Transcript WP1: Definition of Meteorological Situations

EMS Conference September 2013
The dependence of contrail
formation on weather pattern and
altitude in the North Atlantic
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
• The climate impact of persistent contrails and contrail cirrus could
be comparable to CO2 impact (e.g. Burkhardt and Kärcher, 2011)
• Persistent contrails only form when aircraft fly through cold icesupersaturated regions (ISSRs) in the upper-troposphere
• an AVOIDABLE climate impact of aviation
Lee et al (2009)
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Motivation
• Climate optimal aircraft routing: find the route which
minimises the climate impact of the aircraft’s emissions on a
flight-by-flight basis (REACT4C project)
• Aircraft routes depend on the large-scale weather pattern
 What are preferred locations and altitudes for ISSRs?
New
York
London
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Climatological ISSR frequency over
the North Atlantic in ERA-Interim
300 hPa, FL300
250 hPa, FL340
200 hPa, FL390
• Qualitatively reproduces satellite climatologies (Spichtinger 2003;
Lamquin 2012)
• Case studies show ISSRs are associated with anticyclonic flow (Kästner
1999; Immler 2008) and warm conveyor belts (Spichtinger 2005)
Methodology
• Identify cold ice-supersaturated regions (ISSRs) in ERA-Interim as
regions where temperature < 233 K, relative humidity w.r.t. ice >
100 %
• Two methods:
– Synoptic weather pattern analysis links contrail formation
conditions to specific meteorological features
(Irvine et al., 2013 Met Apps and Irvine et al., 2012 GRL)
– Lagrangian trajectories are used to investigate long-lived icesupersaturated air which can support long-lived contrails
(Irvine et al., 2013 JGR – in review)
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Cold ISSR frequency by winter
weather pattern and altitude
300 hPa
250 hPa
200 hPa
W1. Zonal jet
W2. Tilted jet
W4. Confined jet
Eastbound routes
Westbound routes
• Location linked to various features: jet stream, Greenland, ridges
• Altitude distribution depends on weather pattern
%
Probability of persistent contrail
formation along a route
Eastbound
W1. Zonal jet
W2. Tilted jet
Westbound
W4. Confined jet
Eastbound routes
Westbound routes
•
Flying higher does not always produce fewer contrails!
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Trajectory Analysis
T+0
T+48 h
T-48 h
• Trajectories released on 1°x1°grid covering north Atlantic, from 200
hPa, 250 hPa and 300 hPa
• Lagrangian trajectory code (Methven, 1997) run on ERA-Interim data
• Generated 249,874 trajectories with ice-supersaturation (winter)
Trajectories of air that becomes
ice-supersaturated over the UK
24 h before…
24 h after…
• For trajectories starting in the troposphere with ice-supersaturation
duration of 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
• Long-lived ISS air comes from a more southerly direction and has a
slower speed than short-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
• ERA-Interim re-analysis data are used to analyse regions where
persistent contrails could be formed, for the north Atlantic region.
• Preferred locations for persistent contrail formation are in regions
of uplift associated with the jet stream, around the northern
periphery of high-pressure ridges, and over Greenland.
• The formation of contrails shows a strong dependence on altitude
in a given weather pattern
• Air parcels which remain ice-supersaturated for long periods (and
therefore can support long-lived contrails) may be associated with
certain weather features, e.g. 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 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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Duration of ice-supersaturation
ALL ISS points
Tropospheric ISS
Stratospheric ISS
• Median duration of ice-supersaturation is less than 6 hours
• % ice-supersaturated air parcels that have duration of at least 24 h:
• 5% (tropospheric air)
• 23% (stratospheric air)