© crown copyright met office predictability of the stratosphere and associated teleconnections adam...
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© Crown copyright Met Office
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
31st Jan
Easterly winds develop aloft
Descended with time to the surface
Snow in early February 2009
Cold and dry impact on N Europe/U.S.
Marshall and Scaife 2010
N European cooling due to –ve NAO
Better predicted (12d vs 8d) in deep domain model
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Decadal changes in extremes also depend on the stratosphere (1960s to 1990s)
Modelled Decrease in FrostsObserved Decrease in Frosts
Nicely reproduced – but only if stratospheric flow simulated
Without stratospheric change
Scaife et al., J.Clim., 2008
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Winter 2005/6
Zonal wind at 50hPa
Exp
CtlObs
SST only
SST + Strat forcing
Observations
Cold European signal from IMPOSED stratospheric warming in Hadley Centre model
Implies stratospheric influence
Other examples in winters 2008/9, 2009/10, 2011/12
Scaife and Knight, QJRMS, 2008
U wind through the winter
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The stratosphere is a source of predictability
Negative AO in winter 2003/4
Initialise stratosphere with real anomaly or climatology
=> Predictability from stratosphere
(Kuroda, 2008)
No Stratospheric information
Predicted wind 2003/4
Real time Monthly forecasts for Jan 2013
Obs Fcast
Jan 2013 – SSW appearing from 21st DecOperational forecasts from late Dec => increased risk ACTIONABLE
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How Predictable are Stratospheric Warmings?
Improved intraseasonal prediction of European winter cold spells:
StandardExtended
0.6 | 0.30.6 | 0.40.7 | 0.30.7 | 0.20.4 | 0.1Peak easterly magnitude(fraction of observed)
12 | 89 | 612 | 1215 | 1013 | 5Maximum lead time for capture (days)
EventMean
26 Feb1999
15 Dec1998
7 Dec1987
24 Feb1984
(Ext | Stand)
Marshall and Scaife, JGR, 2010
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 2002
2012 vs 2002: zonal mean zonal wind at 10mb
2012 warming is interesting but much weaker than the 2002 event
Harry Hendon
Sea Level Pressure Anomalies
2012 2002
Harry Hendon
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Predictability from the QBO (After Ebdon 1975)
QBO -> extratropics -> surface NAO
Large signal in observations, potentially important
Marshall and Scaife, 2009.
Surface Temp’ QBOE-QBOW
Observed tropical wind oscillations
Hurrel and Van Loon, 1997
NAO Power Spectrum
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QBO predictability
Maria Athanassiadou
High levels of predictability for following winter
At least as high as ENSO
Probably the longest range predictable signal internal to the atmosphere
Predictability of 30hPa winds as a function of lead time
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Observed solar variabilitySolar maximum minus solar minimum from the 11 year cycle
Descending wind anomalies, Winter only, strongest in NH
N. Hemisphere winter
S. Hemisphere winter
Kuroda and Kodera, 2002, JMSJ
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Some experiments have shown encouraging signs:
Solar Max => Low gph over Arctic in some months
Matthes et al., JGR, 2006
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Predictability from Solar Variability
Similar to wave-mean flow interactions seen in other contexts
Ineson et al, 2011.
Sea level pressure
-ve NAO/AO at solar minimum
Oct Nov Dec Jan Feb Mar
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Mechanism: descent through the stratosphere
increase in planetary wave driving F
deceleration just below easterly wind anomaly
descent of the anomaly
zonal mean zonal wind (contours) and EP flux divergence (cols)
After Andrews and McIntyre 1978
Ineson et al., Nat. Geosci., 2011.
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Winter 2009/10: stronger Arctic pressure signal
Forecasts span observations but only when stratospheric effects added
=> Improved predictability for this key winterFereday et al., 2012
Winter 2009/10: retrospective forecasts
L38L85
Zonal wind anomalies, ensemble mean
Extended Model Standard Model
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El Niño – Southern Oscillation
Model Observations
PMSL
Temp
El Nino => easterly winds in UK
Occurred in 2009/10
Ineson and Scaife, Nat. Geosci., 2009
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ENSO teleconnections
Descending El Nino signals
Slower at lower altitudes
Indicative of wave-mean flow interaction from a Rossby wave source in the troposphere
Model Temperature Model Zonal wind
Ineson and Scaife, Nat. Geosci., 2009
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ENSO is contributing toextratropical predictions
Ineson & Scaife 2008
Nick Dunstone
Descending El Nino signals in hindcasts
Direct evidence of influence on forecast winds…
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Seasonal Predictability of the NAO!
Significant NAO skill r~0.6 (c.f. ECMWF 0.16, NCEP 0.25: Kim et al 2012)
Significant at the 98% level
Stratosphere important via ENSO
Retrospective winter forecasts
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Climate Change
Standard (IPCC) models wetter in winter
Makes a robust difference
Error is similar size to original signal
European climate prediction needs extended models
Standard Model 1
Standard Model 2 Extended - Standard 2
Extended - Standard 1
Scaife et al 2011, in press Clim. Dyn.Scaife et al, Clim. Dyn., 2012
= 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
Fractional change in 500hPa eddy activity
Possible mechanism: transient eddies and upper level baroclinicity
Scaife et al (2012)
Climate change in storminess (%)
• 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…
Summary