© Crown copyright Met Office Stratospheric Influences on the Troposphere Adam Scaife December 2010

© Crown copyright Met Office Outline Monthly variability: sudden stratospheric warmings predictability surface impacts Seasonal/Interannual variability El Nino-Southern Oscillation Quasi-Biennial Oscillation Summary

© Crown copyright Met Office Sudden Stratospheric Warmings 26 th Jan th Jan 1963 Figure courtesy of Colombia Uni. Usual situation: polar cyclone, eastward flow Sudden warming: Filling of the polar cyclone, net westward flow, ~50K rise in few days! Wave driven (wave 2 here): (Note that is the coldest UK winter of the 20 th century…..)

© Crown copyright Met Office Early studies suggested an NAO/AO response to imposed stratospheric changes in GCMs Observations show downward propagation of wind anomalies from the upper stratosphere to the troposphere Some studies show additional predictability from the stratosphere on monthly to seasonal timescales Monthly Variability

© Crown copyright Met Office Dynamical forecast Dynamical forecast + 70hPa stat fcast Christiansen 2005 Downward propagating winds Baldwin and Dunkerton 2001 See also: Kodera et al 1990, Boville 1984 Surface wind at 60N

© Crown copyright Met Office Cold Eurasian winter 2005/6 Colder than over much of Europe 2nd coldest in 10 years using area mean T Record snowfall in parts of central Europe Late winter colder than early winter Intense sudden stratospheric warming January 2006February 2006December 2005 Zonal wind through the winter

© Crown copyright Met Office Winter 2005/6 Atmospheric model 50/25 members HadISST as a boundary condition Atmospheric model + stratospheric forcing: 25 members HadISST as lower boundary condition Perturbed stratosphere from 1 st Jan Zonal wind at 50hPa Exp Ctl Obs SST only SST + Strat forcing Observations Cold European signal from IMPOSED stratospheric warming Even clearer example in winter 2008/9 Scaife and Knight, QJRMS, 2008

© Crown copyright Met Office Sudden Stratospheric Warming 2009 E.g. Jan 2009; easterlies (in blue) descend from the upper atmosphere: Followed by extreme snowfall in Feb 2009 Similar events in winter 2009/10 Jan 2009 zonal winds

© Crown copyright Met Office Cold Air Outbreaks across NH Scandinavian blocking precedes warmings Negative Arctic Oscillation / North Atlantic Oscillation follows Cooling across the whole of northern Eurasia and Eastern USA Kolstad et al (2010)

© Crown copyright Met Office Standard model Extended model 40km 85km Predictability and vertical resolution

© Crown copyright Met Office Predictability of stratospheric warmings Improved seasonal 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 Zonal wind (10hPa,60N) (Ext | Stand) Marshall and Scaife, in press

© Crown copyright Met Office It is not only the ocean which contains a long memory - stratospheric processes have a long memory too! The QBO has a period of 2-3 yrs and is predictable for 1-2 cycles. Key mechanisms of interannual to decadal variability can also involve stratospheric processes. Two recent examples….. Seasonal to Interannual Variability

© Crown copyright Met Office El Nino ENSO peaks in winter Remarkable levels of predictability even 6 months ahead Remote effects? ENSO forecast skill

© Crown copyright Met Office ENSO teleconnections Model El Nino anomaly (50hPa geopotential height) Observations (Hamilton, 1993) Stratospheric component appears in models ( Van Loon and Labitzke 1987, Hamilton, 1993, Manzini et al ) ENSO events produce a –ve NAO-like response ( e.g. Moron and Gouirand 2003, Bronniman et al ) Clearly visible in 2/3 of observed El Nino events ( Toniazzo and Scaife 2006 ) Reproduced in numerical models ( Cagnazzo and Manzini 2009, Ineson and Scaife 2009 )

© Crown copyright Met Office Downward progression Descending signals Slower at lower altitudes Indicative of wave-mean flow interaction from a steady (tropospheric) wave source TemperatureZonal wind

© Crown copyright Met Office Surface Climate Impact ModelObservations PMSL Temperature Precipitation Ineson and Scaife, Nat. Geoscience, 2009 Big enough to affect forecasts

© Crown copyright Met Office StandardObservationsExtended Effects of vertical resolution (actually domain) See Ineson and Scaife, Nat. Geosci., 2009

© Crown copyright Met Office Winter 2009/10 Moderate El Nino and negative Arctic Oscillation Not a coincidence! El Nino N Atlantic Oscillation

© Crown copyright Met Office Testing extended model in winter 2009/10 predictions: Winter 2009/10 New SystemOld System GloSea4 system showed cold signal for Europe last winter Also predicted –ve NAO ~5hPa Extended model with improved ENSO teleconnection strengthens this signal

© Crown copyright Met Office Quasi-Biennial Oscillation Quasi-periodic 2-3 year period Nonlinear driving from small scale waves Propagates down with time (c.f. ENSO and SSW!) Scaife et al, GRL 2000, JAS 2002.

© Crown copyright Met Office QBO Forecast Skill Standard model drifts to weak winds (c.f. Boer and Hamilton 2008) Extended model simulates realistic QBO Surface impacts? QBO anomaly, 30hPa, initialised in December DECJANFEBMARAPR Eastward phase Westward phase

© Crown copyright Met Office Quasi-Biennial Oscillation QBOE-QBOW MODEL T Highly predictable for 2 years at least Initialised in current models but decays after few months Eurasian (NAO like) signal: QBO -> extratropics -> surface Signal comparable to year-to-year variability and therefore important Marshall and Scaife, J. Geophys. Res., OBS T

© Crown copyright Met Office CLIVAR-WGSIP Stratospheric Historical Forecast Project Extended Model Hindcasts Parallel to standard model WGSIP-CHFP Extended models Initialising extra atmosphere Integrations 4 month lead times (1 st November and 1 st May start dates) 2 seasons (DJF and JJA) Case study years: 1989 onwards At least 6 members for each hindcast season

© Crown copyright Met Office Participants: InstituteModelResolutionModel top ReferenceContact Met Office HC HadGEM N96L85 N96L38 85km 40km Arribas et al., Mon. Wea. Rev., 2011 Meteo France Arpege OPA L91 L hPa 10hPa Gueremy et al, 2005, Tellus, 57A, p ECMWF IFS L91 L hPa 5hPa ? CCCMA CMAM T63L71 T63L41 ~100km ~31km Scinocca et al 2008, ACP, 8, NCEP CFS v1 L64 ? ? Saha et al, J.Clim., vol.19, no.15, p CPTEC ?? ? IFM- GEOMAR ECHAM5 T63L31 T63L47 10hPa 0.01hPa Roeckner et al 2003, MPI report No. 349, 127pp Manzini et al 2006, J. Clim., 19,

© Crown copyright Met Office SUMMARY Stratospheric dynamics are important for monthly to seasonal surface variability and project onto the NAO: Sudden Warmings -> 30-60d anomalies –ve NAO ENSO -> extratropics -> stratosphere -> NAO Volcanoes -> stratosphere -> extratropics -> NAO QBO -> extratropics -> NAO There are also longer term influences (outside the scope of this talk) Necessary to include these effects to maximise prediction skill in the extratropics CLIVAR-WGSIP is carrying out an experiment with international groups to characterise the benefits in predictability from including these processes