Planetary Weather Systems Part I: The Coriolis Effect

Okay. I have to start here with a confession. I’m not perfect! There, I said it. I leapt into giving our world weather systems and geographical zones without keeping one very important thing in mind. The very nature of a rotating ball of rock, magma, and water sets certain rules that weather systems go by. Let’s take a look at some of the things I have to consider before I redo the previous article with a better scientific approach.

The Earth is a great big spinning ball of stuff--I know, not a very scientific explanation, but it’s good enough for my purposes as this point. Any object that spins is subject to a collection of forces. One of these is called the Coriolis Effect or Coriolis Force, and is responsible for a number of any planet’s weather patterns. What you’ll find here is a breakdown of some of the simpler aspects that all fall into place with this force.

When a circle rotates, each individual little bit of the surface is moving in its own direction at its own speed. I’ve done my best to illustrate this in the associated figure as seen from above the circle.

Now we have to make the leap into three dimensions. Picture a ball, globe, orange, or whatever you need to in order to follow this. Now chop that object into a bunch of very thin slices and stack them back up in the same shape. You still have a ball. The point I’m trying to illustrate here is that a ball is just a huge stack of circles. Some are wider than others, and together they all make a three-dimensional object when stacked from top to bottom. At any point on the surface of this ball as it rotates, that point has an almost unique direction and speed. I say almost because the ball is identical whether you’re looking from the top to its centerline, or from the bottom to its centerline. It’s symmetrical. So, each point is going to have a twin in the other hemisphere that’s going the exact same direction and speed.

If you’re standing on the edge of a spinning circle or sphere, you are moving at the same speed and direction as the point you’re standing on. It’s always odd to think that you’re moving even when you’re standing still since the Earth is rotating, but there you go. The Coriolis Effect comes into place when you’re on the rotating object and, say, throw something. It’s called an Effect more than a Force because, really, it’s not really a force. It’s just an explanation for something that looks very strange from certain points of view. The associated image illustrates a rotating circle from overhead, and from the side. The dot and the square on the left match the head shapes on the right.

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