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Tropical Cyclones and Climate Change in a High Resolution General Circulation Model, HiGEM. Ray Bell Supervisors: Prof. P.L. Vidale, Dr. Kevin Hodges and Dr. Jane Strachan. Outline. Research Objective Investigate the changes in TC activity with climate change focusing on:

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Tropical cyclones and climate change in a high resolution general circulation model higem

Tropical Cyclones and Climate Change in a High Resolution General Circulation Model, HiGEM

Ray Bell

Supervisors: Prof. P.L. Vidale, Dr. Kevin Hodges and Dr. Jane Strachan


Outline General Circulation Model,

  • Research Objective

    • Investigate the changes in TC activity with climate change focusing on:

    • - location , frequency,

    • - intensity, structure and duration

  • HiGEM model

  • TRACKing algorithm

  • TC changes

  • Large scale forcing changes

  • Conclusions


  • Idealised GCM simulations General Circulation Model,

    HiGEM

    UK’s High-Resolution Global Environmental Model (Shaffreyet al, 2009)

    HiGEM 4xCO230 yrs

    HiGEM Transient 2% CO2/yr 70 yrs

    N144

    HiGEM 2xCO230 yrs

    1.25ox0.83o, ∆x50N = 90 km

    HiGEM CTRL ~5x30 yrs

    HiGEM 1.1 CTRL 150 yrs

    1/3o ocean model

    HadGAM N48 (~270km) HiGAM is part of our HIERARCHY OF AGCMs

    HadGAM N96 (~135km)

    HiGAM N144 (~90km)

    NUGAM N216 (~60km)

    HadGEM3H N216 (~60km)

    HadGEM3H N320 (~40km)

    HadGEM3H N512(~25km)

    New Hadley Centre Model with double vertical resolution and higher model top (85km)


    Tracking algorithm (TRACK; General Circulation Model, Bengsttonet al, 2007)

    A 20 year time-slice of GCM simulated tropical storms

    1) Locate and track all centres of high relative vorticity 35000/yr

    2) Apply a 2-day filter to the tracks  8000 storms / yr

    3) Analyse vertical structure of storm for evidence of warm-core (tropical storm structure)  120 storms / yr


    Validating the model General Circulation Model,

    AMIP

    (TRACK)

    Atmosphere only

    Coupled

    At this model resolution we are able to realistically capture location and frequency

    Strachan et al (2012) in review


    Climate General Circulation Model, Change Simulations

    Track density difference

    2xCO2 – CTRL

    4xCO2 – CTRL

    Stippling if outside 5x30yr CTRL variability


    Climate General Circulation Model, Change Simulations

    TC frequency difference

    CTRL

    Error bars show 5x30yr CTRL variability


    Sea Surface Temperature General Circulation Model, Difference

    JASO

    2xCO2 –

    CTRL

    4xCO2 –

    CTRL

    Stippling not shown

    significant everywhere

    • Tongue of relatively less warm water compared to the rest of the tropics

    • Grave results of TCs in this vicinity (NAtl).

    • Leads to increased vertical wind shear (VWS) via thermal wind balance

    Zhao et al (2009)


    Walker Circulation General Circulation Model, Difference

    JASO 0-10N°

    CTRL

    2xCO2

    - CTRL

    4xCO2

    - CTRL

    -ω difference (Pa/s) and divU difference (m/s)

    • Weakening of the tropical circulation inline with other studies (Vecchi and Soden, 2007)

    • Favours development in the CPac and reduces TC frequency is the NWPac(Li et al, 2010; Murakami et al, 2011)


    Vertical Wind Shear General Circulation Model, Difference

    JASO

    2xCO2

    - CTRL

    4xCO2

    - CTRL

    • VWS spreads to the NEPac especially in the 4xCO2

    • Detrimental affect on TCs.

    • Reduced VWS in CPac favours development

    Vecchi and Soden(2007)


    Large scale forcing General Circulation Model,

    NAtl

    %

    change

    CTRL

    %

    change

    NEPac

    CTRL

    Similar to Held and Zhao (2011)


    Conclusions General Circulation Model,

    • HiGEM realistically captures the geographical location and NH TC frequency compared to those identified in reanalyses and observations.

    • HiGEM simulates a decrease of TC frequency in most regions except for the North Indian basin and North Central Pacific region.

    • A weaker Walker circulation suppresses activity in the North West Pacific and enhances activity in the North Central Pacific.

    • An increase in VWS in the 4xCO2 over the North Atlantic spreads to the North East Pacific and decreases TC frequency.


    Future work General Circulation Model,

    • Investigate different types of El Niño in the control simulation and how these may change with climate change.

    • Investigate TC changes with varying model resolutions with a focus on intensity.

    • Investigate TC changes in a transient forcing vs. a stabilised forcing


    Validating the model General Circulation Model,

    At this model resolution we are able to realistically capture location and frequency

    Strachan et al (2012) in rev


    AMIPII SSTs (1979-2002) JASO mean (for General Circulation Model, HiGAM)

    Differences in TC counts

    as we substitute observed SSTs with SSTs generated by HiGEM

    HiGEM SSTs (30 years) JASO mean

    HiGEM-AMIPII SST bias (JASO)

    AMIPII SSTs (1979-2002) DJFM mean (for HiGAM)

    HiGEM SSTs (30 years) DJFM mean

    Jane Strachan

    HiGEM-AMIPII SST bias (DJFM)


    Track hodges 1995 bengstsson et al 2007
    TRACK General Circulation Model, Hodges (1995); Bengstssonet al. (2007)

    • T42 ξ850 – Reduce noise. Comparison of different spatial resolution data

    • Minimum lifetime of 2 days and no constraint on the minimum displacement distance. Capture more of TC lifecycle

    • Cyclogenesis (0-30oN over ocean)

    • Coherent vertical structure and warm core

    • Max T63 vor at each level from 850hPa to 250hPa

    • Intensity threshold T63 ξ850 > 6x10-5 s-1, ξ850 – ξ200 > 6x10-5 s-1 , for at least 1 day (4 x 6hr).

    • Search for warm core between p levels 850-500, 500-200hPa (+ ξ value)

    • Statistical packages


    Validation of track against obs
    Validation of TRACK against General Circulation Model, obs

    Robert Lee


    Are the modelled TCs really warm core storms ? General Circulation Model,

    Is the near-core circulation correct; do we see changes with resolution ?

    Had-Hi-NUGAM, MIROC, ECHAM: 100 most intense TCs in 25 yrs

    Hurricane Mitch

    200hPa

    200hPa

    200hPa

    500hPa

    500hPa

    500hPa

    850hPa

    850hPa

    850hPa

    135km

    resolution

    60km

    HadGAM-HiGAM-NUGAM tangential wind


    Validation of TC frequency (AVG) General Circulation Model,


    Absolute track densities and natl changes
    Absolute track densities and General Circulation Model, NAtl changes


    Climate General Circulation Model, Change Simulations



    Absolute walker circulation changes
    Absolute Walker circulation changes General Circulation Model,


    Natl hadley cell changes
    NAtl General Circulation Model, Hadley cell changes


    Higem absolute vws and sh change
    HiGEM absolute General Circulation Model, vws and SH change


    Nh diff in winds
    NH diff in winds General Circulation Model,


    Change in rh 700
    Change in RH General Circulation Model, 700

    Vecchi and Soden (2007)


    Change in 5 00
    Change in – General Circulation Model, ω500


    Change in ppt
    Change in General Circulation Model, ppt


    Large scale tropical change
    Large scale tropical change General Circulation Model,


    Held and zhao 2011
    Held and Zhao (2011) General Circulation Model,


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