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39-685: From satellite data, Nan, et al. (2011) concluded there are three intrusion paths for the Kuroshio Current into the SCS. A northward flowing WBC (like the Kuroshio Current) can deform at a gap in a western boundary and form an anticyclonic current loop if the gap is wide enough. This results in a looping path , where water from the Kuroshio flows through the middle of the Luzon Strait into the SCS and out in

78-484: A leaping path across the Luzon Strait and into the SCS. This is seen as a strengthening of the Luzon Cyclonic Gyre to the west of the strait while the Kuroshio continues northwards along the eastern Taiwanese coast. The anticyclonic gyre normally present in the SCS is significantly weakened as a result. The Luzon Strait and SCS experience seasonally reversing monsoon winds; these are southwestward and stronger in

117-466: A decreasing trend in Kuroshio intrusion strength over time, which correlates with a decrease in the cross-Luzon Strait pressure gradient, thereby supporting this theory. However, the exact mechanism for a pressure gradient-induced intrusion is not yet fully understood. The proposed equation describing the transport Q {\displaystyle Q} between the SCS and the Pacific Ocean basins

156-500: Is Ekman pumping as the tradewinds shift to westerlies causing a pile up of surface water. Some assumptions of the fluid dynamics involved in the process must be made in order to simplify the process to a point where it is solvable. The assumptions made by Ekman were: The simplified equations for the Coriolis force in the x and y directions follow from these assumptions: where τ {\displaystyle \tau \,\!}

195-836: Is based on a two-layer ocean model. Q = { g f H 1 Δ η + H 2 2 f g ′ Δ h , if  R < W 0 g f H 1 Δ η + κ ( 2 3 ) 3 / 2 H 2 W 0 g ′ Δ h , otherwise {\displaystyle Q={\begin{cases}{\frac {g}{f}}H_{1}\Delta \eta +{\frac {H_{2}}{2f}}g'\Delta h,&{\text{if }}R<W_{0}\\{\frac {g}{f}}H_{1}\Delta \eta +\kappa \left({\frac {2}{3}}\right)^{3/2}H_{2}W_{0}{\sqrt {g'\Delta h}},&{\text{otherwise}}\end{cases}}} It depends on

234-468: Is based on the assumption of a steady state, which is not realistic since the Kuroshio intrusion process is unstable. There are many eddies near the Luzon-Taiwan coast, especially to the east of the Kuroshio axis. Most eddies propagate westward with a mean speed of 7.2 cm/s and are deflected due to the Kuroshio current. This could be a source of Kuroshio intrusion into the SCS. However, few eddies from

273-493: Is due to purely wind-driven Ekman flow. Nevertheless, wind-driven Ekman drift still influences the inflow angle and speed of Kuroshio intrusion A build up of water has been observed on the Pacific side of the Luzon Strait by Y. T. Song (2006), which results in a pressure gradient across the strait. This could initiate the bending of the Kuroshio Current into the Luzon Strait, thereby resulting in eventual leakage. Satellite data show

312-414: Is large-scale wind patterns in the open ocean. Open ocean wind circulation can lead to gyre-like structures of piled up sea surface water resulting in horizontal gradients of sea surface height. This pile up of water causes the water to have a downward flow and suction, due to gravity and mass balance. Ekman pumping downward in the central ocean is a consequence of this convergence of water. Ekman suction

351-399: Is part of Ekman motion theory, first investigated in 1902 by Vagn Walfrid Ekman . Winds are the main source of energy for ocean circulation, and Ekman transport is a component of wind-driven ocean current. Ekman transport occurs when ocean surface waters are influenced by the friction force acting on them via the wind. As the wind blows it casts a friction force on the ocean surface that drags

390-509: Is the Trade Winds both north and south of the equator pulling surface waters towards the poles. There is a great deal of upwelling Ekman suction at the equator because water is being pulled northward north of the equator and southward south of the equator. This leads to a divergence in the water, resulting in Ekman suction, and therefore, upwelling. The third wind pattern influencing Ekman transfer

429-499: Is the wind stress , ρ {\displaystyle \rho \,\!} is the density, u {\displaystyle u\,\!} is the east–west velocity, and v {\displaystyle v\,\!} is the north–south velocity. Integrating each equation over the entire Ekman layer: where Here M x {\displaystyle M_{x}\,\!} and M y {\displaystyle M_{y}\,\!} represent

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468-411: Is the component of Ekman transport that results in areas of upwelling due to the divergence of water. Returning to the concept of mass conservation, any water displaced by Ekman transport must be replenished. As the water diverges it creates space and acts as a suction in order to fill in the space by pulling up, or upwelling, deep sea water to the euphotic zone. Ekman suction has major consequences for

507-455: Is the flow speed at the current core and θ {\displaystyle \theta } is the angle between the velocity vector and the positive x {\displaystyle x} -axis. Notice that the model is dependent on the inflow speed ν c 0 {\displaystyle \nu _{c0}} and angle θ 0 {\displaystyle \theta _{0}} . However, this theory

546-481: Is the vertical eddy viscosity coefficient. This gives a set of differential equations of the form In order to solve this system of two differential equations, two boundary conditions can be applied: Things can be further simplified by considering wind blowing in the y -direction only. This means is the results will be relative to a north–south wind (although these solutions could be produced relative to wind in any other direction): where By solving this at z =0,

585-399: The Luzon Strait. This can result in an anticyclonic bending of the Kuroshio flow into the Luzon Strait, from which a branch detaches into the SCS. A cyclonic gyre forms northwestward of the Luzon Strait as a result of this leaking path . This theory is based on observations by D.Z. Qiu, et al. (1984) from floaters but more recently no such branch has been observed The Kuroshio can also take

624-461: The Pacific can propagate into the Luzon Strait, since it is blocked by the Kuroshio current. Mesoscale eddies can impact the strength of the Kuroshio and its inflow angle at the Luzon Strait by changing the local background flow. Furthermore, seasonal variations in eddy strength and frequency correlate with seasonal variations in Kuroshio intrusion and Luzon Strait transport, suggesting that the two could nevertheless be linked. The water intruding into

663-964: The SCS, potential vorticity must be conserved across the Luzon Strait. This means that intrusion must be in the form of current loops or rings that rotate either cyclonically or anticyclonically depending on the potential vorticity balance. The equation describing this motion is for a frictionless beta plane in a steady state with reduced gravity. d θ d y sin ⁡ θ = − β ν c + ν c 0 ν c d θ d y | y = 0 sin ⁡ θ 0 {\displaystyle {\frac {d\theta }{dy}}\sin {\theta }=-{\frac {\beta }{\nu _{c}}}+{\frac {\nu _{c0}}{\nu _{c}}}{\frac {d\theta }{dy}}{\bigg |}_{y=0}\sin {\theta _{0}}} Here, ν c {\displaystyle \nu _{c}}

702-426: The biogeochemical processes in the area because it leads to upwelling. Upwelling carries nutrient rich, and cold deep-sea water to the euphotic zone, promoting phytoplankton blooms and kickstarting an extremely high-productive environment. Areas of upwelling lead to the promotion of fisheries, in fact nearly half of the world's fish catch comes from areas of upwelling. Ekman suction occurs both along coastlines and in

741-450: The boreal winter and northeastward and weaker in the boreal summer. This results in negative wind-driven Ekman transport in the winter, strengthening Kuroshio intrusion, and positive transport in the boreal summer, weakening intrusion. Wind-driven Ekman transport could therefore contribute to westward flow through the Luzon Strait and hence to Kuroshio leakage into the SCS. However, research has shown that less than 10% of Luzon Strait transport

780-474: The coastline. Due to the Coriolis effect , surface water moves at a 90° angle to the wind current. If the wind moves in a direction causing the water to be pulled away from the coast then Ekman suction will occur. On the other hand, if the wind is moving in such a way that surface waters move towards the shoreline then Ekman pumping will take place. The second mechanism of wind currents resulting in Ekman transfer

819-558: The coasts as well as in the open ocean. Along the Pacific Coast in the Southern Hemisphere northerly winds move parallel to the coastline. Due to the Coriolis effect the surface water gets pulled 90° to the left of the wind current, therefore causing the water to converge along the coast boundary, leading to Ekman pumping. In the open ocean Ekman pumping occurs with gyres. Specifically, in the subtropics, between 20°N and 50°N, there

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858-540: The left (in the South Hemisphere) of the wind currents, and the surface water diverges along these boundaries, resulting in upwelling in order to conserve mass. Ekman pumping is the component of Ekman transport that results in areas of downwelling due to the convergence of water. As discussed above, the concept of mass conservation requires that a pile up of surface water must be pushed downward. This pile up of warm, nutrient-poor surface water gets pumped vertically down

897-400: The model outcome depends strongly on the delineation of the SCS and Pacific Ocean basins.... The beta effect describes the changing of the Coriolis parameter f {\displaystyle f} with latitude. This effect will cause a WBC like the Kuroshio current to intrude into a meridional gap. The intrusion can then either penetrate the gap, or leap over it continuing its flow on

936-438: The north of the strait. The current loop in the SCS forms due to Ekman transport resulting from northeasterly winds that push Kuroshio surface water westward. Anticyclonic eddies can shed from the current loop and penetrate farther into the SCS, as has been observed by Li (1997) During the winter monsoon season, Kuroshio intrusion strengthens. Winds blow in the northwestward direction, thereby pushing Kuroshio surface water into

975-467: The northern SCS from the Kuroshio current is relatively nutrient-rich. Therefore it enriches dissolved organic matter stores and enhances ammonia oxidation in the SCS. Bacteria and phytoplankton use these resources to grow and support their biogeochemical activities. Microzooplankton are particularly affected by the influx of nutrients since they have limited transport mechanisms compared to zooplankton Kuroshio current intrusion has oxidized and increased

1014-541: The northern hemisphere and left in the southern hemisphere). This is called the Ekman spiral . 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. There are three major wind patterns that lead to Ekman suction or pumping. The first are wind patterns that are parallel to

1053-533: The open ocean, but also occurs along the equator. Along the Pacific coastline of California, Central America, and Peru, as well as along the Atlantic coastline of Africa there are areas of upwelling due to Ekman suction, as the currents move equatorwards. Due to the Coriolis effect the surface water moves 90° to the left (in the South Hemisphere, as it travels toward the equator) of the wind current, therefore causing

1092-438: The other side. Which flow path occurs depends on the ratio of flow inertia (which encourages leaping) to beta effect (which encourages penetrating). There can also be a transition between flow states as this ratio changes. Two different flow states can arise from the same external forcings depending on the past flow state; there is hysteresis in the system Research by Nan et al. (2011) suggests that during Kuroshio intrusion into

1131-450: The pressure gradient and W 0 {\displaystyle W_{0}} is the strait width. According to this mechanism, H 1 Δ η {\displaystyle H_{1}\Delta \eta } describes the transport in the upper layer of the Luzon Strait, which is dominated by geostrophic balance. This model has a few drawbacks: it only divides the ocean into two layers which reduces accuracy, and

1170-410: The reduced gravity g ′ = g Δ ρ ρ 0 {\displaystyle g'={\frac {g\Delta \rho }{\rho _{0}}}} , κ = ± ( Δ p b − Δ η ) {\displaystyle \kappa =\pm (\Delta p_{b}-\Delta \eta )} determines the direction of

1209-399: The salinity of the sedimentary environment northwest of Luzon Island in the SCS. The intrusion transports sediment high in illite and chlorite concentrations from around Taiwan southwestward into the deep sea environment. Pearl river sediment, high in concentrations of kaolinite and titanium , are also transported southwestward by the intrusion Ekman transport Ekman transport

Kuroshio Current Intrusion - Misplaced Pages Continue

1248-636: The surface and bottom layer depths H 1 {\displaystyle H_{1}} and H 2 {\displaystyle H_{2}} respectively, the sea surface height difference between the two basins Δ η {\displaystyle \Delta \eta } and the height difference of the layer interface between the two basins Δ h {\displaystyle \Delta h} . The Rossby radius of deformation R = 2 g ′ Δ h f {\displaystyle R={\frac {\sqrt {2g'\Delta h}}{f}}} uses

1287-415: 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

1326-409: The upper 10-100m of the water column with it. However, due to the influence of the Coriolis effect , the ocean water moves at a 90° angle from the direction of the surface wind. The direction of transport is dependent on the hemisphere: in the northern hemisphere , transport occurs at 90° clockwise from wind direction, while in the southern hemisphere it occurs at 90° anticlockwise. This phenomenon

1365-453: The water column, resulting in areas of downwelling. Ekman pumping has dramatic impacts on the surrounding environments. Downwelling, due to Ekman pumping, leads to nutrient poor waters, therefore reducing the biological productivity of the area. Additionally, it transports heat and dissolved oxygen vertically down the water column as warm oxygen rich surface water is being pumped towards the deep ocean water. Ekman pumping can be found along

1404-703: The water to diverge from the coast boundary, leading to Ekman suction. Additionally, there are areas of upwelling as a consequence of Ekman suction where the Polar Easterlies winds meet the Westerlies in the subpolar regions north of the subtropics, as well as where the Northeast Trade Winds meet the Southeast Trade Winds along the Equator. Similarly, due to the Coriolis effect the surface water moves 90° to

1443-446: The wind-driven portion of circulation seen in the surface layer. 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. 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

1482-429: The zonal and meridional mass transport terms with units of mass per unit time per unit length. Contrarily to common logic, north–south winds cause mass transport in the east–west direction. In order to understand the vertical velocity structure of the water column, equations 1 and 2 can be rewritten in terms of the vertical eddy viscosity term. where A z {\displaystyle A_{z}\,\!}

1521-626: Was first noted by Fridtjof Nansen , who recorded that ice transport appeared to occur at an angle to the wind direction during his Arctic expedition of the 1890s. Ekman transport has significant impacts on the biogeochemical properties of the world's oceans. This is because it leads 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. Ekman theory explains

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