The start of rains in early June marked the end of the dry winter and the onset of the wet summer monsoon. Mumbai, India, during monsoon rainfall. Image: Indranibasu. Monsoons produce the very wet summers and dry winters that occur on nearly all of the tropical continents.
A monsoon is not a storm like a hurricane or a summer thunderstorm, but a much larger pattern of winds and rain that spans a large geographic area — a continent or even the entire globe. Weather and climate are very different in the tropics and mid-latitudes, and it is not just a matter of the tropics being warmer. In Europe, North America, and other mid-latitude regions, temperatures undergo large changes over the seasonal cycle; weather events in these regions last a few days as high- and low-pressure systems drift slowly eastward, rearranging the locations of warmer and colder air masses as they go.
This might make it cool and rainy one day and warm and sunny the next. The seasonal cycle over tropical continents is marked by an oscillation between dry and wet periods brought about by monsoons. Weather events in the tropics — such as typhoons, thunderstorms, and other rainstorms — are actually embedded within the much larger monsoons. Billions of people live in the monsoon climates of South Asia, Africa, and the tropical Americas, and every spring they wait for monsoon rains that will end the winter dryness even though they might also cause disastrous floods.
There is often too little water or too much. However, monsoons are not the same throughout the tropics, because the specific locations of continents and oceans influence the regional patterns of winds and rain.
Classic conditions for strong monsoons are found where the Indian Ocean and the Pacific Ocean meet. This region includes India and South Asia to the north of the equator and Australia south of the equator. Strong swings between wet summers and dry winters are found in those places as the ITCZ moves back and forth across the equator. The South Asian monsoon, which includes the Indian monsoon, is especially strong because the Himalayas and other mountains block dry air in the north from getting to the humid monsoon region.
The seasonally wet and dry region just south of the Sahara Desert in West Africa and the Sahel is another classic monsoon region. Monsoons occur in the Americas too, but tend to be weaker than in other regions. The animated map below shows how precipitation varies through a typical year.
Notice that most precipitation occurs in the tropics and swings north and south of the equator with the seasons. This seasonal shift in the location of tropical precipitation indicates a shift in the location of the ITCZ and is the reason why there are distinct wet and dry seasons on tropical continents. Patterns of precipitation through the year Image: University of Oregon. From December until February, the monsoon rains move south of the equator towards Australia while South Asia experiences dry monsoon conditions.
There is even an East Asian monsoon that brings summer rain to China, Japan, and Korea, but it is caused by a different type of wind pattern associated with the jet stream. Monsoons bring large amounts of rain to a location, often leading to large-scale vegetation growth. Image: University of Oregon. Monsoon winds in the tropical parts of North America, Central America, and South America cause the amount of rainfall to vary with the seasons, even in areas where precipitation is plentiful and rainforests thrive.
From June to August, which are summer months in the Northern Hemisphere, there is more rainfall north of the equator in Costa Rica, Nicaragua, Panama, and western Mexico. From December to February there is more rainfall south of the equator in Brazil.
The North American monsoon does bring moisture from the warm waters of the Pacific into the U. Southwest, but its peak rainfall occurs in Mexico, and the U. These areas are typically dry but can receive enough rainfall to quell a wildfire if moist monsoon winds blow in summer.
An area of summer rainfall along the U. East Coast is associated with what some might call a mid-latitude version of monsoon rainfall. This phenomenon is most associated with the Indian Ocean where its effects greatly impact South Asian countries.
The summer monsoon, which occurs between April and September, brings the wet season. Warm, moist air from the Indian Ocean moves inland and brings heavy rainfall and a humid climate. In contrast, the winter monsoon occurs between October and April and brings the dry season, but it is often weaker than the summer monsoons as the Himalaya Mountains prevent most of the dry air from reaching coastal countries. Monsoons in South Asian countries contribute to many industries, such as farming and electricity, however, there are adverse effects.
Negative Impacts of Monsoons in South Asian Countries Here is a closer look at how monsoons have impacted some countries. Relief Efforts The countries above are only a few of the several areas affected by monsoons in the region.
These goals include recovery of a complete record of erosion through the Paleogene 66—23 Ma ; key areas include the Murray Ridge in the Arabian Sea, the Bengal Fan, and the Red River delta. This time period is important because of recent suggestions that the monsoon may have strengthened much earlier than generally proposed, around 36 Ma.
Furthermore, if the formation of the Greater Himalayas after 23 Ma was climatically triggered, then an erosional record spanning their birth is required to test this hypothesis. In general, if we are to make progress in quantifying erosion in the sedimentary record, then we must understand the 3D structure of the submarine fans through seismic surveys linked to ocean drilling. Concerning reconstruction of past continental environments, the research community aims to produce a regional Miocene vegetation cover map and to determine feedbacks between vegetation and monsoon climate.
We also thank the U. Peter D. Clift pclift lsu. Clift, P. Published on 25 June The authors. Any reuse without express permission from the copyright owner is prohibited.
Iddris et al. Skip to content The summer monsoon delivers rain to the rolling hills near Jawhar, a town near the western coast of India. Last January, scientists gathered to discuss the many interacting factors that have driven the evolution of the Asian summer monsoon over millions of years.
When Continents Collide Even distant tectonic changes have contributed to the evolution of the Asian monsoon, producing widely varying climate conditions in different regions. Erosion Effects Paleoprecipitation reconstructions based on leaf wax records indicate that the Himalayas were exposed to a wet monsoon through most of the Miocene 23—8 Ma , and precipitation levels were then relatively stable through the Pliocene until the beginning of the Pleistocene about 2.
Credit: Peter Clift. As the summer monsoon blew in from the southwest, it first hit the state of Gujarat. More than people died. Then, the monsoon rains hit the state of Maharashtra. Flooding in Maharashtra killed more than 1, people. On July 26, , the city of Mumbai, Maharashtra, received almost a meter The Indian Oceans winter monsoon, which lasts from October to April, is less well-known than its rainy summer equivalent. The dry winter monsoon blows from the northeast.
These winds start in the air above Mongolia and northwestern China. Winter monsoons are less powerful than summer monsoons in Southeast Asia, in part because the Himalaya Mountains prevent much of the wind and moisture of the monsoons from reaching the coast.
The Himalayas also prevent much of the cool air from reaching places like southern India and Sri Lanka, keeping them warm all year. Winter monsoons are sometimes associated with drought s. Not all winter monsoons are dry, however. Unlike the western part of Southeast Asia, the eastern, Pacific coast of Southeast Asia experiences its rainy season in the winter. Other Monsoons. This huge monsoon wind system then stretches into the Indian Ocean.
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