1 00:00:00,089 --> 00:00:04,860 There's an invisible force shaping our lives, affecting the weather, climate, land, economy, 2 00:00:04,860 --> 00:00:10,710 and whether a flag looks majestic or just kind of... sits there. I'm talking, of course, about the wind. 3 00:00:10,710 --> 00:00:14,251 Large parts of the globe are brought warmth and water thanks to wind. In Europe, wind 4 00:00:14,251 --> 00:00:18,862 energy is one of the most popular renewable energies, thanks to wind turbines that harness its power. 5 00:00:18,862 --> 00:00:22,170 Ships with sails have followed the path of the wind for centuries, bringing trade and 6 00:00:22,170 --> 00:00:24,010 entire empires along with them. 7 00:00:24,010 --> 00:00:27,750 Fierce winds can also bring destruction, stripping soil away from the ground or even ripping 8 00:00:27,750 --> 00:00:28,860 apart buildings. 9 00:00:28,860 --> 00:00:32,397 Trying to protect ourselves from the wind might feel like we're battling an imaginary foe. 10 00:00:32,397 --> 00:00:36,970 But wind is definitely not imaginary -- geographers have defined it and have tools to measure 11 00:00:36,970 --> 00:00:42,059 it! Whether it's a gentle sea breeze or gale-force gusts, wind is any horizontal movement of 12 00:00:42,059 --> 00:00:46,829 air. And air is a mixture of nitrogen, oxygen, and other gases that blend together so well, 13 00:00:46,829 --> 00:00:48,329 they tend to act as one. 14 00:00:48,329 --> 00:00:51,829 Winds are named based on what direction they come from, and some people are even named 15 00:00:51,829 --> 00:00:57,280 after winds! My name, Alizé, means the northeasterly trade winds in French -- or les vents Alizés, 16 00:00:57,280 --> 00:01:01,260 the Alizé winds. With a French sailor for a father who used to love sailing the warm 17 00:01:01,260 --> 00:01:04,309 northeasterly trade winds, it’s no surprise where this came from! 18 00:01:04,309 --> 00:01:08,670 So let's get deeper into the science of where wind comes from -- it’ll be a whirlwind 19 00:01:08,670 --> 00:01:09,670 of an adventure. 20 00:01:09,670 --> 00:01:12,274 I’m Alizé Carrère and this is Crash Course Geography. 21 00:01:12,274 --> 00:01:19,979 INTRO 22 00:01:19,979 --> 00:01:23,509 If we zoom out to look at the globe as a whole, we can see that there are global wind patterns 23 00:01:23,509 --> 00:01:26,979 just like there are global air temperature patterns. And these are intimately linked. 24 00:01:26,979 --> 00:01:30,849 We know that insolation from the Sun doesn’t get distributed evenly and ends up heating 25 00:01:30,849 --> 00:01:35,060 places differently. The temperature of a place is tied to several key factors like latitude, 26 00:01:35,060 --> 00:01:39,469 elevation, how far it is from the ocean or sea, and even what type of surface it is and 27 00:01:39,469 --> 00:01:41,299 how much of the Sun’s energy it absorbs. 28 00:01:41,299 --> 00:01:45,329 No matter where we are though, air that’s warm is lighter, less dense, and tends to 29 00:01:45,329 --> 00:01:49,700 rise. Cool air, on the other hand, is heavier, more dense, and tends to sink. 30 00:01:49,700 --> 00:01:53,509 And you did hear me correctly -- there's lighter air and heavier air because air molecules 31 00:01:53,509 --> 00:01:58,200 all have weight. Not a lot, but still weight. The weight of air then leads to atmospheric 32 00:01:58,200 --> 00:02:03,094 pressure, which comes from all the air above that's pressing down on whatever air there is below. 33 00:02:03,094 --> 00:02:06,239 So the pressure is much higher where I’m standing in Miami than if we were filming 34 00:02:06,239 --> 00:02:11,400 this close to outer space. Down here, there’s all 480 kilometers of atmosphere squishing 35 00:02:11,400 --> 00:02:15,599 down on us. In fact, it’s likely close to standard sea level pressure -- which is exactly 36 00:02:15,599 --> 00:02:18,590 what it sounds like: the average atmospheric pressure at sea level. 37 00:02:18,590 --> 00:02:22,269 We don’t crumple like aluminum cans under this enormous pressure because the air and 38 00:02:22,269 --> 00:02:26,659 water inside us exert an equal amount of pressure outwards. And the exact atmospheric pressure 39 00:02:26,659 --> 00:02:31,159 in other places will be different depending on where we are, the season, or even the time of day. 40 00:02:31,159 --> 00:02:34,629 Wind is actually the atmosphere’s way of smoothing out pressure differences, which 41 00:02:34,629 --> 00:02:38,709 can be created by the daily and seasonal air temperature patterns across Earth’s surface. 42 00:02:38,709 --> 00:02:42,459 Meteorologists, who study the atmosphere, use air pressure measurements to forecast 43 00:02:42,459 --> 00:02:46,629 the weather. Like, a weather report on TV might show a map full of H’s and L’s, 44 00:02:46,629 --> 00:02:48,430 which is actually a map tracking air pressure. 45 00:02:48,430 --> 00:02:53,659 A giant L stands for low pressure, or a low. On a global scale, a low is an area where 46 00:02:53,659 --> 00:02:57,380 the pressure near the surface is less than standard sea level pressure. But on a local 47 00:02:57,380 --> 00:03:01,060 scale like on your local weather report, a low can also be an area where the pressure 48 00:03:01,060 --> 00:03:04,700 is less than in the surrounding area because there’s actually slightly less air pressing 49 00:03:04,700 --> 00:03:06,510 down on that part of the Earth. 50 00:03:06,510 --> 00:03:10,269 Lows go by lots of names. Like you might hear it called a depression or even a cyclone. 51 00:03:10,269 --> 00:03:13,959 Though it’s not the giant spinning vortex of air we might think of -- that’s a specific 52 00:03:13,959 --> 00:03:17,749 weather event that only forms in tropical oceans. But we’ll come back to that in upcoming 53 00:03:17,749 --> 00:03:18,749 episodes. 54 00:03:18,749 --> 00:03:22,260 To keep it simple, we’ll just call it a low. Lows exist either because air is being 55 00:03:22,260 --> 00:03:26,780 heated and expands up and out, or air higher up in the atmosphere is spreading out, so 56 00:03:26,780 --> 00:03:29,030 there’s less air pressing down on Earth’s surface. 57 00:03:29,030 --> 00:03:32,859 Down on the ground, we might even be able to tell we’re in a low. As air expands and 58 00:03:32,859 --> 00:03:36,470 rises, winds are drawn towards the center. The rising air cools, and moisture in the 59 00:03:36,470 --> 00:03:40,210 air condenses into droplets. So if we happen to be in the center of a low, the weather 60 00:03:40,210 --> 00:03:41,930 would often be pretty cloudy and rainy. 61 00:03:41,930 --> 00:03:45,890 The giant H’s on the map mark high pressure areas, which we call a high or anticyclone. 62 00:03:45,890 --> 00:03:50,560 In a high pressure cell, either the air is cooling and becoming denser, so it sinks, 63 00:03:50,560 --> 00:03:54,099 or the atmosphere high above is piling up, pushing the air below it downward. 64 00:03:54,099 --> 00:03:57,969 Sinking compresses air molecules together and makes them warm. So any water vapor in 65 00:03:57,969 --> 00:04:02,079 the air won’t cool to condense into liquid water. That means high pressure systems bring 66 00:04:02,079 --> 00:04:03,599 weather that’s clear and sunny, which 67 00:04:03,599 --> 00:04:05,520 I remember as H stands for “happy”. 68 00:04:05,520 --> 00:04:10,260 High and low pressure cells are usually large -- like they can be 1000 kilometers across. 69 00:04:10,260 --> 00:04:13,900 And air moving between these vast areas to balance out energy in the atmosphere helps 70 00:04:13,900 --> 00:04:17,930 us understand and identify the winds. The key is the difference or change in pressure 71 00:04:17,930 --> 00:04:22,590 between highs and lows, which is called a  pressure gradient. Like any fluid, air wants 72 00:04:22,590 --> 00:04:24,110 to flow from high to low pressure. 73 00:04:24,110 --> 00:04:27,500 Let’s start on a small scale, and look at an island. When the beaches and land warm 74 00:04:27,500 --> 00:04:32,169 up faster during the day than the surrounding sea, the air over the island expands, rises, 75 00:04:32,169 --> 00:04:35,540 and lowers the pressure at the surface.  That leaves room for air from the sea to rush 76 00:04:35,540 --> 00:04:39,520 onto the land, and voilà -- any windsurfer or sun tanner will get a cool sea breeze in 77 00:04:39,520 --> 00:04:40,520 the afternoon. 78 00:04:40,520 --> 00:04:44,670 And similar things happen at a bigger scale across the globe! Air at the equator is consistently 79 00:04:44,670 --> 00:04:48,639 warmed by the Sun and tends to expand and rise, so we get a belt of low pressure around 80 00:04:48,639 --> 00:04:52,740 the Earth called the equatorial trough. And we’d expect the poles to experience high 81 00:04:52,740 --> 00:04:54,819 pressure, because the air there is cold and sinking. 82 00:04:54,819 --> 00:04:59,150 But winds don’t just blow north and south. This is because the Earth rotates. To see 83 00:04:59,150 --> 00:05:02,509 what really happens to these winds, let’s imagine we’re flying an airplane from the 84 00:05:02,509 --> 00:05:07,400 North Pole to the South Pole, with a layover in Ecuador on the equator. Let’s go to the Thought Bubble. 85 00:05:07,400 --> 00:05:08,979 Hello this is Captain Carrère speaking. 86 00:05:08,979 --> 00:05:13,479 If you look out the windows, you’ll see the surface of the Earth slowly rotating eastwards. 87 00:05:13,479 --> 00:05:17,580 So in order to stay on a “straight” path, we have to constantly make little turns. 88 00:05:17,580 --> 00:05:21,870 This phenomenon that causes moving objects -- like our plane or air or water -- to 89 00:05:21,870 --> 00:05:26,110 seem like they curve as they travel over the rotating Earth is known as the Coriolis effect. 90 00:05:26,110 --> 00:05:30,550 The Earth is rotating beneath our plane, but also as we travel towards the equator, the 91 00:05:30,550 --> 00:05:34,400 Earth actually rotates faster because the Earth is bigger at the equator and it has 92 00:05:34,400 --> 00:05:35,569 to move faster to keep up. 93 00:05:35,569 --> 00:05:39,569 It’s like a marching band turning a corner -- if they want to stay together in a straight 94 00:05:39,569 --> 00:05:43,540 line, the marchers on the inside of the circle take much smaller steps and move slower than 95 00:05:43,540 --> 00:05:44,690 the marchers on the outside. 96 00:05:44,690 --> 00:05:47,770 So if we’re at the poles, we’d just kind of spin in place. 97 00:05:47,770 --> 00:05:51,840 But as latitude decreases, our rotational speed increases until we get to the equator 98 00:05:51,840 --> 00:05:57,000 and the Earth’s surface practically zooms by at 1600 kilometers per hour -- which is 99 00:05:57,000 --> 00:05:59,541 about twice as fast as our plane. 100 00:05:59,541 --> 00:06:03,479 Then as our plane gets closer and closer to Ecuador and the equator, our rotational momentum 101 00:06:03,479 --> 00:06:07,039 comes from the slow speeds at the North Pole, not the rapidly rotating equator. 102 00:06:07,039 --> 00:06:11,039 Which means we end up getting deflected to the right into the Pacific Ocean and have 103 00:06:11,039 --> 00:06:12,760 to make little left turns to get to Ecuador. 104 00:06:12,760 --> 00:06:16,330 Something similar happens on our second flight toward the South Pole. 105 00:06:16,330 --> 00:06:19,639 But this time we started out rotating faster than our final destination. 106 00:06:19,639 --> 00:06:24,409 So as we make our final approach to the South Sandwich Islands we’d get deflected left 107 00:06:24,409 --> 00:06:27,140 and end up east of where we want to be if we didn’t correct. 108 00:06:27,140 --> 00:06:31,831 Please make sure your seatbelts are fastened and your tray tables are stowed as we prepare for landing! 109 00:06:31,831 --> 00:06:36,000 Thanks, Thought Bubble. In general, the Coriolis effect deflects objects to the right in the 110 00:06:36,000 --> 00:06:38,560 Northern Hemisphere and to the left in the Southern Hemisphere. 111 00:06:38,560 --> 00:06:42,099 Which is how we get those wind spirals around the low and high pressures areas on our weather 112 00:06:42,099 --> 00:06:46,759 map, and why they’re also called cyclones and anticyclones. The air wants to rush directly 113 00:06:46,759 --> 00:06:49,949 from the center of the high to the center of the low but gets deflected. 114 00:06:49,949 --> 00:06:54,229 So in our model, the heated air at the equator first rises upward towards the tropopause, 115 00:06:54,229 --> 00:06:57,240 which is the boundary between the troposphere and the stratosphere, as it tries to move 116 00:06:57,240 --> 00:06:59,160 poleward high up in the atmosphere. 117 00:06:59,160 --> 00:07:02,930 Then as it moves away from the equator, the Coriolis effect causes air traveling northwards 118 00:07:02,930 --> 00:07:07,759 to turn right, speeding faster east the further north it gets. The air is also cooling, and 119 00:07:07,759 --> 00:07:11,430 by the time it sinks back to the surface, it’s only reached around 30 degrees latitude. 120 00:07:11,430 --> 00:07:15,509 So instead of one big circulation cycle, as proposed by George Hadley, an English lawyer 121 00:07:15,509 --> 00:07:20,470 and amateur meteorologist, who first described it in 1735, we get a more complicated circulation 122 00:07:20,470 --> 00:07:22,460 system containing the Hadley cell. 123 00:07:22,460 --> 00:07:25,780 Hadley wanted to understand why surface winds that should have blown straight south towards 124 00:07:25,780 --> 00:07:29,189 the equator -- along the pressure gradient from high pressure to low pressure -- took 125 00:07:29,189 --> 00:07:33,449 a turn west. Solving that mystery would help ensure European trading ships would safely 126 00:07:33,449 --> 00:07:36,210 reach the shores -- and goods -- of the Americas. 127 00:07:36,210 --> 00:07:39,830 This isn’t the first time our understanding of the winds has gone hand in hand with exploration, 128 00:07:39,830 --> 00:07:43,669 and trade, wealth, and power were driven by the winds. For instance, new technologies 129 00:07:43,669 --> 00:07:47,949 created in the 1400s like the quadrant and the astrolabe enabled accurate navigation 130 00:07:47,949 --> 00:07:50,449 and mapping of ocean currents, winds, and trade routes. 131 00:07:50,449 --> 00:07:54,289 Over the years many more scientific minds have explored the implications of Hadley’s 132 00:07:54,289 --> 00:07:57,250 theory, and we’re still learning more as we explore the movement of energy between 133 00:07:57,250 --> 00:07:58,860 the atmosphere and biosphere. 134 00:07:58,860 --> 00:08:03,439 We know now that in reality, air in both hemispheres converges in the narrow band around the equator 135 00:08:03,439 --> 00:08:06,227 called the intertropical convergence zone and rises. 136 00:08:06,227 --> 00:08:10,090 The surface winds, or doldrums, that form here as the air converges and rises upwards 137 00:08:10,090 --> 00:08:14,830 are light and not super reliable. Sailing ships could get stuck in the doldrums for days. 138 00:08:14,830 --> 00:08:18,439 Similarly weak winds are found on the poleward edges of the Hadley cells, where air is being 139 00:08:18,439 --> 00:08:22,220 forced down, creating high pressure zones centered at about 30 degrees latitude called 140 00:08:22,220 --> 00:08:24,440 the subtropical high pressure belts. 141 00:08:24,440 --> 00:08:28,669 Sailors of yore were often forced to eat their horses or throw them overboard in these “horse 142 00:08:28,669 --> 00:08:32,410 latitudes” to conserve drinking water and lighten the weight while the sailing ships 143 00:08:32,410 --> 00:08:37,160 waited for the weak winds at the center of these highs to pick up. [Wow, that’s pretty dark.] 144 00:08:37,160 --> 00:08:39,730 In between these high and low pressure belts, 145 00:08:39,730 --> 00:08:43,590 there are strong and reliable winds spiraling outwards from the subtropical high pressure 146 00:08:43,590 --> 00:08:49,871 belt towards the equator. These are the easterly Trade Winds -- and they’re my favorite winds, obviously! 147 00:08:49,871 --> 00:08:53,320 Many ships have depended on the trade winds, like early Spanish sailing ships as they sought 148 00:08:53,320 --> 00:08:56,690 God, glory, and gold in what we now call Central and South America. 149 00:08:56,690 --> 00:09:00,380 Of course, making the return trip was another matter. The ancient mariners of the Spanish 150 00:09:00,380 --> 00:09:04,420 galleons going home from the Americas plotted a course using the winds blowing poleward 151 00:09:04,420 --> 00:09:08,900 from the subtropical high pressure belt. These Westerlies are strongly deflected to the right 152 00:09:08,900 --> 00:09:10,300 and blow from the southwest. 153 00:09:10,300 --> 00:09:14,250 These strong winds blow towards another low pressure belt called the subpolar lows where 154 00:09:14,250 --> 00:09:18,740 they clash with the polar Easterlies blowing from the frigid, very high pressure poles. 155 00:09:18,740 --> 00:09:21,820 In the Southern Hemisphere, they blow with greater strength as there’s very little 156 00:09:21,820 --> 00:09:24,240 land in these latitudes to interrupt their flow. 157 00:09:24,240 --> 00:09:28,300 So altogether, on our idealized Earth we’ve seen that there are actually seven pressure 158 00:09:28,300 --> 00:09:33,990 belts: two polar highs, two subpolar lows, two subtropical highs and one equatorial low. 159 00:09:33,990 --> 00:09:36,680 And winds flow between these belts of high and low pressure. 160 00:09:36,680 --> 00:09:41,370 On the real Earth, the belts are not so organized. They form cells of pressure and we see more 161 00:09:41,370 --> 00:09:45,200 complex patterns of pressure and wind, as the cells shift with the seasons and vary 162 00:09:45,200 --> 00:09:50,030 between land and water. So our idealized Earth is kind of like a wind and pressure map. It’s 163 00:09:50,030 --> 00:09:53,600 a simplified model that helps us understand what’s happening on the real Earth. 164 00:09:53,600 --> 00:09:57,540 Just like the atmosphere works like a cell membrane, the winds are like Earth’s circulatory 165 00:09:57,540 --> 00:10:01,460 system. So many things vital to our planet flow through the winds. 166 00:10:01,460 --> 00:10:05,130 During the voyages of discovery in the 15th to 18th centuries -- which we now recognize 167 00:10:05,130 --> 00:10:08,990 weren’t really discoveries at all -- the knowledge of winds, ocean currents, natural 168 00:10:08,990 --> 00:10:12,980 harbors and more was an essential foundation for circumnavigating the globe. 169 00:10:12,980 --> 00:10:17,340 And we continue to rely on the winds to power our economies. As a renewable energy source, 170 00:10:17,340 --> 00:10:21,140 this silent force will continue to shape our lives in the future. I hope wherever you are 171 00:10:21,140 --> 00:10:25,220 is in the center of a sunny high pressure area which will be perfect weather to go with 172 00:10:25,220 --> 00:10:28,113 the flow in the ocean, which we’ll talk about next week. 173 00:10:28,113 --> 00:10:32,400 Many maps and borders represent modern geopolitical divisions that have often been decided without 174 00:10:32,400 --> 00:10:37,250 the consultation, permission, or recognition of the land's original inhabitants. Many geographical 175 00:10:37,250 --> 00:10:40,970 place names also don't reflect the Indigenous or Arboriginal peoples languages. 176 00:10:40,970 --> 00:10:44,720 So we at Crash Course want to acknowledge these peoples’ traditional and ongoing relationship 177 00:10:44,720 --> 00:10:47,860 with that land and all the physical and human geographical elements of it. 178 00:10:47,860 --> 00:10:51,200 We encourage you to learn about the history of the place you call home through resources 179 00:10:51,200 --> 00:10:55,790 like native-land.ca and by engaging with your local Indigenous and Aboriginal nations through 180 00:10:55,790 --> 00:10:58,390 the websites and resources they provide. 181 00:10:58,390 --> 00:11:01,550 Thanks for watching this episode of Crash Course Geography. If you want to help keep 182 00:11:01,550 --> 00:11:05,535 all Crash Course free for everyone, forever, you can join our community on Patreon.