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

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Presentation on theme: "© Crown copyright Met Office Predictability of the Stratosphere and Associated Teleconnections Adam Scaife (Head Monthly to Decadal Prediction, UKMO)"— Presentation transcript:

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

2 © Crown copyright Met Office Downward propagating wind anomalies (Kodera et al, Baldwin and Dunkerton….) 16 th Jan 31st Jan Easterly winds develop aloft Descended with time to the surface Snow in early February 2009

3 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

4 © Crown copyright Met Office 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

5 © Crown copyright Met Office Winter 2005/6 Zonal wind at 50hPa Exp Ctl Obs 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

6 © Crown copyright Met Office 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

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

8 © Crown copyright Met Office How Predictable are Stratospheric Warmings? Improved intraseasonal prediction of European winter cold spells: StandardExtended 0.6 | | | | | 0.1Peak easterly magnitude (fraction of observed) 12 | 89 | 612 | 1215 | 1013 | 5Maximum lead time for capture (days) Event Mean 26 Feb Dec Dec Feb 1984 (Ext | Stand) Marshall and Scaife, JGR, 2010

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

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

11 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 Harry Hendon

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

14 © Crown copyright Met Office 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

15 © Crown copyright Met Office 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

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

17 © Crown copyright Met Office Predictability from Solar Variability Similar to wave-mean flow interactions seen in other contexts Ineson et al, Sea level pressure -ve NAO/AO at solar minimum Oct Nov Dec Jan Feb Mar

18 © Crown copyright Met Office 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.

19 © Crown copyright Met Office Winter 2009/10: stronger Arctic pressure signal Forecasts span observations but only when stratospheric effects added => Improved predictability for this key winter Fereday et al., 2012 Winter 2009/10: retrospective forecasts L38L85 Zonal wind anomalies, ensemble mean Extended ModelStandard Model

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

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

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

23 © Crown copyright Met Office 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

24 © Crown copyright Met Office 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 2Extended - Standard 2 Extended - Standard 1 Scaife et al 2011, in press Clim. Dyn. Scaife et al, Clim. Dyn., 2012

25 = 0.3U z f 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 (%)

26 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

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