Anne Sampson, age 11, of Toronto, Ontario Canada, for her question:

What exactly is a monsoon?

We are told that the monsoon was named with an old Arabic word meaning "seasons."Many of us have the idea that the monsoon is a deluging wet season that descends on regions of the Far East. This is only part of the story. A monsoon is a steady wind that reverses direc¬tions with the seasons. In monsoon regions, it brings six months of dry weather and six months of rainy moisture.

During the scorching summer season, we go to the beaches to cool off. The water is cooler because the land absorbs more of the sun's heat. This affects the air above land and ocean. The warm, light air over the land rises and cooler, heavier breezes blow shoreward from over the ocean. The land gains and also loses heat faster than the sea. So at evening the airy sea breezes are reversed.

Sea breezes are daily weather events on a local scale. The monsoon is a seasonal weather event on an almost global scale. But both events are caused by the unequal heating of land and sea areas. In both cases, currents of light rising air draw in winds from the cooler land or sea.

The world's major monsoon climates are in two vast regions, one on either side of the high Himalayas. One determines the seasonal climate of Japan and parts of mainland China. The other is the famous monsoon region including India and parts of Southeast Asia. Here the winter season draws a northwest wind from the great Gobi Desert. This dry, dry monsoon wind blows relentlessly from December to about June, sucking up moisture and parching the soil.

Then, suddenly, the wind makes an about face. For the next six months, it blows from the southeast, bearing loads of moisture absorbed from the Indian Ocean. This is the rainy season monsoon wind. During the next six months, people of the monsoon region expect cloudy skies with plenty of showers and occasional deluges.

This is the world's most extreme monsoon region and life there is adjusted to six months of drought and six months of deluge. But similar weather conditions create milder monsoons in many other parts of the globe. As in all weather events, there is a conflict of different air masses    warm or cool, damp or dry. In this case, the massive contrasts build up with seasonal changes over land and sea areas.

In summer, the continents are warmer than the oceans and in winter they are cooler than the oceans. The air gets its warmth from the land or sea below it    and warm air tends to be lighter than cool air. In summer, the land tends to build up masses of low pressure. This draws in moisture ladened monsoon winds from the sea.

In winter, when the sea is warmer than the land, the air pressure above it tends to be lower than it is over the land. Hence the wind blows from the opposite direction, perhaps from the deep dry heart of a conti¬nent. This is when the bone dry monsoon blows over the land on its way to regions of lower air pressure over the sea.