1. Orographic Influences on Rainfall Associated with Tropical Cyclone
Orographic Influences on Rainfall and Track Deflection Associated with the Passage of a Tropical Cyclone.
Lin et al. 2002, Mon. Wea. Rev., 130,
Numerical Modeling of an Orographically Enhanced Precipitation Event Associated with Tropical Strom Rachel over Taiwan.
Chiao and Lin, 2003, Wea. Forecasting, 18,

2. Orographic Influences on Rainfall and Track Deflection Associated with the Passage of a Tropical Cyclone.
Two major effects of a mesoscale mountain range on the passage of a tropical cyclone (TC) are the generation of heavy orographic rainfall and deflection of the storm track.

3. Supertyphoon Bilis (2000) NOGAPS-analyzed surface chart at 8/22/00UTC.
SFC
700
NOGAPS-analyzed surface chart at 8/22/00UTC.
It produced maximum winds of 75 m/s and heavy rainfall (949 mm in 20h in northeast Taiwan).
500
300

4. Model: COAMPS (Coupled Ocean-Atmosphere Mesoscale Prediction System)
horizontal grid size: and 5-km
30 vertical layers
1-km terrain databases

5. Experiments Design Control experiments (CON):
CON-45, CON-15, CON-5
No-terrain experiments (NT):
NT-45, NT-15, NT-5
All experiments started without implementing a bogus vortex.

7. The CON-15 storm turned cyclonically when it passed over the CMR.
obs
CON-15
NT-15
The CON-15 storm turned cyclonically when it passed over the CMR.

8. OBS
CON-15
CON-5
1212
620
600
400 1

9. Obs 12-15Z 08/22
CON Z 08/22
Obs 15-18Z 08/22
CON Z 08/22

10. Percipitation : the three-dimensional orographic moisture flux
: the general vertical moisture flux
E: the precipitation efficiency
Ls: the horizontal scale of the convective system
Cs: the propagation speed of the convective system

11. 2. 3.

13. 4

14. Discussion
The flux model, along with coarser horizontal resolution model-simulated wind and moisture fields, may be used to help predict the distribution of heavy orographic rainfall associated with landfalling typhoons interacting with mesoscale mountains.
The rainfall that occurred over the mountains was strongly controlled by the orographic forcing, rather than by the original rainbands associated with the typhoon.

15. Numerical Modeling of an Orographically Enhanced Precipitation Event Associated with Tropical Strom Rachel over Taiwan.
They consider a heavy orographic rainfall event associated with the passage of tropical storm Rachel over Taiwan.

16. Model: COAMPS (Coupled Ocean-Atmosphere Mesoscale Prediction System)
3884
Model: COAMPS (Coupled Ocean-Atmosphere Mesoscale Prediction System)
horizontal grid size: and 5-km
30 vertical layers
1-km terrain databases

17. NOGAPS analysis of 500-hPa geopotential height and wind vector.
08/06 12Z
08/07 12Z

18. Best tracks of TS Rachel and TS Paul
The simulated time evolution of TS Rachel’s minimum low pressure (hPa).

19. 15-18
18-21
93.22
115.6
54.7
59.1

20. 00-03
03-06
76.36
132.4
128.9
56.72
72.27

21. 15-18 no-terrain
18-21 no-terrain
15-18
18-21

22. 08/06 21Z
08/07 00Z
08/07 03Z
08/07 06Z 2

23. 08/07 03Z
08/07 06Z
08/07 03Z No-terrain
08/07 06Z no-terrain 1

24. The impinging southwesterly flow was very moist since southern Taiwan was covered with high-θe (≥335K) flow. 3

25. 08/06 21Z
08/07 03Z
08/07 00Z
08/07 06Z

26. 08/07 03Z
08/07 03Z
08/07 06Z
08/07 06Z 4

27. 08/06 21Z
08/07 03Z
08/07 00Z
08/07 06Z 5

28. Conclusions
Three ingredients for producing heavy orographic rainfall :
the favorable mountain geometry.
the strong southwesterly low-level jet in this case.
the high moisture airstream.

29. Conclusions
The positive area of orographically induced vertical moisture flux could be used to help forecast areas of potential heavy rainfall over the windward mountain area.
The general vertical moisture flux (wq) can predict rainfall over a flat surface, which is not predicted by the orographically induced moisture flux.
END

30. Fujiwhara effect
如果兩個颱風靠近時,它們將繞著相連的軸線成環形狀相互作反時鐘方向旋轉(通常影響距離約1000公里),旋轉中心的位置由兩個颱風的相對質量及颱風環流之強度來決定.旋轉時通常較小的一個走得快一些,較大的一個走得慢些,有時可能二合為一,日本氣象學家藤原先生最早研究此種雙颱風旋轉現象,故稱此為藤原效應(Fujiwhara effect)。
(取自颱風氣象局TIC網頁資料)