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Journal of Coastal Research, Special Issue No. 70, 2014

278 Responses of coastal waters in the Yellow Sea to Typhoon Bolaven

Responses of coastal waters in the Yellow Sea to Typhoon Bolaven

Chang S. Kim†, Hak-Soo Lim†, Jin Yong Jeong†, Jae-Seol Shim†, Il-Ju Moon‡∞, You Jung Oh‡, Hak Yoel

You₸

†Coastal Disaster Research Center, Korea

Institute of Ocean Science & Technology, 787 Haeanro, Ansan 426-744, Korea

[email protected], [email protected]

[email protected], [email protected]

‡College of Ocean Science, Jeju National

University, 102 Jeju-Univ. St., Jeju, Korea, [email protected], [email protected]

∞ Corresponding author

₸Oceanographic Division, Korea

Hydrographic and Oceanographic Administration, 351 Haeyang-ro,

Yeongdo-gu, Busan, Korea

[email protected]

INTRODUCTION On average, about three tropical cyclones (hereafter referred to

as typhoons) per year influence the Korean peninsula (KP) and

about one typhoon per year makes landfall on the KP. These

typhoons sometimes lead to extensive damages from strong winds,

high waves, storm surges, and flooding, which has long been one

of the most serious natural hazards to people living in Korea.

In 2012, four typhoons made landfall on the KP, which was the

largest number recorded since 1960. Among them, Typhoon

Bolaven (1215), which hit the Jeju Island (JI) and passed through

the Yellow Sea (YS), caused serious property damages,

particularly for aquaculture and breakwaters along the southwest

coast of the KP due to high waves. At 00 UTC 28 August, the

maximum wind speed (MWS) of Bolaven was 33 m/s (10 min

average value) around the JI, but ocean waves that were higher

than expected destroyed many breakwaters along the coast. This

study investigated the possible causes for the unusually high

waves based on wave simulations and measurements. In addition,

we examined the potential danger of storm surges along the coast

of the YS due to coincidence of peak surges and high tides as well

as resonant coupling between the typhoon, tides, and topography.

Two days after the passage of Bolaven, Typhoon Tembin

(1214) also made landfall on the KP, but the intensity of the

typhoon was not so strong. It was assumed that Bolaven changed

the oceanic conditions ahead of Tembin, resulting in the weakened

intensity of Tembin. This assumption was also verified in this

study.

DATA AND METHODS To investigate the responses of waters along the coast of the KP

to Bolaven, we collected all available data observed during the

passage of the typhoon. The observations came from the Ieodo

Ocean Research Station (IORS), two Korea Ocean Gate Arrays

(KOGA), four Korean Meteorological Administration (KMA)

buoys, and 14 tidal stations (see Figure 1 and Table 1). In

particular, IORS, the KOGA buoys, and the Marado buoy were

very close to Bolaven’s track (Figure 1). We also used satellite

images (Kim et al., 2013; Ryu et al., 2012) and numerical model

results (Lim et al., 2013; Moon et al., 2003b) for the analysis. The

surge heights were calculated by subtracting the predicted tidal

elevation from the observed sea level at the 14 tidal stations. The

predicted tidal elevation was estimated using a harmonic analysis.

Wave simulations were conducted using the WAVEWATCH III

(WW3) model. The WW3 is an ocean surface wave model

developed at NOAA/NCEP in the spirit of the WAM model. The

WW3 has been used in many research programs to study surface

wave dynamics, and as the operational wave model of NCEP for

global and regional wave forecasts (Tolman 2002; Tolman et al.,

2002).

ABSTRACT

Kim, C.S., Lim, H.S., Jeong, J.Y., Shim, J.S., Moon, I.J., Oh, Y.J., You, H.Y., 2014. Response of Coastal Waters in

Yellow Sea to Typhoon Bolaven. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th

International Coastal

Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 278-283, ISSN 0749-0208.

In August 2012, Typhoon Bolaven (1215) passed through the East China Sea (ECS) and the Yellow Sea (YS),

leading to severe coastal damages in Korea. This study investigated the responses of the coastal waters along the

meridional direction of the YS and the ECS to Typhoon Bolaven. This included the causes of record-breaking high

waves in the ECS, the possible danger of coincident peak surges and high tides, resonant coupling between the typhoon,

tides and topography, and the impact of Bolaven-induced sea surface cooling on the intensity of Typhoon Tembin

(1214). Analyses were conducted using observations from an ocean platform, buoys, and tidal stations, as well as a

numerical model during the passage of Bolaven. Results revealed that the western coast of the Korean Peninsula

fortunately avoided severe storm surge damages due to weak tidal action during the passage of Bolaven, although pure

surge components were significantly high. However, we found that there was the possibility of resonant coupling

between surges, tides and topography in the YS, which would contribute to further enhancement of the storm surge.

Based on the wave simulations, it was revealed that a straight track and fast translation of Bolaven maximized the

production of record-breaking high waves in the ECS.

ADDITIONAL INDEX WORDS: Typhoon Bolaven, sea surface cooling, coastal water responses, storm surge, tide,

resonance, waves

www.JCRonline.org

www.cerf-jcr.org

____________________

DOI: 10.2112/SI70-047.1 received 29 November 2013; accepted 21

February 2014. © Coastal Education & Research Foundation 2014

http://www.cerf-jcr.org/


Responses of Coastal Waters in the Yellow Sea to Typhoon Bolaven 279

RESULTS

Bolaven-induced Sea Surface Cooling and its

Impacts In summer, the surface waters in the YS are moderately warm,

approximately 27°C–28°C, while the bottom waters are relatively

cool at approximately 10°C (Kim et al., 2004) due to the year-

round presence of Yellow Sea Bottom Cold Water (YSBCW).

Considering that the average water depth in the YS is about 60 m,

this area is distinguished by a large vertical temperature gradient

of up to 18°C. This unique environment, rarely found in other

regions, produces a strong sea surface cooling when typhoons pass

over the area (Moon and Kwon, 2012).

Figure 2 shows the sea surface cooling after the passage of

Typhoon Bolaven. Warm surface waters of 27°C–28°C were

suppressed to 16°C–20°C, particularly in the southern and western

coastal waters of the KP. Typhoon Tembin passed over the cooled

areas two days after the passage of Bolaven. Considering that

2.5°C cooling in the inner core is sufficient to shut down the entire

energy production of a storm (Emanuel et al., 2004), the large SST

drop seemed to have a significant weakening effect on Typhoon

Tembin when it passed over the area on 28-29 August 2012

(Figure 3).

Potential Danger of Coincident Peak Surges and

High Tides The west coast of Korea is one of the strongest tidal areas in the

world. The tidal range is about 4 m in the south and increases to

about 10 m in the north. During the high spring tides, the tidal

elevation is significantly increased. If the astronomically enhanced

tide levels coincide with the passage of a typhoon, it might be very

threatening to the low land of coastal regions in Korea (Moon et

al., 2003a).

Figure 4 shows the temporal variations of minimum central

pressures, wind speeds, and surge heights during the passages of

Typhoons Bolaven and Tembin. Here, the surge heights were

calculated by subtracting the predicted tidal level from observed

sea level. For the 14 tidal stations, we also calculated peak surge

height (A) and time (tA), predicted tide level (B) at tA, nearest high

tide level (C) and time (tC), nearest spring high tide level (D) and

time (tD), observed sea level (A+B) at tA, extreme sea level

scenario 1 (A+C) at tC, extreme sea level scenario 2 (A+D) at tD,

and time differences (|tC-tA|, |tD-tA|) during the passage of Typhoon

Bolaven (see Table 1). The peak surge heights ranged from 50.2

cm (Busan) to 167.3 cm (Goheung). The surge heights above 140

cm were among the highest records in this region. However, it was

fortunate that the peak surges occurred near low tide (04h 45m <

|tC-tA| < 06h 57m) at most stations on the western coast along

Bolaven’s track (1–10, including JI). Furthermore, Bolaven’s

arrival avoided the spring tide (|tD-tA| > 67h).

We estimated extreme sea levels at the tidal stations assuming

the worst case scenarios that Bolaven landfall at high tide

(scenario 1, A+C) and at spring high tide (scenario 2, A+D). For

example, the observed sea level of 458 cm at YB reached 985 cm

in scenario 1 and 1094 cm in scenario 2. At the other stations,

potential extreme sea levels were estimated based on these

scenarios (Table 1). These results suggested that the coincidence

of peak surge and high tides present tremendous danger along the

coast of the KP and proper preparedness is necessary for the worst

case scenarios.

Figure 1. Observation locations and tracks of Typhoons Bolaven

and Tembin. Names of tidal station are listed in Table 1.

Figure 2. Change in sea surface temperature (SST) after the

passage of Bolaven: (a) before arrival of Bolaven (26 August), (b)

after the passage (28 August). Tembin passed through the cooled areas before landfall on the KP.

Figure 3. Change in intensity of typhoon Tembin (1214) in terms

of minimum central pressure and maximum wind speed.


280 Kim et al.

Figure 4. Time series of minimum central pressure, instant wind speed, 10 min average wind speed (a, c, e, g) and predicted tidal

elevation, observed sea level, surge height (b, d, f, h) with the time difference (DT) between high tide and surge peak occurrence at

various coastal stations in Korea: (a, b) Incheon, (c, d) Daesan, (e, f) Yeonggwang, and (g, h) Goheung during the passages of Typhoons Bolaven and Tembin.



Resonant Coupling Between Typhoon, Tides, and

Topography In this region, another critical situation can occur due to

resonant coupling of typhoon and tide when the storm translation

speed (STS) is comparable to that of the tide. According to the

tidal chart (Fang et al., 2004) and observed tidal data (Lee et al.,

2013), the tidal wave propagates from south to north along the

western coast of Korea and there is a six hour difference in high

tide between Jeju Harbour in the south and Incheon Harbour in

mid-western Korea. The distance between the two tidal stations is

approximately 438 km, yielding a phase speed of about 70 km/h

Figure 5. Temporal variation of wind speed, significant wave height, and maximum wave height observed at oceanographic buoys and

platforms during the passing of Typhoon Bolaven.


282 Kim et al.

for the co-tidal line. If the STS is similar to the phase speed, the

storm surge can ride on the high tide.

Based on the best track data of the typhoon, the STS of Bolaven

was about 40 km/h when it passed over the YS, which is much

slower than the propagation of the co-tidal line in this region.

However, the STS of some historical storms such as Kompasu in

2010 reached up to 70 km/h, suggesting that in the worst case

scenario, the storm surge peaks could be amplified by a resonant

coupling of tides and typhoon along the west coast.

On the other hand, the YS is a semi-enclosed marginal sea of

the northwestern Pacific Ocean, surrounded by the KP, the

Chinese coast, and the Ryukyu Islands. If we assume that the YS

is an open channel closed at one end with a length of 820 km and

depth of 60 m, the natural period of the channel, Tn, can be given

by:

4n

LT

n gh (1)

where n is the number of nodes (n = 1, 3, . . . ), L is the length of

the channel, g is the gravity acceleration, and h is the water depth.

For n = 1 and n = 3, the natural periods, T1 and T3, are 37.8 hours

and 12.6 hours, respectively. The period T3, with three nodes, is

known to reinforce tides by resonance with the semi-tidal period,

resulting in strong tides in this area (Choi, 1980). If the natural

periods (T1 and T3) are similar to the predominant period (Tsurge) of

the surge generated from typhoons passing over this region, the

storm surge can be significantly enhanced by the resonant

coupling (Moon et al., 2003a). The Tsurge can be expressed by:

surge

surge

strom

LT

V (2)

where Lsurge is the length scale of the typhoon and Vstorm is the STS.

In the case of Typhoon Bolaven, if we consider that Lsurge was 600

km (based on mean distributions of wind and air pressure) and

Vstorm was 40 km/h, the predominant period of the surge was about

15 hours, resulting in no significant resonant coupling. However,

depending on the combination of STS and storm size, a potential

enhancement of the storm surge always exists in this region due to

the coupling.

Occurrence of Record-Breaking High Waves One of the most interesting responses of coastal waters during

the passage of Typhoon Bolaven was the observation of high

maximum wave heights (MWH). The MWHs observed at KOGA-

S01, KOGA-S04, IORS, and Mardo buoys were 20.7m, 17.2m,

Table1. Peak surge height (A) and time (tA), predicted tide level (B) at tA, nearest high tide level (C) and time (tC), nearest spring high

tide level (D) and time (tD), observed sea level (A+B) at tA, extreme sea level scenario 1 (A+C) at tC, extreme sea level scenario 2 (A+D)

at tD, and time differences (|tC-tA|, |tD-tA|) at 14 tidal stations during the passage of Typhoon Bolaven. The unit of sea level is [cm]. Here,

|tC-tA | = 0 hour and |tC-tA | = 6 hours represent that the peak surges occur at high and low tides, respectively.

Station A B C D A+B A+C A+D |tC-tA| |tD-tA|

1 Yeongjong Bridge (YB) 159.6 298.4 825.4 934.6 458 984.9 1094.1 04h 50m 79h 06m

2 Incheon 151.5 289.5 807.3 911.7 441 958.8 1063.2 04h 49m 79h 01m

3 Ansan 142.3 270.7 763.1 862.9 413 905.4 1005.2 04h 45m 78h 55m

4 Daesan 110.8 211.2 712.2 797.5 322 823 908.3 05h 16m 79h 26m

5 Boreong 143.2 178.9 676.1 757 322 819.2 900.1 06h 46m 80h 54m

6 Gunsan(out) 124.5 164.5 645.4 721.4 289 769.9 845.9 05h 58m 80h 07m

7 Yeonggwang 119.9 151.1 599.2 670.8 271 719.2 790.7 05h 43m 79h 55m

8 Daeheuksando 84.4 145.7 324.4 362.2 230 408.7 446.6 06h 57m 92h 21m

9 Chujado 98.4 139.6 297.6 317.2 238 396 415.6 06h 24m 67h 37m

10 Seogwipo 111.8 145.2 262 295.3 257 373.8 407.1 06h 06m 92h 24m

11 Wando 136.6 258.4 285.3 384.9 395 421.9 521.5 01h 41m 88h 27m

12 Goheung 167.3 262.7 268.6 369.2 430 436 536.5 00h 47m 87h 37m

13 Gwangyang 101.3 258.7 287.8 385 360 389.1 486.3 01h 35m 85h 14m

14 Busan 50.2 111.8 113.8 145.9 162 164 196.1 00h 40m 86h 07m

Figure 6. (a) Swath of SWH during the passage of Typhoon

Bolaven. Line is the storm track. (b) Dominant MWL (×10, red

solid line), MWS (red dotted line), and STS (black solid line) along the typhoon track.



17.3 m, and 13.7 m respectively (Figure 5). The extraordinarily

high values broke observational records in these regions although

Bolaven was not the strongest typhoon based on the historical

best-track archives of the Regional Specialized Meteorological

Center (RSMC).

It is known that as the STS increases and becomes comparable

to the group speed of dominant waves, waves to the right of the

typhoon track are exposed to prolonged forcing from wind; that is,

they become “trapped” within the typhoon (resonance effect or

dynamic fetch) and grow continuously (Moon et al., 2003b). The

straight translation of the typhoon can maximize the increase of

the dynamic fetch.

Typhoon Bolaven was moving quickly along a straight track

with a high STS of about 9–18 m/s in the ECS and YS (Figure 6),

which may have provided favorable conditions for wave growth.

To support this hypothesis, we simulated the significant wave

height (SWH) for Typhoon Bolaven using the WW3 model

(Tolman, 2002) and calculated the maximum SWH at all grid

points (swath in Figure 6) as well as the dominant mean wave

length (MWL) along the typhoon track (red solid line in Figure 6).

This indicated that asymmetric distribution of the SWH was

evident due to the resonance effect, resulting in high waves to the

right of the typhoon track.

CONCLUSIONS In 2012, five typhoons affected the Korean coastal waters, and

among them, three typhoons made landfall on the KP from late

August to early September. This investigation focused on the

response of coastal waters to the passage of Typhoon Bolaven

(1215) which was the strongest to hit the KP in 2012, and passed

through the ECS and YS, leading to severe damages in Korea. We

analyzed observations from an ocean platform, buoys, and tidal

stations as well as numerical modeling results during the passage

of Bolaven.

Analysis revealed that the western coast of the KP avoided

severe storm surge damages due to weak tidal action during the

passage of Bolaven, although pure surge components were

significantly high. In fact, sea level at the coastal stations along

the track of Bolaven reached peak surges ranging from 50 to 150

cm over the tidal elevation. However, the peak surges fortunately

occurred with a time difference of approximately 4–5 hours from

high tide.

We examined the possible dangers due to coincident peak

surges and high tides as well as resonant coupling between the

typhoon, tides, and topography. Results suggested that if the STS

is similar to the co-tidal amplitude propagation (70 km/h) or the

predominant period of the surge is similar to the natural period of

the YS (12.6 or 37.8 hours), the coasts along the YS would be

very vulnerable to coastal inundation during high and spring tides,

requiring a systematic warning system for the worst situation.

Wave observations and modeling results showed that the

straight and fast translation of Typhoon Bolaven caused unusually

high waves in this region. The SST measurements also indicated

that when Typhoon Bolaven passed through the YS, the surface

water was vertically mixed, lowering the SST from 27°C–28°C to

16°C–20°C. Due to the cooler SST, Typhoon Tembin, which

followed closely after Bolaven, lost energy and ended up a

moderate typhoon.

ACKNOWLEDGEMENTS This research was supported by the project entitled, “Functional

improvement of the Korea Ocean Satellite Center”, funded by the

Korea Institute of Ocean Science & Technology as well as the

project entitled, “Advanced Research on Applied Meteorology”,

funded by the National Institute of Meteorological Research.

Partial support was provided by the projects entitled,

“Construction of Ocean Research Station and their Application

Studies”, “Development of Coastal Erosion Control Technology”,

and “KOOS II”, funded by the Ministry of Oceans and Fisheries,

Korea, and this support was greatly appreciated.

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http://www.po.gso.uri.edu/Numerical/tropcyc/flux/bonniepaper.pdf

http://www.po.gso.uri.edu/Numerical/tropcyc/flux/bonniepaper.pdf

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