Low Pressure System Rotation | Environmental Review
Rotation of Low Pressure Systems
In a rotating reference frame inertial motion is deflected to the right when the rotation is counterclockwise like the Northern Hemisphere when viewed from the North Pole.
Our reference frame here is the earth and the earth is rotating as you all know and so we live in what we call a rotating reference frame. That means inertial motion is going to be deflected to the right because the rotation is counterclockwise in the Northern Hemisphere.
If you view it from the North Pole you will see that the earth is moving counterclockwise. You can think about it in this way, right here we have the equator so we have air that’s being pushed up.
So, the air wants to go straight up, but the earth is rotating counterclockwise like that so what’s going to happen instead the air is going to go up like that because the air trying to move straight up but the earth is moving pulling the air to the right.
That’s why the motion is deflected to the right, so in this case we’re talking about a hurricane and in the middle of a hurricane is an eye. The eye of the hurricane is this area of low-pressure and in a low-pressure system there is less air present than normal.
Outside of this low-pressure system you have all this air with more pressure with more air so nature strives for equilibrium so this air wants to come in and balance out this low pressure and high pressure. This causes nearby air to rush in and fill the space.
That’s what the air is trying to do, rush in and fill the space. But this right here, of the arrow going to the right is what we call the Coriolis effect which is a fictitious force, which is a term we’ve come up to describe what happens when the earth spins, arises from a rotating reference frame.
What happens here, as the air tries to rush in it is deflected to the right, like I said right here. It’s not actually deflected but the Earth is spinning. That’s why I call the Coriolis force or the Coriolis effect a fictitious force because it doesn’t actually exist.
It’s just a term we’ve used to describe what’s going on. The air is staying in a straight path, but the Earth is just moving so as the air veers right it is pushed by other air masses that are also trying to move toward the center of the low-pressure area.
This causes all the air to spin in a circle counterclockwise. Now notice we’ve talked specifically about the Northern Hemisphere because the reason we specify that we are in the Northern Hemisphere is because everything I just told you is opposite in the Southern Hemisphere. The system is going to rotate clockwise. So that’s a look at the rotation of low pressure-systems.