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.

13-22 km

18-37 km

25-44 km

34-51 km

44-58 km

From Bill Randel

ODSs

Ozone

Northern Annular Mode (NAM)

Annular Modes – Latitudinal Profile

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

Composite surface maps for high and low AO index.

(From Thompson and Wallace, Science 2001)

>0.9°C

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.

Ozone Depletion

Simulated and observed geopotential height and Simulated and observed geopotential height and temperature changestemperature changes

Model results from Gillett & Thompson, Science 2003

Tropospheric changesTropospheric changes

Model results from Gillett &

Thompson, 2003

←SAM pattern

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.

Long timescaleLong timescale

Time Time DelayDelay

Baldwin and Dunkerton, 2001

Surface pressure anomalies after stratospheric events look like the Arctic Oscillation.

Baldwin and Dunkerton, 2001

Storm tracks during weak and strong regimes

The Quasi-Biennial The Quasi-Biennial Oscillation (QBO)Oscillation (QBO)

The Equatorial Quasi-Biennial Oscillation

Baldwin et al., Reviews of Geophysics, 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.

mark@nwra.com www.nwra.com/baldwin