Pengguna:NFarras/Proyek 3
Transpor Ekman adalah bagian dari teori pergerakan Ekman yang pertama kali diteliti pada tahun 1902 oleh Vagn Walfrid Ekman. Angin merupakan sumber energi utama bagi terbentuknya sirkulasi laut, termasuk transpor Ekman.[1] Transpor Ekman terjadi ketika permukaan laut dipengaruhi oleh gaya gesek angin di atasnya. Hembusan angin menimbulkan gaya gesek pada permukaan laut dan turut mempengaruhi kolom air sedalam 10-100 meter di bawahnya.[2] Meskipun demikian, efek Coriolis menyebabkan air tidak bergerak searah dengan arah angin, melainkan bergerak membentuk sudut 90° terhadap arah hembusan angin di permukaan.[2] Arah transpor tergantung pada belahan Bumi terjadinya peristiwa tersebut. Pada belahan Bumi utara, transpor memiliki arah 90° searah jarum jam terhadap arah angin. Sementara itu, transpor pada belahan Bumi selatan memiliki arah 90° berlawanan arah jarum jam terhadap arah angin.[3] Fenomena ini pertama kali dicatat oleh Fridtjof Nansen ketika Ia menjalani sebuah ekspedisi pada tahun 1890an. Ketika itu, Ia mengamati es bergerak dengan sudut tertentu terhadap arah angin.[4]
Transpor Ekman berdampak signifikan terhadap properti biogeokimia laut dunia. This is because they lead to upwelling (Ekman suction) and downwelling (Ekman pumping) in order to obey mass conservation laws. Mass conservation, in reference to Ekman transfer, requires that any water displaced within an area must be replenished. This can be done by either Ekman suction or Ekman pumping depending on wind patterns.[1]
Theory
Ekman theory explains the theoretical state of circulation if water currents were driven only by the transfer of momentum from the wind. In the physical world, this is difficult to observe because of the influences of many simultaneous current driving forces (for example, pressure and density gradients). Though the following theory technically applies to the idealized situation involving only wind forces, Ekman motion describes the wind-driven portion of circulation seen in the surface layer.[5][6]
Surface currents flow at a 45° angle to the wind due to a balance between the Coriolis force and the drags generated by the wind and the water.[7] If the ocean is divided vertically into thin layers, the magnitude of the velocity (the speed) decreases from a maximum at the surface until it dissipates. The direction also shifts slightly across each subsequent layer (right in the northern hemisphere and left in the southern hemisphere). This is called the Ekman spiral.[8] The layer of water from the surface to the point of dissipation of this spiral is known as the Ekman layer. If all flow over the Ekman layer is integrated, the net transportation is at 90° to the right (left) of the surface wind in the northern (southern) hemisphere.[3]
- ^ a b Sarmiento, Jorge L.; Gruber, Nicolas (2006). Ocean biogeochemical dynamics. Princeton University Press. ISBN 978-0-691-01707-5.
- ^ a b Emerson, Steven R.; Hedges, John I. (2017). Chemical Oceanography and the Marine Carbon Cycle. New York, United States of America: Cambridge University Press. ISBN 978-0-521-83313-4.
- ^ a b Colling, pp 42-44
- ^ Pond & Pickard, p 101
- ^ Colling p 44
- ^ Sverdrup p 228
- ^ Mann & Lazier p 169
- ^ Knauss p 124.