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Sensitivity of Tropical Cyclone Intensification to Boundary Layer Parameterization Scheme

Explore the impact of different parameterization schemes on cyclone intensification in numerical models. Investigate boundary layer structures for insights on the evolution and intensity of tropical cyclones. Assess sensitivity to scheme variations and examine predictions of various models. Conclusions on scheme realism and inner core validity. Collaborative research by Roger Smith and Gerald Thomsen from Ludwig-Maximilians University of Munich.

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Sensitivity of Tropical Cyclone Intensification to Boundary Layer Parameterization Scheme

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  1. Dependence of tropical cyclone intensification on the boundary-layer parameterization in a numerical model Roger Smith Ludwig-Maximilians University of Munich Collaborator: Gerald Thomsen

  2. Outline • Motivation • New insights into the role of the boundary layer • Dependence of tropical-cyclone evolution and azimuthal-mean structure on the representation of the boundary layer • Conclusions

  3. Motivation In the light of our recent findings that the spin-up of the hurricane inner core occurs in the boundary layer, two important questions arise: • How sensitive is tropical cyclone intensification in a model to the boundary-layer parameterization scheme used? • How large are the differences in boundary-layer structure predicted by different schemes?

  4. The primary circulation Pressure gradient force LO r v sea Centrifugal force and Coriolis force

  5. Frictionally-induced secondary circulation primary circulation Secondary circulation Pressure gradient force r Friction layer v v Centrifugal force and Coriolis force are reduced by friction

  6. “Tea cup” Experiment

  7. Hurricane intensification • Basic principle - Conservation of absolute angular momentum: M = rv + r2f/2 f = Coriolis parameter = 2Wsin(latitude) r v v = M/r - rf/2 If r decreases, v increases! Spin up requires radial convergence

  8. The basic thought experiment for intensification Initial condition Mean sounding Axisymmetric vortex p(z) T(z) q(z) V(r,z) r 27oC sea Nguyen, Smith and Montgomery calculation, QJRMS, 2008: • Idealized numerical model simulations, simple physics, MM5 • 5 km (1.67 km) resolution in the finest nest, 24s-levels

  9. In print In press

  10. From Montgomery, Nguyen & Smith (2009): QJRMS

  11. From Montgomery, Nguyen & Smith (2009): QJRMS

  12. From Montgomery, Nguyen & Smith (2009): QJRMS

  13. From Montgomery, Nguyen & Smith (2009): QJRMS

  14. From Montgomery, Nguyen & Smith (2009): QJRMS

  15. Two mechanisms for TC intensification 15 10 z km 5 M conserved 0 50 r km 100 Mreduced by friction, but strong convergence  small r From Montgomery, Nguyen & Smith (2009): QJRMS

  16. Braun & Tao (2000) Monthly Weather Review

  17. To be submitted

  18. Schemes

  19. 6 - unmod Bulk 1 - mod Bulk 2 - Blackadar 3 – Burk Thompson 5 – Gayno-Seaman 4 - MRF 7 – unmod Gayno-Seaman

  20. unmodified Bulk modified Bulk Radial and tangential wind components

  21. Radial and tangential wind components

  22. unmodified Bulk modified Bulk Total wind

  23. Total wind

  24. unmodified Bulk modified Bulk Vertical velocity

  25. Vertical velocity

  26. unmodified Bulk modified Bulk Net radial force = v2/r + fv (m s-1/hour)

  27. Net radial force = v2/r + fv (m s-1/hour)

  28. 1 – mod Bulk 2 – Blackadar 3 – Burk-Thompson 4 – MRF 5 – Gayno-Seaman 6 – unmod Bulk Comparison with Franklin’s data

  29. 1 – mod Bulk 2 – Blackadar 3 – Burk-Thompson 4 – MRF 5 – Gayno-Seaman 6 – unmod Bulk Surface wind reduction factor

  30. 1 – mod Bulk 2 – Blackadar 3 – Burk-Thompson 4 – MRF 5 – Gayno-Seaman 6 – unmod Bulk Surface inflow angle

  31. 1 – mod Bulk 2 – Blackadar 3 – Burk-Thompson 4 – MRF 5 – Gayno-Seaman 6 – unmod Bulk Surface wind

  32. 1 – mod Bulk 2 – Blackadar 3 – Burk-Thompson 4 – MRF 5 – Gayno-Seaman 6 – unmod Bulk 0 km 1.5 km Pseudo-equivalent potential temperature

  33. Turbulent kinetic energy

  34. Summary, conclusions and open questions • Extended the work of Braun and Tao (2000). • Examined new aspects of the boundary layer structure. • Tropical-cyclone intensification is sensitive to the scheme used including onset time of rapid intensification and the final intensity. • The boundary-layer structure varies considerably between schemes. • Which is the most realistic scheme? • Is boundary-layer theory valid in the inner core region? Answer: see Smith and Montgomery (2009)

  35. Thank you for your attention

  36. 1 – mod Bulk 2 – Blackadar 3 – Burk-Thompson 4 – MRF 5 – Gayno-Seaman 6 – unmod Bulk Surface latent heat flux

  37. 1 – mod Bulk 2 – Blackadar 3 – Burk-Thompson 4 – MRF 5 – Gayno-Seaman 6 – unmod Bulk Surface sensible heat flux

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