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Identifying Tropical Cyclones in Model Simulations

Identifying Tropical Cyclones in Model Simulations . Asuka Suzuki-Parker. NCAR Earth System Laboratory National Center for Atmospheric Research. NCAR is Sponsored by NSF and this work is partially supported by the Willis Research Network and the Research Program to Secure Energy for America.

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Identifying Tropical Cyclones in Model Simulations

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  1. Identifying Tropical Cyclones in Model Simulations Asuka Suzuki-Parker NCAR Earth System Laboratory National Center for Atmospheric Research NCAR is Sponsored by NSF and this work is partially supported by the Willis Research Network and the Research Program to Secure Energy for America

  2. What is a Tropical Cyclone? Large low pressure Circular rotating flow Convective (cluster of thunderstorms) Warm center (or core) A cyclone of tropical origin with maximum sustained wind of >17m/s near the center

  3. Tropical vs Extratropical Cyclones

  4. Pop Quiz: TC or not? Yes: Hurricane Isabel (2003)

  5. Pop Quiz: TC or not? No: a subtropical system

  6. Pop Quiz: TC or not? Yes: TC Erika (2009)

  7. Identifying TCs in Operational Fields Satellite Dvorak technique: estimate TC intensity from cloud pattern Aircraft reconnaissance More accurate measurements of intensity Yup that’s a hurricane ‘cuz we almost crashed!

  8. Identifying TCs and estimating their intensity can be subjective both in the real world and in the model

  9. Defining TCs in the model(The general rule of thumb tracking) Have a distinctive pressure minimum Maximum wind > 17m/s Maximum vorticity > 5x10-5/s Temperature anomaly (dT) > 2K Low level winds > high level winds High level dT > low level dT 2 days lifetime Thresholds differ by model resolution and by research groups

  10. Vorticity Vorticity = measure of rotation For cyclonic rotation, it’s positive for Northern Hemisphere negative for Southern Hemisphere Vertical view Horizontal view

  11. Temperature Anomaly Core Horizontal view Vertical view dT = Tcore - Tenvironment sum(dT300mb + dT500mb + dT700mb) > 2K

  12. Example result from “the general rule of thumb” tracking Looks very reasonable but are they all really TCs? Filter these tracks through Cyclone Phase technique

  13. Cyclone Phase technique Developed by Bob Hart (Florida State Univ.) Comprehensive measure of thermal structure of a storm Symmetricity Vertical variation of thermal structure

  14. Result from Cyclone Phase filtering Before filtering After filtering 20~30% of “the rule of thumb” storms failed to satisfy cyclone phase Picks up subtropical and strong extratropical storms

  15. Summary Identifying TCs can be subjective both in operation and in models Conventional mean of tracking TCs from models may pick up non-TCs Cyclone Phase technique is an effective way of removing non-TCs We’ll be presenting results using simulated TCs that satisfy Cyclone Phase filtering

  16. Extra

  17. Cyclone Phase technique(Hart 2003) Symmetry measure h = +1 for Northern Hemisphere h = -1 for Southern Hemisphere B < 10 for tropical cyclones (Evans and Hart 2003) (Hart 2003)

  18. Cyclone Phase technique(cont.) Thermal wind structure measure -VTL & -VTU > 0 for tropical cyclones (Hart 2003)

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