© University of Reading TAC-3 Conference June 2012 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: 1

Motivation Climate optimal aircraft routing: find the route which minimises the climate impact of the aircrafts emissions on a flight-by-flight basis (REACT4C project) Aircraft routes depend on upper level winds and therefore the large-scale weather pattern 2 London New 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) 3

Objectives Analyse ISSR frequency and location at different altitudes on three different temporal and spatial scales for the north Atlantic region: 4 Results are published in: Irvine et al., 2012, GRL (in press) Increasing relevance to climate optimal routing 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 period 5 Climatological Large-scale weather pattern Individual flight Identify cold ice-supersaturated regions (ISSRs) in ERA-Interim as regions where temperature 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

6 Climatological Large-scale weather pattern Individual flight

Climatological cold ISSR frequency over the North Atlantic 300 hPa, FL hPa, FL 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 ( )

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

The jet stream latitude is related to the North Atlantic Oscillation 10 +ve -ve From: 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 11 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 hPa250 hPa200 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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14 Probability of persistent contrail formation along a great circle route GC

15 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 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 17 How will upper-tropospheric climate change help or hinder aviation industry efforts to reduce their impact on climate?

Thank you! Information from: 18

Climate impact varies with route location, weather and season 18 February January 2010 Flight entirely in stratosphere produces no contrails Flight mostly in troposphere produces persistent contrails Flight level tropopause contrails 19