large-scale context for the uk floods in summer 2007 submitted to weather, 14 may 2008 mike...
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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
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
England-Wales Rainfall (Mar-Aug 2007)
May-July record rainfall : 216% of 1961-1990 average
European Precipitation
(% of normal)
June AugustJuly
May-July
Large-scale evolution: z250 anomaly 45N-60N
15 June
25 June
20 July
Jet streams (isotachs, 250hPa)
12 June – 25 July average
Anomaly
2007Climatology
(ms-1)
Jet streams (isotachs, 250hPa)
12 June – 25 July average
(ms-1)
Streamfunction anomaly
12 June – 25 July average
Upper troposphere : = 0.200 Lower troposphere : = 0.850
(m2s-1)(m2s-1)
Sea Surface Temperature
12 June – 25 July average
OLR
12 June – 25 July average
Anomaly - NCEP reanalysis data Anomaly - NOAA interpolated data
(Wm-2)(K)
SST indices
Niño 3.4 weakly negative in June-July
Circumglobal teleconnections
Ding & Wang (2005, J.Climate)
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
ENSO composites
Ding & Wang (2005, J.Climate)
Monsoon – all-India rainfall
15 June
rainfall
θ(pv2)
Fri 15th 00utc
Wed 13rd 00utc
Tue 12nd 00utc
Thur 14th 00utc
15 June rainfall event
Fri 15th 00utc
Wed 13rd 00utc Tue 12nd 00utc
Thur 14th 00utc
15 June rainfall event
PV on θ=315K
θw on 850hPa
msl pressure Heavy showers
Heavy continuous rain
15 June rainfall event
25 June
rainfall
θ(pv2)
Mon 25th 00utc
Sat 23rd 00utc
Fri 22nd 00utc
Sun 24th 00utc
25 June rainfall event
Mon 25th 00utc
Sat 23rd 00utc Fri 22nd 00utc
Sun 24th 00utc
25 June rainfall event
PV on θ=315K
θw on 850hPa
msl pressure Heavy showers
Heavy continuous rain
25 June rainfall event
20 July
rainfall
θ(pv2)
Fri 20th 00utc
Weds 18th 00utc
Tues 17th 00utc
Thurs 19th 00utc
20 July rainfall event
Fri 20th 00Z
Weds 18th 00Z Tues 17th 00utc
Thurs 19th 00Z
20 July rainfall event
PV on θ=315K
θw on 850hPa
msl pressure Heavy showers
Heavy continuous rain
20 July rainfall event
Herstmonceux sounding
00utc 20 July
Column water vapour
Herstmonceux sounding
12utc 20 July
Weather system schematic for extreme rainfall
(2004)
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