North India’s unusually harsh January 2024 cold wave—six straight days of piercing chill from the 21st to the 26th—was no ordinary winter event. Scientists now say it was triggered not by the region’s typical western disturbances, but by a sudden stratospheric warming (SSW) that unfolded thousands of kilometers away on 16–17 January 2024.
This dramatic atmospheric upheaval disrupted the polar vortex, pushing frigid Arctic air southward into North Asia and Europe before it crept eastward and settled over East Asia, the researchers said.
What followed was the formation of a powerful “dipole block” over the Siberian–East Asian region, funneling icy air downstream into North India and locking the region into an unusually prolonged and intense cold wave, they said.
The 2024 winter season was peculiar, with North India experiencing an intense and prolonged cold wave (CW) in January 2024, lasting for six consecutive days (spanning from the 21st to the 26th) in the absence of a usual western disturbance propagation, according to a research paper published recently in the journal Quarterly Journal of the Royal Meteorological Society.
“Our findings indicate that this CW was a result of the sudden stratospheric warming (SSW) that occurred on 16th and 17th January 2024,” noted the researchers, including corresponding author Raju Attada, Assistant Professor at Indian Institute of Science Education and Research (IISER) Mohali.
“The SSW caused the polar vortex to shift towards lower latitudes (southward), advecting cold Arctic air to the lower latitudes of North Asia and Europe. This cold air mass then gradually moved eastward, eventually settling over East Asia,” they said.
Consequently, the team found that a ‘dipole block’ developed and strengthened, as a result of the SSW, over the Siberian-East Asian region, with the ridge centered over Siberia. The downstream portion of this ridge transported cold air from East Asia to North India, leading to the CW.
The blocking pattern also keeps weather systems stagnant for longer periods, contributing to the prolonged CW conditions. Thus, the SSW event indirectly led to the CW in North India.
“We further examined the impact of SSW on CWs and found that, in addition to the CW in 2024, the CW events in the winters of 2004 and 2019 were also associated with SSWs. A common characteristic feature associated with all three SSW-related CWs is the formation of an atmospheric block that is strengthened by the downward propagation of the stratospheric signal to the troposphere,” said the researchers, including those from National Institute for Space Research, São José dos Campos, Brazil and University of Massachusetts Lowell, US.
The team, including Kalariplakkal Sasi Athira, Mathew Barlow, V. Brahmananda Rao, made use of the two biometeorological indicators – the Universal Thermal Climate Index and the Wind Chill Index (WCI) – to study the implications of the 2024 CW event. It is observed that slight cold stress first emerges over the Indo-Gangetic Plains, which later expands to the northern parts of the country, particularly between 18:00 and 23:00 Indian Standard Time (IST).
A moderate cold stress is experienced in isolated pockets of North and Northwest India between 0:00 and 7:00 IST. WCI indicates discomfort predominating during the evening, night, and early morning hours due to higher wind speeds along with the low temperatures.