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A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in
precipitation In meteorology Meteorology is a branch of the (which include and ), with a major focus on . The study of meteorology dates back , though significant progress in meteorology did not begin until the 18th century. The 19th century saw mod ...

precipitation
, but is now used to describe seasonal changes in
atmospheric An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or 'sphere') is a layer or a set of layers of gases surrounding a planet A planet is an astronomical body orbi ...
circulation and precipitation associated with annual latitudinal oscillation of the Intertropical Convergence Zone between its limits to the north and south of the equator. Usually, the term monsoon is used to refer to the rainy phase of a seasonally changing pattern, although technically there is also a dry phase. The term is also sometimes used to describe locally heavy but short-term rains. The major monsoon systems of the world consist of the
West African West Africa or Western Africa is the westernmost region of Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjac ...
and Asia–Australian monsoons. The inclusion of the
North American Monsoon The North American monsoon, variously known as the Southwest monsoon, the Mexican monsoon, the New Mexican monsoon, or the Arizona monsoon, is a pattern of pronounced increase in thunderstorms and rainfall over large areas of the southwestern Unit ...
and South American monsoon with incomplete wind reversal has been debated. The term was first used in English in British India and neighbouring countries to refer to the big seasonal winds blowing from the
Bay of Bengal The Bay of Bengal is the northeastern part of the Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or 19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to th ...

Bay of Bengal
and
Arabian Sea The Arabian Sea ( ar, بحر العرب ''Bahr al-Arab'') is a region of the northern Indian Ocean The Indian Ocean is the third-largest of the world's oceanic divisions, covering or 19.8% of the water Water is an Inorganic co ...
in the southwest bringing heavy
rainfall Rain is liquid water in the form of droplet Raindrops in a plant. A drop or droplet is a small column of liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformation (mechani ...

rainfall
to the area.


Etymology

The etymology of the word monsoon is not wholly certain. The English ''monsoon'' came from Portuguese ultimately from
Arabic Arabic (, ' or , ' or ) is a Semitic language The Semitic languages are a branch of the Afroasiatic language family originating in the Middle East The Middle East is a list of transcontinental countries, transcontinental region ...

Arabic
(, "season"), "perhaps partly via early modern Dutch ''monson''".


History

Strengthening of the Asian monsoon has been linked to the uplift of the
Tibetan Plateau The Tibetan Plateau (, also known as the Qinghai–Tibet Plateau or the Qing–Zang Plateau () or as the Himalayan Plateau in India, is a vast elevated plateau In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λ ...
after the collision of the Indian subcontinent and Asia around 50 million years ago. Because of studies of records from the
Arabian Sea The Arabian Sea ( ar, بحر العرب ''Bahr al-Arab'') is a region of the northern Indian Ocean The Indian Ocean is the third-largest of the world's oceanic divisions, covering or 19.8% of the water Water is an Inorganic co ...
and that of the wind-blown dust in the
Loess Plateau The Chinese Loess Plateau, or simply the Loess Plateau, is a plateau In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid ...
of China, many geologists believe the monsoon first became strong around 8 million years ago. More recently, studies of plant fossils in China and new long-duration
sediment Sediment is a naturally occurring material that is broken down by processes of weathering Weathering is the deterioration of rocks A rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is cate ...

sediment
records from the
South China Sea The South China Sea is a of the . It is bounded in the north by the shores of (hence the name), in the west by the , in the east by the islands of and northwestern (mainly , and ), and in the south by , and the , encompassing an area of ...

South China Sea
led to a timing of the monsoon beginning 15–20 million years ago and linked to early Tibetan uplift. Testing of this hypothesis awaits deep ocean sampling by the
Integrated Ocean Drilling Program The Integrated Ocean Drilling Program (IODP) was an international marine research program. The program used heavy drilling equipment mounted aboard ships to monitor and sample sub-seafloor environments. With this research, the IODP documented env ...
. The monsoon has varied significantly in strength since this time, largely linked to global
climate change Contemporary climate change includes both the global warming caused by humans, and its impacts on Earth's weather patterns. There have been previous periods of climate change, but the current changes are more rapid than any known event ...
, especially the cycle of the
Pleistocene The Pleistocene ( , often referred to as the ''Ice Age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the earth’s most recent period of repeated glaciations. Before a change finally ...
ice ages. A study of marine plankton suggested that the Indian Monsoon strengthened around 5 million years ago. Then, during ice periods, the sea level fell and the Indonesian Seaway closed. When this happened, cold waters in the Pacific were impeded from flowing into the Indian Ocean. It is believed that the resulting increase in sea surface temperatures in the Indian Ocean increased the intensity of monsoons. Five episodes during the
Quaternary The Quaternary ( ) is the current and most recent of the three period (geology), periods of the Cenozoic era (geology), Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans ...
at 2.22 Ma (PL-1), 1.83 Ma (PL-2), 0.68 Ma (PL-3), 0.45 Ma (PL-4) and 0.04 Ma (PL-5) were identified which showed a weakening of the Leeuwin Current (LC). The weakening of the LC would have an effect on the sea surface temperature (SST) field in the Indian Ocean, as the
Indonesian Throughflow The Indonesian Throughflow (ITF) is an ocean current with importance for global climate as is the low-latitude movement of warm, relative freshwater from the north Pacific to the Indian Ocean. It thus serves as a main upper branch of the global h ...
generally warms the Indian Ocean. Thus these five intervals could probably be those of considerable lowering of SST in the Indian Ocean and would have influenced Indian monsoon intensity. During the weak LC, there is the possibility of reduced intensity of the Indian winter monsoon and strong summer monsoon, because of change in the
Indian Ocean dipole The Indian Ocean Dipole (IOD), also known as the Indian Niño, is an irregular oscillation Oscillation is the repetitive variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more d ...
due to reduction in net heat input to the Indian Ocean through the Indonesian Throughflow. Thus a better understanding of the possible links between
El Niño es, El Niño, translation=The Boy (; ) is the warm phase of the El Niño–Southern Oscillation El Niño–Southern Oscillation (ENSO) is an irregular periodic variation in winds and sea surface temperatures over the Tropics, tropical easte ...
, Western Pacific Warm Pool, Indonesian Throughflow, wind pattern off western Australia, and ice volume expansion and contraction can be obtained by studying the behaviour of the LC during Quaternary at close stratigraphic intervals.


Strength of impact

The impact of monsoon on the local weather is different from place to place. In some places there is just a likelihood of having a little more or less rain. In other places, quasi semi-deserts are turned into vivid green grasslands where all sorts of plants and crops can flourish. The Indian Monsoon turns large parts of India from a kind of semi-desert into green lands. See photos only taken 3 months apart in the Western Ghats. In places like this it is crucial for farmers to have the right timing for putting the seeds on the fields, as it is essential to use all the rain that is available for growing crops.


Process

Monsoons were once considered as a large-scale
sea breeze A sea breeze A sea breeze or onshore breeze is any wind that blows from a large body of water toward or onto a landmass; it develops due to differences in air pressure created by the differing heat capacities of water and dry land. As such ...

sea breeze
caused by higher temperature over land than in the ocean. This is no longer considered as the cause and the monsoon is now considered a planetary-scale phenomenon involving the annual migration of the Intertropical Convergence Zone between its northern and southern limits. The limits of the ITCZ vary according to the land-sea heating contrast and it is thought that the northern extent of the monsoon in South Asia is influenced by the high Tibetan Plateau. These temperature imbalances happen because oceans and land absorb heat in different ways. Over oceans, the air temperature remains relatively stable for two reasons: water has a relatively high
heat capacity Heat capacity or thermal capacity is a physical property A physical property is any property Property is a system of rights that gives people legal control of valuable things, and also refers to the valuable things themselves. Depending on t ...
(3.9 to 4.2 J g−1 K−1), and because both conduction and
convection Convection is single or multiphase fluid flow that occurs Spontaneous process, spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When t ...
will equilibrate a hot or cold surface with deeper water (up to 50 metres). In contrast, dirt, sand, and rocks have lower heat capacities (0.19 to 0.35 J g−1 K−1), and they can only transmit heat into the earth by conduction and not by convection. Therefore, bodies of water stay at a more even temperature, while land temperature are more variable. During warmer months sunlight heats the surfaces of both land and oceans, but land temperatures rise more quickly. As the land's surface becomes warmer, the air above it expands and an area of
low pressure File:Low pressure system over Iceland.jpg, 250 px, This low-pressure system over Iceland spins counter-clockwise due to balance between the Coriolis and pressure gradient force. In meteorology, a low-pressure area, low area or low is a region whe ...
develops. Meanwhile, the ocean remains at a lower temperature than the land, and the air above it retains a higher pressure. This difference in pressure causes
sea breeze A sea breeze A sea breeze or onshore breeze is any wind that blows from a large body of water toward or onto a landmass; it develops due to differences in air pressure created by the differing heat capacities of water and dry land. As such ...

sea breeze
s to blow from the ocean to the land, bringing moist air inland. This moist air rises to a higher altitude over land and then it flows back toward the ocean (thus completing the cycle). However, when the air rises, and while it is still over the land, the air cools. This decreases the air's
ability to hold water
ability to hold water
, and this causes
precipitation In meteorology Meteorology is a branch of the (which include and ), with a major focus on . The study of meteorology dates back , though significant progress in meteorology did not begin until the 18th century. The 19th century saw mod ...

precipitation
over the land. This is why summer monsoons cause so much rain over land. In the colder months, the cycle is reversed. Then the land cools faster than the oceans and the air over the land has higher pressure than air over the ocean. This causes the air over the land to flow to the ocean. When humid air rises over the ocean, it cools, and this causes precipitation over the oceans. (The cool air then flows towards the land to complete the cycle.) Most summer monsoons have a dominant westerly component and a strong tendency to ascend and produce copious amounts of rain (because of the condensation of water vapor in the rising air). 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. Similar rainfall is caused when moist ocean air is lifted upwards by mountains,Dr. Michael Pidwirny (2008)
CHAPTER 8: Introduction to the Hydrosphere (e). Cloud Formation Processes.
Physical Geography. Retrieved on 2009-01-01.
surface heating, convergence at the surface, divergence aloft, or from storm-produced outflows at the surface. However the lifting occurs, the air cools due to expansion in lower pressure, and this produces
condensation Condensation is the change of the state of matter In physics, a state of matter is one of the distinct forms in which matter can exist. Four states of matter are observable in everyday life: solid, liquid, gas, and Plasma (physics), plasma. ...

condensation
.



Summary table


Africa (West African and Southeast African)

The monsoon of western
Sub-Saharan Africa Sub-Saharan Africa (commonly called Black Africa) is, geographically, the area of the continent of Africa that lies south of the Sahara. According to the United Nations, it consists of all list of sovereign states and dependent territories i ...

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 The Sahara (, ; ar, الصحراء الكبرى, ', 'the Greatest Desert') is a desert on the African continent Africa is the world's second-largest and second-most populous continent A continent is any of several large landma ...

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. The dry, northeasterly
trade winds The trade winds or easterlies are the permanent east-to-west prevailing winds that flow in the Earth's equatorial region. The trade winds blow mainly from the northeast in the Northern Hemisphere The Northern Hemisphere is the half of Ear ...
, and their more extreme form, the
harmattan 300px, Harmattan haze surrounding Abuja National Mosque in Abuja ">Abuja.html" ;"title="Abuja National Mosque in Abuja">Abuja National Mosque in Abuja The Harmattan is a season in West Africa, which occurs between the end of November and the m ...

harmattan
, are interrupted by the northern shift in the ITCZ and resultant southerly, rain-bearing winds during the summer. The semiarid
Sahel The Sahel (; ar, ساحل ' , "coast, shore") is the ecoclimatic and of in between the to the north and the to the south. Having a , it stretches across the south-central latitudes of between the Atlantic Ocean and the . The Sahel part o ...

Sahel
and
Sudan Sudan ( or ; ar, السودان, as-Sūdān), officially the Republic of the Sudan ( ar, جمهورية السودان, link=no, Jumhūriyyat as-Sūdān), is a country A country is a distinct territorial body or political entity A ...
depend upon this pattern for most of their precipitation.


North America

The North American monsoon (NAM) occurs from late June or early July into September, originating over Mexico and spreading into the southwest United States by mid-July. It affects Mexico along the
Sierra Madre Occidental The Sierra Madre Occidental is a major mountain range system of the North American Cordillera, that runs northwest–southeast through northwestern and western Mexico, and along the Gulf of California. The Sierra Madre is part of the American Cor ...

Sierra Madre Occidental
as well as
Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak) is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ...

Arizona
,
New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Greater Albuquerque , OfficialLang = None , Languages = English English usually refer ...

New Mexico
,
Nevada Nevada (, ) is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspaper), a daily newspaper i ...

Nevada
,
Utah Utah ( , ) is a U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its so ...

Utah
,
Colorado Colorado (, other variants) is a state in the Mountain states, Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the weste ...

Colorado
,
West Texas West Texas is a loosely defined part of the U.S. state of Texas, generally encompassing the desert climate, arid and semi-arid climate, semiarid lands west of a line drawn between the cities of Wichita Falls, Texas, Wichita Falls, Abilene, Texas, ...
and
California California is a U.S. state, state in the Western United States. With over 39.3million residents across a total area of approximately , it is the List of states and territories of the United States by population, most populous and the List of ...

California
. It pushes as far west as the
Peninsular Ranges The Peninsular Ranges (also called the Lower California province) are a group of mountain ranges that stretch from Southern California Southern California (sometimes known as SoCal; es, Sur de California) is a geographic and cultural region ...
and
Transverse Ranges The Transverse Ranges are a group of mountain ranges of southern California Southern California (popularly known as SoCal; es, Sur de California) is a geographic and cultural region that generally comprises the southern portion of the U.S. stat ...
of Southern California, but rarely reaches the coastal strip (a wall of desert thunderstorms only a half-hour's drive away is a common summer sight from the sunny skies along the coast during the monsoon). The North American monsoon is known to many as the ''Summer'', ''Southwest'', ''Mexican'' or ''Arizona'' monsoon. It is also sometimes called the ''Desert monsoon'' as a large part of the affected area are the
Mojave Mojave or Mohave most often refers to: *Mojave Desert *Mojave River *Mohave people Mojave or Mohave may also refer to: Places * Fort Mojave Indian Reservation * Mohave County, Arizona * Mohave Valley, a valley in Arizona * Mohave Valley, Arizona, ...

Mojave
and
Sonoran desert The Sonoran Desert ( es, Desierto de Sonora) is a North American desert and ecoregion An ecoregion (ecological region) or ecozone (ecological zone) is an ecologically Ecology (from el, οἶκος, "house" and el, -λογία, label=n ...

Sonoran desert
s. However, it is debatable whether the
North North is one of the four compass points The points of the compass are the vectors by which planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydro ...
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 Taiwan, officially the Republic of China (ROC), is a country in East Asia East Asia is the eastern region of Asia Asia () is Earth's largest and most populous continent, located primarily in the Eastern Hemisphere, Eastern and N ...

Taiwan
, Korea and parts of Japan.


South Asian monsoon


=Southwest monsoon

= The southwestern summer monsoons occur from July through September. The
Thar Desert The Thar Desert, also known as the Great Indian Desert, is a large arid region A region is arid when it is characterized by a severe lack of available water, to the extent of hindering or preventing the growth and development Development ...

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, or Himalaya (; Sanskrit Sanskrit (, attributively , ''saṃskṛta-'', nominalization, nominally , ''saṃskṛtam'') is a classical language of South Asia belonging to the Indo-Aryan languages, Indo-Aryan branch of the Ind ...

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 around the beginning of June and fade away by the end of September. 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 The Western Ghats is a mountain range that covers an area of in a stretch of parallel to the western coast of the Indian peninsula, traversing the states State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', ...

Western Ghats
of the coastal state of
Kerala Kerala ( ; ) is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspaper), a daily newspaper ...

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 Konkan is the rugged section of the mid-western coast of India, the coastal hinterland of Konkan consists of numerous riverine islands, river valleys, and the hilly slopes of the Western Ghats, that lead up into the tablelands of the Decca ...

Konkan
and
Goa Goa () is a state on the southwestern coast of India India (Hindi: ), officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by population, second-most populous country, the ...

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 The Bay of Bengal is the northeastern part of the Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or 19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to th ...

Bay of Bengal
heading towards north-east India and
Bengal Bengal (; Bengali language, Bengali: ', ) is a geopolitical, cultural and historical region in South Asia, specifically in the eastern part of the Indian subcontinent at the apex of the Bay of Bengal, predominantly covering present-day Bang ...

Bengal
, picking up more moisture from the Bay of Bengal. The winds arrive at the
Eastern Himalayas] The Eastern Himalayas extend from eastern Nepal across Northeast India, Bhutan, the Tibet Autonomous Region to Yunnan in China and northern Myanmar. The climate of this region is influenced by the monsoon of South Asia from June to September. It i ...

Eastern Himalayas
with large amounts of rain.
Mawsynram Mawsynram () is a town in the East Khasi Hills district of Meghalaya state in northeastern India India (Hindi: ), officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by po ...

Mawsynram
, situated on the southern slopes of the
Khasi Hills The Khasi Hills is a low mountain formation on the Shillong Plateau in Meghalaya state of India. The Khasi Hills are part of the Garo-Khasi-Jaintia range and connects with the Purvanchal Range and larger Patkai Range further east. Khasi Hills, ...
in
Meghalaya Meghalaya (, or , meaning "abode of clouds"; from Sanskrit , "cloud" + , "abode") is a states and union territories of India, state in northeastern India. Meghalaya was formed by carving out two districts from the state of Assam: the United Kha ...

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#REDIRECT Indo-Gangetic Plain Image:India-Pakistan Borderlands at Night.JPG, 250px, Clusters of yellow lights on the Indo-Gangetic Plain reveal numerous cities large and small in this astronaut photograph of northern India and northern Pakistan, ...

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 Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus '' Gossypium'' in the mallow family Malvaceae. The fiber is almost pure cellulose. Under natural condition ...

cotton
,
rice Rice is the seed A seed is an embryonic ''Embryonic'' is the twelfth studio album by experimental rock band the Flaming Lips released on October 13, 2009, on Warner Bros. Records, Warner Bros. The band's first double album, it was relea ...

rice
,
oilseeds Vegetable oils, or vegetable fats, are oil An oil is any nonpolar chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by h ...

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 Bangladesh (, bn, বাংলাদেশ, ), officially the People's Republic of Bangladesh, is a country in South Asia South Asia is the southern region of Asia, which is defined in both geography, geographical and culture, ethno-c ...

Bangladesh
and certain regions of India like
Assam Assam (, ) is a state in Northeast India, northeastern India, south of the eastern Himalayas along the Brahmaputra Valley, Brahmaputra and Barak River valleys. Assam covers an area of . The state is bordered by Bhutan and Arunachal Pradesh to ...

Assam
and
West Bengal West Bengal (, Bengali Bengali or Bengalee, or Bengalese may refer to: *something of, from, or related to Bengal, a large region in South Asia * Bengalis, an ethnic and linguistic group of the region * Bengali language, the language they sp ...

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 The Thar Desert, also known as the Great Indian Desert, is a large arid region A region is arid when it is characterized by a severe lack of available water, to the extent of hindering or preventing the growth and development Development ...

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 Xinjiang (),, SASM/GNC: ''Xinjang''; zh, c=, p=Xīnjiāng; alternately romanized as Sinkiang officially the Xinjiang Uygur Autonomous Region (XUAR) and formerly romanized as Sinkiang, is a landlocked autonomous region An autonomous ...

Xinjiang
. It is estimated that about 70% of all precipitation in the central part of the
Tian Shan Mountains The Tian Shan,, dng, Тянсан, ; otk, 𐰴𐰣 𐱅𐰭𐰼𐰃, ; tr, Tanrı Dağı; mn, Тэнгэр уул, ; ug, تەڭرىتاغ, , ; kk, Тәңіртауы / Алатау, , ; ky, Теңир-Тоо / Ала-Тоо, , ; uz, Tyan-S ...

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"). The effects also extend westwards to the Mediterranean, where however the impact of the monsoon is to induce drought via the Rodwell-Hoskins mechanism.


=Northeast monsoon

= Around September, with the sun retreating south, the northern landmass of the Indian subcontinent begins to cool off rapidly, and air pressure begins to build over northern India. The Indian Ocean and its surrounding atmosphere still hold their heat, causing cold wind to sweep down from the
Himalayas The Himalayas, or Himalaya (; Sanskrit Sanskrit (, attributively , ''saṃskṛta-'', nominalization, nominally , ''saṃskṛtam'') is a classical language of South Asia belonging to the Indo-Aryan languages, Indo-Aryan branch of the Ind ...

Himalayas
and
Indo-Gangetic Plain#REDIRECT Indo-Gangetic Plain Image:India-Pakistan Borderlands at Night.JPG, 250px, Clusters of yellow lights on the Indo-Gangetic Plain reveal numerous cities large and small in this astronaut photograph of northern India and northern Pakistan, ...

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 cold dry wind picks up some moisture from the
Bay of Bengal The Bay of Bengal is the northeastern part of the Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or 19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to th ...

Bay of Bengal
and pours it over peninsular India and parts of
Sri Lanka Sri Lanka (, ; si, ශ්‍රී ලංකාව, Śrī Laṅkā, translit-std=ISO (); ta, இலங்கை, Ilaṅkai, translit-std=ISO ()), formerly known as Ceylon, and officially the Democratic Socialist Republic of Sri Lanka, is ...

Sri Lanka
. Cities like
Chennai Chennai (, ), also known as Madras (List of renamed Indian cities and states#Tamil Nadu, the official name until 1996), is the capital city of the states and territories of India, Indian state of Tamil Nadu. The state's largest city in area ...

Chennai
, 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 Tamil Nadu (; ) is a States and union territories of India, state in South India, southern India. Its capital and largest city is Chennai. Lying in the southern-most part of the Indian subcontinent, Tamil Nadu is bordered by the Indian union t ...

Tamil Nadu
is from the Northeast Monsoon. In Southern Asia, the northeastern monsoons take place from October to December when the surface
high-pressure system A high-pressure area, high, or anticyclone, is a region where the atmospheric pressure Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth File:Atmosphere gas prop ...
is strongest. The
jet stream 250px, Clouds along a jet stream over Canada. Jet streams are fast flowing, narrow, meander File:rio-cauto-cuba.JPG, Meanders of the ''Cauto River, Rio Cauto'' at Guamo Embarcadero, Cuba A meander is one of a series of regular sinuous curve ...
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 stream Image:Airmassesorigin.png, upright=1.25, Different air masses which affect North America as well as other continents, tend to be separated by frontal boundaries In meteorology, an air mass is a volume of air defined by its temperature and water v ...
s which produce clear skies over India. Meanwhile, a low pressure system known as a
monsoon trough The monsoon trough is a portion of the Intertropical Convergence Zone in the Western Pacific,Bin WangThe Asian Monsoon.Retrieved 2008-05-03. as depicted by a line on a weather map 250px, A surface weather analysis for the United States on Oct ...
develops over
South-East Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia or SEA, is the geographical United Nations geoscheme for Asia#South-eastern Asia, southeastern subregion of Asia, consisting of the regions ...
and
Australasia Australasia is a region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Earth and planets. ...

Australasia
and winds are directed toward Australia.


East Asian Monsoon

The East Asian monsoon affects large parts of
Indochina Mainland Southeast Asia, also known as the Indochinese Peninsula or Indochina, is the continental portion of Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia or SEA, is t ...
, the
Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...

Philippines
, China,
Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia East Asia is the eastern region of Asia Asia () is Earth's largest and most populous continent, located primarily in the Eastern Hemisphere, Eastern and N ...

Taiwan
, Korea and Japan. 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 Mainland Southeast Asia, also known as the Indochinese Peninsula or Indochina, is the continental portion of Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia or SEA, is t ...
and the
South China Sea The South China Sea is a of the . It is bounded in the north by the shores of (hence the name), in the west by the , in the east by the islands of and northwestern (mainly , and ), and in the south by , and the , encompassing an area of ...

South China Sea
(May), to the
Yangtze River Basin The Yangtze or Yangzi ( or ) is the longest river in Asia, the third-longest in the world and the longest in the world to flow entirely within one country. It rises at Jari Hill in the Tanggula Mountains The Tanggula ( Chinese: , ...
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

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 The Siberian High (also Siberian Anticyclone; russian: Азиатский антициклон ''Aziatsky antitsiklon'') is a massive collection of cold dry air that accumulates in the northeastern part of Eurasia from September until April. It is ...

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 Borneo (; id, Kalimantan) is the third-List of islands by area, largest island in the world and the largest in Asia. At the geographic centre of Maritime Southeast Asia, in relation to major Indonesian islands, it is located north of Java Is ...

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 the Maritime Continent tends to follow the heating maxima down
Vietnam Vietnam ( vi, Việt Nam, ), officially the Socialist Republic of Vietnam,, group="n" is a country in Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia or SEA, is the ...

Vietnam
and the
Malay Peninsula The Malay Peninsula (Malay Malay may refer to: Languages * Malay language or Bahasa Melayu, a major Austronesian language spoken in Indonesia, Malaysia, Brunei and Singapore ** History of the Malay language#Old Malay, the Malay language f ...
(September), to
Sumatra Sumatra is one of the Sunda Islands The Sunda Islands are a group of islands in the Malay Archipelago. They consist of the Greater Sunda Islands The Greater Sunda Islands are four tropical islands situated within Southeast Asia S ...

Sumatra
,
Borneo Borneo (; id, Kalimantan) is the third-List of islands by area, largest island in the world and the largest in Asia. At the geographic centre of Maritime Southeast Asia, in relation to major Indonesian islands, it is located north of Java Is ...

Borneo
and the
Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...

Philippines
(October), to
Java Java ( id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 147.7 million people, Java is the world's List of ...

Java
,
Sulawesi Sulawesi (), also known as Celebes (), is one of the four Greater Sunda Islands The Greater Sunda Islands are four tropical islands situated within Southeast Asia, in the Pacific Ocean. The islands, Borneo, Java, Sulawesi and Sumatra, are in ...

Sulawesi
(November),
Irian Jaya New Guinea (; Hiri Motu Hiri Motu, also known as Police Motu, Pidgin Motu, or just Hiri, is a language A language is a structured system of communication used by humans, including speech (spoken language), gestures (Signed language, sign ...
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 The Benelux Union ( nl, Benelux Unie; french: Union Benelux; lb, Benelux-Unioun), also known as simply Benelux, is a politico ''Politico'', known originally as ''The Politico'', is an American political journalism Political journalism i ...

Benelux countries
, western Germany, northern France and parts of Scandinavia.


See also

*
Monsoon (photographs) ''Monsoon'' is a series of colour photographs taken by New Zealand photographer Brian Brake, a member of the Magnum Photos Magnum Photos is an international photographic cooperative owned by its photographer-members, with offices in New York Cit ...
of India, 1960 *Tropical monsoon climate


References


Further reading

* International Committee of the Third Workshop on Monsoons
The Global Monsoon System: Research and Forecast
* Chang, C.P., Wang, Z., Hendon, H., 2006, The Asian Winter Monsoon. ''The Asian Monsoon'', Wang, B. (ed.), Praxis, Berlin, pp. 89–127.


External links


National Weather Service: The North American Monsoon

East Asian Monsoon Experiment

Arizona Central monsoon page

Basics of the Arizona Monsoon
{{Authority control Climate of Asia Climate patterns Flood Weather hazards Wind Winds Rain Tropical meteorology Articles containing video clips