Delayed Onset of La Nina: Impacts on India’s Weather and Monsoon Patterns
- September 7, 2024
- Posted by: OptimizeIAS Team
- Category: DPN Topics
Delayed Onset of La Nina: Impacts on India’s Weather and Monsoon Patterns
Sub: Geo
Sec: Climatology
Why in News:
The India Meteorological Department (IMD) has reported that La Niña, a critical climate phenomenon known to influence India’s monsoon, is delayed this year. This delay comes after initial predictions suggested an earlier onset. The neutral phase of the Indian Ocean Dipole (IOD) has also been prevailing over the Indian Ocean, and La Niña conditions are now expected to develop towards the end of the monsoon season. This has raised questions about its potential impact on India’s weather patterns, particularly during the winter season.
What is La Nina?
La Niña, meaning “The Little Girl” in Spanish, is a phase of the El Niño Southern Oscillation (ENSO) and represents the cool phase. It is one of the most significant climate drivers that influences global weather patterns, including India.
Phases of ENSO:
- El Niño: Warmer sea surface temperatures in the eastern Pacific.
- La Niña: Cooler sea surface temperatures, leading to stronger trade winds and more monsoon activity.
- Neutral: The Pacific neither exhibits warm nor cool anomalies.
- ENSO Cycles: These phases occur irregularly every 2-7 years.
Mechanism of La Niña
Normal Conditions: Trade winds blow from east to west, carrying warm surface water towards the western Pacific (Indonesia and Philippines). This causes cooler water to rise near South America.
During La Niña: These trade winds become stronger, pushing larger amounts of warm water to the western Pacific, cooling the eastern Pacific even further.
Impact on Monsoon: La Niña usually enhances the Indian monsoon, bringing more rainfall. Conversely, El Niño is linked to reduced monsoon activity.
Impact on India’s Weather
Southwest Monsoon: While La Niña enhances rainfall during the monsoon season, its late onset means it will not significantly impact this year’s monsoon. August saw a 16% surplus in rainfall, and September is also expected to witness above-normal rains (109% of the long-term average).
Northeast Monsoon: La Niña may influence the northeast (winter) monsoon, particularly in Tamil Nadu, coastal Andhra Pradesh, Rayalaseema, south interior Karnataka, and Kerala.
Cyclogenesis: The north Indian Ocean, including the Bay of Bengal and Arabian Sea, sees cyclone development during La Niña years, with storms being more frequent, intense, and long-lasting.
Colder Winters: La Niña is also associated with harsher and colder winters in northern India, and the coming winter could see below-normal temperatures.
ENSO (El Nino)
- ENSO is one of the most important climate phenomena on Earth due to its ability to change the global atmospheric circulation, which in turn, influences temperature and precipitation across the globe.
- Though ENSO is a single climate phenomenon, it has three states, or phases, it can be in. The two opposite phases, “El Niño” and “La Niña,” require certain changes in both the ocean and the atmosphere because ENSO is a coupled climate phenomenon.
- El Niño: A warming of the ocean surface, or above-average sea surface temperatures (SST), in the central and eastern tropical Pacific Ocean. Over Indonesia, rainfall tends to become reduced while rainfall increases over the tropical Pacific Ocean. The low-level surface winds, which normally blow from east to west along the equator (“easterly winds”), instead weaken or, in some cases, start blowing the other direction (from west to east or “westerly winds”).
- Neutral: Neither El Niño or La Niña. Often tropical Pacific SSTs are generally close to average.
Indian Ocean Dipole
Sustained changes in the difference between sea surface temperatures of the tropical western and eastern Indian Ocean are known as the Indian Ocean Dipole or IOD.
Phases of IOD: The Indian Ocean Dipole (IOD) has three phases—neutral, positive, and negative—that influence the Indian monsoon.
Neutral IOD:
- Normal temperatures across the tropical Indian Ocean.
- Westerly winds blow along the equator.
- No significant impact on the Indian Southwest Monsoon.
Positive IOD:
- Westerly winds weaken, shifting warm water towards Africa.
- Cooler water rises in the eastern Indian Ocean.
- Results in more moisture over the Arabian Sea, leading to increased monsoon rainfall in India.
Negative IOD:
- Westerly winds intensify, concentrating warm water near the eastern Indian Ocean.
- Warmer water in the east and cooler in the west.
- Adversely affects Indian monsoon, leading to below-average rainfall.