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Atmospheric Teleconnections and Climate Change Mike Blackburn National Centre for Atmospheric Science, University of Reading Talk for Lighthill Research.

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Presentation on theme: "Atmospheric Teleconnections and Climate Change Mike Blackburn National Centre for Atmospheric Science, University of Reading Talk for Lighthill Research."— Presentation transcript:

1 Atmospheric Teleconnections and Climate Change Mike Blackburn National Centre for Atmospheric Science, University of Reading Talk for Lighthill Research Network 2 May 2008 © University of Reading 2008

2 Teleconnections - Outline Well known examples: El Niño, North Atlantic Oscillation Processes – atmospheric response to heating – wave propagation Spatial correlations: linked regions of variability; patterns of variability Downstream developments on jet Tropical convection – MJO Climate change: potential methodology; ENSO, NAO examples

3 El Niño and La Niña NOAA, Climate Prediction Center (global teleconnections)

4 El Niño impacts (northern winter) NOAA, Climate Prediction Center La Niña impacts (northern winter)

5 El Niño / La Niña Changes in the location of tropical clouds over the Pacific David Neelin, UCLA Atmospheric response during El Niño (schematic) Pressure and flow in the upper troposphere La Niña - opposite sign to a first approximation, but weaker over N. America

6 Propagation of Rossby waves from a region of tropical convection (schematic) Trenberth et al. (1998)Horel and Wallace (1981)

7 Propagation of Rossby waves Model response to steady heating DJF Meridional wind ~250hPa Ambrizzi and Hoskins (1997) Climatological winds (DJF) Stationary phase (trough/ridge) fast eastward group propagation After 10 days 32ºN

8 Propagation of Rossby waves Model response to steady heating DJF Meridional wind ~250hPa Ambrizzi and Hoskins (1997) Model gives good agreement with theory Great circle paths + refraction by the climatological winds Jet streams are preferential paths for propagation (waveguides) After 15 daysAfter 9 days

9 Taxonomy of Teleconnections 50 years of daily global atmospheric analyses One-point correlation maps centres of action, associated patterns of variability Originally by Wallace & Gutzler (1981): correlations of monthly mean 500hPa height IPCC: from Hurrell et al (2003) PNA Pacific North-American pattern NAO North Atlantic Oscillation * *

10 From by Martin Visbeck NAO+NAO- The North Atlantic Oscillation (an example of regional teleconnections)

11 Sea level pressure pattern Dec-March Hurrell (1995), Science Winter NAO index based on Portugal – Iceland pressure difference Now associated with breaking Rossby waves The North Atlantic Oscillation

12 Summer 2007 UK floods - jet stream - strength of wind at 250hPa - Average from 12 June to 25 July Climatology 2007 Persistent pattern of waves on the jet stream – trough (low pressure) over UK Jet joins up over Europe – possible continuous waveguide & stationary free wave (ms -1 )

13 Summer 2007 UK floods (potential temperature on the tropopause) Air moving equatorwards from the cold polar reservoir becomes cyclonic Repeated pattern of waves associated with each flooding event Slow-moving cyclonic anomalies over UK, forcing air to ascend and rain 15 June25 June20 July

14 THORPEX International Science Plan Impacts of severe weather associated with four Rossby wave-trains that encircled the globe during November 2002

15 Global tropopause trough-ridge pattern (Rossby Waves)

16 Alan Thorpe Time/longitude diagram 250hPa meridional wind (ms -1 ); 35-60ºN 6-28 November 2002

17 Hovmöller diagram of 250-mb meridional wind component (ms -1 ) 28 July -14 August 2002 (40-60ºN) On 1 August 2002, a Rossby wave train was excited by cyclogenesis east of Japan, followed by rapid downstream development of high- amplitude Rossby waves, culminating in severe flooding in Central Europe on 11 August Mel Shapiro, NOAA Prague

18 Madden-Julian Oscillation (MJO) Main mode of intraseasonal variability in tropical convection and rainfall Rainfall Composite life-cycle (DJF) mm/day Adrian Matthews, University of East Anglia

19 MJO teleconnections (1) Acts as a moving source of extra-tropical wave-trains cloudyclear Source: U.S. CLIVAR

20 MJO teleconnections (2) Modulation of Atlantic hurricane activity in Summer, especially strongest (cat. 3-5) Source: U.S. CLIVAR

21 Madden-Julian Oscillation (MJO) Main mode of intraseasonal variability in tropical convection and rainfall Propagates eastwards from Indian Ocean to west Pacific time lagged correlations along the equator a moving source of waves propagating into mid-latitudes Modulation of the Asian Summer monsoon (active/break cycle) Poorly simulated in models (latest ECMWF model much improved) Potential for extended predictability in both tropics and extra-tropics (few weeks)

22 Teleconnections and climate change Increasing analysis of variability in models (IPCC, AR4) El Niño Southern Oscillation (ENSO) NAO and Northern Annular Mode (NAM) Other possible changes: jet stream waveguide characteristics; triggering More understanding of present day variability is needed to underpin this e.g. apparent phase locking; persistence of anomalies Assess simulations of present day variability and teleconnections

23 Oldenborgh et al (2005) in IPCC, AR4 (2007) Climate Change - El Niño Weak tendency for change in mean Pacific state to be El Niño like No agreement on El Niño variability Weaker teleconnections over N. America

24 Climate Change - NAO

25 Average change projects onto Northern Annular Mode (NAM) Recent variability not captured (NAM) Caveat on methodology Climate Change – Annular Indices Miller et al (2006) in IPCC, AR4 (2007)

26 Teleconnections - Conclusions Remote effects of modes of variability, e.g. El Niño, NAO Wave propagation – tropics; great circles; jet streams as waveguides Downstream developments on the jet stream: examples of linked weather, e.g. November 2002, August 2002 triggering: storm growth; tropical cyclone transitions persistent anomalies, e.g. Summer 2007 (Autumn 2000) Tropical convection – MJO: eastward propagation - time lagged correlations in tropics moving source of waves for extra-tropics (predictability) Climate change: uncertainty, even for El Niño and NAO potential methodology

27 - End -


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