For centuries, people have tried to understand what causes the Southeast
Asian or Indian Ocean monsoon to arrive each June and die down each
September. Before the modern era of weather satellites and sophisticated
computers, climate scientists had only a basic understanding of how these
atmospheric forces collide to make a monsoon. The Asian monsoon is an important
climate system that affects the live of billions of people in the world.
Undoubtedly, a better
understanding of this mechanism is important.
A monsoon is a term from early Arabs called the "Mausin," or "the season of winds." This was in reference to the seasonally shifting winds in the Indian Ocean and surrounding regions, including the Arabian Sea. These winds blow from the southwest during one half of the year and from the northeast during the other. There are seasonal changes which are particularly noticed as northeast winds prevailing in the winter in the Southeast Asia and southwest winds in the summer. Monsoons will occur in other parts of the world like Australia and in the Southwest portions of the United States. Now as monsoons have become better understood, the definition now indicates climatic systems anywhere in which the moisture increases dramatically in the warm season. The Asian monsoon, which affects the Indian subcontinent and southeast part of the Asia, is probably the most noted of the monsoons.
A monsoon seasonal change is characterized by a variety of physical mechanisms which produce strong seasonal winds, a wet summer and a dry winter. All monsoons share three basic physical mechanisms: differential heating between the land and oceans; Coriolis forces due to the rotation of the Earth; and the role of water which stores and releases energy as it changes from liquid to vapor and back (latent heat). The combined effect of these three mechanisms produces the monsoon's characteristic reversals of high winds and precipitation. Scientists say that the two key ingredients needed to make a monsoon are a hot land mass and a cooler ocean. In India, for instance, the land absorbs heat faster from the sun than the surrounding Indian Ocean does. This causes air masses over the land to heat up, expand, and rise. As the air rises, cooler, moister, and heavier air from over the ocean will replace it.. Over India, this damp, cool layer can be up to three miles thick. As the cool air arrives, the winds also shift. During the dry season, the winds blow offshore, from land to sea. Then, as the monsoon begins, the winds blow onshore, from sea to land. In the case of the Indian Ocean Monsoon the first and third mechanisms produce more intense effects than any other place in the world.
Picture of Summer Monsoon
Source Mr. Drowling's
How much rain is does this area get in comparison? These are yearly precipitation estimates for some selected cities extracted from the GEOS-1 Multiyear Assimilation. Calcutta and NW Burma are in the heart of the Indian monsoon region.
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