I bet that the last time you went to the beach, the wind was blowing in off the water.
我敢打赌，你最后一次去海滩的时候，海风正从水面吹来。
Maybe it was just a pleasant breeze, maybe something a little stronger.
或许是令人愉快的微风，也或许是更强一点的风。
But it was definitely coming in off the water.
但是它的确来自于水面。
What's more, a breeze will be coming in off the water the next time you go to the beach.
更重要的是，你下次去海滩的时候微风又会徐徐吹来。
How do I know? Easy.
我为什么会知道？那太容易了。
Wind is caused by differences in the temperature of air.
风是由空气的温差引起的。
If you have a lot of hot air in one location and a lot of cold air next to it, the line where they meet will be windy.
如果一个地方有大量的热空气，它的旁边又有大量的冷空气，那么冷热空气相交的地方就会形成风。
That's because the hot air is rising and the cold air is rushing in to fill the space left behind. Whoosh!
因为热空气上升，冷空气就会迅速冲到热空气留下的位置里并填满整个空间。
Now, here we are at the beach.
现在我们站在海滩上。
What do you notice?
你注意到了什么？
Well, the sand under your feet retains heat pretty effectively. Once it is hot, it stays hot.
你脚下的沙子能够有效的保持热量。一旦它变热了，它就会维持热度。
Not so for ocean water, which is much harder to heat.
可是海水却很难变热。
Think of how cold the water feels when you step into it off a hot beach.
想想当你从水中踏入炙热的沙滩时，会发现海水是多么的寒冷啊！
This distinction is true of land and sea in general.
总的来说，这就是陆地和海洋的真实区别。
On a sunny day, the land stays hotter than the sea.
阳光明媚的日子，陆地比海洋要热很多。
That means the air over the beach will be hotter than the air over the water.
那意味着海滩上空的空气将会比水面上空的空气热。
And that means the air will be rising over the beach.
也就是说海滩上的热气将会上升。
As the hot beach air rises up, the relatively cooler air over the water moves in to take its place.
随着海滩上空热空气的上升，水面上相对寒冷的空气就会流动过来代替热空气的位置。
The result? A sunny day in summer creates its own breeze.
结果是什么呢？在夏天一个阳光灿烂的日子里有微风吹过。
