The Meso-scale Features

Associated with Typhoon Mindulle (2004)

When It Was Affecting Taiwan

Cheng-shang Lee, Yi-chin Liu (NTU), Fang-ching Chien (NTNU)

Operational fixes of Mindulle (CWB)

Mindulle and the following southwesterlies brought 1,860 mm rainfall to Taiwan– locally called 7-2 flood.

July 1

July 2

Daily Rainfall (mm)

Rainfall on July 1 (max ~ 383 mm)-- mainly by the terrain slope lifting of typhoon circulation

Rainfall on July 3 - 4 (max over 700 mm) (Chien et al. 2006)

-- mainly by the southwesterly flow (occurred over CMR)

Rainfall on July 2 (max ~ 787 mm)-- multiple factors (meso-scale features) are playing roles.

Focus of this talk:

Meso-scale processes occurred on July 2 - focus on the evolution of the secondary center

Interaction between secondary center and main center.

The influences of secondary center and typhoon circulation on the heavy rainfall.

Surface analysis and visible satellite imageries

A secondary low formed over Taiwan Strait -

moved toward the ENE, made landfall and then dissipated.

1500 UTC 1 July 2100 UTC 1 July

Composite radar reflectivity (CWB)

0702 1700 UTC

0702 0200 UTC

0702 1200 UTC Heavy rainfall ~highly related torainbands,

which occurred to the south of the secondary center.

0702 0600 UTC

MM5 model setup• Initial data: EC Advanced Data Set

TC bogus at 12 h before initial time (Jien et al., 2003, 2005)

• Simulation time:

0100~0300 UTC July, 2004

• D1: 160×160， 45km

D2: 154×154 ,15km

D3: 133×133 , 5km

• Physics options

Cumulus: Grell

PBL: MRF

IMPHYS: Mixed-Phase

• Objective analysis: little-r

• FDDA

Analysis based on MM5 model simulation

Tracks of primary and secondary centers -model simulation vs. observation

Secondary center

Primary center

Model simulates reasonably welltracks of primary and secondary centers.

(0206)

(0123)

701

739

500

Accumulated daily rainfall (July 2, 2004)

Simulation (24~48h)Observation

Model reproduces reasonably well the rainfall distribution.

12 h 20 h 28 hEvolution of primary (red) and secondary (blue) centers

3 h before landfall 5 h after landfall 13 h after landfall

32 h 36 h 42 h

2 h after moving off-shore 6 h after 12 h after

Evolution of primary (red) and secondary (blue) centers

Trajectories during the developing phase of the secondary low (backward trajectory: 18 hr 8 hr)

Two groups of air parcel trajectories

Over CMR

Around CMR

2

21

1

Subsidence warming produced the initial low pressure.

Flow around the northern tip of CMR brought in shear vorticity for the further development of the secondary low.

P and Theta at 1.5 km AGL

Vorticity averaged inside box A (include matured vortex)

Height

time

Stages of low-level vortex:developing – 12 ~ 20 hmature – 20 ~ 26 h max vorticity ~ 2.5X10-4 s-1

disappearing – 26 ~ 30 h

A

925 hPa vorticity (shaded)P msl and 10 m winds

The low level ( 950 ~ 800hPa )

Times LC HA VA DT TT RT

12-20 h 4.3 3.5 -0.03 1.0 1.6 -1.820-26 h 0.16 -5.4 9.1 9.9 -7.4 -6.1

26-30 h -6.0 -17.0 5.6 10.5 -3.3 -1.9

The midlevel ( 800 ~ 500 hPa )

Times LC HA VA DT TT RT

12-20 h 2.9 3.6 0.56 -1.6 0.53 -0.1620-26 h 2.1 0.74 1.9 -0.83 0.83 -0.57

26-30 h -1.1 -3.6 3.4 0.90 -1.4 -0.36

TRp

u

y

ω

p

v

x

ωvζf

p

ζωζfv

t

ζ

Vorticity budgetLC HA VA DT TT RT

HA ~ advection of shear vorticity from the north of the CMR

HA ~ vorticity of primary center moved across the CMR

Before landfall After landfall

LL

Evolution of secondary center – a schematic diagram

L

For the secondary vortex at mature stage Area-averaged vorticity ~ 2.5X10-4 s-1

Rossby radius of deformation ~ 120 km (if c = 30 m/s). Heating would be efficient for secondary vortex to develop.

Why the secondary vortex didn’t replace the primary center?

1.5 PVU at σ= 0.9 (27- 33 h)

What has happened to the low-level primary center?

The strong vorticity remnant associated with the primary center moved northward on the eastern side of the CMR.

The primary center re-developed after it moved off shore.

An unique feature of a northward- moving typhoon?

(Similar for Ofelia, 1990)

After primary center re-developed over the ocean ~7/2 0500 UTC 7/2 0700 UTC

7/2 0900 UTC 7/2 1100 UTC

Shaded: PV at σ= 0.9, Contour: 900 hPa gpm

Two centers rotated cyclonically wrt each other

landfall of secondary center

(dissipated over land)

A reasonable result for a typhoon with such track pattern.

28 h

34 h

28 h

34 h

Sensitivity test (no initial vortex) no typhoon and no secondary vortex

Div at σ= 0.9 (strong conv shaded)

SW flow

Meso-scale circulation Terrain

Summary

Horizontal vorticity advection is important to the spin-up of the secondary vortex (Lin et al. 2006).

It is difficulty for the secondary center to replace the primary center for a typhoon northward moving (along the east coast of Taiwan).

Several factors are affecting the heavy rainfall on 2 July for Mindulle (2004) case:

typhoon circulation, secondary centersouthwesterly flow, Taiwan topography.

Thank you!