THE SECONDARY LOW AND HEAVY RAINFALL ASSOCIATED WITH TYPHOON MINDULLE (2004)

Speaker : Deng-Shun ChenAdvisor : Prof. Ming-Jen Yang

Lee, C.-S., Y.-C. Liu and F.-C. Chien, 2008:The Secondary Low and Heavy Rainfall Associated with Typhoon Mindulle(2004). Mon. Wea Rev., 136, 1260-1283.

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The 7-2 Flood Was Caused by MINDULLE

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College Entrance Examination

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Outline 4

Case description Model design and verification a) model settings b) verification of the simulation The evolution of the primary and the

secondary centers Budget analyses during the formation of

secondary low a) thermal budget b) vorticity budget The roles of the secondary low Discussion and conclusion

Case description 5

Synoptic Scale 6

500 hPa 7/1 1200Z

500 hPa 7/2 1200Z

Mesoscale Surface Analyses7

1500Z 1 July surface

0000Z 2 July surface

Visible Satellite8

NCU Radar Observation 9

0241Z & 0316Z 2 July

CWB Radar Reflectivity 10

20Z 1July

02Z 2 July

12Z 2 July

17Z 2 July

24-h Accumulation Rainfall (mm)

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00Z 1 July – 00Z 2 July

00Z 2 July – 00Z 3 July

00Z 3 July – 00Z 4 July

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Model design and verification

a) model setting b) verification of the simulation

Model MM5

Domain D1:45 km ; D2: 15 km ; D3: 5 km , two-way interaction

Levels 31 levels, extend vertically up to100 hPa

Microphysics Resiner Mixing – Phase ( Reisner et al. 1998)

PBL Medium-Range Forecast (MRF) PBL (Hong et al.)

Radiation Simple Cooling Radiation Scheme

ICECMWF/TOGA 1.125 。 X 1.125 。 resolution

BC

cumulus Grell cumulus parameterization (Grell et al. 1994)

Model Setting 13

Accumulation Rainfall (Sim. vs. Obs.)

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Simulation

Observation

00Z 2 July – 00Z 3 July

Geopotential Height at 925-hP and Reflectivity

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28 h 34 h

The Evolution of Primary & Secondary Low (I)

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12 h 20 h 28 h

The Evolution of Primary & Secondary Low (I)

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32 h 36 h 42 h

Geopotential Height & Potential Vorticity

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TT

T

T TCC C

500 hPa

17h 19h 21h

23h 25h 27hPrimary center merged with secondary low

Horizontal Wind & Potential Temperature

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6h 12h

At 2 km AGL

SLP & PV (I)21

8 h 12 h

SLP : Sea Level Pressure, PV : Potential Vorticity

SLP & PV (II)22

16 h 20 h

SLP & PV (III)23

30 h 34 h

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Budget analyses during the formation of secondary low

a) Thermal budget b) Vorticity budget

Thermal Budget 27

8h 18h

1 2 3 4 5

Condensational heating

Thermal Budget Result28

Model 8 h

Vertical advection

Model 8 h

Local change term

Model 18 h

Vertical advection

Model 8 h

Local change term

Potential Temperature & Trajectory

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The Representation of Trajectory

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Trajectory 1 The sinking motion resulted in adiabatic

warming also is the early stage formation of the secondary low at low level.

Trajectory 2 The air parcels that transported vorticity

to the low pressure region which assisted the development of the secondary low.

Vorticity Budget 31

Local Change LC

Horizontal Advection

HA

Vertical Advection

VA

Divergence Term

DT

Tilting Term TT

Residual Term RT

Vorticity Budget Result32

DevelopingMatureDisappearing

DevelopingMatureDisappearing

Distribution of LC, HA and DT

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12-16 h

16-20 h

LC HA DT

The Roles of the Secondary Low (I)

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The interaction between the primary center and the secondary center

Fujiwhara effect

The reason why secondary low did not replace the original center

The Roles of the Secondary Low (II)

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Impact of the secondary low and the typhoon circulation on rainfall

III

I

28h 34h

Conclusion (I)36

Two processes resulted in the formation of a secondary low ,1) downslop adiabatic warming ,2) the shear vorticity that circled around the northern tip of the CMR.

The low level horizontal vorticity advection and then local convergence further concentrated the vorticit.

The vortex stretching and advection are dominant terms during the formation of the secondary low(Chang ,1982)

Conclusion (II)37

Mindulle can be treated as a ‘‘quasi-continuous track’’

Such results are somewhat different form the previous studies that show weaker typhoons having more chances to induce a secondary low. (Chang 1982)

The secondary low and the typhoon circulation played an important role in the heavy rainfall over the central and southern parts of the island west of the CMR.

Conclusion (III)38

It is impossible to isolate the role of typhoon circulation and secondary low on the heavy rainfall.

The secondary low should play a role as a modification of environmental flow, which could result in the west-east convergence lines.

Question ?