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Large-scale context for the UK floods in Summer 2007 Submitted to Weather , 14 May 2008

Large-scale context for the UK floods in Summer 2007 Submitted to Weather , 14 May 2008 Mike Blackburn 1 John Methven 2 and Nigel Roberts 3 (1) National Centre for Atmospheric Science, University of Reading (2) Department of Meteorology, University of Reading

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Large-scale context for the UK floods in Summer 2007 Submitted to Weather , 14 May 2008

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  1. Large-scale context for the UK floods in Summer 2007 Submitted to Weather, 14 May 2008 Mike Blackburn1 John Methven2 and Nigel Roberts3 (1) National Centre for Atmospheric Science, University of Reading (2) Department of Meteorology, University of Reading (3) Met Office, Joint Centre for Mesoscale Meteorology

  2. Summer 2007 and UK Flooding • Outline: • UK and European regional rainfall • Global context: evolution and averages • Synoptic development for 3 rainfall events: • Upper-air precursors • Synoptic structure and rainfall • Warm air-mass trajectories

  3. England-Wales Rainfall (Mar-Aug 2007) May-July record rainfall : 216% of 1961-1990 average

  4. European Precipitation (% of normal) May-July June July August

  5. 15 June 25 June 20 July Large-scale evolution: z250 anomaly 45N-60N

  6. Anomaly Jet streams (isotachs, 250hPa) 12 June – 25 July average Climatology 2007 (ms-1)

  7. Jet streams (isotachs, 250hPa) 12 June – 25 July average (ms-1)

  8. Streamfunction anomaly 12 June – 25 July average Upper troposphere :  = 0.200 Lower troposphere :  = 0.850 (m2s-1) (m2s-1)

  9. Sea Surface Temperature 12 June – 25 July average OLR 12 June – 25 July average Anomaly - NCEP reanalysis data Anomaly - NOAA interpolated data (K) (Wm-2)

  10. SST indices Niño 3.4 weakly negative in June-July

  11. Circumglobal teleconnections Hemispheric teleconnection pattern Associated with Indian Summer Monsoon variability correlates with SST (La Nina), due to effect on ISM Note Atlantic/European pattern changes through summer season Ding & Wang (2005, J.Climate)

  12. ENSO composites Ding & Wang (2005, J.Climate)

  13. Monsoon – all-India rainfall

  14. 15 June rainfall θ(pv2) Tue 12nd 00utc Wed 13rd 00utc Thur 14th 00utc Fri 15th 00utc

  15. 15 June rainfall event Tue 12nd 00utc Wed 13rd 00utc Thur 14th 00utc Fri 15th 00utc

  16. Heavy continuous rain     Heavy showers 15 June rainfall event PV on θ=315K θw on 850hPa msl pressure

  17. 15 June rainfall event

  18. 25 June rainfall θ(pv2) Fri 22nd 00utc Sat 23rd 00utc Sun 24th 00utc Mon 25th 00utc

  19. 25 June rainfall event Fri 22nd 00utc Sat 23rd 00utc Sun 24th 00utc Mon 25th 00utc

  20. Heavy continuous rain     Heavy showers 25 June rainfall event PV on θ=315K θw on 850hPa msl pressure

  21. 25 June rainfall event

  22. 20 July rainfall θ(pv2) Tues 17th 00utc Weds 18th 00utc Thurs 19th 00utc Fri 20th 00utc

  23. 20 July rainfall event Tues 17th 00utc Weds 18th 00Z Thurs 19th 00Z Fri 20th 00Z

  24. Heavy continuous rain     Heavy showers 20 July rainfall event PV on θ=315K θw on 850hPa msl pressure

  25. 20 July rainfall event

  26. Herstmonceux sounding 00utc 20 July Column water vapour

  27. Herstmonceux sounding 12utc 20 July

  28. Weather system schematic for extreme rainfall (2004)

  29. Summary: • Soil moisture pre-conditioned (May rain) • Persistent large-scale pattern, June-July • Jet displacement associated with hemispheric wave pattern • Quasi-stationary UK upper trough • forcing from upper levels • slow-moving weather systems • 3 major UK rainfall events • Warm air-mass origin over subtropical Atlantic • Cool SST anomalies south & west of UK • Air was warm & moist due to location of origin

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