How do Long-Term Changes in the Stratosphere Affect the Troposphere? Mark P. Baldwin Northwest...
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Transcript of How do Long-Term Changes in the Stratosphere Affect the Troposphere? Mark P. Baldwin Northwest...
How do Long-Term Changes in the How do Long-Term Changes in the Stratosphere Affect the Stratosphere Affect the
Troposphere?Troposphere?
Mark P. BaldwinMark P. BaldwinNorthwest Research Associates, Seattle, WA, USANorthwest Research Associates, Seattle, WA, USA
IAGA/ICMA/CAWSES Trends WorkshopIAGA/ICMA/CAWSES Trends Workshop
St. Petersburg, Russia 9-13 September 2008St. Petersburg, Russia 9-13 September 2008
OutlineOutline
1) Stratospheric vortex variability affects the troposphere and weather.
2) Ozone loss has affected Antarctic climate.3) Will increasing GHGs produce a trend in polar
vortex strength?4) Will increasing GHGs affect the variability of the
stratosphere?5) Ozone will recover, reversing the trend from the
past ~25 years.
What are “annular What are “annular modes?”modes?”
They are patterns that maximize variance Not exactly annular in the troposphere Close to annular in the stratosphere Similar to North Atlantic Oscillation Arctic Oscillation (AO), Northern &
Southern Annular Mode (NAM, SAM)
Northern Annular Mode (NAM)1000 hPa (Arctic
Oscillation)
Annular mode patterns are similar from Earth’s surface to 50+km.
10 hPa
Southern Hemisphere surface Southern Hemisphere surface climate response to ozone climate response to ozone
depletiondepletion
Springtime ozone loss appears to drive changes in surface climate from late spring to summer.
Simulated and observed geopotential height and Simulated and observed geopotential height and temperature changestemperature changes
Model results from Gillett & Thompson, Science 2003
NAM index for 1998–1999.
The lowest level is the AO index.From Baldwin and Dunkerton, Science 2001
Weak Winds Strong Winds
Composites of strong Composites of strong and weak vortex eventsand weak vortex events Select strong events based only on
the daily 10-hPa NAM index. Form positive and negative
composites. Examine average behavior for the
composites.
Surface pressure anomalies after stratospheric events look like the Arctic Oscillation.
Baldwin and Dunkerton, 2001
Possible Dynamical Possible Dynamical MechanismsMechanisms
Direct effect of stratospheric wave driving and stratospheric temperature anomalies
Indirect effects involving waves: -Effect on baroclinic waves/life cycles -Effect on planetary-scale waves Wave reflection in the stratosphere
The Future of the The Future of the Stratosphere?Stratosphere?
Increasing greenhouse gases cool the stratosphere.
Ozone recovery reverses cooling trends. Stratospheric NAM index trend would depend on
relative cooling of the polar cap. Many (most?) models show a warmer, weaker
NH vortex in winter.
How Will Climate Change Affect How Will Climate Change Affect Ozone Recovery?Ozone Recovery?
Colder stratosphere slows ozone-depleting reactions.
Colder stratosphere increases PSCs; more ozone loss in spring.
Ozone recovery will not be a simple reversal of ozone depletion.
How will stratospheric change affect surface climate? The answer depends on
1) trends in the strength of the polar vortex
2) future variability of the polar vortex
The Future of the The Future of the Stratosphere?Stratosphere?
Increasing greenhouse gases cool the stratosphere.
Ozone recovery reverses SH trends. Stratospheric NAM index trend would depend on
relative cooling of the polar cap. Most models show a warmer, weaker NH vortex
in winter and spring.
SummarySummaryChanges to the circulation of the lower stratosphere affect surface climate.
The future evolution of the stratosphere will depend on increasing GHGs, ozone changes, and changes to the troposphere.
We do not know how the stratosphere will change in the coming decades and centuries, and we do not know how surface climate will be affected.
We do not fully understand the dynamics of stratosphere-troposphere coupling.
[email protected] www.nwra.com/baldwin