Summary table Africa (West African and Southeast African) The monsoon of western
Sub-Saharan Africa is the result of the seasonal shifts of the
Intertropical Convergence Zone and the great seasonal temperature and humidity differences between the
Sahara and the equatorial Atlantic Ocean. The ITCZ migrates northward from the equatorial Atlantic in February, reaches western Africa on or near June 22, then moves back to the south by October. It is also sometimes called the
Desert monsoon as a large part of the affected area are the
Mojave and
Sonoran deserts. However, it is controversial whether the
North and South American weather patterns with incomplete wind reversal should be counted as true monsoons.
Asia The Asian monsoons may be classified into a few sub-systems, such as the Indian Subcontinental Monsoon which affects the Indian subcontinent and surrounding regions including Nepal, and the East Asian Monsoon which affects southern China,
Taiwan, Korea and parts of Japan.
South Asian monsoon Southwest monsoon The southwestern summer monsoons occur from June to September. The
Thar Desert and adjoining areas of the northern and central Indian subcontinent heat up considerably during the hot summers. This 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 into the subcontinent. These winds, rich in moisture, are drawn towards the
Himalayas. The Himalayas act like a high wall, blocking the winds from passing into Central Asia, and forcing them to rise. As the clouds rise, their temperature drops, and
precipitation occurs. Some areas of the subcontinent receive up to of rain annually. The southwest monsoon is generally expected to begin between the end of May and beginning of June and fade away between the end of September and start of October. The moisture-laden winds on reaching the southernmost point of the
Indian Peninsula, due to its topography, become divided into two parts: the
Arabian Sea Branch and the
Bay of Bengal Branch. The
Arabian Sea Branch of the Southwest Monsoon first hits the
Western Ghats of the coastal state of
Kerala, India, thus making this area the first state in India to receive rain from the Southwest Monsoon. This branch of the monsoon moves northwards along the Western Ghats (
Konkan and
Goa) with precipitation on coastal areas, west of the Western Ghats. The eastern areas of the Western Ghats do not receive much rain from this monsoon as the wind does not cross the Western Ghats. The
Bay of Bengal Branch of Southwest Monsoon flows over the
Bay of Bengal heading towards north-east India and
Bengal, picking up more moisture from the Bay of Bengal. The winds arrive at the
Eastern Himalayas with large amounts of rain.
Mawsynram, situated on the southern slopes of the
Khasi Hills in
Meghalaya, India, is one of the wettest places on Earth. After the arrival at the Eastern Himalayas, the winds turns towards the west, travelling over the
Indo-Gangetic Plain at a rate of roughly 1–2 weeks per state, pouring rain all along its way. June 1 is regarded as the date of onset of the monsoon in India, as indicated by the arrival of the monsoon in the southernmost state of Kerala. The monsoon accounts for nearly 80% of the rainfall in India. Indian agriculture (which accounts for 25% of the GDP and employs 70% of the population) 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 roads take a battering every year. Often houses and streets are waterlogged and slums are flooded despite drainage systems. A lack of city infrastructure coupled with changing climate patterns causes severe economic loss including damage to property and loss of lives, as evidenced in the
2005 flooding in Mumbai that brought the city to a standstill.
Bangladesh and certain regions of India like
Assam and
West Bengal, also frequently experience heavy floods during this season. Recently, 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" (i.e., monsoon-driven) origin (as opposed to "
local convection"). In Southern Asia, the northeastern monsoons take place from October to December 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 known as a
monsoon trough develops over
South-East Asia and
Australasia and winds are directed toward Australia. In the Philippines, northeast monsoon is called
Amihan.
East Asian monsoon , Philippines The East Asian monsoon affects large parts of
Indochina, the
Philippines, China,
Taiwan, Korea, Japan, and
Siberia. It is characterised 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,
Jangma 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 premonsoonal 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
Indochina and the
South China Sea (May), to the
Yangtze River Basin and Japan (June) and finally to northern China and Korea (July). When the monsoon ends in August, the rain belt moves back to southern China.
Australia , Australia The rainy season occurs from September to February and it is a major source of energy for the
Hadley circulation during boreal winter. 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/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
devastating flood of Jakarta in 2007. The onset of the monsoon over
Australia 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 of topography, wind and sea, as demonstrated by its abrupt rather than gradual withdrawal from the region. The Australian monsoon (the "Wet") occurs in the southern summer when the monsoon trough develops over
Northern Australia. Over three-quarters of annual rainfall in Northern Australia falls during this time.
Europe The
European Monsoon (more commonly known as the
return of the westerlies) is the result of a resurgence of westerly winds from the Atlantic, where they become loaded with wind and rain. These westerly winds are a common phenomenon during the European winter, but they ease as spring approaches in late March and through April and May. The winds pick up again in June, which is why this phenomenon is also referred to as "the return of the westerlies". The rain usually arrives in two waves, at the beginning of June, and again in mid- to late June. The European monsoon is not a monsoon in the traditional sense in that it doesn't meet all the requirements to be classified as such. Instead, the return of the westerlies is more regarded as a conveyor belt that delivers a series of low-pressure centres to Western Europe where they create unsettled weather. These storms generally feature significantly lower-than-average temperatures, fierce rain or hail, thunder, and strong winds. The return of the westerlies affects Europe's Northern Atlantic coastline, more precisely Ireland, Great Britain, the
Benelux countries, western Germany, northern France and parts of Scandinavia. ==See also==