The Stratospheric Link
Between the Sun and Climate
The Stratospheric Link
Between the Sun and Climate
Mark P. Baldwin
Northwest Research Associates, USA
SORCE, 27 October 2004
Overview
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Climatology of the stratosphere
The Quasi-biennial Oscillation (QBO)
Effects of tropical oscillations on the
extratropics
Annular modes, Arctic Oscillation
Connection between the stratosphere and
surface climate (winter)
Speculation on summer vertical coupling
The Equatorial Quasi-Biennial Oscillation
Wind Anomalies
Holton-Tan Effect
500-hPa (mid-troposphere)
500-hPa (mid-troposphere)
Lack of observations
Solar/Ozone
Heating
QBO?
Solar-QBO-SAO
Lack of observations in the equatorial
stratosphere
ƒ Holton-Tan: upper or lower
stratosphere?
ƒ Solar/QBO interaction (Labitzke-van
Loon)
ƒ Solar modulation of the QBO itself
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A Mechanism for Solar Variability
Effects on Surface Climate
Mark P. Baldwin
Northwest Research Associates
Bellevue, WA USA
IUGG 9 July, 2003
Northern Annular Mode (NAM)
1000 hPa (Arctic Oscillation)
10 hPa
Annular mode patterns are the leading EOF of low-frequency Z variability.
Annular mode patterns are similar from Earth’s surface to 50+km.
Annular Mode Terminology
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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.
Annular mode index.
Composite surface maps for
high and low AO index.
(From Thompson and
Wallace, Science 2001)
>0.9°C
250-day running mean AM time series.
Weak Winds
Strong Winds
NAM index for 1998–1999.
23 separate levels are used.
The lowest level is the AO index.
Composites of strong and
weak vortex events
Select strong events based only on the
daily 10-hPa NAM index.
ƒ Include only strong events.
ƒ Examine average behavior for the
composites.
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If solar variability can
affect the strength of the
stratospheric polar vortex,
then surface climate will be
affected.
Time
Delay
Long timescale
500-hPa (mid-troposphere)
Surface pressure anomalies after stratospheric
events look like the Arctic Oscillation.
During winter changes to the
lower stratosphere affect
surface climate
Summer
500-hPa (mid-troposphere)
Labitzke-van Loon “crescent”
500-hPa (mid-troposphere)
Volcanoes
ƒInduce changes to the atmosphere through
volcanic aerosols (radiative effects, ozone
depletion)
ƒAppear to induce a negative AO anomaly for
~two years
Autocorrelation of daily surface AO index
(W. Norton, GRL, 2003)
ControlModel
Run
Normal
Model with damped
stratosphere
Without stratospheric variability, the
timescale of the surface AO is shorter.
In the troposphere the longest timescale occurs
during winter.
Does this effect depend on the stratosphere, or
is it simply an annual cycle?
Possible Dynamical Mechanisms
Movement of mass within the
stratosphere (Dave Thompson)
ƒ Effect on baroclinic waves/life cycles
ƒ Effect on planetary-scale waves
ƒ Wave reflection in the stratosphere
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Predictability Beyond 10 Days—a
role for the stratosphere?
Boundary Conditions (SSTs, Snow and
Ice, Soil Moisture, etc.)
ƒ Persistent Phenomena (MJO, QBO,
ENSO, etc.)
ƒ Persistent stratospheric anomalies—can
they affect the troposphere?
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Statistical AO Forecasts
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Exploit the enhanced timescale of the AO
during winter.
Predict the average AO during a future time
period, such as 10–40 days.
Use one or more linear predictors:
1) The present value of the AO
2) The present values of the annular modes at
all other levels, including the stratosphere.
Cross-validated AO
Forecasts
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Remove one winter at a time; forecast the
remaining winter.
150-hPa NAM only during DJF: skill is
reduced from 20% to 18%.
AO predicts AO: cross-validated skill is 12%
Adding the the AO as a second predictor
does not improve skill.
Lagged
MCA
between
daily 150hPa Z and
monthlymean 1000hPa Z
beginning
10 days
later yields
patterns
nearly
identical to
the NAM.
NAM
Maximum
Covariance Analysis
(MCA)
What are “annular modes?”
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Not fundamental dynamical quantities
Not the solution to any equation
Why do they look so similar in the Northern and Southern
Hemispheres and in the troposphere & stratosphere?
Why does the atmosphere tend to vary in “ring-like” structures?
Why not multiple rings?
The latitude of the peak in the jet is very different in the
stratosphere and troposphere, yet the node in the annular mode
pattern is at a similar latitude. Why?
How are annular modes related to jets?
Why does the effect of stratospheric anomalies look almost
exactly like the NAM at 1000 hPa?
Can we construct a simple analytic model that produces annular
modes?
AGU Chapman Conference:
“Jets and Annular Structures
in Geophysical Fluids”
Time: 2005 or 2006
ƒ Place: not decided
ƒ Lead Convener: Walt Robinson
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Southern Hemisphere surface climate
response to ozone depletion
Observations and model
ƒ Springtime ozone loss appears to drive
changes in surface climate from late
spring to summer.
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Simulated and observed geopotential height and
temperature changes
Model results from Gillett & Thompson, 2003
Tropospheric changes
Model results
from Gillett &
Thompson, 2003
A stronger, colder vortex?
With increasing GHGs, the modeled
stratospheric vortex becomes stronger
and colder, and there is a positive AO
trend.
Shindell et al., [1999]
With increasing GHGs, “the model NAO
index decreases significantly from 1990
to 2015.” The polar stratosphere becomes
warmer.
Schnadt and Dameris, [2003]
Polar vortex response to 4x CO2
January Temperature Change
January U Change
• The polar vortex gets weaker and warmer due to
enhanced wave driving from the troposphere.
• These plots show the response in a 4xCO2
integration - easier to distinguish from noise (from
Jamie Kettleborough).
Satellite Observations of Tropospheric
Temperatures
Cooling
Warming
From Fu et al., Nature, 6 May 2004
Summary
ƒSolar/ozone
effects in the context of QBO, SAO. Indirect
pathway through the stratospheric polar vortex.
ƒChanges
to the circulation of the lower stratosphere affect
surface climate.
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climate-change timescales, we do not know how the
stratosphere will change, and we do not know how surface climate
will be affected.
ƒWe
do not fully understand the dynamics of stratospheretroposphere coupling.
ƒReprints.
mark@nwra.com
www.nwra.com/baldwin