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

Abstract

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 Experiment (SAGE) II solar occultation instrument and the Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument measured ozone profiles in the stratosphere and mesosphere from 1984-2005 and 2002-2012, respectively. 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 inter-calibrate 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 GOMOS' measurements to different extents. 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 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 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 1 month in time and 10 • 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 inflection point (so-called "hockey stick" form). The best estimate for the point of inflection was found to be the year 1997 for ozone between altitudes 35 and 45 km. At all latitudes and altitudes from 35 to 50 km we find a clear change in ozone trend before and after the inflection time. From 38 to 45 km, 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 % per decade. At mid-latitudes, the negative trend of 4-8 % per decade has changed to 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.

Sunset–sunrise difference in solar occultation ozone measurements (SAGE II, HALOE, and ACE–FTS) and its relationship to tidal vertical winds

“…The SSD near the stratopause is quantitatively consistent with the HALOE result of Brühl et al (1996), although they only analyzed two latitude bands at around 18 • N and 18 • S. SAGE II (red solid curve) shows a similar result to HALOE and ACE-FTS, at least qualitatively, but the SSD in the upper stratosphere is approximately twice as large as those resulting from the other data sets. The SAGE II results are essentially consistent with the results of McLinden et al (2009) and Kyrölä et al (2013), although the latter may be partially contaminated by seasonal/interannual ozone variations (see Sect. 3).…”

“…We see that the SR and SS profiles are not distributed evenly; e.g., there are no SR (SS) profiles from November to January (May to July) between 2001 and 2005 for SAGE II. This indicates that if the SSD is calculated by simply averaging all SR and SS profiles for a certain period (e.g., Kyrölä et al, 2013), it could be significantly contaminated by seasonal/interannual variations in ozone concentrations. In fact, Kyrölä et al (2013) reported that the SSD profile for 2001-2005 was considerably different to those recorded in the other periods (1985-1990, 1991-1995, and 1996-2000); we attribute this to contamination caused by uneven sampling during this period.…”

“…This indicates that if the SSD is calculated by simply averaging all SR and SS profiles for a certain period (e.g., Kyrölä et al, 2013), it could be significantly contaminated by seasonal/interannual variations in ozone concentrations. In fact, Kyrölä et al (2013) reported that the SSD profile for 2001-2005 was considerably different to those recorded in the other periods (1985-1990, 1991-1995, and 1996-2000); we attribute this to contamination caused by uneven sampling during this period. To resolve this issue, we calculated the SSD in SR-SS pairs that have both SR and SS profiles measured at almost the same time (see the open stars in Fig.…”

“…However, note that there are few observations of diurnal variations in the stratosphere and thus the above assumption has not been confirmed. In addition, factor (3) may not have been properly considered in some studies (e.g., in the context of interannual variations of the SSD, as shown by Kyrölä et al, 2013;see Sect. 3).…”

“…For SAGE II, the SSD is reported to be up to 10 % between altitudes of 35 and 55 km, with a maximum occurring in the tropics (cf. SAGE II version 5.9 data: Wang et al, 1996;version 6.2 data: McLinden et al, 2009; version 7 data: Kyrölä et al, 2013). For HALOE (version 17 data), Brühl et al (1996) reported an SSD of approximately 5 % in the tropical stratopause.…”