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THE STRANGE PHENOMENON CALLED EL NIÑO Recently, all TV channels extensively covered the influence on the world climate of the meteorological and oceanographical phenomenon known as El Niño. Actually, what is El Niño? What are its effects? THE "TERRIBLE" CHILD Text by Guglielmo Mammucari Originally fishermen on the coasts of Latin America related the drastic reduction in the catch with the increase in sea temperature and called this phenomenon El Niño. The fact that it generally occurred at the beginning of the year and around Christmas time led them to call it El Niño, the Spanish name for The Child, in this case referred to the Child Jesus.

In addition to the name El Niño linked to popular tradition, the scientific community also called it ENSO. Even though it occurs in an area of the world that is very far from Europe, that is to say, in the southern and central Pacific Ocean, some say it affects the meteorological pattern of the Mediterranean geographical zone. The only flaw of TV information was that, in general, little importance was given to what El Niño actually is, when and how frequently it occurs and why its effects are so vast. Let us try to fill some gaps and, at the same time, to extend our knowledge in oceanography - a very interesting subject to whoever really loves the sea and not only for spending one's own vacations. In the southern and central Pacific Ocean, under normal conditions, winds at low altitudes and the sea currents they generate move westward, i.e. from the coast of Chile toward Indonesia and Australia. The superficial water mass existing along the coast of South America is pushed westward and is replaced by water coming from the ocean bed (fig. 1). This mass of water is colder than the water on the surface - heated by the sun - and is rich in nutritional elements that favor the proliferation of the fish species of the area and, in turn, the fishing activity along the Chilean coast. The accumulation of "warm" water (the temperature difference between the water on the western coast and of the eastern coast is of approximately 46 F) along the western coast of the southern Pacific considerably affects the local climate, heats the atmosphere and creates the necessary conditions for frequent regular rainfall. In addition, the effect of the wind on the water mass generates a considerable difference in water level: the water level along the western coast is approximately 2" higher than along the eastern coast. When the superficial air mass reaches the western coast of the Pacific Ocean, it rises and returns toward the eastern coast, thus closing its cycle. At irregular intervals the low altitude wind force decreases and almost disappears for reasons yet unclearly specified scientists.

Figure 1 - Normal circulation When El Niño does not appear, the so-called "Walker circulation" regulates rainfall along the equatorial belt. It is a convection system where the rising branches of damp air resulting from a temperature increase in the Western Pacific, the Amazon basin and Central Africa, accumulate vapor at higher altitudes. This vapor is conveyed toward the equatorial areas of the eastern Pacific, the Atlantic and the Indian Ocean where returns to the sea as rainfall. Figure 2 - Anomalous circulation When El Niño appears, an actual climatic mutation occurs. Heating areas shift eastward by thousands of kilometers over the Pacific. Even the convection system considerably shifts, causing severe droughts in areas where it normally should rain - as it happened this year in Australia, Indonesia, Central America, etc. - and heavy rainfall elsewhere. The diagram clearly shows that the line dividing the cold and the warm water loses its typical curve and flattens near the bottom, thus highlighting the anomalous heating of considerable layers of water near the seabed. Figure 3 - Distribution of probable effects linked to "El Niño"

This weakening in wind intensity creates a series of interconnected effects. The warm water accumulated along the western coasts of the southern Pacific Ocean flows eastward. The water found along the Chilean coast is not pushed westward anymore therefore deep cold water does not rise to the surface. The mass of damp air that is normally found over the western coast of the Atlantic Ocean moves toward the central Atlantic and the wind circulation at higher and lower altitudes changes radically. An observer along the Pacific Coast of South America only notices the second effect listed above, i.e. the rising in the water temperature that the local inhabitants call El Niño. As a result, El Niño is not the cause but one of the effects of the reduced wind force that generally blows in the southern Pacific. El Niño is generally followed by La Niña, marked by a considerable decrease in the superficial water temperature of the ocean. By itself, El Niño has the negative effect of eliminating the supply of cold water rich in nutrients rising from the sea bottom. This missing supply of nutrients provokes the death of great quantities of fish on the Chilean coast and consequently severely affects the national economy. Yet, the other changes in the air mass circulation produce the greatest repercussions. The missing supply of damp air on the western coast of the southern Pacific turns the climate of the area extremely dry favoring severe fires as it recently occurred in Australia and Indonesia. The unbalance of the general air circulation on a global scale even affects the most remote areas (fig. 3). On one hand, together with El Niño and La Niña, there is considerable rainfall increase in North America and in Asia - already subject to monsoons - which provokes severe floods and consequently damage and destruction. On the other hand, on the southern coast of Africa, long droughts damage corn plantations, the staple of the region. El Niño occurs at 3 to 5-year intervals. According to the statistics, the severest effects on the world climate and therefore, the most devastating ones on the world economy were recorded in 1982-83, totaling damages for 8 billion dollars by the "El Niño of the century", as scientists call it. Oceanography and meteorology researchers are carrying out studies to determine with greater precision the causes and the effects of these phenomena and to find whether there could be a way to anticipate this event in order to limit damage. Automatic oceanographical buoys were positioned for this aim along the coast of South America, most particularly in the Pacific area; These buoys continuously monitor the water temperature and by means of radio or satellite transmission, send the readings to the monitoring stations on land where experts analyze them. Figure 4 - This graph shows the incidence of El Niño since the year 1550. The 1982/83 record levels will most probably be overcome by this year's readings. In fact, the peak temperature of 86 F was recently recorded on the surface of the Pacific Ocean near the coasts of Peru leading to a considerable temperature increase of up to 48 F at 3,100 feet below sea level. Figure 5 - The graphs relative to the 1981/82 period show the water temperature changes when El Niño occurs. This phenomenon may last from 12 to 18 months and it is generally followed by another anomalous climatic phase featuring a cooler- than-average water temperature in the Pacific Ocean known as "La Niña".

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