The effects of orography on cloud and rainfall patterns during typhoon Ketsana (2009)

Abstract

The objective of this study is to investigate the effects of orography on the rainfall, wind, and cloud systems of the TCs in Malaysia and Indochina. To determine the relationship of the typhoon with the orographic effect, remote sensing techniques such as the Global Digital Elevation Model (GDEM) from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite, rainfall data from the Fengyun 2D (FY-2D), and radiosonde data were applied in this study. From this study, the following conclusions can be drawn: 1) rainfall tends to be distributed over high mountain regions; 2) wind flow will change its direction upon encountering any restrictions, especially those of high terrain regions; and 3) cloud patterns are deformed by high mountains and tend to flow with the mountains' structure because of the orographic effects. The regions most affected by Typhoon Ketsana in the study area were Vietnam in Indochina, Sabah in East Malaysia (EM), Kelantan and Terengganu in Peninsular Malaysia (PM). From the comparison among the study areas, it was found that Indochina had the most significant results for the orographic effects on typhoon activity, followed by the tail effects in EM. This phenomenon was found in PM, although it was not as significant as the other study areas. This remote sensing technique allows tropical cyclones to be forecasted and their impacts to be defined, and it allows disaster zones to be determined.

Full text

The effects of orography on cloud and rainfall patterns during typhoon Ketsana (2009)
Tan Fuyi, Mohd Zubir MatJafri, Hwee-San Lim and Khiruddin Abdullah
School of Physics, University Sains Malaysia, 11800 Penang, Malaysia
ABSTRACT
The objective of this study is to investigate the effects of orography on the rainfall, wind, and cloud systems of the TCs
in Malaysia and Indochina. To determine the relationship of the typhoon with the orographic effect, remote sensing
techniques such as the Global Digital Elevation Model (GDEM) from the Advanced Spaceborne Thermal Emission an
d
Reflection Radiometer (ASTER) satellite, rainfall data from the Fengyun 2D (FY-2D), and radiosonde data were applied
in this study. From this study, the following conclusions can be drawn: 1) rainfall tends to be distributed over high
mountain regions; 2) wind flow will change its direction upon encountering any restrictions, especially those of high
terrain regions; and 3) cloud patterns are deformed by high mountains and tend to flow with the mountains' structure
b
ecause of the orographic effects. The regions most affected by Typhoon Ketsana in the study area were Vietnam in
Indochina, Sabah in East Malaysia (EM), Kelantan and Terengganu in Peninsular Malaysia (PM). From the comparison
among the study areas, it was found that Indochina had the most significant results for the orographic effects on typhoon
activity, followed by the tail effects in EM. This phenomenon was found in PM, although it was not as significant as the
other study areas. This remote sensing technique allows tropical cyclones to be forecasted and their impacts to be
defined, and it allows disaster zones to be determined.
Keywords: Typhoon Ketsana, Orography, Wind, Cloud, Rainfall, Mountain, Radiosonde, FY-2D
1. INTRODUCTION
Complex mesoscale mountain structure has led to many difficulties in weather prediction especially during typhoon
season. The complicated interaction of the typhoon on orography effects cause to many uncertainty on the forecast
events. Therefore, basic understanding of these effects can be helpful for investigating and precisely evaluating the
synoptic and mesoscale weather variation. In the previous study, many scientists have studied the typhoon activities on
orography effects in term of variation in pressure, track propagation, intensity and precipitation for further understanding
of typhoon nature and forecast purpose [1-8]. These studies also proved that the typhoon event may have a very close
relationship with orographic effects. When the typhoon activity is close to the continental region, the complicated
mesoscale mountain will influence the current synoptic weather or atmospheric conditions, and indirectly cause to
variation of the various parameters of typhoon events.
The purpose of this study is to compare the impacts of typhoon in term of wind, cloud, and rainfall for the three different
locations in Southeast Asia (SEA). To determine the interaction effect of typhoon and orography in SEA, Typhoon
Ketsana was chosen in this study because this typhoon was known as one of the top 10 catastrophes of 2009 [9].
Typhoon Ketsana was reported highest amount of destroying (7.4 million), third highest death amount (645 people) and
ninth highest economic losses (1.03 billion) in the world. Therefore, this is an interest typhoon case for the scientific
study purpose.
2. STUDY AREA
Southeast Asia is located in one of the world’s most active cyclogenetic basins Northwest Pacific and South China Sea.
The region experiences 27 cyclones per year on average, with almost half of them reaching typhoon intensity [10].
Typhoons progressing in straight moving path over this basin will affect SEA [11]. Figure 1 indicated the study areas are
divided into 3 interest areas: French Indochina, or simply Indochina, including Vietnam (1), Loas (2), Cambodia (3) (red
region); Sabah (4) and Sarawak (5) in east Malaysia (pink region); and Kelantan (6), Terengganu (7), and Penang (8) in
peninsular Malaysia (green region). Figure 2 has shown the topography with different elevation level to indicate the low
Earth Resources and Environmental Remote Sensing/GIS Applications III, edited by Daniel L. Civco, Manfred Ehlers,
Shahid Habib, Antonino Maltese, David Messinger, Ulrich Michel, Konstantinos G. Nikolakopoulos, Karsten Schulz,
Proc. of SPIE Vol. 8538, 853819 • © 2012 SPIE • CCC code: 0277-786/12/$18 • doi: 10.1117/12.974796
Proc. of SPIE Vol. 8538 853819-1

plain region
interested in
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Proc. of SPIE Vol. 8538 853819-2

Before discu
s
p
erforming a
n
Ketsana. Se
c
p
eninsular
M
considered a
s
p
atterns in t
h
to identify h
o
orographic e
f
4.1 Compar
i
The
and fairly st
r
Ketsana in
M
When the ar
e
troposphere
c
Thr
e
the troposph
e
the data sele
c
(CAPE) resu
l
1), but the ta
i
the typhoon
a
(maximum v
a
were stronge
r
The
(only as man
y
the Malaysia
that the stren
g
level (LCL),
o
b
ecause the
c
In addition, t
h
Figure 3. The
S
show the insta
b
the University
s
sing the co
m
n
appropriate
c
ond, the tail
M
alaysia (PM)
.
s
a factor tha
t
h
e related regi
o
w much inf
l
f
fec
t
s in these
i
son the radi
o
radiosonde r
e
r
ong wind al
o
M
alaysia only
e
a encounters
c
olumn above
e
e parameters
e
re among th
e
c
tion was de
p
l
ts showed th
a
i
l effects of T
y
a
nd in areas t
h
a
lue was > 3
0
r
at EM due t
o
lifted index
(
y
as -2.38),
b
region. The
l
g
th of the tail
o
r the cloud
b
c
loud base ca
n
h
e cloud base
a)
S
kew-T charts
b
ility of the at
m
of Wyoming.
4
m
parison, a b
a
comparison.
F
effects (or i
n
.
Each study
a
t
alters the i
m
on. At the be
g
l
uence Typho
study areas a
r
o
sonde data
a
e
sults in Ind
o
o
ng the low
resulted in o
c
the direct im
p
it and vice v
e
have been u
s
e
three study
a
p
endent on th
e
a
t the direct i
m
y
phoon Kets
a
h
at were too
fa
0
00 Jkg-1) th
a
o
the shorter
d
(
lift) for the
d
b
ut higher ne
g
l
ift results in
M
effects of T
y
b
ase, was not
v
n
be even low
e
will be form
e
for a) 0000 U
T
m
osphere and
w
4
. RESU
L
a
sic understa
n
F
irst, the Ind
o
n
direct impa
c
a
rea has a di
f
m
pacts of typ
h
g
inning of th
i
on Ketsana
h
r
e discussed.
a
mon
g
the st
u
o
china showe
d
to middle le
v
c
casionally h
i
p
acts of the t
y
e
rsa.
s
ed to identif
y
a
reas (Table
e
impact peri
o
m
pacts of Typ
a
na in Malay
s
fa
r from the t
a
a
n PM (maxi
m
d
istance betw
e
d
irect impact
g
ative numbe
r
M
alaysia wer
e
y
phoon Ketsa
n
v
ery close to
t
e
r during the
t
e
d at a higher
T
C 27, b) 0000
w
ind character
a
L
TS AND
D
n
ding of the
d
o
china region
s
c
ts) of Typho
f
ferent topogr
a
h
oons in ter
m
i
s section, th
e
h
ad in these
s
u
d
y
areas
d
the direct i
m
v
el troposph
e
i
gh relative h
u
y
phoon, the d
e
y
the interacti
o
1), and differ
e
o
d of the typ
h
hoon Ketsan
a
s
ia were high.
a
il effects to b
m
um value
w
e
en the study
a
of Typhoon
K
r
s (approxima
t
e
not much d
i
n
a was differ
e
t
he ground su
r
t
ail effects of
altitude af
t
er
t
b
)
UTC 28, and
c
a
long the tropo
s
D
ISCUSSI
O
d
ifferences a
m
s
encountere
d
on Ketsana
w
a
phic structu
r
m
of variatio
n
weather con
d
s
tudy areas.
T
m
p
acts of Ty
p
e
re (Figure 3
)
u
midity and
w
e
w point temp
o
ns of weath
e
e
nt dates wer
e
h
oon event.
T
a
in Indochin
a
The CAPE
b
e influenced.
w
as approxim
a
a
rea and the t
y
K
etsana in In
d
t
ely -5.0 but
n
i
fferent betw
e
e
nt on differe
n
r
face during t
h
the typhoon (
m
t
he tail effect
s
c
) 1200 UTC 2
s
phere column,
O
NS
m
ong the stu
d
d
the landfall
(
w
ere closer t
o
r
e. Therefore,
n
s of rainfall,
d
itions of the
T
hen, only th
e
p
hoon Ketsa
n
)
. However,
t
w
eak low-lev
e
erature over
t
e
r conditions
d
e
chosen am
o
T
he convectiv
e
a
were low (m
a
b
ecame fairly
In addition, t
h
a
tely 2400 Jk
g
y
phoon.
d
ochina exhi
b
n
ot more tha
n
e
en EM and
P
n
t days. How
e
h
e direct imp
a
m
ore than 93
0
s
pass over.
9 September 2
0
respectively.
T
d
y areas is a
p
(
direct impact
o
east Malay
s
orographic e
f
cloud type,
a
study areas
w
e
typhoon’s i
m
n
a were extre
m
t
he tail effec
t
e
l winds (Fig
u
t
hat area incr
e
d
uring Typh
o
o
ng the study
e
available p
o
a
ximum valu
e
low after the
h
e CAPE wa
s
g
-1)
b
ecause
t
b
ited low neg
n
-6.0) for th
e
P
M; the only
d
e
ver, the lifte
d
a
cts of the ty
p
0
mb but less
c)
0
09 at Da Nan
g
T
hese diagram
s
p
rerequisite t
o
s) of Typhoo
n
s
ia (EM) tha
n
f
fects must b
e
a
nd wind flo
w
w
ere discusse
d
m
pacts on th
e
m
ely moist ai
r
s of Typhoo
n
u
res 4 and 5
)
e
ases along th
e
o
on Ketsana i
n
areas becaus
e
o
tential energ
y
e
was 800 Jk
g
tail effects o
s
higher at E
M
t
he tail effect
s
ative number
s
e
tail effects i
n
d
ifference wa
s
d
condensatio
n
p
hoon (926 m
b
than 960 mb
)
g
, Vietnam is t
o
s
are cou
r
tesy o
o
n
n
e
w
d
e
r
n
)
.
e
n
e
y
g
-
f
M
s
s
n
s
n
b
)
)
.
o
f
Proc. of SPIE Vol. 8538 853819-3

Figure 4. The
1200 UTC for
courtesy of th
e
a)
d)
variation of th
e
26 September
e
University of
W
a)
e
atmospheric
c
in year 2009 a
t
W
yoming.
d)
c
onditions duri
n
t
Kota Kinabal
u
b
)
e)
n
g Ketsana pe
r
u
, Sabah (a, b,
b
)
r
iod was plotte
d
c) and Bintulu
e)
d
at 0000 UT
C
, Sarawa
k
(d,
e
c)
f)
C
for 25, and at
e
, f). These dat
a
c)
0000 UTC an
d
a
were provide
d
d
d
Proc. of SPIE Vol. 8538 853819-4

B
e
e
C
b
fr
t
h
m
Figure 5. The
1200 UTC for
was missing a
t
Table 1. Soun
d
C
I
n
Ea
s
P
e
M
4.2 Compar
i
B
ase on the cl
e
levation info
r
e
ach other. W
h
C
hu Yang Si
n
b
ecause the c
l
fr
om pressure
h
is region be
c
m
ountains als
o
f)
variation of th
e
27 September
t
Kuantan site.
T
d
ing parameter
s
C
ountr
y
n
dochina
s
t Malaysia
e
ninsula
r
M
alaysia
i
son of Rainf
a
oud base inf
o
r
mation from
h
en Typhoon
n
, the outer
c
l
oud base of
t
to altitude).
T
c
ause these
h
o
have elevat
i
e
atmospheric
c
in year 2009 a
t
T
hese data wer
e
s
during Typho
o
Date
(Sep 2011)
27
28
29
25
26
25
26
26
27
26
27
26
27
a
ll Distributi
o
o
rmation (CL
C
Table 2, the
b
Ketsana appr
o
c
irculation of
t
he outer part
T
he yellow an
d
h
igh terrains
o
i
on more tha
n
c
onditions duri
n
t
Kota Bharu (
a
e
provided cou
r
o
n Ketsana in
S
Time
(UTC)
0000
0000
1200
0000
0000
1200
0000
0000
1200
1200
0000
1200
1200
T
0000
1200
1200
0000
1200
o
n Patterns
a
C
) from the T
a
b
locking effe
c
o
ached the c
o
the typhoon
of Ketsana i
s
d
purple colo
u
o
f at least 84
0
n
2000 m, th
e
g)
n
g Ketsana pe
r
a
, b, c), Kuant
a
r
tesy of the Un
i
S
eptember 200
9
State
--
Sabah
Sarawak
Kelantan
T
erengganu
Penang
a
mon
g
the St
u
a
ble 1, the to
p
c
ts by the mo
u
o
astline and t
h
brought the
r
s
approximat
e
u
rs in Figure
2
0
m were hi
g
e
refore most
p
r
iod was plotte
d
a
n (d, e), and P
e
i
versity of Wy
o
9
for comparis
o
Soundi
n
Statio
n
Da Nan
g
108.20°
E
16.03°
N
Kota Kina
b
116.05°
E
5.93°
N
Bintul
u
113.03°
E
3.20°
N
Kota Bh
a
102.28°
E
6.16°
N
Kuanta
n
103.21°
E
3.87°
N
Penan
g
100.26°
E
5.30°
N
u
d
y
Areas
p
ography ima
g
u
ntain can be
en encounter
e
r
ainclouds,
w
e
ly only 650-
6
2
indicate tha
t
g
her than the
p
art of cloud
b
d
at 1200 UT
C
e
nang (f, g, h).
o
ming.
o
n among the t
h
ng
n
CAP
E
(Jkg-
1
g
E
N
133
800
200
b
alu
E
N
1786
3482
93
u
E
N
47
385
1789
a
ru
E
N
3079
1609
2389
n
E
N
2246
--
1074
g
E
N
108
1407
1586
g
e from Figu
r
obviously sh
o
e
d the mount
a
w
hich were d
e
6
82 m (Table
t
the rainfall
c
cloud base a
t
b
ase of Typh
o
h)
C
for 26, and at
0000 UTC 27
h
ree study area
s
E
1
)
Li
L
(
-0.52
-2.38
-0.48
-3.88
9
-5.64
9
0.28
-0.07
-2.14
-3.59
-5.77
-4.00
-4.67
-5.45
--
-3.11
-1.41
-2.53
-5.12
r
e 2 and sele
c
o
wed by com
p
a
in ranges of
N
e
formed (Fig
u
1, LCL valu
c
loud might b
t
650-682 m.
o
on Ketsana
w
0000 UTC an
d
September dat
a
s
.
L
CL
(
mb)
912
926
921
9
26.5
9
58.3
874
898
906
932
934
930
936
900
--
893
864
931
909
ted mountain
s
p
arison amon
g
N
goc Linh an
d
u
re 6). This i
s
e is converte
d
e disturbed b
y
Both of thes
e
w
as disturbe
d
d
a
s
g
d
s
d
y
e
d
.
Proc. of SPIE Vol. 8538 853819-5

The mountain ranges also caused the rainfall distribution patterns to vary and part of it was become intense. The results
indicate that part of the lower level clouds of the typhoon were trapped by these mountains, resulting in heavy rainfall
from the surrounding high terrain regions to the coastal line due to the friction and blocking of the island topography.
The Kinabalu, Trusmadi, and Tambuyukon mountains play an important role in affecting the weather conditions. A total
of five distinct results were found for this cloud and rainfall-orography interaction during the typhoon activity. 1) Portions
of the clouds were blocked by the Crocker Range, causing the rainfall event to temporarily slow down. 2) Heavy rainfall
occurred around this mountain range. 3) The variation of the cloud and rainfall distribution pattern was related to the
shapes of the mountains. 4) If the rainclouds were high enough and there was extra outside energy (typhoon system), the
rainfall process may have been forced to move forward and pass through this mountain range. 5) The heavy rainfall
distribution was more affected by the high mountains close to the shoreline than by the interior region of the island. These
rainfall distribution variations can be determined by the rainfall cloud base because the cloud base over Kota Kinabalu
was between 685 m and 744 m and between 814 m and 1177 m in Bintulu (Table 1, LCL value is converted from pressure
to altitude). Hence, when the cloud base correlates with the terrains in Figure 2 and mountains altitude from Table 2, we
understand that the high mountain ranges over EM play an important role in the rainfall distribution patterns because EM
is covered by much high terrain which more than 840 m at the interior region.
Table 2. Mountains in the studied countries that affect the wind variation of the Typhoon Ketsana. *
Country Mountain Name Elevation
(m)
Latitude
(°N)
Longitude
(°E)
Vietnam Ngoc Linh 2598 ~15.1 ~108.0
Chu Yang Sin 2405 ~12.4 ~108.4
Laos Phou Bia 2819 ~19.0 ~103.2
Phou Soaydao 2102 ~17.7 ~101.0
Cambodia Phnum Aôral 1813 ~12.0 ~104.2
Phnŭm Tumbôt 1165 ~12.4 ~103.0
State of East Malaysia Mountain Name Elevation
(m)
Latitude
(°N)
Longitude
(°E)
Sabah Kinabalu 4095.2 ~6.08 ~116.55
Trusmadi 2642.0 ~5.55 ~116.52
Sarawak
Tambuyukon
Murud
Mulu
Batu Lawi
2579.0
2423.0
2376.0
2046.0
~6.22
~3.91
~4.04
~3.88
~116.65
~115.50
~114.93
~115.38
State of Peninsular
Malaysia
Mountain Name Elevation
(m)
Latitude
(°N)
Longitude
(°E)
Pahang Tahan 2187 ~4.63 ~102.23
Perak Korbu 2183 ~4.68 ~101.30
Perak Yong Belar 2181 ~4.73 ~101.33
Perak Gayang 2173 ~4.76 ~101.37
Penang-Kelatan Chamah 2171 ~5.13 ~101.33
Pahang Benum 2107 ~3.83 ~102.10
* Source: [12-14]
Rainfall distribution patterns are distinctly affected by the Titiwangsa Mountain range and other mountains in PM
(especially in the northern part), which were able to influence the movement and distribution of the rainclouds during the
tail effects of the typhoon. Normally, the central of Titiwangsa Mountains range with at less elevation 840m (Figure 2)
can separate the rain distribution into two areas: the eastern and western sides of Peninsular Malaysia. Sometimes, rain
can fall on both sides simultaneously when certain weather conditions exist, such as synoptic circulation caused by a
Proc. of SPIE Vol. 8538 853819-6

t
y
p
m
t
a
t
h
t
o
y
phoon syste
m
p
eriod becaus
e
m
in PM, are
a
a
il end effect
h
e low cloud
s
o
the wind fl
o
a) 001
5
Figure 6. The
s
units. Red tria
n
Figure 7. The
s
geostationary
s
m
. However,
e
of their pos
i
a
lso able to c
h
of Typhoon
K
s
will follow t
o
w pushing th
e
5
UTC 27 2009
s
e FY-2D’s im
a
n
gles in the fig
u
s
e rainfall (in
s
atellite.
this study s
h
i
tion and the t
h
ange the rai
n
K
etsana) are
l
he mountains
e
clouds up.
Sep
b
a
ges show hou
r
u
re indicate mo
mm) images
f
h
owed that K
e
opographic d
i
n
fall distribut
i
l
ower than th
i
’ shape, or th
e
b
) 0015 UTC 2
r
ly precipitatio
n
untains in the
s
f
rom 0515 UT
e
lantan and
T
i
stri
b
ution of
P
i
on patterns,
a
i
s elevation.
W
e
y may travel
8 Sep 2009
n
products for
T
s
tudy area, whi
c
C – 1615 UT
C
T
erengganu a
r
P
M. The oth
e
a
s some rainc
l
W
hen rainclo
u
towards the
t
c) 121
5
T
yphoon Kets
a
c
h are listed in
T
C
on 25 Sept
e
r
e the most
a
e
r mountains,
l
ouds (appro
x
u
ds encounter
t
op and then
p
5
UTC 29 Sep
2
a
na on 3 differ
e
T
ables 2.
e
mber 2009 w
e
a
ffected durin
g
which are hi
g
x
imately 650-
9
the high mo
u
p
ass over the
m
2
009
e
nt days with
m
e
re acquired f
r
g
the typhoo
n
g
her than 200
0
9
00 m for thi
s
u
ntain region
s
m
ountains du
e
m
illimetre (m
m
r
om the FY-2
D
n
0
s
s
,
e
m
)
D
Proc. of SPIE Vol. 8538 853819-7

Figure 8. Thes
e
triangles in th
e
From the rai
n
images in Fi
g
However, th
e
the rainfall e
v
the rainfall s
rainfall rate
w
From the ob
s
the distributi
o
important rol
Vietnam, its
i
b
locked and
t
enough to pa
s
In EM, the t
a
inland regio
n
typhoon. Th
e
typhoon, in
w
different tim
e
p
atterns in th
e
In contrast, t
h
tail effects o
affected by
a
PM, which i
s
rainfall even
t
the rainfall
m
conditions c
a
The similarit
i
slowed by th
p
atterns may
p
atterns on
o
strengths of t
h
This study p
r
ranges were
significant o
r
properties (s
u
a) 0015 UTC
e
are 5 selecte
d
e
figure indicat
e
n
fall distribu
t
g
ure 6 show
t
e
rainfall eve
n
v
ent in PM o
n
cale, the rai
n
w
as found in
P
s
ervation of t
h
o
n patterns in
e in blocking
i
ntensity is r
e
t
hen slowed
b
s
s over Vietn
a
a
il effects of
n
along Sabah
e
rainfall eve
n
w
hich the rain
f
e
, resulting i
n
e
region base
d
h
e rainfall ev
e
f the typhoo
n
a
typhoon sys
t
s
full of mou
t
at the weste
r
m
ovement, a
n
a
n exist on the
i
es of the rai
n
e orography;
have followe
o
rographic e
ff
h
e typhoon s
y
r
ovides an e
x
able to influ
e
r
obvious the
r
u
ch as track
o
b
) 011
d
hourly FY2D
e
mountains in
t
t
ion observati
o
t
hat the rainf
a
n
t in EM (onl
y
n
ly lasted a fe
w
n
fall rate was
P
M.
h
e rainfall di
s
each study a
r
and disrupti
n
e
duced due to
b
y the high
m
a
m and reach
the typhoon
i
to Sarawa
k
(
n
t was unlike
t
f
all event wa
s
n
different r
a
d
on the orog
r
e
nt in PM wa
s
n
). This type
t
e
m
(Figure
8
ntainous regi
o
r
n coastal regi
n
d the rainfa
l
eastern and
w
n
fall distributi
2) the rainfa
l
d the high te
r
ff
ects among
y
stem’s impa
c
x
ample of ho
e
nce the dist
r
r
elationship b
e
o
r location, i
n
5 UTC
satellite image
s
t
he study area,
w
o
n, Indochin
a
a
ll event was
c
y
the tail effe
w
hours (Fig
u
highest in I
n
s
tribution patt
r
ea. The mou
n
n
g the typhoo
n
the force of
f
m
ountain rang
e
Laos and Ca
m
i
n terms of r
a
(
Figure 7), es
p
t
he rainfall e
v
s
separate fro
m
a
infall intensi
t
r
aphic distrib
u
s
caused by th
of rainfall c
a
8
). The rainfa
l
o
ns, because
on of PM fro
m
l
l distributio
n
w
estern coast
s
on patterns o
n
l
l rate may h
a
r
rain shapes (
m
the study ar
e
c
t on the diffe
r
5.
w the orogr
ap
r
ibution of th
e
tween the or
o
n
tensity and
d
c) 0215 UTC
s
a) to e) in a r
a
w
hich are liste
d
a
was the reg
i
c
ontinuous a
n
cts of the typ
u
re 8) due its
g
n
dochina amo
erns on orog
r
n
tain ranges i
n
n
’s moveme
n
f
riction of Vi
e
in Vietna
m
m
bodia, even
t
a
infall pattern
p
ecially the
m
v
ent in Indoc
h
m
the typhoo
n
t
y. However,
u
tion.
e synoptic sc
a
a
n only last
a
l
l event accu
m
the Titiwang
s
m
traveling t
o
n
patterns al
s
s
of PM.
n
orographic
a
ve increased
m
ountain stru
c
e
as is the di
f
r
ent orograph
i
CONCL
U
ap
hic effect i
s
e cloud and
r
o
graphy and
t
d
iameter). T
h
d) 03
1
a
infall distribut
i
d
in Tables 2.
i
on that was
n
d that it last
e
h
oon) lasted
a
g
reater distan
c
ng the study
r
aphy, it was
n
Indochina,
e
n
t. When the
t
etnam’s topo
g
(Figure 6).
H
t
hough its int
e
s was obvio
u
m
ountainous r
e
h
ina, as EM
w
n
system. The
r
the rainfall
a
le circulatio
n
a
few hours,
m
ulated at th
e
s
a Mountain
o
the other sid
s
o vary base
d
effects are as
when it slo
w
c
tures). The
o
f
ferent intens
i
i
c distributio
n
U
SION
s
important t
o
r
ainfall patte
r
t
he typhoon's
h
e impacts of
1
5 UTC
i
on patterns st
u
directly hit b
y
e
d a few days
a
p
proximatel
y
c
e from the t
y
areas, follo
w
found that or
o
e
specially alo
n
t
yphoon appr
o
g
raphy. Thus
,
H
owever, the
t
e
nsity was re
d
u
sly influence
d
e
gions in Sab
a
w
as only affec
t
r
efore, the rai
n
events have
s
n
of the typho
o
and its distr
i
e
northeaster
n
Range (alon
g
e of the rang
e
d
on its sha
p
follows: 1) t
h
w
ed down; an
d
o
nly differenc
e
i
ties of the r
a
n
s.
o
weather fo
r
r
ns during th
e
impacts were
the TCs on
t
e) 0415 UTC
u
dy at 27 Septe
m
y
Typhoon
K
during the t
y
y
half a day (
F
y
phoon. More
o
w
ed by EM,
a
o
graphic effe
c
n
g central Vi
e
o
aches the co
a
,
the rainfall
e
t
yphoon syst
e
d
uced.
d
b
y the hig
h
a
h, which we
r
t
ed by the tai
l
n
fall event in
v
s
imilar rainf
a
o
n system (th
e
i
bution patter
n
n
region at th
e
g
central PM)
e
. Mount Tah
a
p
e. Thus, dif
f
h
e rainfall’s
m
d
3) the rainf
a
e of the rainf
a
a
infall due t
o
r
ecasters, as
h
e
typhoon se
a
depended on
t
hese study
a
m
ber 2009. Re
d
K
etsana, so th
e
y
phoon perio
d
F
igure 7), an
d
o
ver, based o
n
a
nd the lowe
s
c
ts may affe
c
e
tnam, play a
n
a
stal region o
e
vent was fir
s
e
m was stron
g
h
terrain in th
e
r
e close to th
e
l
effects of th
e
v
aded EM at
a
a
ll distributio
n
e
other type o
n
is distinctl
y
e
east coast o
restricted th
e
a
n also slowe
d
f
e
r
ent weathe
r
m
ovement wa
s
a
ll distributio
n
a
ll distributio
n
o
the differe
n
h
igh mountai
n
a
son; but ho
w
the typhoon’
s
a
reas are mor
e
d
e
d
.
d
n
s
t
c
t
n
f
s
t
g
e
e
e
a
n
f
y
f
e
d
r
s
n
n
n
t
n
w
s
e
Proc. of SPIE Vol. 8538 853819-8

significant when they are associated with orographic effects. However, the different results in these study areas are
believed to be due to the position of the typhoon system according to whether the typhoon moves in a straight path upon
landfall and how far away the regions of Southeast Asia are from the system. However, further study is needed because
the interactions of typhoons with complex terrains are complex and dynamic.
6. ACKNOWLEDGE
The authors gratefully acknowledge the financial support under the RU grant 1001/PFIZIK/811152 and Universiti Sains
Malaysia (USM) – Short term grant 304/PFIZIK/6310057. We would like to thank the technical staff who participated in
this project. Thanks are also extended to USM for support and encouragement. We also would like to thank the
University of Wyoming to provide free sounding data and China Meteorological Administration for provided the free
satellite data used in this project.
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Proc. of SPIE Vol. 8538 853819-9