Problems with the Circulation Model
Problem #1: The Coriolis Effect
Rotation of the Earth deflects moving air or water away from initial . This is called the Coriolis Effect after Gaspard Gustave de Coriolis. Thus, objects above the Earth appear to be deflected because the Earth is moving beneath them. Magnitude of deflection due to:
- Distance from equator
- Velocity
The Earth spins at a steady rate, but the actual velocity of any point varies with latitude: more at the equator and less at the poles.
Why is the Earth spinning more at the equator and less at the poles? Imagine if you could cut the Earth in half at the equator. Now, imagine a line extending from the very center out to the edge. If you were to follow that line as the planet spun, you would see the outermost part of the line is moving faster than the innermost part. Watch the animated gif below to see this in action.
The Coriolis Effect affects the atmospheric circulation cells. The convection cells in the atmosphere still occur, but are deflected.
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To the right in the northern hemisphere →
To the left in the southern hemisphere ←
Problem #2: Earth’s axis is tilted ~23 ½º
Seasons occur due to variations in the amount of incoming solar energy as the Earth orbits around the sun. Currently, our planet's axis tilts approximately 23½º from the vertical, but it can range from 22.0° to 24½°
The direction of this tilt remains the same as our planet orbits the sun. What this means is that on the Winter (December) Solstice our axis is pointing away from the sun; at the Summer (June) Solstice it is pointing towards the sun (see image below). Thus, in the Winter Solstice, the northern hemisphere is tilted away from the sun, and therefore the incoming solar radiation is less direct, and the southern hemisphere is tilted towards the sun and therefore the incoming solar radiation is more direct. The opposite is true during the Summer Solstice.
The Earth's tilt also means that the amount of solar radiation - and therefore heating - varies with latitude and season. During the Winter Solstice the north pole receives no sunlight at all, and the number of hours of daylight increases until the south pole is reached, which has 24 hours of daylight. As the planet continues on it's orbit around the sun the number of hours of daylight changes (either more or less) until the Spring Equinox, where both hemispheres receive 12 hours of daylight. As Earth continues along it's orbit, the number of hours of daylight change again (increase or decrease) until the Summer Solstice, and the north pole now receives 24 hours of daylight and the hours of daylight decrease until the south pole, which is experiencing 24 hours of darkness.
The two cell circulation model is modified by the effects of the Coriolis Effect and the tilt of our axis. There are now 6 cells - three per hemisphere. These cells are the fourth way our planet moderates it's temperature: excess heat is moved out of the equatorial region and excess cold out of the polar caps.
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