IV. Climate Phenomena

2. La Niña

La Niña, the comparative term for El Niño, originates from Spanish, meaning baby girl. Both El Niño and La Niña refer to the abnormal changes of sea temperature and ocean current in the eastern Pacific region. The observation area is within 5° N and 5° S, and 90° to 150° W (Niño 3 region). A five month moving average of sea temperature is used in the calculation. If the result is 0.5 °C higher than the climate mean, then an El Niño phenomenon is regarded to exist. If the temperature is 0.5 °C lower than the climate mean, a La Niña phenomenon is regarded to exist (ref: Kevin E. Trenberth, 1997: The Definition of El Niño, Bulletin of the American Meteorological Society, Vol 78, No. 12, p.2772). Under normal climate conditions, the atmospheric pressure of the east tropical Pacific is higher than that of the west; this difference of pressure generates the easterlies and leads the east Pacific current west. During the La Niña, the normal east-west sea temperature difference is enlarged and therefore enhanced as mentioned. Since the change of sea temperature is one of the major factors of climate changes, during El Niño the world will experience abnormal cool summers and warm winters, and during La Niña, hotter summers and colder winters.