Where Does Wind Come From? Crash Course Geography #8 - Free Educational videos for Students in K-12

Where Does Wind Come From? Crash Course Geography #8 - By Math and Science

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00:0-1	there's an invisible force shaping our lives affecting the weather
00:02	, climate , land economy and whether a flag looks
00:05	majestic or just kind of sits there . I'm talking
00:08	of course about the wind . Large parts of the
00:10	globe are brought warmth and water thanks to wind In
00:13	europe , wind energy is one of the most popular
00:15	renewable energies , thanks to wind turbines that harness its
00:17	power . Ships with sails have followed the path of
00:19	the wind for centuries , bringing trade and entire empires
00:22	along with them . Fierce winds can also bring destruction
00:25	, stripping soil away from the ground or even ripping
00:27	apart buildings trying to protect ourselves from the wind might
00:29	feel like we're battling an imaginary foe , but wind
00:32	is definitely not imaginary . Geographers have defined it and
00:35	have tools to measure it , whether it's a gentle
00:37	sea breeze or gale force gusts . Wind is any
00:40	horizontal movement of air and there is a mixture of
00:43	nitrogen , oxygen and other gases that blend together so
00:46	well . They tend to act as one winds are
00:47	named based on what direction they come from . And
00:50	some people are even named after winds . My name
00:52	Elise means the north easterly trade winds in french or
00:55	live analyses the alleys winds with a french sailor .
00:58	For a father who used to love sailing the warm
01:00	north easterly trade winds . It's no surprise where this
01:03	came from . So let's get deeper into the science
01:05	of where wind comes from . It will be a
01:07	whirlwind of an adventure . I'm al is a career
01:09	and this is crash course geography . Mhm . Yeah
01:19	. If we zoom out and look at the globe
01:20	as a whole , we can see that there are
01:22	global wind patterns , just like there are global air
01:24	temperature patterns and these are intimately linked . We know
01:26	that insulation from the sun doesn't get distributed evenly and
01:29	ends up heating places differently . The temperature of a
01:32	place is tied to several key factors like latitude elevation
01:35	, how far it is from the ocean or sea
01:37	and even what type of surface it is and how
01:39	much of the sun's energy it absorbs . No matter
01:41	where we are though , air that's warm is lighter
01:43	, less dense and tends to rise . Cool air
01:46	on the other hand , is heavier , more dense
01:48	and tends to sink . And you did hear me
01:49	correctly , there's lighter air and heavier air because air
01:52	molecules all have weight , not a lot , but
01:55	still weight . The weight of air then leads to
01:57	atmospheric pressure , which comes from all the air above
02:00	that's pressing down on whatever air there is below .
02:02	So the pressure is much higher where I'm standing in
02:04	Miami than if we were filming this close to outer
02:06	space Down here , there's all 480 km of atmosphere
02:10	squishing down on us . In fact , it's likely
02:12	close to standard sea level pressure , which is exactly
02:15	what it sounds like the average atmospheric pressure at sea
02:17	level . We don't crumple like aluminum cans under this
02:20	enormous pressure because the air and water inside us exert
02:23	an equal amount of pressure outwards , and the exact
02:25	atmospheric pressure in other places will be different depending on
02:27	where we are the season or even the time of
02:29	day . Wind is actually the atmosphere's way of smoothing
02:32	out pressure differences , which can be created by the
02:35	daily and seasonal air temperature patterns across Earth's surface .
02:37	Meteorologists who studied the atmosphere use air pressure measurements to
02:41	forecast the weather . Like a weather report on tv
02:44	might show a map full of H . S .
02:45	And L's . Which is actually a map tracking air
02:47	pressure . A giant L . Stands for low pressure
02:50	or a low on a global scale . A low
02:52	area is where the pressure near the surface is less
02:54	than standard sea level pressure . But on a local
02:56	scale , like on your local weather report , a
02:58	low can also be an area where the pressure is
03:00	less than in the surrounding area because there's actually slightly
03:03	less air pressing down on that part of the earth
03:05	. Lows go buy lots of names . Like you
03:07	might hear it called a depression or even a cyclone
03:09	though it's not the giant spinning vortex of air we
03:11	might think of that's a specific weather event that only
03:14	forms and tropical oceans . But we'll come back to
03:16	that in upcoming episodes to keep it simple . We'll
03:18	just call it a low . Lows exist either because
03:21	air is being heated and expands up and out or
03:23	air higher up in the atmosphere is spreading out so
03:26	there's less air pressing down on Earth's surface down on
03:28	the ground . We might even be able to tell
03:30	we're in a low as their expands and rises ,
03:32	winds are drawn toward the center , the rising air
03:34	cools and moisture in the air condenses into droplets .
03:37	So if we happen to be in the center of
03:38	a low , the weather would often be pretty cloudy
03:40	and rainy . The giant H is on the map
03:42	mark . High pressure areas which we call a high
03:44	or anti cyclone in a high pressure cell , either
03:47	the air is cooling and becoming denser so it sinks
03:49	, or the atmosphere high above is piling up ,
03:51	pushing the air below it downward , sinking , compresses
03:54	air molecules together and makes them warm so any water
03:57	vapor in the air won't cool to condense into liquid
03:59	water . That means high pressure systems bring weather that's
04:02	clear and sunny , which I remember as a church
04:04	stands for happy high and low pressure cells are usually
04:06	large like they can be 1000 km across and air
04:10	moving between these vast areas to balance out energy in
04:12	the atmosphere helps us understand and identify the winds .
04:15	The key is the difference or change in pressure between
04:17	highs and lows which is called a pressure gradient .
04:20	Like any fluid air wants to flow from high to
04:22	low pressure . Let's start on a small scale and
04:25	look at an island . When the beaches and land
04:26	warm up faster during the day than the surrounding sea
04:29	, the air over the island expands , rises and
04:31	lowers the pressure at the surface . That leaves room
04:33	for air from the sea to rush onto the land
04:35	and wanna any windsurfer a son tanner will get a
04:38	cool sea breeze in the afternoon and similar things happen
04:40	at a bigger scale . Across the globe . Air
04:42	. The equator is consistently warmed by the sun and
04:45	tends to expand and rise . So we get a
04:46	belt of low pressure around the Earth called the equatorial
04:49	trough . And we'd expect the polls to experience high
04:51	pressure because the air there is cold and sinking ,
04:54	but winds don't just blow north and south . This
04:56	is because the earth rotates to see what really happens
04:59	to these winds . Let's imagine we're flying an airplane
05:01	from the north pole to the south pole with a
05:03	layover in Ecuador on the equator . Let's go to
05:05	the thought bubble . Hello , this is Captain Career
05:08	speaking . If you look out the windows , you'll
05:10	see the surface of the earth slowly rotating eastwards .
05:12	So in order to stay on a straight path ,
05:14	we'd have to constantly make little turns . This phenomenon
05:17	that causes moving objects like our plane or air or
05:20	water to seem like they curve as they travel over
05:23	the rotating Earth is known as the Coriolis effect .
05:25	The Earth is rotating beneath our plane , but also
05:28	as we travel towards the equator . The Earth actually
05:30	rotates faster because the Earth is bigger at the equator
05:33	and it has to move faster to keep up .
05:35	It's like a marching band turning a corner . If
05:37	they want to stay together in a straight line ,
05:39	The marches on the inside of the circle take much
05:41	smaller steps and moves slower than the marchers on the
05:43	outside . So if we're at the polls , we
05:45	just kind of spin in place . But as latitude
05:48	decreases , our rotational speed increases until we get to
05:50	the equator and the Earth's surface practically zooms by its
05:54	1600 km/h , which is about twice as fast as
05:57	our plane . Then , as our plane gets closer
05:59	and closer to Ecuador and the equator are rotational momentum
06:03	comes from the slow speeds at the north pole ,
06:04	not the rapidly rotating equator , which means we end
06:07	up getting deflected to the right into the pacific ocean
06:10	and have to make little left turns to get to
06:12	Ecuador . Something similar happens on our second flight towards
06:15	the south Pole , but this time we started out
06:17	rotating faster than our final destination . So as we
06:20	make our final approach to the South sandwich Islands ,
06:22	we'd get deflected left and end up east of where
06:25	we want to be . If we didn't correct ,
06:26	Please make sure your seatbelts are fastened and your tray
06:29	tables are stowed as we prepare for landing . Thanks
06:31	, that bubble in general , the Coriolis effect deflect
06:34	objects to the right in the Northern Hemisphere and to
06:36	the left in the southern hemisphere , which is how
06:38	we get those winds spirals around the low and high
06:40	pressure areas on our weather map , and why they're
06:42	also called Cyclones and anti cyclones . The air wants
06:45	to rush directly from the center of the high to
06:47	the center of the low but gets deflected . So
06:49	in our model , the heated air at the equator
06:51	first rises upward towards the trope a pause which is
06:53	the boundary between the troposphere and stratosphere as it tries
06:56	to move poll word high up in the atmosphere .
06:58	Then , as it moves away from the equator ,
07:00	the coriolis effect causes air traveling northwards to turn right
07:03	, speeding faster east . The further north it gets
07:05	, the air is also cooling and by the time
07:07	it sinks back to the surface , it's only reached
07:09	around 30 degrees latitude . So instead of one big
07:11	circulation cycle , as proposed by George Hadley , an
07:14	english lawyer and amateur meteorologist who first described it in
07:17	17 35 we get a more complicated circulation system containing
07:20	the Hadley Cell . Had we wanted to understand why
07:23	surface winds that should have blown straight south towards the
07:25	equator , along the pressure gradient from high pressure to
07:27	low pressure , took a turn west , solving that
07:30	mystery would help ensure european trading ships would safely reach
07:33	the shores and goods of the Americas . This isn't
07:36	the first time our understanding of the winds has gone
07:38	hand in hand with exploration and trade , wealth and
07:40	power were driven by the winds . For instance ,
07:42	new technologies created in the 14 hundreds , like the
07:44	quadrant and the astrolabe enabled accurate navigation and mapping of
07:48	ocean currents , winds and trade routes . Over the
07:50	years , many more scientific minds have explored the implications
07:53	of Hadley's theory , and we're still learning more as
07:55	we explore the movement of energy between the atmosphere and
07:57	the biosphere . We now know that in reality ,
07:59	air in both hemispheres converges in the narrow band around
08:02	the equator called the intertropical convergence zone and rises the
08:05	surface winds , or doldrums that form here as air
08:08	converges and rises upwards are light and not super reliable
08:11	sailing ships could get stuck in the doldrums for days
08:14	. Similarly weak winds are found on the pole word
08:16	edges of the Hadley cells where air is being forced
08:18	down , creating high pressure zone centered at about 30
08:20	degrees latitude . Called the subtropical high pressure belts .
08:23	Sailors of Your were often forced to eat their horses
08:26	or throw them overboard in these horse latitudes to conserve
08:29	drinking water and lighten the weight . While the sailing
08:31	ships waited for the week winds at the center of
08:33	these highs to pick up , wow , that's pretty
08:36	dark in between these high and low pressure belts ,
08:39	there are strong and reliable winds spiraling outward from the
08:41	subtropical high pressure belt towards the equator . These are
08:45	the easterly trade winds and they're my favorite winds .
08:48	Obviously many ships have depended on the trade winds like
08:51	early spanish sailing ships as they sought God glory and
08:53	gold . In what we now call central and south
08:55	America , of course , making the return trip was
08:57	another matter . The ancient Mariners of the spanish galleons
09:00	, going home from the Americas plotted a course using
09:02	the winds blowing poll Word from the subtropical high pressure
09:05	belt , these westerly are strongly deflected to the right
09:08	and blow from the southwest . These strong winds blow
09:10	towards another low pressure belt called the sub polar lows
09:13	, where they clashed with the polar easterly blowing from
09:15	the frigid , very high pressure polls in the southern
09:18	hemisphere . They blow with greater strength as there's very
09:21	little land in these latitudes to interrupt their flow .
09:23	So all together on our idealized Earth , we've seen
09:26	that there are actually seven pressure belts to polar highs
09:29	, to sub polar lows to subtropical highs and one
09:32	equatorial low . And winds flow between these belts of
09:34	high and low pressure on the real earth . The
09:37	belts are not so organized , they form cells of
09:40	pressure and we see more complex patterns of pressure and
09:42	wind as the cells shift with the seasons and vary
09:44	between land and water . So our idealized Earth is
09:47	kind of like a wind and pressure map . It's
09:49	a simplified model that helps us understand what's happening on
09:52	the real earth , just like the atmosphere works like
09:54	a cell membrane . The winds are like earth circulatory
09:56	system , so many things vital to our planet flow
09:59	through the winds during the voyages of discovery in the
10:02	15th to 18th centuries , which we now recognize weren't
10:04	really discoveries at all the knowledge of winds , ocean
10:07	currents , natural harbors and more was an essential foundation
10:10	for circumnavigating the globe and we continue to rely on
10:13	the winds to power our economies as a renewable energy
10:16	source . This silent force will continue to shape our
10:18	lives in the future . I hope , wherever you
10:20	are , is in the center of a sunny high
10:22	pressure area , which will be perfect weather to go
10:24	with the flow in the ocean , which is what
10:26	we'll talk about next week . Many maps and borders
10:28	represent modern geopolitical divisions that have often been decided without
10:31	the consultation , permission or recognition of the land's original
10:34	inhabitants . Many geographical place names also don't reflect the
10:38	indigenous or aboriginal peoples languages . So we have crash
10:41	course , want to acknowledge these people's traditional and ongoing
10:43	relationship with that land and all the physical and human
10:46	geographical elements of it . We encourage you to learn
10:48	about the history of the place you call home through
10:50	resources like native land dot C . A . And
10:52	by engaging with your local indigenous and aboriginal nations through
10:55	the websites and resources . They provide thanks for watching
10:58	this episode of Crash Course Geography . If you want
11:00	to help keep all crash Course free for everyone forever
11:03	, you can join our community on Patreon .

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