Monsoon
The monsoon ( from Arabic موسم mausim, Season ') is a large-scale air circulation of the lower troposphere in the field of tropical and subtropical regions in the sphere of influence of the trade winds. The main feature of a monsoon are its very directionally stable monsoon winds in conjunction with a two-time reversal of the most common wind direction in the course of a year.
The monsoon winds and the monsoon as such are mainly caused by the migration of the zenith position of the sun between the tropics, the different heating and cooling properties of different soil surfaces and the coriolisbedingte windage.
His strongest expression and at the same time his word origin, the term monsoon in the Indian Ocean area, especially in relation to the Indian, but also on the North Australian and East African monsoon.
The monsoon has a strong influence on the summer humid climate of the affected regions of them, which one therefore also called monsoon climate primarily due to the entrained in the monsoon wind in the summer high humidity. Most of this is associated with a strong monsoon and monsoon forest. For this very strong influence on the natural environment, the high economic and cultural significance derives in particular the Indian monsoon.
- 2.1 Cultural History
- 2.2 Influence on the Marine
- 4.1 History of monsoon research
- 4.2 Scientific monsoon definition
- 5.1 Literature
- 5.2 External links 5.2.1 Regional Monsoons
- 5.2.2 Cultural and Historical Meaning
- 5.2.3 Climatic change and its consequences
Meteorology and climatology
In the monsoon climate, the seasons (dry and rainy season) differ primarily in the amount of precipitation. The monsoon dominates the climate in tropical and subtropical area crucial - for example, in India and Southeast Asia.
In contrast, the climate in the temperate zone is mainly influenced by temperature variations - for example, in Central Europe and large parts of North America.
Emergence of a monsoon
Main article: Origin of a monsoon
Seasonal changes in wind direction occur initially because of the displacement of the intertropical convergence zone ( intertropical convergence ITC), a trough of low pressure, which is caused by the warming and the rising of the air in the vicinity of the equator. By the relatively low pressure air is attracted to the ITC and there are winds that trade-winds. The intertropical convergence zone follows with a slight delay caused by the tilt of Earth's axis migration of the zenith position of the sun between the tropics. The ITC, in case of monsoon phenomenon influenced by a continental surface low, which is also called a monsoon low and which is caused by the strong heating of the air masses located over the continents. Reason for the increased heating of the air over the continents are the different thermal properties of land and ocean. The warming and the cooling of the land surface is carried out for about two to three times as fast as the water.
Core areas of ITC influenced by a monsoon low, for example, form the Indus plain and the Tibetan Plateau (Lit.: Weischet 2002). However, due to this influence the ITC move, so do the trade winds. The winds in the northern hemisphere obtained by the moving direction deflecting to the right Coriolis force an easterly component, as long as the air masses to move to the equator, so that a northeast trade arises. In the southern hemisphere the trade wind is deflected by the Coriolis force, in contrast to the northern hemisphere in the direction of movement to the left, ie, to the west, to a southeast trade winds. The sun is near the Tropic of Cancer, so there is also the ITC. All air masses now flow into this trough of low pressure. This air from the south-east trade winds, however, must exceed the equator, the Coriolis force now causes a clockwise rotation, the wind shifts from southeast to southwest: The southwest monsoon (actually southwest monsoon wind ) (Lit.: Borchert 1993). If the sun is south of the equator enters the northwest monsoon (actually northwest monsoon wind) on; However, due to the constraints ( monsoon low) and the few existing land masses in the southern hemisphere, this effect is weaker.
While on his way from the ocean to the continent of the monsoon wind takes over the bodies of water for moisture and rains this from the Luv of weather sheaths such as the Himalaya to a large extent. The summer monsoon is therefore characterized in these regions due to very humid conditions, which assume the character of a rainy season and lead, especially in recent times, above-average flood conditions.
In each winter, however, high -pressure areas form over the continents. The ITC shifts in the sequence again near the equator, or above in the direction of the other hemisphere. Thus, the northeast trade winds are in the Northern Hemisphere and the southeast trade winds in the southern hemisphere for each dominant wind. These are also known as winter monsoon and cause dry, continental air masses along with them. They therefore are also manifested mostly in a pronounced dry season.
Regional monsoon phenomena
There are many different regions with full monsoons monsoons with a low resistance, or those which have only one monsoon trend. It is monsoon phenomena of different degrees and forms with numerous regional characteristics. These have in the entire history of the people there have always played a huge role, which also led that you were different regional names most recurring winds. Due to the abundance of different monsoon phenomena and their strong regional effects resolved, it is only possible in the following to give a very large-scale survey.
One key factor of regional differentiation is the orography of the continent and the effect primarily of very high mountains as the weather sheaths with storage rain and hair effects. This can topographically separated areas, such as on the leeward and windward side of a mountain range, some have significant differences in annual rainfall and the prevailing wind direction as the course of the monsoon can vary greatly. Additionally, influences play a role by other environmental factors or adjacent climate zones. Also, ocean currents and changes in local sea surface temperature can affect the distribution of precipitation and the monsoon as a whole.
It should be noted that this diversity and regional differentiation at any generalized statement contrary to, and also represent many regional monsoon phenomena in severity and etiology particularly a field of research that is not yet fully understood and therefore as represented in this framework can be considered. A correct picture of the current state of research in this article is also not feasible.
- Charif
- Indian monsoon
- Nordaustralischer monsoon
- East Asian monsoon tendency
- West African monsoon system
- American monsoon system
- Monsoon trend in the Mediterranean
Even outside of the cases examined so far, a monsoon occur, such as in Southeast Asia and Northern Australia or lesser strength in southern Japan and East Asia, South Africa and Central America. Here, a strong north-south distribution of ocean and land masses exerts a stimulating effect on the monsoon, as damage to the migration of the zenith position of the sun will be best met. Generally, we can roughly all coastal areas between each 5 ° and 25 ° poleward specify as appearance area for monsoon phenomena from the equator, and which, although here can also seasonal precipitation cycles occur, but do not or hardly connected to a dominant wind direction ( ref: Goudie 2002). Because of the superposition by the west wind zone you can see them only rarely monsoon -related characteristics in the areas north and south. The example of the Meltemi ( Etesian ), summer north winds in Greece, but can be discovered even in the Mediterranean monsoon influences.
Influence on the vegetation
A very pronounced monsoon climate transforms landscapes that resemble during the dry season, a semi-desert during the rainy season in fertile green land.
Plants that grow in the monsoon climate, so do not need to be adjusted to reflect actual frost. But you must be adapted both to long periods of drought as well as to heavy rain to survive. This means that during a long period of drought they do not dry out. In times of heavy rain they should be able to grow quickly to take advantage of the rain, and they should be strongly rooted, not to be washed away.
Accordingly, must cultivate crops that can withstand these conditions farmers in the monsoon climate. Plants that need lots of water to grow (for example, rice) have to be grown during the rainy season - or need to be irrigated.
The monsoon forest thus consists of plants that are adapted to these conditions.
Climate change
A special importance has the monsoon in relation to the dynamics of climate change. It is with him a very unstable climatic element, but with a very high influence on the climate of large parts of the earth. It follows that even cause small changes and developments himself at the regional level a monsoon or weaken or can change its appearance it significantly, even and especially in relatively short periods of time. Orogeny, tectonic plate movements, change of large wind and ocean currents, and the change of the thermal behavior of continental surfaces, for example by lowering the albedo in the wake of global warming, provide examples dar. Especially in the latter case shows that even short-term, human-induced interference with the climate system can change all climates, even if, statistically adjusted on a global level, only relatively small changes occur.
Climate history of the monsoon
Monsoon phenomena exist on Earth, since there are oceans and land masses. Since the climate history is necessary to understand the present climate and to predict its future performance properly, therefore also benefits the monsoon phenomena past geological eras ( Paläomonsun ) an important significance. The caused by them in the past precipitates were also stored in many places of the earth in low-lying rock layers and are today, despite eventual climate change and continental drift, in these areas than fossil drinking water sources. Since these are often here to Wüstenklimate, these underground deposits are of huge economic importance to the people living there. The occurrence of old Monsunphänonomene is explored through paleoclimatology. Here, it is assumed that monsoon phenomena, especially in ages in the earth, in which a super continent existed, have played an enormous role. These very large land masses could cause by their thick continental thermal low monsoon phenomena that went far beyond the strength of today's monsoons addition. Due to the very large periods can be this, however, hardly secure proofs.
For the importance of the monsoon in the Oceanology see monsoon drift.
Impact on the people
The importance of monsoons for the world's food, drinking water supply and irrigation of agricultural soils is of fundamental nature. More than 60% of the world population is directly or indirectly affected by monsoon phenomena, especially in India and southern China. It shows the full double character of the monsoon precipitation as guarantor on the one hand and, due to their variability (see monsoon rains ), as a cause of droughts and floods on the other side.
All cultures that developed in the affected regions of monsoon phenomena were, and are dependent on the weather. A change of the monsoon is always associated with a change in the lifestyle of the people affected by it. This is especially true for embossed on agriculture agrarian societies in places where monsoon phenomena in full scale development, for example in the Indian region.
Cultural History
The variability of the monsoon, which has always existed for millennia and determined people's lives, not only has a purely economic significance. The interrelationships between monsoon and man - in particular its dependence on the monsoon - went down in culture, art, religion, and even in thinking and philosophy, in turn, especially in India. This is already in the Indus Valley Civilization, whose dependence is explained by the monsoon rains in the article Indian monsoon. In addition, the monsoon winds were many centuries of cultural exchange carrier in the Indian Ocean, which brings up a section arrives closer.
Influence on shipping
In the years 120-117 BC, Eudoxus of Cyzicus took out a reconnaissance trip to India he realized that the importance of the monsoon winds for sailing ships in the Indian Ocean. Eudoxus was his knowledge of the monsoon winds then probably Hippalus further, what this discovery is attributed to the Periplus of the Erythraean Sea. Hippalus therefore became legendary sailor and he was considered a long time for the first of the monsoon wind took advantage. The monsoon was therefore formerly also referred to in the greater of the Indiks as Hippalus. It is likely, however, that both Greeks were not the first, the monsoon took advantage, as Yemeni sailors operated long before in this space trade.
As navigators use the South Arabians their knowledge of the monsoon winds in the vicinity of the Indian Ocean and tick even today, for over two thousand years, with their dhows between the Arab, Indian and African coasts, where they are the changing winds of the monsoon, the Kaskasi and the Kusi, take advantage in annual trading voyages.
In addition to the incense trade of Yemen had in the 8th century BC already close trade contacts with India and East Africa. Especially those in Africa were so tight that originated in Eritrea colonies of South Arabian settlers. Due to the extensive trade and cultural influences from the Middle East could be effective in Yemen. Thus, the South Arabian script was developed in the 8th century BC, from the Phoenician alphabet. Furthermore, influence gained the Hellenistic culture in Yemen, which over here also indirectly entered into trade relations with the countries bordering the Indian Ocean since the 3rd century BC. This show still preserved cultural heritage of Hellenic origin in this space.
In the cultural exchange of goods and traditions arose on the East African coast from the embossed trade and Islam mixed culture of the Swahili. The Arabs brought Islam to Africa, mingled with the local Bantu peoples and founded towns such as Lamu, Mombasa and Sofala.
It should be noted that the sailing ships represented using the monsoon winds along with the great caravans ( Silk Road, Incense Route ) for centuries often only economic and cultural connection of the Orient and therefore the West with the Indian and especially Southeast Asia. The monsoon served as a mediator between these cultures, promoted their exchange and is therefore in the space of Indiks, in addition to its economic importance for the maritime trade in the culture as civilization history of central importance.
With the disappearance of the sailing ships and especially by the "container revolution " play the monsoon winds in general are no more prominent role for sea. On the other hand, caused by the monsoon weather conditions are the determining factor for the frequency of pirate hijacking off the coast of Somalia.
Etymology
Arab navigators described with the word mausim / موسم / Season ' the phenomenon of wind in the Arabian Sea, which changes with the season. Basically, the term monsoon pushes even today a change in wind direction between seasons from when he was subject to a change in the modern era and with the understanding of the causes of these winds. The scientific understanding of the term has evolved in the course of this cognitive process from a purely phenomenological wind or a season through to all of the causes, dynamics and effects which cause this phenomenon. We therefore speak frequently to illustrate this understanding of the term, of a monsoon system or a monsoon circulation. The monsoon is therefore dar. also a climate factor
Monsoon monsoon research and scientific definition
History of monsoon research
The exploration of the monsoon and hence its definition of terms has a long history, which is usually closely linked to the effects on humans. This is also explained why the term monsoon is often used as a synonym for the Indian summer monsoon and its rainfall. Even in the last century showed up here the simple relationship between the complex dependence on the monsoon and the interest in its exploration.
Meteorological records of the monsoon rains in India's space was conducted for more than 2000 years, if they are also survives only in fragments and do not constitute a continuous series of measurements. In modern times, made Edmond Halley (1668 ) pioneering work in the monsoon research and realized its thermal conditionality. This later joined the research by Blanford (1860 ), Supan (1881 ) and Todd (1888), which were in the years 1877/78 particularly in the wake of exceptionally weak monsoon. A very important role was played in the episode the research of Gilbert Walker (1909, 1924), which explored the interrelationships of the eponymous Walker circulation and later Jacob Bjerknes allowed to set the monsoon in relation to other climate phenomena such as El Niño.
More precise predictions can be made as part of a weather forecast.
Scientific monsoon definition
Today's most widely used term definition is probably that of SP Chromov (1957). He meant by a monsoon wind phenomenon in which a change in direction of the prevailing wind directions of at least 120 ° occurring between January and July. This is known as a monsoon angle angle. The main wind directions have to have in January and July averaged certain frequencies, so that one can speak of a monsoon. With over 60% naming monsoon applies at 40 % to 60 % one speaks of a monsoon low resistance and less than 40 %, the main wind directions only a monsoon trend.
Another limitation of Monsunklimate took place in 1971 by Ramage, which is why you called the resulting criteria the monsoon definition as Ramage Chromov criteria or short Ramage criteria. In addition to a monsoon angle of at least 120 ° and an average frequency of prevailing wind direction of about 40 % in January and July, must therefore, in these months, a wind speed of at least 3 m / s occur in the resultant wind direction and it may only be a cyclone - anticyclone - change every two years by five degrees of longitude occur over an area of five degrees of latitude.
At this comparatively strict definition you reach that many non- tropical weather and climate phenomena are not counted with the monsoons, as their monsoon -like symptoms, such as a wind reversal or seasonal drought, usually have monsoon foreign causes. The distinction made in Article monsoon classification refers to this definition and thus only the Indian and Southeast Asian, and African monsoon phenomenon nordaustralische also be classified as monsoons (see section regional monsoon phenomena ).