Nancy 0'Reilly, age 9, of Ottawa, Ill., for her question:
What is a monsoon?
We expect our weather to bring us a cold winter season and a warm summer season. But certain faraway lands have monsoon seasons instead. They are warm countries where the winters are never cold enough for snow. But their summer monsoons may bring deluges of pelting rain.
A monsoon is really a special kind of wind. The Arabs of North Africa noticed that it blew at certain times of the year and they named it the monsoon. Half the year a southwest monsoon wind blows steadily across North Africa. Then it changes, and for six months it blows from the northwest. Monsoon winds blow over India, Australia, Vietnam and other parts of Asia.
Most monsoon lands have hot summer seasons and warm winter seasons. The changeable wind blows from one direction in summer and from another through the winter. As a rule the winter monsoon is dry. But the summer monsoon is wet and rainy. When people talk about a monsoon season, they usually mean the wet rainy monsoon of the summer season.
The winds are moving rivers of air that blow over land and sea. They blow because the filmy air has warm patches and cool patches, dry patches and moist patches. Over the sea the breezy winds gather up moisture and fill their clouds with rain. When the clouds drop their rain on the land the winds lose their moisture and become dry.
In sunny weather the land gets warmer than the sea and the land winds are warmer than the ocean winds. In coaler weather the sea stays warmer than the land and ocean winds are warmer than land winds. The weather tends to make cooler air blow toward warmer places. The changing monsoon winds are caused by pockets of warm dry air and cooler moist air.
In monsoon countries, the land in winter is cooler than the nearby sea. The warm wind blows from the land toward the sea. It gathers up no moisture from the dry land, forms no clouds and sheds no rain. Then comes the warmer summer season and the land gets hotter than the nearby sea. The monsoon changes around and blows from the ocean across the land. This wind is wet with moisture from the sea. The summer monsoon season douses the land with showers.
Sometimes we have a slight monsoon season in America. In winter a northerly wind blows over the eastern states. In summer it may change to a southerly wind and the southeastern states get a humid and wet monsoon season. But the big monsoon seasons happen in parts of China and Asia and in faraway India. There the winters are warm and very dry. But the summer monsoon brings a season of deluging downpours.