Great Disasters and Horrors in the World's History

by Allen Howard Godbey

O the seasons tread their ceaseless round in the temperate zones, and to a certain degree in the colder regions of the earth. But when we examine the change of seasons in the tropical world, we find a state of things so different that we are at once led to inquire the reason: and it will be found primarily in certain periodical winds.

When the sun is north of the equator: that is, while our northern summer is in progress, India enjoys a steady sea wind from the southwest, which brings a rainy season to the corresponding coasts of Hindostan and Farther India. When the sun returns to the south, the winds set in from the opposite direction, coming down across the great upland plateau of Central Asia, sometimes called, from its immense height and extent, the “Roof of the World.” These periodic winds are called monsoons: a corruption of the Arabic word Moussin, season. They are in reality a modification of the trade-winds.

A glance at a map will show that the northern half of the great Indian Ocean is enclosed by land masses as no other large body of water is. Consequently, while in the southern section the southeast trade is present, the northeast trade of the northern part is so modified by the surrounding land areas as to almost entirely lose its distinctive character. Hence, most tropical regions have, properly speaking, but two seasons: the rainy, and the dry. As the clouds swept in meet with an intensely heated region, the trade never chills them sufficiently to produce snow, except in extremely elevated regions.

This is the direct cause of the monsoons: During the northern summer, southern Asia, being under the rays of the vertical sun, becomes intensely heated; and the cooler and denser air of the adjacent ocean, and of southern Africa, flows towards it, producing the southwest monsoon, which lasts from April or May to September or October. The time of its beginning and its close varies in different latitudes, according to the time at which the sun is vertical in each.

During the southern summer, southern Africa being under the vertical sun and intensely heated, the cooler air of the surrounding seas, and of southern Asia, flows towards it. This produces the northeast monsoon, which lasts from October or November to April. This monsoon is, in fact, only the regular northeast trade-wind somewhat intensified.

A similar exchange takes place between Asia and Australia, but it is less marked, owing, perhaps, to the great islands lying between these continents.

The period of transition of the monsoons, in spring and autumn, is marked by sudden and violent gales, and terrific thunder storms. Destructive hurricanes, also, are of frequent occurrence. This corresponds with the period of equinoctial storms in higher latitudes.

There are narrow monsoon belts in the Atlantic, along the coast of Africa and of Brazil, also on the Pacific coasts of North and South America; but the phenomena they exhibit are of a much less striking character. On the African coast, in general, the winds blow from sea to land in summer, from land to sea in winter; on the Brazilian, the wind is from the northeast in summer, while in winter the southeast trade resumes its sway. The monsoons of the Pacific coast of America blow from the northwest and north during the southern summer; from the southwest and south during the northern. The regular trade-wind makes itself so strongly felt in northern Brazil, which is unusually level, that a boat can sail almost as rapidly up the swift current of the Amazon as it can row down: and Humboldt records that he found it of great strength at the foot of the eastern slope of the Andes.

Another modification of the northeast trade is found in the Etesian winds of Greece and the adjacent archipelago. This is a true intermittent trade, blowing only in the daytime, however, and lasting from July to September. The cool air of the peninsula rushes toward the extremely heated regions of the Mediterranean and north Africa.

Somewhat similar are the northers, or blizzards, of our Western States. By the laws already given, it is seen that northerly winds can prevail in any region only when some region further south is unusually heated. Now, the northern portion of America may be roughly compared to a trough. The cold polar current sets to the southward across the continent, and is turned to the east by the Rocky Mountain range, giving it a general southeast course. Hence, when the southern summer is in progress, our prevailing winds are from the northwest; and when the heated portion of the world is north of the equator, we have the return trade, giving us as our prevailing wind that from the southwest. When our return trade is unusually prolonged, we have a late fall; and if the southern summer is unusually warm, we have the polar current longer than usual, and a late spring in consequence. The polar current seldom makes its presence felt beyond the Texan plains; though occasionally it reaches the Mexican plateau, or sweeps across the Gulf to the Antilles.