Combined SAGE II–GOMOS ozone profile data set for 1984–2011 and trend analysis of the vertical distribution of ozone

摘要

We have studied data from two satellite occultation instruments in order togenerate a high vertical resolution homogeneous ozone time series of 26 yr. The Stratospheric Aerosol and Gas Experiment (SAGE) II solaroccultation instrument and the Global Ozone Monitoring byOccultation of Stars (GOMOS) instrument measured ozoneprofiles in the stratosphere and mesosphere from 1984–2005 and 2002–2012, respectively. Global coverage, good verticalresolution, and the self-calibrating measurement method make data from theseinstruments valuable for the detection of changes in vertical distribution ofozone over time. As both instruments share a common measurement period from2002–2005, it is possible to inter-calibrate the data sets. We investigatehow well these measurements agree with each other and combine all the data toproduce a new stratospheric ozone profile data set. Above 55 km, SAGE IImeasurements show much less ozone than the GOMOS nighttime measurements as aconsequence of the well-known diurnal variation of ozone in the mesosphere.Between 35–55 km, SAGE II sunrise and sunset measurements differ from GOMOS' measurements to different extents. Sunrise measurements show 2% less ozone than GOMOS, whereas sunsetmeasurements show 4% more ozone than GOMOS. Differences can be explainedqualitatively by the diurnal variation of ozone in the stratosphere recentlyobserved by SMILES and modeled by chemical transport models. Between 25–35 km, SAGE II sunrise and sunset measurements and GOMOS measurements agree within 1%.The observed ozone bias between collocated measurements of SAGE IIsunrise/sunset and GOMOS night measurements is used to align the two datasets. The combined data set covers the time period 1984–2011, latitudes60° S–60° N, and the altitude range of 20–60 km. Profile data aregiven on a 1 km vertical grid, and with a resolution of 1 month in time and10° in latitude. The combined ozone data set is analyzed by fitting atime series model to the data. We assume a linear trend with an inflectionpoint (so-called "hockey stick" form). The best estimate for the point ofinflection was found to be the year 1997 for ozone between altitudes 35 and45 km. At all latitudes and altitudes from 35 to 50 km we find a clearchange in ozone trend before and after the inflection time. From 38 to 45km, a negative trend of 4% per decade (statistically significant at 95%level) at the equator has changed to a small positive trend of 0–2% perdecade. At mid-latitudes, the negative trend of 4–8% per decade has changedto to a small positive trend of 0–2% per decade. At mid-latitudes near 20 km, the ozone loss has still increased whereas in the tropics a recovery is ongoing.