Transcript WP1: Definition of Meteorological Situations

ARAM AMS January 2013
Relating the climate impact of
trans-Atlantic flights to typical north
Atlantic weather patterns
Emma Irvine, Keith Shine, Brian Hoskins
Meteorology Department, University of Reading
Contact: [email protected]
© University of Reading 2012
www.met.reading.ac.uk/~gb902035
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Motivation for classifying
weather patterns
Daily Minimum time routes, Dec. 2009
Westbound 12 UTC
Eastbound 00 UTC
• Large variation in route location and time due to upper-level winds
• Daily minimum time routes for 3 winters provided by the Met Office
• Met data from ERA-Interim analyses at 250 hPa (FL340), 1989-2010
Winter weather patterns are
characterised by the jet stream
W1. strong zonal jet
W2. Strong tilted jet
W4. Confined jet
Irvine et al., 2012, Met. Apps., in press
Composite 250 hPa geopotential height (black) and wind speed > 40 ms-1 (red).
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Winter weather patterns are
characterised by the jet stream
Eastbound
Westbound
W1. strong zonal jet
W2. Strong tilted jet
W4. Confined jet
Irvine et al., 2012, Met. Apps., in press
Composite 250 hPa geopotential height (black) and wind speed > 40 ms-1 (red).
Individual time-optimal aircraft routes between London and New York (blue).
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Climate impact in different
weather patterns: CO2
• Proxy for the CO2 impact of a flight: time to fly the minimum time
route, assuming a constant airspeed and altitude
Climate impact in different
weather patterns: CO2
• Proxy for the CO2 impact of a flight: time to fly the minimum time
route, assuming a constant airspeed and altitude
Occurrence of cold
ice-supersaturated regions
300 hPa
250 hPa
200 hPa
Route location
W1. Zonal jet
W2. Tilted jet
W4. Confined jet
%
Eastbound
Westbound
• Location linked to various features: jet stream, Greenland, ridges
• Altitude distribution depends on weather pattern
Irvine et al., 2012 GRL
Trajectory Analysis
• Lagrangian trajectory code (Methven, 1997) run on ERA-Interim data
• Trajectories released on a 1x1 degree grid, over North Atlantic from
250 hPa
Origin of icesupersaturated air
T-48 h
T+48 h
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T+0
Lifetime of icesupersaturated air
Trajectory Analysis
• Lagrangian trajectory code (Methven, 1997) run on ERA-Interim data
• Trajectories released on a 1x1 degree grid, over North Atlantic from
250 hPa
Origin of icesupersaturated air
T-48 h
T+48 h
22
T+0
Lifetime of icesupersaturated air
• Total ~ 100,000 trajectories with ice-supersaturation (ISS)
• Of these, ~ 60% start in the troposphere, ~ 40% in stratosphere
Trajectories of air that become
ice-supersaturated over the UK
24 h before…
24 h after…
• For trajectories starting in the troposphere with lifetime at least 24 h
• Air that becomes ice-supersaturated over the UK comes from the
south-west and moves north-eastwards.
Comparison of longer-lived ISS air
with shorter-lived ISS air
Direction air comes from
W
Speed of air (along trajectory)
S
• Air which stays ISS for > 24 h comes from a more southerly
direction and has a slower speed than shorter-lived ISS air
• This suggests that a greater proportion of long-lived ISS air is
associated with high-pressure ridges rather than the jet stream
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Summary
Using characteristic weather patterns for the north Atlantic winter
season, we find that:
• The CO2 and contrail impacts vary by weather pattern
• Eastbound routes benefit from the jet stream and therefore have
a (<20%) smaller CO2 impact than westbound flights
• The formation of contrails shows a strong dependence on altitude
in a given weather pattern
• Preferred locations for contrail formation are over Greenland,
around high-pressure ridges and in regions of uplift near jet
streams
• Air which becomes ice-supersaturated over the UK comes from
the SW; air which stays ice-supersaturated for at least 24 h may
be associated with high-pressure ridges
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Thank you!
Information from:
[email protected]
www.react4c.eu
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Dependence of route latitude
on the jet stream
Eastbound: New York - London
fly in the jet stream
Westbound: London - New York
avoid the jet stream
Irvine et al., 2012, Meteorological Applications, in press
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Probability of persistent contrail
formation along a great circle route
GC
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Probability of persistent contrail
formation along a route
W
GC
E
Estimates of contrail formation are
very sensitive to route location!
• Flying higher forms LESS contrails (type W1, both directions)
• Flying higher forms MORE contrails (types W2 and W3 eastbound)
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