Haven Davis, age 11, of High Point, N.C., for his question:
HOW ARE RAINDROPS FORMED?
Our old world couldn't get along without rain. It seems to provide a renewal of life on earth. Did you know that at any given moment rain is falling somewhere? The record stands at 45,000 thunderstorms in one day, or 1,800 an hour. That's a lot of rain! The spot on earth with a record for the most thunderstorms is the island of Java, which averages 223 stormy days each year.
While it is true that rain is the water that falls out of clouds in drops, that simple statement doesn't tell it all. There are some cloudy days when it doesn't rain, and other cloudy days when it does. Why?
The formation of rain depends on the moisture that is taken into the air. It's called evaporation when moisture is picked up from the ocean or the earth's surface. The moisture, called water vapor, is so fine that it cannot be seen.
As the water vapor mixes with gases in the air, it moves upward with wind currents. The moisture loaded air cools as it rises because air expands as it goes up. The air continues to rise until the temperature is the same as that of the air surrounding it. When the temperature is equalized, the upward climb of the air mass stops.
The amount of water vapor air can hold decreases as it rises and cools. When the air is completely saturated, it reaches a condition called the dew point. At this time some of the water vapor condenses into particles of water so tiny that they are called water dust. Water dust is known as clouds or fog, according to whether it is high in the air or lying on or near the earth's surface. Still greater cooling of the air causes the tiny particles to unite into drops so large and heavy that they fall.
The one condition necessary for rain to form is the lowering of the temperatures to a point where the air cannot hold all of the moisture in it.
What is a raindrop's shape? If you said it looks like a teardrop, you are wrong. Actually, all raindrops are always perfectly round. Gravity's pull does not change this round shape into a teardrop shape as many people believe.
As raindrops fall through the atmosphere heading for earth, they help to wash dust and other impurities from the
air. It has been estimated that two days of rain over a city can wash tons of solid impurities from the air.
Highest rainfall for an area in one year was recorded in Cherrapunji, India, where 1,041 inches fell. In the tropics the average yearly rainfall is about 1C0 inches. The earth's average yearly rainfall is 32 inches.
Here are some interesting raindrop facts: The average thundercloud will hold 100,000 tons of water, or about 6 trillion raindrops. Driest state with an annual rainfall of only 8.8 inches is Nevada, while Hawaii wins wettest honors with a yearly average of 70 inches.