Why East Coasts Lack Deserts (Usually)
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- čas přidán 8. 08. 2023
- Rather than seeing consistent “band of deserts” in the subtropics on our planet, we actually see a major asymmetry: subtropical deserts are almost always absent from eastern coastlines. This is true in North America, South America, Australia, Southern Africa, and Australia. In general, rainfall is much greater on the eastern side of a landmass at subtropical latitudes. Why do we see this pattern? Why are eastern coastlines, at subtropical latitudes, usually much more humid? This is critical to understanding the geography of deserts.
Image Sources:
Arizona State University
Wikipedia Creative Commons (Shwollo)
Google Earth
earth.nullschool.net
NASA
Information Sources:
Nicholson, S. E. (2011). Dryland Climatology. United Kingdom: Cambridge University Press.
Ahrens, C. D. (2013). Meteorology Today (10th ed., pp. 490-492). Brooks/Cole, Cengage Learning.
Koster, R., Jouzel, J., Suozzo, R., Russell, G., Broecker, W., Rind, D., & Eagleson, P. (1986). Global sources of local precipitation as determined by the Nasa/Giss GCM. Geophysical Research Letters, 13(2), 121-124. doi:10.1029/gl013i002p00121
Zemp, D. C., Schleussner, C.-F., Barbosa, H. M. J., van der Ent, R. J., Donges, J. F., Heinke, J., … Rammig, A. (2014). On the importance of cascading moisture recycling in South America. Atmospheric Chemistry and Physics, 14(23), 13337-13359. doi:10.5194/acp-14-13337-2014
Ampuero, A., Stríkis, N. M., Apaéstegui, J., Vuille, M., Novello, V. F., Espinoza, J. C., … Siffedine, A. (2020). The forest effects on the isotopic composition of rainfall in the northwestern Amazon Basin. Journal of Geophysical Research: Atmospheres. doi:10.1029/2019jd031445
Yang, Z., & Dominguez, F. (2019). Investigating land surface effect on the moisture transport over South America with a moisture tagging model. Journal of Climate. doi:10.1175/jcli-d-18-0700.1
A New Look into the South America Precipitation Regimes: Observation and Forecast. Glauber W. S. Ferreira. Michelle S. Reboita. Atmosphere 2022, 13(6), 873; doi.org/10.3390/atmos13060873
Rocha, V. M., Da Silva, P. R. T., Gomes, W. B., Vergasta, L. A., & Jardine, A. (2018). Precipitation Recycling in the Amazon Basin: A Study Using the ECMWF Era-Interim Reanalysis Dataset. Geography Department University of Sao Paulo, 35, 71-82. doi:10.11606/rdg.v35i0.139494
Agel, L., Barlow, M., Qian, J.-H., Colby, F., Douglas, E., & Eichler, T. (2015). Climatology of Daily Precipitation and Extreme Precipitation Events in the Northeast United States. Journal of Hydrometeorology, 16(6), 2537-2557. doi:10.1175/jhm-d-14-0147.1
eumetrain.org. (2012). Cyclogenesis and Extra-tropical Cyclones Over Southeastern South America. Meteorological Satellite Data Training. resources.eumetrain.org/satma...
Monthly Wind Climatology. Climate Monitoring Technologies, Columbia University. iridl.ldeo.columbia.edu/mapro... - Věda a technologie
Apologies, the link is casualearthdandavis.wordpress.com , I misspoke.
Do the video explaining why the horn of africa is a desert!! (or at least explain it to me here haha). love seeing you back!
That is such a long link and hard to remember lol, could use some simplifying
@@Absorr Unfortunately, it is the only one available without buying my own domain
You sound so much like Grady from Practical Engineering. Wonder if you're from the same part of the US?
I have a question about tidal periods.
They say it's the moon's gravitational pull that causes tides in earth's ocean.
But, but, but.... if you calculate the moon's gravitational pull on earth, it's only about 5.5* 10^-6 g....
Newton's law F = mg = G * M * m / r^2
thus g = G * M / r^2 = (6.67 * 10 ^ -11) * (7.34 * 10^22) / (3 * 10^8)^2 = 5.4 * 10^-5 m/s2
thus, moon's pull on earth = 5.5 *10^-6 g
It's like micro gravity experienced in earth's orbit, which is negligible, which can be easily cancelled by wind force, ocean current, even movement of water due to temperature differential.
More odd is that the Sun's gravitational pull is about 100 times larger on earth than that of the moon.
g = G * M / r^2 = (6.67 * 10 ^ -11) * (1.9 * 10^30) / (150 * 10^9)^2 = 5.6 * 10^-3 m/s2
thus, sun's pull on earth = 5.7 * 10^-4 g
So, by this, tide is definitely NOT caused by the moon.
Have you tracked the position of the moon, max tide timing?
I bet they would not match, not at all.
Besides, tide bulges when the moon is at the opposite side, where the conventional explanation makes no sense.
Let me know what you think, thanks,
That’s explains why the northeast coast of hawaii is wet while Mexico is drier at a similar latitude, since the Pacific Ocean currents are picking up steam on their way up where the Hawaiian archipelago is located.
Many other differences too, scale and rain shadow, plus a large continental land mass adjacent.
One is also an island lmao
No, the eastern side of Hawaii is wet and the west dry because of prevailing winds and the effects of air rising and falling as it goes over the volcanic peaks. As air rises (being forced up as it hits the mountains) it cools and moisture in it condenses then falls as rain. When the air moves over the mountain and down the other side, it warms as it descends. Since it lost its moisture when it was going up, it is now dry and that results in the western slopes of Hawaii being arid.
It also speeds up as it falls, resulting in fast warm dry air. This is actually what is driving the wildfires that are going on there now.
@@Tugela60yep same goes for Madeira Island, despite being in the Mediterranean basin at 32 parallel, it’s incredibly green, all thanks to the mountains. But it does get dry for 2 months during July and August.
Spaniards discovered Polynesian Hawaii first, not the British, ad proven in "The British empire was NOT the biggest."
I live on the East coast of Australia and always wondered why the climate was so different from western Australia since we were on the same latitude; now I know, thanks!
Edit, have to say though, given the choice between Queensland's humidity and the wests dry heat, Id take dry heat every summer...I love our rainforests though, and thats an upside.
I was just going to comment that I'm a bit disappointed that it focussed so heavily on north and south america. The thumbnail had Australia, so I thought it might have been a balanced video for a change, but it tricked me!
@@sherrijennings9309 I discussed South America the most (using North America as a comparison) because it's a great exception. Australia, on the other hand, perfectly illustrates the general rule I'm describing--hence the thumbnail. But of course there is much more to say.
In particular, the Great Dividing Range enhances rainfall on the east coast. It may not be particularly high, but it is relatively consistent. It enhances rainfall not just through orographic effect (physical lifting by the terrain), but also by causing convergence. Trade winds are forced to slow down as they approach Australia and curve poleward, thanks to the Dividing Range. This causes convergence (picture an air pile-up), which makes rising motions more likely, and rising air tends to encourage rainfall.
@casualearth9076 thanks for the explanation. I hadn't really thought about trade winds effecting our weather apart from El Nino/La Nina cycles because where I live in northern Victoria, (and most of the continent), our cold fronts and thus most of our weather comes from the west. An interesting video would be on how the Indian Ocean Dipole effects weather in Australia and Asia more generally. The phase of the IOD seems to coincide with pacific trade wind El Nino/La Nina cycles too. Any idea how/why that might happen?
@@sherrijennings9309 I wouldn't say most of the weather on the continent comes from westerlies, though that's certainly true in Victoria. In summer, prevailing winds in New South Wales, even well south of Sydney, are easterly (northeasterly in that area, to be specific)--this is true along the entire eastern coast in a month like January. At such latitudes, people rarely call them "trade winds", but essentially, they are. In addition, the monsoon that brings rain to most of the interior of the continent comes from the north--it is Indo-Pacific water vapor. You can see this using the monthly wind vector map, created by Columbia university, linked in the description of this video. But yes, it is the westerlies that bring rain to places like Perth, Adelaide, and Melbourne (coastlines on the southern half of the landmass that face west or south).
@casualearth9076 I have to confess I don't pay much attention to the weather in Sydney/Brisbane. That narrow slice of the east coast accounts for a disproportionate amount of the population, but only a tiny slice of the weather, which i guess was the point in your video. the rest of the southern part of the country looks to the west, or south west during winter, for our incoming weather fronts. if you look at Victoria in July, most of the weather fronts come up from the southern ocean through the great Australian Bight, or accross from Western Australia
My 2 main takeaways:
1- the amazon rainforest makes total sense, now that I see where the wind comes from.
2- there's a dry line from Dakar to Urumqi, and to me as a History geek, that is some very interesting background context to be aware of.
I've subscribed. Cheers.
A lot of the dry lines around the world, and the deserts, come down to how easy it is to keep flocks of goats.
They eat everything, to cook one the you need firewood, and that is your forest cover gone. They go feral and now goats eat everything right up to the alpine line, and the deforestation over centuries results in erosion and that makes the local climate turn to desert. This is ABSOLUTELY why the Arabian peninsular is all desert. Camels and goats for thousands of years.
This isn't guesswork. Europeans have gone to parts of Arabia and killed all the feral goats, and convinced ( with money ) the locals not to cut down the little trees to sell as firewood, and Voila, just 22 years and they proved that Arabia without humans = forest.
@uncletiggermclaren7592 Really? That's super interesting, do you have a link to that story? I'd love to read about it!
The sad thing about the Amazon is that if it keeps getting destroyed to make room for farmland and pastures, it'll lose its ability to sustain itself with rain (as we're starting to see right now). It could cause a redesertification, drying along the whole interior South America.
In Brazil, we learn that the Southeast coast is not a desert because of how much water evaporates in the Amazon and comes down here because of "flying rivers".
Yes, I love the term "flying river"--a very evocative description.
@@casualearth9076 Bet you can find dragons up there too lmao
So the Sertao isn’t a desert?
@@moistmellow1198 There is a semi-arid region in Northeast Brazil, but between it and the east coast is the Atlantic Forest (tropical rainforest and monsoon forest), a narrow humid region.
@@casualearth9076 What causes this dry area of northeastern Brazil? It's an abnormal east coast tropical desert.
I've always had an affinity for geography (I remember my obsession with maps in elementary school), though in the last few years I had forgotten its wonders due to my immersion in professional studies. Channels like these are just a treat; I really appreciate the soft-spoken voice and only necessary imagery. Keep up the fantastic work, sir, and have a great day
For me, I need the information to make realistic terrain and climate for my fictional worlds I'm making. Most people just put random mountains and biomes anywhere.
Dude, same! When I was in 5th grade, I won my entire school’s (K-9th grade school) geography bee. For some odd reason, geography fascinated my interests as a young kid
Same
This just blew my mind! That the orientation of a continent can affect rainfall (i.e. Northeastern US vs. Southern Argentina) makes complete sense but is something I never thought of. Awesome video!
Argentina is in a rainshadow of the andes mountains.
Something really cool about the southern Andes is you can physically see the rain shadow flip as the prevailing wind flips: it goes from
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to
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Pretty much instantly due to the prevailing wind flipping at the more southern latitudes
Look up the satellite of South America, very cool
@@ForageGardenerthe eastern US too certainly is rain-shadowed too.
@@ForageGardener But the point is that isnt the only reason.
@@bentownsend4017 On thng is tha Sourthern Andes arent high enough to be a real rain shadow.
2:09 I wish badly to see a video about this area. Heck, a video on the Sahara + Arabian Peninsula deserts would be cool to hear about
One of the only cool things about that region.
Yes, that will be the next video. Thanks for watching!
@@casualearth9076will you cover Somalia as well?
@@SMiki55 Yes!
@@casualearth9076 Why is Somalia is hot & dry year-round?
Hey, you're back! Such a great channel :)
I know I was stoked
Thanks! I plan on doing many more in the future, despite the temporary slowdown. I began a career as an educator last year, and my first year, I had to make all the material for my courses. Once the summer began, I then had to take a class to get my licensure. Once these things are knocked out, I'll be free to spend every summer making loads of videos, which I'll release throughout the year on a more regular basis. For now, I'm just doing what I can. Thanks for staying a subscriber, you are keeping this dream afloat for me more than anyone else!
@@casualearth9076Take it easy and good luck on your career man!
The first few years of teaching can be brutally busy. I am hoping (finally) for a lighter academic load this year, since (finally) all of my classes are repeats.
@@joshuaharper372 Same situation here, thankfully. Hope you have a good year!
Hands down, the most easily digestable geography videos on youtube. There are other greats on yt (i like atlas pro too) but yours hit a particular sweet spot of delivering valueable information in a tight package.
I really hope you keep making these. I read in another post that you have ~100 scripts written. I hope everything is well on your life and things continue to allow you the time to work on this project, it is so worth it and important!
I'm a very visual person and I just want to say thank you for including the graphic at 3:30. That map tells me everything I need to know and I understand now. Great content, and I'm now subscribed.
I can’t wait for the video on why Somalia is a desert - I’ve always been confused by it!
This channel is amazing.
Interesting topics, quality scientific rigor, and no stupid ads or sponsors. Just the facts.
A sweet nectar like this channel seems rarer and rarer these days on this website. It’s like being at an oasis binging your few videos.
Please keep making them! They are awesome!
I am from Argentina, and I always thought it was just the Andes rainshadow. Very interesting. I guess that if the Patagonian steppe was more east, it would be all green. The Falklands for instance, seem a better place for trees and its way more green than the land to its west.
Hey, Raleigh NC native here!
Enjoyed this video, I learned a lot. I subbed, looking forward to more
So glad to see Casual Earth is back in production- I have really missed it. Excellent videos. The voice is so perfect for this, and the visuals are so professional! I use these in my teaching!
Thanks so much!
Well New England’s high rainfall is also due to the presence of Great Lakes directly to the west of it meaning that westerlies pick up moisture from the Great Lakes before reaching New England. And it’s not just Patagonia but Siberia and northeast China is also much drier than New England especially in winter due to not having equivalent of Great Lakes
True--the Great Lakes add significant precipitation, though this is mostly on the other side of the Appalachians. Siberia and Northeast China do have much drier winters, though they have heavy rainfall in summer and have much more precipitation than the Patagonian steppe.
That's what I was wondering, thanks!
Siberia and China are dry in winter because of the high pressure system known as the Siberia High, not because of the absence of lakes
@@solomon4554 The Siberian high is important, but cold dry air masses from the Canadian High are analogous---and when they cross the Great Lakes, they gain significant moisture. When the cold, dry air from the Siberian high crosses the Sea of Japan, the same thing happens.
But I guess one thing that I find fascinating that relates to the topic: a lot of Newfoundland has winter precipitation maximums due to low pressure systems, I guess that’s also a cool tidbit,
great geography information + calm voice = I subscribe ☺ content like yours really sparks my curiosity, thanks!
Excellent presentation of this topic. I've been pondering this for years and now it makes sense. Thank you!
There used to be a major east coast desert, fom southeastern Brazil to central Argentina. Most famously, there are marks of it on the seashore, at the base of the stone pillars of the city of Torres, which are composed of red sandstone, while the rest of the rocks is basalt.
It sat at about the same latitudes as the Kalahari desert and Western Australia.
Thankfully, the rising of the Andes saved the region, as it traps moisture from the Atlantic and Amazon, and pours it down east as rain. Those mountains made, perhaps, the best land on the planet.
Nothing I love more than getting detailed and interesting answers to questions I never had, but wish I did. Fantastic vid, time to go through your backlog :)
This channel has some really good videos! And I actually lived in North Carolina for a few years so that’s cool to see that you’re from there
I've been wanting to find videos like this that explain the science behind biome placement in our own world for worldbuilding maps of alien planets, and this video already explains a ton of stuff I never knew. Keep up the good work!
Your ability to answer multiple questions I have always wondered about our Earth in one short video that was randomly recommended to me just earned you a new sub! Great content!
Just got this in my recommended and this is my first time watching this channel. This is fabulous!! This is the best-presented earth science content I've ever seen on CZcams. It's not filled with the highly technical jargon of nerd channels (I like those too but they're tough to digest), nor is it filled with the spectacular yet dubious claims of edutainment channels. I can't wait until you get popular, keep up the great work!!!
Those mainstream science channels are cringeworthy. The narrator speaks in a fast, enthusiastic tone that is off-putting. Lots of irrelevant stock photos/videos, etc. I like this calm, slow narration with using relevant illustrations.
I have no clue how you managed to make the topic interesting, but you did. Kudos. And I will be keeping these lessons in mind when designing my TTRPG world map.
Your content is extremely well produced and well researched. I look forward to all your future projects!
This channel is an absolute gem! Keep up the good work!
Excellent video!
Great fan of the channel
The day i first found a video of yours y immediately subscribed and proceeded to binge watch all your released videos.
I always thought that this platform missed the kind of content you create. There are many good videos which talk about climate for sure, but you are the one who directly talks about and answers many of my questions i have been formulating for years but haven't quite found the answer to.
I for example really enjoyed your video about the dry climate of northern Columbia and Venezuela, i took a look at the region many times when spending my free evenings looking at Atlases or flying across the world on Google Earth. But it was only when i saw your video that i first saw an explanation to that weird phenomenon on that rather obscure part of the world.
Your content is interesting, concise and very appealing to someone like me who has spent way to many weekend looking at maps and Geography books.
There is something beautiful about seeing all those different fields like climate science, biology, human history and economics interacting through cause and effect to create the stunning world we live in.
Keep up the good work!
And if you ever run out of ideas, which i doubt, me and other viewers will sure have some in reserve.
Thanks so much!
I certainly relate to your anecdote of spending a plethora of free hours perusing Google Earth and likewise maps. Keep asking questions; the world needs more inquisitive folks, especially geography geeks.
This guy should have more subs
He is really underrated!
I love the technical content in these videos but explained clearly enough for a layperson to understand. I can feel so lonely as someone like me who is interested in weather and climate...this is exactly what I've been looking for! Subscribed!
One thing that struck me is that there is no ocean cycle in the northern Indian ocean , which helps explain the deserts of southwestern Asia, which are at similar latitudes to the Sahara.
I never realized that the coast of Patagonia goes away from the current while the coast of North America parallels the Gulf Stream. At least through Nova Scotia. Labrador's a different matter.
You mean the current parallels the continent and the continent parallels the upper winds.
Amazing, I always knew this but wanted a more in depth vid like this
@Casual Earth - Superb job. This is a very interesting topic. I like the way your voice sounds and how the information is presented. I grew up just north of the 41st line of latitude not too far from the Atlantic Ocean. I also lived in Argentina and always wondered why Patagonia did not receive its own version of our winter Nor’easters. Question answered!
Fantastic video. These videos answers all the questions I ever had in High school geography class. Can’t wait for more videos. 👍
Great channel, deserves more traction! One thing that might help is to move the sources to another location, YT doesn't like lots of links off-site in the description
I've been looking for some good geography videos on CZcams, yours are amazing. Thank you! Hope you make more!
Very interesting, easy to hear the audio, no annoying music, easy to read text and graphics. Thanks.
Great to see you back to uploading. Keep going, your ideas are very interesting, the perfect content for geographers and geography curious minds. Can’t wait to see next one, bro
As a school-aged child I made the observation that what we experienced in New Mexico summers was somewhat analogous to the monsoon of India, many years before I heard it called a monsoon by an official source.
Yes, this is the Southwest Monsoon, also called Mexican Monsoon or North American Monsoon. I discussed it in my last video, on summers in the USA. It is a true monsoon, covered by most literature on monsoon regions of the world.
@@casualearth9076 Your channel is finally blowing up haha. Quarter million views on your comeback video...Excellent.
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Fascinating! Learning new stuff, 9+ minutes of transfixion! Thanks for uploading. 👍
Love your videos, love your voice, love the topics of the things you cover. Seriously underrated channel!
Couldn't agree more. It's nice to hear a logical presentation of a topic at a moderate pace at a reasonable volume.
Thanks!
Just discovered this channel with this latest video. Already subscribed, will be binge watching your previous work
Very happy to see one of your videos popping upp in my recomended vids again😊
Finally new video! Always great to see!
just found your channel and was pleasantly surprised to see you have revived it after a year break, thank you for these interesting videos!
Excellent video. It covers a lot of details that the usual explanations miss.
I'm very happy I found your channel. Keep up the amazing work!
Dude this video was so interesting please keep grinding you will be a big channel soon.
Subscribed! Loved the way you explain the topics
Love your videos! Please continue making great content
This is packed with good info, thanks
Just binged all of your content, and I love it. Keep it up!
this channel slaps, love it
Wonderful, love this channel!
Your videos are fantastic. I wish there were more because they’re so interesting!
Wonderful explanation of some important global weather. Thank you! Former pilot from Australia.
3:36 is a mind-blowing picture, now knowing why it lines up so well.
What an amazing channel! Thanks for your work!
fr best channel on youtube thanks for making this stuff
Any channel that cites their sources gets a like from me. I greatly respect that
This was in my recommendations. I liked it so much I watched four more of your videos and sub’d.
This is some quality content! Keep up the good work
I’m glad this video popped up in my recommended this channel is great
So happy you’re back
Thanks for the upload. Great video m8!
Fascinating.
Please do a video on why the desert belt from the Sahara to the Gobi seem so much drier than other deserts.
Australia is mostly shrubland (perhaps almost Savanna?), save the Simpson desert. Similarly the deserts in North America are also shrublands save the Sonoran. As is most of the Somali and Namib deserts save the coastal strip.
But the Sahara, Arabian, Iranian, Karakum/Kyzylkum and Gobi deserts are mostly Dune seas or Barren rock without much shrubland at all.
The exception to the Sahara-Gobi belt is the Atacama.
The ESA worldcover map shows this quite well.
Could you go into why some deserts are dune seas and others are shrublands
Yeah I’ve always had a hard time reconciling calling Australia mostly desert, as you say most of Australia’s interior is shrubbery, savanna, even woodlands and wetlands and every 3 years or so the entire outback is flooded into a massive delta, I don’t see that happening across the sahara, gobi and Sonora deserts, they are actual sandy dry deserts, I don’t get it but I’m not a scientist. Also according to Wikipedias country by rainfall map, Australia receives about 170mm less rainfall a year than the USA, so not that much less, I guess the boils down to where the rainfall falls, etc but I feel like Australia’s “desertsness” so to speak is highly exaggerated
I just found your channel and watched this and a few other videos. Great stuff, keep it up!
"I've been through the desert on a horse with no name. It felt good to be out of the rain. In the desert, you can remember your name."
---Albert Einstein
I hope you get more subs soon man your videos are great!
What a very informative video! I really learned a lot about something I didn’t even know I had a question about!
Glad to see you back !
Great video, as always. I'd love to see a video about Victoria BC one day, some very interesting microclimates here.
There is also a large semiarid area in (tropical) northeastern Brazil, which may become a desert in the future.
Yes, the Caatinga. There is, however, a tropical rainforest (the Atlantic forest) on the east coast between the Caatinga and South Atlantic (though much of it has now been converted to agriculture).
Love your videos ♡
After a year, Casual Earth is back! Don't be casual about bringing new videos, thanks!
Such a great channel, you deserve way more than 33k subs
This is a brilliant video. Well done
Excellent video, thank you!
Love your work thank you
I've been seeing your sub count increase by thousands every day - congrats! You definitely deserve it, this is an excellent channel.
Great video and great channel!
Just found your channel and it's great! I really hope you will continue to upload frequently in the times to come. 🌲🌳🌴🌵
this is so interesting i love this video. glad i found this channel
this channel really cool and awesome!
awesome video man. please make a video about patagonia.
Maine has a desert! It's called the Desert of Maine (super creative) and it's a great place to take your kiddos if you made the mistake of planning a vacation in Maine.
dont spoil Maine keep them city folk away!
I live in seattle Washington and have been fascinated by the multi faceted geographies in the state. The rain shadows of the Olympic and the cascade ranges are super interesting to me. Any chance you’d be willing to do a video on that?
this is such a good channel!
This is something I never thought, pretty interesting.
Hey! Fellow mid-North Carolina viewer here. Great video, subbed!
More videos please! I just found your channel, do some more botany vids! Hope your summer is going well 😊
Congratulations on the video my friend, I just binge watched a lot of your content and I must admit I love it. It's very hard to find informative videos on such a niche subject. I only know a couple of youtube channels that explain it that well and your work is definitely way up there too. Can't wait for the video about the dry east african coast !
Very interesting. Thanks for the video
There is a lot of information in this ten minute video. Thank you
Omg I miss u! I knew I recognized ur voice. Welcome back!!!
Great lessons, thank you.
Really interesting thanks!
@3:20 -- _"In the northern hemisphere, high-pressure systems spin clockwise..."_
It would be helpful if you could explain why the Coriolis force works backwards for high-pressure systems, since most people know that hurricanes in the northern hemisphere go counter-clockwise.
Air moves toward low pressure systems, while it moves away from high pressure systems. Because they're going in opposite directions, the coriolis force will create a curved path in the opposite direction.