Реферат: El Nino And La Nina Weather Essay
El Nino And La Nina Weather Essay, Research Paper
Before venturing to El Nino, a little background on scientific studies tracking this event are in order. Leonardo DaVinci compared oceans to air movement in the 16th century. From his comparisons, scientists started looking at the oceans in order to understand the atmosphere. What they found were eddy currents/eddy fields these are found near ocean currents and are swirling water caused by the jet stream. A spinning eddy in the sea has been compared to a tornado in the atmosphere. From these and other studies, it was realized the ocean clearly drives the atmosphere (Blue Planet). Weather was tracked in the 17th century by the Royal Society of London and the Academia del Cimento of Florence, Italy (Boeson 14).
Because life on earth is shaped by its climate and the earth s climate changes as dramatically as the atmosphere, Man can ascertain climate from the past by observing the sea and soil. Climate cycles last 100,000 years, where the first half is colder and the second, warmer. Inside these are sub-cycles lasting 20,000 years; it has been noted that all cold places have been warm, all wet, dry, and vice versa. Scientists are studying how seawater and air are partners, mirror images of each other. Additionally, because the ocean is more dense than the atmosphere, scientists study it because it has memory and can predict what will happen in the air, creating as it were, a duet and counterpoint of sea and sky (Blue Planet).
El Nino has been recorded for over 2,000 years and is so-named because fisherman noticed the waters off Peru warming near Christmas. El Nino means little boy or Christ child. It has been observed to happen every two to seven years. (For some reason, every few years, the current is stronger and warmer than usual). El Nino is warm water coming north and mixing with the Humboldt Current. It is a complex interaction between ocean and atmosphere, a chain reaction with far-reaching effects on worldwide weather and economy (Facklam 42).
Scientifically, El Nino is known as ENSO, El Nino Southern Oscillation (Facklam 46). Herbert Boomerang Walker, a British meteorologist coined the term southern oscillation in 1928 when he developed a theory about high pressure in the Pacific Ocean causing low pressure in the Indian Ocean. He noticed when this occurred, India had monsoons, Africa had rain and Canada experienced above normal temperatures (Facklam 49). Presently, scientists have called this phenomenon a teleconnection because it affects weather in other parts of the world. Weather is the result of a worldwide swirl of energy, and changes in climate can cut across political and economic boundaries.
Sun, rain, wind and sea are linked as they circle the globe. The sun heats low lying air in the tropics, which rises. Colder, heavier air over the north and south poles flows toward the equator. In the Northern Hemisphere, air is forced to the right (clockwise), while in the Southern Hemisphere, air twists left (counter clockwise). The winds created by these events are known as the trade winds (Gold 19).
Near the equator, general air circulation consists of a north-south cell also known as the Hadley Cell. Near the equator, large-scale convection causes air to rise into the upper troposphere, where it flows pole-ward. (The atmosphere is a kind of heat engine that extracts energy from a warm source (equator) and deposits the unused energy at a cold sink (the poles). This is how the general atmospheric circulation works (www.sciam.com), and helps one to understand El Nino s worldwide effects on weather.
Also included in this mix is the jet stream, which is a narrow band, 25,000 – 35,000 feet above the earth along which high-speed winds blow from west to east, affecting weather from North America to Africa and Asia. In the winter, the jet stream can travel more than 600mph (Falklam 6).
Normally, strong trade winds on the ocean s surface drive currents west in the equatorial Pacific, causing cold water from the deep ocean to rise to the surface, bringing nutrient-rich food for marine life. These westward-blowing winds trap warm ocean water along Australia and Indonesia. During El Nino, the winds relax and water flows downhill, across the ocean eastward to Peru and Ecuador. Sometimes the winds reverse direction and speed the warm water eastward. When this happens, a huge underwater mass called a Kelvin Wave is formed. This giant wave travels east at five knots (5.8 mph), covering 125 miles a day. Spread out across 6,000 miles (9,655 km), this El Nino has more force than one million atomic bombs enough to heat an ocean of water the size of Canada (Gold 23).
When the trade winds push the warm top layer of ocean away from the west coast of South America towards the coasts of Australia and Indonesia, this raises the ocean level in the western Pacific about + meter higher in Australia and Indonesia than in Peru. As this reversal of sea and air pressure occurs, El Nino emerges.
El Nino itself doesn t create rain, snow, ice or drought; it sets the stage for this weather to occur (Gold 25). Warm water heats the air above it affecting air pressure, sea level and the winds that blow across the Pacific, which affects weather, causing rains in dry areas and droughts in those usually humid (Gold 14). This area can be so large and deep in the atmosphere that upper air wind currents are affected. Because these currents steer the weather system in the middle latitude across North America, the storm paths in the United States (US) are affected. Whenever large amounts of water vapor are found in the atmosphere where there normally isn t any, scientists take that as a sign that El Nino has arrived. El Nino appears around the December March timeframe and usually lasts 12 18 months; its impacts are typically seen in the winter.
An El Nino twin was discovered in the Indian Ocean. Winds that normally blow toward the African coast shift and blow eastward, which takes moisture away from India and southern Africa. This simultaneous warming of the Indian Ocean helps explain El Nino s effect on areas beyond the Pacific borders (Gold 33).
During El Nino years, the wind currents can cause short-term climate changes in Australia, Indonesia, Brazil, India and Africa. All may experience drought because the storms are shifted from these areas by wind currents. Conversely, Argentina, South China, southern Brazil and Japan may experience heavy rains and flooding. Additionally, the Gulf of Mexico and the western Atlantic have less hurricanes, while they increase in the Pacific. In the US, El Nino years reduce the amount of snowfall in central sections of the northern US states and western Canada due to the warmer than normal temperatures (Fagan 10). There are also less tornadoes in the central US during El Nino years (Fagan 11).
The Japanese Meteorological Agency (JMA) index is used to measure El Nino years. The index states an El Nino is 150o east and 90o west as measured along the equator and the water temperature averages .5oC (1oF) above normal for at least six months (Arnold 9).
Scientists estimate the top three meters (10 ft) of the ocean contains as much heat as the entire atmosphere. The central Pacific Ocean is an important influence on world weather because it s the largest expanse of open water on the earth (Arnold 11).
In 1957-58, nations agreed to join forces to study earth, atmosphere and oceans, called The Scientific Committee for Oceanographic Research. It wasn t until 1972-73 that El Nino gained worldwide attention, because of the world food shortages it caused.
In 1977 there was an El Nino that was responsible for the blizzard in New York. It was so mild in Alaska that year that the polar bears didn t hibernate (Arnold 16). Because of these events, scientists actively tracked El Nino, but were still unprepared for the monstrous one that occurred during 1982-83. That is known as the year El Nino went crazy, changing weather patterns around the world and played havoc with ecosystems worldwide (Facklam 2).
During the winter of 1982, there were raging surfs in California, hurricanes in Tahiti (six in five months), severe drought in southeast Australia, no winter rains in Africa, record snow in Utah with spring floods. There were high tides, giant waves and torrential rains along the coast of Canada, the US and Mexico (Gold 38). In 1983, the US had the rainiest spring ever. Also during that time, more rain feel on Peru than ever recorded any place on earth (Gold 4).
The 1982-83 El Nino was the worst since 1891. A warm tongue of water stretched eight kilometers along the equator, heating water as much as 10oC (14oF) above normal (Gold 38). Warning signs were abundant about this El Nino. Some of them came from a Dr. Barber, a marine biologist from Duke University Marine Lab who was working in the equatorial Pacific. He happened upon the beginning of this El Nino when he noticed no fish in the ocean, the weather was hot and muggy and the sea surface temperatures soared. When his engine quit, his boat was pushed by the equatorial current going the wrong way. He noticed a complete reversal of normal currents. (They should ve been westward, with the trade winds) (Falklam 78).
Concurrently, the computers at the National Oceanic Atmospheric Agency (NOAA) were sending in what the scientists thought were skewed data and reprogrammed them to reject it as defective. When Dr. Barber corroborated the data, the scientists then knew they were at the start of a major warm El Nino, but it was too late to warn about it (Falklam 82).
During this El Nino scientists learned that the forces resulting from the ocean were strong enough to slow down the rotation of the earth. By doing so, El Nino added 1/5 millisecond to several days in January 1983 during its rampage (Arnold 42). Worldwide, the 1982-83 El Nino cost more than $40 billion dollars in damages to land, crops, marine life and livestock, and caused over 2,000 deaths (Gold 74).
While the 1982-83 El Nino was the worst to date economically, the one that occurred in 1997-98 has been categorized as a super El Nino (called El Meano). Damages are still being tallied today from this event but some examples of what it did are: torrential rains turned Peru s Sechura Desert into the second largest lake 90 miles (144 km) long, 20 miles (32 km) wide and 10 feet (16 km) deep in that country; the northeast US had the warmest winter on record, which helped citizens save five billion dollars on energy costs; rain washed smog from Los Angeles air to result in the cleanest air in the region in 50 years; although classified as a super El Nino, 1997-98 was the first time meteorologists were able to forecast the event more than six months in advance, thereby saving regions from unnecessary destruction (Gold 3).
While El Nino triggers weather that is opposite what is normally seen in an area, La Nina (little girl) tends to make usual weather conditions extreme. It may follow an El Nino, but this doesn t always happen. One third of the time La Nina amplifies the more normal weather pattern, one third it won t seem to occur at all and one third it will equalize the effects of El Nino (Gold 4).
La Nina is also known as an ENSO cold event and La Viejo (the old man). La Ninas are observed every four years but can be as much as 10 years apart (Arnold 51). During La Nina years, easterly winds in the Americas are stronger than usual, driving the warm sea surface water westward, causing larger than normal volumes of deep chilling water to rise to the surface, producing a cold tongue along the equator, 3,000 miles long from Ecuador to Samoa (www.ogp.noaa.gov/enso). It is also noted by increased east to west winds across the eastern Pacific, and west to east winds in the eastern Pacific in the upper atmosphere. Sea level is also lower in the eastern Pacific and a reduced thermocline (the boundary in the ocean separating warm from cold water) increases the slope, making it come close to the surface for extended periods. Another example of La Nina is the absence of convective activity (www.sciam/oct).
The JMA index says a La Nina occurs when average sea surface temperature is more than 5oC (1oF) colder than normal for a period of six months (Gold 10). La Ninas change the path of the jet streams, which move high altitude air west to east across the ocean. This allows the polar jet stream to move further south bringing frigid air to the US.
During La Nina, rainfall and thunderstorms diminish over the central equatorial Pacific and confines itself to Indonesia and the western Pacific, northern South America and southern Africa during the December February timeframe. In June through August, it s wetter over southeast Australia. The La Nina December February period produces drier than normal conditions along the coast of Ecuador, northwest Peru and equatorial eastern Africa. These dry conditions are seen over South Brazil during June August (www.ogp.noaa.gov/enso).
There are large scale temperature departures worldwide, with especially abnormal cooling conditions: 1) below normal December February in southeastern Africa, Japan, south Alaska, western/central Canada and southeastern Brazil; 2) a colder than normal June August in India, southeastern Asia, west coast of South America, across the Gulf of Guinea to northern South American to portions of Central America, and 3) warmer than normal December February temperatures along US Gulf Coast (www.nationalgeographic.com/elnino).
Overall, during La Nina, droughts become heavy rains, balmy winters beget record-breaking snowfalls and freezing temperatures, as well as more hurricanes and tornadoes appear in the Gulf Coast and Atlantic Ocean. Southern Atlantic states have more violent thunderstorms. In the US there are warmer waters in the southeast, colder winters from the Great Lakes to the Pacific Northwest and unsettled conditions on the Northeast and Mid-Atlantic states (www.ogp.noaa.gov/enso).
La Nina is also the result of Kelvin Waves, only with cold water. It carries water deep under the ocean to the eastern Pacific. It usually brings cold water where El Nino brought warm. It disrupts the jet stream, cools sea temperatures and produces weather patterns opposite El Nino. While not as powerful as El Nino, it still delivers problems. Areas with drought have fire, then rain, with no brriers which creates floods. La Nina usually, but not always, marks the end of El Nino. The cooling it brings sometimes cancels out El Nino s effects and just returns the ocean to normal conditions. Sometimes it cools it enough to set off a reverse cycle of violent weather. It is noted in the US and Caribbean by increased hurricane activity (Gold 30).
La Nina s conditions usually last approximately nine to twelve months, but it can be up to two years. They occur on the average every three to five years, but can vary from two to seven years. Since 1975, La Ninas have been half as frequent as El Ninos. Because La Nina impacts are less severe, little attention was given it until its teleconnections were recognized in the 1980s, then more research on it began (www.crystalinks.com/weather).
In 1973-74, La Nina caused an especially wet summer in southern Africa and contributed to an epidemic of West Nile fever. It also caused an encephalitis outbreak in Brazil, killing 61 (Arnold 70). As noted, La Nina years show increased hurricane activity and the La Nina in 1998-99 was the deadliest of the past two centuries. The Pacific Northwest was wetter in winter, California had less rain, and northern areas had record cold and snow. Drought was in the southern plains and there were nine hurricanes and five tropical storms in the Atlantic. More than 100 tornadoes occurred in the South in January 1999 and gave Buffalo NY 63.5 (161 cm) of snow. La Nina caused ocean temperatures to drop 8oC in only two weeks (Gold 30).
Although La Ninas are rarer and less intense than El Ninos, they re harder to predict (Fagan 15). Currently, near neutral conditions exist as far as El Nino/La Nina are concerned (www.ogp.noaa.gov/enso).
Scientists are trying to figure out when bad El Ninos will occur, since they are not cyclical. Currently, that estimate is every 7.2 years. If we understand ENSO, we ll understand how the atmosphere-ocean climate works. One must remember that El Nino and La Nina are not disasters, anomalies or cruel twists of fate they are how the earth works (www.abcnews.go.com). There is no normal El Nino or La Nina although they do follow certain patterns.
The past 98 years have seen 23 El Ninos and 15 La Ninas, with the four strongest occurring since 1980. Since El Nino produces the same type of climate a warmer world has, scientists are actively studying it (www.sciam/oct). Due to these studies, advance warning will assist people with planning better as far as fishing, agriculture, forestry, energy and economics are concerned. Australia, Brazil, Ethiopia, India and Peru use these predictions to manage their agriculture (Gold 76).
ENSO models predict weather disasters and diseases will become more prevalent. Since 1976, the intensity, duration and pace of El Ninos have increased. During the 1990s, every year was marked by an El Nino or La Nina extreme, which does not bode well for the 21st Century, especially because during these years, vector borne and waterborne diseases climb (www.sciam/oct).
Human activities are beginning to affect weather and climate with a force equal to that of natural events (Falklam 30). Although it has been said that climate is what you expect, weather is what you get.
Arnold, Caroline. El Nino, Stormy Weather for People and Wildlife. Clarion Books, NY. 1998
Boesen, Victor. Doing Something About the Weather. G.P. Putnam Sons. NY. 1975.
Facklam, Margery and Howard. Changes In The Wind, Earth s Shifting Climate. Harcourt Brace Javanovich. NY. 1986
Fagan, Brian. Floods, Famines and Emperors El Nino and the Fate of Civilizations. Basic Books. NY. 1999
Gold, Susan Dudley. Blame It On El Nino. Steck-Vaughn Publishers. TX. 2000
MacArthur, John D. and Catherine T. Foundation Library Video Classics Project. Planet Earth. Episode 2: The Blue Planet. Films Inc. IL. 1985
MacArthur, John D. and Catherine T. Foundation Library Video Classics Project. Planet Earth. Episode 3: The Climate Puzzle. Films Inc. IL. 1985
EL NINO/LA NINA AND ITS EFFECT ON GLOBAL WEATHER
This report is on the weather phenomena known as El Nino and La Nina and how they affect weather patterns globally.
El Nino is known as the El Nino Southern Oscillation (ENSO) because of the strong link discovered between the air pressure in Darwin, Australia and Tahiti. It is basically a disruption of the entire oceanic atmospheric system in the tropical Pacific Ocean.
Not as much is known about La Nina because it occurs one third as much as El Nino and studies on it didn t really begin until the 1980s. La Nina is also known as an ENSO cold event and/or La Viejo (old man), and it basically amplifies normal weather patterns in a region.
Due to increased scientific studies and predictions, these events aren t as catastrophic as in the past because people can be forewarned about the event and adequately prepare for it.