El Nino

                                          El Nino

   El Nino is triggered when -for unknown reasons-the trade winds ( trade winds: a wind blowing steadily toward the equator from the northeast in the northern hemisphere or the southeast in the southern hemisphere, especially at sea. Two belts of trade winds encircle the earth, blowing from the tropical high-pressure belts to the low-pressure zone at the equator) weaken or reverse direction and blow from west to east. This process allows a large majority of water from Indonesia, to move eastward along the equator until i reaches the South American coast.
   The name 'El Nino' or 'Christ Child', was used by the fisher men along the coast of the equator and Peru, but the El Nino warmed their cool nutrient rich waters they depended on. This warming disrupted their marine food chain in the district causing the local economy to suffer from the loss of fish. 
   El Nino is a wide-range warming of the near-surface of the water in the equatorial Pacific Ocean between South America and the international date line. The warming happens in the connection with changes in the atmosphere over the same district, which are known as the 'southern Oscillation'. 'Southern oscillation' means opposing swings of surface atmosphere pressure between the eastern and the western tropical pacific ocean, associated with El Nino and La Nina.
   During El Nino occurrence, there are two distinct changes:
                          (1) Cold coastal waters are replaced by warm waters.
                          (2) The height of the ocean surface drops over Indonesia and rises on the eastern Pacific Ocean, forcing the thermocline ( a zone of the ocean in which the temperature decreases rapidly with depth) lower near south America and preventing upwelling. 
    Meteorologist's use satellites to measure both of these features that comes with El Nino with an active sensor called an 'Altimeter'. (Below shows what they see from the Altimeter).

     El Nino is an example of the interaction between the atmosphere and the ocean, and how these interactions can affect the climate. 
     Waters off the western coast of South America, is a typical area to experience upwelling. Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water. This is because the Southerly winds combined with the Subtropical high causes the water to be moved off shore, to the left of the wind. 'Subtropical': Bordering on the characteristics warm, subtropical waters, also called 'Semitropical'.
     The upwelling waters are cold and rich in nutrients. Every few years, the upwelling slows or sometimes stops in the district, turning the ocean warmer sometimes reaching 7 °F above normal. This warming occurrence usually first appears around Christmas, off the coast of South America. this can last for several months. El Nino warming have occurred systematically every 2-7 years in the past century. (The red shows El Nino, while the blue shows La Nina).

     In normal circumstances the SST's (Sea Surface Temperature) off the coast of Peru are cold because of upwelling, and waters from the Western equilateral Pacific are warm. Off South American's western coast the SST's are 14 degree's cooler that the SST's in the western Pacific. Steady trade of winds from the east, push the water toward Indonesia. This raises the the level of the ocean by about 1/2 meters higher compared to the South American coast. The water flows westward, it warms up . This is a result of hindrance of solar energy and heat exchange with the atmosphere. Over the Pacific ocean, the warm water evaporates and is followed by precipitation.  
     

                  EL NINO'S AFFECT ON GLOBAL WEATHER                                                     PATTERNS

   The western Pacific experiences below- normal precipitation, as heavy rain follows the warm water and more eastward toward South America, during El Nino.
    The shift in the large Tropical Rain Clouds alters the patterns of the Subtropical Jets Streams. Subtropical Jet Streams: a region of strong winds typically found in the upper Troposphere (see 'The Layers Of The Atmoshpere') between 20 and 40 degrees latitude. The are rising in these thunder storms moves north and strengthens the Subtropical Jet Streams over South America. (The picture below shows the connection between El Nino and thunderstorms).