GEO1030 Fall 2005
Exercises wind-driven ocean currents.
1. What forces are acting on the ocean in order to produce the Ekman spiral? How do
these forces vary with depth?
2. An ice-sheet moves in the x-direction with speed 1 m/s over a 100 m deep ocean (see
figure).
a) What is the final velocity distribution in the water beneath the ice if the only force
acting is frictional force (i. e. disregard the Coriolis force)?
b) How large is the total transport (per unit width) underneath the ice?
c) How does the flow change if it is affected by Earth’s rotation?
3. What direction will the Ekman transport have if it is induced by a wind that blows
a) Northward in the Northern Hemisphere
b) Southward in the Southern Hemisphere
c) Westward in the Southern Hemisphere
d) Southward in the Northern Hemisphere
4. The wind-stress τ W (N/m2) induced by a wind blowing at speed U m/s can be
calculated from the formula
τ W = 1 ⋅ 10 −3 U 2 N/m2
Using this, how large is the Ekman transport induced by a wind blowing at 5 m/s if the
Coriolis parameter is 1 ⋅ 10 −4 s-1?
GEO1030 Fall 2005
5. The wind is blowing northwards, parallel to a coast (see sketch below). The wind stress
is 0.1 kg/m/s2 and the Coriolis parameter 1.1·10-4 s-1.
a) How much water (in kg/s/m) is down-welled next to the coast?
b) How many m3 per second is this in total, if the coast is 500 km long?
c) If the down-welling takes place in a 20 km wide belt next to the coast, what is the
average downward velocity in this region?
d) If the sea is 30 m deep next to the coast, how long does it take to replace all the
water in the down-welling zone?