Atmos. Chem. Phys. Discuss., 10, 20405-20460, 2010
© Author(s) 2010. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
NDACC UV-visible total ozone measurements: improved retrieval and comparison with correlative satellite and ground-based observations
F. Hendrick1, J.-P. Pommereau2, F. Goutail2, R. D. Evans3, D. Ionov2,4, A. Pazmino2, E. Kyrö5, G. Held6, P. Eriksen7, V. Dorokhov8, M. Gil9, and M. Van Roozendael1
1Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
2LATMOS, CNRS, and University of Versailles Saint Quentin, Guyancourt, France
3Earth System Research Laboratory/Global Monitoring Division, National Oceanic and Atmospheric Administration (NOAA), Boulder, Colorado, USA
4Department of Atmospheric Physics, Research Institute of Physics, St. Petersburg State University, St. Petersburg, Russia
5Arctic Research Center, Finnish Meteorological Institute (FMI), Sodankyla, Finland
6Meteorological Research Institute, Universidade Estadual Paulista, Bauru, São Paulo, Brazil
7Danish Meteorological Institute, Copenhagen, Denmark
8Central Aerological Institute, Dolgoprudny, Russia
9Instituto de Tecnica Aerospacial (INTA), Torrejón de Ardoz, Spain

Abstract. Accurate long-term monitoring of total ozone is one of the most important requirements for identifying possible natural or anthropogenic changes in the composition of the stratosphere. For this purpose, the NDACC (Network for the Detection of Atmospheric Composition Change) UV-visible Working Group has made recommendations for improving and homogenizing the retrieval of total ozone columns from twilight zenith-sky visible spectrometers. These instruments, deployed all over the world in about 35 stations, allow measurements of total ozone twice daily with little sensitivity to stratospheric temperature and cloud cover. The NDACC recommendations address both the DOAS retrieval parameters and the calculation of air mass factors (AMF) needed for the conversion of O3 slant column densities into vertical column amounts. The most important improvement is the use of O3 AMF look-up tables calculated using the TOMS V8 O3 profile climatology, that allows accounting for the dependence of the O3 AMF on the seasonal and latitudinal variations of the O3 vertical distribution. To investigate their impact on the retrieved ozone columns, the recommendations have been applied to measurements from the NDACC/SAOZ (Système d'Analyse par Observation Zénithale) network. The revised SAOZ ozone data from eight stations covering all latitude regions have been compared to TOMS, GOME-GDP4, SCIAMACHY-TOSOMI, OMI-TOMS, and OMI-DOAS satellite overpass observations, as well as to those of collocated Dobson and Brewer instruments. A significant improvement is obtained after applying the new O3 AMFs, although systematic seasonal differences between SAOZ and all other instruments remain. These are shown to mainly originate from i) the temperature dependence of the ozone absorption cross sections in the UV being not or improperly corrected by some retrieval algorithms, and ii) the longitudinal differences in tropospheric ozone column being ignored by zonal climatologies. For those measurements sensitive to stratospheric temperature like TOMS, OMI-TOMS, Dobson and Brewer, the application of a temperature correction results in the almost complete removal of the seasonal difference with SAOZ, improving significantly the consistency between all ground-based and satellite total ozone observations.

Citation: Hendrick, F., Pommereau, J.-P., Goutail, F., Evans, R. D., Ionov, D., Pazmino, A., Kyrö, E., Held, G., Eriksen, P., Dorokhov, V., Gil, M., and Van Roozendael, M.: NDACC UV-visible total ozone measurements: improved retrieval and comparison with correlative satellite and ground-based observations, Atmos. Chem. Phys. Discuss., 10, 20405-20460, doi:10.5194/acpd-10-20405-2010, 2010.
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