Pressure is one of the most important aspects of the atmosphere. Actually, if all you knew, if all the data you had was say like pressure and temperature and maybe wind speed, you could still say a lot about what the weather was going to be like wherever you were. This is because pressure is such a huge driver for atmospheric motion.

I think one of the most intuitive ways to think about atmospheric pressure is to think of it as the weight of the air above you. So, if this is the Earth and this is the atmosphere and this is Timmy, and this is the air above Timmy, then the atmospheric pressure on Timmy right now is five, because I drew five dots. But if Timmy were to get up and climb a ladder then when he's higher up the pressure on Timmy here would only be two. There's less air above him so the pressure has gone down.

This silly little picture gives us a pretty intuitive understanding of why pressure decreases with height. The higher up you go, the less air there is above you, the less weight there is pressing down on your head.

For atmospheric stuff, we're going to measure pressure in either hecto-Pascal or millibar. Hecto-Pascal is written "h" "P" "a", millibar is "m" "b". They're actually about the same, and in either unit, surface pressure is about 1000 millibars or hecto-Pascal.

At the beginning of this video, I told ya'll that if all you knew about your location was the surface pressure and the temperature you could still say a lot about the weather. Well, that's because low surface pressure is generally associated with stormy weather and rain whereas high surface pressure is generally associated with sunny, clear skies.

Let's take a brief look at why that is and how pressure drives atmospheric motion. This blob I just drew? Think of it as like - it's a, it's a container that filled with a liquid. Honestly? I think of it as like a waterbed. Right now, as I've drawn it, the pressure on the surface of this water bed is pretty constant. The pressure there is about the same as it is over here.

But what would happen if I came in and I pressed down really hard on this side? So we're going to make this a region of high surface pressure. So you could imagine that this surface would sort of dip down, but then the rest of it has to go somewhere. The water that was there has to go somewhere. We would expect it to pop up over here.

So then this green line would be our new surface of our water bed. Ah! I broke my chalk. Notice that over here, we actually have moved up. So now, we would say that the pressure over here is higher than the pressure over here, so I have a low pressure, low surface pressure over here and in general, we had water move from high to low.

This is the same fundamental principle that happens in the atmosphere. We get, say, high pressure at one region for one reason or another and then that causes air on the surface to move away from that high-pressure region. We'll end up at a low-pressure region and eventually we'll start to have rising air.

One of the things we're going to talk a lot about in this series is how rising air is related to, like, clouds and storms and things like that. So, just by these variations in pressure, we get a lot of motion of the atmosphere, right, we're going to move from high to low pressure, and even going to cause air to start to move up, get that rising motion in the atmosphere.

One thing to keep in mind is that high surface pressure is associated with air going down, um, and low surface pressure is associated with air going up. So we have sinking motion over regions of high pressure and rising motion over regions of low pressure.

That pretty much covers the very basics of atmospheric pressure. It's a topic we're going to talk about a whole lot in this series. So don't worry there is more to come. More atmospheric pressure to come for all of ya'll. But for now, I think that gives you a good intuitive understanding of how pressure relates to like, air movement.