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进入7月，北京已经悄然入汛。最近一周，雨水几乎是天天来报到。天气变化多端，小编提醒亲爱的窗友们出门要提前查看天气哦！
虽然现在电脑预报天气的技术越来越先进，但是天有不测风云，天气预报总有不准的时候。早在古代，人们就已经会“看云识天气”，学会看云的形状，你就能预知几小时后天气的变化。
今天就跟小编一起来认识几种常见的气象云吧~
01
Cumulus 积云
图片来源：新华网
Clouds form when air cools to the dew point, the temperature at which the air can no longer hold all its water vapour. At this temperature, water vapour condenses to form droplets of liquid water, which we observe as a cloud.
空气冷却到露点的时候就会形成云，在这个温度，空气已经无法承载所有的水汽。在露点温度下，水汽凝结成小滴的液态水，也就是我们所看到的云。
For this process to happen, we require air to be forced to rise in the atmosphere, or for moist air to come into contact with a cold surface.
要形成云，需要空气被迫在大气中上升，或者湿润的空气和冰冷的表面接触。
On a sunny day, the sun's radiation heats the land, which in turn heats the air just above it. This warmed air rises by convection and forms Cumulus. These "fair weather" clouds look like cotton wool.
在晴天时，阳光让大地升温，从而让大地上方的空气也升温。这些温暖的空气通过对流上升，形成积云。这些“好天气”的云看上去就像棉絮一般。
If you look at a sky filled with cumulus, you may notice they have flat bases, which all lie at the same level. At this height, air from ground level has cooled to the dew point.Cumulus cloudsdo not generally rain – you're in for fine weather.
如果你看见天空布满了积云，你可能会注意到它们的底部都是平的，而且都位于同一水平线上。在这个高度，来自地面的空气已经冷却到露点。积云一般不会化成雨，它预示着好天气。
02
Cumulonimbus 积雨云
