will be used to investigate the tropical mean trend as well as temporal and local changes in the trends. Also, a comparison with modelled tropospheric ozone data and the respective trends might be given.

As a second data product we provide the global S5P-BASCOE tropospheric ozone data. The complete time series of the S5P total ozone columns has been reprocessed recently. The reprocessing includes an update of the Level1 data as well as reprocessed cloud and O3 total columns. We use the reprocessed OFFL ozone data set in combination with BASCOE assimilation constrained stratospheric ozone profiles to calculate the tropospheric ozone columns. Relative to ground-based observations the total OFFL columns show a small positive bias. Before the retrieval of the tropospheric ozone column this bias is subtracted. The updated tropospheric ozone columns might also be compared to modelled tropospheric ozone columns.