Quadrennial Ozone Symposium Edinburgh, Scotland 5. – 9. September 2016 Total Ozone Column above Hohenpeissenberg – Comparison of different ground based and satellite borne instruments U.H. Köhler and W. Steinbrecht Deutscher Wetterdienst, Met. Obs. Hohenpeissenberg, Hohenpeissenberg, Germany (ulf.koehler@dwd.de) Summary Regular total ozone column (TOC) measurements using different types of spectrometers (Dobson No. 104 since 1967, Brewer No. 010 since 1983) have been performed at the Meteorological Observatory Hohenpeissenberg (MOHp) for almost 50 years. The observation of the ozone layer with satellite borne instruments started in the early 1970ties. Comparison of D104 and BR010 show very good agreement (rel. diff. less than 0.5%) with the well known annual oscillation of about 1.5%. Application of the real effective temperature Teff (provides individual Effective Ozone Absorption Coefficients EACs) of the ozone layer reduces this annual oscillation significantly. The comparison of various satellite data sets (SBUV, TOMS, EPTOMS, OMI, GOME, GOME2, SCIAMACHY) with the ground based instruments shows some differences between Dobson and Brewer as well as between different satellite data. The application of Teff in the ozone layer instead of -46O C (resulting in Dobson-EACs improves the agreement with some of satellite data (OMI, SBUV, Sciamachy, GOME & GOME2). Comparison Dobson No. 104 and Brewer No. 010 Original data and Dobson data Teff-corrected Figure 1. Comparison of simultaneous (within 15 minutes) Dobson No. 104 and Brewer No. 010 TOC-data as monthly means. Blue curve: original data, red curve Dobson data corrected applying effective temperature of the ozone layer, Brewer data corrected using mue-values valid for MOHp height of the ozone layer Comparison Dobson and Brewer Fig.1 represents the comparison of the two independently calibrated spectrophotometers at MOHp: D104 since 1968, calibrated against the world standards D083 and D065 (both from NOAA, Boulder); BR010 since 1984, calibrated against the traveling standard BR017 (IOS/Environment Canada). The relative differences of simultaneous measurements (within 15 minutes, blue curve for monthly means) agree within -0.5% in the long term average with an annual oscillation of up to 1.5%. The use of a constant temperature of the ozone layer to define nominal absorption coefficients for each instrument type was detected as reason for this characteristic. The application of real Teffs from sonde data - their effect on Dobson is larger than on Brewer - improves the agreement significantly (red curve: use of EACs incl. a slight correction for the imprecise calculation of the slant path through the ozone layer (Brewer Mue-value)). Comparison Dobson/Brewer with satellite instruments The comparison of both spectrometer with various satellite borne instruments in fig. 2 (Dobson) and 3 (Brewer) shows the good and prevailingly constant agreement between the observations from ground and space. The monthly means of the relative differences are mostly within ± 2% (except some outliers) with only small trends. Only TOMS Vs8 (BR010), EPTOMS (both), OMI (both) and especially GOME2 (both) have a larger bias. Significant annual oscillations are visible only between Dobson and SCIA and GOME, respectively (see fig. 5 and 6). Application of effective ozone absorption coefficients on Dobson data The effect of a Teff-based EACs-correction for the Dobson data is shown in fig. 4: The only obvious change is, that the agreement with TOMS Vs8 gets worse, which is probably due to the incomplete EAC-correction before 1984 (sonde data not processd yet). A detailed examination of individual satellite data, however, reveals that the observed annual oscillation between Dobson and GOME (see as example figure 5 and 6) and SCIA is reduced. Dobson data are now closer to the Brewer. Comparison D104 and BR010 with various satellite instruments Comparison D104 and BR010 with various satellite instruments Comparison D104 and BR010 with various satellite instruments Figure 2. Comparison of D104 with TOMS Vs. 8, SBUV, EPTOMS Vs. 8, OMI, SCIAMACHY, GOME and GOME2; monthly means of daily overpasses Figure 3. Comparison of BR010 with TOMS Vs. 8, SBUV, EPTOMS Vs. 8, OMI, SCIAMACHY, GOME and GOME2; monthly means of daily overpasses Figure 2. Comparison of D104 with TOMS Vs. 8, SBUV, EPTOMS Vs. 8, OMI, SCIAMACHY, GOME and GOME2; monthly means of daily overpasses Figure 3. Comparison of BR010 with TOMS Vs. 8, SBUV, EPTOMS Vs. 8, OMI, SCIAMACHY, GOME and GOME2; monthly means of daily overpasses Comparison D104 (Teff-corrected) with various satellite instruments Figure 4. Comparison of D104 (Teff-corrected since 1984) with TOMS Vs. 8, SBUV, EPTOMS Vs. 8, OMI, SCIAMACHY, GOME and GOME2; monthly means of daily overpasses Comparison D104 (original & Teff-corrected) and BR010 with GOME Conclusion The agreement of D104 and BR010 and of both instruments with the satellites are prevailingly good with similar patterns. Application of Dobson-EACs significantly improves the Dobson-Brewer agreement and the Dobson - SCIA- and GOME-comparison (smaller annual oscillations). The deterioration of the TOMS Vs. 8 comparison is probably caused by the incomplete EAC-correction. Acknowledgement Satellite data were provided by various data sources. Thanks to the colleagues from NASA, NOAA, ESA, EUMETSAT, University of Bremen and University of Thessaloniki for operating the satellite instruments, processing the data and making these data records available for scientific investigations. Figure 5. Comparison of D104 (ori.)& BR010 (ori.) with GOME ; monthly means of daily overpasses Figure 6. Comparison of D104 (Teff-corrected ) & BR010 (ori.) with GOME ; monthly means of daily overpasses Meteorological Observatory Hohenpeissenberg http://www.dwd.de/ozon