Asymmetric Precipitation Structure of a Concentric Eyewall Tropical Cyclone

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Asymmetric Precipitation S tructure of a Concentric E yewall Tropical Cyclone Ren-Feng Liu Ren-Feng Liu 1,2 1,2 and Ben Jo and Ben Jo ng-Dao Jou ng-Dao Jou 1 1. 1. Department of Atmospheric Science Department of Atmospheric Science s, National Taiwan University , Taipei, T s, National Taiwan University , Taipei, T aiwan aiwan 2. 2. Central Weather Bureau, Taipei, Tai Central Weather Bureau, Taipei, Tai wan wan 2001/09/25/1135UTC

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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. - PowerPoint PPT Presentation

Transcript of Asymmetric Precipitation Structure of a Concentric Eyewall Tropical Cyclone

Page 1: Asymmetric Precipitation Structure of a Concentric Eyewall Tropical Cyclone

Asymmetric Precipitation Structure of a Concentric Eyewall Trop

ical Cyclone

Ren-Feng LiuRen-Feng Liu1,21,2 and Ben Jong- and Ben Jong-Dao JouDao Jou11

1.1.Department of Atmospheric SciencDepartment of Atmospheric Sciences, National Taiwan University , Taipes, National Taiwan University , Taipei, Taiwanei, Taiwan 2.2.Central Weather Bureau, Taipei, TaiCentral Weather Bureau, Taipei, Taiwanwan

2001/09/25/1135UTC

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1.Motivation & Objectives

1. It is generally believed that the evolution of the structure is responsible for the intensity change of a TC.

2. Because of their significance in hurricane intensity changes, the eyewall replacement processes have attracted significant attention since the publication of Willoughby et al. (1982)

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Concentric eye walls was observed by Taiwan radar network

Bilis(2000) Lekima(2001) Dujuan(2003)

Maemi(2003)

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2.Simulation • Shapiro and Willoughby (1982) and Schubert and H

ack (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.

* 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.

Hurricane Gilbert(1988)

09132141-2354UTC

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Concentric eyewalls (09242232UTC-09252359UTC)

0924/2231UTC 0925/0647UTC 0925/1135UTC

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Typhoon Lekima(2001)

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A complete concentric eyewall replacement

Typhoon Lekima(2001)

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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)

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Space and time section of Lekima’s inbound and outbound base velocities (m/s)

outbound inbound

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typhoon center

1.4 m/s

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

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• 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.

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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)

3.Fourier expansion of typhoon Lekima

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

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Radius- time hovmöller of wavenumber one from the cyclone center to 150kmWhen the concentric eyewall formed, the wavenumber one co

mponent 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.

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Both Formation stage and decaying stage are anticyclonic rotation. 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.

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1. Detailed structure change of a complete concentric eyewall replacement cycle is studied by using radar reflectivity and radial velocity observations.

2. The Fourier expansion of reflectivity data showed that the asymmetric structure was dominated by wavenumber one during both the formation and decaying stages.

3. 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.

Summary and discussions

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THE END

Thank you for your attention!

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Space and time section of Lekima’s inbound and outbound base velocities (m/s)

outbound inbound

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typhoon center

1.4 m/s