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Context:
A study by India’s National Centre for Polar and Ocean Research (NCPOR) and South Korea’s Korea Polar Research Institute, published in Remote Sensing of Environment (June 2023), shows the seasonal changes in Arctic sea ice affecting the Indian monsoon.
Indian Summer Monsoon Rainfall (ISMR)
- The Indian summer monsoon rainfall (ISMR) occurs from July to September, with most rains recorded in July and August. It is one of the most prominent monsoon systems in the world.
- During summer, the Central Asian and Indian landmass heats faster than surrounding oceans, creating a low-pressure band at the Tropic of Cancer, known as the intertropical convergence zone.
- Trade winds from the southeast, deflected by the Coriolis force, blow over the Arabian Sea and gather moisture, bringing rain to India.
- The southwest monsoon splits into two:
- The Arabian Sea arm brings rain to the west coast.
- While the Bay of Bengal arm brings rain to eastern and northeastern India, converging over Punjab and Himachal Pradesh.
Climate Change and Monsoon Patterns
- Climate change plays a significant role in altering monsoon patterns.
- As the complex interactions of surface temperature, pressure gradients, air currents, and sea ice in bringing rain to India.
Influence of Global Factors on ISMR
Climate models reveal that the surface temperatures of the Indian, Atlantic, and Pacific Oceans, and the circum-global teleconnection (CGT), significantly influence the ISMR.
Influence of Arctic Sea Ice on Indian Monsoon
- Declining Arctic sea ice levels due to climate change have been linked to influencing the Indian monsoon’s behavior.
- Researchers used observational data (1980-2020) and climate models (Coupled Model Intercomparison Project Phases 5 and 6) to analyze how Arctic sea ice affects atmospheric circulations, influencing ISMR.
- Less sea ice in the central Arctic results in lower rainfall in western and peninsular India but higher rainfall in central and northern India.
Effects of Lower Sea Ice in High Latitudes
- Lower sea ice levels in the Barents-Kara Sea region (encompassing Hudson Bay, Gulf of St. Lawrence, and Sea of Okhotsk) delay the monsoon’s onset and make it more unpredictable.
- Low sea ice levels in the Barents-Kara Sea region create high pressure over southwest China, correlating with a positive Arctic Oscillation.
- This causes high pressure over the northern Atlantic and Pacific oceans, weakening the CGT.
- As sea ice decreases, heat rises from the Barents-Kara Sea, creating anticyclonic circulation (clear skies) over northwest Europe, disturbing the upper atmospheric region over subtropical Asia and India.
High Rainfall Over Northeastern India
This instability, combined with high surface temperatures of the Arabian Sea and moisture from surrounding water bodies, promotes high rainfall over northeastern India while central and northwest regions receive less rain.
Atmospheric Systems Influencing Monsoon Patterns
- Increased sea ice in the Central Arctic causes heat transfer from the ocean to the atmosphere, triggering cyclonic circulation at lower latitudes (North Atlantic).
- This strengthens Rossby waves, resulting in high pressure over northwest India and low pressure over the Mediterranean, enhancing the Asian jet stream over the Caspian Sea and shifting the subtropical easterly jet northward.
- The resulting anomalous high-pressure region over Central Asia disrupts atmospheric stability over India, bringing more rain to western and peninsular India.
Details: Monsoon: https://www.iasgyan.in/daily-current-affairs/monsoon-43
Role of Climate Change
- Climate change accelerates the reduction of Arctic sea ice, exacerbating the variability and unpredictability of the ISMR.
- Reduced Arctic sea ice can cause frequent and severe droughts in some regions while leading to excessive rainfall and flooding in others.
Impact of Arctic Sea Ice on Indian Monsoon
- Incessant rainfall has caused devastation in India’s southeast, leaving 17 dead in Andhra Pradesh and thousands homeless due to floods in Telangana.
- The Indian Meteorological Department has warned of heavy rains in parts of Gujarat, Himachal Pradesh, and Delhi.
- Unpredictable and erratic rainfall is becoming the norm for the Indian monsoon, shifting from being a bringer of relief to a cause of droughts and floods.
Need for Further Research
- The study highlights the physical pathways through which Arctic sea ice affects the Indian monsoon.
- It underscores the urgent need for expanded research on climate dynamics and the development of more accurate monsoon forecasts due to increasing variability.
Annual Rainfall: https://www.iasgyan.in/daily-current-affairs/onset-of-monsoon
Source:
https://www.thehindu.com/sci-tech/science/what-role-does-arctic-sea-ice-play-in-indian-monsoon/article68600899.ece
https://rmets.onlinelibrary.wiley.com/doi/10.1002/joc.8337#:~:text=The%20Arctic%20Sea%20ice%20loss,extreme%20precipitation%20in%20Indian%20regions.
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PRACTICE QUESTION
Q. Quantify the association between Arctic Sea ice extent and Indian precipitation. 150 words
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