Changes in Vertical Distribution of Ozone as Seen by SAGE-II, GOMOS and OSIRIS
Tamminen, Johanna¹; Kyröllä, Erkki¹; Sofieva, Viktoria¹; Laine, Marko¹; Adams, Cristen²; Degenstein, Doug²; Zawodny, Joseph^3
1Finnish Meteorological Institute, FINLAND; ²University of Saskachewan, CANADA; ³NASA Langely, UNITED STATES

We present the evolution of the vertical distribution of the stratospheric ozone by combining data from three satellite instruments measuring ozone with good (1-3 km) vertical resolution: ERBS/SAGE II (1984-2005), Odin/OSIRIS (2001-), and Envisat/GOMOS (2002-2012). SAGE II is a solar occultation instrument, GOMOS a stellar occultation instrument and OSIRIS measures in limb geometry scattered solar light in terminator conditions. Only nighttime measurements of GOMOS are considered.

The three instruments have common measurement period in 2002 - 05, which is used for assessing systematic differences in the data sets. The overall agreement between these instruments is found to be excellent. The difference between SAGE II and GOMOS is within 3% and relatively constant in latitude below 35 km. Diurnal variability of ozone causes differences above 35 km and it is also seen as a difference between SAGE II sunset and sunrise measurements. Above 40 km the diurnal variability becomes larger and stronger differences between nighttime GOMOS measurements and sunrise/sunset measurements of SAGE II are found. The overall agreement between GOMOS and OSIRIS is also very good and around 2% at 23-50 km. The occultation technique of SAGE II and GOMOS is in principle self calibrating, but still a special attention on possible instrumental drifts is needed. The common measurement period of GOMOS and OSIRIS in 2002-2012 can be used to investigate possible drifts between GOMOS and OSIRIS.

In this presentation we discuss SAGE II - GOMOS combined data set (1984 - 2011), which covers latitudes 60S-60N. The data set is analyzed by fitting a time series model to the data. At altitudes 25 -50 km clear change in ozone trend is found around year 1997. This data set does not cover the high latitudes because the two instruments do not measure the same seasonal periods. By including also OSIRIS measurements we can extend the time series to cover also the polar areas. Time series analysis will be performed for the combined SAGE II - GOMOS - OSIRIS (1984 - 2011) data set as well.