© Crown copyright Met Office Predictability of the Stratosphere and Associated Teleconnections Adam...

© Crown copyright Met Office

Predictability of the Stratosphere and Associated Teleconnections

Adam Scaife

(Head Monthly to Decadal Prediction, UKMO)


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


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


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


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


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


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


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


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


Some experiments have shown encouraging signs:

Solar Max => Low gph over Arctic in some months

Matthes et al., JGR, 2006


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


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.


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


El Niño – Southern Oscillation

Model Observations

PMSL

Temp

El Nino => easterly winds in UK

Occurred in 2009/10

Ineson and Scaife, Nat. Geosci., 2009


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


ENSO is contributing toextratropical predictions

Ineson & Scaife 2008

Nick Dunstone

Descending El Nino signals in hindcasts

Direct evidence of influence on forecast winds…


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


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

© Crown copyright Met Office Predictability of the Stratosphere and Associated Teleconnections Adam...

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