Earth Science: The Coriolis Effect and Global Wind Patterns
How Earth's rotation shapes winds and circulation cells
Earth Science: The Coriolis Effect and Global Wind Patterns
How Earth's rotation shapes winds and circulation cells
Earth Science - Grade 9-12
- 1
Explain why the Coriolis effect occurs on Earth. Include the role of Earth's rotation in your answer.
Think about how points near the equator travel farther in one day than points near the poles.
The Coriolis effect occurs because Earth rotates beneath moving air and water. As air travels over long distances, its path appears to curve relative to Earth's surface because different latitudes move at different speeds during rotation. - 2
State the direction that moving air is deflected by the Coriolis effect in the Northern Hemisphere and in the Southern Hemisphere.
Moving air is deflected to the right of its direction of motion in the Northern Hemisphere. Moving air is deflected to the left of its direction of motion in the Southern Hemisphere. - 3
A wind begins moving directly north from the equator into the Northern Hemisphere. Describe how its path will appear to curve and explain why.
In the Northern Hemisphere, the Coriolis deflection is always to the right of the moving object's path.
The wind will appear to curve toward the east, or to the right of its direction of motion. This happens because the air keeps some of its faster eastward motion from the equator as it moves into latitudes that rotate more slowly. - 4
Name the three main global wind belts in each hemisphere and give the approximate latitude range for each one.
The trade winds blow from about 0 degrees to 30 degrees latitude. The prevailing westerlies blow from about 30 degrees to 60 degrees latitude. The polar easterlies blow from about 60 degrees to 90 degrees latitude. - 5
The trade winds in the Northern Hemisphere generally blow from the northeast toward the southwest. Explain how pressure belts and the Coriolis effect combine to create this wind direction.
Wind is named for the direction it comes from, not the direction it travels toward.
Air moves from the subtropical high-pressure belt near 30 degrees latitude toward the equatorial low-pressure belt near 0 degrees latitude. In the Northern Hemisphere, the Coriolis effect deflects this southward-moving air to the right, producing winds that blow from the northeast toward the southwest. - 6
Complete this comparison: A low-pressure system in the Northern Hemisphere has surface winds that spiral in which direction, and why?
A low-pressure system in the Northern Hemisphere has surface winds that spiral counterclockwise and inward. Air moves inward toward lower pressure, and the Coriolis effect deflects that moving air to the right, creating the counterclockwise rotation. - 7
Why is the Coriolis effect weakest at the equator and strongest near the poles?
The amount of apparent turning depends on latitude.
The Coriolis effect is weakest at the equator because motion there is not strongly turned relative to Earth's axis of rotation. It becomes stronger toward the poles because the change in rotational motion with latitude has a greater effect on moving air and water. - 8
Describe the Hadley cell. Include where air rises, where it sinks, and how it helps form the trade winds.
In a Hadley cell, warm air rises near the equator where heating is strongest. The air moves poleward high in the atmosphere, cools, and sinks near 30 degrees latitude. Surface air then flows back toward the equator and is deflected by the Coriolis effect, forming the trade winds. - 9
At about 30 degrees latitude, many deserts are found, such as the Sahara and Australian deserts. Explain how global circulation contributes to dry conditions there.
Rising air usually cools and can form clouds, while sinking air usually warms and dries out.
Many deserts form near 30 degrees latitude because air sinks there in the descending branch of the Hadley cell. Sinking air warms and becomes drier, which reduces cloud formation and precipitation. - 10
Explain the difference between a wind's direction of movement and the name of the wind. Use the prevailing westerlies as an example.
A wind is named for the direction it comes from, not the direction it moves toward. The prevailing westerlies are called westerlies because they blow from the west toward the east. - 11
A weather balloon is released at 45 degrees north latitude and moves with the prevailing westerlies. In what general direction will it likely travel, and what global wind belt is affecting it?
Forty-five degrees north is in the mid-latitudes.
The balloon will likely travel generally from west to east. It is being affected by the prevailing westerlies, which dominate the mid-latitudes from about 30 degrees to 60 degrees north. - 12
Draw or describe a labeled model of global atmospheric circulation from the equator to the North Pole. Include the Hadley, Ferrel, and Polar cells, plus the major surface wind belts.
Use latitude lines at 0 degrees, 30 degrees north, 60 degrees north, and 90 degrees north to organize the model.
A correct model should show the Hadley cell from 0 degrees to 30 degrees north, the Ferrel cell from 30 degrees to 60 degrees north, and the Polar cell from 60 degrees to 90 degrees north. It should label the northeast trade winds from 30 degrees north toward the equator, the prevailing westerlies from 30 degrees to 60 degrees north, and the polar easterlies from 90 degrees to 60 degrees north.