1. © University of Reading 2012 www.met.reading.ac.uk/~gb902035 ARAM AMS January 2013 Relating the climate impact of trans-Atlantic flights to typical north Atlantic weather patterns Emma Irvine, Keith Shine, Brian Hoskins Meteorology Department, University of Reading Contact: e.a.irvine@reading.ac.uk 1

2. Motivation for classifying weather patterns Large variation in route location and time due to upper-level winds Daily minimum time routes for 3 winters provided by the Met Office Met data from ERA-Interim analyses at 250 hPa (FL340), 1989-2010 Westbound 12 UTC Eastbound 00 UTC Daily Minimum time routes, Dec. 2009

3. Winter weather patterns are characterised by the jet stream Irvine et al., 2012, Met. Apps., in press 3 W1. strong zonal jet W2. Strong tilted jet W4. Confined jet Composite 250 hPa geopotential height (black) and wind speed > 40 ms -1 (red).

4. Winter weather patterns are characterised by the jet stream Eastbound Westbound Irvine et al., 2012, Met. Apps., in press 4 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).

5. Climate impact in different weather patterns: CO 2 Proxy for the CO 2 impact of a flight: time to fly the minimum time route, assuming a constant airspeed and altitude

6. Climate impact in different weather patterns: CO 2 Proxy for the CO 2 impact of a flight: time to fly the minimum time route, assuming a constant airspeed and altitude

7. 300 hPa250 hPa200 hPa W1. Zonal jet W2. Tilted jet % W4. Confined jet Route location Location linked to various features: jet stream, Greenland, ridges Altitude distribution depends on weather pattern Eastbound Westbound Irvine et al., 2012 GRL Occurrence of cold ice-supersaturated regions

8. 22 Trajectory Analysis Lifetime of ice- supersaturated air Origin of ice- supersaturated air T+0 T-48 h T+48 h Lagrangian trajectory code (Methven, 1997) run on ERA-Interim data Trajectories released on a 1x1 degree grid, over North Atlantic from 250 hPa

9. 22 Trajectory Analysis Lifetime of ice- supersaturated air Origin of ice- supersaturated air T+0 T-48 h T+48 h Lagrangian trajectory code (Methven, 1997) run on ERA-Interim data Trajectories released on a 1x1 degree grid, over North Atlantic from 250 hPa Total ~ 100,000 trajectories with ice-supersaturation (ISS) Of these, ~ 60% start in the troposphere, ~ 40% in stratosphere

10. Trajectories of air that become ice-supersaturated over the UK For trajectories starting in the troposphere with lifetime 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…

11. Air which stays ISS for > 24 h comes from a more southerly direction and has a slower speed than shorter-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 11 W S Direction air comes fromSpeed of air (along trajectory)

12. Summary 12 Using characteristic weather patterns for the north Atlantic winter season, we find that: The CO 2 and contrail impacts vary by weather pattern Eastbound routes benefit from the jet stream and therefore have a (<20%) smaller CO 2 impact than westbound flights The formation of contrails shows a strong dependence on altitude in a given weather pattern Preferred locations for contrail formation are over Greenland, around high-pressure ridges and in regions of uplift near jet streams Air which becomes ice-supersaturated over the UK comes from the SW; air which stays ice-supersaturated for at least 24 h may be associated with high-pressure ridges

13. Thank you! Information from: e.a.irvine@reading.ac.uk www.react4c.eu 13

14. 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 14 Irvine et al., 2012, Meteorological Applications, in press

15. 15 Probability of persistent contrail formation along a great circle route GC

16. 16 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!