mcarthurBy Claire

I know that Australia is commonly referred to as the land “down under”, but I personally prefer to think we’re on the top.

As you know, I have been in New York for the last week or so, beginning some work in palaeoclimate modelling for my PhD. I’m finally settling into life as a temporary American, but I find that things here are backwards. No, this isn’t a political commentary piece. I am talking about the atmosphere.

I’ve written a couple of posts before (here and here in case you’re interested), explaining how you could go about interpreting a mean sea level pressure chart to understand why the weather is the way it is. Well, one really important thing that I left out of those posts, is that those interpretations are only true if you live in the Southern Hemisphere. In the Northern Hemisphere, everything is backwards.

Deflection caused by the Coriolis Effect
Deflection caused by the Coriolis Effect

In the Southern Hemisphere, air moves around a high pressure system in an anticlockwise direction, and around a low pressure system in a clockwise direction. This is due to something known as the Coriolis Effect. Basically it’s a force that comes about from the rotation of the Earth.

Think of it this way. You’re standing at the North Pole and you throw a ball in a straight line towards the equator. The rotation of the Earth means that the ball doesn’t actually travel directly south, it is deflected to the right and travels in more of an arc shape.

The Coriolis Force is hugely important in determining the flow of air and water around the planet. If you look at a map of ocean or atmospheric circulation patters, you’ll notice that they’re essentially a mirror image of each other. This is because of the different Coriolis deflection in each hemisphere.

Simple atmospheric and oceanic circulation.
Simple atmospheric and oceanic circulation.

Now normally this wouldn’t be an issue, however, I came to the USA with the express intent of studying climate.

That means that I now have to start thinking backwards.