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ENSO or El Niño-Southern Oscillation |
| Posted by Administrator (admin) on 9th February, 2010 |
El Niño-Southern Oscillation, often called simply ENSO, is a climate pattern that occurs across the tropical Pacific Ocean on average every five years, but over a period which varies (see here and here) from three to seven years, and is therefore, widely and significantly, known as "quasi-periodic." ENSO is best-known for its association with floods, droughts and other weather disturbances in many regions of the world, which vary with each event. Developing countries dependent upon agriculture and fishing, particularly those bordering the Pacific Ocean, are the most affected.
ENSO is composed of an oceanic component, called El Niño (or La Niña), which is characterized by warming or cooling of surface waters in the tropical eastern Pacific Ocean, and an atmospheric component, the Southern Oscillation, which is characterized by changes in surface pressure in the tropical western Pacific. The two components are coupled: when the warm oceanic phase (known as El Niño) is in effect, surface pressures in the western Pacific are high, and when the cold phase is in effect (La Niña), surface pressures in the western Pacific are low. Mechanisms that cause the oscillation remain under study.
Definition
El Niño is defined by sustained differences in Pacific-Ocean surface temperatures when compared with the average value. The accepted definition is a warming or cooling of at least 0.5°C (0.9°F) averaged over the east-central tropical Pacific Ocean. When this happens for less than five months, it is classified as El Niño or La Niña conditions; if the anomaly persists for five months or longer, it is called an El Niño or La Niña "episode." Typically, this happens at irregular intervals of 2–7 years and lasts nine months to two years.
The first signs of an El Niño are:
- Rise in surface pressure over the Indian Ocean, Indonesia, and Australia
- Fall in air pressure over Tahiti and the rest of the central and eastern Pacific Ocean
- Trade winds in the south Pacific weaken or head east
- Warm air rises near Peru, causing rain in the northern Peruvian deserts
- Warm water spreads from the west Pacific and the Indian Ocean to the east Pacific. It takes the rain with it, causing extensive drought in the western Pacific and rainfall in the normally dry eastern Pacific.
El Niño's warm current of nutrient-poor tropical water, heated by its eastward passage in the Equatorial Current, replaces the cold, nutrient-rich surface water of the Humboldt Current. When El Niño conditions last for many months, extensive ocean warming occurs and its economic impact to local fishing for an international market can be serious.
In popular usage, El Niño-Southern Oscillation is often called just "El Niño". El Niño is Spanish for "the boy" and refers to the Christ child, because periodic warming in the Pacific near South America is usually noticed around Christmas. "La Niña" is Spanish for "the girl."
ENSO and global warming
It is well-known by now that during the last several decades the number of El Niño events increased, and the number of La Niña events decreased. The question is whether this is a random fluctuation or a normal instance of variation for that phenomenon, or the result of global climate changes towards global warming.
The studies of historical data show that the recent El Niño variation is most likely linked to global warming. For example, one of the most recent results is that even after subtracting the positive influence of decadal variation, shown to be possibly present in the ENSO trend, the amplitude of the ENSO variability in the observed data still increases, by as much as 60% in the last 50 years.
It is not certain what exact changes will happen to ENSO in the future: different models make different predictions (cf.) It may be that the observed phenomenon of more frequent and stronger El Niño events occurs only in the initial phase of the global warming, and then (e.g., after the lower layers of the ocean get warmer as well), El Niño will become weaker than it was. It may also be that the stabilizing and destabilizing forces influencing the phenomenon will eventually compensate for each other. More research is needed to provide a better answer to that question, but the current results do not completely exclude the possibility of dramatic changes.
Last changed: 9th February, 2010 at 17:00:05
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| Richard | By Unknown on 16th May, 2010 at 00:36:59 |
| Most people know why the name El Nino “The Christ Child” due to its occurrence near Christmas in South America. Now why Southern and why Oscillation? Oscillation some can exemplify with a pendulum, but ENSO has nothing of regular, predictable and lately has been more on than off: http://www.earthgauge.net/2010/climate-trivia-el-nino-frequency http://www.drroyspencer.com/global-warming-background-articles/the-pacific-decadal-oscillation/ The Charts aforementioned in themselves would explain cold years from 1950-1975 (baseline for the Warmists) and the warm years after that. What makes it called Oscillation is still acceptable because it keeps reoccurring. What makes it Southern? If the main source of Heat is the Sun, why not Hawaii, or the Philippines? http://www.climate4you.com/SeaTemperatures.htm#Tropical%20sea%20surface%20temperature%20and%20global%20surface%20air%20temperature http://maps-pacific.com/ Where does it originate? No one seems to have an absolute answer… http://www.agiweb.org/geotimes/mar05/feature_ENSO.html How about a second source of energy that makes oceans currents to change on the Earth’s largest open body of water? To the point that trade winds reverse up o the International Date Line and sometimes to the eastern Pacific? What makes an El Nino stronger than others? What makes an El Nino suddenly disappear, or reoccur some years in a row? There could be several explanations out there and several “we don’t know” http://www.agiweb.org/geotimes/mar05/feature_ENSO.html Nevertheless, one sticks out on its own. Firstly, let’s see the effect of cooling in what is documented as the eruption of Mexico’s El Chichón volcano in the impacts of the 1982-1983 El Niño, and Mt Pinatubo in 1991: http://en.wikipedia.org/wiki/Mount_Pinatubo http://wattsupwiththat.com/2010/04/17/volcanoes-cause-climate-change/ http://www.drroyspencer.com/latest-global-temperatures/ These would be called as mini Volcanic Winters. The real ones would fall in this category: http://en.wikipedia.org/wiki/Volcanic_winter What would be a good indication of volcanic activity? Quakes near a volcanic area? The Big ones first: http://www.thehorizonproject.com/earthquakes.cfm Now the correlation between quakes, volcanoes, and ENSO: http://www.michaelmandeville.com/vortectonics/Votex_Tectonics_Equation.pdf http://www.michaelmandeville.com/vortectonics/vortex_correlations2.htm Are El Ninos a version of Volcanic Summers or underwater Volcanic warmers? http://iceagenow.com/Ocean_Warming.htm Is it too farfetched? Is there anyone with a better explanation? |
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