Assignment 4 Section B (15 points) updated 12 PM 10/27/06
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Deadline: Tuesday, October 31, 2006 11 PM
Ekman transport is a short-term, transient response of the upper ocean to a change in wind speed and/or direction. Ekman transport is not an equilibrium condition, however. After several days or longer of a particular wind pattern, the effects of Ekman processes in the upper ocean begin creating geostrophic currents, which are a long-term equilibrium response to cumulative wind acting over periods of weeks or months.
The following questions concern the processes that act on the water carrying a drift bottle in the North Atlantic Ocean. Suppose that the ocean and wind are motionless and the sea surface is flat, and that then, prevailing winds (Figure 1) suddenly begin blowing.
In the table below, fill in the blanks (0.5 pts. ea.) to indicate the direction of the processes acting to produce Ekman transport. Be sure to note the distinction between the compass direction (north, south, etc.) and the clock direction (clockwise, counterclockwise) of a force or motion. Also keep in mind that winds are identified by the direction from which they blow, while currents are identified by the direction toward which they flow.
1. Compass direction from which the wind blows at 50˚ N From the ___Now suppose that the prevailing winds have been blowing steadily for weeks or months. Changes in the upper ocean cause Ekman transport to shift toward geostrophic flow. In the table below, fill in the blanks (0.5 pts. ea.) to indicate the direction of the processes acting to produce an equilibrium called geostrophic current. Be sure to distinguish between the compass direction (north, south, etc.) and the clock direction (clockwise, counterclockwise) of a force or motion.
2. Compass direction of surface current (Ekman) at 50˚ N Toward the ___
3. Compass direction of Ekman transport at 50˚ N Toward the ___
4. Compass direction from which the wind blows at 10˚ N From the ___
5. Compass direction of surface current (Ekman) at 10˚ N Toward the ___
6. Compass direction of Ekman transport at 10˚ N Toward the ___
7. Compass direction of resulting sea surface slope at 10˚ N Rising toward _____
8. Compass direction of resulting sea surface pressure gradient at 10˚ N Toward the ___
9. Name of resulting geostrophic current at 10˚ N
10. Compass direction of resulting geostrophic current at 10˚ N Toward the ___
11. Compass direction of coriolis effect acting on geostrophic current at 10˚ N Toward the ___
12. Clock direction of currents in gyre (circle one) at 10˚ N Clockwise/counterclockwise
13. Compass direction of resulting sea surface slope at 50˚ N Rising toward the ___
14. Compass direction of resulting sea surface pressure gradient at 50˚ N Toward the ___
15. Name of resulting geostrophic current at 50˚ N
16. Compass direction of resulting geostrophic current at 50˚ N Toward the ___
17. Compass direction of coriolis effect acting on geostrophic current at 50˚ N Toward the ___
18. Clock direction of currents in gyre (circle one) at 50˚ N Clockwise/counterclockwise
Fig. 2 is illustrated with several types of arrows indicating processes affecting winds.
19. (0.5 pts.) Which type of arrow indicates the direction in which pressure gradient force tends to push air?
20. (0.5 pts.) Assume that air starting at rest begins to move in response to pressure. Which type of arrow indicates the direction in which the Coriolis effect tends to make these winds turn as the air begins to move?
21. (0.5 pts.) Which type of arrow indicates the direction that the resulting winds flow around this low?
22. (0.5 pts.) Is the clock sense of this flow clockwise or counterclockwise?
23. (0.25 pts.) Which type of arrow indicates the direction that the coriolis effect acts on these final resulting (geostrophic) winds?
Figure 3 depicts a coastline in the North Atlantic Ocean. The gray arrow indicates the geostrophic wind direction. From this information, you can determine the distribution of atmospheric pressure and the season.
24. (0.5 pts.) Where is the pressure high, over the land or the ocean?
25. (0.75 pts.) How do you know?
26. (0.5 pts.) What season is it, summer or winter?
27. (0.75 pts.) How do you know?