英語(yǔ)時(shí)差:一天中最冷的時(shí)候

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 Don: Anyone with the gumption to be up before dawn will tell you that when those first rays of light come over the horizon after a clear night, it gets warmer, and...

Yael: Don?

D: Uh, Yael. I'm trying to do a radio program here..

Y: Yes, but when the sun first rises it doesn't get warmer right away.

D: I-it doesn't.

Y: No, it actually feels colder. In fact, barring any storm fronts, the coldest time of day is sometime just after dawn.

D: It is?

Y: See, the sun is kind of like a microwave and the ground is kind of like a frozen TV dinner.

D: Okay. I like dinner. Go on.

Y: The earth absorbs some heat from the atmosphere during the night. Sort of like putting your dinner out to thaw, but during the day, the sun acts like a microwave and quickly heats up the ground. Once the sun sets, the ground cools off by radiating heat out to the atmosphere and some escapes into space. Just as when the microwave stops, your dinner starts to cool down.

D: That makes sense.

Y: At dawn, the first rays of sunshine are weak. It takes time for the incoming radiation from the sun to counteract the rate that the ground is losing heat. Contrary to what you might think, that means the temperatures are coldest after dawn. It doesn't get warmer until the sun is stronger and the ground starts to absorb heat again.

D: So it's like if I put my frozen dinner in the microwave for, say, 20 seconds, it's still frozen. It takes the microwave time to warm up your dinner enough to unfreeze it.

Y: Exactly.

D: I think I'm hungry. Let's go eat.