Part 5 — Forces & Global Circulation

What is the Coriolis force?

An apparent force caused by Earth's rotation that deflects moving air.

Which way does Coriolis deflect moving air in the Northern Hemisphere?

To the right of its direction of motion.

Which way does Coriolis deflect moving air in the Southern Hemisphere?

To the left of its direction of motion.

Why is Coriolis deflection minimal near the Equator?

The Coriolis effect is zero at the Equator and increases toward the poles.

What is friction's effect on surface winds?

It slows wind, weakens Coriolis deflection, and allows wind to cross isobars toward low pressure.

What is centrifugal force?

An apparent outward force associated with motion along a curved path.

What is geostrophic balance?

Aloft, pressure gradient and Coriolis forces balance, producing flow parallel to isobars.

Which two forces create geostrophic balance?

Pressure gradient force and Coriolis force.

What is geostrophic wind?

Wind aloft flowing approximately parallel to straight isobars when PGF and Coriolis balance.

Why are winds faster where isobars are closer together?

A stronger pressure gradient produces a stronger pressure gradient force.

How do surface winds circulate around a low in the Northern Hemisphere?

Counterclockwise and inward toward the low.

How do surface winds circulate around a high in the Northern Hemisphere?

Clockwise and outward away from the high.

Why do surface winds cross isobars?

Friction weakens Coriolis balance, allowing wind to move toward lower pressure.

What is a sea breeze?

Daytime wind from cooler water toward warmer land at the surface.

Why does a sea breeze form during the day?

Land heats faster; warm air rises over land and cooler marine air moves inland.

What is a land breeze?

Nighttime wind from cooler land toward relatively warmer water at the surface.

Why does a land breeze form at night?

Land cools faster than water; relatively warmer air rises over water and surface air flows offshore.

What is Hadley's single-cell model?

A simplified model with air rising at the Equator and sinking at the poles.

What is one shortcoming of Hadley's single-cell model?

It cannot explain midlatitude westerlies.

What are the three cells in the multicell model?

Hadley, Ferrel, and Polar cells.