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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, C08046, doi:10.1029/2007JC004555, 2008

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ArticleSeasonal variations of the Yellow River plume in the Bohai Sea:
A model study
Qiang Wang,1 Xinyu Guo,1 and Hidetaka Takeoka1
Received 15 September 2007; revised 7 May 2008; accepted 13 May 2008; published 28 August 2008.

[1] We investigated the behavior of the Yellow River plume in the Bohai Sea through ayear and its controlling mechanisms using a numerical model driven by monthly
averaged wind stress, heat flux, and river discharge. The model produced a clear seasonal
behavior of the Yellow River plume. In summer, the Yellow River plume extends
northeastward into the central Bohai Sea; in autumn, it turns southward and flows into
Laizhou Bay along the coast; in winter, most of the diluted water is found aroundsoutheastern corner of Laizhou Bay; and in spring, a low-salinity area appears insouthwest Laizhou Bay. With the same model, several well-designed numericalexperiments were performed to investigate the effect on the behavior of the Yellow River
plume of tidal current, river discharge, wind stress, and thermal stratification. The tidal
currents promote the offshore spread of diluted water, while the tide-induced residual
currents prevent the plume from extending further downstream (in the direction of
Kelvin wave propagation). Wind stresses lead to pronounced changes in the path andshape of the plume. In autumn and winter, northwesterly or northerly winds drive thebuoyant water into Laizhou Bay along the coast. In summer, the combination ofsoutheasterly winds and thermal stratification drives the plume extend northeastward into
the central Bohai Sea. By changing only the magnitude of wind stress or riverdischarge in the experiments, we examined the sensitivity of summertime plume to themagnitude of wind stress and river discharge.
Citation: Wang, Q., X. Guo, and H. Takeoka (2008), Seasonal variations of the Yellow River plume in the Bohai Sea: A model
study, J. Geophys. Res., 113, C08046, doi:10.1029/2007JC004555.

1. Introduction[2] River plumes are an important phenomenon in coastal
regions. In areas with high rates of river discharge, plumes
clearly influence coastal dynamics and to a large extent
determine the fate of river-borne materials such as sand,nutrients, and pollutants. River plumes generally show two
noticeable features: an anticyclonic bulge near the rivermouth and a downstream coastal current in the direction of
Kelvin wave propagation [Garvine, 1995]. Moreover, thebehavior of a river plume can be affected by local geography, the prevailing wind stress, ambient currents, andstratification [Kourafalou, 1999; Xing and Davies, 2002].
In particular, winds that favor upwelling/downwelling canchange both the horizontal shape and vertical structure of aplume [Fong and Geyer, 2001; Lentz and Largier, 2006].
[3] The Yellow River is the largest river in northern
China. According to official reports of the Ministryof Water Resources of China, the river delivers 3.1 1010 m3 of freshwater and 7.8  108 tons of sand into the
Bohai Sea every year (Lijin Station, 1952– 2005). With thedeposition of such a large amount of sediments, the Yellow
1
Center for Marine Environmental Studies, Ehime University,
Matsuyama, Japan.

Copyright 2008 by the American Geophysical Union.
0148-0227/08/2007JC004555$09.00

River created a fast-growing delta, the Yellow River Delta(Figure 1b) and changed its route into the Bohai Sea for anumber of times in the past several decades [Chu et al.,2006]. The most dramatic change in the route of the riveroccurred in May 1976, when the river shifted from the
Diaokou course to the Qingshuigou course, and the locationof river mouth moved from northern coast to eastern coastof the delta (Figure 1b). Due to both natural variation andhuman influences, discharge from the Yellow River has
fallen rapidly in recent decades (Figure 2; see Wang et al.
[2006] for more details on the causes of reduced riverdischarge); consequently, the sea surface salinity in the
Bohai Sea has increased gradually since the 1960s [Lin etal., 2001].
[4] The Bohai Sea, into which the Yellow River discharges, is a semi-enclosed body of shallow water with anaverage depth of 18 m (Figure 1b). The sea is connectedto the Yellow Sea through the Bohai Strait. The Bohai Sea isgenerally divided into four parts: Laizhou Bay, Bohai Bay,
Liaodong Bay, and the central area. The major rivers thatflow into the Bohai Sea include the Yellow River, the Haihe
River, the Luanhe River, and the Liaohe River (see Figure
1b for their positions). Among these, the Yellow River is thelargest, accounting for more than half of the total riverdischarge into the Bohai Sea (Table 1).
[5] The Yellow River plume is a significant feature in the
distribution of surface salinity throughout the Bohai Sea.

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Figure 1. (a) Model domain and (b) bathymetry of the Bohai Sea. The positions of the Changjiang and
Yalu rivers are given in Figure 1a, while those of the Yellow, Haihe, Luanhe, and Liaohe rivers are in
Figure 1b. Dashed line in Figure 1b denotes the abandoned Diaokou course of Yellow River before May
1976. Line AB denotes the section along which temperature and salinity were presented (Figures 6 and 8,
respectively). Numbers next to triangles denote the tidal stations where tidal harmonic constants arecompared between simulations and observations (see Figure 4).
According to the results of several comprehensive surveys
conducted over the periods 1958 – 1960 [Guan and Chen,
1964], 1982 – 1983 [Zhou et al., 1991], and 1992 – 1993
[Zhou et al., 1997], the distribution of low-salinity watercorresponding to the Yellow River plume shows an apparent
seasonal variation. The low-salinity area extends northeastward into the central Bohai Sea during summer, and appears
in the southeastern part of Laizhou Bay in winter. Spring
and autumn represent transitional seasons, when most of thediluted water is located in the southwestern part of Laizhou
Bay. The same observation results also indicate that theplume depends closely on the river discharge. The river
plume is most pronounced in summer, when the riverdischarge reaches its maximum. In different decades, therange of the plume changed a lot. The river discharge washigher in the 1950s than in the 1980s and 1990s (Figure 2);
consequently, in any given season the plume was more
pronounced in the former decade than the latter decades.
[6] Many numerical studies have investigated tidal andsubtidal currents in the Bohai Sea. Early works were limited
to the assumption of homogenous conditions, and therefore
concentrated on tidal and wind-driven currents [e.g., Sun etal., 1990; Zhao and Shi, 1993; Zhao et al., 1995; Zhao andCao, 1998]. In recent years, attention has shifted to stratified
subtidal currents induced by heating and their interaction
with tidal and wind-driven currents [e.g., Huang et al.,
1999; Liu et al., 2003a; Wan et al., 2004; Hainbucher et al.,2004]; however, because the discharge from the Yellow
River was not directly considered in these numerical works,
the behavior of the Yellow River plume remains poorly
understood.
[7] As stated above, seasonal variation is the strongest
signal in the behavior of the Yellow River plume; consequently, this signal was chosen as the first objective in ourmodeling efforts. The remainder of this paper is organized
as follows. Section 2 describes the model configuration, andFigure 2. Annual discharge of the Yellow River overthe period 1950– 2002, as observed at Lijin Station (seeFigure 1 for the position of Lijin Station).

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Table 1. Monthly Averaged River Discharge (in m3s1) of the Six
Rivers Included in the Model
Month

ChangjiangRiveraYalu
RiverbYellow
RivercLiaoheRiverb

LuanheRiverbHaihe
RiverbJanuary
February
March
April
May
June
July
AugustSeptember
OctoberNovember
December
Annual mean

10,83412,017
17,171
25,282
33,18839,942
52,84044,95240,32332,117
22,136
13,77628,715

656
657
709
693
695
828
1353
2117
1158
699
678
685
911

378
296
299
209
216
271
907
1481
1345
1084
619
440
629

36
40
100
133
134
193
559
1144
513
279
158
90
282

3
25
37
33
12
23
341
467
134
76
63
37
104

12
19
22
13
8
18
283
651
273
66
53
27
120

a

Observed at Datong Station and averaged during 1965 – 1999.
[Chen, 1992].
cObserved at Lijin Station and averaged during 1977 – 2002.
b

section 3 presents the results of a standard simulation that
captures most of the features of the Yellow River plume.
Section 4 presents the results of a series of numericalexperiments designed to examine the influences of tidal
currents, seasonal variation in the river discharge, windstress, and thermal stratification on the behavior of the
Yellow River plume. This section also discusses the sensitivity of summertime plume to the magnitude of wind stress

C08046and river discharge. Finally, the results of the study arebriefly summarized in section 5.

2. Model Configuration[8] The employed numerical model is based on a threedimensional free-surface primitive equation ocean model
known as the Princeton Ocean Model (POM) [Blumberg
and Mellor, 1987; Mellor, 2003]. The model adopts the
Arakawa C grid in the horizontal and sigma-coordinates inthe vertical, and incorporates the level-2.5 Mellor – Yamada
turbulence closure model [Mellor and Yamada, 1982] incalculating vertical viscosity and diffusivity, and the Smagorinsky scheme in parameterizing horizontal viscosity anddiffusivity. For details of the model, readers can refer toMellor [2003].
[9] The model domain is 117.5° –131.5°E and 24° – 41°N
(Figure 1a), covering the Bohai, Yellow, and East China
Seas. The model has a resolution of 1/18° in both the zonal
and meridian directions, and 21 sigma levels vertically(0.000, 0.002, 0.004, 0.010, 0.020, 0.040,
0.060, 0.080, 0.100, 0.120, 0.140, 0.170,
0.200, 0.300, 0.400, 0.500, 0.650, 0.800,
0.900, 0.950, and 1.000), with a fine-scale resolution
near the surface and bottom. The external and internal time
steps are 6 and 360 s, respectively. The open boundary is set
far away from the Bohai Sea, favoring a correct representation of water exchange between the Bohai Sea and the
Yellow Sea through the Bohai Strait.

Figure 3. Monthly ERS-1/2 wind stress over the Bohai Sea in February, May, August, and November,averaged from 1991 to 2000.
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C08046in eastern areas than western areas, indicating a negative
vorticity [Zhao et al., 1995]. In spring and summer,
relatively weak (0.2 dyn/cm2) southeasterly winds prevailover the Bohai Sea.
[12] The density field in the Bohai Sea is affected byseasonal heating/cooling and seasonal inputs of freshwater.
The heat flux Q is given by a Haney-type formula [Barnier,1998]:Q ¼ Q0 þ k  ðTm  T0 Þ;

Figure 4. Comparison of harmonic constants derived fromsimulations (ordinate) and observations (abscissa) at 29 tidal
stations as shown in Figure 1 for (a) amplitude and (b)phase. Different symbols denote different tidal constituents.

[10] The bathymetry used in the model is based on a highresolution data set (10  10 [Choi et al., 2002]). Somemodifications were made in the Bohai Sea due to frequentchanges in the geography of Yellow River Delta in recent
decades. The mouth of the Yellow River is set to the east
(Figure 1b), approximately corresponding to its position in
the 1980s. Along the open boundary, the bathymetry of a
triply nested ocean model (NEST3 in Guo et al. [2003]) isused. The minimum depth in the model is set to 5 m. Before
calculations, the bathymetry was smoothed to meet thecriterion stated by Mellor et al. [1994] to reduce thepressure gradient error in the sigma-coordinate model.
[11] Being controlled by the Asian Monsoon, the winds
over the Bohai Sea show an apparent seasonal variation:
northerly winds prevail in winter and southeasterly winds insummer (Figure 3). The monthly averaged European Remote Sensing Satellite ERS-1 and ERS-2 (ERS-1/2) windstresses from 1991 to 2000 (http://www.ifremer.fr/cersat)
were used in this study, with a bilinear interpolation in space
and a linear interpolation in time. In autumn and winter,
relatively strong (0.6 dyn/cm2) northerly and northwesterly
winds prevail over the Bohai Sea. The winds are stronger

where Qo denotes the monthly net downward heat flux [daSilva et al., 1994a], k is the retroaction coefficient (=35 Wm2K1, as used in Guo et al. [2003]), Tm is the calculated
sea surface temperature, and To is the monthly sea surface
temperature from Levitus and Boyer [1994], with rectification in the Bohai Sea by referring to the Marine Atlas ofBohai Sea, Yellow Sea, and East China Sea [Chen, 1992](hereafter referred to as ‘the atlas’).
[13] The model includes six rivers: the Changjiang River,the Yalu River, the Yellow River, the Liaohe River, theLuanhe River, and the Haihe River (Figure 1). In the model,
river discharges were treated as downward vertical velocities over the river grids, as described by Oey [1996].
Monthly discharges of all the rivers, along with relevant
references, are given in Table 1. In this study, the monthly
discharge of the Yellow River was calculated from data forthe period from 1977 to 2002, matching the geomorphologyof the Yellow River Delta employed in the model. The
discharge of the Yellow River reaches a maximum inAugust (1500 m3s1) and is at a minimum in April(200 m3s1). In addition to river discharge, monthly
evaporation and precipitation rates [da Silva et al., 1994b]
were also included in the model.
[14] Along the open boundary, monthly temperature,salinity, subtidal currents and sea level elevation calculated
by a nested ocean model [Guo et al., 2003] were used. In
calculations involving tides, the tidal currents of four major
constituents (M2, S2, K1, and O1) provided by NAO.99b[Matsumoto et al., 2000] were linearly superposed to thesubtidal currents along the open boundary.
[15] The model runs from December 1, using the resultsof the nested ocean model [Guo et al., 2003] as initialconditions. Because the freshwater flux into the Bohai
Sea from rivers is not balanced by evaporation andprecipitation, the mean salinity in the Bohai Sea slowly
increased during the initial state of integration. After 3 years
of integration, the rate of increase in average salinity
within the Bohai Sea was less than 0.2/year; thus, the results
for the 4th year, when a quasi-equilibrium state had beenreached, were saved hourly and then filtered to remove tidal
signals [Hanawa and Mitsudera, 1985]. In calculating therepresentative value (of velocity, temperature, and salinity)
for each month, the results of 15 days centered about the
middle of the month were averaged to avoid contaminationby spring and neap tidal cycles.

3. Results[16] Tidal motion is one of the dominant hydrodynamic
processes in the Bohai Sea. Due to the important effects of
tidal currents on river plumes [Isobe, 2005; Guo and Valle-

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Figure 5. Seasonal variations in water temperature in the surface layer (upper panels) and the bottom
layer (lower panels). Contour interval is 2°C. The results shown in the panels were calculated according
to the procedures described at the end of section 2.
Levinson, 2007], four major tidal constituents (M2, S2, K1,
and O1) were included in our simulations. The calculated
harmonic constants of the four major tides show a similar
distribution to those reported in previous studies [e.g.,
Huang et al., 1999; Fang et al., 2004]. A comparison of
tidal harmonic constants at 29 stations between model
results and observations taken from the Admiralty Tide
Tables [Admiralty, 2004] indicates a good reproduction of
the four major tidal constituents in the Bohai Sea (Figure 4).
[17] The water temperature in the Bohai Sea shows strong
seasonal variation (Figure 5). In winter, the water temperature is vertically homogenous but shows a horizontal
gradient: the water is 5 °C warmer in the Bohai Strait than
within the Bohai Sea. In spring, stratification occurs fromthe central area to the Bohai Strait. The water around thecoast remains vertically homogenous and becomes warmer
than that of the central area and the strait. In summer, thefeatures are the same as those in spring, but the stratification
is clearly intensified. In autumn, the water again becomes
vertically homogenous, and cooling induces the wateraround the coast colder than that in the central area andthe strait.
[18] A comparison between calculated results (Figure 5)
and the atlas of water temperature in the Bohai Sea (notshown here) indicates little difference in the horizontal
distribution of water temperature. A further comparison
was performed for the vertical distribution of water temperature along the transect AB (see Figure 1b for its location).
The model results (left panels in Figure 6) show similarseasonal variations to those in the atlas (right panels in
Figure 6). As expected from Figure 5, seawater is homogeneous in autumn and winter but stratified in spring andsummer. A feature of the stratification is the occurrence of

two cold-water cores in the deep basin areas; these can befound in both the model results and the atlas.
[19] The calculated sea surface salinity (upper panels in
Figure 7) is compared with the climatology (lower panels in
Figure 7) for February, May, August, and November given
recently by Liu et al. [2003b]. This climatology was
averaged from all of the available data for the period1970 – 1996, making it more suitable for verifying ourmodel results than the atlas because the atlas also included
data from the 1950s and 1960s.
[20] A number of features are common to both thecalculations and observations shown in Figure 7. In winter,
the water with the lowest salinity is located at the southeastern corner of Laizhou Bay; in summer the low-salinity
water extends northeastward toward the central Bohai Sea;and in spring and autumn the low-salinity water is located at
the southwestern part of Laizhou Bay. The major difference
between the model results and observations is the salinity
value along the coast of Laizhou Bay, which is lower in thecalculations than in the observations. The averaging of
long-term observed data during different years is one
possible explanation of the higher salinity in the climatology (lower panels in Figure 7), as the area with the lowest
salinity can differ year-by-year, and the averaging procedure
actually smoothes the salinity field in space. A second
possible explanation is that most of the hydrographicalsurveys undertaken in Laizhou Bay did not focus on theriver plume, meaning that sampling sites were generally
located away from the coast; consequently, it is possible thatthe lower-salinity water close to the river mouth and thecoast was not sampled by these surveys.
[21] As with temperature, salinity is vertically homogeneous in autumn and winter (Figure 8). The halocline

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Figure 6. Distribution of water temperature along transect AB in February, May, August, andNovember. Left panels show the results of simulations; right panels the results from the atlas. Contour
interval is 1°C.

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Figure 7. Comparison of simulated sea surface salinity (upper panels) and the climatology (lower
panels; produced based on the data used in Liu et al. [2003b]) in February, May, August, and November.
Contour interval is 1 in upper panels and 0.5 in lower panels.
strengthens in spring and reaches a maximum in summer.
Being limited by river discharge, the halocline is locatedclose to the coast. The same features along this transect arealso found in the atlas, but a direct comparison is difficult
because the atlas is based on data from the 1950s to 1990s.
In recent decades, the position of the river mouth haschanged for a number of times, which to a great extent
has determined the distribution of salinity along this transect. Furthermore, the discharge of the Yellow River has
decreased markedly in recent decades (Figure 2), thereby
influencing the spatial distribution of low-salinity water.
[22] The surface currents in the Bohai Sea also show
apparent seasonal variations (Figure 9), which in turnsignificantly affect the path of the Yellow River plume. In
summer, the prevailing southeasterly winds produce northeastward surface currents offshore of the Yellow Rivermouth, driving the low-salinity water into the central Bohai
Sea; consequently, the river plume shows a strong northeastward extension (as described below, the large riverdischarge and summertime thermal stratification also contribute to this extension). In autumn, northwesterly winds
turn the surface currents to the southeast: the same direction
as the downstream movement of the Yellow River plume.
Accordingly, the Yellow River plume flows straight into
Laizhou Bay along its west coast. In winter, the northerly
winds prevail over the Bohai Sea and the surface currents in
Laizhou Bay are similar to those in autumn. The Yellow
River plume continues to extend in a downstream direction
along the coast, finally reaching the southeastern corner of
Laizhou Bay. Because the discharge from the Yellow Riverdecreases markedly in winter (Table 1), there is an insufficient supply of freshwater to the plume, resulting in alargely isolated low-salinity area in the southeastern cornerof Laizhou Bay. In spring, although the northeastward
surface currents induced by the prevailing southeasterly
winds tend to move the plume offshore, the developmentof a low-salinity area is limited by the fact that springtime
records the lowest river discharge of the year.

4. Discussion
4.1. Effects of Different Factors on the Yellow
River Plume[23] To examine the effects of different factors on the
Yellow River plume, we carried out a series of fivenumerical experiments with realistic topography (Table 2).
In the first experiment (case 1), a constant freshwater supply(annual discharge, 630 m3s1) is the only external forcing.
The model starts from rest with a constant temperature(10 °C) and a constant salinity (32) over the entire domain,
and runs from December 1 to the end of the following year.
As tidal motions always exist, four tidal constituents (M2,S2, K1, and O1) were included in the second experiment(case 2). Seasonal variations in the discharge from the
Yellow River were added in case 3, and seasonal windstresses in case 4. In the final experiment (case 5), seasonalheat fluxes were added.
[24] Case 1 demonstrates the evolution of the Yellow
River plume under the influence of the Coriolis force andthe constraint of topography. After 2.5 months of freshwater
input, low-salinity water forms along the west coast of
Laizhou Bay, and the 30-isohaline reaches the southeastern
corner of the bay (Figure 10a). Although low-salinity water
can be found in the upstream direction, most of the
freshwater flows downstream. As the integration continues,
the low-salinity area expands in both the alongshore and7 of 14

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Figure 8. Distribution of simulated salinity along transect
AB in February, May, August, and November. Contour
interval is 0.5.
offshore directions. As shown in Figures 10a and 10b, the27-isohaline moves 90 km along the coast over a period of
6 months.
[25] When tidal forcing is included (Figures 10c and10d), low-salinity water spreads to a greater extent in an
offshore direction rather than alongshore. The 30-isohaline
reaches only the head of Laizhou Bay after 2.5 months ofintegration (Figure 10c), being 90 km closer to the rivermouth than in case 1 (Figure 10a). In case 2, the downstream movement of the 27-isohaline is 80 km over a
period of 6 months: 10 km less than that in case 1. The
reduced alongshore expansion of low-salinity water in case
2 is likely to be associated with enhanced offshore spreading due to intensified horizontal and vertical diffusion by
tidal currents.
[26] In contrast, the upstream spread of low-salinity water
is not weakened. This provides a reminder that the distri-C08046bution of low-salinity water is not only influenced by tidal
mixing, but also by tide-induced residual currents. As an
additional experiment to case 2, we turned off freshwater
input and ran the model again (case 2a). The tide-induced
residual currents obtained by this barotropic calculation isnorthward in the area offshore the Yellow River mouth(Figure 11), and further flow into the central Bohai Sea,
forming a clockwise circle in the Laizhou Bay and thecentral area of the Bohai Sea. This clockwise flow patternapparently hinders the downstream movement of low-salinity water along the coast of Laizhou Bay.
[27] Seasonal variations in the discharge from the Yellow
River also affect plume formation (Figures 10e and 10f).
Discharge is lower than the annual mean from December toJune and higher than the annual mean in July and August(Table 1); consequently, the accumulated freshwater input
up to February and that up to August are both less in case 3
than in case 2. Due to low river discharge in February andreduced accumulated freshwater input up to February, thelow-salinity area near the river mouth and its degree ofdownstream expansion are both smaller in case 3 than incase 2 (Figures 10e and 10c). As a result of high riverdischarge in August and reduced accumulated freshwater
input up to August, as well as the short duration (45 days)of high river discharge, the low-salinity area near the rivermouth is larger in case 3 than in case 2, but the degree ofdownstream expansion is smaller in case 3 than in case 2(Figures 10f and 10d).
[28] Wind stresses induce an apparent seasonal variationin sea surface salinity (Figures 10g and 10h), which isconsistent with that shown in Figure 7. In winter, theprevailing northerly winds produce southward currents
offshore from the Yellow River Delta, which drive thediluted water into the southeastern corner of Laizhou Bay.
In this season, the discharge from the Yellow River does not
supply sufficient freshwater to the plume, and therefore alow-salinity area forms in the southeastern corner of
Laizhou Bay. In summer, the prevailing southeasterly winds
drive an offshore and upstream movement of the plume (seeisohaline in Figure 10h), thereby hindering the downstream
extension of the plume.
[29] The effects of seasonal heat fluxes on the distributionof low-salinity water are apparent only in summer(Figure 10j). The heating from spring to summer induces
the presence of stratification in summer while the cooling in
winter does not change the vertical structure of water
because the initial temperature is constant. With the presence of thermal stratification in summer, surface currents incase 5 (Figure 10j) become stronger than case 4 (Figure 10h),
which is especially evident in the offshore area northeastof river mouth. Consequently, more low-salinity water
spreads northeastward into the central Bohai Sea in case 5(Figure 10j) than in case 4 (Figure 10h).
[30] The plume also changes vertically for the different
experimental cases. In case 1, the different isohalines alongtransect CD (see Figure 10a for the position of this transect)are inclined offshore with similar angles (Figure 12a).
Bottom mixing due to tidal currents induce the isohalines
extend vertically from the bottom up to a certain depth(Figure 12b). The variation in river discharge affects thedegree of expansion of low-salinity water but does not alter
its vertical structure (Figure 12c). The southeasterly wind

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Figure 9. Subtidal currents in the surface layer (1 m depth) in February, May, August, and November.
not only promotes the offshore movement of the plume, butalso leads to more steeply inclined isohalines at the surface(Figure 12d). The presence of thermal stratification promotes the offshore expansion of the plume only in thesurface layer. This in turn leads to the strongest isohalines
along transect CD (Figure 12e).
4.2. Dependence of the Yellow River Plume on
Summertime Wind Stress and River Discharge[31] The Yellow River plume is most prominent insummer, partly because summertime records the largest
annual river discharge, and partly due to the combined
effects of southeasterly winds and thermal stratification. A

large river discharge favors the downstream expansion of
low-salinity water along the coast, as indicated in case 3(Figure 10f), while the combined effects of southeasterly
winds and thermal stratification promote the northeastward
expansion of the plume into the central Bohai Sea(Figure 10j). As shown in Figure 2, river discharge has
decreased significantly in recent decades. In addition, themagnitude of wind stress around the Yellow River Delta candiffer from monthly averaged wind stress from ERS-1/2. It
was therefore necessary to carry out additional numericalexperiments to examine the response of the river plume toriver discharge and the magnitude of wind stress.

Table 2. Conditions Used in the Experiments for Cases 1 – 5Open Boundary Conditions

Case

Tidal
Currents

River
Discharges

Wind
Stresses

Heat
Flux

Initial Values(Water Temperature, Salinity,
and Velocity)

1

No

Annual meanNo

No

10°C, 32, rest

Fixed to 10°C and 32

2

Yes

Annual mean

No

No

Same as above

Same as above

2a
3
4
5

Yes
Yes
Yes
Yes

No
Monthly mean
Monthly mean
Monthly mean

No
No
Yes
Yes

No
No
No
Yes

Same as above
Same as above
Same as above
Use the temperature on
December 1 of third year
calculated by standard case.
The salinity and velocity are
the same as above.

Same as above
Same as above
Same as above
Use the calculated
temperature bystandard case.
The salinity is
the same as above.

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Water Temperatureand Salinity

Velocity
Radiation condition
without a given
inflow and outflow
Radiation condition
with given
tidal currents
Same as above
Same as above
Same as above
Same as standard
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WANG ET AL.: YELLOW RIVER PLUME IN THE BOHAI SEA

Figure 10. Sea surface salinity and surface currents calculated for cases 1 –5. The left panels show theresults for February; the right panels for August. Salinity is less than 27 in the dark gray area and 27– 30
in the light gray area. The line CD in Figure 10a denotes the transect shown in Figure 12.

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Figure 11. Tide-induced residual currents in the surface
layer simulated for case 2a.

C08046[32] In this series of experiments, the monthly wind stressor monthly river discharge is multiplied by a factor that
increases gradually over a given interval. The model runs
from June 1 to September 30. For convenience, we defined
the Yellow River plume path index (r, q) according to the
distribution of sea surface salinity on August 15 (Figure 13).
The index r is defined as the maximum distance between
the river mouth and the 30-isohaline in domain A; q is
defined as the angle between an eastward direction and theline linking the river mouth and the point corresponding toindex r.
[33] Model results indicate a strong dependence of the
Yellow River plume on the magnitude of summertime windstress (Figure 14a). When the wind stress is turned off, theplume flows into Laizhou Bay (q 0°) and the maximum
distance is 80 km. As a weak southeasterly wind (<0.5times the magnitude of monthly wind stress) is added, thedistance responds first (increase from 80 to 90 km); subsequently, the angle starts to respond (change from 0° to 5°).
As the southeasterly wind is intensified to the magnitude ofmonthly wind stress, the distance changes little but the

Figure 12. Salinity distribution along transect CD in August, as calculated for cases 1 – 5. Contour
interval is 2.
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C08046>45° to 25°), indicating that the Coriolis force turns to be
more important and leads to a southward shift in plumeorientation.

5. Conclusions

Figure 13. Definitions of the Yellow River plume pathindex r and q. Index r is the maximum distance between theriver mouth and the 30-isohaline in domain A (enclosed by
the dashed line) on August 15; q is the angle between
eastward direction and the line of index r.
angle increases significantly (from 5° to >40°). As the wind
is further intensified, the increase in distance ceases ataround two times the magnitude of monthly wind stress.
The angle also keeps increasing, but not to the same degree
as that in response to the increase recorded for winds from
0.5 to 1.0 times the magnitude of monthly wind stress.
Therefore, the most sensitive response of plume orientation
to wind is recorded from 0.5 to 1.25 times the magnitude ofmonthly wind stress, and the most sensitive response ofplume range to wind is from 0.75 to 2.0 times the magnitudeof monthly wind stress.
[34] The strong dependence of Yellow River plume on themagnitude of summertime wind stress can be attributed tothe competing effect of wind-driven currents and densityinduced currents on the plume. In the offshore area northeast of the Yellow River Delta, density-induced currents
tend to flow southeastward in the surface layer in summer[Huang et al., 1999; Liu et al., 2003a]. However, thesoutheasterly winds prevailing in summer tend to drive
the surface currents to flow northwestward or northward.
Therefore, the wind-driven currents counteract the densityinduced currents to some extent. Furthermore, the densityinduced currents in the case as the wind stress was turned
off were comparable with the wind-driven currents inmagnitude. Consequently, the plume orientation responds
more sensitively than the plume range when the wind stresschanges around the normal value (0.5 to 1.25 times), while
the plume range responds more sensitively than the plumeorientation when the wind stress turns to be large (1.25 to
2.0 times).
[35] The response of the plume to river discharge is much
simpler than to the magnitude of wind stress (Figure 14b).
As the river discharge increases from 0.25 to 3.0 times themonthly river discharge, the maximum distance of theplume shows a continuous increase, with a rapid increase
up to 1.0 times (from 70 to 95 km) and a gradual increase
after 1.0 times (from 95 to 115 km); however, the angle
showed a steady decrease over this range of discharge (from[36] In response to seasonal variations in the wind field,
thermal stratification, and river discharge, the Yellow River
plume in the Bohai Sea shows an apparent seasonal behavior. The plume is most prominent in summer, when it
extends northeastward into the central Bohai Sea. Under
the northwesterly wind in autumn, the plume turns downstream and flows into Laizhou Bay along the coast. Under
the northerly wind in winter, low-salinity water propagatescontinuously along the coast, forming an area with thelowest recorded salinity at the southeastern corner of
Laizhou Bay due to the insufficient supply of freshwaterfrom the Yellow River. In spring, with a change in winddirection, the low-salinity area appears again in the southwestern part of the bay.
[37] The effects of various physical factors on the Yellow
River plume were clarified via a series of numerical experiments in which tidal currents, seasonal variation in the riverdischarge, wind stresses, and thermal stratification wereintroduced into the model step-by-step. The model results
indicate that the tidal currents promote the offshore spreadof low-salinity water and hinder alongshore downstream
expansion of the plume. The seasonal wind fields evidently

Figure 14. Yellow River plume path index (r, q) versus(a) wind stress factors and (b) river flux factors, which were
multiplied to the monthly wind stress and monthly riverdischarge, respectively.

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act to change the path and shape of the plume. The
northerly/northwesterly winds in autumn and winter drive
the low-salinity water into Laizhou Bay along the coast,
while the southeasterly winds in spring and summer expand
the plume offshore. With the presence of thermal stratification in summer, the plume shows a strong northeastward
extension into the central Bohai Sea.
[38] The results of experiments regarding the sensitivityof the plume to the magnitude of summertime wind stresssuggest that the most sensitive response of the plumeorientation occurs as the wind varies from 0.5 times to
1.25 times the monthly wind stress; the most sensitive
response of the plume range occurs as the wind varies from0.75 times to 2.0 times the monthly wind stress. Experiments regarding the sensitivity of the summertime plume toriver discharge suggest that the plume range increases withincreasing discharge and the plume orientation turns southward; however, under the summertime monthly windstresses, the plume is unable to flow into Laizhou Bay even
if the river discharge is multiplied by a factor of three.
[39] It is necessary to note that the coastline and bathymetry employed in present study roughly correspond to theconditions in the 1980s. In the past two decades, the morphology off the river mouth has been modified by the
sediment load from the Yellow River. The successful
reproduction of seasonal variation of diluted water in thisstudy suggests that the bay scale movement of diluted water
is controlled by large-scale forcing, while the effect ofchanging in morphology off the river mouth on plume
movement may be confined to the area near the river mouth.
The latter, however, needs to be quantitatively investigatedin the near future.
[40] Acknowledgments. We thank Dr. Zhe Liu for providing theclimatology salinity field for the Bohai Sea, Dr. Y. Fukushima for providing
Yellow River discharge at Lijin Station, and Dr. T. Yanagi for his helpfulcomments. This study was initiated as part of the Yellow River Project
promoted by the Research Institute for Humanity and Nature and is part of
the National Basic Research Program of China (No. 2002CB412402). The
study was also supported by a Grant-in-Aid for the Global COE Programfrom the Ministry of Education, Culture, Sports, Science and Technology,
Japan (MEXT), and the Japan Society for the Promotion of Science (JSPS).
We are also very thankful to two anonymous reviewers for their constructive comments on the original manuscript.

References
Admiralty (2004), Admiralty Tide Tables and Tidal Stream Tables, vol. 4,
Pacific Ocean, Hydrogr. of the Navy, London.
Barnier, B. (1998), Forcing the ocean, in Ocean Modeling and Parameterization, edited by E. P. Chassignet and J. Verron, pp. 45 – 80, Kluwer
Acad., Norwell, Mass.
Blumberg, A. F., and G. L. Mellor (1987), A description of a three-dimensional coastal ocean circulation model, in Three-Dimensional Coastal
Ocean Models, Coast. Estuar. Sci., vol. 4, edited by N. Heaps, pp. 1 – 16,
AGU, Washington, D. C.
Chen, D. (1992), Marine Atlas of Bohai Sea, Yellow Sea and East China
Sea: Hydrology, 524 pp., China Ocean Press, Beijing, China.
Choi, B. H., K. O. Kim, and H. M. Eum (2002), Digital bathymetric andtopographic data for neighboring seas of Korea (in Korean), J. Korean
Soc. Coast. Ocean Eng., 14, 41 – 50.
Chu, Z. X., X. G. Sun, S. K. Zhai, and K. H. Xu (2006), Changing patternof accretion/erosion of the modern Yellow River (Huanghe) subaerialdelta, China: Based on remote sensing images, Mar. Geol., 227, 13 – 30.
da Silva, A., C. Young-Molling, and S. Levitus (1994a), Atlas of Surface
Marine Data 1994, vol. 1, Algorithms and Procedures, NOAA Atlas
NESDIS 6, NOAA, Silver Spring, Md.
da Silva, A., C. Young-Molling, and S. Levitus (1994b), Atlas of Surface
Marine Data 1994, vol. 4, Anomalies of Fresh Water Fluxes, NOAA Atlas
NESDIS 9, NOAA, Silver Spring, Md.

C08046

Fang, G., Y. Wang, Z. Wei, B. H. Choi, X. Wang, and J. Wang (2004),
Empirical cotidal charts of the Bohai, Yellow, and East China Seas from
10 years of TOPEX/Poseidon altimetry, J. Geophys. Res., 109, C11006,
doi:10.1029/2004JC002484.
Fong, D. A., and W. R. Geyer (2001), Response of a river plume during
an upwelling favorable wind event, J. Geophys. Res., 106, 1067 –1084.
Garvine, R. W. (1995), A dynamical system for classifying buoyant coastal
discharges, Cont. Shelf Res., 15, 1585 – 1596.
Guan, B., and S. Chen (1964), The current systems in the near-sea area of
the China Seas (in Chinese), in Report of Comprehensive Oceanographic
Survey in Chinese Oceans in 1958, vol. 5, edited by Ocean Comprehensive Survey Office, Ocean Division, State Science and Technology Committee, pp. 1 – 85, State Sci. Tech. Comm., Beijing, China.
Guo, X., and A. Valle-Levinson (2007), Tidal effects on estuarine circulation and outflow plume in the Chesapeake Bay, Cont. Shelf Res., 27, 20 –42.
Guo, X., H. Hukuda, Y. Miyazawa, and T. Yamagata (2003), A triply nested
ocean model for simulating the Kuroshio—Roles of horizontal resolutionof JEBAR, J. Phys. Oceanogr., 33, 146 – 169.
Hainbucher, D., H. Wei, T. Pohlmann, J. Sündermann, and S. Feng (2004),
Variability of the Bohai Sea circulation based on model calculations,J. Mar. Syst., 44, 153 – 174.
Hanawa, K., and H. Mitsudera (1985), On daily average of oceanographic
data (in Japanese), Coast. Oceanogr. Bull., 23, 79 – 87.
Huang, D., J. Su, and J. O. Backhaus (1999), Modelling the seasonal
thermal stratification and baroclinic circulation in the Bohai Sea, Cont.
Shelf Res., 19, 1485 – 1505.
Isobe, A. (2005), Ballooning of river-plume bulge and its stabilization by
tidal currents, J. Phys. Oceanogr., 35, 2337 – 2351.
Kourafalou, V. H. (1999), Process studies on the Po River plume, North
Adriatic Sea, J. Geophys. Res., 104, 29,963 – 29,985.
Lentz, S. J., and J. Largier (2006), The influence of wind forcing on the
Chesapeake Bay buoyant coastal current, J. Phys. Oceanogr., 36, 1305 –1316.
Levitus, S., and T. P. Boyer (1994), World Ocean Atlas 1994, vol. 4,
Temperature, NOAA Atlas NESDIS 4, 129 pp., NOAA, Silver Spring, Md.
Lin, C., J. Su, B. Xu, and Q. Tang (2001), Long-term variations of temperature and salinity of the Bohai Sea and their influence on its ecosystem, Prog. Oceanogr., 49, 7 – 19.
Liu, G., H. Wang, S. Sun, and B. Han (2003a), Numerical study on density
residual currents of the Bohai Sea in summer, Chin. J. Oceanol. Limnol.,21, 106 – 113.
Liu, Z., H. Wei, and S. Jiang (2003b), Characteristics of seasonal variationof monthly mean temperature and salinity fields in the Bohai Sea andanalysis of the related dynamics (in Chinese), J. Ocean Univ. Qingdao,
33, 7 – 14.
Matsumoto, K., T. Takanezawa, and M. Ooe (2000), Ocean tide models
developed by assimilating TOPEX/POSEIDON altimeter data into hydrodynamical model: A global model and a regional model around Japan,
J. Oceanogr., 56, 567 – 581.
Mellor, G. L. (2003), Users guide for a three-dimensional, primitive equation, numerical ocean model (2003 version), report, 53 pp., Program in
Atmos. and Ocean Sci., Princeton Univ., Princeton, N. J.
Mellor, G. L., and T. Yamada (1982), Development of a turbulence closure
model for geophysical fluid problems, Rev. Geophys. Space Phys., 20,851 – 875.
Mellor, G. L., T. Ezer, and L.-Y. Oey (1994), The pressure gradient conundrum of sigma coordinate ocean models, J. Atmos. Ocean. Technol.,11, 1126 – 1134.
Oey, L.-Y. (1996), Simulation of mesoscale variability in the Gulf of Mexico: Sensitivity studies, comparison with observations and trapped wave
propagation, J. Phys. Oceanogr., 26, 145 – 175.
Sun, Y., S. Chen, and K. Zhao (1990), A three-dimensional baroclinic
model of the coastal water: (I) Numerical simulation of tidal and residual
currents in the Bohai Sea (in Chinese), J. Ocean Univ. Qingdao, 20,
11 – 24.
Wan, X., X. Bao, D. Wu, and H. Jiang (2004), Numerical diagnostic simulation of summertime tide-induced, wind-driven and thermohaline currents in the Bohai Sea (in Chinese), Chin. J. Oceanol. Limnol., 35,
41 – 47.
Wang, H., Z. Yang, Y. Saito, J. P. Liu, and X. Sun (2006), Interannual andseasonal variation of the Huanghe (Yellow River) water discharge overthe past 50 years: Connections to impacts from ENSO events and dams,
Global Planet. Change, 50, 212 – 225.
Xing, J., and A. M. Davies (2002), Influence of topographic features
and along shelf flow upon the Ebro plume, Cont. Shelf Res., 22,
199 – 227.

13 of 14

C08046

WANG ET AL.: YELLOW RIVER PLUME IN THE BOHAI SEA

Zhao, B., and D. Cao (1998), Dynamic analysis and numerical modeling of
forming mechanisms of winter circulations in the Bohai Sea (in Chinese),
Chin. J. Oceanol. Limnol., 29, 86 – 96.
Zhao, B., G. Zhuang, D. Cao, and F. Lei (1995), Circulation, tidal residual
currents and their effects on the sedimentations in the Bohai Sea (inChinese), Chin. J. Oceanol. Limnol., 26, 466 – 473.
Zhao, J., and M. Shi (1993), Numerical modeling of three-dimensional
characteristics of wind-driven current in the Bohai Sea, Chin. J. Oceanol.
Limnol., 11, 70 – 79.

C08046

Zhou, S., J. Chen, S. Ma, and J. Zhao (1997), The hydrological environment and variation features of enhancement in Bohai Sea (in Chinese),
Mar. Fish. Res., 18, 86 – 100.
Zhou, S., S. Ma, C. Li, and D. Qiu (1991), Hydrographic chart for reproduction environment in the Bohai Sea (in Chinese), Mar. Fish. Res., 12,
93 – 122.
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X. Guo, H. Takeoka, and Q. Wang, Center for Marine Environmental
Studies, Ehime University, 2-5 Bunkyo-Cho, Matsuyama 790-8577, Japan.
(guoxinyu@dpc.ehime-u.ac.jp)

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