Introduction

El Nino and La Nina events have long influenced India’s monsoon patterns, but a recent study suggests a novel connection between these weather phenomena and air quality, particularly during the winter months of 2022.

Understanding El Nino and La Nina

El Nino and La Nina are two opposite phases of the El Nino-Southern Oscillation (ENSO) cycle.
ENSO is a naturally occurring phenomenon that involves the interaction between the ocean and atmosphere in the equatorial Pacific.

Here is a detailed comparison of El Nino and La Nina

	El Nino	La Nina
Definition	Warmer-than-normal sea surface temperatures	Cooler-than-normal sea surface temperatures
Frequency	Every two to seven years	Every two to seven years
Duration	Several months to a year or more	Several months to a year or more
Impact on winds	Weakens trade winds, leading to changes in patterns	Strengthens trade winds, leading to changes in patterns
Impact on rains	Reduces rainfall and can cause droughts	Increases rainfall and can cause flooding
Impact on temp.	Warmer-than-average temperatures	Colder-than-average temperatures
Global effects	Droughts in Asia and Africa, floods in Americas	Floods in Asia and Africa, droughts in South America

El Nino	La Nina
Associated with weak monsoons and drought-like conditions in India	Associated with above-normal rainfall and floods in India
Sea surface temperature in the equatorial Pacific Ocean rises above normal levels	Sea surface temperature in the equatorial Pacific Ocean drops below normal levels
Changes in the atmospheric circulation patterns	Changes in the atmospheric circulation patterns
Shift in the location of the jet stream, affecting the strength and direction of the monsoon winds	Increase in the strength of the monsoon winds, bringing more moisture and rainfall to India
Results in reduced rainfall, dry spells, and heatwaves, leading to crop failures and water scarcity	Excessive rainfall can also lead to floods and landslides, causing damage to crops and infrastructure

El Nino and its impact on Indian monsoon: El Nino refers to abnormal warming of surface waters in the equatorial Pacific Ocean, which tends to suppress monsoon rainfall in India.
Phases of El Nino Southern Oscillation (ENSO): ENSO consists of three phases in the Pacific Ocean: El Nino, La Nina (abnormal cooling), and a neutral phase with sea surface temperatures close to long-term averages.
Ocean and atmospheric conditions: ENSO involves not only temperature abnormalities of sea surface waters but also atmospheric conditions, including differences in sea-level air pressure and wind strength and direction.
Southern oscillation and the role of winds: Southern Oscillation Index measures the difference in sea-level air pressure over the western and eastern sides of the Pacific Ocean, while wind patterns play a crucial role in ENSO.

Wind Direction Shift: The study identified a significant alteration in wind circulation patterns during the winter of 2022, with winds typically blowing from the northwest direction diverted towards the south due to the prolonged La Nina effect.
Anomalous Behavior: This deviation led to a bypass of pollutant-laden winds from Punjab and Haryana away from Delhi towards southern regions, impacting cities like Mumbai, Bengaluru, and Chennai.
Extended La Nina Effect: The persistence of La Nina conditions over three years intensified the impact on wind patterns, culminating in noticeable changes in air quality distribution across India.
Uncertainties and Further Exploration: While the study highlights the role of La Nina in altering wind circulation and subsequent air quality, uncertainties remain regarding the potential impact of El Nino events on air quality dynamics.

The study underscores the need for continued exploration into the interplay between global weather phenomena like La Nina, local meteorological conditions, and air quality dynamics in India.
Understanding these complex relationships can inform policy measures aimed at mitigating air pollution and enhancing environmental resilience in the face of climate change challenges.