everybody its mr. Smith and today we'll be talking about topic 4.5 which is global wind patterns so we'll be learning how the basic properties of air as well as how the rotation of earth give us the wind patterns that we see on earth and how they're also responsible for the weather patterns that we see our objective for the day is to be able to explain environmental factors that result in atmospheric circulation and in order to do that we need to understand three basic factors those are the intensity of energy from the Sun properties of air such as density and the spinning of the earth on its axis which produces something known as the Coriolis effect our suggested science skill to practice today is explaining relationships between characteristics of environmental concepts or models that are presented visually so as I mentioned the first factor that determines atmospheric circulation is how airs density changes under different conditions so the first property of air related to its density is that warm air is less dense than cold air so it rises if you've ever been in a house with an attic in the summer the difference in temperature between the attic and the basement is a really great example of this property we also need to understand that warm air holds less moisture than cold air so think about how dry and cracked your skin gets in the winter versus summer that's because cold winter air holds less moisture now another factor we need to understand is that as warm air rises it cools and that causes it to expand and because cold air can't hold as much moisture the water vapor that's in warm rising air will condense into liquid which forms precipitation in the atmosphere and that eventually falls down to earth as rain or snow or sleet and finally after air has risen cooled and expanded it's spread out and then eventually it sinks back down and we'll see that happen here in the diagram at 30 degrees north and south so these properties of air help us understand the diagram to the left here which is called a Hadley cell the Hadley cell is this cycle of air circulation between 0 degrees and 30 degrees and it's largely responsible for our global wind patterns on earth so now that we have our basic properties of air down which is the first factor influencing atmospheric circulation now we're going to introduce second factor which is energy from the Sun so because sunlight is most direct at the equator that's going to cause air here to warm and rise so we can see that as step one in the diagram as warm air rises it cools and expands and because cool air holds less moisture than warm air the water vapor has to condense into rain and so if we look at step two in the diagram that's why we see such intense rain at the equator because that warm rising air has its water vapor condensed and then fall down to earth is rain in step three the air continues to rise cool and expand further in step four this air is expanding and spreading out even further and then in Step five we have cool dry air is sinking back down to earth right around 30 degrees north and south and as we can see in the diagram this is going to explain why we see this predictable pattern of deserts forming all over the earth around 30 degrees north and south it's because the air that's descending back down to earth here is incredibly dry so we get deserts however we're not quite done understanding the Hadley cell if we look at the diagram we'll see that we have this arrow here that's going from 30 degrees back towards the equator so why is air moving along Earth's surface from 30 degrees back to the equator well we have high pressure at 30 degrees north and south that's because we have this column of cool dry air that's sinking back down to earth and when a column of air is pushing down on earth it gives us high pressure meanwhile at the equator we have low pressure and that's because warm air being heated from the Sun is rising at the equator and we know that air moves from high to low pressure so along Earth's surface we'll see this air from 30 degrees flowing back towards the equator that's because we're moving from high to low pressure another way to think about this though is we have to get back to step one of the cycle somehow and so we need replacement air to come in and fill this vacuum or this gap of air left by the air that's rising at the beginning of the Hadley cell so we've covered why air rises and expands at the equator sinks back down at 30 degrees and then moves along Earth's surface back towards the equator but that's only two of the three factors that determine atmospheric circulation the third factor is Earth's rotation so believe it or not if earth were standing still rather than spinning wind would move more or less just straight north and south because the earth is rotating though that means that objects such as wind or this baseball we'll talk about here in a second that our traveling through Earth's atmosphere are actually deflected in the opposite direction of Earth's rotation so another way to try to understand the Coriolis effect is to imagine that you're standing at the North Pole and you're throwing a baseball straight south so you may be aiming the baseball along this line here but because Earth's rotation is causing the ground beneath the baseball to spin the baseball will actually be deflected the opposite direction of the spin so even though the ball was traveling on this trajectory it's going to end up here to the left of where you aimed it because the ground beneath the earth is spinning now the same thing is true of the wind between 0 and 30 degrees so because this air at 30 degrees is moving from a high pressure system back down to a low pressure system it would flow directly south are directly north in the southern hemisphere but because earth is spinning this direction the wind from 0 from 30 to 0 degrees is deflected the opposite direction so what we get is wind moving from east to west between 30 and 0 degrees now because 30 degrees is a higher pressure area than 60 degrees wind is also moving from 30 degrees out to 60 degrees the wind in this direction though is deflected in the opposite direction as between 30 and 0 and that's because the earth at 30 degrees is spinning so much faster than it is at higher latitudes at 80 or even at 60 that the wind is actually going to be deflected in the same direction as Earth's spin now that's a confusing concept so let's talk about this using the example of a treadmill imagine that you're running along a treadmill that's going 15 miles an hour and suddenly you've jumped to a treadmill right next to you moving in the same direction but only moving two miles an hour so it's moving far more slowly you're going to have so much momentum coming from the 15 mile an hour treadmill that jumping onto the 2 mile an hour treadmill is going to cause you to run forward quite a bit and so that's why we see wind from 30 degrees to 60 degrees actually traveling in the same direction as Earth's spin it's because the earth is spinning so much faster at 30 degrees than 60 degrees that the wind is deflected in that direction of our spin now we'll put together all three factors so the sun's energy air properties like density and the Coriolis effect to take a look at how Earth's global wind patterns are the result of those factors so the first thing I want to do here is point out that our Hadley cell here still works the same way we're just looking at it from a side view where we see all of Earth rather than looking at it from the viewpoint of being on Earth's surface like we did in our first slide so if we look at the Hadley cell we can remember that the sun's rays are striking the equator most directly so that's heating the air here and causing it to rise then it sinks back down at 30 degrees and because of this high pressure system at 30 degrees air is going to be moving out towards 0 degrees and 60 degrees we can see here that with our low pressure at the equator our higher pressure at 30 degrees and then our low pressure again at 60 we're going to get air moving out from 30 degrees towards 60 and towards the equator but remember that the air does not move in a straight line it's deflected based on the direction of Earth's spin and so between 0 and 30 degrees we have our air moving from east to west and we call those Eastern trade winds because they used to drive trade from the east to the west because the ships are dependent on sails this also drives the circulation of the ocean currents in a clockwise direction in the northern hemisphere and in a counterclockwise direction in the southern hemisphere then remember that between 30 and 60 degrees the wind is blowing from west over to the east and this is because the earth at 30 degrees is moving so much faster than out at 60 degrees or 80 degrees that the wind is deflected in that same direction as the spin so it moves from west to east now this means that in North America where we live we get our weather from the West so if you're looking at the radar to try to see if we're going to have a snow day you're gonna look over at Chicago and Wisconsin because you know that their storms are headed our direction because we have westerlies or western prevailing winds which means our weather moves from the western United States over to the eastern United States our suggested science Gale for practice up for cue 4.5 today is explaining relationships between characteristics of environmental concepts or models that are represented visually so I want you to see if you can explain how is the Sun responsible for the pattern of air circulation that we see in cycles see on the diagram here alright everybody thanks for tuning in today don't forget to like this video if it was helpful subscribe for future apes video updates and check out other notes over here to the side and as always think like a mountain write like a scholar