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: e.a.irvine@reading.ac.uk
© University of Reading 2012
www.met.reading.ac.uk/~gb902035
1
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
2
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:
• Does our dataset (ERA-Interim)
reproduce the observed climatology?
Large-scale
weather pattern
Individual flight
Increasing relevance to
climate optimal routing
Climatological
• Are there preferred locations for ISSRs
within weather patterns?
• What is the likelihood of encountering
an ISSR at a particular altitude?
• Results are published in: Irvine et al., 2012, GRL (in press)
4
Methodology
• 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:
Climatological
Large-scale
weather pattern
Individual flight
• Winter mean frequency over 1989-2010
period
• 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
5
Climatological
Large-scale weather
pattern
Individual flight
6
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
Climatological
Large-scale weather
pattern
Individual flight
8
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
9
The jet stream latitude is related
to the North Atlantic Oscillation
NAO +ve = northerly jet stream
NAO -ve = southerly jet stream
+ve
-ve
From: http://www.ldeo.columbia.edu/res/pi/NAO/
10
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).
11
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
%
Eastbound
Westbound
• Location linked to various features: jet stream, Greenland, ridges
• Altitude distribution depends on weather pattern
Climatological
Large-scale weather
pattern
Individual flight
13
Probability of persistent contrail
formation along a great circle route
GC
14
Probability of persistent contrail
formation along a route
W
GC
E
Estimates of contrail formation are
very sensitive to route location!
• Flying higher forms LESS contrails (type W1, both directions)
• Flying higher forms MORE contrails (types W2 and W3 eastbound)
15
Summary
• 21 years of ERA-Interim re-analysis data are used to analyse cold
ISSRs at 3 scales for the north Atlantic region.
Climatological
• The locations of ISSRs in ERA-Interim agree
well with satellite climatology although the
frequencies are reduced
Large-scale
weather pattern
• Preferred locations for ISSRs are over
Greenland, around high-pressure ridges and
in regions of uplift near jet streams
Individual flight
• The probability of contrailing either increases
or decreases with altitude, dependent on
weather pattern and aircraft route through this
• Results published in Irvine et al., 2012, GRL (in press)
16
Future Directions
• New 3-year NERC-funded project starting in January 2013:
How will upper-tropospheric climate change help or hinder
aviation industry efforts to reduce their impact on climate?
• 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
Thank you!
Information from:
e.a.irvine@reading.ac.uk
www.react4c.eu
18
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
19