What is Ekman transport What is its role in wind driven circulation?

May 29, 2019 Off By idswater

What is Ekman transport What is its role in wind driven circulation?

Ekman transport is the net motion of fluid as the result of a balance between Coriolis and turbulent drag forces. In the picture above, the wind blowing North in the northern hemisphere creates a surface stress and a resulting Ekman spiral is found below it in the water column.

When the wind blows southward along the California coast which way does Ekman transport make the surface water move?

Coastal Upwelling Along the coast of California, the local prevailing winds blow towards the south. Ekman transport moves the surface layer 90o to the right of the wind, meaning the net Ekman transport is in an offshore direction.

What is surface wind stress?

In physical oceanography and fluid dynamics, the wind stress is the shear stress exerted by the wind on the surface of large bodies of water – such as oceans, seas, estuaries and lakes. Also, the wind stress can be described as the flux of horizontal momentum applied by the wind on the water surface.

How is wind stress calculated?

Since 1916, wind stress has traditionally been calculated from the product of air density, a drag coefficient, and the quantity wind speed squared [29]. Unlike wind density and speed, which are measurable quantities, the drag coefficient must be approximated as a function of speed, offering ample room for flexibility.

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 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.

What causes wind stress curl?

The water converges at the second location, pushing the water downward. This is how the curl of the wind stress (the northward wind changing in the east-west direction) is related to the water convergence (the eastward current changing in the east-west direction) and hence to water being pushed down or pulled up.

What does wind shear do?

Wind shear is often the most critical factor controlling hurricane formation and destruction. In general, wind shear refers to any change in wind speed or direction along a straight line.

What is the difference between the Ekman spiral and Ekman transport?

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.

How are the Coriolis effect and Ekman transport related?

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. This creates a spiral called the Ekman spiral.

What is the difference between Ekman transport and geostrophic flow?

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.

How are wind stress and Ekman mass tranport related?

Wind Stress and Ekman Mass Transports along CalCOFI Lines: 67,70 and 77 Introduction Wind driven currents from Ekman’s hypothesis can be explained as the frictional stress that balances Coriolis force with a resultant mass transport at right angles to the wind direction (1905).

How does Ekman transport work in the northern hemisphere?

where τ is the vector wind stress and k is the unit vector in the vertical direction. Therefore, in the Northern Hemisphere (f > 0), upwelling into the Ekman layer results from positive wind stress curl, and downwelling results from negative wind stress curl. Downwelling is referred to as Ekman pumping.

Where does ekmust balance the surface wind stress?

Ekmust balance the wind stress term: (units m2s-1) Hence the winds drive an Ekman transport that is directed at a right angle to the surface wind stress. It is directed to the right of the wind in the northern hemisphere and to the left of the wind in the southern hemisphere.

How is the Ekman layer related to the surface wind?

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.