Transcript Scaife, Adam

Predictability of the Stratosphere
and Associated Teleconnections
Adam Scaife
(Head Monthly to Decadal Prediction, UKMO)
© Crown copyright Met Office
Downward propagating wind anomalies
(Kodera et al, Baldwin and Dunkerton….)
16th Jan
Easterly winds develop aloft
Descended with time to the surface
Snow in early February 2009
31st Jan
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Cold and dry impact on N Europe/U.S.
N European cooling due to –ve NAO
Better predicted (12d vs 8d) in deep domain model
Marshall and Scaife 2010
Decadal changes in extremes also depend on
the stratosphere (1960s to 1990s)
Observed Decrease in Frosts
Modelled Decrease in Frosts
Without stratospheric change
Scaife et al., J.Clim., 2008
Nicely reproduced – but only if stratospheric flow simulated
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SST only
Winter 2005/6
U wind through the winter
SST + Strat forcing
Zonal wind at 50hPa
Cold European signal from
IMPOSED stratospheric warming
in Hadley Centre model
Implies stratospheric influence
Obs
Ctl
Exp
Scaife
and Knight,
© Crown
copyright QJRMS,
Met Office2008
Other examples in winters
2008/9, 2009/10, 2011/12
Observations
The stratosphere is a source of predictability
Predicted wind 2003/4
Negative AO in winter 2003/4
No Stratospheric information
Initialise stratosphere with real anomaly
or climatology
=> Predictability from stratosphere
© Crown copyright Met Office
(Kuroda, 2008)
Real time Monthly forecasts for Jan 2013
Obs
Jan 2013 – SSW appearing from 21st Dec
Operational forecasts from late Dec => increased risk
Fcast
ACTIONABLE
How Predictable are Stratospheric Warmings?
24 Feb
7 Dec
1984
1987
(Ext | Stand)
Maximum lead time for
13 | 5
15 | 10
capture (days)
15 Dec
1998
26 Feb
1999
Event
Mean
12 | 12
9|6
12 | 8
Peak easterly magnitude
(fraction of observed)
0.7 | 0.3
0.6 | 0.4
0.6 | 0.3
0.4 | 0.1
0.7 | 0.2
Improved intraseasonal prediction of
European winter cold spells:
Extended
Marshall
and
Scaife,Met
JGR,
2010
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copyright
Office
Standard
Similar effects in the Southern Hemisphere:
Thompson et al 2003
Effects on ozone
2002
2012
Minor warming in
2012, based on high
ozone in October
Comparable ozone
shift to 2002
Harry Hendon
2012 vs 2002: zonal mean zonal wind at 10mb
2012
2002
2012 warming is interesting but much weaker than the 2002 event
Harry Hendon
Sea Level Pressure Anomalies
2012
2002
Harry Hendon
Predictability from the QBO
(After Ebdon 1975)
Observed tropical wind oscillations
NAO Power Spectrum
Hurrel and Van Loon, 1997
Surface Temp’ QBOE-QBOW
Marshall and Scaife, 2009.
QBO -> extratropics -> surface NAO
Large signal in observations, potentially important
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QBO predictability
Predictability of 30hPa winds
as a function of lead time
High levels of predictability for following winter
At least as high as ENSO
Probably the longest range predictable signal internal to the atmosphere
© Crown copyright Met Office
Maria Athanassiadou
Observed solar variability
Solar maximum minus solar minimum from the 11 year cycle
Descending wind anomalies, Winter only, strongest in NH
N. Hemisphere winter
S. Hemisphere winter
© Crownand
copyright
Met2002,
Office JMSJ
Kuroda
Kodera,
Some experiments have shown
encouraging signs:
Solar Max => Low gph over Arctic in some months
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copyright
Met Office
Matthes
et al.,
JGR, 2006
Predictability from Solar Variability
Oct
Nov
Dec
Jan
Feb
Mar
Similar to wave-mean flow interactions seen in other contexts
Sea level pressure
-ve NAO/AO
at solar
minimum
© et
Crown
copyright Met Office
Ineson
al, 2011.
Mechanism: descent through the stratosphere
zonal mean zonal wind (contours) and EP flux divergence (cols)
After Andrews and McIntyre 1978
increase in
planetary wave
driving F
 deceleration just
below easterly wind
anomaly
 descent of the
anomaly
© Crown
Office 2011.
Ineson
etcopyright
al., Nat. Met
Geosci.,
Winter 2009/10: retrospective forecasts
Zonal wind anomalies, ensemble mean
Standard Model
Extended Model
Winter 2009/10: stronger Arctic pressure signal
L85
L38
© Crown copyright Met Office
Fereday
et al., 2012
Forecasts span observations but only when
stratospheric effects added
=> Improved predictability for this key winter
El Niño – Southern Oscillation
Model
Observations
PMSL
El Nino => easterly winds in UK
Occurred in 2009/10
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Temp
Ineson and Scaife, Nat. Geosci., 2009
ENSO teleconnections
Model Temperature
Model Zonal wind
Descending El Nino signals
Slower at lower altitudes
Indicative of wave-mean flow interaction from a Rossby wave source in the troposphere
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Ineson and Scaife, Nat. Geosci., 2009
ENSO is contributing toextratropical
predictions
Ineson & Scaife 2008
Descending El Nino signals in hindcasts
Direct evidence of influence on forecast winds…
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Nick Dunstone
Seasonal Predictability of the NAO!
Retrospective winter forecasts
Significant NAO skill r~0.6
(c.f. ECMWF 0.16, NCEP 0.25: Kim et al 2012)
Significant at the 98% level
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Stratosphere important via
ENSO
Climate Change
Standard Model 1
Extended - Standard 1
Standard Model 2
Extended - Standard 2
Standard (IPCC) models
wetter in winter
Makes a robust difference
Error is similar size to original
signal
European climate prediction
needs extended models
Scaife
et al 2011, inMet
press
© Crown
OfficeClim. Dyn.
Scaife
et al, copyright
Clim. Dyn., 2012
Possible mechanism: transient eddies and
upper level baroclinicity
Fractional change in
500hPa
eddy
activity
Climate
change
in storminess
(%)
 = 0.3Uzf
NH
Interaction with storm tracks via upper troposphere
Increased growth rate at high latitudes in standard models
from increased vertical shear and at mid-latitudes in
extended models  increased mid-latitude storminess
Scaife et al (2012)
Summary
• Clear evidence of improved predictability from
including stratospheric effects
• Sudden warmings, ENSO, QBO…..others
• SH effects also important such as SSW in 2002
• Improved monthly, seasonal and climate predictions
now achieved by including stratospheric effects and
available as hindcasts and real time forecasts.
• More work on mechanisms needed: PV inv., wave
reflection, tropopause movement, baroclinic eddy
growth and propagation effects…