Richard Hood, age 12, of Portland, Maine, for his question:
What is a monsoon
The word monsoon comes from an Iurabic word. meaning seasons. We tend to think that the monsoon is a pouring deluge which strikes India during the rainy season, actually, this is only a part of it. The monsoon is a year round climate and it engulfs too coastal region of China and southeastern Asia as well as the peninsula of India. In a way it is a changeable sea breeze on a gigantic scale, a tug of war between vast air masses over land and see.
The sea is slow to absorb the sun's heat and slow to let it go. The land absorbs the sun's heat fast and is just as fast to let it go when the sun no longer shines. The air gets its heat from the surfaces it touches below. The air, then, like the face of the earth, is heated and cooled in uneven patches.
Cool air tends to be heavy and warm air tends to be light. These differences are recorded on the barometer as air pressure, at sea level is 17.7. When air is light, there is less weight pressing down on the column of mercury, The meter shows low pressure. When the air is heavy,‑high‑‑pressure , and winds tend to blow from regions of high pressure to regions of low pressure, just as water tends to downhill.
The sea breezes give us a small example of these forces in operation during the day, the land is hotter than the sea. Its air pressure is lower. A cool breeze blows from the region of high pressure over the water to the region of lower pressure over the land, At night, the land cools faster than the sea, The regions of high and low pressure are reversed and the breeze now blows from the land out to sea.
On. a far grander scale, the great monsoon does a turnabout with the seasons, The spinning earth twists the winds to blow in a huge spiral which at one point crosses the equator. In winter, the air pressure is high over the chilly center of Asia. Summer is below the equator, creating regions of low pressure So the wind blows .from the north, spiraling around as it goes. In northern China, the winter monsoon wind blows from the northwest, in southern China from the north and in India from the northeast. This is a dry wind for it has not blown over the sea.
When the sun crosses the equator again, summer returns to the northern hemisphere. The movement of air is now from the regions of higher pressure below the equator to regions of lower pressure north of the equator. The summer monsoon wind is a southerly wind.
Just before the monsoon wind turns, the air has been sitting on the Indian Ocean, southwest of India. It hag gathered up all the warm moisture it can hold. As it turns to blow over India, the Himalayas force the wind to rise. This cools the air, causing it to drop its moisture. This is Indicts rainy monsoon wind.. But actually it is only a part of the total worldwide monsoon climate.