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TC-Relative Helicity and Its Impact on Intensity and Development

Explore the implications of varying helicity values on tropical cyclone (TC) intensification alongside wind shear. The study delves into observational estimates versus WRF simulations, focusing on the role of environmental helicity in TC development. Investigate Nolan's Point-Downscaling framework and its impact on TCs. Modeling results and data analysis from reanalyses highlight the importance of helicity in modulating TC intensity. Future research aims to enhance modeling tools for time-varying environmental profiles in TC studies.

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TC-Relative Helicity and Its Impact on Intensity and Development

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  1. TC-Relative Helicity and Its Impact on Intensity and Development Matt Onderlinde Student Seminar Wed. Sept. 25, 2013

  2. Helicity Refresher

  3. Motivation • 850-200 mb wind shear is commonly used to diagnose the favorability of TC environments • For the same value of shear, helicity can change significantly

  4. Research Questions • What are the implications of different values of helicity? • Does environmental helicity have as much predictive value as shear? • How do observational estimates compare to the WRF simulations? i.e., do we see any signal in nature?

  5. Background • Many studies show vertical wind shear is important for TC intensity change (e.g., DeMaria and Kaplan 1999) • Nolan (2011) suggests that helicity may be important • Point-Downscaling (PDS) developed by Nolan (2011) as a framework to control the environment around a TC

  6. Background – Point-Downscaling The circled term is an artificial force that is equal in magnitude to the pressure gradient that would exist if temperature gradients were allowed to exist.

  7. Methodology – Model Setup • Use PDS in WRF to simulate the effects of helicity on TCs • Idealized nudging is also applied to further restrict changes to this prescribed environment.

  8. Modeling Results – WRF Simulations

  9. Methodology – Reanalysis Data • Calculate TC-relative helicity (TCSRH) from ERA-Interim reanalyses and GFS analyses • TCSRH computed from the average wind profile in annuli around TCs Hugo 1989

  10. Methodology – Best Track Data

  11. Results – ERA-Interim Reanalysis Data

  12. Modulation of local helicity by environmental helicity through TC tilt

  13. Methodology – Idealized TC Tilt

  14. Summary • WRF simulations suggest helicity is important when it comes to TC intensification • Reanalysis data suggests that this signal is weak in nature • Idealized shifting of wind fields shows how environmental helicity can modulate the impact of local storm helicity • In nature, it is very uncommon for the environment to remain constant for a long enough period during which helicity could make an impact on intensity. • Shear still has more predictive ability than helicity… but this isn’t surprising.

  15. Future Work • Currently developing a new WRF modeling tool to allow for time varying of environmental wind profile while still using BOTH nudging and PDS simultaneously. • This will allow for simulations where shear and helicity can be gradually (realistically) ramped up or down.

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