A re-evaluated Canadian ozonesonde record: measurements of the verticaldistribution of ozone over Canada from 1966 to 2013

[摘要] In Canada routine ozone soundings have been carried at ResoluteBay since 1966, making this record the longest in the world. Similarmeasurements started in the 1970s at three other sites, and the network wasexpanded in stages to 10 sites by 2003. This important record forunderstanding long-term changes in tropospheric and stratospheric ozone hasbeen re-evaluated as part of the SPARC/IO₃C/IGACO-O₃/NDACC(SI²N) initiative. The Brewer–Mast sonde, used in the Canadian networkuntil 1980, is different in construction from the electrochemical concentration cell (ECC) sonde, and the ECCsonde itself has also undergone a variety of minor design changes over theperiod 1980–2013. Corrections have been made for the estimated effects ofthese changes to produce a more homogeneous data set.

The effect of the corrections is generally modest. However, the overallresult is entirely positive: the comparison with co-located total ozonespectrometers is improved, in terms of both bias and standard deviation, andtrends in the bias have been reduced or eliminated. An uncertainty analysis(including the additional uncertainty from the corrections, whereappropriate) has also been conducted, and the altitude-dependent estimateduncertainty is included with each revised profile.

The resulting time series show negative trends in the lower stratosphere ofup to 5 % decade⁻¹ for the period 1966–2013. Most of this declineoccurred before 1997, and linear trends for the more recent period aregenerally not significant. The time series also show large variations fromyear to year. Some of these anomalies can be related to cold winters (in theArctic stratosphere) or changes in the Brewer–Dobson circulation, which maythereby be influencing trends.

In the troposphere, trends for the 48-year period are small and for the mostpart not significant. This suggests that ozone levels in the freetroposphere over Canada have not changed significantly in nearly 50 years.

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