1. Predictability of the Stratosphere and Associated Teleconnections
Adam Scaife
(Head Monthly to Decadal Prediction, UKMO)
© Crown copyright Met Office

2. 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
© Crown copyright Met Office

3. 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

4. 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
© Crown copyright Met Office

5. Winter 2005/6 U wind through the winter Obs Ctl Exp SST only
SST + Strat forcing
Winter 2005/6
U wind through the winter
Cold European signal from IMPOSED stratospheric warming in Hadley Centre model
Implies stratospheric influence
Other examples in winters 2008/9, 2009/10, 2011/12
Zonal wind at 50hPa
Exp
Ctl
Obs
Observations
Scaife and Knight, QJRMS, 2008
© Crown copyright Met Office

6. The stratosphere is a source of predictability
Predicted wind 2003/4
Negative AO in winter 2003/4
Initialise stratosphere with real anomaly or climatology
=> Predictability from stratosphere
No Stratospheric information
© Crown copyright Met Office
(Kuroda, 2008)

7. Real time Monthly forecasts for Jan 2013
Obs
Fcast
Jan 2013 – SSW appearing from 21st Dec
Operational forecasts from late Dec => increased risk ACTIONABLE

8. How Predictable are Stratospheric Warmings?
24 Feb
1984
7 Dec
1987
15 Dec
1998
26 Feb
1999
Event
Mean
(Ext | Stand)
Maximum lead time for capture (days)
13 | 5
15 | 10
12 | 12
9 | 6
12 | 8
Peak easterly magnitude
(fraction of observed)
0.4 | 0.1
0.7 | 0.2
0.7 | 0.3
0.6 | 0.4
0.6 | 0.3
Improved intraseasonal prediction of European winter cold spells:
Standard
Extended
Marshall and Scaife, JGR, 2010
© Crown copyright Met Office

9. Similar effects in the Southern Hemisphere:
Thompson et al 2003

10. Effects on ozone
2002
2012
Minor warming in 2012, based on high ozone in October
Comparable ozone shift to 2002
Harry Hendon

11. 2012 vs 2002: zonal mean zonal wind at 10mb
2012 warming is interesting but much weaker than the 2002 event
Harry Hendon

12. Sea Level Pressure Anomalies
2012
2002
Harry Hendon

13. Observed tropical wind oscillations Surface Temp’ QBOE-QBOW
Predictability from the QBO (After Ebdon 1975)
Observed tropical wind oscillations
Surface Temp’ QBOE-QBOW
NAO Power Spectrum
Hurrel and Van Loon, 1997
Marshall and Scaife, 2009.
QBO -> extratropics -> surface NAO
Large signal in observations, potentially important
© Crown copyright Met Office

14. Predictability of 30hPa winds as a function of lead time
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

15. 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
Kuroda and Kodera, 2002, JMSJ
© Crown copyright Met Office

16. Some experiments have shown encouraging signs:
Solar Max => Low gph over Arctic in some months
Matthes et al., JGR, 2006
© Crown copyright Met Office

17. 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
Ineson et al, 2011.
© Crown copyright Met Office

18. 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
Ineson et al., Nat. Geosci., 2011.
© Crown copyright Met Office

19. Winter 2009/10: retrospective forecasts
Zonal wind anomalies, ensemble mean
Extended Model
Standard Model
Winter 2009/10: stronger Arctic pressure signal
Forecasts span observations but only when stratospheric effects added
=> Improved predictability for this key winter
L85
L38
© Crown copyright Met Office
Fereday et al., 2012

20. El Niño – Southern Oscillation
Model
Observations
PMSL
El Nino => easterly winds in UK
Occurred in 2009/10
Temp
© Crown copyright Met Office
Ineson and Scaife, Nat. Geosci., 2009

21. 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
© Crown copyright Met Office
Ineson and Scaife, Nat. Geosci., 2009

22. ENSO is contributing toextratropical predictions
Nick Dunstone
ENSO is contributing toextratropical predictions
Ineson & Scaife 2008
Descending El Nino signals in hindcasts
Direct evidence of influence on forecast winds…
© Crown copyright Met Office

23. 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
Stratosphere important via ENSO
© Crown copyright Met Office

24. Climate Change Standard (IPCC) models wetter in winter
Standard Model 1
Extended - Standard 1
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 2
Extended - Standard 2
Scaife et al 2011, in press Clim. Dyn.
Scaife et al, Clim. Dyn., 2012
© Crown copyright Met Office

25. 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)

26. 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…