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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. Pier Luigi Vidale, Dr. Kevin Hodges and Dr. Jane Strachan. Introduction. Motivation Socio-economic impacts and changing risk with climate change.

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

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  1. Tropical Cyclones and Climate Change in a High Resolution General Circulation Model, HiGEM Ray Bell Supervisors: Prof. Pier Luigi Vidale, Dr. Kevin Hodges and Dr. Jane Strachan

  2. Introduction Motivation • Socio-economic impacts and changing risk with climate change. • Impacts on the climate system, removing heat and moisture from the ocean affecting large scale circulation. • Research Objectives • Investigate the changes in TC activity (location, frequency, intensity and structure) with climate change. • Investigate a change of natural variability mechanisms on TC activity e.g. ENSO. • Investigate the impact of atmospheric resolution on TC activity with climate change.

  3. GCM HiGEM UK’s new High-Resolution Global Environmental Model (Shaffreyet al, 2009) HiGEM 4xCO2 30 yrs HiGEM Transient 2% CO2/yr 70 yrs 1.25ox0.83o, ∆x50N = 90 km HiGEM 2xCO2 30 yrs HiGEM CTRL 150 yrs 1/3o ocean model HiGEM CTRL 150 yrs

  4. Tracking algorithm (TRACK; Bengstton et al, 2007) 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

  5. Climate Change Simulations Track density difference 2xCO2 - CTRL 4xCO2 - CTRL Stippling if outside 5x30yr CTRL variability Storms/month/106km2

  6. Sea Surface Temperature difference Jul-Oct 2xCO2 - CTRL 4xCO2 - CTRL Sea Surface Temperature difference (°C) • Tongue of relatively less warm water compared to the rest of the tropics (NAtl) • Decreases TC frequency in the NAtl. • Leads to increased vertical wind shear (VWS) via thermal wind balance

  7. Vertical Wind Shear difference Jul-Oct 2xCO2 - CTRL 4xCO2 - CTRL Stippling if outside 5x30yr CTRL variability Vertical Wind Shear difference (m/s) • VWS spreads to the NEPac • Detrimental affect on TCs

  8. Walker Circulation anomaly Jul-Oct 0-10N° 2xCO2 - CTRL 4xCO2 - CTRL -ω (Pa/s) and divU anomaly (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

  9. Conclusion • TCs become less frequent in the CO2 increased experiments globally. • A tongue of relatively less warm water in the tropical North Atlantic increases VWS and decreases upward motion which reduces the frequency. • A weaker Walker circulation suppresses activity in the NW Pac and enhances activity in the NC Pac. • Future work • Understand ENSO variability, as well as the two types of El Niño. • Investigate how different atmospheric resolutions of the model simulates gradients and the global circulation, and their impact on changing TC activity with climate change.

  10. Tracking algorithm IBTrACS (’79-’02) ERA-Interim (’79-’10) HiGEM CTRL 150 years Track density

  11. Climate Change Simulations

  12. Climate Change Simulations

  13. Climate Change Simulations

  14. Change in duration

  15. Regional Change in duration

  16. Change in structure 100 most intense TCs at most intense Earth relative winds Below 35oN NH Avg 30 yr ctrl 4xCO2 2xCO2 10o radius 850hPa

  17. 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) • Wind speed must attain 20m/s at 850hPa (change in slightly more intense TCs) [att20 dataset] • Statistical packages

  18. Change in SST Zhao et al (2009)

  19. Klotzbach and Gray (2011) AMO ~= AMOC

  20. Change in vws Vecchi et al (2007)

  21. Change in RH700 Vecchi et al (2007)

  22. Change in –ω500

  23. Change in ppt

  24. 2 types of ENSO in HiGEM Kug and Ham (2011) • Investigate change in TC activity with the 2 types of El Nino. • Investigate the change in types of ENSO in HiGEM inc. CO2 and the TC relation

  25. Large scale tropical change

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