# On the Coriolis effect and weather

I learned in classical mechanics that the Coriolis Effect curves everything with speed to the right in the northern hemisphere and to the left in the southern hemisphere, my question is then why storms rotate counterclockwise in the northern hemisphere as opposed to clockwise as their bending to the right would indicate.

The image is one I created some years ago. It's also on wikipedia, uploaded by me.
Red arrows: coriolis effect
Grey: flowing air mass

The formation of cyclonic flow, simplified to the barest essentials, is something of a dance of two effects. The image is for formation of flow around a low pressure area, northern hemisphere. The blue arrows represent pressure gradient force, the red arrows represent the coriolis effect.

If you have a low pressure area you have of course that the surrounding air mass has a tendency to flow towards lowest pressure, just flowing down the pressure gradient. The Coriolis effect tends to bend that flow to the right. The flow is coming in from all directions, and all those flows together shepherd each other into a flow pattern around the low pressure area. In the diagram the inward blue arrows around the circle are a bit longer than the red arrows representing the coriolis effect.

So: for the flow pattern of cyclonic flow we have that the coriolis effect is away from the area of lowest pressure. The pressure gradient force is stronger, and thus the actual cyclonic flow bends to the left.

The interplay of pressure gradient force continues for as long as the cyclonic flow lasts.
Friction drains kinetic energy from the cyclonic flow, so the overall flow distribution tends to contract. That contraction is an inward motion. The coriolis effect tends to bend that inward motion back to flowing around motion. That is why a low pressure area can last for weeks. The interplay of pressure gradient force and coriolis effect tends to sustain the flowing around motion.

It's easy to think of something spinning clockwise as spinning "to the right", but that's not the case - the bottom half of something spinning clockwise is moving to the left! To get a better idea of how this works, put a round object like a plate on a table. Move your finger toward the center of the plate, but deflect it to the right like the Coriolis force does. You'll see that this introduces a counterclockwise rotation to the plate.

• well yes but the air particles are deflected to the right as the earth is spinning counterclockwise in the northern hemisphere and the air particles are the one's making up the storm so shouldn't the storm be going clockwise as the air particles are constantly going to the right? (I probably am just not seeing something sorry)
– nemo
Commented Aug 16, 2019 at 17:49

I think I got it I didn't count for the fact that the air particles move from high pressure gradients to low pressure as low pressure gradients have the form of circles molecules from all approaching sides move to the right inwards and thus create a counterclockwise storm.