An Analysis of Mass Budget in the South China Sea

An Analysis of Mass Budget in An Analysis of Mass Budget in the South China Seathe South China Sea

Reporter: Shih-Ming HuangReporter: Shih-Ming Huang11

Adviser: Prof. Chung-Hsiung SuiAdviser: Prof. Chung-Hsiung Sui1,1,22

1:Department of Atmospheric Sciences1:Department of Atmospheric Sciences,, NCU, Taiwan NCU, Taiwan

2:2:Institute of Institute of Hydrological and Oceanic Sciences,Hydrological and Oceanic Sciences, NCU, TaiwanNCU, Taiwan

OutlineOutline::• IntroductionIntroduction• Ocean Data and General characteristicsOcean Data and General characteristics• Luzon StraitLuzon Strait and SCS Mass Transportand SCS Mass Transport• SummarySummary

IntroductionIntroduction::• Being the largest marginal sea in the tropics, the South China Sea (SCS) co

nnects with two major oceans, the Pacific and Indian Oceans [Shaw et al.,1996; Xie et al.,2003; Chang et al., 2008].

• Circulation in the SCS basin is driven by the southwest monsoon in summer and the northeast monsoon in winter. The resulting summer anti-cyclonic gyre and the winter cyclonic gyre as well as the transition between them have been documented by Wyrtki’s [1961].

• At shallow depths, upwelling is present off Vietnam in summer and off northwest Luzon in winter, and shelf break upwelling appears on the edge of Sunda Shelf from October to December, when the southward coastal jet impinges on the shelf [Chao et al., 1996].

• We use the Simple Ocean Data Assimilation (SODA) monthly data to estimate the annual and interannual change of the mass budgets in the South China Sea (SCS).

•Model: POP based on MOM2•Time: 44 yrs; 1958~2001; monthly•Resolution: 0.25°x 0.4° ave on 0.5°x 0.5°; 40 levels•Data: Hydrography (XBTs, CTDs …); Satellites (SST…)•Forcing: ERA-40 wind stress; GPCP precipitation; Bulk formulae for heat fluxes(Carton et al., 2006)

Simple Ocean Data Assimilation 1.4.2 (SODA) :1. Ocean Data:

Ocean Data and General characteristics:Ocean Data and General characteristics:

Strait Lon (°E) Lat (°N)

Luzon 120.75 18~22.5

Mindoro 120.25~122.25 11.25

Sunda Shelf 103.5~109 0.25

Taiwan 115~121 22.75

Singapore 103.25 0.7~1.3

Balabac 117.75 6.5~8.5

Winter: northeast monsoon wind→wund stress Curl (+ in south, upwelling;- in north ,downwelling)→cyclonic gyre

Summer:southwest monsoon wind→wund stress Curl (+ in north, upwelling; - in south, downwelling)→anticyclonic gyre

2. General characteristics:

yxCurl

Curlf

We

xy

1

(a)

(b)

Centurioni et al.,2006 JPO

(a)

(c)

(b)

(d)

Drifters data

1987~2002

(JFM)

(JAS)

(AMJ)

(OND)

Centurioni et al.,2006 JPO

(a)

(b)

Driftersdata

Zonal current (u)

Meridional current (v)

Vertical velocity (w)114.25°E 117.25°E

16.75°E

19.75°E

(E)(w)

(N)

(S)

(bottom=400m)

Transport : Net transport: Net zonal + Net meridional (Positive In /Negative Out)

(Suf=0)

0 b

b

m

m

z

z

dAwdAvdAu

Luzon StraitLuzon Strait & SCS Mass Transport:& SCS Mass Transport:

unit: 106 m3/s = Sv

FIG. Vertical distribution of the Luzon Strait transport (104 m2 s-1) against depth (m): (a) annual mean; (b) seasonal variation.

Sandwiched vertical structure (Tian et al., 2006)(a) (b) SE monsoon Wind

1. Luzon Strait transport:

44yr Annual mean (u):LST(0~381) = -2.40 SvLST(0~bottom) = -1.77 Sv

ADCP obs Oct 4~16,2005(Tian et al., 2006)

(a) (b)

Sandwiched vertical structure•Winter: KT↓→LST↑NE-wind → KT↓→LST↑Mindanao Dome → KT↓→LST↑(Yaremchuk and Qu 2004)

•Summer: KT ↑→LST↓SW-wind → KT ↑→LST↓

Con, Downwelling

Div, Upwelling

2. SCS Mass transport:

•44yr Annual mean (In/Out):Luzon = 2.40 SvSingapore = -0.13 SvBalabac = 0.3 SvSunda = -0.91 SvTaiwan = -0.96 SvMindord = -0.01 SvNet transport (0~381m) = 0.69 Sv

•The annual cycle of mass balance in the SCS is dominated by the mass flux into the Luzon Strait in the upper layer that is largely balanced by the horizontal mass flux through the Sunda Shelf and Taiwan Strait, and downward flux into the deeper water in the SCS.

(a)

•Winter:Upwelling : south China continental slop, off Vietnam, off Palawan, edge of sunda shelf

Downwelling : central SCS, west side of Luzon & Luzon strait

→ Basin-wide circulation induced downwelling & coast upwelling & shelf break upwelling

•Summer:Upwelling : off Vietnam, off Palawan, edge of sunda shelf

Downwelling : west side of Luzon & Luzon strait

→Wind induced coast upwelling off Vietnam→ Basin-wide circulation induced downwelling & coast upwelling & shelf break upwelling

(a)

(b)

Wind Stress & Curl

Current transport & W

SummarySummary• The SODA data can reasonably simulate and represent the character

istic of observation data (drifter and ADCP) of the SCS.

• The annual cycle of mass balance in the SCS is dominated by the mass flux into the Luzon Strait in the upper layer (above 400 m) that is largely balanced by the horizontal mass flux through the Sunda Shelf and Taiwan Strait, and downward flux into the deeper water in the SCS.

• The latter leaves the SCS through the Luzon Strait below 400 m. The mass flux through the Luzon Strait is strong (weak) in the winter (summer) when the Kuroshio transport is weak (strong).

• The basin-wide circulation dominated the vertical transport in the SCS, but the upwelling off Vietnam primarily caused by Wind in summer.

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