Air flows northward toward a low-pressure center in the Northern Hemisphere. The Coriolis force deflects it:
ATo the left (westward), causing clockwise hurricane rotation
BTo the right (eastward), contributing to counter-clockwise hurricane rotation
CDownward, toward the Earth's surface
DIt has no effect on air flowing exactly northward
In the Northern Hemisphere, the Coriolis force deflects ALL moving objects to their right. Northward-moving air is deflected rightward (eastward). When air flows inward from all directions toward a low-pressure center, consistent rightward deflection produces counter-clockwise circulation. Option A gives the Southern Hemisphere result.
Question 2 Multiple Choice
Why do tropical cyclones never form right at the equator?
AOcean surface temperature at the equator is too low to generate the needed energy
BThe vertical component of Earth's angular velocity ω is zero at the equator, so there is no horizontal Coriolis deflection
CTrade winds blow too strongly at the equator to permit organized rotation
DThe Coriolis force is strongest at the equator, producing chaotic rather than organized flow
The Coriolis acceleration for horizontal motion is 2ωv sinφ, where φ is latitude. At the equator (φ = 0°), sinφ = 0 and horizontal Coriolis deflection vanishes. Without deflection, inflowing air cannot develop organized rotation. Cyclones require a minimum latitude (roughly 5°) for sufficient Coriolis effect.
Question 3 True / False
The Coriolis force is a real physical force that acts on objects moving in any reference frame, not just rotating ones.
TTrue
FFalse
Answer: False
The Coriolis force is a fictitious (inertial) force that appears only when motion is analyzed in a rotating reference frame. In an inertial frame, no Coriolis force acts — the 'deflection' is simply inertial straight-line motion viewed from a rotating frame. Fictitious forces are real in their effects within rotating frames but have no physical cause independent of the choice of frame.
Question 4 True / False
The Coriolis effect deflects moving objects in the Southern Hemisphere to the left of their direction of motion.
TTrue
FFalse
Answer: True
This follows from F = −2m(ω×v). In the Southern Hemisphere, the local vertical component of ω points downward (opposite to the Northern Hemisphere), reversing the deflection direction. Moving objects are deflected to their left, which is why Southern Hemisphere cyclones rotate clockwise as inflowing air is deflected leftward from all directions.
Question 5 Short Answer
Explain why Coriolis deflection causes hurricanes to rotate counter-clockwise in the Northern Hemisphere — trace the deflection of air flowing inward from different directions rather than just citing the rule.
Think about your answer, then reveal below.
Model answer: Air flows inward from all directions. Northward-moving air (from the south) is deflected right = eastward. Southward-moving air (from the north) is deflected right = westward. Eastward-moving air (from the west) is deflected right = southward. Westward-moving air (from the east) is deflected right = northward. Each inflow direction gets a rightward push that consistently contributes to counter-clockwise rotation around the center.
The CCW rotation is the cumulative result of independent rightward deflections from every compass direction of inflow. In the Southern Hemisphere, leftward deflection from all directions produces clockwise rotation by the same logic. The pattern emerges from the geometry of right-deflection applied symmetrically around a central low.