Monsoon Facts….
By Maxwell Pereira
maxpk@vsnl.com


The ‘mon-soon’ this year is ‘mon-late’… screamed a headline the other day, describing what’s foremost on the minds of most people ‘midst this blistering season of heat in Delhi and most other parts of north India around this time. As the heat wave sweeps across the land with its mercy-less broom, everyone is waiting in anticipation for the rains to come and cool down the climes, to relieve all from the furnacy climate that makes life a living hell, miserable and scorching.

To escape the rigours of the blistering summer, a minimissal few who can afford head to hill-stations or lands across the seas or mountains. While those who cannot, just suffer and wilt away even while hoping for the desert-ly loo bearing dusty winds to change to moisture laden rain bearing ones, for relief and succour to fauna, flora and the human stock alike.

In actual fact, the much awaited ‘monsoon’ hardly touches Delhi and surrounding parts of north India – unlike it does most of south India or north-eastern India that experience its real impact. For some of us who grew up in the South, monsoon meant the rains and the rainy season, there being only three seasons in a year – the summer, rainy and the winter, to contend with.

Even so, the very term ‘monsoon’ owes its origin, we are told, to the Arabic mausin or mausem which means season (…or the season of winds) - most often applied to the seasonal reversals of the wind direction along the shores of the Indian Ocean, and especially in the Arabian Sea, that blow from the southwest during one half of the year and from the northeast during the other.

Traditionally, the legendary Greek sailor Hippalus was credited to have been the first to use the monsoon to speed across the Indian Ocean, and so the ancient name for the monsoon was also called Hippalus. But perhaps he was simply the first Greek to master the monsoon, since Yemeni sailors were known to be trading with India long before his time.

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 vapour and back. The combined effect of these three mechanisms produces the monsoon's characteristic reversals of high winds and precipitation.

Scientists have described two key ingredients needed to make a monsoon – a hot land mass and a cooler ocean. Monsoons occur when land heats up and cools down quicker than water. In summer, the land reaches a higher temperature than the ocean, making the air over it to rise – thereby causing an area of low pressure to make winds from areas of high pressure to blow over areas of low pressure. The constant moisture laden wind thus blowing from the ocean causes rainfall when it rises up and gets cooled. Conversely, in winter since the land cools down quickly, the ocean is warmer. Air then rises, causing a low over the ocean. The wind then blows back out over the ocean. Since the temperature difference between the ocean and land is less than in summer, this wind is not as constant.

Along this basic principle, the land mass of the Indian sub-continent absorbs heat faster from the sun than the surrounding Indian Ocean does. Consequently as the air rises, a cooler, moistier, and heavier air from over the ocean replaces it. This damp, cool layer over India is estimated to be up to three miles thick. As the cool air arrives, the winds also shift. During 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 in any other place in the world.

Monsoons do occur in other parts of the world too, like in Australia and in the southwest portions of the United States. As monsoons have gradually been understood better, the term has now been broadened to include almost all phenomena associated with the annual weather cycle within the tropical and subtropical continents of Asia, Australia and Africa, and the adjacent seas, and to indicate 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 the most noted of the monsoons.

The more popular south-western summer monsoons occur from June to September. Intense low pressure developed over central Asia, makes the jet stream of south-eastern winds to blow over this area, passing over south-east Asia, which experiences large amounts of rainfall in this period. Meanwhile, the south-west monsoon is drawn towards the Himalayas, creating winds blowing rain clouds towards India, which receive up to 400 or more inches of rain in some areas.

The north-eastern winter monsoons take place from December to early March – when temperatures over central Asia are lower, creating a zone of high pressure there. The resultant jet stream directing north-easterly winds to blow across south Asia create dry air streams that produce clear skies over India from the months of November to May. Meanwhile, a low pressure system develops over northern Australia and winds are directed towards Australia. During the NE winter monsoon, apart from north-eastern India, south-east Asia and Australia too receive large amounts of rainfall.

900 words: Copy Right © Maxwell Pereira: 3725 Sec-23, Gurgaon-122002. You can interact with the author at http:// www.maxwellperira.com and maxpk@vsnl.com

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