kuliah 10 arus (sirkulasi lautan)

Arus(Current or Ocean Circulation)

Massa air yang bergerak dari suatu tempat ketempat yang lain di dalam laut

Apa penyebabnya?

• Angin (Wind-driven Circulation): di permukaan(surface circulation)(surface circulation)

• Perbedaan densitas (Density Current):di perairan dalam (Deep Sea Circulation)

densitas=fungsi (suhu, salinitas, tekanan);Thermohaline Circulation

Physics of Ocean CurrentsAll ocean currents are the result of thebalance of four forces:

• Pressure gradient

• Coriolis• Coriolis• Wind stress

• Friction

The Horizontal Equations of MotionThe horizontal motion of ocean currents on the rotating Earth are described byNewton’s 2nd Law of Motion (F = ma), represented by the momentum equation(Navier-Stokes equation):

u u u u p

Acceleration terms Forcing terms

advectivelocal Coriolis p.g. stress

0zxu u u u p

u v w fvt x y z x z

f = the Coriolis parameter

The Coriolis parameter varies from –.000146 s–1 at the South Pole to .000146 s–1 at the NorthPole. (f = 0 at the equator)

Gulf Stream

Contoh arus: (a) Small eddies dan(b) Strong Current (Gulf Stream)

wind speed W [m/s]

wind generates a sea surface wind stress

|| = aCwW2

with components

.

sea surface

x = aCwW.Wx

y = aCwW.Wy

Besar tegangan geser ini bergantung kepada besar kecilnya kecepatanangin, kekasaran permukaan laut (pa) dan densitas udara (Cw ) dan Wadalah kecepatan angin (m/det) yang umumnya diukur pada ketinggian 10m diatas permukaan laut.

DesOktAug

JunAprFeb

Beberapa Contoh Instrumentasiuntuk mengukur arus

Current Meter (Type Aandera CM7)

Contoh hasil mooring

ADCP= Acoustic Doppler Current Profiler

Reversing Thermometers and CTD cast

5

10

15

20

25

Fig.4 Trajectories of satellite-tracked drift buoys(from WOCE data set). Dark lines show thetrajectoriesof the drifter deployed in or entering into theSouth China Sea;light lines show these not entering into theSouth China Sea.The trajectories clearly show that in winter acurrent intrudes intothe South China Sea through the Luzon Strait,and formsa throughflow branch toward the KarimataStrait and the Indonesian Seas.

100 105 110 115 120 125-15

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