Interocean circulation and heat and freshwater budgets of the South China Sea

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Interocean circulation and heat and freshwater
budgets of the South China Sea

• Guohong Fang
• First Institute of Oceanography,
• State Administration, China
• E-mail fanggh_at_fio.org.cn

Collaborators Yonggang Wang, Zexun Wei, and
Fangli Qiao

• 2007-11-26

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Outlines

• Introduction
• Numerical model
• Statistical methods
• Mean state Volume, heat, salt and freshwater
  budgets
• Seasonal variations
• Interannual variations
• Conclusions

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Introduction

• We previously used a global ocean
  diagnostic model results to evaluate the volume,
  heat snd salt budgets for the East and South
  China Seas (Fang et al., 2003). Recently we have
  refined the model and prognostically simulated
  the global ocean circulation for 21 years. This
  model result is used in the present study for
  evaluating the heat and freshwater budgets of the
  South China Sea.

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Introduction

• Map of the South China Sea and surrounding
  oceans

Straits connecting SCS to outer oceans Strait
Outer ocean Sill depth Luzon W Pacific
2500 m Taiwan East China lt50
m Mindoro Sulu 400 m Balabac
Sulu lt50 m Karimata Java
lt50 m Malacca Andaman lt50 m
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Numerical model Model grid
Model grid. The meridional spacing is 1?/6 for
the band from 20?S to 50?N and 2? for the rest
part. The zonal spacing is 1?/6 for the band from
99? to 150?E and 2? for the rest part.
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Numerical model - Forcing

• Simulation period 1983-2003 (21 years)
• Surface forcing
  NCEP reanalysis wind stress
  SST nudged toward
  Renolds data set SSS nudged toward
  Levitus monthly climatology
• See Wang et al,. 2006 (JGR) for details

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Numerical model SCS currents
Model-produced mean surface layer (0-58m) current
fields (from Fang et al., 2005)
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Statistical methods Lateral boundary sections
and vertical layers
Location of the boundary cross-section

• The SCS is vertically divided into 4 layers
• Surface layer, 1-58 m
• Subsurface layer, 58-427 m
• Deep layer, 427-2054 m
• Bottom layer, 2054-seabed
• Sill depths of Taiwan, Balabac, Karimata, and
  Malacca Strait are all
• lt 58 m
• Sill depth of Mindoro Strait
• lt427 m
• Sill depth of Luzon Strait
• lt 2801 m

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Statistical methods
Formulas for calculating transports through a
vertical section
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Statistical methods - Steps

• (1) Calculating monthly values (21 x 12)
• (2) Averaging for each particular month to obtain
  12 climatologically monthly mean values
• (3) Averaging 12 monthly climatologies to obtain
  ensemble mean value (21-yr mean)

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Mean state Volume budget (Sv)

• Horizontal

Vertical ECSEast China Sea, SSSulu Sea JSJava
Sea, ASAndaman Sea
SCS
W Pacific
Luzon St
Sea surface
ECS
1.71
1.03
1.49
SS
AS
0.16
1.16
- 58 m
JS
2.58
0.73
3.56
SS
- 427 m
0.25
0.56
- 2054 m
0.31
0.31
Seabed
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Mean state Heat budget

• Schematic of the heat budget of the SCS

NHF Total net heat flux 0.059
PW Mean net heat flux 17 W/m2
-2
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Mean state Freshwater budget

• Schematic of the freshwater budget of the SCS

RP-E River discharge
Precipitation - Evaporation
0.112 Sv 3.53 x 1012 m3/yr Total
discharge of 6 largest rivers to the SCS
0.84 x 1012 m3/yr 0.027 Sv If other
discharges from the land are neglected, then P-E
0.085 Sv P-E per unit area 0.75 m/yr NOTE
46 of RP-E goes to the Java Sea
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Mean state Volume budget

• Schematic of the volume budget of the SCS

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Seasonal variations
Seasonal variation of volume transport

• NOTE
• Transport of Luzon St surface layer is
  reversed (eastward)
• Transport of Karimata St is also reversed
  (northward)

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Seasonal variations-Circulation patterns
Summer
Winter
Circulation patterns of the South China Sea and
Indonesian Seas, with emphasis on the trans-South
China Sea flows. (a) Winter. (b) Summer. The
short-dashed lines represent subsurface currents.
The long-dashed lines indicate that the currents
are drawn only on the basis of model results. The
abbreviations stand for the following GDCC,
Guangdong Coastal Current HE, Halmahera Eddy
KS, Kuroshio KSTF, Karimata Strait Throughflow
LG, Luzon Gyre LSSIF, Luzon Strait Subsurface
Inflow MC, Mindanao Current ME, Mindanao Eddy
MSTF, Makassar Strait Throughflow NEC, North
Equatorial Current NECC, North Equatorial
Countercurrent NG, Nansha Gyre NGCC, New Guinea
Coastal Current NGCUC, New Guinea Coastal
Undercurrent SEC, South Equatorial Current
SCSWC, South China Sea Warm Current TSTF, Taiwan
Strait Throughflow VOC, Vietnam Offshore Current.
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Seasonal variations
Seasonal variation of heat transport
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Seasonal variations
Seasonal variation of salt transport
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Seasonal variations
Seasonal variation of freshwater transport

• NOTE Freshwater transport through Karimata St
  gets the largest in winter, and reversed in summer

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Interannual variation - Volume transports
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Interannual variation - Heat transports
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Interannual variations-Correlation with Nino3.4
NOTE - Significance level 90 for rgt0.30 95
for rgt0.35
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Conclusions

• An annual mean volume transport of 4.80 Sv from
  the western Pacific flows into the South China
  Sea through the Luzon Strait, of which 1.71 Sv
  returns to the Pacific and 3.09 Sv flows toward
  the Indian Ocean (1.76 Sv to the Sulu Sea, 1.16
  Sv to the Java Sea, and 0.16 Sv to the Andaman
  Sea, respectively).
• The annual mean Luzon Strait heat transports is
  0.445 PW, of which 0.178 PW returns to the
  Pacific. The heat transport toward the Indian
  Ocean is 0.326 PW. The total outward heat
  transport exceeds the inward one by 0.059PW,
  indicationg a mean net downward heat flux of 17
  W/m2 across the South China Sea air-sea
  interface.
• The annual mean Luzon Strait salt transport is
  169.91 Gg/s, of which 60.16 Gg/s returns to the
  Pacific. The salt transport toward the Indian
  Ocean is 105.78 Gg/s. The inward salt transport
  exceeds the total outward one by 3.97 Gg/s,
  indicationg a mean net freshwater flux (from
  river discharge and precipitation minus
  evaporation) of 0.112Sv, 46 of which goes toward
  the Java Sea.
• Total discharge of 6 largest rivers to the SCS
  is 0.027 Sv. If other discharges from the land
  are neglected, then the total P-E over the SCS is
  0.085 Sv, or, P-E per unit area is 0.75 m/yr.

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• THANK YOU !