Earth's weather, and in fact the weather of all the studied planets, amounts to a planetary wide thermal exchange. It is this exchange that results in the wind and ocean currents, and to understand the how the spin of the earth impacts these currents, which in turn drives the weather patterns, we need to look a little deeper into the heat transfer that is occurring at all times.

Most of us were taught long ago that hot air rises and cold air sinks. The reason for this is that as gases or fluids become warmer, the atoms and molecules in them become more energetic. This means that they take up a greater volume, and in the process they become less dense. The less dense the air is, the less hold gravity has on the atoms and molecules, so they rise. The opposite reasoning occurs with air that cools, sinking low as it does.

Because of the tilt of Earth, the area around the equator receives more sunlight, and the sun's rays strike the ground more directly than they do at the poles. This causes the Polar Regions to be colder than the equatorial regions. Air over the equator rises. In turn, this creates a low-pressure area, and air must flow into the area just vacated by the hotter air. Colder air is perfect for this, since it is denser and already closer to the ground.

As the air over the poles is the coldest and densest, air heats at the equator and flows toward the poles at higher altitude while air from the poles cools, sinks and flows toward the equator in a perpetual motion oval. As the air at the poles cools back down, it sinks, ready to make the trip again, to be heated up at the equator.

Clouds, and ultimately storms, are formed as water evaporates while the air is heating up, and the circulation just described distributes the cloud cover all over the globe. If the earth were stationary, the only breaks in the cycle would occur when cold air was forced over and around obstacles. In fact, this does happen and is what produces the hot dry winds such as the Santa Anna winds of Southern California in the US and the Sirocco wind of the Mediterranean and Sahara.

Still, an earth that was not spinning would allow for a roughly oval airflow from the equator to the poles and back again, discounting mountains and other obstacles. The earth is not stationary, though. It revolves one time in just a little over 24 hours. The speed of revolution is greater than the speed of the heat transfer, so instead of air moving north-south-north, it moves northwest toward

• 1
• 2
• next page >>

---

Add your voice

Know something about How the Earth's spin affects weather?
We want to hear your view. Write now!