Atmos. Chem. Phys. Discuss., 13, 10661-10700, 2013
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Combined SAGE II-GOMOS ozone profile data set 1984–2011 and trend analysis of the vertical distribution of ozone
E. Kyrölä1, M. Laine1, V. Sofieva1, J. Tamminen1, S.-M. Päivärinta1, S. Tukiainen1, J. Zawodny2, and L. Thomason2
1Finnish Meteorological Institute, Earth Observation Unit, P.O. Box 503, 00101 Helsinki, Finland
2NASA Langley Research Center, MS-475, Hampton, VA 23681-2199, USA

Abstract. We have studied data from two satellite occultation instruments in order to generate a high vertical resolution homogeneous ozone time series of 26 yr. The Stratospheric Aerosol and Gas Experimen (SAGE) II solar occultation instrument from 1984–2005 and the Global Ozone Monitoring by Occultation of Stars instrument (GOMOS) from 2002–2012 measured ozone profiles in the stratosphere and mesosphere. Global coverage, good vertical resolution and the self calibrating measurement method make data from these instruments valuable for the detection of changes in vertical distribution of ozone over time. As both instruments share a common measurement period from 2002–2005, it is possible to intercalibrate the data sets. We investigate how well these measurements agree with each other and combine all the data to produce a new stratospheric ozone profile data set. Above 55 km SAGE II measurements show much less ozone than the GOMOS nighttime measurements as a consequence of the well-known diurnal variation of ozone in the mesosphere. Between 35–55 km SAGE II sunrise and sunset measurements differ from each other. Sunrise measurements show 2% less ozone than GOMOS whereas sunset measurements show 4% more ozone than GOMOS. Differences can be explained qualitatively by the diurnal variation of ozone in the stratosphere recently observed by SMILES and modelled by chemical transport models. For 25–35 km SAGE II sunrise and sunset and GOMOS agree within 1%.

The observed ozone bias between collocated measurements of SAGE II sunrise/sunset and GOMOS night measurements is used to align the two data sets. The combined data set covers the time period 1984–2011, latitudes 60° S–60° N and the altitude range of 20–60 km. Profile data are given on a 1 km vertical grid, and with a resolution of one month in time and ten degrees in latitude. The combined ozone data set is analyzed by fitting a time series model to the data. We assume a linear trend with an inflexion point (so-called "hockey stick" form). The best estimate for the point of inflexion was found to be the year 1997 for ozone between altitudes 35 and 45 km. At all latitudes and altitudes from 25 km to 50 km we find a clear change in ozone trend before and after the inflexion time. From 38 km to 45 km a negative trend of 0–3% per decade at the equator has changed to a small positive trend of 0–2% per decade except in the altitude range of 30–35 km where the ozone loss has even increased. At mid-latitudes the negative trend of 4–10% per decade has changed to to a small positive trend of 0–2% per decade.

Citation: Kyrölä, E., Laine, M., Sofieva, V., Tamminen, J., Päivärinta, S.-M., Tukiainen, S., Zawodny, J., and Thomason, L.: Combined SAGE II-GOMOS ozone profile data set 1984–2011 and trend analysis of the vertical distribution of ozone, Atmos. Chem. Phys. Discuss., 13, 10661-10700, doi:10.5194/acpd-13-10661-2013, 2013.
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