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A study by researchers from India’s National Centre for Polar and Ocean Research (NCPOR) has found that seasonal variations in Arctic Sea ice are impacting the Indian monsoon.

What is the Indian Summer Monsoon Rainfall?

The Indian Summer Monsoon Rainfall (ISMR), occurring from July to September, is one of the most significant monsoon systems globally. During the summer, the Central Asian and Indian landmasses heat up more quickly than the surrounding oceans. This temperature difference creates a low-pressure zone at the Tropic of Cancer known as the intertropical convergence zone (ITCZ). Trade winds from the southeast are then deflected toward the Indian subcontinent due to the Coriolis effect and the low pressure they encounter after crossing the equator. As these winds pass over the Arabian Sea, they pick up moisture and bring rain to India. The southwest monsoon divides into two branches over the Indian landmass. The Arabian Sea branch delivers rain to the west coast, while the Bay of Bengal branch brings rain to the eastern and northeastern parts of India. These branches converge over Punjab and Himachal Pradesh, with the Arabian Sea branch moving inward and the Bay of Bengal branch following the Himalayas.

Complexity of the Indian Summer Monsoon Rainfall

Recent climate models have revealed that the ISMR is influenced by the surface temperatures of the Indian, Atlantic, and Pacific Oceans. Additionally, the circum-global teleconnection (CGT), a large-scale atmospheric wave at mid-latitudes, also plays a significant role in affecting the monsoon.

Influence of Arctic Sea Ice on the Indian Monsoon

The study indicates that reduced sea ice in the central Arctic results in decreased rainfall in western and peninsular India, but increased rainfall in central and northern India. Conversely, lower sea ice levels in the upper latitudes, especially in the Barents-Kara Sea region, delay the onset of the monsoon and make it more unpredictable.

Other Atmospheric Systems Influencing the Pattern

When sea ice levels in the central Arctic rise, the heat transferred from the ocean to the atmosphere triggers cyclonic circulation at lower latitudes, such as the North Atlantic. This process enhances Rossby waves—fast-moving air currents created by Earth's rotation and temperature differences—which move from west to east. These waves cause high pressure over northwest India and low pressure over the Mediterranean region, strengthening the Asian jet stream over the Caspian Sea and shifting the subtropical easterly jet northward. This shift leads to increased rainfall in western and peninsular India. On the other hand, decreased sea ice in the Barents-Kara Sea generates an anticyclonic circulation (clear skies) over northwest Europe. This disturbance affects the upper atmosphere over subtropical Asia and India, resulting in increased rainfall in northeastern India while leaving central and northwest regions drier.

Role of Climate Change

Climate change accelerates the reduction of Arctic sea ice, which intensifies the variability and unpredictability of the ISMR. Lower Arctic sea ice contributes to more frequent and severe droughts in some areas, while causing excessive rainfall and flooding in others. The study underscores the urgent need for expanded research on climate dynamics and more accurate monsoon forecasts to address these changing patterns.