Presentation on theme: "How do Long-Term Changes in the Stratosphere Affect the Troposphere?"— Presentation transcript:
1 How do Long-Term Changes in the Stratosphere Affect the Troposphere? Mark P. BaldwinNorthwest Research Associates, Seattle, WA, USAIAGA/ICMA/CAWSES Trends WorkshopSt. Petersburg, Russia 9-13 September 2008
2 OutlineStratospheric vortex variability affects the troposphere and weather.Ozone loss has affected Antarctic climate.Will increasing GHGs produce a trend in polar vortex strength?Will increasing GHGs affect the variability of the stratosphere?Ozone will recover, reversing the trend from the past ~25 years.
3 From Bill Randel44-58 km34-51 km25-44 km18-37 km13-22 km
10 What are “annular modes?” They are patterns that maximize varianceNot exactly annular in the troposphereClose to annular in the stratosphereSimilar to North Atlantic OscillationArctic Oscillation (AO), Northern & Southern Annular Mode (NAM, SAM)
11 Northern Annular Mode (NAM) 1000 hPa (Arctic Oscillation)10 hPaAnnular mode patterns are similar from Earth’s surface to 50+km.
12 Composite surface maps for high and low AO index. (From Thompson and Wallace, Science 2001)>0.9°C
14 Annular Mode Terminology Arctic Oscillation (AO): At or near Earth’s surface.North Atlantic Oscillation (NAO): Very similar to AO, but more oriented to the Atlantic sector.Northern Annular Mode (NAM): Same as the AO, but can describe higher levels in the atmosphere.The surface NAM is the Arctic Oscillation.
15 Southern Hemisphere surface climate response to ozone depletion Springtime ozone loss appears to drive changes in surface climate from late spring to summer.
27 The Equatorial Quasi-Biennial Oscillation Baldwin et al., Reviews of Geophysics, 2001
28 Possible Dynamical Mechanisms Direct effect of stratospheric wave driving and stratospheric temperature anomaliesIndirect effects involving waves:-Effect on baroclinic waves/life cycles-Effect on planetary-scale wavesWave reflection in the stratosphere
29 The Future of the 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.
30 IPCC: Altitude of the Model Top StratopauseTropopauseNumber of levelsFinally in relation to CO2 or greenhouse warming there is the vexatious question of the role of cloud.GO THROUGHTo some extent the role of cloud depends on its height in the atmosphere. Low level cloud tends toward warming through long wave trapping, while high level cloud leads to cooling through solar radiation reflectionIn our final slide today, lets briefly look at surface characteristics.(IPCC slides from Eugene Cordero)
31 How Will Climate Change Affect 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.
32 How will stratospheric change affect surface climate 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
33 The Future of the 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.
34 email@example.com www.nwra.com/baldwin SummaryChanges 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.