Tammy Waxham, age 8, of Shreveport, Louisiana, for her question:

What is the monsoon rain?

Every year the monsoon rains fall on Vietnam, India and other parts of the world. They are expected to start in early summer and for the next six months the weather is wet. It showers or drizzles almost every day. Then the wet monsoon changes to a dry monsoon. For the next six months the weather is clear. The monsoon seasons change because the winds turn around twice each year.

Warm air over the ocean soaks up moisture and changes it into misty clouds. The winds blow the clouds this way and that way. And sooner or later the clouds drop their rainy moisture down on the earth. As a rule, the winds decide where and when the rain will fall. Certainly they bring the rainy summer season to India9 Vietnam and other monsoon regions. The people there call them the monsoon winds.

All through the winter, these winds blow across Asia toward the sea. They cannot soak up moisture because they blow across hundreds and hundreds of miles of dry land. So for six months the winter season is dry. But in early summer, the winds suddenly turn around in the opposite direction. Now they blow from the ocean toward the land. These monsoon winds from the vast ocean are loaded with misty moisture and heavy rain clouds.

In India and Vietnam, the rainy monsoon usually starts in June. Suddenly there are heavy showers. The roads are clogged with mud; the forests are soggy with falling rain. Then the weather clears up a little. But for the next six months there are drizzling showers or heavy rain almost every day. The water sinks down into the thirsty ground and feeds the growing crops. And people carry umbrellas all through the season. Come fall, the monsoon wind changes around again    and no rain is expected through the winter.

All of this happens because of the winds. And winds are really masses of moving air. They seem to blow just where they please. But actually they must obey certain weather rules. They are ruled by vast masses of air above the land and ocean. There are masses of warm light air and masses of cool heavier air. Cool air tends to flow toward warm air    and this is what starts a wind blowing.

In summer we go to the beaches because the sea is cooler than the land. This is true in monsoon countries and everywhere else. In summer the wet monsoon wind blows from the cooler ocean and sheds rain on the land. When winter comes, the sea stays warmish while the land grows cooler. Then the big monsoon wind blows from the cooler dry land toward the warmer ocean.

Many countries have wet and dry monsoon seasons every year. Most of them are places where large continents face vast oceans. India and Vietnam are near the edge of the large land mass of Asia. Their shores face the sea, where winds can blow back and forth across the vast Pacific Ocean.