What Does the Atmosphere Do??

Watch our videos and review your learning with the Crash course app. Supplemental content is now available for these courses. Here, side by side, we see all of life and life in its smallest package, a single cell, like an intricate fractal. When we zoom in and out, the structures of life don't look that much different. What allows both these structures to survive is a thin layer of protection. The cells membrane, or outer barrier, selectively filters what goes in and out of the cell. For Earth, we have our atmosphere, or the envelope of gases, held around the planet by gravity that axes, quote, the world's biggest memory. The physician and writer Louis Thomas most famously made this comparison in 1973. Like a cell membrane, the atmosphere filters what's allowed in and out like different wavelengths of light. Thomas marveled at how photographs like the famous Earth Rise showed the sterile surface of the Moon, with the exuberant Earth rising in the background. It seemed miraculous that the Earth was so alive, while everything around it seemed so not. Most of us take the atmosphere for granted, and rarely think about what it's made of or how it moves or changes. We notice it when bad weather inconveniences us, or appreciate it when enjoying the outdoors. But it's been 5 billion years in the making, and it's how we and every other cell of life are able to survive. I'm alice a career, and this is crash course geography.

Earth s atmosphere is a unique reservoir that forms a protective boundary between outer space and the biosphere, which is where all life exists..On earths surface, air is really a mixture of gases that are odorless, tasteless, colorless, formless, and blend together so well that they tend to act like a single gas. The recipe close to earth's surface is 99% nitrogen and oxygen, slightly less than 1% argon. And a tiny percent of volume comes from minor gases like carbon dioxide. But this mostly consistent mixture starts to deviate as we get towards the outer edge of the Atmosphereto better study the progression, we can break up the atmosphere into vertical layers, or spheres, using several different characteristics. The four layers we hear about most are the troposphere, stratosphere, mesosphere and thermosphere, and they come from studying the atmosphere based on its temperature structure. Each layer has a different starting temperature that decreases or increases as we move towards outer space. Temperature even affects the thickness of the layers. The layer closest to the Earth, where all the weather and most of the air molecules exist. The troop was fear can extend out anywhere from eight to 16 km above the surface, depending on the season or latitude where you are on the globe. That sounds kind of arbitrary, but really it's just physics. When the air molecules are cold, they huddle together, making the air denser and more compact. So in winter or near the poles, the troop was fear is thinnest and its thickest, where the air molecules spread out, like in warm places at the equator. When we moved to the stratosphere, the next layer, temperatures tend to be layer to get progressively warmer. Here we have the ozone layer, which is the section of the atmosphere with the highest concentration of ozone, one of the minor gases in our recipe. The ozone layer lets the wavelengths of light conducive to life to pass through, while filtering out those that are harmful, like most of the ultraviolet waves. Observing UV rays is what causes temperatures to increase in the stratosphere, then temperatures drop in the mesosphere and increase again in the incredibly hot thermosphere, where the few air molecules floating around out there can get to be 1100 degrees Celsius. Altogether, the atmospheric extends 480 km above earth's surface, which sounds like a lot, but the diameter of the Earth is 12756 km. Compared to that, the atmosphere seems like the peel of an orange. This thin layer of gas is so critical for life to exist, which is why it's so important to talk about early on in our journey into physical geography. Without the atmosphere, none of the processes will study in the hydrosphere, lithosphere and biosphere would function. Energy from the Sun is constantly passing through the different layers of the atmosphere's waves, landing on and being absorbed into the earth's surface to provide the heat and warmth for life. Really, that energy is electromagnetic radiation, or different wavelengths of energy that travel away from the surface of an object. All objects like the Sun, the Earth, are skin, are constantly emitting waves of electromagnetic radiation. Very hot and high energy objects like the Sun emit vast amounts of energy as short wavelengths or solar radiation in the form of light. Cooler objects like the Earth emit much longer heat waves or terrestrial radiation. Since there's constant sunlight passing through the atmosphere, we might expect temperatures to keep increasing, like when you're sitting under a blanket and you get so hot that you want to throw it off. Fortunately, the Earth doesn't get swelteringly hot, because the Earth in the atmosphere naturally balance the short wave solar energy that arrives with the long wave energy set back to space. This is the atmospheric energy budget, which is achieved with three types of energy transfers. The 1st type of energy transfer is that radiation we've been talking about, which is more generally the transfer of energy through waves, like when we warm our hands over a campfire insulation, or incoming solar radiation reaches us by, you guess it, radiation. Imagine a riding sunbeam of solar radiation trying to navigate the atmosphere as hurdles toward the surface. The atmosphere protects the earth by filtering sunlight, so there are quite a few obstacles to make it through. If our sunbeam has 100 units of radiant energy, most of those units will be intercepted before we make it to the surface. Let's go to the thought level. The outer layer of the Sun is extremely hot thanks to its intense energy. So our sunbeam radiates at short wavelength. This radiant energy can pass easily through oxygen and nitrogen molecules, because there are basically teeny little windows letting short wave energy in and out. But other gases throughout the atmosphere absorb short wave energy, like a sponge filling up with water. In the stratosphere, ozone is a major obstacle, and in the troposphere, water vapor in the clouds is the enemy. Overall, 19 units of radiant energy g from our sunbeam are intercepted by absorption. Other particles in the air are pesky too. Dust, smoke and volcanic emissions scatter radiation and change the direction of the light's movement without altering its wave. Eight units of energy from our sunbeam will get return to space, while 20 units will get scattered as diffuse radiation, but persevere to reach earth's surface. At this point, 53% of our sunbeam is still headed towards the earth's surface. Our next obstacles are clouds. Thick clouds are actually capable of reflecting up to 80% of total incoming radiation like a mere bouncing the energy back into space. And even when we make it to the surface, our sunbeam isn't safe. The ground can reflect short wave radiant energy too. Snow and ice have higher albedos and reflect most of the solar energy that hits them, while a black pavement has a low albedo and absorbs all of the incoming solar energy. On average, 26 units of solar energy are reflected back into space by clouds or albedo on the ground. If we add it all up, just 27% of our original sunbeam reaches the earth's surface without being absorbed, scattered or reflected, thanks that bubble. So after that rocky journey, 47 units or so of radiant energy gets through to the ground as a combination of direct radiation that doesn't get absorbed, scattered or reflected, and diffuse radiation that got scattered briefly, but still makes it through the atmosphere. As my personal hero, david Attenborough, might say, that 47% is just enough for life on our planet anymore, and the surface might be too hot for life like Mercury any less, and it would be too cold for life as we know it after being absorbed into the surface, incoming radiation is eventually re radiated by the Earth as terrestrial radiation. Here, the two other types of heat transfer have a role in moving heat energy away from earth's surface to the atmosphere and out into space. Heat is carried upwards from the Earth in conviction currents, e.g. insulation, heats water from the earth's surface, which evaporates, becomes water vapor and condenses into clouds in the troposphere. As the water vapor condenses and changes from a gas to a liquid, the energy that gets released heats up nearby air molecules. This is like when water is boiled. Conviction currents let hot water molecules flow upwards and cool. And some heat is actually transferred by conduction or through actual contact, like when you go to grab the hot handle of that pot of boiling water. Heat is transferred to your palm through the physical contact you make with the pot. Conduction is most important in the lower most layers of air in contact with the ground. But air is actually a pretty poor conductor of heat, so the small amount of heat transferred through conduction ends up being carried further upwards by conviction. So the solar radiation coming in equals the terrestrial radiation plus conviction, plus conduction coming out of Earth. It's balanced. The atmosphere actually traps quite a bit of the long wave terrestrial radiation, re radiating and reflecting these heat waves back again in a continuous energy exchange. So the atmosphere is actually heated, mostly from below. Certain gases can absorb solar radiation on its way to Earth, but other trace gases, like carbon dioxide, methane, water vapor and nitrous oxide, are great at absorbing long wave terrestrial radiation and sending it back to the earth's surface. This produces the natural greenhouse effect. In a greenhouse, the glass lets in insulation, but doesn't allow the warmer inside to escape. These greenhouse gases do the same thing in our atmosphere. Greenhouse gases get a lot of negative attention, but without the natural greenhouse effect, earth's surface would be too cold for human life. But we're running into problems because human activities like burning fossil fuels and massive deforestation have increased the concentrations of greenhouse gases, so more heat energy stays in the atmosphere. This produces a warming trend, which upsets the ecological systems of Earth. When the atmosphere energy systems become unbalanced, there's a cascading effect on other physical and biological processes, from sea levels rising to changing distributions of plants and animals. Where we are in the globe, plays a big role in how much energy is trapped by the greenhouse effect or allowed to escape. In our previous episode, we learned every location on Earth doesn't get the same amount of solar energy because of how the Earth tilts and moves the atmosphere. Ends up emphasizing this imbalance, e.g. at the equator, when the Sun is overhead, the incoming radiation only has to get through the vertical thickness of the atmosphere, and a fairly large amount does get through. But at high latitudes, the insulation doesn't hit head on and has more atmosphere to make it through. So there's more opportunity for scattering and reflection in theory. If the vertical atmospheric energy budget was all we had, tropical areas would actually get warmer, and the Arctic and Antarctic even colder. But this doesn't happen. Instead, large horizontal circulation systems, like ocean currents and wind systems, move the excess heat the Earth receives at low latitudes to the poles. Soon will see how this energy transfer from the equator to the poles is one of the fundamental driving forces behind the general circulation of the atmosphere around the globe. In the next several episodes will explore how the atmosphere and its energy systems are the basic ingredients for weather and climate, like how the atmosphere ultimately makes it possible for rice to grow in hot and wet places like Vietnam, or wine cold snowy places like Siberia, houses have steeply pitched roofs. So much of how humans interact with our environment is shaped by how energy, heat and water move through the atmosphere. Far from being a boring blanket of air, the atmosphere is an intelligent, sophisticated shield that performs complex functions to make life viable on our planet. Thanks for watching this episode of Crash Course Geography, which was made with the help of all these nice people. If you want to help keep crash course free for everyone forever, you can join our community on Patrion.?

譯文：

大氣有什么作用？

觀看我們的視頻并使用速成課程應用程序回顧您的學習內(nèi)容。

這些課程現(xiàn)已提供補充內(nèi)容。在這里，我們并排看到了所有生命……以及生命在其最小的包裝中：單個細胞。就像復雜的分形一樣，當我們放大和縮小時，生命的結構看起來并沒有太大不同。使這兩種結構得以幸存的是一層薄薄的保護層。細胞膜或外屏障選擇性地過濾進出細胞的物質。對于地球來說，我們有大氣層，或者說是通過重力包圍地球的氣體包層，它充當“世界上最大的“膜”。醫(yī)生兼作家劉易斯·托馬斯 (Lewis Thomas)在 1973 年做出了最著名的這一比較。就像細胞膜一樣，大氣會過濾允許進出的物質，就像不同波長的光一樣。托馬斯驚嘆于著名的“地出”等照片如何展現(xiàn)出貧瘠的月球表面，而背景中卻是“生機勃勃”的地球升起。地球如此生機勃勃，而它周圍的一切卻顯得那么……不，這似乎是一個奇跡。我們大多數(shù)人都認為大氣是理所當然的，很少考慮它是由什么構成的，或者它是如何移動或變化的。 當惡劣天氣給我們帶來不便時，我們會注意到它，或者在享受戶外活動時欣賞它。 但它的形成已經(jīng)經(jīng)歷了 50 億年，這也是我們和所有其他生命細胞得以生存的方式。我是艾麗澤·卡雷爾，這是地理速成課。地球大氣層是一個獨特的水庫，它形成了外層空間和生物圈之間的保護性邊界，生物圈是地球表面所有生命存在的地方?？諝鈱嶋H上是多種氣體的混合物，這些氣體無臭、無味、無色、無形，并且混合得很好，它們往往像單一氣體一樣。靠近地球表面的成分是99% 的氮氣和氧氣，略少于1% 的氬氣，還有一小部分來自二氧化碳等微量氣體。 但當我們到達大氣層的外緣時，這種基本一致的混合物開始偏離。為了更好地研究這一過程，我們可以使用幾種不同的特征將大氣分解為垂直層或“球體”。我們最常聽到的四個層是對流層、平流層、中間層和熱層，它們來自于基于大氣溫度結構的研究。每層都有不同的起始溫度，當我們向外太空移動時，該溫度會降低或升高。

溫度甚至影響層的厚度。 對流層是距離地球最近的一層，所有天氣和大多數(shù)空氣分子都存在于此，它可以延伸到地表以上 8 到 16 公里的任何地方，具體取決于地球上的季節(jié)或緯度。這聽起來有點隨意，但這實際上只是物理學：當空氣分子冷時，它們會擠在一起，使空氣變得更稠密、更緊湊。 所以在冬季或兩極附近，對流層最薄?？諝夥肿訑U散的地方最厚，比如赤道溫暖的地方。當我們進入下一層平流層時，溫度往往會分層并逐漸變暖。 這里有臭氧層，它是大氣中臭氧濃度最高的部分，臭氧是我們配方中的次要氣體之一。臭氧層允許有利于生命的光波長通過，同時過濾掉有害的光，例如大多數(shù)紫外線。 吸收紫外線是導致平流層溫度升高的原因。然后中間層的溫度下降，并在極其炎熱的熱層中再次升高，那里漂浮的少數(shù)空氣分子的溫度可能達到 1,100 攝氏度！大氣層總計距地球表面 480 公里。 聽起來很多，但地球的直徑是 12,756公里。 相比之下，氣氛就好像……橘子皮一樣。這層薄薄的氣體對于生命的存在至關重要，這就是為什么在我們進入自然地理學的旅程中盡早討論這一點如此重要。如果沒有大氣層，我們將在水圈、巖石圈和生物圈中研究的任何過程都無法發(fā)揮作用。來自太陽的能量不斷地以波的形式穿過大氣層的不同層，登陸并被地球表面吸收，為生命提供熱量和溫暖。實際上，這種“能量”是電磁輻射，或者是從物體表面?zhèn)鞑コ鋈サ牟煌ㄩL的能量。所有物體——太陽、地球、我們的皮膚——都在不斷地發(fā)射電磁輻射波。非常熱和高能量的物體，如太陽，以光的形式以短波長或太陽輻射的形式發(fā)射大量能量。 較冷的物體，如地球，會發(fā)射更長的熱波或地面輻射。由于陽光持續(xù)穿過大氣層，我們可能會預期溫度會持續(xù)升高，就像當你坐在毯子下時，會感到很熱，想要把它扔掉一樣。幸運的是，地球不會變得悶熱，因為地球和大氣層會自然地平衡到達的短波太陽能與發(fā)送回太空的長波能量。這是大氣能量收支，通過三種常見類型的能量轉移來實現(xiàn)。第一種類型的能量轉移是我們一直在談論的輻射，更一般地說是通過波進行能量轉移。 就像我們在篝火上取暖一樣。 日照，或者說傳入的太陽輻射，是通過——你猜對了！?——輻射。想象一下，我們正乘著一束太陽輻射，試圖在大氣層沖向地表時穿過它。 大氣層通過過濾陽光來保護地球，因此要穿過大氣層會遇到很多障礙。如果我們的陽光有 100 個單位的輻射能，那么其中大部分單位將在我們到達地表之前被攔截。 讓我們進入思想泡泡。 由于其強大的能量，太陽的外層非常熱，因此我們的陽光以短波長輻射。這種輻射能可以輕松穿過氧和氮分子，因為它們基本上是讓短波能量進出的微小窗口。但大氣中的其他氣體會像海綿充滿水一樣吸收短波能量。在平流層，臭氧是一個主要障礙。在對流層中，云層中的水蒸氣是敵人。總的來說，來自陽光的 19 個單位的輻射能被吸收攔截?？諝庵械钠渌w粒也很煩人！灰塵、煙霧和火山排放物會散射輻射并改變光的運動方向，但不會改變其波長。來自陽光的 8 個單位的能量將返回太空，而 20 個單位的能量將作為漫射輻射被散射，但仍會持續(xù)到達地球表面。此時，53% 的陽光仍然射向地球表面。我們的下一個障礙是云。厚厚的云實際上能夠反射高達 80% 的總入射輻射，就像一面鏡子將能量反射回太空。即使我們到達地面，我們的陽光也并不安全——地面也可以反射短波輻射能。雪和冰的反照率較高，會反射大部分照射到它們上的太陽能，而黑色路面的反照率較低，會吸收所有入射的太陽能。平均有 26 個單位的太陽能被云層或地面反照率反射回太空。如果我們將其全部加起來，只有 27% 的原始陽光到達地球表面而沒有被吸收、散射或反射！感謝思想泡泡！ 因此，在這段巖石之旅之后，47 個單位（左右）的輻射能以不會被吸收、散射或反射的直接輻射和短暫散射但仍能通過的漫射輻射的組合形式到達地面。 大氣。正如我心目中的偶像大衛(wèi)·阿滕伯勒 (David Attenborough) 可能會說的那樣，47% 的能量足以維持我們星球上的生命。再多的話，表面可能就太熱了，不適合生命存在，就像水星一樣。 再少一點，對于我們所知的生命來說，就會變得太冷了。入射輻射被地表吸收后，最終被地球重新輻射為地面輻射。 這里，其他兩種類型的熱傳遞在將熱能從地球表面轉移到大氣層并進入太空方面發(fā)揮著作用。熱量通過對流從地球向上攜帶。 例如，日照加熱地球表面的水，水蒸發(fā)，變成水蒸氣，并在對流層中凝結成云。當水蒸氣凝結并從氣體變成液體時，釋放的能量會加熱附近的空氣分子。這就像水沸騰時：對流讓熱水分子向上流動并冷卻。有些熱量實際上是通過傳導或通過實際接觸傳遞的。 就像當你去抓住那壺開水的熱把手時。熱量通過您與鍋的身體接觸傳遞到您的手掌。傳導在與地面接觸的最下層空氣中最為重要，但空氣實際上是一種很差的熱導體。 因此，通過傳導傳遞的少量熱量最終會通過對流進一步向上傳遞。因此，進入的太陽輻射等于地面輻射，加上對流，加上從地球發(fā)出的傳導。 很平衡！大氣層實際上捕獲了相當多的長波地面輻射，在連續(xù)的能量交換中重新輻射和反射這些熱波。 所以大氣實際上是從下面被加熱的。某些氣體可以在到達地球的途中吸收太陽輻射，但其他微量氣體，如二氧化碳、甲烷、水蒸氣和一氧化二氮，非常適合吸收長波地面輻射并將其發(fā)送回地球表面。 這會產(chǎn)生自然的溫室效應。在溫室里，玻璃可以讓陽光進入，但不允許里面的暖空氣逸出。 這些溫室氣體在我們的大氣中也起著同樣的作用。溫室氣體受到了很多負面關注，但如果沒有自然溫室效應，地球表面對于人類生命來說將會太冷。但我們遇到了問題，因為人類活動（例如燃燒化石燃料和大規(guī)?？撤ド郑┰黾恿藴厥覛怏w的濃度。 因此更多的熱能留在大氣中。這產(chǎn)生了擾亂地球生態(tài)系統(tǒng)的變暖趨勢。 當大氣能量系統(tǒng)變得不平衡時，會對其他物理和生物過程產(chǎn)生連鎖效應，從海平面上升到動植物分布變化。我們在地球上的位置對于有多少能量被溫室效應困住或允許逸出起著重要作用。 在上一集中，我們了解到，由于地球傾斜和移動的原因，地球上的每個位置都無法獲得相同數(shù)量的太陽能。氣氛最終強調了這種不平衡。例如，在赤道，當太陽位于頭頂時，入射輻射只需穿過大氣層的垂直厚度，并且確實有相當大的量可以穿過。但在高緯度地區(qū)，陽光不會正面照射，并且有更多的大氣層可以穿過。 因此有更多的機會進行散射和反射。理論上，如果我們只有垂直大氣能量收支，熱帶地區(qū)實際上會變得更溫暖，而北極和南極地區(qū)甚至會更冷。 但這并沒有發(fā)生。

相反，大型水平環(huán)流系統(tǒng)（例如洋流和風系統(tǒng)）將地球在低緯度地區(qū)接收到的多余熱量轉移到兩極。 很快我們就會看到這種從赤道到兩極的能量轉移如何成為全球大氣環(huán)流背后的基本驅動力之一。在接下來的幾集中，我們將探討大氣及其能量系統(tǒng)如何成為天氣和氣候的基本成分。 就像大氣最終使水稻能夠在越南這樣炎熱潮濕的地方生長一樣。 或者為什么在像西伯利亞這樣寒冷多雪的地方，房屋的屋頂很陡。人類與環(huán)境的互動很大程度上取決于能量、熱量和水在大氣中的移動方式。大氣層絕不是一層無聊的空氣，而是一個智能而復雜的屏障，它執(zhí)行復雜的功能，

使我們的星球上的生命得以生存。感謝您觀看這一集的地理速成課程，它是在所有這些好人的幫助下制作的。 如果您想幫助所有人永遠免費使用速成課程，您可以加入我們的 Patreon 社區(qū)。

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