Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 6 3 2006 10.5194/acpd-6-3883-2006 http://www.atmos-chem-phys-discuss.net/6/3883/2006/ http://www.atmos-chem-phys-discuss.net/6/3883/2006/acpd-6-3883-2006.html http://www.atmos-chem-phys-discuss.net/6/3883/2006/acpd-6-3883-2006.pdf 3883 3912 2006-05-16 Search for evidence of trend slow-down in the long-term TOMS/SBUV total ozone data record: the importance of instrument drift uncertainty and fingerprint detection R. S. Stolarski S. Frith NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA Science Systems and Applications, Inc., Lanham, MD 20706, USA We have developed a merged ozone data (MOD) data set for the period October 1978 through October 2005 combining total ozone measurements (version 8 retrieval) from the TOMS (Nimbus 7, Meteor 3, and Earth Probe) and SBUV/SBUV2 (Nimbus 7, NOAA 9/11/16) series of satellite instruments. We use MOD to search for evidence of ozone recovery in response to the observed leveling off of chlorine compounds in the stratosphere. A crucial step in any time series analysis is the evaluation of uncertainties. In addition to the standard statistical time-series uncertainties, we evaluate the possible instrumental drift uncertainty for the MOD data set. We combine these two sources of uncertainty and apply them to a cumulative sum of residuals (CUSUM) analysis for trend slow-down. For the quasi-global mean between 60° S and 60° N, the apparent slow-down in trend is found to be clearly significant if instrument uncertainties are ignored. When instrument uncertainties are added, the slow-down becomes marginally significant at the 2σ level. For the mid-latitudes of the northern hemisphere (30° to 60° N) the trend slow-down is significant. For the mid-latitudes of the southern hemisphere (30° to 60° S) it is not significant. The fingerprint of ozone recovery expected from model calculations suggests both northern and southern mid-latitude total ozone levels should recover together. Our result fails this fingerprint test and is therefore not a demonstration of the response of total ozone to the leveling off of chlorine.