What Is A Monsoon History Essay

A monsoon is traditionally defined as a seasonal reversing wind accompanied by seasonal changes in precipitation, but is now used to describe seasonal changes in atmospheric circulation and precipitation. The major monsoon systems of the world consist of the West African and Asia-Australian monsoons. The inclusion of the North and South American monsoons with incomplete wind reversal may be debated. The term was first used in English in British India (now India, Bangladesh and Pakistan) and neighboring countries to refer to the big seasonal winds blowing from the Bay of Bengal and Arabian Sea in the southwest bringing heavy rainfall to the area. In hydrology, monsoon rainfall is considered to be that which occurs in any region that receives the majority of its rain during a particular season. This allows other regions of the world to qualify as monsoon regions. The monsoon is a seasonal wind. In the summer it blows northwards over India and Bangladesh bringing wet weather. In the winter it blows southwards over these countries towards northern Australia. This cause dry weather conditions in Mumbai. These winds give distinct wet and dry season. When the rains come, rivers flood the land and fish spawn in the rice fields. People put away their ploughs and get out their fishing net as fields turn into huge lakes. In Mumbai, nearly 2000mm of rain falls in the summer but very little falls at any other time. Further inland, away from the sea, temperatures are higher and there is less rain. The north-west is a particularly arid region.

Abstract

The relationship between the evolution of the Asian summer monsoon and equatorial sea-surface-temperature anomalies has been studied using results from integration with the UK Universities’ Global Atmospheric Modelling Programme (UGAMP) General Circulation Model (UGCM). The integration was performed as part of the Atmospheric Model Intercomparison Project and thus used the observed sea surface temperatures for the decade January 1979 to December 1988. The mean evolution of the Asian summer monsoon has been successfully simulated in terms of many aspects of the rapid transition of the large-scale circulation during the boreal spring and summer. However, the results for individual years showed considerable interannual variability, both in the strength of the monsoon and in the time of onset. A relationship has been identified between the evolution of the monsoon flow and the phase of the El Niño Southern Oscillation. In agreement with observed results, years with warm SST anomalies in the equatorial central and east Pacific Ocean El Niño have a weaker monsoon circulation and a delayed onset. An opposite behavior is noted for those years with cold Pacific SST anomalies La Niña. Diagnostics from analyses from the National Meteorological Center and the European Centre for Medium-range Weather Forecasts, and from data on the outgoing long-wave radiation observed by the Advanced Very High Resolution Radiometer, have been used to verify the model results. A description of the mechanism by which the phase of ENSO remotely influences the dynamics of the Asian summer monsoon has been developed involving changes in the heating patterns over Indonesia and the west Pacific in the preceding spring.

Etymology and definition

The English monsoon came from Portuguese monção, ultimately from Arabic mawsim “season”, “perhaps partly via early modern Dutch monsun”. The Arabic-origin word mausam is also the word for “weather” in Hindi, Urdu, and several other North Indian languages. The definition includes major wind system that changes direction seasonally. Most summer monsoons have a dominant westerly component and a strong tendency to ascend and produce copious amounts of rain. The intensity and duration, however, are not uniform from year to year. Winter monsoons, by contrast, have a dominant easterly component and a strong tendency to diverge, subside and cause drought.

What causes monsoon?

The standard explanation of monsoons is that they are a wind system driven by thermal convection and pressures on a seasonal cycle. During the summer, the sun is high over land masses of Asia and heats up the atmosphere over the plateaus. The warm air rises, low-pressure areas are created, and air is drawn in from the Indian Ocean to replace the rising air. As the moisture-laden air is lifted over the land by high plateaus and mountains, it drops rain, sometimes in torrents, over the land. Thus in summer, the sea-to-land air brings rain. In winter the process is reversed as the sun moves southward over the water, creating areas of low pressure, toward which air is drawn from the cooling land mass. Meteorologists are now finding, however, the ore complex than previously supposed. They developed not only from thermal convections but also involve basic wind pattern and atmospheric disturbances in the form of cyclones, convections, and high and low areas.

South Asian monsoon

-Southwest Asian Monsoon

The southwestern summer monsoons occur from June through September. The Thar Desert and adjoining areas of the northern and central Indian subcontinent heats up considerably during the hot summers, which causes a low pressure area over the northern and central Indian subcontinent. To fill this void, the moisture-laden winds from the Indian Ocean rush in to the subcontinent. These winds, rich in moisture, are drawn towards the Himalayas, creating winds blowing storm clouds towards the subcontinent. The Himalayas act like a high wall, blocking the winds from passing into Central Asia, thus forcing them to rise. With the gain in altitude of the clouds, the temperature drops and precipitation occurs. Some areas of the subcontinent receive up to 10,000 mm of rain. The southwest monsoon is generally expected to begin around the start of June and fade down by the end of September. The moisture-laden winds on reaching the southernmost point of the Indian Peninsula, due to its topology, become divided into two parts: the Arabian Sea Branch and the Bay of Bengal branch. The monsoon accounts for 80% of the rainfall in India Indian agriculture is heavily dependent on the rains, for growing crops especially like cotton, rice, oilseeds and coarse grains. A delay of a few days in the arrival of the monsoon can badly affect the economy, as evidenced in the numerous droughts in India in the 1990s. The monsoon is widely welcomed and appreciated by city-dwellers as well, for it provides relief from the climax of summer heat in June. However, the condition of the roads takes a battering each year. Often houses and streets are waterlogged and the slums are flooded in spite of having drainage system. This lack of city infrastructure coupled with changing climate patterns causes’ severe economical loss including damage to property and loss of lives, as evidenced in the Bombay floods of 2005. Bangladesh and certain regions of India like Assam and West Bengal, also frequently experience heavy floods during this season. And in the recent past, areas in India that used to receive scanty rainfall throughout the year, like the Thar Desert, have surprisingly ended up receiving floods due to the prolonged monsoon season. The influence of the Southwest Monsoon is felt as far north as in China’s Xinjiang. It is estimated that about 70% of all precipitation in the central part of the Tian Shan Mountains falls during the three summer months, when the region is under the monsoon influence; about 70% of that is directly of “cyclonic”.

-Northeast Asian monsoon

Around September, with the sun fast retreating south, the northern land mass of the Indian subcontinent begins to cool off rapidly. With this air pressure begins to build over northern India, the Indian Ocean and its surrounding atmosphere still holds its heat. This causes the cold wind to sweep down from the Himalayas and Indo-Gangetic Plain towards the vast spans of the Indian Ocean south of the Deccan peninsula. This is known as the northeast monsoon or retreating monsoon. While travelling towards the Indian Ocean, the dry cold wind picks up some moisture from the Bay of Bengal and pours it over peninsular India and parts of Sri Lanka. Cities like Madras, which get less rain from the Southwest Monsoon, receive rain from this monsoon. About 50% to 60% of the rain received by the state of tamil nadu is from the northeast monsoon. In southern Asia, the northeastern monsoons take place from December to early March when the surface high-pressure system is strongest. The jet stream in this region splits into the southern subtropical jet and the polar jet. The subtropical flow directs northeasterly winds to blow across southern Asia, creating dry air streams which produce clear skies over India. Meanwhile, a low pressure system develops over South-East Asia and Australasia and winds are directed toward Australia known as a monsoon trough.

-East Asian Monsoon

The East Asian monsoon affects large parts of Indo-China, Philippines, China, Korea and Japan. It is characterized by a warm, rainy summer monsoon and a cold, dry winter monsoon. The rain occurs in a concentrated belt that stretches east-west except in East China where it is tilted east-northeast over Korea and Japan. The seasonal rain is known as Meiyu in China, Changma in Korea, and Bai-u in Japan, with the latter two resembling frontal rain. The onset of the summer monsoon is marked by a period of preonsoonal rain over south china and Taiwan in early may. From May through August, the summer monsoon shifts through a series of dry and rainy phases as the rain belt moves northward, beginning over Indo-china and the South China Sea (May), to the Yangtze River Basin and Japan (June) and finally to North China and Korea (July). When the monsoon ends in August, the rain belt moves back to south china.

Monsoon in Africa

In winter, the wind indeed blows from the cool continent to the warm ocean. Following the Sun apparent movement in the course of the year, the continent warms faster than the ocean. This thermal contrast drives the surface pressure contrast between the ocean (high pressure) and the continent (low pressure) and the set up of the monsoon circulation. Similarly to a giant sea-breeze, at the beginning of the summer, the wind changes and eventually blows from the ocean to the continent. The West African Monsoon differs in many aspects from the Asian Monsoon. Over West Africa, the large scale structure is very symmetric in the zonal direction while over the Indian subcontinent the flow is more complex. Another important difference, among many, lies in the fact the Indian monsoon seems more resilient that the African one in terms of rainfall. Over the 20th century, India never experienced more than two consecutive years of droughts while the Sahelian region suffered from a long lasting drought for the last twenty years.

Australia

Also known as the Indo-Australian Monsoon. The rainy season occurs from September to February and it is a major source of energy for the Hadley circulation during boreal winter. The Maritime Continent Monsoon and the Australian Monsoon may be considered to be the same system, the Indo-Australian Monsoon. It is associated with the development of the Siberian High and the movement of the heating maxima from the Northern Hemisphere to the Southern Hemisphere. North- easterly winds flow down Southeast Asia, are turned north-westerly by Borneo topography towards Australia. This forms a cyclonic circulation vortex over Borneo, which together with descending cold surges of winter air from higher latitudes, cause significant weather phenomena in the region. Examples are the formation of a rare low-latitude tropical storm in 2001, Tropical Storm Vamei, and the devasting flood of Jakarta in 2007. The onset of the monsoon over the Maritime Continent tends to follow the heating maxima down Vietnam and the Malay Peninsula (September), to Sumatra, Borneo and the Philippines (October), to Java, Sulawesi (November), Irian Jaya and Northern Australia (December, January). However, the monsoon is not a simple response to heating but a more complex interaction topography, wind and sea, as demonstrated by its abrupt rather than gradual withdrawal from the region. The Australian monsoon or rainy seasons occurs in the austral summer when the monsoon through develops over Northern Australia. Over quarters of annual rainfall in Northern Australia fall during this time.