Arctic Sea Ice is Linked to Monsoon Patterns in India

Syllabus: GS1/ Geography

Context

• In a study researchers from India’s National Centre for Polar and Ocean Research (NCPOR), have found that seasonal changes in the Arctic sea ice is affecting the Indian monsoon.

What is the Indian Summer Monsoon Rainfall?

• The Indian summer monsoon rainfall (ISMR) over the Indian subcontinent, from July to September, is one of the most prominent monsoon systems in the world.
• In summer months, sunlight warms the Central Asian and Indian landmass more and faster than the surrounding ocean.
  • This creates a low pressure band at the Tropic of Cancer called the intertropical convergence zone (ITCZ).
• Trade winds blowing from the southeast are subsequently deflected towards the Indian landmass due to the Coriolis force and the low pressure after they cross the equator.
  • As they blow over the Arabian Sea, the winds pick up moisture and deposit that as rain over India.
• Over the landmass, the southwest monsoon splits into two. The Arabian Sea arm brings rain to the west coast while the other arm travels to the Bay of Bengal and brings rain to India’s eastern and northeastern parts.
• The arms finally converge over Punjab and Himachal Pradesh as the Arabian Sea arm moves inward and the Bay of Bengal arm moves along the Himalaya.

Complexity of the Indian Summer Monsoon Rainfall

• In the last two decades, climate models have shown that the surface temperatures of the Indian, the Atlantic, and the Pacific Oceans affect the ISMR. 
• The circum-global teleconnection (CGT), a large-scale atmospheric wave flowing at the mid-latitudes, seemed to significantly influence the monsoon as well.

Influence of Arctic sea ice on the Indian monsoon

• The research reveals that less sea ice in the central Arctic leads to lower rain in western and peninsular India but more rain in central and northern India.
• On the other hand, lower sea ice levels in the upper latitudes, particularly in the Barents-Kara Sea region encompassing the Hudson Bay, the Gulf of St. Lawrence and the Sea of Okhotsk, delay the monsoon’s onset and render it more unpredictable.

Other atmospheric systems influencing pattern

• The scientists found that when sea ice levels in the Central Arctic increase, the heat transferred from the ocean to the atmosphere triggers a cyclonic circulation at slightly lower latitudes, like in the North Atlantic.
• This creates the Rossby waves, viz a fast-flowing stream of air, created by the earth’s rotation and differences in temperature and weather systems that move west to east.
• It results in high pressure over northwest India and low pressure over the Mediterranean region.
  • This in turn strengthens a narrow, concentrated band of wind, called the Asian jet stream, over the Caspian Sea, causing the subtropical easterly jet, a jet stream blowing over the Indian subcontinent during summer,  to shift northward.
  • It brings more rain over western and peninsular India.
• On the other hand, as sea ice levels decrease in the region, heat rises from the Barents-Kara sea, creating an anticyclonic circulation (calm, clear skies) over northwest Europe. 
  • This disturbs the upper atmospheric region over subtropical Asia and India and  promotes high rainfall over northeastern India while leaving central and northwest regions of the country without much

Role played by climate change

• Climate change, by accelerating the reduction of Arctic sea ice, exacerbates the variability and unpredictability of the ISMR.
• Lower Arctic sea ice can lead to more frequent and severe droughts in some regions while causing excessive rainfall and flooding in others.
• Further the study shows the urgent need to expand research on climate dynamics and for scientists to prepare more accurate forecasts of the ever-changing monsoons. 

Source: TH