Interactive comment on “Long term changes in the upper stratospheric ozone at Syowa, Antarctica” by K. Miyagawa et al

The history of depletion of stratospheric ozone over Antarctica in the austral spring is well known and well documented from the time of the discovery [Farman et al, 1985]. The rapid increase in this depletion during the 1990s [Solomon, 1999] is now being followed by a leveling off of the annual depletion [Salby et al., 2011]. The cause of this depletion again is well known; excess stratosphere chlorine from man-made chlorofluorocarbons (CFCs) entering into chemical reactions at various heights and temperatures [Molina and Roland, 1974; Solomon et al., 1986]. The first stage of the atmospheric response to the implementation of the 1987 Montreal Protocol and subsequent revisions, a lessening in the ozone reduction has been noted in the Northern mid-latitudes [Newchurch et al., 2003]. The second stage response, a statistically significant ozone increase has not yet been detected [Solomon et al., 2005; WMO, 2011]. Over Antarctica, no stage of recovery however has yet to be detected [WMO, 2011; and references therein]. The Dobson ozone spectrophotometer measurements provide not only estimates of total ozone column above the surface, but also vertical profile information. The Umkehr technique has been used since the 1930s [Götz et al., 1934] to derive the vertical ozone profile from zenith sky measurements. The algorithm is described elsewhere [Petropavlovskikh et al., 2009]. We investigate the information in the data from Syowa ground-based station (69.0S, 39.6E) which has been collecting ozone profiles from Dobson Umkehr measurements since 1977 [Miyagawa et al., 2009a], for long-term changes in the upper and middle stratospheric ozone. The re-evaluated Umkehr data-sets from the Syowa Japanese ground-based Dobson station [Miyagawa et al., 2009b] are used for this study (Section 2), with some further data analysis, and more data. The primary investigation is upper stratosphere where the variability is controlled by chemical reactions influenced by the anthropogenic ozone-depleting substances (ODS) and should be the place for detection of ozone recovery [Newchurch et al., 2003]. The high inter-annual variability in the Antarctica region and the changes in the atmosphere from other factors since 1977 must be well quantified to be able to detect the signal due to ODS. We will be using a number of well-known proxies (Table 1) to remove the effects of both dynamic and long term variables, as well as the EESC record, using various age-of-air scenarios. The ODS concentrations are often represented by the time series of the EESC (equivalent effective stratospheric chlorine) concentration that are based on the known budgets of the anthropogenic and natural sources of CFCs, halogens and bromines, understanding of the life-time of these species in the atmosphere, and estimates of the transport/mixing of ODS from the tropical troposphere to stratosphere and from tropics to high latitudes by a meridional transport and vertical mixing (Brewer Dobson Circulation, or BDC). The ODS concentrations over Polar region (or EESC curves) are defined by the “age of the transported air” [WMO, 2011]. We complement and verify the analysis of ground-based measurements with the recently released SBUV Merged Ozone Dataset Version 8.6, Overpass data.