Questions and Answers at end of notes for Topic 3A
1. Show how the circulation pattern of the winds between 0-30º, 30-60º and 60-90º would
change if the earth’s direction of rotation was reversed (clockwise looking down at the north
pole). Hint: what happens to the Coriolis Force?
a. In the Northern Hemisphere, the Trades Winds (0º to 30º) would blow from the
northwest to southeast, the “Westerlies” (30º to 60º) would blow from the southeast to
northwest and “Polar Easterlies” (60º to 90º) would blow from northwest to southeast. In
the Southern Hemisphere, the Trades Winds would blow from the southwest to northeast,
the “Westerlies” would blow from the northeast to southwest and “Polar Easterlies”
would blow from southwest to northeast.
2. What would be CF effects on a cylindrical shaped rotating earth?
There would be no Coriolis force on the sides of a cylindrical earth, because the radius of
rotation would equal for all latitudes. However, on the top and bottom of the cylinder,
there would be a Coriolis Force, as there is on a merry-go-round, because the rotational
speed decreases toward the center.
3. Explain why the earth isn’t heating up in the tropics and cooling at the poles given the
surface heat flux distribution shown in Fig. 15.
Winds and ocean currents transport heat away from the tropics and towards the poles.
This oceanic and atmospheric heat transport exactly offsets the excess heat input in the
tropics and the heat deficit in the polar latitudes.
4. Can you explain why the Coriolis effect increases with increasing latitude (poleward)?
(Hint: picture how the circumference of the latitude lines changes with latitude. Where is
the change rate the greatest and least?)
The Coriolis effect increases with increasing latitude (poleward in both hemispheres)
because the rate of change of the earth’s radius of rotation increases with increasing
latitude (poleward). That is, there is a greater change in the earth’s radius of rotation per
degree of latitude (i.e., Δradius/Δlatitude) near the poles than near the equator. This
means that there is a greatest change in the rotational speed per degree of latitude near the
poles and the least change near the equator. Looking at Fig. 10 you can see that the
change in rotational speed between 60ºN and 90ºN is 800 km/hr, whereas between 0º and
30ºN the change in rotational speed is only 200 km/hr. Thus the Coriolis effect increases
poleward.
5. What two effects cause the observed wind directions on earth (Fig. 12) to deviate from
the idealized (water covered earth) wind patterns (Fig. 7)?
First, unequal heating rate of continents and ocean. Since the oceans heat capacity is
much greater than the continents, the seasonal air temperature changes are greater for air
masses over continents than over the ocean. Thus in summer, air over continents is
warmer, thus less dense and air pressure is lower than for air masses over the ocean. In
winter, air over continents is colder, thus more dense and air pressure is higher than for
air masses over the ocean. (See the seasonal changes in the position of lows and highs in
Fig. 12).
Second, mountain chains (e.g Rockies, Andes, Himalayas) act as barriers to air motion
and thus deflect winds.