1. Topographic Effects on Typhoon Toraji (2001)
Yang, M.-J. and L. Ching, 2004: A Modeling Study of Typhoon Toraji (2001): Physical Parameterization Sensitivity and Topographic Effect. Terr. Atmos. Ocean. Sci., 16,
Lin, Y.-L., D. B. Ensley, S. Chiao, and C.-Y. Huang, 2002: Orographic Influences on Rainfall and Track Deflection Associated with the Passage of a Tropical Cyclone. Mon. Wea. Rev., 130,
Lin, Y.-L., S. Y. Chen, C. M. Hill, and C.-Y. Huang, 2005: Control Parameters for the Influences of a Mesoscale Mountain Range on Cyclone Track Continuity and Deflection. J. Atoms. Sci., 62,

2. Introduction
In this study, we will discuss the topographic effects on Toraji, which include the generation of heavy orographic rainfall and the degree of deflection of storm’s track by Taiwan’s topography.

3. Case Description 24 hours accumulated rainfall on 30 July 2001 (LST).
The JTWC best track

4. Model Setting
The MM5 model configuration includes three nested domains with grid size of 60, 20, and 6.67 km, respectively.

5. Physics schemes used by each numerical experiment.

6. Ensemble-analyzed tracks
Ensemble analysis
Ensemble-analyzed tracks
Cumulus
Microphysic
PBL

7. The maximum rainfall around 664 mm over the south peak of CMR
The simulated 24-h accumulated rainfall (in mm) of the ensemble average plus one stand deviation.
Cumulus
Microphysic
PBL
The maximum rainfall around 664 mm over the south peak of CMR
346.5
430.3
544

8. Orographic Rainfall
Follow the flux method of Lin et al. (2002) to see how much Toraji’s precipitation over Taiwan is related to topography-enhanced moisture flux (Wu and Kuo 1999; Lin et al. 2001; Wu et al. 2002).

9. Orographic Rainfall
Lin et al. (2001) proposed the orographic precipitation approximated by this formula:
: the three-dimensional orographic moisture flux
: the general vertical moisture flux

10. before landfall
Simulated 1-h accumulated rainfall valid for UTC 29 July.
General vertical moisture flux valid at 7/29/12 UTC.
Orographically induced vertical moisture flux valid at 7/29/12 UTC.

11. passed land
Simulated 1-h accumulated rainfall valid for UTC 30 July.
General vertical moisture flux valid at 7/30/00 UTC.
Orographically induced vertical moisture flux valid at 7/30/00 UTC.

12. Track Deflection
A momentum budget is conducted to understand the physical mechanisms responsible for the track turning right before Toraji’s landfall on Taiwan.
obs
model

13. Analyzed sea level pressure at 7/29/14 UTC. (Wang et al. 2001)
Simulated sea level pressure at 7/29/12 UTC.

14. The u- and v-momentum equations in the MM5 (Grell et al. 1994) are:
TEN
local tendency
ADV
advection
PGF
pressure-gradient force
COR
Coriolis force
TUB
turbulent mixing and friction

15. Vertical profile of (a) u-momentum and (b) v-momentum budget terms averaged over a square area around Toraji’s center and over a 1-h period

16. velocity vectors of the time- (1-h) and tropospheric-averaged steering flows around Typhoon Toraji

17. Control parameter analysis
Lin et al. (2002) indicated that when Vmax/Nh > 1.6, Vmax/U > 7.0, and Vmax/Rf > 4.0, the TC track would be continuous.
Lin et al. (2004) showed that when R/Ly < 0.35 with strong blocking, the TC track would be discontinuous. The TC would be deflected anticyclonically.

18. Vmax/Nh
The nondimensional parameter may be regarded as a vortex Froude number of the typhoon tangential circulation.
When Vmax/Nh is large, it is easier for the TC vortex to pass over the mountain because the kinetic energy is more than enough to overcome the work required to lift the stratified flow against gravity and the orographic potential energy barrier.

19. Vmax/U
Vmax/U may also be viewed as the ratio of the vortex Froude number to the basic-flow of Froude number, (Vmax/Nh) / (U/Nh).
A large Vmax/U represents a stronger vortex and, based on the energy arguments above, makes it easier for the vortex to pass over the mountain.

20. Vmax/Rf
Vmax/Rf is a measure of the ratio of vortex vorticity (Vmax/R) to planetary vorticity (f).
When Vmax/Rf is large, the TC vortex is more stable and it is easier to pass over the mountain.

21. R/Ly
R/Ly is the ratio of the size of the TC to the length of the mountain chain.
When R/Ly is small, the TC vortex is more difficult to climbing over the mountain. The TC track would be discontinuous, and the track deflection is large.

22. When TC is easy to pass over the mountain

23. When TC is difficult to pass over the mountain

24. < < > <0.35

25. Control parameter analysis

26. Conclusions
A combination of the topographically- and environmentally-induced vertical moisture fluxes, calculated based on the flux model of Lin et al. (2001), corresponded well to the hourly surface rainfall distribution.
The positive area of orographically induced vertical moisture flux cloud be used to help predict the following rainfall distribution.
The general vertical moisture flux can predict rainfall over a flat surface, which is not predicted by the orographically induced moisture flux.

27. Conclusions
The westward turning of Toraji’s track right before the landfall may be caused by horizontal advection process, on the basis on a momentum budget analysis.
An analysis of nondimensional parameters for typhoon’s track continuity over the Taiwan island shows that Typhoon Toraji’s track discontinuity is consistent with the control parameter analysis proposed by Lin et al. (2002).

28. Thanks