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Factors Contributing to the Summer 2003 European Heatwave

Factors Contributing to the Summer 2003 European Heatwave Emily Black, Mike Blackburn, Giles Harrison, Brian Hoskins and John Methven CGAM and Department of Meteorology, The University of Reading, U.K. Weather, 59 (8), 217-223 (August 2004, special issue). Summer 2003.

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Factors Contributing to the Summer 2003 European Heatwave

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  1. Factors Contributing to the Summer 2003 European Heatwave Emily Black, Mike Blackburn, Giles Harrison, Brian Hoskins and John Methven CGAM and Department of Meteorology, The University of Reading, U.K. Weather,59(8), 217-223 (August 2004, special issue)

  2. Summer 2003 Record European temperature anomalies Over 14,000 excess deaths in France alone Widespread wild fires Reduced crop yields Reduced river discharges Power generation restrictions (cooling water) Increased melting of Alpine glaciers A taste of future conditions?

  3. 2003 Surface Air Temperature ECMWF Analyses (ERA-40 climatology)

  4. May June Streamfunction anomalies 850hPa European anticyclonic anomaly Low pressure west of UK Relativelystationary pattern July August ECMWF Analyses (ERA-40 climatology) 106 m2s-1

  5. Outgoing Longwave Radiation (OLR) June May July August Wm-2 Monthly anomalies - NOAA satellite observations

  6. Sea Surface Temperature anomalies degC Response to radiative anomalies?

  7. Air Parcel Trajectories • Trajectories arriving at 500m over Paris, 6-12 August • Anticyclonic descent • Importance of local energy budget in determining temperatures Colour: arrival date (red to blue) ECMWF Analyses

  8. θv profiles : Paris, 6-12 August Deep daytime boundary layer (18UTC, red) Shallow nocturnal surface layer (06UTC, black) ECMWF Analyses

  9. Regional Energy Budget: anomalies Surface drying amplified radiative forcing of surface temperature ECMWF 0-24 hour forecast data: 0-20°E; 42.5-52.5°N land only

  10. Reading Observations: August Upward ground heat-flux: 10Wm-2 heats 100m layer at ~0.3Khr-1

  11. Reading Observations: 10th August Upward ground heat flux slows nocturnal cooling Elevated nocturnal temperatures prolong heat stress, important for human mortality

  12. Ensemble Modelling Unified Model (HadAM3) Control ensemble forced by Reynolds/NCEP SST preceding decades 2003 global SSTs, or omitting specific regions European warmth captured by 2003 global SST ensemble Evidence for forcing from Indian Ocean SST Opposing effect of Mediterranean SST? - See poster by Emily Black and Rowan Sutton -

  13. 1864-2003 Observations 1961-1990 2071-2100 Model Variability of Swiss summer temperature and precipitation anomalies Regional modelling over Europe up to present-day and for late 21st century. Driven by high-resolution GCM climate-change expts Schaer et al (2004), Nature Model data from PRUDENCE EU project

  14. 1864-2003 Observations 1961-1990 2071-2100 Model Variability of Swiss summer temperature and precipitation anomalies By the end of this century, under a high-emissions scenario, summer 2003 European temperatures could be seen as “normal”! Schaer et al (2004), Nature Model data from PRUDENCE EU project

  15. - A recent climatology - Central England temperature (CET) Summer (JJA) 1860-2003 2003 anomaly relative to the 1961-90 average is large Temperature (degC) Year

  16. - An evolving climatology - Central England temperature (CET) Summer (JJA) 1860-2003 Using an evolving climatology reduces the 2003 anomaly: 2003: 1.4 vs. 2.4 * Std.Dvn. 8% vs. 0.9% probability 13 vs. 110 year return period (gaussian assumption) Temperature (degC) Year Black: 1860-2002 average (very close to 1961-90) Red: evolving climatology – smoothed spline

  17. 2003 Summer CET probabilities Probability density Temperature (degC) Red: PDF relative to fixed climatology Pale: PDF relative to evolving climatology at 2003

  18. Ranking of extremes Central England summer temperature (JJA) 2003 Relative to evolving climate Temperature (degC) Relative to fixed climate  coolest Rank warmest  2003 was 12th warmest (not 3rd) relative to the evolving climatology

  19. Evolving Climatology - Issues • Sensitive parameters and deductions: • Partitioning into inter-annual and forced variability • Attribution: robust estimation; confidence measures (Stott et al, 2004) • Increasing importance as climate change accelerates • Magnitude of anomalies • Return periods • Ranking of extreme events • PDFs

  20. Conclusions Anticyclonic anomaly dominated: Stationary pattern in European – Atlantic sector Evidence for remote influence Non-stationary climatology - implications A taste of things to come? • Weak advection; local energy budget dominates • Soil drying a positive feedback on surface temperature • Upward ground heat flux limits nocturnal cooling

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