El Niño and La Nina

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2.5 El Niño and La Nina

El Niño and La Niña is an un-regularly weather phenomena which occur as the result from interaction between the surface of the ocean and the atmosphere in the tropical pacific. Changes in the ocean have impact to the atmosphere and climate patterns around the globe. In turn, changes in the atmosphere have impact to the ocean temperatures and currents. The system oscillates between warm El Niño to neutral or cold La Niña conditions with an on average every 3-4 years NOAA, 1998. El Niño is characterized by unusually warm of ocean temperatures in the Equatorial Pacific, as opposed to La Niña, which characterized by unusually cold ocean temperatures in the Equatorial Pacific. El Niño is an oscillation of the ocean- atmosphere system in the tropical Pacific having important consequences for global weather NOAA, 2010. Figure 2.4: El Niño Condition source: NOAA 2010 As shown in Figure 2.4, the condition on western part of Pacific Ocean there is increasing of the air pressure, causing inhibition of cloud formation upon Eastern Indonesian sea, so that’s why in some region in Indonesia the rainfall was declined far from normal condition also Figure 2.5, El Niño in Indonesia is usually related to drought condition. Gutman et al. 2000 said, that the El Niño made long dry period, declining of evaporation and precipitation, so that usually causing decreasing in food production. Furthermore El Niño has beneficial effect to the fishermen in Indonesia due to cold temperature of sea surface because of pull all warmer water mass to the 13 middle of ocean pacific region. This condition uplift chlorophyll-a content and up- welling so that can increase the number of fish catches. Up-welling mean the transport movement of deeper water to shallow levels. The year 2010 is anomalies for the climate in Indonesia because it affected by the extreme climate with is strong El-nino followed by strong LaNina see appendix 1 and appendix 2. In July 2010, the extreme climate had caused displacement of large currents circulation appendix 9, especially in the transition period between la- nina and el-nino, causing the sea levels rise. Meanwhile, December 2010 was in the strong LaNina phase sea level rise, with an additional mass of water in the sea of rain water appendix 10 and also wind current from southwest of the Java islands Indian Ocean region. Figure 2.5: Normal Conditions source: NOAA 2010 As shown in Figure 2.6, La Niña is essential the opposite of an El Niño. During a La Niña, trade winds in the western equatorial Pacific are stronger than normal, and the cold water that normally exists along the coast of South America extends to the central equatorial Pacific NASA, 2010. During La Niña, rainfall and thunderstorm activity diminishes over the central equatorial Pacific, and becomes confined to Indonesia and the western Pacific. The area experiencing a reduction in rainfall generally coincides quite well with the area of abnormally cold ocean surface temperatures NOAA, 2005. 14 Figure 2.6: La Nina Condition source: NOAA 2010 SOI Southern Oscillation Index used as indicator for describing El Nino and La Nina occurrences. The Southern Oscillation Index SOI is calculated from the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin the western and Eastern tropical Pacific during El Niño and La Niña episodes. The SOI graphics can be seen in appendices section. Positive values of the SOI are associated with stronger Pacific trade winds and warmer sea temperatures to the north of Australia, popularly known as a La Niña episode. While negative values refer to El Niño condition NOAA, 2009. Figure 2.7: Niño3.4 Sea Surface Temperature Anomaly source: OOPC 2010 The Niño3.4 SST anomaly index is an indicator of central tropical Pacific El Niño conditions. It is calculated with SSTs in the zone 170°W - 120°W, 5°S - 5°N 15 Figure 2.7 the red colour is in El-nino condition while blue is La-Nina. The anomaly is calculated relative to a climatologically seasonal cycle based on the years 1982-2005 OOPC, 2010. Nino3.4 zone condition is a reference to determine phase of El nino – La Nina because it is located in the middle of tropical Pacific zone and the movement of the currents started from here. The Oceanic Nino Index ONI from 1950 – 2010 can be seen in appendix 2; the ONI is calculated using Version 3b of the extended reconstructed sea surface temperature ERSST dataset. The extended reconstructed sea surface temperature ERSST was constructed using the most recently available International Comprehensive Ocean-Atmosphere Data Set ICOADS SST data and improved statistical methods that allow stable reconstruction using sparse data.

2.6 Tidal Wave