© 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: e.a.irvine@reading.ac.uk

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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

Thank you!

Information from:

e.a.irvine@reading.ac.uk

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

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