A major climatic event in the Pacific Ocean will shape India’s upcoming winter, prompting meteorologists to forecast a notably colder season.The culprit is La Niña, a phase of the El Niño-Southern Oscillation (ENSO) cycle, which recent data from the India Meteorological Department (IMD) indicates has now taken hold. This natural climate pattern, characterized by unusually cold ocean temperatures in the equatorial Pacific, is linked to a more severe winter across the Indian subcontinent.
This article will break down the science behind La Niña, its key differences from its counterpart El Niño, and specifically, how this “Little Girl” phenomenon intensifies winter conditions across the Indian subcontinent.
What is La Niña?
In simple terms, La Niña, which translates to “The Little Girl” in Spanish, is the cold phase of the ENSO cycle. It is characterized by the unusual and sustained cooling of sea surface temperatures (SSTs) in the central and eastern equatorial Pacific Ocean. This cooling is a result of stronger-than-normal easterly trade winds that blow across the Pacific. These winds push warm surface water westward towards Asia and Australia, allowing cooler, nutrient-rich water from the deep ocean to “upwell” or rise to the surface in the eastern Pacific.
This shift in ocean temperatures and atmospheric pressure creates a chain reaction that alters global weather patterns.While La Niña temporarily cools the planet’s average temperature, it creates far-reaching and often severe impacts in specific regions.
El Niño vs. La Niña: A Tale of Two Phases
El Niño and La Niña are two sides of the same coin, representing opposite extremes of the ENSO cycle. Understanding their differences is crucial to grasping their respective impacts.
- Ocean Temperatures: The most fundamental difference lies in sea surface temperatures. El Niño is the “warm phase,” marked by the warming of SSTs in the eastern Pacific. Conversely, La Niña is the “cold phase,” defined by the cooling of these same waters.
- Trade Winds: The behavior of trade winds is a key driver of these phenomena. During an El Niño event, the easterly trade winds weaken or even reverse. During La Niña, these winds are unusually strong, which is what drives the cold water upwelling in the eastern Pacific.
- Global Impacts: These changes in the Pacific have distinct teleconnections, or linked effects, on global weather.
- El Niño often leads to drought and warmer-than-average conditions in many parts of the world, including a weak and deficient Indian monsoon. It can also cause heavier rainfall and floods in regions like the western coast of South America.
- La Niña, on the other hand, typically results in above-average rainfall and enhanced monsoons in regions like India and Australia, while causing drier conditions in parts of the Americas.
How La Niña Intensifies Winter in the Indian Subcontinent
While La Niña is often associated with a positive impact on India’s monsoon season—bringing enhanced rainfall that benefits agriculture—its effects on the winter are quite the opposite. The strong likelihood of a La Niña event this year is a key factor behind predictions of a colder-than-average winter, particularly across northern India. Here’s a breakdown of the atmospheric mechanisms at play:
- Shift in Atmospheric Circulation: The cooling of the Pacific during a La Niña event directly influences the Walker Circulation, an atmospheric cell that moves air across the Pacific. The stronger trade winds intensify this circulation, causing a descending branch of the circulation to strengthen over the Indian subcontinent. This can promote colder, drier air to sink and settle, leading to more stable, and thus colder, conditions.
- Modulation of Jet Streams: La Niña alters the position and strength of global atmospheric currents, including the polar jet stream. The colder conditions in the Pacific can cause the jet stream to dip southward over Asia. This shift effectively acts as a conduit, allowing frigid, high-latitude air from Siberia and the polar regions to penetrate deeper into the Indian subcontinent.
- Strengthening of Western Disturbances: La Niña can also influence the frequency and intensity of Western Disturbances (WDs). These are extratropical storms that originate in the Mediterranean region and travel eastward, bringing rain and snow to northern India and the Himalayas during the winter. With the atmospheric conditions favorable for channeling cold air, WDs during a La Niña winter are often more robust, leading to heavier snowfall in the Himalayan region. This snow cover acts as a cold-air source. Northerly winds then transport this air across the northern plains, which significantly lowers temperatures and increases cold wave frequency.
- Increased Cold Wave Frequency and Duration: Research, including studies by institutions like IISER Mohali, confirms that La Niña years are correlated with a higher frequency and longer duration of cold wave events in north India. The strengthened northerly winds, a result of the atmospheric circulation changes, efficiently transport cold air, leading to biting cold spells and a prolonged winter.
In conclusion, while the enhanced monsoon rains brought by La Niña are a boon for India’s agriculture, the same phenomenon presents a significant challenge in the form of a harsh winter. As environmental science students, it’s essential to understand that these climate patterns, though naturally occurring, are taking place within the broader context of anthropogenic climate change. This makes their behavior less predictable and their impacts, particularly the extremes, more pronounced. The impending La Niña winter serves as a timely reminder of the need for robust climate preparedness and adaptive strategies to protect vulnerable populations and infrastructure from the dual benefits and challenges of this powerful climate driver.
