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NARRATOR:Listen to part of a lecture in a meteorology class.
MALE PROFESSOR:Now, Earth's atmosphere is sort of like a giant weather machine, right? With air and water being its key components.A machine powered by energy from the Sun.So, we need to consider the role that air, or more specifically, wind, plays in this machine.
So wind is really nothing more than moving air, right?Now, as air is heated and becomes warmer, it expands, it becomes less dense.When air in a particular area is heated, you get a concentration of warm air, an area of low pressure.Likewise, when you get a concentration of cold air, that air's gonna be very dense, so it's gonna create an area of high pressure.If you have an area of high pressure next to an area of low pressure, the colder, high pressure air will start moving toward the area of low pressure, right?And the warmer air will move away, rising above the cooler air. Okay?
Uh...yes. Linda?
FEMALE STUDENT:[unsure] So wind is actually generated by the Sun?
MALE PROFESSOR:Well, Earth's rotation plays a role, and there are other factors and we'll come back to all that, but principally, yes.The Sun creates the temperature differential that creates the areas of high pressure and low pressure that create wind.
FEMALE STUDENT:Um...l don't get what...how it causes a temperature differential.
MALE PROFESSOR:Right. Good. This will take us to the role of wind in the climate.The key is that the Sun warms up different parts of Earth at different rates, and to different degrees.For example [searching for examples], at sunrise, the land heats up faster than the ocean…that's why you get morning sea breezes.The air over the water heats more slowly than air overland, so during the early morning, it's cooler and denser than air overland, so it moves in toward land -- a sea breeze.
What else?
The Sun's energy is more intense near the equator than it is near the poles.So you've got masses of warmer air over the equatorial regions and masses of cooler air over polar regions and these masses are constantly interacting with each other, which is critically important for Earth's climate.
Uh, one result of these interactions is that equatorial air masses move away from the equator and in the process those equatorial winds actually take heat away from the equator and transfer it to some cooler part of Earth.And by redistributing this energy—the Sun's energy really—winds play a critical role in maintaining a temperature balance from the poles to the equator.
Now, winds also help Earth maintain its balance in another way: by transporting water from one part of Earth to another.Water is contained in the air in the form of vapor—mostly through evaporation, mostly from the oceans—and so when the air moves, it carries the vapor with it to some other parts of Earth, where it can deposit it as rain or snow, or some other form of precipitation.
Now, actually, the transfer of heat and water by way of the wind are very closely related… because a primary way that heat energy is transferred by wind is mediated by the process of evaporation.What happens is that a certain amount of heat energy is required to convert liquid water into vapor.So when water evaporates from the ocean, it takes energy to convert that water into a gaseous form, into water vapor.But that heat energy, that conversion energy, doesn't raise the temperature of the water vapor or the air, it's just stored in the water vapor.Then later when the water vapor converts back to liquid water, that energy is released.
[recapping] So: when water evaporates, energy’s taken from the ocean, and it’s stored in the water vapor, in the air.Then the air—the wind—transports the water vapor to some other part of Earth.Then the water vapor converts back into liquid water—It rains, in other words—and the heat energy that was stored in the water vapor is released into the new environment.Okay? So the transfer of heat and the transfer of water are very closely related.And what's the primary vehicle for this transfer?The wind! So wind is a very critical element in the redistribution of both the Sun's energy and Earth's water.
旁白：请听气象学课上的部分内容。
教授：地球的大气层有点像一个巨大的气象仪器，对吗？以空气和水为主要组成。靠太阳能提供动力的机器。所以我们要考虑空气的作用，或者更具体地来说，风在这台机器中所起的作用。
风只是运动着的空气而已，对吧？现在，当空气被加热，变得更温暖时，它会膨胀，密度会变得更小。当某一特定区域的空气被加热时，暖空气汇集形成一个低气压的区域。同样的，当冷空气汇集时，那片空气的密度就会变得很大，所以就会创造出一片高压区域。如果在一个低压区域旁边有一个高压区域，那么较冷的高压空气就会开始朝着低压区域移动，对吧？而暖空气便会离开，上升到冷空气之上。
Linda，请说？
学生：所以风实际上是由太阳产生的咯？
教授：地球的循环也起了作用，而且还有其他因素，我们稍后都会讲的，但是从原则上来说是这样的。太阳造成了温度差别，从而产生了高压和低压区域，由此形成了风。
学生：我没听懂......它是怎么产生温度差别的呢？
教授：好的，这就要说到风在气候中扮演的角色了。关键点是太阳会以不同的速度将地球不同的部分加热到不同的温度。比如，在日出时，陆地热得比海洋快，这就是会有晨间海风的原因。水面上方的空气热得比陆地上方的空气慢，所以在晨间，水面上的空气就比陆地上方的空气更凉爽，密度也更大，所以它就会朝着陆地移动，形成海风。
还有什么呢？
赤道附近的太阳能比两极附近的更强。所以赤道地区上方会有暖空气团，而两极地区上方会有冷空气团，这些空气团时常互相产生影响，而这对地球的气候至关重要。
这些相互作用的一个结果是赤道的空气团会远离赤道，在这一过程中，这些赤道风实际上带走了赤道的热量，把它转移到了地球上一些更冷的地方。通过重新分配这种能量，实际上是太阳能，风在维持从两极到赤道的温度平衡中起着重要作用。
风还用另一种方式帮助地球保持平衡：通过把水分从地球的一个部分运送到另一个部分。水以蒸汽的形式包含在空气中，大部分是通过从海洋中蒸发而来。所以当空气移动时，它就把蒸汽一起带到了地球的某些其他地方，在这些地方它能把蒸汽作为雨水或雪沉积下来，或者以一些其他的降水形式。
事实上，通过风转移热量和水分是非常紧密相关的，因为热能通过风转移的一个主要方式就是通过蒸发来调节的。具体过程是：将液体水转化成蒸汽需要一定量的热能。所以当水从海洋中蒸发时，它需要能量来将水转化成气体形式，转化成水蒸汽。但是那种热能，那种转化用的能量不会提高水蒸汽或空气的温度，只是储存在水蒸汽中。接着稍后当水蒸汽再度转化成液体水时，那种能量就被释放出来了。
所以当水蒸发时，海洋中的能量就减少了，被储存在了水蒸汽，即空气中。然后空气，风把水蒸汽运到了地球上的某个其他地方。接着水蒸汽便再度转化成了液体的水，换句话说就是会下雨，而这种储存在水蒸汽中的热能就被释放进了新环境中。对吧？所以热能的转移和水分的转移是紧密相连的，这种转移的主要工具是什么？风！所以风在重新分配太阳能和地球上的水中起着至关重要的作用。
选项分析：
教授一上来就强调风在地球大气中的重要性，介绍风的形成原因是因为温差，接着介绍温差原因是陆地海洋变热速度不同以及地区接受热量不同，然后介绍风可以转移水因此可以转移分配热量，最后强调风对于调节地球气候，对于水和热的循环至关重要，对应选项C中：The role of wind in regulating Earth’s climate。
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