The dependence of contrail formation on weather pattern and altitude in the North Atlantic

1. 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: e.a.irvine@reading.ac.uk

2. 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 New York London

3. 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)

4. Objectives • Analyse ISSR frequency and location at different altitudes on three different temporal and spatial scales for the north Atlantic region: • 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? Climatological Large-scale weather pattern Increasing relevance to climate optimal routing Individual flight • Results are published in: Irvine et al., 2012, GRL (in press)

5. Methodology • Winter mean frequency over 1989-2010 period • 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 Climatological Large-scale weather pattern Individual flight

6. Climatological Large-scale weather pattern Individual flight

7. Climatological cold ISSR frequency over the North Atlantic • 21 years of winter data, ERA-Interim (1989-2010) 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

8. Climatological Large-scale weather pattern Individual flight

9. 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

10. The jet stream latitude is related to the North Atlantic Oscillation +ve NAO +ve = northerly jet stream NAO -ve = southerly jet stream -ve From: http://www.ldeo.columbia.edu/res/pi/NAO/

11. Winter weather types are characterised by the jet stream Eastbound Westbound W1. strong zonal jet W2. Strong tilted jet W4. Confined jet Irvine et al., 2012, Met. Apps., in press Composite 250 hPa geopotential height (black) and wind speed > 40 ms-1(red). Individual time-optimal aircraft routes between London and New York (blue).

12. Cold ISSR frequency by weather pattern and altitude 300 hPa 250 hPa 200 hPa Route location W1. Zonal jet W2. Tilted jet W4. Confined jet EastboundWestbound % • Location linked to various features: jet stream, Greenland, ridges • Altitude distribution depends on weather pattern

13. Climatological Large-scale weather pattern Individual flight

14. Probability of persistent contrail formation along a great circle route GC

15. Probability of persistent contrail formation along a route W GC Estimates of contrail formation are very sensitive to route location! E • Flying higher forms LESS contrails (type W1, both directions) • Flying higher forms MORE contrails (types W2 and W3 eastbound)

16. 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 Summary • 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

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

18. Thank you! Information from: e.a.irvine@reading.ac.uk www.react4c.eu

19. Climate impact varies with route location, weather and season 18 February 2010 26 January 2010 contrails Flight level tropopause Flight entirely in stratosphere produces no contrails Flight mostly in troposphere produces persistent contrails