Problem Set 7
Ocean 210, Autumn 2008
SOLUTIONS
1. Rotation and the Coriolis force on a spherical Earth
a. The coriolis force is not a real force, it is an ‘apparent’ force.
b. The coriolis force is caused because the earth is a rotating sphere. We study the
coriolis force because it causes the deflection of ocean currents and winds.
c. Counter-clockwise.
d. What is the Earth’s rotation frequency in s-1? The rotation rate is the number or
revolutions per second. So if the earth rotates once per day, the rotation rate is
!
f=1rotation
1day "1day
24hr "1hr
60min "1min
60sec
f=1.15 #10$5s$1
e. The equator or 0°.
f. The poles, 90°N or 90°S.
g. Because the rate of change of the circumference increases with increasing latitude,
with a minimum at the equator and a maximum at the poles.
h. It does not change because the earth’s radius does not change along lines of constant
longitude.
2. Rotation and the Coriolis force on non-spherical Planets
Now, imagine you are on each one of the crazy planets described below. These planets are
rotating too, just like the Earth.
• Planet One is a cylinder rotating at the same rate and in the same direction as the Earth,
and with a radius the same as the Earth.
i. There will be no local apparent force because the cylinders radius does not change
along its sides. However on top of the cylinder, the winds will be deflected to the
right because the radius does change!
ii. It will be at a maximum in the center of the top of the cylinder, where the radius is
changing. I will also accept there is no maximum if you only thought about the sides
of the cylinder.
iii. It will be zero on the sides of the cylinder or there is no minimum.
iv. The craziolis will not change with latitude.
• Planet Two is a cone. The radius of its equator is the same as the Earth’s radius and the
direction and rate of rotation are the same as on Earth (assume the point of the cone is
north)
i. The winds will be deflected towards the right.
ii. There is no minimum.
iii. There is no maximum.
iv. The Crazilolis effect will be the same over the entire cone because the rate of change
of the radius remains constant.
• Planet Three is shaped just like the Earth, the rotation rate magnitude is the same but
this crazy planet is rotating in the opposite direction.
