Howdy everyone and thank you for for making it to the final video of module 8. In this module, we're going to briefly introduce the jetream which is so important in controlling a lot of the weather events that we see in the mid latitudes including Texas. So jet streams are these rivers of airs that we kind of talked about when we looked at atmospheric circulation cells and they occur in between our different circulation cells. remember our Hadley, our fair, our polar cells. And these jetreams heavily influence weather systems. So, especially in the middle and higher um latitudes. So, here's the United States. You can see this weather system that's kind of moving through here. And this is where we have our jetream, those rivers of air that are being um that are carrying weather systems horizontally across the planet. And they're also responsible for separating air masses. So we have air masses that are south of the jetream and air masses that are north of the jetream. And air masses very rarely cross the jetream. So in order to get these cold air masses into Texas, the jetream has to actually dip beyond Texas to bring that colder air. It's not going to pass the jetream. So the jetream is actually kind of protecting us in Texas from that colder air. But of course, as we saw, the jetream is constantly moving. And in 2021, the jetream moved so drastically that it brought arctic air into Texas, causing that Texas freeze. So jet streams are really important to study if we want to understand some of these weather systems and how things can change. Now, what is the jetream? The it's the atmosphere's response to where temperature gradient is the strongest, which is also where the greatest density change occurs. So although jet streams in itself is not a weather system, they do control the formation and the movement of most of our weather systems especially in the mid latitudes and the United States because we have those three large circulations in the transport of heat to the poles and cold air towards the equator and those jet streams are for where we have temperature change at its greatest. So the jet streams and circulations follows the sun and that they move north and south as the sun's zenith changes each season and at the equator air is converging remember and it's it's forced to rise forming that ITCZ the intertropical convergent zone but at 30° north the air is descending um and that's the latitude where most of our deserts are located and then at 60° we have rising air again leading much to rainfall in many of the world's forests and then descending air at the poles leading to our desert-like conditions. Now, in between each of those circulation cells again is where we have jet streams because we have such a drastic change in temperature at those locations. Now, the jetream is identified when and where wind speed is over 50 knots. Um, so this is just where it's located in within um altitude in the atmosphere. So these are fairly fast wind speeds over 50 knots and can exceed 200 knots in some cases. So this is what's carrying a lot of those weather systems. And it's also what's carrying a lot of our airborne particles like from our volcanoes, our ash. If ash gets ejected high enough after a volcanic eruption reaches our jetream, that's how we can get ash dispersed in large areas, right? That's why it's such an extensive hazard. Now, here is that cross-sectional area of our circulation cells. Again, this is where we have the equator, lots of warm air rising. We have 30° north, our air is going to start to sink here. So, we don't have a lot of cloud formation. And right in between the Pharaoh and Hadley cell, because we have such drastic changes in temperature, this is where our subtropical jetream is. This is a cross-sectional view. So, our subtropical jet stream exists around 30 degrees north, but it can bounce back and forth. And then we have our polar jet. Same thing. It's in between our polar cells and our fereral cells. So, here showing the polar jetream and the subtropical jetream as it looks on our planet Earth. So, again, our subtropical jetream, it's separating those Hadley and feral cells. and our polar jet stream are separating those polar and those and those feral cells. So, lots of cold air here, lots of warm air here, and the jet streams are kind of controlling and keeping those air masses where they belong. But you'll notice that it's very wiggly. So, these things can change with latitude and bring warmer and colder air where it doesn't typically go, but it also is moving in these directions, causing our weather patterns to move as well. Now, jet streams are referred to as a river of air, but they're more like a tube of air, and it's depicted as a line on a weather map, but it's actually a three-dimensional thing. Now, right here is where we have our 500 mibar level. This is the solid red line. And when determining the location of our jetream, we often look at the 300 mibar line and the 200 mibar line. So remember, air pressure is decreasing as we go up in altitude. So in between our 200 and 300 mibar line is typically where we see our jetream. So here over Denver, Colorado, we have our jetream that's about 40,000 um feet high in the atmosphere. So this is where where we're looking for our jetream. Now they really are a river of air in a sense that they are kind of flowing air and it's flowing fairly quickly. And the jetream across the Pacific Ocean actually was responsible for pushing this flight to as high as 791 miles per hour relative to the ground. Whereas the actual air speed of the aircraft was only 580 mph. So it was the wind that was giving it its additional speed. And I don't know if you travel often, but you might notice depending on which direction you're traveling, you travel faster going from the west to the east than you do from east to the west. So, if you've ever flown to Denver from here, you probably notice that it takes a little bit longer to fly to Denver than it does to fly back. Now, not only does the jetream change with latitude, as we saw, it's kind of wiggly across our globe. Sometimes it brings colder air farther south than it typically goes, but it's also changing um with height as well. And it's located physically lower in the atmosphere in troughs um as compared to ridges. So why the dips and ridges where colder more dense air means pressure levels occur closer to the earth's surface where we have warmer less dense air the pressure levels occur higher in the atmosphere. So remember our jetream is usually in between 200 and 300 millibars of pressure. So if our pressure is changing at the surface it's going to change as you move up as well. So that's going to cause our jetream to dip and go up in certain places. And the air gets cooler in the troughs of the jetream and they're warmer in the ridges of the jetream. Now the vertical motion of the jetream as it's moving up and down also imparts an upward and downward force. And where the jetream decreases in elevation the fastest, that's going to produce the greatest downward motion in the atmosphere. Conversely, where the jetream is increasing in elevation the fastest, where it's going up the fastest, that's where we're going to have the greatest upward motion occurring in the atmosphere. So, the jetream's vertical motion therefore determines the location of fair or foul weather. This explains why the majority of inclement weather occurs between the trough and the downstream ridge. It's promoting air to rise and where our fair weather typically occurs between the ridge and the downstream trough because we have air sinking. Remember, we need air to rise to form clouds and precipitation and ultimately a lot of the inclement weather that we receive. Now the vertical motion of the jetream creates high and low surface pressure centers. So this is responsible for creating those air pressure centers. Remember air is going to move into a low pressure center out of a high. And there we have our low pressure center. You can see this is where we have the elevation of the jetream increasing the greatest. So we're causing we're allowing air to rise. When the air is rising, it's not pressing on our surface very much. It's causing low pressure. And the greatest decrease in height is typically where surface high pressure is located right here. So it all kind of makes sense. It's all coming together. Now the greatest downward motion increases air pressure at the surface and the greatest upward motion decreases air pressure at the surface. Remember those isobars are lines of equal pressure drawn on a surface weather map as shown here and that indicates where the greatest upward and downward motion is occurring in our jetream. Now what direction does the wind blow around high and low pressure areas? Remember the pressure gradient is the difference between two pressure centers. At its basic level, the pressure gradient moves air and causes wind from high to low pressure. Now let's look at how the coralolis effect impacts the wind direction again. Wind is deflected to the right in the northern hemisphere, deflects in the opposite direction in the southern hemisphere. But here in the United States, we're deflecting the wind to the right. And wind spirals away from the high pressure in a clockwise direction, but it spirals towards the low pressure in a counterclockwise direction. But the wind is constantly wanting to turn to the right because of the coralolis effect. Opposed to that is the pressure gradient force which wants to take air from high pressure to low pressure. And these two opposing forces balance each other. Now the tugofwar between the corololis effect turning the wind to the right and the pressure gradient force the wind flowing from high pressure to low pressure becomes more or less balanced and the wind parallels the isobars. This results um in a wind direction called the geostropic wind that we won't really get into too much here. But friction also causes the wind to slow slightly and therefore wind flows out of high pressure and into low pressure across isobars at shallow angles. Now the air's motion around high and low pressure can create sharp boundaries. cold fronts, which are cold air replacing warm air like one shown here. And this occurs regardless of the temperature difference. And in extreme cases, cold front boundaries can be shockingly strong. The daily weather summary for Springfield, Missouri is shown here from November 11th, 1911. Look at that temperature graph. You can see a sharp decrease in temperature. That's because we had a cold front with arctic air behind it. It caused a dramatic decrease of 40 degrees Fahrenheit in only 15 minutes. The air dropped 40° in 15 minutes after that cold front passed by the weather station. Another oddity on the same day occurred in Oklahoma City that set a record high for that date of 83° F. So, we went from 80° at 3:45 to 40° at 4:00. That's crazy. But the temp the temperature record high in Oklahoma City of 83° F, the day before they hit their record high, their temperature was 17°, a record low for the same day. So all these drastic changes in temperature are usually responsible for these cold fronts. And that's when we have air masses that are moving because our jetream is allowing them to move in areas they don't typically exist. But warm fronts cause things too where we have warm air replacing cold air. Warm front boundaries tend to not be as well defined as our cold front boundaries. And we also get stationary fronts that can become warm or cold if the boundary begins to warm or it begins to move. So we have really no movement of air. It's at a standstill. Something will eventually change, but we do have these stationary fronts. So, reminder of cold fronts. Cold fronts are when we have cold air that's advancing. It's colder, it's more dense, and it undercuts the warmer, less dense air, which forces it over the front. And that rapid forceful rising of the warm air is why thunderstorms often form on cold fronts. But we also have warm fronts where the lighter, denser, warm air moves faster than the retreating warm front, forcing it to rise. And clouds and rain develop ahead of the warm front. Occasionally, the warm air lifted over the front is unstable enough for the formation of thunderstorms. But most of our thunderstorms are associated with those cold fronts. We don't get as much intensity as we do um from these warm fronts. and we return back to the beginning and complete our weather cycle. Inclement weather occurs near fronts as these locations are where the air is most readily lifted. And thank you for making it through to the end of module 8. A lot of these atmospheric processes that we talked about are going to be so important as we explore climate change in our next module, but also as we explore inclement weather with several modules after that. Thank you. So, I'll see you in module 9.