© 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

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

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).

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).

Climate impact in different weather patterns: CO2

• Proxy for the CO2 impact of a flight: time to fly the minimum time route, assuming a constant airspeed and altitude

Climate impact in different weather patterns: CO2

• Proxy for the CO2 impact of a flight: time to fly the minimum time route, assuming a constant airspeed and altitude

300 hPa 250 hPa 200 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

22

Trajectory Analysis

Lifetime of ice-supersaturated air

Origin of ice-supersaturated air

T+0T-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

22

Trajectory Analysis

Lifetime of ice-supersaturated air

Origin of ice-supersaturated air

T+0T-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

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…

• 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 from Speed of air (along trajectory)

Summary

12

Using characteristic weather patterns for the north Atlantic winter season, we find that:

•The CO2 and contrail impacts vary by weather pattern

•Eastbound routes benefit from the jet stream and therefore have a (<20%) smaller CO2 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

Thank you!

Information from:

e.a.irvine@reading.ac.uk

www.react4c.eu

13

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

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

15

Probability of persistent contrail formation along a great circle route

GC

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!