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 © Crown copyright Met Office

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 © Crown copyright Met Office

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

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)

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

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

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 warming is interesting but much weaker than the 2002 event Harry Hendon

Sea Level Pressure Anomalies 2012 2002 Harry Hendon

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

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

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

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

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

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

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

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

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

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

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

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

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…