夏天的風(fēng)

Why is it always (1)breezy at the beach? Find out on this Moment of Science. I bet that the last time you went to the beach, the wind was blowing in off the water. Maybe it was just a pleasant breeze, maybe something a little stronger. But it was definitely coming in off the water. What’s more, a breeze will be coming in off the water the next time you go to the beach. How do I know? Easy. Wind is caused by differences in the temperature of air. 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 (2)windy. That’s because the hot air is rising and the cold air is rushing in to fill the space left behind. Whoosh! Now, here we are at the beach. What do you notice? Well, the sand under your feet retains heat pretty (3)effectively. Once it is hot, it stays hot. Not so for ocean water, which is much harder to heat. Think of how cold the water feels when you step into it off a hot beach. This distinction is true of land and sea in general. On a sunny day, the land stays hotter than the sea. That means the air over the beach will be hotter than the air over the water. And that means the air will be rising over the beach. As the hot beach air rises up, the relatively cooler air over the water moves in to take its place. The result? A sunny day in summer creates its own breeze.