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Why was Winter 2009/10 so cold? Mike Blackburn National Centre for Atmospheric Science, University of Reading With input from Chris Bell, Thomas Toniazzo,

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Presentation on theme: "Why was Winter 2009/10 so cold? Mike Blackburn National Centre for Atmospheric Science, University of Reading With input from Chris Bell, Thomas Toniazzo,"— Presentation transcript:

1 Why was Winter 2009/10 so cold? Mike Blackburn National Centre for Atmospheric Science, University of Reading With input from Chris Bell, Thomas Toniazzo, Tim Woollings (NCAS; University of Reading); Brian Hoskins ( Grantham Institute, Imperial College) Thomas Jung, Laura Ferranti, Frederic Vitart (ECMWF) Royal Meteorological Society, 5 February 2011

2 Summary of observed anomalies UK global Circulation patterns NAO & blocking The phenomena Remote influences Predictability – forecasts Early winter 2010/11 – comparison Attribution studies Outline Reading, 6 January 2010

3 Winter 20009/10 in the UK DJF averages Reading: T max, T min DJF 0910 Temperature Mean 1.6°C 2.0°C below average Precipitation (%) Total 249mm 75% of average Mike Stroud

4 European anomalies - DJF NOAA Climate Prediction Center TemperaturePrecipitation (% normal)

5 Surface air temperature December 2009January 2010February 2010 DJF average Persistence Warm Arctic + sub-tropics NOAA ESRL

6 Cold mid-latitudes, amid global warmth NASA Goddard Institute for Space Studies – Hansen et al (2010) Annual temperature anomalies relative to Monthly comparison, 2010 vs. previous years DJF 2010 global average T s second warmest on record to 2007 Contribution from El Niño Global temperature is rising as fast in the past decade as in the prior two decades, despite year-to-year fluctuations associated with the El Niño-La Niña cycle of tropical ocean temperature, Hansen et al (2010)

7 Westerly winds – DJF climatology U 250hPaU 850hPa NOAA ESRL

8 U 250hPaU 850hPa NOAA ESRL Westerly winds – DJF 2009/10

9 NOAA ESRL Pressure – DJF 2009/10 anomalies MSL PressureGeopotential height 500hPa

10 P MSL anomaly NCEP reanalysis DJF 2009/10 Z500 anomaly DJF average Arctic Oscillation (AO) North Atlantic Oscillation (NAO) Z500 P MSL NOAA CPC

11 DJF average Arctic Oscillation (AO) North Atlantic Oscillation (NAO) Z500 P MSL NAO and AO time-series NOAA CPC

12 DJF average Arctic Oscillation (AO) North Atlantic Oscillation (NAO) Z500 P MSL NAO and AO time-series NOAA CPC; Colorado State University Strongest AO- on record (>1900) Iceland / Azores sea level pressure difference (NOAA ESRL)

13 NAO impacts in winter Martin Visbeck, Columbia University Positive phaseNegative phase

14 NAO - example surface charts UK Met Office NAO Positive phase 2 February 2011 NAO Negative phase 5 January 2010

15 Upper troposphere height at 250hPa Weekly averages NAO index Greenland / Atlantic blocking is a strong NAO- flow regime Woollings et al (2008, JAS; 2010, JCL) ECMWF analyses

16 NOAA Climate Prediction Center (Tibaldi & Molteni blocking index) NAO and blocking during winter 2009/10 NAO Index

17 Winter 2008/9Winter 2009/10 Giacomo Masato, University of Reading Blocking frequency - percentage of days (Pelly & Hoskins blocking index) Blocking frequency anomalies

18 Early December onset of cold weather ECMWF analyses Animation for 04 – 11 Dec 2009: /anims/Z250.large.gif Animation for 11 – 18 Dec 2009: /anims/Z250.large.gif

19 NAO and blocking are natural variations of Atlantic weather What factors influence them – alter the chance of high/low values? Low extended range predictability (weeks, months) complex interactions; multiple factors Look at historical relationships with individual factors What did these factors predict for DJF 2009/10? Influences on NAO & Atlantic blocking

20 El Niño and La Niña NOAA, Climate Prediction Center Tropical convection generates Rossby waves that propagate into the extra- tropics, creating teleconnections with weather around the globe.

21 El Niño NOAA ESRL SST anomaly DJF 09/10 OLR anomaly DJF 09/10 NOAA Climate Diagnostics Bulletin

22 El Niño Teleconnections P MSL DJF 09/10 P MSL response to moderate El Nino, Jan-Feb Toniazzo & Scaife (2006) Tropospheric teleconnections from a moderate El Niño Project onto negative NAO Expect response to be captured in seasonal forecasts

23 Dynamical DJF Forecast versus NCEP reanalysis Z500 NCEP Reanalysis Forecast for JFM

24 24 Z500 Anomalies: DJF 2009/10

25 Solar activity and Atlantic blocking Woollings et al (2010)

26 Solar activity and Atlantic blocking Woollings et al (2010) Blocking frequency – composite anomalies ( )

27 Stratosphere – structure & variability 20°S 80°S 60°S40°S20°N40°N60°N80°N0°0° 20°S 80°S 60°S40°S20°N40°N60°N80°N0°0° ERA-40 reanalysis Tropopause ~10km (cold) Stratopause ~50km (warm) Polar vortex Summer easterlies Stratospheric variability: Sudden Stratospheric Warmings (SSW) Planetary waves Quasi-Biennial Oscillation (QBO) QBO waves Latitude mean wind

28 Solar activity – mechanism 1 Kodera & Kuroda (2002) At solar maximum: Stratopause heating (UV+O 3 ) Alters planetary wave forcing Weakens Brewer-Dobson circulation Cools polar stratosphere, strengthens polar vortex Downward influence on troposphere (Northern Annular Mode, NAM) Potential interaction with tropical winds (QBO) (Gray et al (2001)

29 Solar activity – mechanism 2 Haigh et al (2005), Simpson et al (2009) Idealised model response to lower stratospheric heating Feedback between winds and weather systems in the storm-track 5K 0K Equatorial heating Zonal wind climatology Zonal wind response Cold equatorial stratosphere in winter 2009/10 (solar-min + QBO?) Temperature anomaly DJF 2009/10

30 Did we expect a disturbed stratospheric vortex in winter 2009/10? DJF 09/10 QBO – equatorial winds Modified mean state: Solar minimum (Labitzke & Van Loon 1988; Kodera and Kuroda 2002) QBO East (Holton & Tan 1980) Trend (stronger Brewer-Dobson circulation) (Charlton et al 2008; Bell et al 2010) …all fit weaker than average polar vortex Met Office analyses, University of Reading Labitzke and Kunze (2010, JGR) QBO- east 30hPa height, North Pole

31 Did we expect a disturbed stratospheric vortex in winter 2009/10? Increased planetary wave activity El Niño (Ineson and Scaife, 2009; Bell et al 2009) Blocking (Martius et al 2010) 25 of 27 SSWs in the period were preceded by blocking SSW type is related to blocking location Blocking frequency preceding stratospheric sudden warming (SSW) events,

32 Key features of stratospheric flow: Minor warming – early December Strong vortex until mid-January – major stratospheric sudden warming (SSW) Weak, disturbed vortex late winter – persistent easterlies over polar cap North Pole temperature at 10hPa Zonal wind at 60N 10hPa Courtesy Andrew Charlton-Perez Minor Major Stratospheric vortex, DJF 2009/10

33 Pressure Dec-01Jan-01Feb-01Mar-01Dec-15Jan-15Feb-15 NAM index Zonal mean zonal wind 60-90N Pressure Dec-01Jan-01Feb-01Mar-01Dec-15Jan-15Feb-15 ECMWF operational analysis lower stratospheric splitStrong mid-winterdisplacement SSW event

34 Early December wave-2 simultaneous with blocking, confined to lower stratosphere Growth in vertical EP-flux is pre-blocking Was it driven by PNA-type pattern (El Niño)? January blocking precedes SSW Also strong PNA-like pattern, no NAO Low EP flux (10hPa) in late winter due to persistence of easterly anomalies in lower stratosphere 16 NOV16 DEC16 JAN16 FEB16 MAR16 APR EP-flux vector (10hPa, 60N) 16 NOV16 DEC16 JAN16 FEB16 MAR16 APR Vertical EP-flux (100hPa) EQ 90N Tropospheric precursors? NOV 500hPa Z Japan Meteorological Agency; Freie Universtät Berlin

35 Eurasian snow cover in October Cohen et al (2007, 2009)

36 AO - NAO - Blocking El Niño Eurasian snow cover (October) Solar minimumQBO east Stratospheric vortex Tropical Atlantic Planetary waves PNA Waves NAM latitude height Atlantic SST?

37 Attribution studies (1) Cattiaux et al (2010) Use past relationship to predict magnitude of Winter 2010 anomaly European temperature Flow analogues Warm residual (1963 similar dynamics but colder)

38 Attribution studies (2) Osborn (2011) in Weather Surface temperature Linear regression to estimate contribution of NAO- Residual shows European warmth Unexplained cold anomalies, USA, Siberia

39 Attribution studies (3) NOAA Attribution Team (2010), ESRL US east coast snow Past snowstorms related to El Niño and NAO- Combine El Niño + NAO- regressions to account for temperature anomalies Surface Air Temperature anomalies

40 Compare early Winter 2010/11 NOAA ESRL Surface Air Temperature anomaly December 2009December 2010 Remarkably similar temperature pattern Europe colder than 2009 North Pacific & western USA differ

41 Compare early Winter 2010/11 NOAA CPC and ESRL Circulation change in mid- November across N.Hemisphere Strong NAO- again Pacific differs, short jet (La Niña) Differing factors: La Niña, QBO west Solar activity remains low Strong stratospheric vortex 250hPa wind speed

42 Persistent equatorward shift of jet stream Blocking, negative NAO Increased forecast skill – El Niño signal + persistence Possible origins – factors working together? ….or chance, unpredictable? Attempts to attribute cold & snow anomalies Further work Forecast & hindcast diagnosis; anomalous forcing Conclusions


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