El Niño & La Niña PDF

The Pacific Ocean This is the largest and deepest ocean on earth. There is a strong link between ocean and atmosphere. It is crucial for the formation of trade winds and influences weather patterns, marine life and ocean currents. Wind has a dragging effect which creates oce...

The Pacific Ocean This is the largest and deepest ocean on earth. There is a strong link between ocean and atmosphere. It is crucial for the formation of trade winds and influences weather patterns, marine life and ocean currents. Wind has a dragging effect which creates ocean currents. Walker Air Circulation (Walker Cell) normal conditions The tropical Easterlies blow across the pacific ocean and push moist air and warm surface water (South Equitorial Current) towards the Western pacific (Indonesia and Australia). This creates a low pressure over the western pacific Cold, nutrient-rich water (Peruvian current) upwells along the eastern pacific (coast of South America). Creates a temperature gradient with warm water in the western Pacific and cooler water in the eastern Pacific. Results in rising air and low pressure over the warm western Pacific, and sinking air and high pressure over the cooler eastern Pacific. Thermocline: the transition layer between the warmer mixed water at the surface and the cooler deep water below Upwelling: The rising of cold, nutrient-rich water from the deep ocean to the surface, typically occurring off the coast of South America. ATMOSPHERE – WALKER CELL LP HP Trade Winds Equatorial current ne South ocli g m llin r America Indonesia The we & Dry, cold Australia PACIFIC OCEAN – condition from up Rising sea level, CONVECTION CURRENT rising cold possible floods water and no & rainfall rainfall  El-Niño El Niño: A climatic event characterized by the warming of the central and eastern Pacific Ocean, leading to significant weather changes globally. PROCESS: The tropical easterlies weaken and the warm surface waters start to flow eastwards towards the eastern pacific. This suppresses the upwelling of cold water in the east. This creates a lower pressure (than normal) over the eastern and central pacific. Cooler than normal waters collect towards the western pacific and there is less rainfall. This creates a higher pressure than normal over the western pacific. Creating wetter conditions over south America and the central pacific And drier conditions in the western pacific (Indonesia). El Niño HP HP LP Trade Winds Equatorial current The South rmo America No of w Indonesia clin e up ate & we r Australia Warmer PACIFIC OCEAN – lli Cooler than conditions & ng flooding from normal & receives CONVECTION CURRENT rising sea level, less rainfall = droughts no more fishing  Extreme El-Niño EXTREME El Niño Extreme Extreme LP HP Winds Reversed Trade Equatorial current The rmo South Up wa Indonesia clin e America we te & lli r Australia Warmer ng Cooler than PACIFIC OCEAN – conditions & of flooding from normal & receives CONVECTION CURRENT rising sea level, less rainfall = droughts no more fishing  La-Niña La Niña: is the cooling of the central and eastern tropical Pacific Ocean, which also influences global weather patterns. La Niña is an intensified walker atmospheric circulation cell. Stronger tropical easterlies blow across the tropical pacific ocean. And brings warm, moist air and warmer surface waters towards the western pacific. This creates a lower pressure than normal over the western pacific. An increase of cold water upwells along the eastern pacific (cold Peruvian current). This creates a higher pressure than normal over the eastern pacific. This creates drier conditions over south America and wetter conditions in the western pacific. La Niña LP HP Trade Winds Equatorial current cline South g Indonesia rmo llin America & The we Dry, cold Australia PACIFIC OCEAN – condition from up Rising sea level, possible floods CONVECTION CURRENT rising cold & increased water and no rainfall rainfall What factors Trigger El- Nin1o and La-Niña Events? Warm ocean waters in the central and eastern pacific ocean Atmospheric pressure changes Tropical cyclones Seasonal change global patterns Local land and sea interactions Human activities (burning fossil fuels and cloud seeding)  Effects of El Niño and La Niña Events During an El Niño, AFRICA experiences Drought conditions: Smaller harvests - especially maize in Africa. Stock farmers slaughter their animals to avoid high food costs. Meat prices drop at first, then rise sharply when meat becomes scarce. Food insecurity occurs = Starvation and malnutrition. In PERU- Peruvian fishermen: Normal conditions = upwelling of cold water, rich in nutrients, near Peru. (One of the world's richest fisheries is off the coast of Peru) These provide nourishment for plankton. Plankton provides food for anchovies and other fish. The fish in turn supply food for seabirds. Not only is the fish catch economically important, but the harvesting of bird excrement (guano) provides a supply of valuable fertilizer. Economic consequences of El Niño: devastating effect on the Peruvian anchovy fisheries, populations of fish and seabirds vanish, and anchovy catches dwindle (decrease) during El Niño.  Effect in Africa South of Africa North of Africa Below the equator Above the equator La Niña = flooding La Niña = drought El Niño = drought El Niño = flood El Niño La Niña The Dipole The dipole refers to the difference in ocean temperatures between two regions of the pacific ocean The ENSO dipole has 2 contrasting poles The eastern pacific becomes significantly warmer during the El Niño (one pole) And the western pacific becomes significantly cooler (the opposite pole) The Indian Ocean Dipole (IOD) is a climate phenomenon characterized by differences in sea surface temperatures between the western and eastern parts of the Indian Ocean. Similar to the El Niño-Southern Oscillation (ENSO) in the Pacific Ocean, the IOD influences weather patterns across the Indian Ocean region and beyond.