The El Nino and La Nina phases of the El Nino-Southern Oscillation (ENSO) cycle are opposed. The El Nino Southern Oscillation (ENSO) is a recurrent climatic phenomenon characterized by shifts in sea surface temperature, upper and lower-level wind patterns, sea-level pressure, and the distribution of tropical rainfall over the Pacific Ocean and its surrounding waters. El Nino is the common name for ENSO while it is in its warm phase, whereas La Nina is the common name for it when it is in its cold phase. These temperature departures from the norm at the Earth's surface may have a significant effect on the world's climate and weather.
Learn about La Nina and El Nino and how they affect the climate in India.
Scientists have shown that El Nino and the Southern Oscillation co-occur in the 1930s, thanks to the research of Sir Gilbert Walker. When coastal waters in the eastern tropical Pacific become warmer, the air pressure above the ocean drops (El Nino). Climatologists call the relationship between El Nio and the Southern Oscillation "El Nino-Southern Oscillation" (ENSO). Most professionals in the field now refer to El Nio and ENSO as "El Nio" and "ENSO" respectively.
The Indian Ocean has lower pressure than the other oceans because it is warmer than they are. Hence, rain winds move from the western Pacific to the Indian Ocean. As the continent of India has a lower pressure than the Indian Ocean, winds carrying moisture from the sea can travel further inland. If the average pressure distribution is altered, the monsoons will be affected.
El Nino warms cold surface water off the coast of Peru. The typical trade winds die out or change directions when the water gets too warm. This causes winds carrying rain and cloudiness from the western Pacific to be channeled toward the coast of Peru (the region near northern Australia and South East Asia). During an El Nino, it causes heavy precipitation in Peru but prevents the usual monsoon rains from reaching the Indian subcontinent. When there is a significant difference in temperature and pressure, there is also a substantial difference in the amount of rainfall that falls in India.