ENES or, El Niño/La Niña Southern Oscillation is achange from normal climate system in the Pacific Ocean that occurs periodically.Changes in the surface pressure, water temperature, and wind direction in thesouthern, eastern, and central regions of the Pacific cause the climate anomaly.Accompanying these changes are changes in the specific regions averagetemperature. These situations occur in a much shorter amount of time then thenormal current flow of the Pacific climate, which is why when it occurs theevent is commonly referred to as El Niño. Lastly, the drastic changes insurface pressures and temperatures that cause El Niño are commonly known toresult in heavy floods and droughts through out the Pacific because of how theevent changes a regions climate. In order to go into further debt about what ElNiño is, you must understand the basic facts of what causes El Niño, how itdiffers from the normal current flow of the Pacific climate, and the overallconsequences of El Niño.
ElNiño’s causes are resorted to a relationship between changes in the “surfacelayers of the ocean and the overlying atmosphere in tropical Pacific” (McPhadenet al., “Frequently Asked Questions about El Niño and La Niña”). Differences in the sea-level pressure are oneof the first indices that indicate that an El Niño is starting to occur. It isindicated by the Southern Oscillation Index, “which is given by the differencein sea-level pressure between Tahiti and Darwin, Australia, and the Nino 3index, which refers to the anomalous SST (surface sea temperature) within theregion bounded by 5N-5S and 150W-90W.” (McPhaden et al., “Frequently AskedQuestions about El Niño and La Niña”). Inthe normal current flow strong winds blow from the east to the west in thePacific. Strong winds that blow from the east to the west in the Pacific areanother cause of El Niño. This actually creates a change in the watertemperatures in the eastern in western pacific, “in the eastern part, deeperwater (which is colder than the sun-warmed surface water) gets pulled upfrom below to replace the water pushed west.” (Pierce et al., “So What is an ElNiño, Anyway?”). However another indices of the El Niño coming shows a changein the winds strong east-west flow. “In an El Niño, the winds pushing thatwater around get weaker. As a result, some of the warm water piled up in thewest slumps back down to the east, and not as much cold water gets pulled upfrom below. Both these tend to make the water in the eastern Pacific warmer,which is one of the hallmarks of an El Niño.” (Pierce et al., “So What is an ElNiño, Anyway?”). Lastly, a warmer ocean makes the winds weaker, which in turnmakes the ocean even warmer. “This is called a positive feedback, and iswhat makes an El Niño grow.” (Pierce et al., “So What is an El Niño,Anyway?”). The last a final index that indicates an El Niño occurring relatesto out going long wave radiation or OLR. “The deeper the cumulus convection,the colder the cloud tops, which means the thermal or infrared radiation to spaceis reduced.” (McPhaden et al., “Frequently Asked Questions about El Niño and LaNiña”). As you may infer these indices show us what cause El Niño events.
Like previously stated, in thenormal current flow strong winds blow from the east to the west in the Pacific.“In the eastern Pacific, the trade winds pull up cold, deep, nutrient-richwaters along the equator from the Ecuadorian coast to the central Pacific. Thewarmth of the western Pacific results in a particularly vigorous hydrologiccycle there with towering cumulus clouds and tropical storms that"radiate" atmospheric waves and disturbances across vast regions ofthe globe. Heat and moisture lofted into the upper atmosphere by the clouds andstorms are distributed by high-altitude winds across vast regions of the globe.”(Reynolds et al., “Effects of El Niñoon Streamflow, Lake Level, and Landslide Potential”). However in El Niño thetrade winds are weakened which allows for cold water to rise in thewestern/central Pacific and for warm water in the eastern part to be pushedtowards the western and central Pacific. This results in warmer water in the eastern,western and central parts of the Pacific. The last change from the normalcurrent flow is that as a result of the water getting warmer the “atmosphericpressure gradients along the equator weaken, and the trade winds diminish evenmore.” (Reynolds et al., “Effects of ElNiño on Stream flow, Lake Level, and Landslide Potential”). Over all, thechanges in trade winds, oceanic temperature, and atmospheric pressure show ushow an El Niño differs from what the normal conditions in the Pacificclimate are.
The consequences of El Niño must belooked at on two different global and regional scales. Globally El Niño’sconsequences are shown “by shifts in tropical rainfall, which affect windpatterns over much of the globe.” (McPhaden et al., “Frequently Asked Questionsabout El Niño and La Niña”). The scattered tropical rain clouds in turn disruptthe airflow, which in turn sends the heavy rainfall that is normally centeredin the western Pacific to the eastern and central pacific regions. Regionalconsequences are thus suffered due to the change in the Pacific regionsclimates. “A strong El Niño is often associated with wet winters over thesoutheastern US, as well as drought in Indonesia and Australia.” (Pierce etal., “So What is an El Niño, Anyway?”). Keep in mind that every time an El Niñoevent occurs you aren’t guaranteed these consequences; it’s just that when ElNiño occurs they tend to be the typical consequence. As one may infer when aregion with a dry climate experiences heavy weather and a region with a wetclimate experiences dry weather, floods, droughts, and other consequencesassociated with extreme weather are bound to happen.
The complexities of El Niño and itsperiodical occurrence give us an idea of how to understand it. Changes in thesurface pressure, water temperature, and wind direction in the southern,eastern, and central regions of the Pacific cause the climate situation. Lastly,El Niño is unique because when these changes occur they are drasticallydifferent from the normal flow of the climate and there are extremeconsequences that are felt in the regions the event effects.EndFragment