0:00:00.089,0:00:04.860 There's an invisible force shaping our lives,[br]affecting the weather, climate, land, economy, 0:00:04.860,0:00:10.710 and whether a flag looks majestic or just[br]kind of... sits there. I'm talking, of course, about the wind. 0:00:10.710,0:00:14.251 Large parts of the globe are brought warmth[br]and water thanks to wind. In Europe, wind 0:00:14.251,0:00:18.862 energy is one of the most popular renewable[br]energies, thanks to wind turbines that harness its power. 0:00:18.862,0:00:22.170 Ships with sails have followed the path of[br]the wind for centuries, bringing trade and 0:00:22.170,0:00:24.010 entire empires along with them. 0:00:24.010,0:00:27.750 Fierce winds can also bring destruction, stripping[br]soil away from the ground or even ripping 0:00:27.750,0:00:28.860 apart buildings. 0:00:28.860,0:00:32.397 Trying to protect ourselves from the wind[br]might feel like we're battling an imaginary foe. 0:00:32.397,0:00:36.970 But wind is definitely not imaginary -- geographers[br]have defined it and have tools to measure 0:00:36.970,0:00:42.059 it! Whether it's a gentle sea breeze or gale-force[br]gusts, wind is any horizontal movement of 0:00:42.059,0:00:46.829 air. And air is a mixture of nitrogen, oxygen,[br]and other gases that blend together so well, 0:00:46.829,0:00:48.329 they tend to act as one. 0:00:48.329,0:00:51.829 Winds are named based on what direction they[br]come from, and some people are even named 0:00:51.829,0:00:57.280 after winds! My name, Alizé, means the northeasterly[br]trade winds in French -- or les vents Alizés, 0:00:57.280,0:01:01.260 the Alizé winds. With a French sailor for[br]a father who used to love sailing the warm 0:01:01.260,0:01:04.309 northeasterly trade winds, it’s no surprise[br]where this came from! 0:01:04.309,0:01:08.670 So let's get deeper into the science of where[br]wind comes from -- it’ll be a whirlwind 0:01:08.670,0:01:09.670 of an adventure. 0:01:09.670,0:01:12.274 I’m Alizé Carrère and this is Crash Course[br]Geography. 0:01:12.274,0:01:19.979 INTRO 0:01:19.979,0:01:23.509 If we zoom out to look at the globe as a whole,[br]we can see that there are global wind patterns 0:01:23.509,0:01:26.979 just like there are global air temperature[br]patterns. And these are intimately linked. 0:01:26.979,0:01:30.849 We know that insolation from the Sun doesn’t[br]get distributed evenly and ends up heating 0:01:30.849,0:01:35.060 places differently. The temperature of a place[br]is tied to several key factors like latitude, 0:01:35.060,0:01:39.469 elevation, how far it is from the ocean or[br]sea, and even what type of surface it is and 0:01:39.469,0:01:41.299 how much of the Sun’s energy it absorbs. 0:01:41.299,0:01:45.329 No matter where we are though, air that’s[br]warm is lighter, less dense, and tends to 0:01:45.329,0:01:49.700 rise. Cool air, on the other hand, is heavier,[br]more dense, and tends to sink. 0:01:49.700,0:01:53.509 And you did hear me correctly -- there's lighter[br]air and heavier air because air molecules 0:01:53.509,0:01:58.200 all have weight. Not a lot, but still weight.[br]The weight of air then leads to atmospheric 0:01:58.200,0:02:03.094 pressure, which comes from all the air above[br]that's pressing down on whatever air there is below. 0:02:03.094,0:02:06.239 So the pressure is much higher where I’m[br]standing in Miami than if we were filming 0:02:06.239,0:02:11.400 this close to outer space. Down here, there’s[br]all 480 kilometers of atmosphere squishing 0:02:11.400,0:02:15.599 down on us. In fact, it’s likely close to[br]standard sea level pressure -- which is exactly 0:02:15.599,0:02:18.590 what it sounds like: the average atmospheric[br]pressure at sea level. 0:02:18.590,0:02:22.269 We don’t crumple like aluminum cans under[br]this enormous pressure because the air and 0:02:22.269,0:02:26.659 water inside us exert an equal amount of pressure[br]outwards. And the exact atmospheric pressure 0:02:26.659,0:02:31.159 in other places will be different depending[br]on where we are, the season, or even the time of day. 0:02:31.159,0:02:34.629 Wind is actually the atmosphere’s way of[br]smoothing out pressure differences, which 0:02:34.629,0:02:38.709 can be created by the daily and seasonal air[br]temperature patterns across Earth’s surface. 0:02:38.709,0:02:42.459 Meteorologists, who study the atmosphere,[br]use air pressure measurements to forecast 0:02:42.459,0:02:46.629 the weather. Like, a weather report on TV[br]might show a map full of H’s and L’s, 0:02:46.629,0:02:48.430 which is actually a map tracking air pressure. 0:02:48.430,0:02:53.659 A giant L stands for low pressure, or a low.[br]On a global scale, a low is an area where 0:02:53.659,0:02:57.380 the pressure near the surface is less than[br]standard sea level pressure. But on a local 0:02:57.380,0:03:01.060 scale like on your local weather report, a[br]low can also be an area where the pressure 0:03:01.060,0:03:04.700 is less than in the surrounding area because[br]there’s actually slightly less air pressing 0:03:04.700,0:03:06.510 down on that part of the Earth. 0:03:06.510,0:03:10.269 Lows go by lots of names. Like you might hear[br]it called a depression or even a cyclone. 0:03:10.269,0:03:13.959 Though it’s not the giant spinning vortex[br]of air we might think of -- that’s a specific 0:03:13.959,0:03:17.749 weather event that only forms in tropical[br]oceans. But we’ll come back to that in upcoming 0:03:17.749,0:03:18.749 episodes. 0:03:18.749,0:03:22.260 To keep it simple, we’ll just call it a[br]low. Lows exist either because air is being 0:03:22.260,0:03:26.780 heated and expands up and out, or air higher[br]up in the atmosphere is spreading out, so 0:03:26.780,0:03:29.030 there’s less air pressing down on Earth’s[br]surface. 0:03:29.030,0:03:32.859 Down on the ground, we might even be able[br]to tell we’re in a low. As air expands and 0:03:32.859,0:03:36.470 rises, winds are drawn towards the center.[br]The rising air cools, and moisture in the 0:03:36.470,0:03:40.210 air condenses into droplets. So if we happen[br]to be in the center of a low, the weather 0:03:40.210,0:03:41.930 would often be pretty cloudy and rainy. 0:03:41.930,0:03:45.890 The giant H’s on the map mark high pressure[br]areas, which we call a high or anticyclone. 0:03:45.890,0:03:50.560 In a high pressure cell, either the air is[br]cooling and becoming denser, so it sinks, 0:03:50.560,0:03:54.099 or the atmosphere high above is piling up,[br]pushing the air below it downward. 0:03:54.099,0:03:57.969 Sinking compresses air molecules together[br]and makes them warm. So any water vapor in 0:03:57.969,0:04:02.079 the air won’t cool to condense into liquid[br]water. That means high pressure systems bring 0:04:02.079,0:04:03.599 weather that’s clear and sunny, which 0:04:03.599,0:04:05.520 I remember as H stands for “happy”. 0:04:05.520,0:04:10.260 High and low pressure cells are usually large[br]-- like they can be 1000 kilometers across. 0:04:10.260,0:04:13.900 And air moving between these vast areas to[br]balance out energy in the atmosphere helps 0:04:13.900,0:04:17.930 us understand and identify the winds. The[br]key is the difference or change in pressure 0:04:17.930,0:04:22.590 between highs and lows, which is called a [br]pressure gradient. Like any fluid, air wants 0:04:22.590,0:04:24.110 to flow from high to low pressure. 0:04:24.110,0:04:27.500 Let’s start on a small scale, and look at[br]an island. When the beaches and land warm 0:04:27.500,0:04:32.169 up faster during the day than the surrounding[br]sea, the air over the island expands, rises, 0:04:32.169,0:04:35.540 and lowers the pressure at the surface. [br]That leaves room for air from the sea to rush 0:04:35.540,0:04:39.520 onto the land, and voilà -- any windsurfer[br]or sun tanner will get a cool sea breeze in 0:04:39.520,0:04:40.520 the afternoon. 0:04:40.520,0:04:44.670 And similar things happen at a bigger scale[br]across the globe! Air at the equator is consistently 0:04:44.670,0:04:48.639 warmed by the Sun and tends to expand and[br]rise, so we get a belt of low pressure around 0:04:48.639,0:04:52.740 the Earth called the equatorial trough. And[br]we’d expect the poles to experience high 0:04:52.740,0:04:54.819 pressure, because the air there is cold and[br]sinking. 0:04:54.819,0:04:59.150 But winds don’t just blow north and south.[br]This is because the Earth rotates. To see 0:04:59.150,0:05:02.509 what really happens to these winds, let’s[br]imagine we’re flying an airplane from the 0:05:02.509,0:05:07.400 North Pole to the South Pole, with a layover[br]in Ecuador on the equator. Let’s go to the Thought Bubble. 0:05:07.400,0:05:08.979 Hello this is Captain Carrère speaking. 0:05:08.979,0:05:13.479 If you look out the windows, you’ll see[br]the surface of the Earth slowly rotating eastwards. 0:05:13.479,0:05:17.580 So in order to stay on a “straight” path,[br]we have to constantly make little turns. 0:05:17.580,0:05:21.870 This phenomenon that causes moving objects[br]-- like our plane or air or water -- to 0:05:21.870,0:05:26.110 seem like they curve as they travel over the[br]rotating Earth is known as the Coriolis effect. 0:05:26.110,0:05:30.550 The Earth is rotating beneath our plane, but[br]also as we travel towards the equator, the 0:05:30.550,0:05:34.400 Earth actually rotates faster because the[br]Earth is bigger at the equator and it has 0:05:34.400,0:05:35.569 to move faster to keep up. 0:05:35.569,0:05:39.569 It’s like a marching band turning a corner[br]-- if they want to stay together in a straight 0:05:39.569,0:05:43.540 line, the marchers on the inside of the circle[br]take much smaller steps and move slower than 0:05:43.540,0:05:44.690 the marchers on the outside. 0:05:44.690,0:05:47.770 So if we’re at the poles, we’d just kind[br]of spin in place. 0:05:47.770,0:05:51.840 But as latitude decreases, our rotational[br]speed increases until we get to the equator 0:05:51.840,0:05:57.000 and the Earth’s surface practically zooms[br]by at 1600 kilometers per hour -- which is 0:05:57.000,0:05:59.541 about twice as fast as our plane. 0:05:59.541,0:06:03.479 Then as our plane gets closer and closer to[br]Ecuador and the equator, our rotational momentum 0:06:03.479,0:06:07.039 comes from the slow speeds at the North Pole,[br]not the rapidly rotating equator. 0:06:07.039,0:06:11.039 Which means we end up getting deflected to[br]the right into the Pacific Ocean and have 0:06:11.039,0:06:12.760 to make little left turns to get to Ecuador. 0:06:12.760,0:06:16.330 Something similar happens on our second flight[br]toward the South Pole. 0:06:16.330,0:06:19.639 But this time we started out rotating faster[br]than our final destination. 0:06:19.639,0:06:24.409 So as we make our final approach to the South[br]Sandwich Islands we’d get deflected left 0:06:24.409,0:06:27.140 and end up east of where we want to be if[br]we didn’t correct. 0:06:27.140,0:06:31.831 Please make sure your seatbelts are fastened[br]and your tray tables are stowed as we prepare for landing! 0:06:31.831,0:06:36.000 Thanks, Thought Bubble. In general, the Coriolis[br]effect deflects objects to the right in the 0:06:36.000,0:06:38.560 Northern Hemisphere and to the left in the[br]Southern Hemisphere. 0:06:38.560,0:06:42.099 Which is how we get those wind spirals around[br]the low and high pressures areas on our weather 0:06:42.099,0:06:46.759 map, and why they’re also called cyclones[br]and anticyclones. The air wants to rush directly 0:06:46.759,0:06:49.949 from the center of the high to the center[br]of the low but gets deflected. 0:06:49.949,0:06:54.229 So in our model, the heated air at the equator[br]first rises upward towards the tropopause, 0:06:54.229,0:06:57.240 which is the boundary between the troposphere[br]and the stratosphere, as it tries to move 0:06:57.240,0:06:59.160 poleward high up in the atmosphere. 0:06:59.160,0:07:02.930 Then as it moves away from the equator, the[br]Coriolis effect causes air traveling northwards 0:07:02.930,0:07:07.759 to turn right, speeding faster east the further[br]north it gets. The air is also cooling, and 0:07:07.759,0:07:11.430 by the time it sinks back to the surface,[br]it’s only reached around 30 degrees latitude. 0:07:11.430,0:07:15.509 So instead of one big circulation cycle, as[br]proposed by George Hadley, an English lawyer 0:07:15.509,0:07:20.470 and amateur meteorologist, who first described[br]it in 1735, we get a more complicated circulation 0:07:20.470,0:07:22.460 system containing the Hadley cell. 0:07:22.460,0:07:25.780 Hadley wanted to understand why surface winds[br]that should have blown straight south towards 0:07:25.780,0:07:29.189 the equator -- along the pressure gradient[br]from high pressure to low pressure -- took 0:07:29.189,0:07:33.449 a turn west. Solving that mystery would help[br]ensure European trading ships would safely 0:07:33.449,0:07:36.210 reach the shores -- and goods -- of the Americas. 0:07:36.210,0:07:39.830 This isn’t the first time our understanding[br]of the winds has gone hand in hand with exploration, 0:07:39.830,0:07:43.669 and trade, wealth, and power were driven by[br]the winds. For instance, new technologies 0:07:43.669,0:07:47.949 created in the 1400s like the quadrant and[br]the astrolabe enabled accurate navigation 0:07:47.949,0:07:50.449 and mapping of ocean currents, winds, and[br]trade routes. 0:07:50.449,0:07:54.289 Over the years many more scientific minds[br]have explored the implications of Hadley’s 0:07:54.289,0:07:57.250 theory, and we’re still learning more as[br]we explore the movement of energy between 0:07:57.250,0:07:58.860 the atmosphere and biosphere. 0:07:58.860,0:08:03.439 We know now that in reality, air in both hemispheres[br]converges in the narrow band around the equator 0:08:03.439,0:08:06.227 called the intertropical convergence zone and rises. 0:08:06.227,0:08:10.090 The surface winds, or doldrums, that form[br]here as the air converges and rises upwards 0:08:10.090,0:08:14.830 are light and not super reliable. Sailing[br]ships could get stuck in the doldrums for days. 0:08:14.830,0:08:18.439 Similarly weak winds are found on the poleward[br]edges of the Hadley cells, where air is being 0:08:18.439,0:08:22.220 forced down, creating high pressure zones[br]centered at about 30 degrees latitude called 0:08:22.220,0:08:24.440 the subtropical high pressure belts. 0:08:24.440,0:08:28.669 Sailors of yore were often forced to eat their[br]horses or throw them overboard in these “horse 0:08:28.669,0:08:32.410 latitudes” to conserve drinking water and[br]lighten the weight while the sailing ships 0:08:32.410,0:08:37.160 waited for the weak winds at the center of[br]these highs to pick up. [Wow, that’s pretty dark.] 0:08:37.160,0:08:39.730 In between these high and low pressure belts, 0:08:39.730,0:08:43.590 there are strong and reliable winds spiraling[br]outwards from the subtropical high pressure 0:08:43.590,0:08:49.871 belt towards the equator. These are the easterly[br]Trade Winds -- and they’re my favorite winds, obviously! 0:08:49.871,0:08:53.320 Many ships have depended on the trade winds,[br]like early Spanish sailing ships as they sought 0:08:53.320,0:08:56.690 God, glory, and gold in what we now call Central[br]and South America. 0:08:56.690,0:09:00.380 Of course, making the return trip was another[br]matter. The ancient mariners of the Spanish 0:09:00.380,0:09:04.420 galleons going home from the Americas plotted[br]a course using the winds blowing poleward 0:09:04.420,0:09:08.900 from the subtropical high pressure belt. These[br]Westerlies are strongly deflected to the right 0:09:08.900,0:09:10.300 and blow from the southwest. 0:09:10.300,0:09:14.250 These strong winds blow towards another low[br]pressure belt called the subpolar lows where 0:09:14.250,0:09:18.740 they clash with the polar Easterlies blowing[br]from the frigid, very high pressure poles. 0:09:18.740,0:09:21.820 In the Southern Hemisphere, they blow with[br]greater strength as there’s very little 0:09:21.820,0:09:24.240 land in these latitudes to interrupt their[br]flow. 0:09:24.240,0:09:28.300 So altogether, on our idealized Earth we’ve[br]seen that there are actually seven pressure 0:09:28.300,0:09:33.990 belts: two polar highs, two subpolar lows,[br]two subtropical highs and one equatorial low. 0:09:33.990,0:09:36.680 And winds flow between these belts of high[br]and low pressure. 0:09:36.680,0:09:41.370 On the real Earth, the belts are not so organized.[br]They form cells of pressure and we see more 0:09:41.370,0:09:45.200 complex patterns of pressure and wind, as[br]the cells shift with the seasons and vary 0:09:45.200,0:09:50.030 between land and water. So our idealized Earth[br]is kind of like a wind and pressure map. It’s 0:09:50.030,0:09:53.600 a simplified model that helps us understand[br]what’s happening on the real Earth. 0:09:53.600,0:09:57.540 Just like the atmosphere works like a cell[br]membrane, the winds are like Earth’s circulatory 0:09:57.540,0:10:01.460 system. So many things vital to our planet[br]flow through the winds. 0:10:01.460,0:10:05.130 During the voyages of discovery in the 15th[br]to 18th centuries -- which we now recognize 0:10:05.130,0:10:08.990 weren’t really discoveries at all -- the[br]knowledge of winds, ocean currents, natural 0:10:08.990,0:10:12.980 harbors and more was an essential foundation[br]for circumnavigating the globe. 0:10:12.980,0:10:17.340 And we continue to rely on the winds to power[br]our economies. As a renewable energy source, 0:10:17.340,0:10:21.140 this silent force will continue to shape our[br]lives in the future. I hope wherever you are 0:10:21.140,0:10:25.220 is in the center of a sunny high pressure[br]area which will be perfect weather to go with 0:10:25.220,0:10:28.113 the flow in the ocean, which we’ll talk[br]about next week. 0:10:28.113,0:10:32.400 Many maps and borders represent modern geopolitical[br]divisions that have often been decided without 0:10:32.400,0:10:37.250 the consultation, permission, or recognition[br]of the land's original inhabitants. Many geographical 0:10:37.250,0:10:40.970 place names also don't reflect the Indigenous[br]or Arboriginal peoples languages. 0:10:40.970,0:10:44.720 So we at Crash Course want to acknowledge[br]these peoples’ traditional and ongoing relationship 0:10:44.720,0:10:47.860 with that land and all the physical and human[br]geographical elements of it. 0:10:47.860,0:10:51.200 We encourage you to learn about the history[br]of the place you call home through resources 0:10:51.200,0:10:55.790 like native-land.ca and by engaging with your[br]local Indigenous and Aboriginal nations through 0:10:55.790,0:10:58.390 the websites and resources they provide. 0:10:58.390,0:11:01.550 Thanks for watching this episode of Crash[br]Course Geography. If you want to help keep 0:11:01.550,0:11:05.535 all Crash Course free for everyone, forever,[br]you can join our community on Patreon.