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THE GLOBAL WIND SYSTEM AND THE CURRENT SYSTEMS OF THE OCEAN
Transcript of THE GLOBAL WIND SYSTEM AND THE CURRENT SYSTEMS OF THE OCEAN
The action of the wind in creating ocean currents is the stress of wind blowing across the sea that cause the surface layer of water to move. This motion is transmitted to each succeeding layer below the surface, but due to internal friction within the water, the rate of motion decrease with depth. The current is called
EKMAN WIND CURRENT
. Although there are many variable, it is generally true that a steady wind for about 12 hours is needed to establish such a current.
A wind-driven current dose not flow in the direction of the wind being deflected by Coriolis force due to rotation of the earth. This deflection is toward the right in the northern hemisphere and toward the left in the southern hemisphere. The Coriolis force is greater in higher latitudes and is more effective in deep water. In general, the difference between wind direction and surface in current direction varies at about 15° along shallow coastal areas to maximum of 45° in deep oceans. As the motion is transmitted to successive deeper layers, the Coriolis force continues to deflect the current.At several hundred fathoms the current may flow in the opposite direction to the surface current. This shift of current directions with depth combined with the decrease in velocity with depth is called the Ekman spiral.
The speed of the current depends upon the speed of the wind, its constancy, the length of time it has blown, and other factors. In general, however, about two (2) percent of the wind speed or a little less is a good average for deep water where the wind has been blowing steadily for at least 12 hours.