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Comparison of phytoplankton blooms triggered by two typhoons with
different intensities and translation speeds in the South China Sea
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Hui Zhao1, DanLing Tang1* and Yuqing Wang2
1 Remote Sensing and Marine Ecology (RSME), LED, South China Sea Institute of
Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou
510301, China; and Graduate University of Chinese Academy of Sciences, China
2 Department of Meteorology and International Pacific Research Center, School of Ocean
and Earth Science and Technology, University of Hawaii at Manoa,
Honolulu, HI 96822, USA
October 28, 2007 14
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Dateline
Revised for Marine Ecology Progress Series 20
* Corresponding author’s Email: [email protected] and [email protected]; Tel/Fax: +86 20 89023203.
Abstract Two phytoplankton blooms triggered by two typhoons with different intensities
and translation speeds in the South China Sea (SCS) are compared using remote sensing
data of chlorophyll-a (Chl-a), sea surface temperature (SST), vector wind fields, and the
best-track typhoon data. Typhoon Ling_Ling (2001) was a category 4 storm with maxi-
mum sustained surface wind speed of 59m s
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-1 and fast-moving at a mean translation speed
of 4.42 m s-1. Typhoon Kai_Tak (2005) was a category 2 storm with its maximum sus-
tained surface wind speed of 46 m s-1 and slow-moving with a mean translation speed of
2.9 m s-1. It is shown that the slow-moving typhoon induced phytoplankton blooms of
higher Chl-a concentration, whereas the strong typhoon induced blooms over a larger area.
About 7 typhoons on average per year affect the SCS, among which 41% are strong and
59% are weak, and about 64% are fast-moving and 36% are slow-moving. It is estimated
that these typhoons might contribute 16% to the annual new primary production in the
oligotrophic SCS.
Keywords: Typhoon · Chlorophyll-a · Translation speed · Remote sensing · Primary pro-
duction · South China Sea
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INTRODUCTION 37
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Typhoons are violent weather systems with the maximum sustained surface wind
speed larger than 33 m s-1 and formed over the tropical western Pacific. They can trigger
phytoplankton blooms by increasing primary productivity in the ocean near their paths
through producing oceanic eddies and upwelling (Chang et al. 1996; Chen et al. 2003; Lin
et al.2003; Zheng & Tang 2007). In addition to the pre-existing mixed-layer depth and the
strength of the thermocline, the response of the phytoplankton to the typhoon forcing also
depends on the duration (or translation speed) and intensity of the typhoon itself. Previous
studies have mostly focused on the contributions to the primary production by individual
typhoons in the western Pacific and South China Sea (Lin et al. 2003; Zheng & Tang
2007). The possible effects of translation speed and intensity of the typhoon on the under-
lying water are yet to be examined from observations.
The South China Sea (SCS, Fig. 1) is the largest marginal sea in the western Pacific
Ocean, with a total area of about 3.5 million km2. East Asian monsoons dominate in the
SCS and largely control the upper ocean circulation (Wyrtki 1961). Because most of the
SCS belongs to tropical oligotrophic water with ample light, nutrients are important fac-
tors controlling the primary productivity (Tang et al. 2004a, b). Recent studies show that
cyclones/typhoons have important effects on chlorophyll-a (Chl-a) and phytoplankton
blooms in the SCS (Chang et al. 1996; Lin et al. 2003). Zheng and Tang (2007) showed
that Typhoon Damrey of September 2005 triggered two phytoplankton blooms in the
northern SCS by producing upwelling and vertical mixing which supplied new nutrients to
the surface layers, as well as by runoff from land. Lin et al. (2003) estimated that tropical
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cyclones could contribute roughly 20-30% to the annual new production in the SCS based
on an average of 14 tropical cyclones passing over the SCS per year.
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By their translation speed, typhoons can be classified into fast and slow movers; while
by their intensity (maximum sustained surface wind speed and curl), they can be classified
into strong and weak ones. Both intensity and translation speed are important factors in-
fluencing marine oceanographic environments. It has been known for decades that a slow
moving typhoon or a strong typhoon could cause stronger cooling in the upper ocean due
to the longevity or the strength of the forcing than the fast moving, weak typhoons (e.g.,
Bender et al. 1993). The cooling of SST in turn could limit the intensity of the typhoon
(Emanuel 1999; Wang and Wu 2004). As a result, generally slow-moving typhoons can
not be very strong, especially when their translation speeds are less than about 3 m s-1
(Zeng et al. 2007).
Translation speed and intensity of a typhoon may have different effects on phytoplank-
ton biomass and primary production. This, however, has not been investigated previously
from observations although it is physically arguable and understandable. As a first step
toward an improved understanding of this issue we first compare the impacts of two ty-
phoons that had different intensities and translation speeds on phytoplankton bloom and
primary production in the SCS. Secondly, we try to estimate the contribution of typhoons
to the annual primary production in the SCS based on the best-track typhoon data from
1945 to 2005.
DATA AND METHODOLOGY
Satellite Products and Typhoon data
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The following products based on satellite measurements are used here. The daily mean
sea surface temperature (SST) is obtained from the Tropical Rain Measuring Mission
(TRMM) Microwave Imager, which is nearly free of cloud influence over the global trop-
ics. Both products have a horizontal resolution of 0.25
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o longitude/latitude (Wentz et al.
2000). The surface wind data used are products based on the microwave scatterometer
SeaWinds on the QuikSCAT satellite, which measures surface wind stress (Liu et al.
2000). In addition, monthly mean wind data called Tropical Indian Winds
(http://www.coaps.fsu.edu) are also used.
SeaWiFS derived Chl-a and cloud-corrected surface Photosynthetically Active Radia-
tion (PAR) with 9 × 9 km2 spatial resolution were obtained from the Distributed Active
Archive Center (DAAC), National Aeronautics and Space Administration (NASA)
(http://oceancolor.gsfc.nasa.gov/cgi/level3.pl).
The typhoon data were downloaded from the Unisys Weather website
(http://weather.unisys.com/hurricane/w_pacific/), which is based on the best-track typhoon
data from the Joint Typhoon Warning Center (JTWC). The data include the maximum sus-
tained surface wind speed and the longitude/latitude of the typhoon center at every 6
hours. The translation speed of the typhoon is here thus estimated based on the 6-hourly
positions of the typhoon center.
Data Processing
Ekman pumping velocity (EPV) was estimated based on the daily and monthly mean
wind data. The climatological daily mean wind, EPV, SST, rainfall, and Chl-a were ob-
tained by averaging the daily mean data during 1998 and 2004 with year 2001 excluded.
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The climatologies were constructed for the period by mapping the calendar days of the
two chosen typhoons (Figs. 2A). Surface wind stress/EPV was constructed for the day
with the strongest sustained surface wind speed for each typhoon (10 Nov. 2001 for Ty-
phoon Ling_Ling and 30 Oct 2005 for Typhoon Kai_Tak). Time series of satellite data
were based on area averages in the appropriate regions (Fig. 2) to investigate the temporal
evolution of the ocean response to the typhoon passage (Figs. 3 and 4).
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Primary production is a key index to phytoplankton biomass, ecosystem health, and
carbon cycling. By applying the SeaWiFS-derived Chl-a, PAR data, and SST to the verti-
cally generalized production model (VGPM of Behrenfeld and Falkowski 1997), the
depth-Integrated Primary Production (IPP) can be estimated:
Popt=-3.27 × 10-8×T7+3.4132 ×10-6 × T6-1.348 ×10-4×T5+2.462×10-3×T4-0.0205×T3
+0.0617×T2+0.2749×T+1.2956; (1)
PPeu=0.66125×Popt×(E0/(E0+4.1))×Zeu×Csat×Dirr; (2)
IPP= PPeu×S×N; (3)
here, T is SST in o
C; E0 the sea surface daily PAR in mol quanta m-2; Zeu the depth receiv-
ing 1% of E0 in meters; PPeu daily carbon fixation integrated from the surface to Zeu in mg
C m-2 d-1; Csat sea surface satellite Chl-a concentration in mg m-3; Dirr photoperiod in
decimal hours; Popt maximum carbon fixation rate within a water column in mg C (mg
Chl)-1 h-1; S the area in m2 for the region of vertical integrations (the region for Ling_Ling
is 12.5-16.5oN, 113-116oE; the region for Kai_Tak is 13-16oN, 110-113oE, i.e., the bold
rectangular boxes in Figs. 2E2 and 2E3, respectively); N the number of days. Zeu was es-
timated from the empirical relation with Chl-a in Case I waters (Behrenfeld and Falkowski
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1997; Morel and Berthon 1989). In addition, phytoplankton blooms were defined when
Chl-a concentration reached 0.5 mg m
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-3 in this study.
RESULTS AND DISCUSSION
Description of Typhoon Cases
Two typhoons, namely, Typhoon Ling_Ling (2001, hereafter L-L) and Typhoon
Kai_Tak (2005, hereafter K-T) are analyzed (Table 1). L-L traversed from east to west
over the SCS for three days during November 9-12, 2001 (Fig. 2A1). K-T passed over the
SCS for 4 days during October 29-November 2 (Fig. 2A2). L-L and K-T had quite differ-
ent characteristics (Table 1 and Figs. 2A1 and 2A2). L-L was a category 4 typhoon with
maximum sustained surface wind speed ≥ 54 m s-1 and moved fast at a mean translation
speed > 4.4 m s-1. K-T was category 2 typhoon with maximum sustained surface wind
speed ≤ 46 m s-1 and moved slowly with a mean translation speed ≤ 2.9 m s-1.
For convenience, we define a typhoon as a fast (slow) moving typhoon when its mean
translation speed larger (smaller) than 4.4 m s-1, and as a strong (weak) typhoon when its
maximum sustained surface wind speed higher (lower) than 50 m s-1. Thus, K-T was a
weak, slow moving typhoon, while L-L was a strong, fast moving typhoon. K-T reached
its peak surface wind speed and the lowest translation speed when it moved to the western
SCS, about 100~200 km from the coastline, while L-L reached its peak surface wind
speed and the lowest translation speed when it was located over the central SCS. The cli-
matology displayed low surface wind speed (SWS) and weak upwelling, as seen from
EPV (SWS < 10 m s-1, EPV< 0.4*10-5 m s-1) in the whole SCS (Fig. 2B1).
SWSs associated with the two typhoons were 2-5 times stronger than that of the clima-
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tology in the same areas on the typhoon paths (Figs. 2B2 and 2B3). L-L (Fig. 2B2) had
stronger surface winds than K-T (Fig. 2B3). L-L’s peak wind speed was 1.4 times of K-T
and also had a larger area coverage than K-T (Figs. 2B2 and 2B3). Upwelling increased
significantly during the typhoons’ passage. As seen from Figs. 2B2 and 2B3, EPV in-
creased up to 10×10
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-4 m s-1 (the regions with deep red colors) near the paths of the ty-
phoons, which is about two orders larger than the peak values in the climatology (<0.1×10-
4m s-1, Fig. 2B1). The region of the high EPV (>10×10-4 m s-1) induced by L-L (Fig. 2B2)
in the central SCS (13-14oN, 112-114oE) was broader and achieved larger values than K-T
(Fig. 2B3) in the western SCS (13.5-14.5oN, 111.5-112.5oE), consistent with the higher
surface winds of L-L (Table 1).
Oceanographical responses to typhoons’ passage
Response of SST
The climatological SSTs are generally over 28oC with an evident northwest-southeast
gradient (Fig. 2C1). After the typhoons’ passage, SST fell quickly by far more than 1 oC in
the white boxes in Fig. 2C2 for L-L and Fig. 2C3 for K-T, respectively (Table 1). The low
SST (≤ 26oC) patch induced by L-L was located in the central SCS while that caused by
K-T was in the western SCS. The area of the low SST patch associated with L-L was lar-
ger than that associated with K-T (Table 1). The cold SST anomaly averaged in Box A in
Fig. 2C2 induced by L-L during 12-21 Nov 2001 was also larger than that caused by K-T
during 2-11 Nov 2005 (-1.35oC versus -0.62oC).
The size of low SST patches appeared to be comparable with the radius of the typhoon
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for each case (Figs. 2B and 2C). Since the stronger Typhoon L-L exerted stronger surface
cyclonic wind stress curls with larger area coverage on the underlying ocean than the
weaker Typhoon K-T, it induced stronger mixing and upwelling in its wake. The larger the
radius of strong winds, the larger and colder a low SST patch would be (Figs. 2B and 2C),
as suggested from our observations (Figs. 2B and 2C) and numerical results of Bender et
al. (1993).
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On the other hand, given the same distribution and strength of the surface wind speeds
in a typhoon, slow translation can enhance the mixing/upwelling and thus cooling of the
upper ocean mixed layer due to the longer time of action. It is thus expected that the slow
moving K-T enhanced its effect on upper-ocean cooling, whereas the fast moving L-L re-
duced such an effect. As a result, the low-SST patches with <27℃ induced by the stronger
Typhoon L-L were roughly equivalent to that induced by the weaker Typhoon K-T based
on the averaged SST data after typhoon’s passage (Figs. 2C2 and 2C3) if neglecting the
higher SST over the region before L-L.
To examine the temporal evolution, we show in Fig. 3A the time series of SSTs aver-
aged in a large area of 6×105 km2 in Box A given in Fig. 2C2 for climatology and the two
typhoon cases. The climatological SST during 1998-2004 fell gradually from Oct 28 to
Dec 2 (Fig. 3A) due to decreasing solar radiation. Before L-L’s arrival, the daily mean
SST (~29.1oC) was about 1
oC higher than the climatology (~28.1
oC). After the passage of
L-L, the SST fell rapidly to 26.7 oC on Nov. 12, 2001 with a drop of 2.4
oC (and, hence,
1.4 oC lower than the 1998-2004 climatology). Similar results were observed for K-T, but
K-T maintained a shorter period of low SST. Although K-T was weaker, it produced a SST
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drop during its passage almost like L-L. The SST for K-T reached a minimum of 26.9 oC
on 2 Nov 2005 with a peak anomaly of 1.5
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oC from the climatology. This further indicates
the effects of storm intensity and translation speed on ocean environments.
Biological responses to the typhoons’ passage
Phytoplankton blooms
Satellite-derived Chl-a is generally low (<0.14 mg m-3) in the SCS (Fig. 2E1). After L-
L’s passage, Chl-a (time mean for 9-29 Nov 2001) increased quickly to 0.5 mg m-3 in the
central SCS, as averaged in an area of ~4.6×104 km2 in the black box in Fig. 2E2. The
peak reached up to 3 mg m-3 where the typhoon surface wind speed was strongest (Figs.
2B2 and 2E2). Similarly, with the passage of K-T, Chl-a (time mean for 29 Oct 29–17
Nov 2005) increased to 0.5 mg m-3 in an area of ~ 4×104 km2 in the box shown in Fig.
2E3, which coincided roughly with the center of the strongest wind speed, lowest SST,
and peak rainfall. L-L induced a larger area of Chl-a bloom (> 0.5 mg m-3) than K-T, but
the area of Chl-a of greater than 1 mg m-3 induced by L-L was smaller than that caused by
K-T.
The difference in the Chl-a blooms in the two typhoon cases appeared to result mainly
from the difference in storm translation speed. As we see from Figs. 4B1 and 4B2, the
daily mean Ekman pumping velocity induced by L-L was stronger than that resulting from
K-T (2.2×10-4 m s-1 versus 1.7×10-4 m s-1). Because of the fast translation speed, the up-
welling vertical height due to L-L was only 21.7 m, compared with up to 23.5 m due to the
slow moving K-T (Figs. 4B), as estimated from the area-averaged EPV and the typhoons’
traversing time.
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The temporal evolution of the Chl-a averaged in Box A in Fig. 2C2 is shown in Figs.
4A1 and 4A2 for Typhoons L-L and K-T, respectively. The climatological Chl-a (the
black curves in Figs. 4A1-A2) is low (<0.2 mg m
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-3). After the passage of L-L, Chl-a rose
to 0.36 mg m-3 in the first week, but fell to 0.54 mg m-3 in the second week. After the pas-
sage of K-T, high Chl-a (>1mg m-3) appeared in the first week and reduced to 0.37 mg m-3
in the second week. Chl-a fell to the normal level by about 4 weeks after the typhoon pas-
sage in both cases.
Primary production
Based on equations (1), (2) and (3), we estimated the corresponding IPP to be about
293 mgC m-2 d-1 averaged in the black bold rectangular region in Fig. 2E2 for October-
November in a general year without typhoon events (Table 1). This is close to the annual
mean IPP in the SCS (354 mgCm-2d-1) estimated by Liu et al. (2002) and Lin et al. (2003).
After the passage of the two typhoons, IPP shot up to 2610 mgCm-2d-1 on 14 Nov. 2001
for L-L and 4101 mgCm-2d-1 on 6 Nov. 2005 for K-T (Table 1). Given the fact that the es-
timated mean ƒ-ratio (i.e. the ratio of new IPP to IPP) of the SCS is 0.12 (Liu et al. 2002)
and the area of the oligotrophic SCS is 2.76×106 km2 beyond the 200 m isobath (Lin et al.
2003), the annual new IPP (NIPP) might be about 42 Mt (Table 1). Therefore, L-L and K-
T would roughly contribute 2.9% and 1.9%, respectively, to the annual new IPP in the SCS
(Table 1) based on an estimate for 20 days of the direct/indirect effect from each storm.
Contribution of typhoons to the SCS annual primary production
Results discussed in previous sections demonstrate that both intensity and translation
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speed of a typhoon are primary factors affecting the oceanographic environment in the
SCS. In general, a strong typhoon can cause intense mixing/upwelling to bring up cold and
nutrients-rich water into the upper layer in a larger area than a moderate typhoon. How-
ever, due to the shorter time spent over the SCS, a typhoon with fast translation speed may
have limited influence on mixing/EPV, resulting in a reduced tendency of increasing Chl-
a. As we showed in the above text, Typhoon K-T with slow translation speed had more
time for mixing/EPV effects in the region during its passage, inducing a stronger phyto-
plankton bloom than the fast-moving Typhoon L-L, even though the latter was a stronger
storm.
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To estimate the possible contribution of typhoons to the annual new IPP in the SCS,
we classified the typhoons affecting the SCS between 1945 and 2005 based on their inten-
sity and translation speed, as we did previously for Typhoons L-L and K-T. During 1945-
2005, there were 425 typhoons (with maximum wind speed ≥ 33 m s-1) in total affecting
the SCS, or about 7 typhoons per year on the average (Fig. 5A). Among them, about 64%
were fast moving typhoons with translation speeds > 4.4 m s-1 (Fig. 5B) and 41% were
strong typhoons with maximum sustained surface winds >50 m s-1 (Fig. 5C). Namely, ac-
cording to their intensities, 41% typhoons were similar to L-L and 59% typhoons were
similar to K-T (Fig. 5C).
A very rough estimation based on the response of the SCS to L-L and K-T indicates
that typhoons can contribute 1.7% to annual IPP and 16 % to the annual NIPP in the
oligotrophic SCS. This estimation is rather conservative because we considered only
bloom regions and integrated for only 20 days. Actually, bloom regions can be wider and
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high Chl-a may continue for longer than 20 days after the typhoon passage. In addition,
tropical cyclones with peak wind speeds <33 m s
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-1 were not considered in the above esti-
mation. Therefore, our results are very preliminary and subjective. More quantitative esti-
mation of the influence of tropical cyclones on the SCS primary production will be a topic
for future studies based on both observations and numerical models.
SUMMARY
It has been known that tropical cyclones have effect on the underlying ocean current
and sea surface temperature. For the two typhoon cases in the present study, the slow-
moving Typhoon Kai_Tak had longer time affecting mixing/upwelling on the region
around its wake, inducing a stronger phytoplankton bloom, the strong Typhoon Ling_Ling
induced a bloom in a larger area. In general, strong typhoons exert strong surface cyclonic
wind stress curls with large area coverage on the underlying ocean surface, producing
strong vertical mixing and upwelling on its wake in the ocean, and thus bringing up cold
and nutrients-rich water to upper layers in a large area. A slow-moving typhoon can en-
hance the tendency of increasing both cooling of the mixed layer and phytoplankton bio-
mass. As a result, the response of phytoplankton bloom to a typhoon is closely related to
moving speed and intensity of the typhoon, which should be considered in estimating new
primary production.
Based on a classification of typhoons affecting the SCS during 1945-2005 according to
intensity and translation speed, we estimated that typhoons could contribute 1.7% to the
annual IPP and 16% to the annual NIPP, respectively, in the oligotrophic SCS. This esti-
12
mation was rather conservative and preliminary, the detailed estimation and mechanism of
influence of typhoons on IPP/NIPP will be investigated further using numerical models in
future studies.
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Acknowledgements: This study is supported by the grants awarded to DL Tang: (a) Key
Innovation Project of Chinese Academy of Sciences (CAS) (KZCX3-SW-227-3) and “The
One Hundred Talents Program”, (b) National Natural Science Foundation of China
(40576053), and (c) International Cooperation Team Project (SCSIO, CAS). YW has been
supported by U.S. Office of Naval Research Grant N0014-21-0532 and JAMSTEC, Japan
and U.S. NASA, through their sponsorships to the International Pacific Research Center at
the University of Hawaii. The authors would to thank Dr. D.X. Wang of the South China
Sea Institute of Oceanology for his kind suggestion of the study.
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Table 1. Two typhoons and their contribution to IPP and NIPP in the SCS. (1Mt=1012g). EPV: Ekman pumping velocity.
350 351
Parameter L-L, 2001 K-T, 2005
Low SST patch (<26 oC) 85600 km2 51900 km2
Crossing-distance 1145.2 km 975.5 km
Maximum wind speed 59m/s 46m/s Mean translation speed 4.4 m/s 2.9 m/s Mean wind speed 48 m/s, fast 34 m/s, slow P
hysi
cal e
ffec
ts
Maximum EPV 10m/day 4m/day Location of Chl-a blooms The central SCS The western SCS
Surface Chl-a conc. (Csat)* 0.45 mg m-3 0.56 mg m-3
Location of the integrations (12.5-16.5 oN, 112.5-116
oE) (13-16
oN, 110-113
oE)
Maximum Primary productivity 2607 mgCm-2d-1 4101 mgCm-2d-1
Mean Primary productivity* 634 mgCm-2d-1 674 mgCm-2d-1
IPP* induced 2.1 Mt (upon 20 days)* 1.5 Mt (upon 20 days)*
Typh
oons
’ in
fluen
ces
New IPP induced* 1.2 Mt 0.8 Mt The climatology of Chl-a* 0.14 mg m-3 0.15 mg m-3
General Primary productivity* 274 mgCm-2d-1 312 mgCm-2d-1
Clim
a-to
lo-
gies
General IPP* 0.92 Mt 0.67 Mt Annual Mean IPP** 352 mgCm-2d-1
The area of the oligotrophic SCS 2.76×106 km2
Annual IPP ** 352.6 Mt Annual NIPP (f= 0.12) ** 42.3 Mt Contribution to annual IPP 1.7% (upon 7 typhoons year-1)
Typh
oons
con
tribu
-tio
n
Contribution to annual NIPP 15.9 % (upon 7 typhoons year-1)
* Averaged in the region (113-116oE; 12.5-16.5oN) from Nov. 13-Dec.02, 2001 for L-L
and in the region (110-113
352
353
354
oE; 13-16oN) from Nov. 03-Nov. 22, 2005 for K-T; ** (Liu et
al, 2002).
17
Figure Captions: 355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
Figure 1. (A) South China Sea (SCS), with Box S the study area and depth in meters.
Figure 2. (A) Track and intensity of Typhoons L-L (2001) and K-T (2005), respectively,
(B) surface wind vectors (speed and direction) and Ekman pumping velocity (EKP,
contours/color shading in 10-4 m s-1), (C) SST (oC), (D) rainfall (mm day-1), and (E)
Chl-a (color shaded, mg m-3), for the climatology of the period (left column), Ty-
phoon L-L (middle column), and Typhoon K-T (right column).
Figure 3. Time series of SST and Rainfall. (A) SST (oC) for the sampling area (12-17
oN,
108-118oE, Box A in Fig. 2C2) and (B) Rainfall (mm day-1) for the sampling area (10-
19oN, 107-119
oE, Box A in Fig. 2D2) during the two typhoons. Mean SST is the av-
erage for the corresponding period during 1998-2004 exclusive of 2001 for the same
area.
Figure 4. Time series of Chl-a and Ekman Pumping Velocity (EPV). (A) Mean Chl-a
concentration for 8-days: (A1) averaged for the region 12-16oN, 112-118
oE (Box in
Fig. 4A1) in 2001 and (A2) averaged for the region 13-16oN, 110-112
oE (Box in Fig.
4A2) in 2005. The bars present the typhoons and the black lines the average of Chl-a
from 1997 to 2004 exclusive of 2001. (B) EPV: (B1) averaged for the region 13-16oN,
111-116oE (Box in Fig. 4A2) during L-L, 2001 and (B2) averaged in the region (110-
114oE, 13-16
oN, Box in Fig. 4A2) during K-T, 2005.
Figure 5. (A) Annual occurrences of typhoons during 1945-2005 affecting the SCS; (B)
percentage of fast/slow-moving typhoons; (C) percentage of strong/weak typhoons.
18
376
377
378
Figure 1
19
379
Figure 2
20
A. Rain
20012005
23-O
ct
27-O
ct
31-O
ct
08-N
ov
04-N
ov
12-N
ov
16-N
ov
20-N
ov
24-N
ov
28-N
ov
400
300
200
100
0
Rai
n (m
m)
26
27
28
29
30A.Mean
B.2001
C.2005
SST
(℃)
A. SST
28-O
ct
01-N
ov
05-N
ov
13-N
ov
09-N
ov
17-N
ov
21-N
ov
20-N
ov
25-N
ov
A. Rain
20012005
23-O
ct
27-O
ct
31-O
ct
08-N
ov
04-N
ov
12-N
ov
16-N
ov
20-N
ov
24-N
ov
28-N
ov
400
300
200
100
0
Rai
n (m
m)
A. Rain
20012005
23-O
ct
27-O
ct
31-O
ct
08-N
ov
04-N
ov
12-N
ov
16-N
ov
20-N
ov
24-N
ov
28-N
ov
400
300
200
100
0
A. Rain
20012005
23-O
ct
27-O
ct
31-O
ct
08-N
ov
04-N
ov
12-N
ov
16-N
ov
20-N
ov
24-N
ov
28-N
ov
23-O
ct
27-O
ct
31-O
ct
08-N
ov
04-N
ov
12-N
ov
16-N
ov
20-N
ov
24-N
ov
28-N
ov
400
300
200
100
0
400
300
200
100
0
Rai
n (m
m)
26
27
28
29
30A.Mean
B.2001
C.2005
SST
(℃)
A. SST
28-O
ct
01-N
ov
05-N
ov
13-N
ov
09-N
ov
17-N
ov
21-N
ov
20-N
ov
25-N
ov26
27
28
29
30A.Mean
B.2001
C.2005
SST
(℃)
A. SST
28-O
ct
01-N
ov
05-N
ov
13-N
ov
09-N
ov
17-N
ov
21-N
ov
20-N
ov
25-N
ov28
-Oct
01-N
ov
05-N
ov
13-N
ov
09-N
ov
17-N
ov
21-N
ov
20-N
ov
25-N
ov 380
381
Figure 3
21
382
383
384
Figure 4
22
385
Figure 5
23
