the basic ingredients of the north atlantic storm track david brayshaw, brian hoskins and mike...
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The basic ingredients of the North Atlantic storm track
David Brayshaw, Brian Hoskins and Mike [email protected]
• Brayshaw et al. (2008) The storm track response to idealized SST perturbations in an aquaplanet GCM, J. Atm. Sci, 65, 2842-2860.
• Brayshaw et al. (2009) The basic ingredients of the North Atlantic storm track. Part I: land-sea contrast and orography, J. Atm. Sci, 66, 2539-2558.
• Brayshaw et al. (2011) The basic ingredients of the North Atlantic storm track. Part II: sea surface temperatures, J. Atm. Sci, minor revisions.
• Sauliere et al. (2011) Further investigation of the impact of idealised continents and SST distributions on the Northern Hemisphere storm tracks, J. Atm. Sci, in prep.
Introduction
NH storm tracks
Strongest in winter
Two primary regions
Strong impact on European climate and weather
Fig: NCEP storm tracks
Fig from Ulbrich et al (2008).Winter storm track activity (2-6d BPF Geo 500)
From Ulbrich et al (2008).
CMIP3 C20ensemble
NCEP CMIP3 -NCEP
From Ulbrich et al (2008).
CMIP3 C20ensemble
NCEP CMIP3 -NCEP
Errors in storm track:Location, strength, orientation
From Ulbrich et al (2008).
CMIP3 C20ensemble
NCEP CMIP3 -NCEP
CMIP3:C21 – C20
Errors in storm track:Location, strength, orientation
From Ulbrich et al (2008).
CMIP3 C20ensemble
NCEP CMIP3 -NCEP
CMIP3:C21 – C20
Errors in storm track:Location, strength, orientation
Changes in storm track:Location, strength, orientation
From Ulbrich et al (2008).
CMIP3 C20ensemble
NCEP CMIP3 -NCEP
CMIP3:C21 – C20
Errors in storm track:Location, strength, orientation
Changes in storm track:Location, strength, orientation
What features determine the basic structure of the storm track?
• Land-sea contrast?• Orography?• SST gradients/ anomalies?• Tropical circulation structures?
In isolation and in combination
North Atlantic experimental design
Full atmospheric GCM (HadAM3 @1.5o resolution)
Perpetual equinox
Orographic, land surface and SST profiles based on “real” boundary condition data
Accompanying full-aquaplanet simulations
Land properties
OrographySST profiles
Control simulation (no land)
Statistically zonally symmetric storm track and jet
Broad jet – “almost split”
Storm track 850 hPa
2-6 day band pass filtered
geopotential height variance (m2)
30N
60N
90W 0E 90E
Baroclinicity
Eady growth rate (850 hPa)
30N
60N
90W 0E 90E
Extratropical land-sea contrast:A small rectangular continent
Storm track 850 hPa
Storm track weakened over land:• reduced moisture availability• increased surface drag
Baroclinicity enhanced over land:• stronger surface dT/dy• increased surface drag
Baroclinicity 850 hPa
Colours =absolute values, contours = differencehatches (on storm track plots) = 90% signif
Extratropical land-sea contrast:A small rectangular continent
Storm track weakened over land:• reduced moisture availability• increased surface drag
Baroclinicity enhanced over land:• stronger surface dT/dy• increased surface drag
Stronger storm track downstream
Storm track 850 hPa Baroclinicity 850 hPa
Extratropical land-sea contrast:The “Atlantic” sector
30N
60N
90W 0E
Small rectangular continent Semi-realistic North American continent
Storm track localised over North Atlantic
ocean basin
Storm track 850 hPaStorm track 850 hPa
Colours =absolute values, contours = differencehatches (on storm track plots) = 90% signif
The Rocky Mountains
Introduce orographic feature
Temperature (shading) and streamfunction (contours) anomalies at 700 hPa
Streamfunction at 1000 hPa
The Rocky Mountains
Temperature (shading) and streamfunction (contours) anomalies at 700 hPa
Streamfunction at 1000 hPa
Northward deflection:isentropic ascent
“over” the hill
Southward deflection:isentropic descent
“around the hill” or blocked return flow
The Rocky Mountains
Cold dry air pool to NWWarm moist air to SE
Enhanced baroclinicity along SW-NE axis of coastline
Eady growth rate 850 hPa
Temperature (shading) and streamfunction (contours) anomalies at 700 hPa
Streamfunction at 1000 hPa
The Rocky Mountains
Temperature (shading) and streamfunction (contours) anomalies at 700 hPa
Streamfunction at 1000 hPa
Enhanced storm growth along SW-NE axis of coastline
Storm track 850 hPa
The Gulf Stream
Storm track 850 hPa
Gulf Stream in aquaplanet
Tight SST gradient
The Gulf Stream
Storm track 850 hPa
Gulf Stream in aquaplanet
Tight SST gradient
Enhanced storm track
The Gulf Stream
Storm track 850 hPa
Gulf Stream in aquaplanet
Tight SST gradient
Enhanced storm track
Gulf Stream in “semi-realistic”
The Gulf Stream
Storm track 850 hPa
Gulf Stream in aquaplanet
Tight SST gradient
Enhanced storm trackEnhanced storm track
Weaker storm track
(BC reduced at coast)
Gulf Stream in “semi-realistic”
Other features
North Atlantic Drift (warm NE Atlantic):
weakens storm track
possible northward shift
North Atlantic SSTs include (sub)tropics
Affects tropical circulation and subtropical jet
Relationship between subtropical jet and extratropical SST gradients important
South American continent
Southern Eurasia
Pacific sector (with Jerome Sauliere, submitting to JAS.)
Extensions/links
NERC Fellowship
• “Semi-realistic” framework
• Mediterranean storm track
• Relationship to poleward energy transport
UK hydrological extremes project (NERC CWC)
Other• UK/European energy systems
• Holocene storm track changes (last 12,000 years)
Brayshaw, Hoskins and Black; Phil Trans A (2010)
The basic ingredients of the North Atlantic storm track
David Brayshaw, Brian Hoskins and Mike [email protected]
• Brayshaw et al. (2008) The storm track response to idealized SST perturbations in an aquaplanet GCM, J. Atm. Sci, 65, 2842-2860.
• Brayshaw et al. (2009) The basic ingredients of the North Atlantic storm track. Part I: land-sea contrast and orography, J. Atm. Sci, 66, 2539-2558.
• Brayshaw et al. (2011) The basic ingredients of the North Atlantic storm track. Part II: sea surface temperatures, J. Atm. Sci, minor revisions.
• Sauliere et al. (2011) Further investigation of the impact of idealised continents and SST distributions on the Northern Hemisphere storm tracks, J. Atm. Sci, in prep.