为什么会下雨WhyDoesItRain( 二 ) _这世界为什么总有雨呢英文

Be patient but keep watching the cloud, especially it's edges.
有点耐心，一直注视着它，尤其是它的边缘。
You will see the edges change, either growing larger or getting smaller.
你会看到它的边缘发生变化，要么变大，要么变小。
This is cloud formation in action.
下面是云的形成过程。
The cloud grows because more of those water droplets are condensing out of the air.
云变大是因为有更多空气中的水滴凝结在了一起。
And when it shrinks, you are seeing the droplets evaporating, or changing from visible liquid water into invisible water vapor.
变小是因为这些水滴正在蒸发，或是从可见的液态水变成了看不见的水蒸气。
But not every cloud has rain pouring out of it.
但并不是每片云彩都有雨。
So, how does the formation of a cloud become actual rain?
那么是如何因云成雨的呢？
For rain to be produced, the water condensing in the clouds has to become so heavy that it will fall to Earth, or else the tiny droplets will just stay suspended in the cloud, in the same way we see fog just hang there.
要产生雨水，云里凝结的水要足够重才能落到地面，否则这些小水滴就会悬浮在云层里，我们看到的雾就是这样。
To become heavier, the droplets need to grow into drops, and to do this, they have to acquire more water and become larger.
要变得更重，这些水滴就要聚集在一起，水多了，水滴也变得更大。
As the droplets collide with each other, some will combine and become larger, and others will grow as more water condenses out the air directly into the droplet, until they become condensed and heavy enough to fall to the earth as rain.
水滴间相互碰撞时，有些通过结合变得更大，有些则由空气直接凝结成水滴，持续变大，直到重得落向地面成为雨水。
Or if the weather is very cold, the tiny droplets freeze and fall down as snow, hail, or sleet.
或者在天气非常寒冷的时候，空气中的小水滴就会凝固，以雪、冰雹、雨夹雪的形式落下来。
So, there you go – that's what a cloud is, and how it creates rain.
所以这就是云和雨的形成过程。
But what causes the air to cool in the first place?
但首先，是什么原因导致空气变冷的呢？
We mentioned earlier, that cooling the air reduces its ability to hold water, and triggers the formation of water droplets.
我们之前说过，给空气降温会减少空气中的水蒸气含量，从而形成水滴。
To create clouds, and to have rain, the air has to be cooled.
【为什么会下雨WhyDoesItRain】要想产生云彩，进而下雨，空气遇冷是必要条件。
Most of the science journals we looked at state that there are three main ways in which this happens.
我们研究的大多数科学期刊都指出，雨的形成主要有三种方式。
These are known as relief rain, frontal rain, and convectional rain.
这些雨被称为地形雨、锋面雨和对流雨。
Let's take a look at how each of these work.
让我们看看这些类型的雨是怎么形成的。
Relief rain, sometimes referred to as orographic rain, is caused when air is forced to cool as it rises over a physical obstruction, such as a mountain range, or big hills.
地形雨的形成是当空气上升遇到物理障碍(如山脉或大山)时被迫冷却，然后就会产生这种现象。
As the warm air rises over the obstruction, it cools, and clouds form.
当暖空气上升到障碍物时，就会冷却，形成云。
Relief rain is common in mountainous areas where it can lead to more extreme local rainfall patterns, because the rain clouds form very quickly.
地形雨在山区很常见，它可以导致更极端的局部降雨，因为雨云形成非常快。