Module 6 Atmospheric Circulation

Well, we're going to have some pretty interesting stuff. We're going to talk about, uh, it's probably one of the only lectures I'll talk about climate, uh, because, of course, you know, all the stuff that we deal with as pilots is weather-related. Um, you know, kind of here and now, we're going to fly today or, you know, within a week or so, and so that's that's all still weather. Um, but the cool thing is, is as you, when you start to, hopefully, when you see how the air circulation works globally, uh, and then you see where climates are, uh, on on Earth, uh, it's, you know, some of that stuff starts to make sense. You're like, oh, that's that's why that's there, you know, like a desert or something. So we'll talk about that and how that works. And, uh, just keep in mind, of course, as you know, we do talk a little bit about climate, um, the whole point, uh, of that is, I'll use the desert as an example. So if you're going to fly into a desert region, that for the most part, the desert is going to, well, have weather that's consistent with a desert, right? But we all know that, uh, Mother Nature comes in and does her own thing, and, uh, you know, there's wet seasons in the desert areas and all that kind of stuff. So, uh, you can have different types of weather within climates. Um, but for the most part, overall, when you talk about climates, there'll be certain parts of the world, um, where you'll get a consistent type of weather or overall. So we'll get into that a little bit later. Um, has nothing to do with like climate change or anything. It has to do with actual climate in and of itself. So you guys can have that discussion later if you'd like. But, uh, in atmospheric circulation, we need to know more of a bigger picture of, uh, what the atmosphere is doing relative to specific regions, not only around the world but the kind of weather that we can anticipate. And, uh, so we'll be talking about, uh, come on, there we go. Uh, we'll be talking about a few things. So I just mentioned climate, of course. Uh, we talk about winds. Now, we talked about pressure gradients and stuff, um, but, uh, we'll include that when it comes to directions and all that kind of stuff. Uh, the Coriolis effect will be, you'll be able to see it a little bit better on a bigger scale, uh, even though we know that it happens at a very small scale by, you know, those little pools as they demonstrated what the Coriolis effect was, um, but in this case, we're looking at kind of bigger stuff, right? Um, and keep in mind when I mentioned conduction and convection, um, that the air circulation around the globe, uh, not only goes from north to south, south to north, but it also goes up and down, right? So convection is a big deal. So we'll start off the conversation with that. Um, but we will be talking about global air masses, what those are, where those are located, what you can anticipate as far as weather and stuff is concerned, uh, as those, as those masses start to move, create fronts, and all that kind of stuff, so the weather is associated with it. And then we'll see a little bit about charting, even though the second half of the semester is more about kind of looking at charting, um, but we'll get exposed to it today because the whole idea is for me to build on some of these concepts so you'll feel comfortable with them by the end of the semester.

Convection currents, we'll start off with those, uh, as we look at this picture, uh, which is kind of nice. Any of you guys been down to like Huntington Beach, uh, having a bonfire of some kind? Uh, those are always a lot of fun. And, uh, of course, all you're doing is roasting marshmallows, right? So, uh, other things like if you go camping or whatever, um, you know, where you have a big fire on a cool night, uh, it's kind of neat. So, but the nice thing about this example is you can describe a convection current real well, uh, or really well, uh, with this example. So let's say all of you guys showed up and, uh, you brought your lawn chairs and whatever else you wanted to bring to the bonfire. In addition, everybody brought some wood, right? So you pile up the wood in the area that you want to have your bonfire. Of course, beach, there are pits. Don't, don't make sure you don't have fires outside of that. They, they frown on it. Um, but you pile on the wood and you're ready to go. And, uh, of course, somebody wants to start the fire faster than anybody else, so they throw like some kind of fuel on the fire to get it going. That's okay because it's good for the example. So before you start the fire, you know, you notice the atmosphere is kind of like in equilibrium, right? It's, it's not really doing much except for maybe a little breeze or whatever the case may be. Um, but then you light the fire. So they throw a match on it, big fire, uh, and all sorts of stuff starts happening. Of course, you can't see it necessarily, but you can feel it. So next time you guys go to a bonfire, start to think about what's happening around you as far as the atmosphere. I'm sure that's all you'll be thinking about. And, um, but because of the fire that's at the base, uh, all that heat that's generated, of course, we know that it's going to warm up the air that's just above it. And, of course, we know warm air rises. So as that warm air rises and continues to go up, of course, it's going to cool off and then eventually cycle its way back down. Now, the difference is, is as the air at the base of the fire starts to go up, something needs to fill that back in. Kind of like that example I used with a bucket at the end of a pier. You pull a bucket up full of water, and then, of course, the water just fills right back in due to that pressure. So the same thing happens because air and water work on fluidics, which are the same concepts. So when the air goes up, it creates a very low pressure area, and then, of course, the heavier, denser, cooler air starts to refill, uh, that void that was created because of the fire. So you put that all together, you have the rising air coming up, you have the cooler air coming in, and all of a sudden, you start to get this, this circulatory pattern. So as the circulatory pattern starts to happen, you get a number of different things. You physically start to feel some of that, uh, heat that's coming off of the bonfire itself. So that radiant heat, you'll also, if you guys are sitting down in your chairs or just standing around, you'll notice that not only do you feel the warmth of the radiant heat against yourself, but you'll also notice that, uh, your back or, you know, your back that's, uh, towards the heavier, denser, cooler air, as that starts to move forward to fill that void from the fire, you notice, of course, it gets very cool. Of course, in the evening, most likely you're going to have, uh, you know, put a blanket on or jacket or whatever, and it's because of this convective current, uh, that's continuing to go on as long as that fire is going, um, which is, it's just kind of neat. So, hope of that explains very simply, uh, what a convective current is. And remember, it's the vertical part or portion of the, uh, the example that I'd like you to remember because there's that vertical motion of air in addition to, uh, kind of that north-south, uh, movement of the air.

And we'll go ahead and take a look at that, um, in there we go. So in general circulation, the interesting part about this is in this example, in this picture, uh, you see the world or the globe. You see a line for the equator, and the reason why we want to point out the equator is because that's where the sun heats the Earth the most during the day. So because of that, it's just like the fire. It creates a lot of heat, and of course, that air travels upwards. You can see it doing that, uh, in this example, as it goes upwards in the atmosphere. Just like the fire, it's going to cool and start moving. Well, in this case, it's going to move towards the poles. So as it starts to move towards the poles and gets cooler and denser, the air that was already at the poles starts to move down to fill that void created by all the heat at the equator. Now, of course, this is like an option or, you know, like an optimal kind of picture, right? Uh, it's, it would be great to a certain extent because weather would never change and everything would be the same, same. And of course, we like to mix it up here on Earth. So we go ahead and start spinning that little ball, uh, around about a thousand miles an hour at the equator. And because of that and that little tilt of 23 and a half degrees, we start to get a different, there we go, we get a broken-up, uh, uh, set of cells, uh, as that one big cell gets broken up into three, uh, because of a variety of different forces. As the world turns, which I think that's a daytime like show, isn't it? They even have those things anymore. So anyway, so in this picture, we have the northern atmosphere or atmosphere, we have the Northern Hemisphere and the Southern Hemisphere, and, uh, they're essentially mirror images of each other. And I'm sure you've seen those on the videos we've seen already. Um, so we really don't have to kind of talk about it twice. We'll just do that once, spare yourself. So, uh, just remember, of course, that they are mirror images of them. And when we talk about like the Coriolis effect, where it goes to the right in our case, uh, in the Northern Hemisphere, it goes to the left, uh, in the Southern Hemisphere. So, uh, what happens to that general circulation pattern or the convective current that goes from the north to the south, uh, or the south to the north, either way, uh, is it breaks up into these three different cells. The three different cells, as you can see, are named Hadley, Ferrel, and Polar, um, on both sides, uh, of of the Northern and Southern Hemisphere. Now, when they found out, uh, about these three different cells, the interesting part about them is is learning about their circulation patterns. So when you look at this convective current, the three different ones, you'll notice that the Hadley cell, that's down towards the equator, and the Polar cell, which is way up at the poles, are all rotating, or both of those are rotating in the same direction, okay? So the Ferrel cell, which is kind of stuck in between, ends up going in the opposite direction. I'll show you a little GIF here in a minute that that gives you a better visual of what's what's happening, but it does turn in the opposite direction. Now, we talked about the Coriolis effect, and the Coriolis effect, when we experience that, uh, it's on the surface, okay? So the red lines that are down at the bottom of all those cells, visualize in the case of the Northern Hemisphere, the arrow that's pointing up or down is going to curve off to the right. So, of course, the Ferrel cell, if you kind of spin the globe a little bit, you'll see that the United States is kind of right underneath the Ferrel cell, and that arrow that's traveling north curves to the right. And what that means to us is that our weather patterns, like fronts and storms and stuff like that, like the one we just had, um, will move from the west coast to the east coast because of the Coriolis effect, as as the world turns, so to say. So, uh, keep that in mind.

Now, of the three, uh, of the three cells, uh, looking at the equator, at the two Hadley cells that are right next to each other, that's kind of like the bonfire. So because of that, there's a tremendous amount of energy that's going from the heated portions of the surface up towards the atmosphere. You get a lot of thunderstorms, a lot of weather in this area. We'll show that as it, as it relates to climate here in a second, but remember that, uh, anytime you have some of these cells that are both pushing upwards, remember that it creates a very low pressure area, right? Low pressure areas means air travels up, and in high pressure areas, of course, air travels downward. So you see a low pressure area at the equator, a low pressure area between the polar and the Ferrel cell because of course those are also going upwards, and then, of course, you have that descending, sinking air that's in between the Ferrel and the Hadley cell, which creates a more high pressure area, okay? So because this is meteorology and there are three different cells, you'll probably need to remember that for something coming up right around the middle of the semester, right? And so, uh, in order to remember those, I put a little mnemonic together to hopefully help you remember, you know, what these words are. So Polar cell, I attach the word "pretty," um, not because it's pretty, but because it begins with P, will make sense in a minute. The Ferrel cell, of course, I'm trying to keep it clean here, and we'll use the word "forlorn," um, which works out really well. I picked that up from a sitcom that was on TV. It's a great way to fake that word. And then the last one, of course, is "hot" due to all the heat that is generated at the equator making everything go up. So the whole idea for you is to remember the names and also to understand a little bit more about, uh, global circulation as it starts to to move air not only in the in the particular area that it's in, but also as we'll see, there's ways for the air to travel from the equator all the way up to the poles and vice versa to come back down, that skips over, uh, the top of these three main circulatory areas. But the three main circulatory areas, of course, we'll show you. Here's the GIF that kind of shows you how the the, uh, the cells work, uh, with each other, uh, to get, you know, those cells to rotate around each other, which is kind of neat. Uh, so that one's pretty basic, right? Um, but because of this, as we, as we mentioned earlier, we talked about the high pressure areas and the low pressure areas. So here's another picture, just a little bit more colorful, and you can see that the low pressure areas at the equator where there's a lot of weather. What is under climate-wise, uh, these areas? Well, if you look closely, you can see that there are tropical rainforests right underneath this, which is good, you know, it's a good thing. Um, underneath the higher pressure areas are where all the deserts are located. So as you start to rotate the globe, if you have one at home, those used to be a thing probably before I was born, but, you know, they still exist, is if you spin them around, you realize all the deserts are located right around that area in between these two cells, right? So you have like the Arabian, Gobi, I wrote a couple of them down, Sahara, Kalahari are examples, uh, of some of the desert regions that are underneath these two large cells. Now, of course, at the top, you also have between the Polar cell and the Ferrel cell, uh, more, of course, low pressure areas, which create, think like, like Oregon, Seattle, Canada, uh, or where you start to get more of those, you know, heavily deciduous pines, you know, green areas up north where there's a lot more rain compared to where we are, where it's kind of deserty right now. Uh, of course, this, this picture also will show you the sun itself and it's kind of its angle of incidence. So it's as it's hitting the, uh, the equator, you see it's at 0 degrees, uh, where, of course, it gets the most, and then, of course, it goes, as it goes up, you'll notice that the deflection is a little bit more, therefore it doesn't get a, you know, direct hit. And of course, that's why you have big differences. So that is also a driver of the differences between the different cells is how much energy it gets from the sun that creates that, that circulatory pattern.

Let's take a look at the, uh, Intertropical Convergence Zone. So I think earlier this semester, someone had asked about international flying. This is one of the issues that you have to deal with when you're flying some of the bigger aircraft and you have to go through this area because, of course, because there's a lot of heat generated, some of these thunderstorms can get quite large, and of course, you want to make sure that you, you stay away from them. Um, interesting, one of the big accidents that happened, um, where an Airbus went down in the Atlantic, it was because of this, uh, Intertropical Convergence Zone because of not only the weather, the thunderstorms that they were flying around, but also it created like, uh, those, those, uh, wind storms in the, uh, like they call them haboobs or shukos, where they had these huge storms creating a bunch of dust, and that dust came off of, I think it was Africa, and then it came because there were thunderstorms, it drew that dust up into the thunderstorm and eventually created little crystals that didn't melt as quick, uh, and blocked all the pitot tubes of an Airbus A380, and it went down. I, it was A380, pretty sure. Yeah, A380 that went down in the Atlantic. Um, it was really unfortunate. I think it was Air France 447 or something like that. You probably look that up, but it was little ice crystals. So we'll talk about that when we get into icing, um, not that accident, but just that one popped into my head when I was thinking about this convergence zone, because things can happen, you have to be prepared for it. So anyway, pretty amazing stuff, um, how everything kind of relates, uh, especially comes back to aviation.

So other areas of the globe, because of these three different, uh, cells, you get what's called the Horse Latitudes. So the Horse Latitudes are around this 60-degree latitude, uh, kind of line, right where those two cells come together. And because where they come together, it gets to a point where there's, there's no wind generated. So if you were sailing a sailing vessel, right, like which they did back in the day, think of like Pirates of the Caribbean or something, you know, where they get to those doldrums where there's no wind in the sails and they're just kind of floating around listlessly based upon the currents. This is, this is the area in which that happens. Now, of course, uh, back then, there were other ways for them to deal with it by popping oars out of the side of the, uh, the ship and being able to row the ship till it gets past that area so it can start to sail again. I think I actually have an arrow pointing to where Hawaii is because if you get high enough or low enough in these areas, right, you'll start to get a very consistent because those two cells coming together, you'll have a consistent flow of, uh, of air traveling. And if you've ever been to Hawaii, they have trade winds, and the trade winds are associated with those two big cells that are located above it and the very consistent, uh, flow of air that goes over those islands. But if you're wondering why they call them the Horse Latitudes, this is, I don't know if it's actually true, but usually, usually there's usually some truth associated with it. They call it the Horse Latitudes because back when they had ships that carried cargo and animals, they had, this gives you a picture what it looked like, looks like how they did it. Of course, at certain points, if they weren't moving fast enough to be able to get through this particular area, they unfortunately, because of the horses drinking most of the water on the ship and, of course, the crew can't get through it, it was like us or the horses, and unfortunately, they had to let some of the horses go. So that's where apparently the term Horse Latitudes came from. I don't know if it's a myth or not, but it's a, I think it's possible. Kind of sad, but hey, you know, so at least you know where the history of that comes from. Um, see all the fun stuff you learn in this class.

So let's get back to weather and, uh, we'll look at things called Rossby waves. So Rossby waves, if you, if you look at them, you'll, you'll notice that they kind of look like the jet stream, which the jet stream is associated with it. We'll talk about that on the next slide, but Rossby waves are interesting. So back in the 1930s, uh, what was his name? Carl's, Carl Rossby. So Carl Rossby had noticed particular patterns. And the interesting thing is when you have that cold, dense air that's in the poles, right, it kind of, it sinks, and of course, nothing happens perfectly, right? So it doesn't sink, you know, equally, you know, like a dome or a bowl or something like that on the top of of the North Pole. It, it happens interspersed with these little undulations in it. So you'll notice all the lows, uh, that are indicated, of course, by the red L's, and then off of the lows are, uh, will be the, you'll notice the the troughs that come off of it, and then in between those troughs will be the ridges. So what does that do? Well, the nice thing about these, it allows the circulation to go from the poles to the equator and then from the equator back to the poles on the ridges, uh, to do a larger circulatory pattern. So you have the individual cells that creates the climate on the earth, and then they have these Rossby cells or Rossby waves that allow air to travel, uh, longer distances. It's pretty interesting, and the fact that this guy figured it out in the 1930s, I mean, it's not like you can see them, but you'd have to like measure that kind of stuff on, like over a long period of time to be able to figure it out. But hey, it's, it's pretty interesting because you'll notice a lot of like convergent and divergent winds, uh, in between the lows and the highs. So we're tying all these terms together so you understand a little bit bigger picture about how the world works. And we have jet streams, which, of course, we need to pay attention to as pilots because we can either get really great tailwinds to really jam in your aircraft or really sad days where unfortunately you might be affected by it in the opposite direction. So, uh, anyway, so the upper features of the jet stream are pretty, uh, pretty interesting. We have, uh, the polar jet stream, which is a lot faster, versus the subtropical jet, which, of course, is slower. And I'll show you the, the video I'm going to show you in a second, we'll touch on it, and then, of course, I'm going to show you like a cross-section, uh, of this kind of picture here as far as the jet streams are concerned, and you can see the differences on why, uh, one jet stream is much stronger than the other. Of course, we're affected the most by the polar jet stream, uh, where we're located in the United States, as you can see it goes over the top. You'll see in the video where it goes north and south. The, I think the smallest plane I've been able to actually get into the jet stream was during, uh, the winter, and it was going down towards Mississippi, and it was really interesting because it was like 25,000 feet in a in a 421, a Cessna 421, and it was a lot of fun to be able to get, you know, a 100-knot tailwind as I was flying down there because it made the trip a lot faster and one less fuel stop, which is pretty awesome. So, uh, of course, the jet stream itself, 24 to 50,000, what time of the year, and they'll explain it better on the video as far as being able to visually see that. Um, they're of course thousands of miles long. They do, because of shear, will break up and, um, and of course, they're, they're only so thick, and that cross-section I'm going to show you in a second will help you understand, you know, why they're kind of restricted on how big they can get, uh, but it is pretty interesting.

So here's a quick video on the jet stream. Uh, it is made with a UK slant to it, of course, because it's made in the UK by Met. And as you watch through, it gives you a great example of how the jet stream works a little bit better. And of course, it talks about pressure, which we've talked about already, but it's just a refresher on how pressure works and how to look at, uh, the levels of our atmosphere.

Jet streams are another name for fast-flowing currents of air. There are many different jet streams that exist at both high and low levels in the atmosphere. Each has an important role to play in the weather experienced on Earth. The major jet streams that circle the Earth are found just below the tropicals at a height ranging from 9 to 16 km and can reach speeds over 200 mph. They are hundreds of kilometers wide but only a few few kilometers deep, so are often described as a ribbon of very strong winds. The major jet streams are the polar front and subtropical jets. These occur in both the Northern and Southern Hemispheres and are part of the larger global circulation. The polar front jet occurs over mid-latitudes and strongly influences the weather over the UK and Europe. The polar front jet is a type of thermal wind that arises due to the strong temperature contrast between cold polar air and warm tropical air. To explain this further, imagine two columns of air: one in the cold air to the north of the jet and one in the warm air to the south. The top of each column is bounded by the tropopause. The shorter column of cold air exerts the same surface pressure as a taller column of warm air. This is because in the cold air column, the air is more dense. This causes atmospheric pressure to decrease more quickly with height. In the warm air column, pressure does not decrease as rapidly with height because the warmer air is less dense. The tropopause in both columns is at the same atmospheric pressure, so if you were to climb to the same height in both columns, you'd find that you would be at a lower atmospheric pressure in the cold air column and a higher atmospheric pressure in the warm air column. The pressure difference caused by this temperature gradient produces a pressure gradient force. The pressure gradient force acts from high to low pressure, so theoretically in the Northern Hemisphere, air flows from south to north. But the Coriolis force, resulting from the Earth's rotation, causes the air to move to the right of the direction of motion in the Northern Hemisphere and to the left of the direction of motion in the Southern Hemisphere. In both hemispheres, the jet stream flows parallel to this temperature gradient, moving from west to east. Theoretically, this jet encircles the Earth in a continuous line, but in reality, it is more broken up as differential heating of land and sea masses lead to west-to-east temperature contrasts as well as north-to-south. As the polar front jet forms due to the temperature contrast, the stronger the temperature gradient, the stronger the jet. This means that the jet is stronger in the winter than the summer, as the poles cool during the winter months, increasing the temperature contrast. In the Northern Hemisphere, the jet tends to be further south in winter and further north in summer. This is due to the tilt of the Earth and that in the winter, the Northern Hemisphere is tilted away from the sun, and in the summer, it is tilted towards the sun. Mid-latitude low-pressure systems occur on the polar or northern side of the jet stream, while more settled, warmer conditions are found to the south. This gives us the wet and windy weather we often see in the UK during the winter months, as low-pressure systems are steered towards us. It can also lead to some disappointingly wet summers if the jet stream remains to the south of the UK. A stationary jet stream pattern will bring frequent low-pressure systems to the same region. When warm air moves further north than normal or cold polar air moves further south, this can change the prevailing west-to-east jet stream pattern. This causes the jet stream to buckle, driving depressions towards different regions or blocking their movements altogether. A straight west-east flowing jet stream won't have much impact on the development of new weather systems or strengthen pre-existing ones. When a jet stream meanders north and south, air accelerates and decelerates around the bends in the flow. These areas of changing speeds are our development areas where the air is accelerating. More air is leaving than entering a certain point. This means that the air is being depleted at this point. To fill this depletion, air from below rises. When air rises, it forms clouds and precipitation. Winds at the surface converge to this rising air column, which causes surface pressure to fall, and a low-pressure system may develop or deepen further. So whilst the jet stream is just an area of fast-flowing air, it has a fundamental effect on our weather. [Music]

Uh, what I've done here in this slide is is giving an idea of where the tropopause is located, which is that red line, uh, in relation to showing the the three different cells, right? And of course, the low pressure or high pressure areas that are made because of the cells. So, uh, the Hadley cell, of course, those are two Hadley cells pushed together, just didn't name the other one, uh, where we get big thunderstorms. And of course, the, the atmosphere, of course, is expanding at the equator because it's warmer, less dense, and it expands. And because of that, the altitude of the tropopause, in other words, from the surface all the way up to where the tropopause might, uh, end, let's say somewhere around, let's say the average is 36,000 feet, of course, it would be much higher at the equator, uh, and then, of course, as you get closer towards the poles, as the air gets colder and denser and starts to contract, the the altitude of the tropopause at the poles will be a lot less. So if the average is 36,000 feet for the top tropopause, it might be 38,000 feet at the equator, right? Or 34,000 feet, or actually less at the poles. Why do I mention that? Because when we start to talk about contour lines, that red line is also considered a contour line, and a contour line is just a consistent, steady, uh, level of pressure, uh, that's that's located along the Earth. So as we start to fly airplanes, uh, there's a difference between whatever is happening at the surface, right, which is very consistent, whatever is happening when you see the surface area charts, uh, it's everything that's that's literally at the surface. But as you start to go up in the atmosphere, all these other components start to take play, uh, in the atmosphere. And of course, things are, well, actually kind of a little, they're actually a little bit more consistent, because of course, you have friction on the surface. But as we go up into the atmosphere, we're now going to start to look at contour lines, uh, because we want to be able to figure out where that area of pressure is located at. In other words, where's the top of the troposphere, uh, especially when it comes to thunderstorms. So there's a little foreshadowing right there for you when we come to talk about thunderstorms, which will be fairly soon, and why thunderstorms stop, for the most part, at the end of the troposphere, right before it gets into the stratosphere. So we get this, since this is a cross-section, we were looking, of course, down at, you know, the air circulation patterns, uh, for global circulation earlier. This slice will actually show the two different jet streams that we have to deal with. Southern California, we actually can be affected by both of them. So the polar jet is what we're familiar seeing, right? So when the weather people talk about the jet stream, that's what they're talking about, the polar jet for the most part. You rarely hear them talk about the subtropical jet, and that's why most of us don't, you know, that's like the first time we've heard about it is probably a class like this. Um, but, uh, as you can see, and what is mentioned in the video, that the biggest difference between temperature is what makes the jet stream bigger or smaller. So if there's a larger contrast, uh, between the temperatures, it gets bigger, as you can tell, it's quite large between the, like that Arctic area and the polar area where these two cells start to come together. The difference, of course, the jet stream does exist right in the between the Hadley and the Ferrel cell, but it's much smaller because the difference between the temperatures, of course, is not as great. So a lot of stuff on that slide, you can use that for studying. If you want to use that red line as a contour line, just to remind you, contour lines are based upon pressure above the surface, and then, of course, the three different cells, it's got a lot of stuff in there to help you out. All right, um, so as we move on, hopefully that'll help as we start to get in more of these concepts, everything will just start to come together.

We're going to talk about fronts. To look to start off talking about fronts, we need to have a little bit better understanding of what some of the, like the air mass characteristics are. So you can tell on this picture, there are seven different air masses. There's mainly six, there's a seventh, which we'll talk about here in a second, that's a little unique and it's seasonal. But for the most part, if you look at all six of these or seven in this case on the on the chart, you'll see three main differences. So you have the temperature of each of the different, uh, uh, air masses, stability associated with them, and of course, how much moisture is contained within that air mass. So as long as an air mass stays in a particular area for a certain length of time, it will start picking up the characteristics of whatever it's over the top of, right? So, uh, if we look at that picture, we can see the maritime polar, maritime, as we'll see, is, uh, is is one of the descriptors giving, or to that talk about any air mass that's over the top of water versus a continental air mass, which of course is over the surface. That's kind of a no-brainer, right? Um, there are breakout ones, but we don't care about those. So in this class, we, we just want to kind of have the big picture to just to understand where a lot of this weather comes from and what we can anticipate as pilots. So, uh, the reason you'll see here in a second why it's so important to understand it because as maybe not as a private, as you're starting to learn, you just want to understand some of the concepts, but as you start to fly more and more, this all of a sudden will become more and more important to you because you'll know where the air is coming from. That's a big deal because you can anticipate a lot of stuff because of it. So each one of these are broken up, uh, so you have the Arctic, Polar, and Tropical. They're all from different areas. So of course, you know, the colder air masses are going to be to the north, the warmer air mass is going to be to the south. That's pretty, pretty straightforward. And, um, and I give you all kind of the data associated with that in the in the slide off to the left, left. But one of the things that is listed here that is different, it's seasonal, is that continental tropic. So the, the continental tropic air mass is the one that creates a lot of that monsoonal weather that we get, uh, in in the south, or and we get like Arizona, New Mexico, Colorado, they get a lot of these really big, huge thunderstorms. And it's all because of that particular air mass. So it's not only getting the heat from Mexico, but it's also pulling up stuff from the Gulf of California and, you know, part of the Gulf of Mexico, as it starts to come up, and it just feeds all that moisture because in that area, think about where like Arizona, New Mexico, it's also warm, it creates that low pressure area, and it draws all this moisture up during that time of the year, which is the reason why we get all that monsoonal weather. So we'll talk a little bit more about monsoonal weather when we, we'll talk about thunderstorms because that's one of the major cool features that we get from monsoons, if you like thunderstorms, at least looking at them, uh, and listening to it, it's pretty awesome.

So, uh, let's see. So now that we understand a little bit more about like air masses themselves, we look at, uh, uh, like what affects Southern California. I had mentioned that, of course, you know, the two different jet streams potentially can impact Southern California. Well, this is why. So if you look at the slide before we get into the next one, um, the maritime polar, which is, as this front moves down, I was kind of, that was what I was looking at, uh, earlier on as far as weather. I wanted to see where the low was and if we're going to get rain. Apparently, we are a little bit later, I think it's on today or early Friday. Uh, but anyway, as it pulls the air down from the north, it's where we get colder temperatures during the winter. We get snow that usually lasts about a month because it's Southern California, um, for the most part. But, uh, we get different types of weather that comes when when everything comes down from the the north. And we get, uh, the jet stream also comes down towards Southern California and usually curves very sharply right around Southern California, and that's where we start to draw our storms in. Sometimes you can get that subtropical jet to kind of push up a little bit further, and when that happens, you get the, um, what do they call it, the Pineapple Express. So every once in a while, we get this weird phenomenon where we get a lot of that, uh, weather that comes up from Mexico, and we get some really warm storms. Unfortunately, they happen during the winter, which is kind of sad because usually we've got a good storm and then this Pineapple Express comes in and just dumps a bunch of water on our snow, which is sad. But anyway, that's usually when that subtropical jet starts to come up and, you know, they think of like El Niños and all that kind of stuff, which I found not as consistent as, you know, they they make you think. So anyway, so there's the all the different air masses, and then when these air masses come together, they create fronts. So, uh, fronts have unique characteristics where you have one air mass that's made up of those certain qualities. And in this case, we'll show you the differentiation between two different air masses. Um, most of them are defined by these four main ones. There's others, but we'll focus on these because as pilots, that's all we really kind of care about. Um, we want to know about wind direction, right, as far as like planning our flights, temperature, of course, we want to make sure that we're, if we have the capabilities in the aircraft, if we have to, you know, go into like icing conditions or something, right? The moisture contained within the clouds, so, uh, which is very important not only for icing but, you know, a VFR versus an IFR pilot. And of course, pressure.

So looking at the picture that in the graphic, you can see this big cold area that's kind of dropping down, you know, uh, this is, I don't know if you guys, do you guys remember the polar vortex was like a couple years ago, and we had, there was a huge area or a big, big area of cold weather that dropped into the United States and caused all sorts of problems. Um, so pretty interesting when this, with this kind of stuff happens, it's just when, you know, cold, dense air, it's just going to go down. And in this particular case, this is an example of it. And you can see that, uh, it has a cold air front that's showing, with the blue line with the little triangles associated or half triangles associated with it. You can see the difference in, uh, temperature between the cold area, cold air mass, and, of course, the air that's on the other side of the cold front. Of course, there's about 20 degrees difference. And then if you look off to the right-hand side, you see the low, it's kind of covered up by that graphic, but then you see a warm front that's located just off to the upper right, which has the red line with the half circles on it. Um, get comfortable with those because, of course, you will be asked what those symbols are as we, uh, get ready to take the midterm, uh, in the near future. And then hopefully, as we explain a little bit more, you'll feel a lot more comfortable with it. Most of these are kind of big things you've been exposed to before, but, um, anyway, let's go ahead and look at different types of fronts and how they look. Uh, in this case, you can see there are two low pressure areas on the graphic, and then, of course, there's a trough that comes off the low, which is fairly typical. And of course, that's, you know, if you, if you look at the airflow as it starts to come in, it dips down into that low pressure area and accelerates as it comes out. And of course, it's that acceleration, or it's that change going from the low towards that high pressure ridge that is in the middle of the country, we start to get weather. So preceding the low, in this particular case, is shows where the weather is located. You can see on the other side of the high, where it's a beautiful sunny day because it's a high pressure area. And then, of course, it mirrors itself, the low on the other side doing the same thing, right where it has the weather that precedes it. So the way you look at this, of course, as a, as a, as an individual, if you were standing on the surface, let's say of the East Coast, everything is moving, right, from the west to the east. You'll notice, of course, as that low comes over the top of you, if you were to look at, you know, measurements like a a barometric pressure, call ADIS or AWOS to kind of take keep an eye on what the the the pressure settings are in your area, you'll notice as the low goes over the top of you, the pressure will continue to drop till it gets to that lowest point, and then once the front moves over the top of you, the pressure, of course, will start to go up. So it's just, of course, the low pressure is going to be maximized during the trough or over at the low pressure area where it'll be the lowest, and then, of course, the the weather associated with it. So, um, you'll notice, I think in the quiz, there'll be a similar question like that. So you kind of have to visualize as these things go over the top of you, what happens to not only the pressure, right, as it goes over the top, but what kind of weather that you can anticipate from those particular areas as they pass over the top, right? So we know that if you're on the East Coast, the low goes over, it's weather. As the high starts to come over, it'll get nicer, and then, of course, the low is just going to ruin your day all over again. So generally speaking, that's what you need to anticipate. This is, of course, generic, as far as a view to help you understand just the basic concepts associated with it. So, uh, going from this.

We need to understand which I mentioned before about some of the um, the symbols that you need to be familiar with for um, for weather. So here I have it's, it's a kind of a good study chart for chart legends. And the four main ones that we're concerned with are the, the four that are located on the left. There are others located on the right. I'll, I'll mention a couple of them here in a second, um, but we mainly need to focus on the ones on the left. So there's a description of each one of those, um, and you can see that their, their shapes are different. Cold has the triangles, warm has the little half circles. The stationary front's interesting because it's a combination of both. And the reason why they alternate, right? The colds in, in this case, the colds traveling in one direction and the warm, uh, air front is traveling in the opposite. And the reason why is because if, for some reason, uh, let's say the cold front would disappear, well, what direction would the warm front go? Well, in this case, it would go, it would continue traveling up in this case. So same thing is if the warm front disappeared, the cold front would travel, continue to travel down. So, in other words, they're going in opposite directions, but they've kind of got to a stalemate, right? So they hit each other and it's that interaction between the two. We'll see what happens when those two meet and they don't move, they hang out for a while, and it's considered stationary because they're not really going anywhere. And then the last one, of course, is the occluded front. And the occluded front is kind of a weird one where you, you have three different air masses that are kind of joining the party, right? So one whacks into, you know, another air mass and, and then the other, you know, there's a third air mass that feels sad and he ends up going up, you know, up in the atmosphere. So I'll show you a picture of what that looks like so you understand why that is initially a dangerous spot, but then eventually it just disappears, uh, because of how these air masses are interacting with each other.

Uh, on the right-hand side, there's, you know, a bunch of other different, uh, uh, you know, legends that show the, the different types of fronts. Uh, we don't have to worry about, you know, frontal genesis and stuff like that, which just means the front starting to be created. Um, but we do need to know about Squall lines. Squall lines at the very top, it kind of looks like, uh, uh, like Morse code. So if you guys are in Stanley's class and you're learning about the communications box and how to identify a VOR or some of that, some of that kind of stuff, um, you need to be able to read Morse code, uh, as you listen to it and you look at your chart, as long as the sound matches the little dots and dashes, as long as it's correct, right? You can now use, let's say, that VOR for navigation, that kind of stuff. Uh, in the case of weather with a Squall line, uh, you really want to pay attention to this particular symbol because you don't want to go there. So the whole idea of recognizing that's a big one. So, uh, Ridge, of course, down below, kind of looks like, uh, like Charlie Brown's t-shirt, um, but that's just a high-pressure area, which, of course, for all of us is like, ah, that means good weather, which is awesome. And then the trough below, uh, for obvious reasons, poor weather, right? So those are the legends that should help you study for that. Of course, I'll have, we have a symbols quiz that comes up, and then I have another separate, uh, study guide for that. So you guys should be fully prepared, you know, before you take any quizzes and, and, uh, tests and stuff. You feel pretty good about that.

So, um, understanding fronts a little bit more, uh, from a check ride perspective. So there comes a time where, of course, you're going to sit in front of an examiner or the CFI as they kind of do a mockup check, you know, exam, and they might quiz you on these fronts. And the important thing is for you to feel confident in your weather, to be able to talk to them about what you see or what you can anticipate as far as weather based upon what kind of cold front or warm front that you're going to be exposed to, or stationary, right? And so, uh, when we look at a cold front, cold fronts are basically like a, like a bulldozer. So you got really cold, dense air, it just kind of mows everything out of the way. So it starts to come across the surface of the Earth, and as it starts to do that, whatever is in front of it, unless it's colder and it can't, you know, keep going, you know, which is stronger, which is usually not the case, but in the case of a, when it, when a cold front starts to move in, it pushes everything not only in front of it forward, but it also allows some of that air mass, whatever was in front of it, to come up and go up and over. So when that happens, of course, we get, uh, a tremendous amount of weather, uh, depending on the difference. It's kind of like the jet stream, the difference between temperature. So if there's a large difference in temperature and moisture, that kind of stuff, uh, you will get a lot of weather. If there's less, well, you might get some weather, you might get some like clouds and stuff like that as it moves through, but you, you know, might not be as unstable. But in this case, we can see the visualization, which is really what you kind of want to imprint, uh, in your mind whenever this question comes up when you're being quizzed later on by your CFI or your DPE or whoever gives your check ride, right?

So, um, important things to see in this slide is not only the cold density, right? But it's actually where the actual front is located. In this picture, you'll notice that just like a bulldozer, it's at the very front. Whatever's pushing it out of the way, that's where the front is located. So the reason why I point that out is because all fronts are not the same. So this was important when it comes to answering questions. If you can visualize this, hopefully it'll help you out. So let's see, it should be another, there we go. Thunderstorms and showers and stuff. So the type of weather that you get from the front, of course, thunderstorms and showers, uh, showery precipitation, in other words, individual showers versus instead of widespread, all right, is mainly because of this kind of bulldozer effect, right? So I'll show you the difference between this cold front and I'm going to show you a warm front next, and you'll notice a big difference between the two. So remember the front is out in front of this particular one because it's stronger, versus a warm front, which is weird because now it looks like the warm front is behind all the weather, uh, that's in front of it, and that's the difference between the two. See, the warmer air is, of course, less dense, so it can't push the cold air out of the way because it's, well, less dense, right? So what does it do? Well, it kind of rises up above, and it's like this big lazy air mass that goes over the top of like a retreating cold front. So it goes up, up, and over the top, and when it does that, the temperature differentials aren't as fast or rough. In other words, the thunderstorms and kind of gnarly unstable weather, so you get a kind of a smoother transition, and in that case, you start to get more widespread showers, uh, a lot of clouds, wispy stuff, you can see the cirrus are high, because of this. So try to remember the differences between the two because with a warm front, most of the weather takes place in front of it because it's actually above that cooler air that's down below it. So you can see that in that slope, that little red line is not as abrupt as like that cold air mass that was mowing everything through. So there are the names of the different clouds, which is kind of nice to know. We'll see some pictures of that, um, I think we did that last lecture, if not, you'll see them today. But anyway, the differences between the two, that's what's so important, um, to understand is what type of weather that you get from the fronts, cold versus warm, because generally speaking, that's all they kind of talk about. And then occasionally they might bring up the other, uh, fronts.

Uh, let's see, there we go. So this is another front, this is kind of unique. Um, I'll show you, I, I have a few pictures of this to help you understand the concept, but this is kind of interesting. So in this picture, you can see three different types. You can see the, the cold air that's on the left-hand side, that kind of bulldozer, right? And originally, if, if we could, if I could do this over time, uh, originally the warm front was, uh, in back of the, the cooler air mass. It's kind of hard to see in this picture, but originally the warm air was here and the cool air was here, and then all of a sudden this cold, uh, cold front comes in, and as it starts to come in, it takes all that warm air that was just kind of sitting there and it pushes it up or occludes it up above in the higher atmosphere as that, uh, cold front continues to move forward and push on the cooler air that's in front of it. So you have three different air masses that are interacting with each other, and when you get three different air masses interacting with each other, well, you can get some pretty volatile weather, but it's a different type of weather. So to take a look at what type of weather you would get, uh, on, on an occluded front, you can see in this picture where you can see the three different, uh, air masses in the low graphic on the left, where we have the cold air coming in, the cool air, that's up on top with the warm air pushing up over the top of it. So, in other words, to keep it simple with occluded fronts, if you're looking at a chart like this, it's the cold air front catching up to the warm air. As soon as the, the cold air, uh, catches up to the warm air, it pushes it up, and because of that, it turns a different color, that purple color, and now you get, uh, the front located, uh, where it shows the, the triangles and the half circles all on one side because it's occluded together, and then it's continuing to rotate. So, uh, the, the difference in this front versus others is you can see on the graphic on the right where that occlusion goes up and swings around to a very low pressure area. Eventually, because of that warm air on the top, it will kind of stabilize everything and this will die out. But initially, when all this stuff happens, you can get some pretty gnarly weather. To put these both together, uh, is kind of a study slide. Uh, you can now see start to visualize a little bit better the three separate air masses, which is important because each, three, each of the three separate air masses have, remember, different qualities, pressure, temperature, moisture, uh, between the two.

So let's see what else we have. Okay, so now I've labeled, uh, on the graphic on the right-hand side where the cold area is, where the cool air mass is, and of course the warmer that's down below that gets pushed up. All right, so that's probably one of the more complicated ones, but it's really just about the cold front catching up to the warm front, pushing the warm air up. All right, what most people do is they forget about the cool air that's in front of it, and of course, that's where they mess up and they can't, like, answer the question. So remember the three different ones, and hopefully that'll help you, uh, study for that and kind of let that stick in your mind. The last one, of course, is the stationary fronts. Stationary fronts are, are, uh, something you see more in the Midwest than you see here in Southern California, but they can happen. They, you'll see sometimes they, they'll be extended across the entire country, and it's usually because you have this colder air mass from Canada and you got the warmer air mass coming up from the Gulf or the Atlantic, and they just kind of, I don't know, hang out. They just don't push each other out of the way. It's kind of even Steven kind of thing. So you get this where you have the alternating, uh, you know, half moons, you know, for the warm front, the cold front symbols. And let's see if we can activate this. There we go. My highly technical graphics for you. Um, and what happens here, and when you, you hear about like flying on the Mississippi and stuff like that, you'll notice that a lot of times it's because of these stationary fronts where these two air masses come together. Air masses do not mix. In other words, they don't combine with each other. They kind of whack up into each other and they just irritate, irritate each other and create weather, uh, in that interaction between the two. So in the case of like Mississippi or the areas where they get a lot of rain, uh, and flooding, it comes from when these two just kind of hang out, continue, they create, create the weather when they come together, and then of course, they don't move. So they just continue to make weather as they hang out until eventually they get pushed off to the side, so, and continue east.

So the last thing I have for you, of course, is a study slide because I want you guys to do well, of course. Um, this is all about pressure systems. So to help you visualize some of the, the lower areas and the highs, see if I, there we go, the lower and the high areas, just remember one, the rotation of highs and lows, super important. Uh, in this case, I show the jet stream that is interacting with the highs and the lows. So it can have an influence of where the jet stream goes depending on how strong the highs and the lows are. Uh, this is called an Omega block because it looks like the Omega, the Greek symbol, the Omega. Um, you don't have to know that, but just take a look at this. You'll realize that as the air comes down around that low, kind of whips around the bottom, you'll see that the airspeed, if you look closely, it increases as it comes around the low. Of course, the jet stream will increase in its wind speed as it comes around, and then you'll notice it again at the bottom of the low that's off on the right-hand side where you see the little lines going along the jet stream as they increase in airspeed. So there's a lot of little nuances to this slide, but it should help you study, uh, when it comes to making sure that you understand not only the direction in which the winds are going, but also don't forget about what, you know, those larger air masses we were talking about, where they pull from. So, you know, do they pull from Canada? Are they pulling up from the Gulf, right? Uh, in order to create or anticipate what type of weather, uh, that you can get in that area based upon where all these things are.

So, oh, the tip I was going to leave you, one last tip, this is kind of fun. So anytime you can anticipate, let's say it's, it's windy, right? That don't count. You can't use this one for, for the San Anas because it's a different kind of wind, right? That's a katabatic wind. So, uh, in the case of like highs and lows, generally speaking, let's say if there was a breeze today and you wanted to figure out where the low pressure area is, right? So you're in the middle of nowhere, you don't have any weather, but you do have winds, and you don't want to fly where the weather is crappier, right? And you know the crappier weather is probably going towards the low, so you want to know where that is. So how you do that is you stand, you feel the wind, and then you turn so the wind is on your back, so it's blowing, you know, from behind you, uh, out into the front of you, right? So as you feel the wind on your back, right, you try to, if you can't feel the wind necessarily because of where you're located, let's say there's buildings or trees or something like that, you can actually look up and look at the clouds and the direction the clouds are going, kind of do the same thing to get an idea. So have the wind in your back, and then you take your left arm and you just stick it out straight off your side and you point, you were pointing at the low pressure area. So if you're flying and you know you're going to go in that direction, the weather most likely was going to get worse, the winds will increase. That's an FAA question, I think I remember that one. So, uh, you know, it's just understanding a little bit more about lows, highs, uh, you know, warm and, and, and cold, uh, fronts as they move through and the type of weather you can get from it. So there's a lot of stuff in this, uh, that you just need to kind of practice. You'll use this for the rest of your aviation career, whether you're going to fly aircraft or work in operations, it's all very helpful.

So I'll go ahead and leave you with a little foreshadow and what we're going to talk about next, which is one of my favorite, uh, uh, subjects because I think they're just cool. But anyway, as this thing starts to build, you can start to see where that huge trough is. It's located off of, uh, comes down just north of Oxnard. So the cold front's already moved through. You can see the direction of the winds, which is kind of handy. See if you can get a bigger picture what it looks like, and if we're lucky, apparently we're going to get rain a little bit later. That's what they say. We'll see if they're right. And, uh, so this is what the surface winds look like, and then if you want to see what the jet stream looks like, it'll build here in a second. There you go. So there's that big curve in the, the polar jet as it comes down south. You can see it's starting to bring down some moisture from, from the north. Better picture. You see kind of whipping around, and then it's following that, that low, low trough as it comes into Southern California. So it's pushing all the weather towards us. We'll see what happens. You see it's pretty gnarly over here. See how wind speeds creep up? Pretty cool stuff. So it's, uh, you can see kind of how the jet stream, it meanders, it tries to stay together, but, you know, it gets to those like really sharp curves, which is where you get clear air turbulence, and it's nasty. So, so this one has a like a hurricane feature on it, which is kind of nice as we start to talk about like hurricanes and stuff. You'll see Sagal that's on the right-hand side, Africa starts to go from there towards Cuba, is is the direction, and it's all based on global circulation, right? Because that one big huge air mass that's the, the, the Hadley cell is pushing air in that direction, and then as it gets towards Cuba, we haven't really talked about it, but there's a big high-pressure area over the Atlantic that pulls those hurricanes up towards, uh, Florida, and then eventually it gets into our Ferrell cell, and then it starts pushing, pushing it towards the east again, which is why they end up going out over the ocean.