© university of reading 2012 gb902035 ems conference september 2013 the dependence of contrail...
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© University of Reading 2012 www.met.reading.ac.uk/~gb902035
EMS Conference September 2013
The dependence of contrail formation on weather pattern and altitude in the North AtlanticEmma Irvine, Keith Shine, Brian Hoskins
Meteorology Department, University of Reading
Contact: [email protected]
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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 ice-supersaturated regions (ISSRs) in the upper-troposphere
• an AVOIDABLE climate impact of aviation
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Lee et al (2009)
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?
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LondonNew York
Climatological ISSR frequency overthe 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
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• 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 ice-supersaturated air which can support long-lived contrails (Irvine et al., 2013 JGR – in review)
300 hPa 250 hPa 200 hPa
W1. Zonal jet
W2. Tilted jet
%
Cold ISSR frequency by winterweather pattern and altitude
W4. Confined jet
• Location linked to various features: jet stream, Greenland, ridges• Altitude distribution depends on weather pattern
Eastbound routes Westbound routes
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Probability of persistent contrail formation along a route
Westbound
Eastbound
W1. Zonal jet
W4. Confined jet
W2. Tilted jet
Eastbound routes Westbound routes
• Flying higher does not always produce fewer contrails!
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
• 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.
24 h before… 24 h after…
• 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
Comparison of longer-lived ISS air with shorter-lived ISS air
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W
S
Direction air comes from Speed of air (along trajectory)
Summary
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• 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
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
13Irvine et al., 2012, Meteorological Applications, in press
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• Flying higher forms LESS contrails (type W1, both directions)• Flying higher forms MORE contrails (types W2 and W3 eastbound)
Probability of persistent contrail formation along a route
GC
W
E
Estimates of contrail formation are very sensitive to route location!
Duration of ice-supersaturation
• 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)
ALL ISS points
Tropospheric ISS
Stratospheric ISS