Intercomparison of vertically resolved merged satellite ozone data sets: interannual variability and long-term trends

摘要

In the framework of the SI2N (SPARC (Stratosphere-troposphere Processes Andtheir Role in Climate)/IOC (International OzoneCommission)/IGACO-O3 (Integrated Global Atmospheric Chemistry Observations – Ozone)/NDACC (Network for the Detection of Atmospheric CompositionChange)) initiative, several long-term vertically resolved merged ozone datasets produced from satellite measurements have been analysed and compared.This paper presents an overview of the methods, assumptions, and challengesinvolved in constructing such merged data sets, as well as the first thoroughintercomparison of seven new long-term satellite data sets. The analysisfocuses on the representation of the annual cycle, interannual variability,and long-term trends for the period 1984–2011, which is common to all datasets. Overall, the best agreement amongst data sets is seen in themid-latitude lower and middle stratosphere, with larger differences in theequatorial lower stratosphere and the upper stratosphere globally. In mostcases, differences in the choice of underlying instrument records that weremerged produced larger differences between data sets than the use ofdifferent merging techniques. Long-term ozone trends were calculated for theperiod 1984–2011 using a piecewise linear regression with a change in trendprescribed at the end of 1997. For the 1984–1997 period, trends tend to bemost similar between data sets (with largest negative trends ranging from −4to −8% decade in the mid-latitude upper stratosphere), in large part due tothe fact that most data sets are predominantly (or only) based on the SAGE-IIrecord. Trends in the middle and lower stratosphere are much smaller, and,particularly for the lower stratosphere, large uncertainties remain. For thelater period (1998–2011), trends vary to a greater extent, ranging fromapproximately −1 to +5% decade in the upper stratosphere. Again, middle andlower stratospheric trends are smaller and for most data sets notsignificantly different from zero. Overall, however, there is a clear shiftfrom mostly negative to mostly positive trends between the two periods overmuch of the profile.