© University of Reading 2012 www.met.reading.ac.uk/~gb902035

TAC-3 Conference June 2012

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

• 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 upper level winds and therefore the large-scale weather pattern

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LondonNew York

Background: ice-supersaturated regions (ISSRs)

• Global picture from satellite data (Spichtinger et al., 2003; Lamquin et al., 2012)

• Case studies show that ISSRs occur with:– anticyclonic flow (Kästner et al., 1999; Immler et al., 2008)– above a warm conveyor belt (Spichtinger et al., 2005a)– gravity waves (Spichtinger et al., 2005b)

• ISSRs are generally shallow so can be avoided by small changes in altitude (Williams et al., 2002; Fichter et al., 2005; Mannstein et al., 2005; Rädel and Shine, 2008)

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Objectives

• Analyse ISSR frequency and location at different altitudes on three different temporal and spatial scales for the north Atlantic region:

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• Results are published in: Irvine et al., 2012, GRL (in press)

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Climatological

Large-scale weather pattern

Individual flight

• Does our dataset (ERA-Interim) reproduce the observed climatology?

• Are there preferred locations for ISSRs within weather patterns?

• What is the likelihood of encountering an ISSR at a particular altitude?

Methodology

• Winter mean frequency over 1989-2010 period

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Climatological

Large-scale weather pattern

Individual flight

• Identify cold ice-supersaturated regions (ISSRs) in ERA-Interim as regions where temperature < 233 K, relative humidity w.r.t. ice > 100 %

• Analyse ISSR frequency at different altitudes on three scales:

• Previously identified 5 typical north Atlantic weather patterns for winter (Irvine et al., 2012, Meteorological Applications, in press)

• Use time-optimal routes on New York – London, assuming a fixed pressure altitude for cruise level

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Climatological

Large-scale weather pattern

Individual flight

Climatological cold ISSR frequency over the North Atlantic

300 hPa, FL300 250 hPa, FL340 200 hPa, FL390

• Qualitatively reproduces satellite climatology, with reduced frequencies

• Overall, the frequency of cold ISSRs decreases with altitude• Maxima: storm track, Greenland, minima: NW Atlantic

• 21 years of winter data, ERA-Interim (1989-2010)

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Climatological

Large-scale weather pattern

Individual flight

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

9Irvine et al., 2012, Meteorological Applications, in press

The jet stream latitude is related to the North Atlantic Oscillation

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+ve

-ve

From: http://www.ldeo.columbia.edu/res/pi/NAO/

NAO +ve = northerly jet stream NAO -ve = southerly jet stream

Winter weather types are characterised by the jet stream

Eastbound Westbound

Irvine et al., 2012, Met. Apps., in press

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W1. strong zonal jet

W2. Strong tilted jet

W4. Confined jet

Composite 250 hPa geopotential height (black) and wind speed > 40 ms-1(red). Individual time-optimal aircraft routes between London and New York (blue).

300 hPa 250 hPa 200 hPa

W1. Zonal jet

W2. Tilted jet

%

Cold ISSR frequency by weather pattern and altitude

W4. Confined jet

Route location

• Location linked to various features: jet stream, Greenland, ridges• Altitude distribution depends on weather pattern

Eastbound Westbound

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Climatological

Large-scale weather pattern

Individual flight

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Probability of persistent contrail formation along a great circle route

GC

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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!

Summary

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• 21 years of ERA-Interim re-analysis data are used to analyse cold ISSRs at 3 scales for the north Atlantic region.

• Results published in Irvine et al., 2012, GRL (in press)

Climatological

Large-scale weather pattern

Individual flight

• The locations of ISSRs in ERA-Interim agree well with satellite climatology although the frequencies are reduced

• Preferred locations for ISSRs are over Greenland, around high-pressure ridges and in regions of uplift near jet streams

• The probability of contrailing either increases or decreases with altitude, dependent on weather pattern and aircraft route through this

Future Directions• New 3-year NERC-funded project starting in January 2013:

• For individual flights within the north Atlantic and north Pacific regions, the project will analyse changes to:–the strength and location of the jet streams–upper-tropospheric humidity –tropopause height

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How will upper-tropospheric climate change help or hinder aviation industry efforts to reduce their impact on climate?

Thank you!

Information from:

e.a.irvine@reading.ac.uk

www.react4c.eu

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Climate impact varies with route location, weather and season

18 February 2010 26 January 2010

Flight entirely in stratosphere produces no contrails

Flight mostly in troposphere produces persistent contrails

Flight level

tropopause

contrails

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