1. Short-term and long-term variation in midlatitude and tropical ozone using the Merged Ozone Dataset
Matt Tully
Bureau of Meteorology
Quadrennial Ozone Symposium
Edinburgh, 4th-9th September, 2016.

2. Traditional latitude bands – eg WMO 2014

3. Australian Dobson data – spring seasonal means
Darwin - 12º South
Brisbane - 27º South
Melbourne - 38º South
Macquarie Island
- 55º South

4. Zonal Means from SBUV
SBUV (Version 8.6) MERGED TOTAL AND PROFILE OZONE DATA SETS "The SBUV MERGED OZONE DATA SETS are monthly-mean zonal and gridded average products constructed by merging individual SBUV/SBUV/2 (total and profile ozone) satellite data sets. NO external calibration adjustments have been applied. Intercalibration of the SBUV instruments in Version 8.6 is accomplished within the algorithm at the radiance level. " (My thanks to Frith, Stolarski, McPeters, Bhartia et al.for making available )

5. The interannual variability has closer resemblance either poleward or equatorward of 50S.

7. The longer-term variations also seem to transition around 50 S
LOESS smoothed S heat flux

12. Define 3 latitude bands and average across them
"SH Midlatitude Mean" 50S-20S
"NH Midlatitude Mean" 20N-50N
"Tropical Mean" 10S-10N
Decompose into "low frequency" and "high frequency" (interannual) components using LOESS smoothing

13. Does it work – how representative is the mean of each band?
The bands are most representative in summer and least representative in autumn.
There is a significant anti-correlation with the equatorial zone in winter in both hemispheres.

15. Spring transport build-upSH NH
(reflected)

16. Long term trend in the defined bands?
Autumn low in SH deeper than NH but increasing since early 2000s
Spring maximum has been increasing since mid-1990s in NH but in SH still decreasing

17. NH spring
SH spring

18. SH-midlatitudes and Tropics are anti-correlated

19. Trend in tropics?
Stable in NH winter but increasing in SH winter

20. If the anti-correlation is assumed to be the result of transport, then an increasing/decreasing trend in the tropics might imply a weakening/ strengthening circulation
SH Midlatitudes
Tropics
Fit to the interannual relationship and apply the same coefficient to the trend to adjust the midlatitude value

21. After adjustment
Eruption of Pinatubo
SH Mean
NH Mean

22. Solar Cycle
SH Mean
NH Mean

23. How good a job does the fit to the mean do year by year across 50-20S?

24. "Gradient adjustment"

25. Mean
Mean + gradient adjustment

26. Mean and "gradient anomaly"

27. Can the mean and gradient anomaly be related to conventional proxies?
QBO
45-75 S Heat Flux

28. Use as basis vectors for regression
Mean
Gradient anomaly

29. Two regimes?
In Southern Hemisphere spring, S and S are totally uncorrelated.
Can therefore be used as orthogonal basis vectors for regression

30. 80-75 S
40-35 S
75-80N
35-40N

31. Conclusions
Replacing traditional bands S/N and 20S-20N with S/N and 10S-10N would be more physically meaningful. NH and SH spring trends agree very closely within these bands if an adjustment is made for tropical trends. The mean of the mid-latitude bands is very significantly influenced by the QBO but the gradient anomaly across the band is related to transport and therefore ozone values poleward of 50º.

32. Thank you…
Matt Tully