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Giorgio S. Taverna 1
School of Earth and EnvironmentINSTITUTE FOR CLIMATE & ATMOSPHERIC SCIENCE
Stratospheric ozone: past, present,
observations
Giorgio S. Taverna, Martyn Chipperfield, Wuhu Feng
ICAS, University of Leeds, UK
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Giorgio S. Taverna 22
The ozone layer
What is ozone and why is so important?
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Giorgio S. Taverna 33
The ozone layer
Satellite profile in
different units
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Giorgio S. Taverna 44
The ozone layer
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Giorgio S. Taverna 55
Ozone Depletion and Recovery
Shepherd et al., (2012).Focussed on ozone loss since 1960.10% decrease in halogen loss since mid 1990s.
Observations and 3-D model show ‘recovery’ in Antarctic ozone loss rates.
Solomon et al., 2016
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Giorgio S. Taverna 66
TOMCAT/SLIMCAT 3-D Model
Model setup:
• Detailed stratospheric chemistry scheme. Specified aerosol SAD (3λ).
• Forced by ECMWF ERA-Interim winds and temperatures (no feedback).
• 1955 – 2015 (repeating 1980 meteorology before 1980)
• 2.8o x 2.8o. 32 levels: surface – 60 km.
Six simulations:
• Control. Forced by observed surface mixing ratios of long-lived ODSs
(CFCs, HCFCs, solvents, CH3Cl…)
• fODS 1960. ODSs fixed at 1960 tropospheric vmr
• fODS 1980.
• fODS 1995. (Peak tropospheric halogen: chlorine + α×bromine).
• World avoided: 3%/year growth in ODS emissions after 1987.
• Repeating 1980 meteorology.
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Giorgio S. Taverna 77
Carbon Tetrachloride
Sensitivity to loss processes and emissionsComparison to global mean surface data (AGAGE and NOAA) Comparison to ACE satellite profiles
Column FTIR observations
τ=42 yrs±10%
Butler et al 2016τ=183 yrs
(147-210)
Rhew + Happell 2016τ=375 yrs
(288-536)
E=39 Tg/yr(-> 45 Tg/yr)
Chipperfield et al., ACP, 2016
ModelACE
Overall model τ=32 yrsE. Mahieu
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Giorgio S. Taverna 88
Hydrogen Fluoride
Trends in growth of HF (%/yr) 2004-2012.
ACE
• Ultimate degradation product for all F in CFCs, HCFCS etc.• Good stratospheric tracer.
HALOE + ACE satellites versus model (1991-2012)
Harrison et al., ACP, 2016
Model: repeating winds
Model
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Giorgio S. Taverna 99
Long-term change in column ozone
Column ozone (DU) from model sensitivity runs
Ozone c
olu
mn (
DU
)
Nb model used repeating 1980 winds before 1980
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Giorgio S. Taverna 1010
Long-term change in ozone profile
Ozone (ppmv) and EESC (ppbv) from model sensitivity runs
SAGE v7 data (bias corrected at 30 km and above)
EESC (p
pb
v)O
zone (
ppm
v)
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Giorgio S. Taverna 1111
Quantifying Ozone Loss and recovery
-9%-14%-16%-31%
-26-40-46-84
-8%-14%-17%-33%
-13-24-29-69
-4%-8%-10%-25%
-9%-14%-16%-31%
Contributions to modelled ozone depletion since 1960
Decrease in ozone depletion from 1996 to 2015: 2% at 40 km, 2-3% at 20 km, 5-6 DU in column
Actual depletion = blue + green
Theoretical ‘world avoided’ = red Recovery since peak halogens = orange
Meteorology
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Giorgio S. Taverna 1212
Polar regions
SH October NH March
-11%-17%-19%-36%
-10%-15%-17%-33%
-9%-16%-20%-51%
-12-22-26-62
-67%-82%-85%-92%
-29-46-52-93
Decrease in ozone depletion from 1996 to 2015: 2% at 40 km, 3-4% at 20 km, 4-6 DU in column
Contributions to modelled ozone depletion since 1960
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Giorgio S. Taverna 1313
Short-lived anthropogenic chlorine
Large and unexplained increase in CH2Cl2(NOAA data – Steve Montzka)
Assumed model scenario(2004-2014 growth rate)
Delay in ozone ‘return date’ of few decades(nb CTM – no circulation feedback)
See poster by Ryan Hossaini
In stratosphere
Direct observations of enhanced CH2Cl2 in the UT over SE Asia.
LeedhamElvidge et al. ACP, (2015).
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Giorgio S. Taverna 1414
Summary
• Understanding of CCl4 budget improved (SPARC report).
Uncertainty in ocean loss and modelled stratospheric lifetime
(transport) large factors in remaining uncertainty.
• Modelled ozone change since 1996 due to decreasing ODSs is
modest. Difficult to separate from variability and climate effects.
Can nonetheless say recovery ‘is on track’.
• Observations show large abundances of anthropogenic CH2Cl2which is not controlled by the Montreal Protocol. Currently
contributes ~100 pptv to stratospheric Cly. Continued increase
could have an impact on timescale for ozone return dates.
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Giorgio S. Taverna 1515
Δozone versus ΔEESC
Since 1980
Since 1960
Since 1995
Meteorology v 1980
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Giorgio S. Taverna 1616
Polar regions