Orographic Influence on Typhoon Orographic Influence on Typhoon Tracks over the Central Mountain Tracks over the Central Mountain

Range of TaiwanRange 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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Continuous Track• strong (Vmax>50m/s)• deep (D>10.7 km)

Discontinuous Track• weak (Vmax: 25-50m/s)• shallow (D<6 km)

1. Effects of CMR on typhoon tracks 1. Effects of CMR on typhoon tracks (Wang 1980)(Wang 1980)

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2. Control Parameters for track 2. Control Parameters for track deflectiondeflection

Based onBased on previous studiesprevious studies (e.g., (e.g., Wang 1980; Wang 1980; Brand and Blelloch 1974; Chang 1982; Yeh and Brand and Blelloch 1974; Chang 1982; Yeh and Elsberry 1993a,b; Zehnder and Reeder 1997; Elsberry 1993a,b; Zehnder and Reeder 1997; Huang and Lin 1997; Lin et al. 1999),Huang and Lin 1997; Lin et al. 1999),

we identified 8 key parameters:we identified 8 key parameters:

VVmaxmax, U, h, R, L, U, h, R, Lxx, L, Lyy, f, N, f, N

which controls the track deflection.which controls the track deflection.

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Based on the Based on the Buckingham-pi theoremBuckingham-pi theorem, we , we may choose the following 6 independent may choose the following 6 independent nondimensional parameters: (8-2=6)nondimensional parameters: (8-2=6)

U/Nh, VU/Nh, Vmaxmax/Nh, h/L/Nh, h/Lxx, R/L, R/Lyy, U/fL, U/fLxx & V & Vmaxmax/fR/fR

Physical meanings:Physical meanings:• U/Nh: U/Nh: basic-flow Froude numberbasic-flow Froude number• VVmaxmax/Nh: /Nh: vortex Froude number vortex Froude number • h/Lh/Lxx: : steepness of the mountain steepness of the mountain • R/LR/Lyy: : ratio of the cyclone and ratio of the cyclone and

mountain sizesmountain sizes• U/fLU/fLxx: : basic flow Rossby numberbasic flow Rossby number• VVmaxmax/fR: /fR: vortex Rossby numbervortex Rossby number

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Effects of orography on TC Effects of orography on TC may be linearly decomposed may be linearly decomposed into:into:

(a) Influence on the basic (a) Influence on the basic flowflow

(b) Influence on the (b) Influence on the cyclone circulationcyclone circulation

Physical meaning of U/Nh and VPhysical meaning of U/Nh and Vmaxmax/Nh/Nh (Lin, Chen, Hill, Huang 2005 JAS)(Lin, Chen, Hill, Huang 2005 JAS)

6VVmaxmax/Nh/Nh

UU//NhNh

VVmaxmax/fR/fR

h/Lh/Lxx

Based on previous Based on previous studies, it was found:studies, it was found:

Track is continuous Track is continuous when when VVmaxmax//Nh > 1.5;Nh > 1.5;

Otherwise it is Otherwise it is discontinuous.discontinuous.

It appears that track It appears that track continuity is mainly continuity is mainly controlled by controlled by VVmaxmax/Nh /Nh (at least for CMR)(at least for CMR)

SS NN

CCDD

CCDD

CCDD

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Verification of previous results by systematic Verification of previous results by systematic idealized numerical simulations idealized numerical simulations (Lin et al. 2005)(Lin et al. 2005)

U/NhU/Nh h/Lh/Lxx

VVmaxmax/fR/fR R/LR/Lyy

Vmax/NhVmax/Nh Vmax/NhVmax/Nh

CCDD CCDD

• Track is continuous (discontinuous) when Track is continuous (discontinuous) when VVmaxmax/Nh/Nh>1.6 (<1.2)>1.6 (<1.2)• Track continuity is mainly controlled by Track continuity is mainly controlled by VVmaxmax//NhNh, , and is lessand is less sensitive to other parameters (for CMR)sensitive to other parameters (for CMR)

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DiscontinuousDiscontinuous

VVmaxmax/Nh=0.8/Nh=0.8

U/Nh=0.13U/Nh=0.13

R/LR/Lyy=0.75=0.75

relativerelative vorticityvorticitystreamlinesstreamlines

ContinuousContinuous

VVmaxmax/Nh=2.0/Nh=2.0

U/Nh=0.5U/Nh=0.5

R/LR/Lyy=1.042=1.042

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With a very small With a very small R/LyR/Ly, the track becomes discontinuous and the , the track becomes discontinuous and the cyclone is even deflected cyclone is even deflected southwardsouthward

Obs.

18/00Z (STY)

18/12Z (TY)

17/12Z (STY)

19/00Z (TY)

120E

121E

122E

25N

24N

23N

22N

123E

★

★

Wu-Fen-Shan

Hua-Lien

(Jian and Wu 2006)

243

6

48

60

72

24

36

48

60

CTRLNT

Our study helps explain the curving of Tphoon Haitang (2005)Our study helps explain the curving of Tphoon Haitang (2005)

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Degree of Track DeflectionDegree of Track Deflection

When When VVmaxmax/Nh/Nh or or U/NhU/Nh is smaller, the track deflection is is smaller, the track deflection is largerlarger

VVmaxmax/Nh/Nh

U/N

hU

/Nh

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(a) Weak blocking(a) Weak blocking• deflected slightly northward deflected slightly northward upstreamupstream• continuous trackcontinuous track

(b) Moderate blocking(b) Moderate blocking• deflected northward upstreamdeflected northward upstream• a secondary vortex forms on a secondary vortex forms on the lee -> discontinuous trackthe lee -> discontinuous track

(c) Strong blocking(c) Strong blocking

• deflected southward upstreamdeflected southward upstream• a secondary vortex forms on a secondary vortex forms on the lee -> discontinuous trackthe lee -> discontinuous track

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U/NhU/Nh

Vmax/NhVmax/Nh

BBTT

Application of the control parameter hypothesis to Application of the control parameter hypothesis to Supertyphoon Bilis (2000) and typhoon Toraji (2001)Supertyphoon Bilis (2000) and typhoon Toraji (2001)

(Lin, Witcraft, Kuo 2006 MWR)(Lin, Witcraft, Kuo 2006 MWR)

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3. Effects of Lanfalling 3. Effects of Lanfalling locations:locations:

R/Ly comes into playR/Ly comes into play

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4. Effects of 4. Effects of impinging anglesimpinging angles

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Upstream of the mountain: vorticity Upstream of the mountain: vorticity advection dominatesadvection dominates

Vorticity Vorticity advectionadvection

Vorticity Vorticity stretchingstretching

Local Local vorticity vorticity tendencytendency

VorticityVorticitytiltingtilting

12121212

1515

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Over the mountain: vorticity stretching Over the mountain: vorticity stretching dominatesdominates

Vorticity Vorticity advectionadvection

Vorticity Vorticity stretchingstretching

1515

12121212

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On the lee side: On the lee side: vorticity advection regains the controlvorticity advection regains the control

Vorticity Vorticity stretchingstretching

Vorticity Vorticity advectionadvection

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5. Summary5. Summary

• Track continuity is more sensitive to Track continuity is more sensitive to VVmaxmax/Nh/Nh and and R/LR/Lyy..

• A combination of small A combination of small VVmaxmax/Nh/Nh, , R/LR/Lyy, , U/NhU/Nh, , U/fLU/fLxx, and , and VVmaxmax/fR/fR and large (small) and large (small) h/Lh/Lxx will will give larger degree of track deflection.give larger degree of track deflection.

(Lin, Chen, Hill, Huang 2005 JAS)(Lin, Chen, Hill, Huang 2005 JAS)

• Blocking plays an essential role in dictating Blocking plays an essential role in dictating the track deflectionthe track deflection

• Tracks are also influenced by landfalling Tracks are also influenced by landfalling location and impinging anglelocation and impinging angle

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Thank You!Thank You!

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• Deflection is controlled by vorticity Deflection is controlled by vorticity advection and stretchingadvection and stretching

• Upstream: Vorticity advectionUpstream: Vorticity advection

Crossing over: Vorticity stretchingCrossing over: Vorticity stretching

Downstream: Vorticity advectionDownstream: Vorticity advection

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3. Application to Track Deflection of Bilis 3. Application to Track Deflection of Bilis and Torajiand Toraji (Lin, Witcraft and Kuo 2006 MWR) (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

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Observed and Simulated Bilis TracksObserved and Simulated Bilis Tracks

TC symbols – ObservedStars – SurfaceSquares – 700 mbCircles – 500 mbTriangles – 300 mb Max wind: 160 knots

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Observed and Simulated Toraji TracksObserved and Simulated Toraji Tracks

TC symbols – ObsStars – SurfaceSquares – 700 mbCircles – 500 mbTriangles – 300 mb*open symbols – coexisting centers Max winds: 95 knots

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

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Toraji: Backward trajectories (7/29/21Z)Toraji: Backward trajectories (7/29/21Z)

Most low-level air Most low-level air parcels are parcels are blocked by CMR blocked by CMR and go around the and go around the mountainmountain

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Obs.

18/00Z (STY)

18/12Z (TY)

17/12Z (STY)

19/00Z (TY)

120E 121E 122E

25N

24N

23N

22N

123E

★

★

Wu-Fen-Shan

Hua-Lien

24

36

48

60

72

24

3648

60

CTRLNT

Tracks:Obs. CTRL NT

(Jian and Wu 2006)