TOPIC INFO (UGC NET)
TOPIC INFO – UGC NET (Geography)
SUB-TOPIC INFO – Climatology (UNIT 2)
CONTENT TYPE – Detailed Notes
What’s Inside the Chapter? (After Subscription)
1. El Nino
1.1. Normal Conditions
1.2. Walker circulation (Occurs during Normal Years)
1.3. During El Nino year
1.4. Effects of El Nino
1.5. How El Nino impacts monsoon rainfall in India
2. El Nino Southern Oscillation (ENSO)
2.1. Southern Oscillation Index and Indian Monsoons
2.2. Indian Ocean Dipole effect
2.3. Impact on IOD on Cyclonogeneis in Northern Indian Ocean
3. The El Niño Modoki
3.1. El Niño Modoki Impacts
4. La Nina
4.1. Effects of La Nina
5. Madden-Julian Oscillation (MJO)
5.1. Phases of Madden-Julian Oscillation
5.2. How Does MJO Affect Indian Monsoon?
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ENSO Events: El Niño, La Niña and Southern Oscillations
UGC NET GEOGRAPHY
Climatology (UNIT 2)
El-Nino and La Niña are opposite phases of what is known as the El Niño-Southern Oscillation (ENSO) cycle. The ENSO is a recurring climatic pattern involving temperature changes in the waters of the eastern and central tropical Pacific Ocean, and changes in the patterns of upper and lower-level winds, sea level pressure, and tropical rainfall across the Pacific Basin.
El Nino is often called the warm phase and La Nina is called the cold phase of ENSO. These deviations from the normal surface temperatures can have a large-scale impact on the global weather conditions and overall climate.
El Nino
The phrase “El Niño” refers to the Christ Child and was coined by fishermen along the coasts of Ecuador and Peru to describe the warming of the central and eastern pacific.
- El Niño is the name given to the occasional development of warm ocean surface waters along the coast of Ecuador and Peru. El Niño events occur irregularly at intervals of 2–7 years, although the average is about once every 3-4 years.
- When this warming occurs the usual upwelling of cold, nutrient-rich deep ocean water is significantly reduced.
- El Niño normally occurs around Christmas and usually lasts for a few weeks to a few months.
- Sometimes an extremely warm event can develop that lasts for much longer time periods. In the 1990s, strong El Niños developed in 1991 and lasted until 1995, and from fall 1997 to spring 1998.
Normal Conditions
- In a normal year, a surface low pressure develops in the region of northern Australia and Indonesia and a high-pressure system over the coast of Peru. As a result, the trade winds over the Pacific Ocean move strongly from east to west.
- The easterly flow of the trade winds carries warm surface waters westward, bringing convective storms (thunderstorms) to Indonesia and coastal Australia. Along the coast of Peru, cold bottom cold nutrient-rich water wells up to the surface to replace the warm water that is pulled to the west.
