Why it Rains More Heavily in Some Places?

why is it that it rains hard in some places and soft in some when gravity is 9.8 newtons all over the earth?
- shashank kaul (age 14)
andover,ma,usa

I'm not quite sure what you mean by raining "hard" and "soft." If you mean how hard a raindrop hits your skin, it has to do with the concept of "terminal velocity." When a raindrop falls from the cloud, it will experience an upward air drag that tries to slow it down. The air drag increases with the falling velocity, and eventually balances the gravitational force. This is when the velocity of the drop reaches the maximum, called the "terminal velocity." The terminal velocity is larger for larger drops so that the air drag can balance the larger gravitational force. As a result, larger drops hurt more because it is faster and heavier.

If you are wondering why some places get more rain than others, it has to do with the local climate. When a cloud rises, it expands and cools down because the surrounding atmospheric pressure decreases. As the parcel gets colder, water vapor condenses on the cloud droplets so they grow in size. When they get too large for the updraft to hold, they fall down as rain. Therefore, places where air rises more frequently get more rain, and it rains more heavily when the updraft is stronger.

- Tsung

(published on 04/27/2010)