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La Niña
Context:
This year, all major global agencies missed the mark in predicting the onset of La Niña.
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- Early projections from multiple global weather models predicted that La Niña conditions would develop by July. However, by mid-July, it became clear that La Niña would be delayed.
- Meteorologists suggest the primary reason for the error is the mild nature of this La Niña, as weather models tend to detect stronger phases more easily.
- Other factors, such as inter-seasonal atmospheric, wind, and pressure variations—particularly influenced by the Madden Julian Oscillation (MJO)—also complicate predictions.
About La Niña
- Definition: La Niña, or “The Little Girl” in Spanish, is one phase of the El Niño Southern Oscillation (ENSO), a major factor driving global climate variability.
- ENSO is marked by shifts in sea temperatures in the tropical Pacific Ocean, influenced by atmospheric changes. These shifts affect global atmospheric circulation and weather patterns.
- Overview: ENSO occurs in irregular cycles, typically lasting two to seven years, and has three phases: warm (El Niño, “The Little Boy” in Spanish), cool (La Niña), and neutral.
- Neutral: In the neutral phase, the eastern Pacific (near northwestern South America) is cooler than the western Pacific (around the Philippines and Indonesia) due to east-to-west trade winds that move warm surface water. Cooler water rises to the surface, replacing the displaced warm water.
- El Niño: During El Niño, these trade winds weaken, leading to less displacement of warm water, causing the eastern Pacific to heat up.
- It causes warming of the ocean surface, resulting in above-average sea surface temperatures (SST) in the central and eastern tropical Pacific Ocean.
- La Niña: In La Niña, the opposite happens: trade winds strengthen, pushing more warm water toward the western Pacific.
- During La Niña events, the trade winds intensify, driving more warm water towards Asia. This results in increased upwelling off the west coast of the Americas, where cold, nutrient-rich water rises to the surface.
El Niño and Indian Monsoon
- In India, El Niño is typically linked to reduced monsoon rainfall, while La Niña supports stronger monsoon activity.
- La Niña typically enhances rainfall during India’s southwest monsoon, which runs from June to September.
- However, with the monsoon nearing its end and La Niña conditions yet to develop in the equatorial Pacific, it hasn’t directly influenced rainfall so far.
- That said, other factors contribute to monsoon rainfall, and the delayed onset of La Niña hasn’t led to poor performance.
- In August, India recorded a 16% rainfall surplus, and the forecast for September remains favourable, with the IMD predicting 109% of normal rainfall across most regions.
- Suppose La Niña begins around late September or October. In that case, it might affect the northeast monsoon (October-December), which brings rainfall mainly to Tamil Nadu, coastal Andhra Pradesh, Rayalaseema, southern interior Karnataka, and Kerala.
- La Niña years tend to increase cyclogenesis, leading to more frequent, intense, and longer-lasting storms.
- Historically, La Niña years are also associated with colder, harsher winters.
Recently,INCOIS (Indian National Centre for Ocean Information Services) has introduced a new forecasting product called the Bayesian Convolutional Neural Network (BCNN) to predict El Niño and La Niña conditions. This product leverages advanced technologies such as Artificial Intelligence (AI), deep learning, and machine learning (ML) to enhance the accuracy and lead time of forecasts related to the phases of the El Niño Southern Oscillation (ENSO).
