Surface Circulation ch 7

How does Ekman transport change with depth relative to the driving wind force on the water surface?

Due to low friction the greater the depth away from wind driven surface the larger the angle of deflection will be

What is eckman tranport?

Ekman transport- the total volume of water in the Ekman layer transported at right angles to the wind direction. Over the depth of the spiral, the average flow of the water set in motion by the wind, or the net flow, moves 90° to the right (Northern Hemisphere) or left (Southern Hemisphere) of the surface wind. Ekman layer- the surface layer of water approximately 100-150 m (330-500 ft) thick in which there is wind-driven motion. Ekman Spiral- Wind-driven surface water sets the water immediately below it in motion. But because of low-friction coupling in the water, this next deeper layer moves more slowly than the surface layer and is deflected off the surface-layer direction. The same is true for the next layer down and the next. The result is a spiral in which each deeper layer moves more slowly and with a greater angle of deflection to the surface flow

How do the continents influence surface currents?

Land forms block currents from being able to be circumpolar. except for the southern flow is circumpolar. others have boundaries created by landforms.

Where would you have water moving in the opposite direction from the wind in Ekman transport? Why?

The spiral extends to a depth of approximately 100 to 150 m (330 to 500 ft), where the much-reduced current will be moving in the opposite direction to the surface current. Take average =125 m/180 degrees= .6944m/degree * (180-45on surface)= 93.75 m will oppose wind direction

What is the driving force for surface circulation?

Trade-Wind driven currents make water flow. Coriolis effect causes deflection from wind at 45 degrees

How is ekman Transport related to the Coriolis effect?

because of low-friction coupling in the water, this next deeper layer moves more slowly than the surface layer and is deflected off the surface-layer direction. The same is true for the next layer down and the next. The result is a spiral in which each deeper layer moves more slowly and with a greater angle of deflection to the surface flow This spiral would not occur without the Coriolis effect. Without this the currents would follow the exact direction of the wind. They would not deflect

What is geostrophic flow and what does it have to do with ocean gyres? How does gravity play into this?

geostrophic flow- horizontal flow of water occurring when there is a balance between gravitational forces and the Coriolis effect. (Gravity trying to make water flow down a hill balanced against the Coriolis effect) This lens will be focused on the western side. Water will travel faster and be deeper on the side of the lens closer to land its west side. This side always flow to the poles carries warmer water East side flows towards equator cooler water slow water. Ekman transport creats a gyrie where water is dircted into. This forms a raised lens in the center. The surface slope of the mound increases as deflected water moves inward until the outward pressure driving the water away from the gyre center equals the Coriolis effect, acting to deflect the moving water into the raised central moundAt this balance point, geostrophic flow is said to exist, and no further deflection of the moving water occurs. Instead, the currents flow smoothly around the gyre parallel to its elevation contours Geostrophic flow (V) exists around a gyre when Fc, the inward deflection force due to the Coriolis effect, is balanced by Fg, the outward-acting pressure force created by the elevated water and gravity.

How are surface and deep currents tracked? Be familiar with some of the tools used for this task.

two groups: (1) those that follow a parcel of the moving water and (2) those that measure the speed and direction of the water as it passes a fixed point. can do indirectly via radar altimetry(look for western rise) dopplar effect, pressure gradients 1) buoys, drift bottles, drouge, floats 2)current meters- include a rotor to measure speed and a vane to measure direction of flow

Where do you get upwelling and downwelling? Understand the processes for these both near the coast or away from the coast (like in an eddy or where you cross the equator). Why does it matter? (think about nutrients or ocean acidification or even climate)

upwelling (divergent zone- When surface currents move away from each other or away from a landmass, they produce a surface divergence) brings up low o2 nutrient rich water high bio productivity, downwelling (convergance zones- at the centers of the large oceanic gyres, and when wind-driven surface currents collide or are forced against landmasses) brings O2 rich water to deep ocean. In coastal areas where trade winds move the surface waters away from the western side of continents, upwelling occurs nearly continuously throughout the year. For example, the trade winds drive upwellings off the west coasts of Africa and South America that are very productive and yield large fish catches. Off the west coast of North America, downwelling and upwelling occur seasonally as the Northern Hemisphere temperate wind pattern changes from southerly in winter to northerly in summer. The downwelling and upwelling occur because of the change in direction of Ekman transport (fig. 7.33). Remember that the wind-driven Ekman transport moves at an angle of 90° to the right or left of the wind direction, depending on the hemisphere Areas of surface-water convergence and divergence occur in association with high- and low-pressure systems over the ocean. In the Northern Hemisphere, a low-pressure system produces cyclonic winds that rotate counterclockwise. These winds result in Ekman transport of water away from the center of the system, creating an area of surface divergence. This surface divergence produces upwelling of deep water (fig. 7.30a). High-pressure systems in the Northern Hemisphere produce anticyclonic winds that rotate clockwise. These winds drive Ekman transport of water toward the center of the system, creating an area of surface convergence. This surface convergence produces downwelling of surface water eddies spin of from a meander if spins in opposing direction from the Coriolis effect it will cause upwelling. if rotates in same direction will cause downwelling. There are five major zones of convergence: the tropical convergence at the equator and the two subtropical convergences at approximately 30° to 40°N and S. These convergences mark the centers of the large ocean gyres. The Arctic and Antarctic convergences are found at about 50°N and S. Surface convergence zones are regions of downwelling. These areas are low in nutrients and biological productivity. There are three major divergence zones: the two tropical divergences and the Antarctic divergence. Upwelling associated with divergences delivers nutrients to the surface waters to supply the food chains that support the anchovy and tropical tuna fisheries and the richly productive waters of Antarctica.