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 the upper 10-100m of the water column with it.
The Ekman spiral is a consequence of the coriolis effect. When the surface water moves by the wind, they drag the deeper layers with them. Each layer of water is moved by friction from the shallower layer and each deeper layer moves more slowly than the layer above it.
What causes Ekman divergence?
Coastal Upwelling
In the northern hemisphere, Ekman divergence occurs when the wind blows parallel to a coastline on its left. For example, during spring and summer the mean winds along the west coast of North America are southward. Associated with these winds is a net westward Ekman transport.
What is true Ekman transport?
Ekman transport is to the right of the wind direction in the Northern Hemisphere. The Coriolis effect causes surface waters to move at an angle relative to the wind direction.In the deeper layers of the Ekman spiral, water can move in a direction opposite of the wind direction.
What causes geostrophic flow?
geostrophic motion, fluid flow in a direction parallel to lines of equal pressure (isobars) in a rotating system, such as the Earth. Such flow is produced by the balance of the Coriolis force (q.v.; caused by the Earth’s rotation) and the pressure-gradient force.
How does Ekman transport cause upwelling?
Ekman transport and the Coriolis Effect make the coastal waters move, on average, 90 degrees to the wind. This means the water near the coast is being pushed west, away from the coast. This, in turn, pulls deep water up to the surface to replace the original surface water. Upwelling can also occur at the equator.
What is Ekman transport How does it establish Geostrophic gyres?
Driven by the long-term average winds in the subtropical highs, Ekman transport causes surface waters to move toward the central region of a subtropical gyre. This transport produces a broad mounding of water as high as 1 m (3 ft) above mean sea level near the center of the gyre (Figure 6.5).
What is Ekman transport quizlet?
Ekman transport: Net movement of water in right angle directions to the wind.
What is Ekman flow?
The Ekman spiral is a structure of currents or winds near a horizontal boundary in which the flow direction rotates as one moves away from the boundary. It derives its name from the Swedish oceanographer Vagn Walfrid Ekman.
What direction is Ekman transport?
The average water particle within the Ekman layer moves at an angle of 90° to the wind; this movement is to the right of the wind direction in the Northern Hemisphere and to its left in the Southern Hemisphere. This phenomenon is called Ekman transport, and its effects are widely observed in the oceans.
How does Ekman cause downwelling?
As wind blows along a coastline, Ekman transport moves the surface layer in a direction 90o to the wind.In any coastal upwelling location, if the winds reverse, surface water moves towards the shore and downwelling is the result. Upwelling can also occur due to geological features of the ocean floor.
How does Ekman transport affect the net transport direction of surface waters relative to wind direction?
The net transport of water through the entire wind-driven column (Ekman transport) is 90 degrees to the right of the wind. The Ekman spiral indicates that each moving layer is deflected to the right of the overlying layer’s movement; hence, the direction of water movement changes with increasing depth.
What is Ekman pumping?
The mechanism by which the effects of boundary layer momentum fluxes are communicated directly to the neighboring (essentially inviscid) fluid. The mechanism involves a forced secondary circulation referred to as Ekman pumping or Ekman suction, depending on its sign.
What are Ekman and geostrophic balances?
The Ekman transport piles up water in the center of the gyre, making the water level higher in the gyre center than on the edges of the gyres.This results in a clockwise current around the central “hill” called geostrophic flow , which moves in the same direction as the rotating gyre.
What factors drive ocean currents?
Oceanic currents are driven by three main factors:
- The rise and fall of the tides. Tides create a current in the oceans, which are strongest near the shore, and in bays and estuaries along the coast.
- Wind. Winds drive currents that are at or near the ocean’s surface.
- Thermohaline circulation.
How does Ekman transport cause upwelling and downwelling?
Coastal upwelling occurs where Ekman transport moves surface waters away from the coast; surface waters are replaced by water that wells up from below. Where Ekman transport moves surface waters toward the coast, the water piles up and sinks in the process known as downwelling.
What makes coastal upwellings and Downwellings occur?
A coastal upwelling and downwellings occurs when the wind blows offshore ore parallel to shore. Sometimes they occur when offshore wind creates a current that pushes the surface water out to sea.
Where does Ekman driven upwelling occur?
The Ekman transport divergence (upwelling) and convergence (downwelling) are represented by the wind stress curl of Figures 5.16d and S9. 3a through Eqs. (7.21) and (7.44). Downwelling regions fill the subtropics and upwelling regions occur in the northern North Atlantic and in the Southern Ocean south of about 50°S.
Which of the following two factors cause geostrophic circulation within a gyre?
Which of the following two factors cause geostrophic circulation within a gyre? temperature and pressure.
What causes the Coriolis effect?
Because the Earth rotates on its axis, circulating air is deflected toward the right in the Northern Hemisphere and toward the left in the Southern Hemisphere. This deflection is called the Coriolis effect.
What is the difference between the Ekman spiral and Ekman transport?
The impact of the Ekman Spiral is enhanced where geographic features create barriers to the movement of water. Ekman transport is the net motion of a fluid (seawater) as the result of a balance between the Coriolis effect and turbulent drag forces (within surface waters and geographic features (shoreline and seabed).
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