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.

Traditional latitude bands – eg WMO 2014

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

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 )

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

The longer-term variations also seem to transition around 50 S LOESS smoothed 45-75 S heat flux

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

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.

Spring transport build-up SH NH (reflected)

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

NH spring SH spring

SH-midlatitudes and Tropics are anti-correlated

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

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

After adjustment Eruption of Pinatubo SH Mean NH Mean

Solar Cycle SH Mean NH Mean

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

"Gradient adjustment"

Mean Mean + gradient adjustment

Mean and "gradient anomaly"

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

Use as basis vectors for regression Mean Gradient anomaly

Two regimes? In Southern Hemisphere spring, 80-75 S and 40-35 S are totally uncorrelated. Can therefore be used as orthogonal basis vectors for regression

80-75 S 40-35 S 75-80N 35-40N

Conclusions Replacing traditional bands 35-60 S/N and 20S-20N with 20-50 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.

Thank you… Matt Tully +61 3 9669 4139 M.Tully@bom.gov.au