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Asymmetric Precipitation Structure of a Concentric Eyewall Tropical Cyclone

Asymmetric Precipitation Structure of a Concentric Eyewall Tropical Cyclone. Ren-Feng Liu 1,2 and Ben Jong-Dao Jou 1 1. Department of Atmospheric Sciences, National Taiwan University , Taipei, Taiwan 2. Central Weather Bureau, Taipei, Taiwan. 2001/09/25/1135UTC. 1.Motivation & Objectives.

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Asymmetric Precipitation Structure of a Concentric Eyewall Tropical Cyclone

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  1. Asymmetric Precipitation Structure of a Concentric Eyewall Tropical Cyclone Ren-Feng Liu1,2 and Ben Jong-Dao Jou1 1.Department of Atmospheric Sciences, National Taiwan University , Taipei, Taiwan 2.Central Weather Bureau, Taipei, Taiwan 2001/09/25/1135UTC

  2. 1.Motivation & Objectives It is generally believed that the evolution of the structure is responsible for the intensity change of a TC. Because of their significance in hurricane intensity changes, the eyewall replacement processes have attracted significant attention since the publication of Willoughby et al. (1982)

  3. Bilis(2000) Lekima(2001) Dujuan(2003) Maemi(2003) Concentric eye walls was observed by Taiwan radar network

  4. 2.Simulation • Shapiro and Willoughby (1982) and Schubert and Hack (1982) used a simple symmetric model of balanced vortex response to specified heating to propose that heating–vorticity interaction can lead to convective-ring contraction. Hurricane Gilbert(1988) ＊ However, the formation of a concentric eyewall was often observed to start from the organization of asymmetric convection outside the primary eyewall into a band that encircled the eyewalls. 09132141-2354UTC

  5. Typhoon Lekima(2001) (09242232UTC-09252359UTC) Concentric eyewalls 0925/1135UTC 0924/2231UTC 0925/0647UTC 0925/1855UTC 0925/2359UTC

  6. I I I I o o o I I o o o I I o o Typhoon Lekima(2001) A complete concentric eyewall replacement A complete concentric eyewall replacement :1.Formation of the outer eyewall2.Contraction of the outer eyewall3.Destruction of the original eyewall4.Weakening of the cyclone (Black and Willoughby, 1992)

  7. 1.4 m/s Space and time section of Lekima’s inbound and outbound base velocities (m/s) 26 25 24 A complete concentric eyewall replacement cycle observed by the radial velocity:1.Formation of the second max. wind 2.Contraction of the second max. wind 3.Destruction of the original max. wind 4.It remains a single max. wind outbound typhoon center inbound

  8. ξlarge ξsmall • Montgomery and Kallenbach (1997) proposed that the concentric eyewalls might be the result of radially propagating linear vortex Rossby waves and the presence of a critical radius in the tropical cyclone.

  9. 3.Fourier expansion of typhoon Lekima 0924/2231UTC 0925/0647UTC 0925/1135UTC 0925/1855UTC 0925/2359UTC Wave1/(Wave0+Wave1+wave2+wave3) (Wave1+Wave2)/(Wave0+Wave1+wave2+wave3) (Wave1+Wave2+Wave3)/(Wave0+Wave1+wave2+wave3)

  10. Wavenumber one component During this study, the wavenumber one component showed pronounced signature and propagated outward.

  11. Radius- time hovmöller of wavenumber one from the cyclone center to 150km When the concentric eyewall formed, the wavenumber one component became weak. During the decaying stage, the wavenumber one component showed pronounced signature and propagated outward again. When pre-formation stage, the wavenumber one component showed pronounced signature and propagated outward.

  12. Both Formation stage and decaying stage are anticyclonicrotation. The waves propagated outward during the formation stage of the outer eyewall (4.44m/s) and then propagated outward with a faster speed again during the decaying period of the inner eyewall (5.56m/s). The propagation speeds of the waves are much slower than the typical values of the gravity waves.

  13. Summary and discussions • Detailed structure change of a complete concentric eyewall replacement cycle is studied by using radar reflectivity and radial velocity observations. • The Fourier expansion of reflectivity data showed that the asymmetric structure was dominated by wavenumber one during both the formation and decaying stages. • However, the wave propagated outward during the formation stage (4.44m/s) and propagated outward with a faster speed (5.56m/s) during the decaying stage. Both of the speeds are somewhat faster than the vortex Rossby waves in theoretical studies.

  14. THE END Thank you for your attention!

  15. Space and time section of Lekima’s inbound and outbound base velocities (m/s) 26 25 24 1.4 m/s outbound typhoon center inbound

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