A. Bracher, L. N. Lamsal, M. Weber, J. P. Burrows

1. Good agreement, but offset of about –2% • No clear seasonal bias • No clear solar zenith angle dependence • SCIA WFD average bias of –1% to –2% to GOME WFD at most latitudes • Larger bias in polar regions Note: retrievals based on level-1 v5.04 and ESM solar data • SCIA WFD shows an average bias of –1% to –2% compared to OMITOMS • Bias only gets larger with SZA >80°, total O3 < 250 DU and low number of comparisons • No clear dependences to seasons, latitudes, SZA, total O3 and cloud fraction are seen in the comparisons Comparison with Brewer measurements from 10 stations in the NH midlatitudes in 2003 (n=488) Summary plot of 63 orbits over Europe in 2003 (~ 9 orbits/ month) Global Comparisons of Total O3 from SCIAMACHY Weighting Function DOAS (WFD) Algorithm to OMI-TOMS, GOME WFD and Groundbased Measurements A. Bracher, L. N. Lamsal, M. Weber, J. P. Burrows University of Bremen, FB 1, Institute of Environmental Physics, P O Box 330440, D-28334 Bremen, Germany FAX: 0421-218-4555, email: bracher@uni-bremen.de Introduction Weighting Function DOAS (WFD) Adaptation to SCIAMACHY Global stratospheric ozone columns are currently derived from UV nadir spectra measured by the satellite instruments OMI on AURA (since 2004), SCIAMA-CHY on ENVISAT (since 2002) and GOME on ERS-2 (since 1995). The weighting function DOAS algorithm (WFD) has been used to derive total ozone from SCIAMACHY and GOME (see poster by Weber et al. 2006 on SCIAMACHY and GOME WFD algorithm). Here we present results from global validation of SCIAMACHY WFD to ground-based data (Brewer) and comparisons to GOME WFD and the OMI TOMS algorithm (OMI-TOMS). • Motivation: Problems in operational data (based on GDP V2.7 algorithm) Very good performance of WFD for GOME (see Weber et al. 2005): compared to Brewer measurements within 1% and no seasonal cycle ! • Adaptation to SCIAMACHY: Use of scaled SCIA FM O3 cross-section by 1.037 & wavelength shifted by +0.016 nm (based on investigation carried out with FTS and Bass and Paur O3 cross-section) Improved climatology (Lamsal et al., 2004) Implementation of appropriate Ring data bases SCIATRAN V2.x included in retrieval (online calculation) SACURA/OCRA cloud information (FRESCO as alternative) Improved topographic data base (15 km x 15 km) • Successful implementation: See first results also in Bracher et al. 2005 • Main feature of WFD (see Coldewey-Egbers et al. 2005): • Taylor expansion of optical depth spectrum around climatological total ozone (TOZclim) • Modelled radiative transfer quantities: reference optical depth (OD) and weighting function parameterised by TOZ, effective albedo, effective scene height, viewing geometry •  Improved treatment of Ring •  Ozone temperature correction •  Cloud cover and effective scene height from oxygen A-band absorption (FRESCO by Koellemeijer et al. 2001) including ghost vertical column correction •  Effective UV albedo (surface reflectance) from 377nm •  Spectral fitting window: 326.6-335nm •  TOMS V7 profile shape climatology (Wellemeyer et al. 1997) •  Vertical columns directly derived with no AMF conversion needed Comparisons to GOME Comparisons to Brewer day of year, 2003 day of year, 2003 solar zenith angle [°] Comparisons to OMI-TOMS algorithm Conclusions & Outlook (OMITOMS – SCIA WFD)/ SCIA WFD : • SCIAMACHY WFD shows constant bias of –1% to –2% to GOME WFD, Brewer measurements and OMI-TOMS. • Constant negative offset can be explained by calibration error in SCIAMACHY level-1 product. • The upcoming SCIAMACHY WFD version will account for the calibration error. • Despite bias, successful adaptation of WFD algorithm to SCIAMACHY: • large improvements compared to recent operat. SCIAMACHY v5.04 • negligible dependencies to seasons, latitudes, SZA, cloud fraction and total ozone. SCIA WFD and OMI-TOMS are compared on 12 days between Oct 2004 to Sep 2005 (one day per month). Because of different spatial resolutions (SCIAMACHY 60 km x 30 km, OMI 24 kmx18 km), data are binned into 1° lat x 1.25° lon spatial bins and then compared. The comparisons are shown for one single day as example with all results including mean relative deviation (mrd) and RMS of mrd and for all compared days only mrd and RMS of mrd as a function of latitude, time, SZA, total ozone and cloud fraction. OMI-TOMS were taken from http://toms.gsfc.nasa.gov/pub/omi/ data/ozone. Analysis - over 13 Apr 2005 - over 12 days from Oct 2004 to Sep 2005 Overview Total ozone distributions Northern Hemisphere Binned SCIA WFD OMITOMS Latitude Solar Zenith Angle (SZA) Southern Hemisphere Binned SCIA WFD OMITOMS References Bracher A., Lamsal L.N., Weber M., Bramstedt K., Coldewey- Egbers M., Burrows J. P. (2005) Global satellite validation of SCIAMACHY ozone columns with GOME WFDOAS. Atmos. Chem. Phys. 5: 2357-2368. Coldewey-Egbers M., Weber M., Lamsal L.N., de Beek R., Buchwitz M., Burrows J.P. (2005) Total ozone retrieval from GOME UV spectral data using the weighting function DOAS approach. Atmos. Chem. Phys. 5: 1015-1025. Lamsal L. N., Weber M., Tellmann S., Burrows J. P. (2004) Ozone column classified climatology of ozone and temperature profiles based on ozonesonde and satellite data, J. Geophys. Res. 109: D20304, doi:10.1029/2004JD004680. Weber M., Lamsal L.N., Coldewey-Egbers M., Bramstedt K., Burrows J. P. (2005) Pole-to-pole validation of GOME WFDOAS total ozone with groundbased data. Atmos. Chem. Phys. 5:1341-1355. Weber M., Lamsal L.N., Coldewey-Egbers M., Dhomse S., Bracher A., Burrows J. P. (2005) Weighting Function DOAS total ozone from GOME and SCIAMACHY during the last decade. ESA Atmos. Science Conference May 2006. Total Ozone Acknowledgements Cloud Fraction We thank DLR and ESA/ESRIN for providing GOME and SCIAMACHY calibrated level 1 spectral, and NASA and the OMI/AURA team for OMI level 3 data. This work is funded by ESA-ESRIN (project SciLoV). The SCIAMACHY and GOME WFDOAS data shown here were calculated on the HLRN (High-Performance Computer Center North) and NIC/JUMP (Juelich Multiprocessor System). Services and support are gratefully acknowledged.