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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

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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


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

Outline

  • 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


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

    Idealised GCM simulations

    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)


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

    Tracking algorithm (TRACK; 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


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

    Validating the 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


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

    Climate Change Simulations

    Track density difference

    2xCO2 – CTRL

    4xCO2 – CTRL

    Stippling if outside 5x30yr CTRL variability


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

    Climate Change Simulations

    TC frequency difference

    CTRL

    Error bars show 5x30yr CTRL variability


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

    Sea Surface Temperature 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)


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

    Walker CirculationDifference

    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)


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

    Vertical Wind Shear 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)


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

    Large scale forcing

    NAtl

    %

    change

    CTRL

    %

    change

    NEPac

    CTRL

    Similar to Held and Zhao (2011)


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

    Conclusions

    • 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.


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

    Future work

    • 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


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

    Validating the model

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

    Strachan et al (2012) in rev


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

    AMIPII SSTs (1979-2002) JASO mean (for 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 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 obs

    Robert Lee


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

    Are the modelled TCs really warm core storms ?

    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


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

    Validation of TC frequency (AVG)


    Absolute track densities and natl changes

    Absolute track densities and NAtl changes


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

    Climate Change Simulations


    Higem absolute sst change and sh sst change

    HiGEM absolute SST change and SH SST change


    Absolute walker circulation changes

    Absolute Walker circulation changes


    Natl hadley cell changes

    NAtl Hadley cell changes


    Higem absolute vws and sh change

    HiGEM absolute vws and SH change


    Nh diff in winds

    NH diff in winds


    Change in rh 700

    Change in RH700

    Vecchi and Soden (2007)


    Change in 5 00

    Change in –ω500


    Change in ppt

    Change in ppt


    Large scale tropical change

    Large scale tropical change


    Held and zhao 2011

    Held and Zhao (2011)


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