Narrator: Listen to part of the lecture in a meteorology class.

旁白：听一个气象学的讲座。

Professor: Now, Earth's atmosphere is sort of like a giant weather machine, right?

教授：现在，地球的大气层有点像一台巨大的气象机器，对吗？

Uh... with air and water being its key components.

嗯……空气和水是它的主要组成部分。

A machine powered by energy from the Sun.

一台由太阳提供能量的机器。

So we need to consider the role that air, or more specifically, wind, plays in this machine.

所以我们需要去考虑空气，或者更具体地，风在这台机器中的角色。

So wind is really nothing more than moving air, right?

所以风真的只不过是移动的空气，对吗？

Now, as air is heated and becomes warmer, it expands, it becomes less dense.

现在，随着空气的加热和变暖，它膨胀起来，它变得稀薄。

When air in a particular area is heated, you get a concentration of warm air in an area of low pressure.

当特定区域的空气被加热时，热空气会聚集在低压区。

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.

同样，冷空气密度较大，所以它会产生一个高压区。

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?

如果有一个高压区在低压区旁边，更冷的高压空气会开始向低压区移动。对吗？

And the warmer air will move away, rising above the cooler air.

并且暖空气会移走，上升到冷空气的上方。

Okay?Uh... yes. Linda?

明白吗？嗯……是。Linda？

Student: So wind is actually generated by the Sun?

学生：所以风实际上是由太阳产生的吗？

Professor: Well, Earth's rotation plays a role. And there are other factors and we'll come back to all that.

教授：嗯，地球自转也起了作用。还有其它的因素，我们之后再回来讲。

But, principally, yes.

但是，主要是由太阳造成的。

The Sun creates the temperature differential that creates the areas of high pressure and low pressure that create wind.

太阳会创造温差，温差会产生高压区和低压区，然后产生风。

Student: Um... I don't get what... how it causes a temperature differential.

学生：嗯……我不明白……怎么导致温差的呢？

Professor: Right. Good. This will take us to the role of wind in the climate.

教授：好的。好。这个会带我们看向风在气候里的角色。

The key is that the Sun warms up different parts of Earth at different rates and to different degrees.

关键是太阳以不同速率和程度温暖地球的不同部分。

For example, at sunrise, the land heats up faster than the ocean.

比如说，在日出，陆地升温比海洋快。

That's why you get morning sea breezes.

这就是为什么早上有海风。

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.

水面上的空气比陆地上的升温慢，所以在清晨，水上空气比陆地上空气更冷和密集，所以它移向陆地。

A sea breeze.

产生海风。

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,

还有呢？太阳能量在赤道附近比极圈更强，所以在赤道地区有大量暖空气，

and masses of cooler air over Polar Regions.

而在极圈有更多冷空气。

And these masses are constantly interacting with each other, which is critically important for Earth's climate.

而且这些空气不断相互作用，对地球的气候非常重要。

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.

这些相互作用的一个结果是，赤道气团远离赤道，在这个过程中，那些赤道风其实从赤道带走热量，转移到地球上较凉爽的地区。

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.

并且，通过重新分配这种能量，太阳能，风在维持极圈和赤道的温度平衡方面起到一个关键的作用。

Now, winds also help Earth maintain its balance in another way: by transporting water from one part of Earth to another.

现在，风也以另一种方式帮助地球维持平衡：通过将地球上的水从一个地方运输到另一个地方。

Water's contained in the air in the form of vapor, mostly through evaporation, mostly from the oceans.

水在空气中以蒸汽的形式存在，主要通过蒸发，大部分来自海洋。

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.

所以当空气移动的时候，它带着蒸汽到地球上的其它地方，那里它以水或雪的形式沉淀，或其它降水形式。

Now, actually, the transfer of heat and water by way of the wind are very closely related,

现在，实际上，通过风进行的热和水的转移是密切关联的，

because a primary way that heat energy is transferred by wind is mediated by the process of evaporation.

因为通过风进行的热量转移的主要方式，是由蒸发过程作为媒介。

What happens is that a certain amount of heat energy is required to convert liquid water into vapor.

所发生的事情是，需要一定量的热能去把液态水转换为蒸汽。

So when water evaporates from the ocean, it takes energy to convert that water into a gaseous form, into water vapor.

所以当水从海洋蒸发，它需要能量把水转换成气体形式，转化成水蒸气。

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.

但是那部分热量，转换的能量，不提高水蒸气或空气的温度，它只是储存在水蒸气中。

Then later when the water vapor converts back to liquid water, that energy is released.

然后当水蒸气转换回液态水，能量得到释放。

So when water evaporates, energy is taken from the ocean, and it's stored in the water vapor, in the air.

所以当水蒸发时，能量被从海洋拿走，并且存在水蒸气和空气中。

Then the air, the wind, transports the water vapor to some other part of Earth.

然后空气/风把水蒸气运输到地球上其它部分。

Then the water vapor converts back into liquid water.

然后水蒸气转换回液态水。

It rains, in other words.

换句话说，也就是下雨。

And the heat energy that was stored in the water vapor is released into the new environment. Okay?

在水蒸气中储存的能量在新环境中得到释放。明白了吗？

So the transfer of heat and the transfer of water are very closely related.

所以热量和水的转移是非常密切相关的。

And what's the primary vehicle for this transfer?

转移的主要媒介是什么呢？

The wind! So wind is a critical element in the redistribution of both the Sun's energy and Earth's water.

是风！所以风是太阳能和地球水重新分配中的一个非常重要的元素。