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El Nino (warming) and La Nina (cooling). The Intertropical Convergence Zone (ITCZ) is the area encircling the earth near the equator where winds originating in the northern and southern hemispheres come together.
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The Intertropical Convergence Zone (ITCZ) is the area encircling the earth near the equator where winds originating in the northern and southern hemispheres come together. • Solar radiation warms the air over the equator, causing it to rise. The rising air then proceeds south and north toward the poles. From approximately 20° to 30° North and South latitude, the air sinks. Then, the air flows along the surface of the earth back toward the equator. • Sailors noticed the stillness of the rising (and not blowing) air near the equator and gave the region the depressing name "doldrums." • The doldrums, usually located between 5° north and 5° south of the equator, are also known as the Intertropical Convergence Zone or ITCZ for short. • The trade winds converge in the region of the ITCZ, producing convectional storms that produce some of the world's heaviest precipitation regions. • The ITCZ appears as a band of clouds, usually thunderstorms, that circle the globe near the equator.
In the Northern Hemisphere, the trade winds move in a southwesterly direction from the northeast, while in the Southern Hemisphere, they move northwesterly from the southeast. • When the ITCZ is positioned north or south of the equator, these directions change according to the Coriolis effect imparted by the rotation of the earth. • For instance, when the ITCZ is situated north of the equator, the southeast trade wind changes to a southwest wind as it crosses the equator. • The ITCZ moves north and south of the equator depending on the season and solar energy received. The location of the ITCZ can vary as much as 40° to 45° of latitude north or south of the equator based on the pattern of land and ocean.
The trade winds are the prevailing pattern of easterly surface winds found in the tropics, within the lower portion of the Earth's atmosphere, in the lower section of the troposphere near the Earth's equator. • The trade winds blow predominantly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere, strengthening during the winter.
Historically, the trade winds have been used by captains of sailing ships to cross the world's oceans for centuries; and enabled European empire expansion into the Americas, and trade routes to become established across the Atlantic and Pacific oceans. • In meteorology, the trade winds act as the steering flow for tropical storms that form over the Atlantic, Pacific, and south Indian Oceans and make landfall in North America, Southeast Asia, and India, respectively. • Shallow cumulus clouds are seen within trade wind regimes, which are capped from becoming taller by a trade wind inversion, which is caused by descending air aloft from within the subtropical ridge. The weaker the trade winds become, the more rainfall can be expected within neighboring landmasses.
NORMAL CONDITIONS • During non-El Niño conditions, the Walker circulation is seen at the surface. • Easterly trade winds move water and air warmed by the sun towards the west. • This also creates ocean upwelling off the coasts of Peru and Ecuador and brings nutrient-rich cold water to the surface, increasing fishing stocks. • The western side of the equatorial Pacific is characterized by warm, wet low pressure weather • Collected moisture is dumped in the form of typhoons and thunderstorms. • The ocean is some 60 centimeters (24 in) higher in the western Pacific as the result of this motion.
2) Trade winds move warm water and air west towards the Caribbean. 1) Heat from the sun warms the Ocean surface Thermocline. layer of water with temperature change: a layer of water, e.g. in a lake or Ocean, where there is an abrupt change in temperature that separates the warmer surface water from the colder deep water 3) Cold water is pulled upwards, replacing the warm surface water. 3) The cooler water is from the Humbolt (peruvian) current and is nutrient rich.
The Thermocline… • “There exists in most ocean areas (apart from polar and sub-polar oceans) a zone where the rate of decrease of temperature is much larger compared with that above and below, hence the definition.” • Depending on the geographical location, the thermocline depth ranges from about 50m to 1000m. • A simplified view is to consider the thermocline as the separation zone between the mixed-layer above, much influenced by atmospheric fluxes, and the deep ocean. • In the tropics, the thermocline can be quite shallow on average, as in the eastern Pacific (50m), or deeper as in the western part (160-200m).
E-N-S-O • El Niño-Southern Oscillation, often called simply ENSO, is a climate pattern • Occurs across the tropical Pacific Ocean on average every five years • but over a period which varies 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.
WHAT IS EL NINO? • ENSO is composed of an oceanic component, called El Niño (or La Niña, depending on its phase), 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. • When the cold phase is in effect (La Niña), surface pressures in the western Pacific are low (volatile weather).
ORIGINS • 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."
This reduces the efficiency of upwelling to cool the surface and cut off the supply of nutrient rich thermocline water to the euphotic zone During El Niño the trade winds relax in the central and western Pacific The latter of which adversely affected higher trophic levels of the food chain, including commercial fisheries in this region This leads to a depression of the thermocline in the eastern Pacific, and an elevation of the thermocline in the west. Storms appear in the central Pacific and a carried by the subtropical jet stream towards the W USA/ Central America/ Andean S America. The result is a rise in sea surface temperature and a drastic decline in primary productivity
The Jet Stream – used by air craft to more faster around the globe.
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 • Economic impact to local fishing for an international market can be serious.
The Southern Oscillation (fluctuation) is the atmospheric component of El Niño. • It is an oscillation in air pressure between the tropical eastern and the western Pacific Ocean waters. The strength of the Southern Oscillation (fluctuation) is measured by the Southern Oscillation Index (SOI). • The SOI is computed from fluctuations in the surface air pressure difference between Tahiti and Darwin, Australia.
Low atmospheric pressure tends to occur over warm water and high pressure occurs over cold water • This is in part because deep convection over the warm water acts to transport air. • El Niño episodes are associated with negative values of the SOI, meaning that the pressure at Tahiti is relatively low compared to Darwin.
Almost a complete reverse of El Nino Air pressure over Tahiti (mid Pacific) is abnormally high and low over Australia Westbound Trade wind is strong, carrying warm surface water further west than normal Storms and heavy rain in Oceana and SE Asia Equatorial cloud is split in the pacific
La Niña are opposite phases of the El Niño-Southern Oscillation (ENSO) cycle, with La Niña sometimes referred to as the cold phase of ENSO and El Niño as the warm phase of ENSO
Bleaching of Coral • Mass bleaching events are primarily caused by elevated sea temperatures. • Sea temperature increases of only 1-2° C above the long term average over an extended period of time are enough to trigger these events. • Mass bleaching, or regional bleaching, can be defined as events in which entire reef tracts or regions completely bleach. • The isolated bleaching that occurs from sedimentation events, disease, and pollution, although damaging, does not reach the scale and severity of mass bleaching. • During El Nino years, up to 40% of global Coral stocks can be lost.
