Global Response of Clear-Air Turbulence to Climate Change - Professor Paul D. Williams University of Reading, UK

Global Response of Clear-Air Turbulence
          to Climate Change
         Professor Paul D. Williams
         University of Reading, UK

Climate change impacts on aviation
                                                            Stronger jet-stream
                  Shifting wind patterns                    wind shears increase
                  modify optimal flight                     clear-air turbulence
                      routes and fuel
                       consumption
                                                     More extreme
                                                     weather causes
                                  Warmer air         disruptions and
                                imposes take-off          delays
                               weight restrictions
 Rising sea levels and
storm surges threaten
    coastal airports

                                                     Puempel & Williams (2016)
                                                     ICAO Environmental Report

The acceleration of the jet stream
                          Pacific   Atlantic

      Jet-stream
 changes driven by                                C20
     CO2 in IPCC                                (10 m/s
 climate simulations                           contours)

 Stronger eastward
 winds & windshears
   at flight cruising
        altitudes
                                               C21 – C20
                                               (0.25 m/s
      u         T
                                             contours)
      z         y

Delcambre et al. (2013)

Changing LHR↔JFK flight times

Likelihood of taking under 5 h 20 min   Likelihood of taking over 7 h 00 min
more than doubles from 3.5% to 8.1%     nearly doubles from 8.6% to 15.3%

                                                            Williams (2016)

Changing LHR↔JFK flight times
• Have these changes already begun?
   – The North Atlantic jet stream wind speeds reached 250 mph on
     8-12 January 2015
   – An eastbound JFK→LHR crossing took only 5 h 16 min, which is
     the current non-Concorde record
   – Westbound LHR→JFK crossings took so long that two flights had to
     make unscheduled refuelling stops in Maine

• Extrapolation to all transatlantic traffic (600 crossings per day)
  suggests that aircraft will collectively be:
   – airborne for an extra 2,000 hours each year
   – burning an extra 7.2 million gallons of jet fuel at a cost of $22 million
   – emitting an extra 70 million kg of CO2 into the atmosphere, equating
     to 7,100 British homes
                                                               Williams (2016)

Turbulence
Aircraft encounter moderate turbulence (>0.5g) 65,000 times and severe
turbulence (>1.0g) 5,500 times annually in the USA. These encounters:
         – cause about 40 fatalities and 100s of serious injuries
         – cause structural damage to planes
         – cause flight diversions and delays     Statistics from:
         – cost airlines $150m–$500m              www.ral.ucar.edu/aap/themes/turbulence.php

                                                      Ralph et al. (1997)

Turbulence injury trends
             Number of serious injuries (including fatalities) caused by turbulence,
                          per million flight departures (US carriers)
FAA (2006)

             1982                                                              2003

Turbulence injury trends
                   Number of flight attendant injuries caused by turbulence,
                            per million hours flown (US carriers)
Tvaryanas (2003)

Clear-air turbulence (CAT)
• CAT occurs in clear skies at cruise altitudes, above weather
  systems like clouds and storms
• CAT is difficult to avoid, because it cannot be seen by pilots or
  detected by satellites or on-board radar
• Aircraft spend about 3% of their cruise time in light CAT (Watkins &
  Browning 1973) and about 1% of their cruise time in moderate CAT
  (Sharman et al. 2006)
• CAT is forecast operationally by computing various diagnostic
  measures from weather prediction models, e.g. those due to Colson
  & Panofsky (1965), Brown (1973), and Ellrod & Knapp (1992)
• World Area Forecast Centres (in London and Washington) use such
  diagnostics to issue global CAT forecasts every six hours (Gill 2012)
• These forecasts show significant skill when evaluated against pilot
  reports of turbulence

What causes CAT?

                                          Stratification
                                          inhibits CAT
height
                                          Wind shear
                                        encourages CAT

CAT occurs if the wind shear is stronger than the stratification.
     Climate change is strengthening the wind shear…

Is CAT increasing?
PRE-INDUSTRIAL                        DOUBLED CO2

                                2                   2
               u    u    v       v u 
       TI1                           
               z     x   y       x   y 

Is CAT increasing?
                          100%

                           Number of
                           turbulence
                           diagnostics
                            indicating
                                an
                            increased
                              median

                          0%
              Williams & Joshi (2013)

Williams (2017)                149%
                                                                              (36-188%)

                                                                127%
                                                              (30-170%)
                                             94%
                                          (37-118%)
                             75%
         59%               (39-96%)
       (43-68%)

“Slight strain against seat       “Definite strain against      “Occupants      are    forced
belts; unsecured objects may      seat belts; unsecured         violently against seat belts;
be displaced slightly; food       objects are dislodged;        unsecured      objects    are
service may be conducted          food     service      and     tossed about; food service
with little difficulty walking”   walking are difficult”        and walking are impossible”

Is CAT increasing?

           Storer, Williams & Joshi (2017)

Is CAT increasing?

           Storer, Williams & Joshi (2017)

Summary
• A basket of CAT measures diagnosed from climate
  simulations is significantly modified if the CO2 is increased
• At cruising altitudes on transatlantic flights in winter, the
  diagnostics show a 59% / 94% / 149% increase in the
  prevalence of light/moderate/severe CAT, with similar
  results on other flight routes and in other seasons
• We conclude that, all other things being equal, climate
  change will lead to bumpier flights later this century
• Flight paths may become more convoluted to avoid
  stronger and more frequent patches of turbulence, in
  which case journey times will lengthen and jet fuel
  consumption will increase

Questions?

       @DrPaulDWilliams
www.met.reading.ac.uk/~williams
  p.d.williams@reading.ac.uk