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Orographic Influence on Typhoon Tracks over the Central Mountain Range of Taiwan

Orographic Influence on Typhoon Tracks over the Central Mountain Range of Taiwan. Yuh-Lang Lin North Carolina State University. Collaborators: C.-Y. Huang, J. Han, D. Hamilton S.-Y. Chen, C. M. Hill, C. Savage, N. C. Witcraft, Y.-H. Kuo, S.-T. Wang.

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Orographic Influence on Typhoon Tracks over the Central Mountain Range of Taiwan

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  1. Orographic Influence on Typhoon Tracks over the Central Mountain Range of Taiwan Yuh-Lang Lin North Carolina State University Collaborators: C.-Y. Huang, J. Han, D. Hamilton S.-Y. Chen, C. M. Hill, C. Savage, N. C. Witcraft, Y.-H. Kuo, S.-T. Wang

  2. 1. Effects of CMR on typhoon tracks (Wang 1980) • Continuous Track • strong (Vmax>50m/s) • deep (D>10.7 km) • Discontinuous Track • weak (Vmax: 25-50m/s) • shallow (D<6 km)

  3. 2. Control Parameters for track deflection • Based onprevious studies (e.g., Wang 1980; Brand and Blelloch 1974; Chang 1982; Yeh and Elsberry 1993a,b; Zehnder and Reeder 1997; Huang and Lin 1997; Lin et al. 1999), • we identified 8 key parameters: • Vmax, U, h, R, Lx, Ly, f, N • which controls the track deflection.

  4. Based on the Buckingham-pi theorem, we may choose the following 6 independent nondimensional parameters: (8-2=6) U/Nh, Vmax/Nh, h/Lx, R/Ly, U/fLx & Vmax/fR • Physical meanings: • U/Nh: basic-flow Froude number • Vmax/Nh: vortex Froude number • h/Lx: steepness of the mountain • R/Ly: ratio of the cyclone and mountain sizes • U/fLx: basic flow Rossby number • Vmax/fR: vortex Rossby number

  5. Physical meaning of U/Nh and Vmax/Nh (Lin, Chen, Hill, Huang 2005 JAS) Effects of orography on TC may be linearly decomposed into: (a) Influence on the basic flow (b) Influence on the cyclone circulation

  6. D C Based on previous studies, it was found: U/Nh S N Track is continuous when Vmax/Nh > 1.5; Otherwise it is discontinuous. D C Vmax/fR It appears that track continuity is mainly controlled by Vmax/Nh (at least for CMR) D C h/Lx Vmax/Nh

  7. Verification of previous results by systematic idealized numerical simulations (Lin et al. 2005) D C D C U/Nh h/Lx Vmax/fR R/Ly Vmax/Nh Vmax/Nh • Track is continuous (discontinuous) when Vmax/Nh>1.6 (<1.2) • Track continuity is mainly controlled by Vmax/Nh, and is less • sensitive to other parameters (for CMR)

  8. Discontinuous Vmax/Nh=0.8 U/Nh=0.13 R/Ly=0.75 Continuous Vmax/Nh=2.0 U/Nh=0.5 R/Ly=1.042 streamlines relativevorticity

  9. Wu-Fen-Shan ★ Hua-Lien ★ 72 CTRL NT 60 Obs. 60 19/00Z (TY) 25N 48 48 36 24 18/12Z (TY) 24N 36 24 18/00Z (STY) 23N 17/12Z (STY) 22N 120E 121E 122E 123E With a very small R/Ly, the track becomes discontinuous and the cyclone is even deflected southward Our study helps explain the curving of Tphoon Haitang (2005) (Jian and Wu 2006)

  10. Degree of Track Deflection U/Nh Vmax/Nh When Vmax/Nh or U/Nh is smaller, the track deflection is larger

  11. (a) Weak blocking • deflected slightly northward upstream • continuous track • (b) Moderate blocking • deflected northward upstream • a secondary vortex forms on the lee -> discontinuous track • (c) Strong blocking • deflected southward upstream • a secondary vortex forms on the lee -> discontinuous track

  12. Application of the control parameter hypothesis to Supertyphoon Bilis (2000) and typhoon Toraji (2001) (Lin, Witcraft, Kuo 2006 MWR) B T U/Nh Vmax/Nh

  13. 3. Effects of Lanfalling locations:R/Ly comes into play

  14. 4. Effects of impinging angles

  15. Upstream of the mountain: vorticity advection dominates Vorticity advection Local vorticity tendency 12 12 15 Vorticity tilting Vorticity stretching

  16. Over the mountain: vorticity stretching dominates Vorticity advection 12 12 15 Vorticity stretching

  17. On the lee side: vorticity advection regains the control Vorticity advection 18 Vorticity stretching

  18. 5. Summary • Track continuity is more sensitive to Vmax/Nh and R/Ly. • A combination of small Vmax/Nh, R/Ly, U/Nh, U/fLx, and Vmax/fR and large (small) h/Lx will give larger degree of track deflection. • (Lin, Chen, Hill, Huang 2005 JAS) • Blocking plays an essential role in dictating the track deflection • Tracks are also influenced by landfalling location and impinging angle

  19. Thank You!

  20. Deflection is controlled by vorticity advection and stretching • Upstream: Vorticity advection • Crossing over: Vorticity stretching • Downstream: Vorticity advection • The deflection of a cyclone encountering a mountain range is largely controlled by vorticity advection and stretching, depending upon the landfall location and approach angle of the cyclone. • The deflection of a cyclone encountering a mountain range is largely controlled by vorticity advection and stretching, depending upon the landfall location and approach angle of the cyclone. • The deflection of a cyclone encountering a mountain range is largely controlled by vorticity advection and stretching, depending upon the landfall location and approach angle of the cyclone.

  21. 3. Application to Track Deflection of Bilis and Toraji (Lin, Witcraft and Kuo 2006 MWR) Use MM5 to investigate the dynamics of track deflection for typhoons crossing over the CMR • Examination of 2 storms: • Super Typhoon Bilis (2000) • Fast-moving; Category 5; Continuous track • Typhoon Toraji (2001) • Slowly-moving; Category 2/3; Discontinuous track

  22. Observed and Simulated Bilis Tracks TC symbols – Observed Stars – Surface Squares – 700 mb Circles – 500 mb Triangles – 300 mb Max wind: 160 knots

  23. Observed and Simulated Toraji Tracks TC symbols – Obs Stars – Surface Squares – 700 mb Circles – 500 mb Triangles – 300 mb *open symbols – coexisting centers Max winds: 95 knots

  24. Bilis: Backward trajectories (8/22/17Z)

  25. Toraji: Backward trajectories (7/29/21Z) Most low-level air parcels are blocked by CMR and go around the mountain

  26. Wu-Fen-Shan ★ Hua-Lien ★ 72 CTRL NT 60 Obs. 60 19/00Z (TY) 25N 48 48 36 24 18/12Z (TY) 24N 36 24 18/00Z (STY) 23N 17/12Z (STY) 22N 120E 121E 122E 123E Tracks: Obs. CTRL NT (Jian and Wu 2006)

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