Updated: January 27, 2022 7:51:34 am
For many people, especially in North India, the winter of 2021-22 is appearing to be unusually cold and unusually long. The days, in particular, have felt colder and chillier than normal. Is the popular impression borne out by data? Why is this happening?
Have the days indeed been colder?
Since December 2021, maximum temperatures across the North, Northwest and Central India regions have persistently remained below normal, resulting in “cold day” conditions. Technically, this means more than just a day that is cold.
The India Meteorological Department (IMD) defines a “cold day” as one in which the maximum temperature falls below 16 degrees Celsius, a phenomenon that is commonly seen during the winter months in the northern plains of India.
This winter, the national capital Delhi witnessed eight days in January (until January 25) when the maximum temperature remained below 16 degrees, with the lowest maximum temperature recorded at 12.2 degrees Celsius on Tuesday (January 25).
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Similarly cold Januaries in recent years were felt in 2003, which saw 19 “cold days” in January, 2015 (11 days), and 2010, 2013, and 2004 (9 days each). There are several days still to go in January 2022.
It isn’t just Delhi either. Since late last week, many places in Maharashtra have experienced “cold day” conditions as well. Maximum temperatures at several places in Madhya Maharashtra and Konkan, including Mahabaleshwar, Pune, Mumbai, and Nashik have been 6 to 8 degrees Celsius below normal.
“Cold days” often mean warmer nights. “Persistent clouding blocks out the rays of the Sun and heating during the day, but keeps the nights warmer than normal,” R K Jenamani, senior scientist at the National Weather Forecasting Centre, Delhi, said.
What weather systems have been active over the country?
Winters over India are directly affected by the intensity and frequency of western disturbances — eastward propagating wind streams as a cyclonic circulation or trough, capable of inducing rain or snow-bearing weather systems along their path of movement.
Until January 25, seven western disturbances had passed over India — nearly all of them strong enough to cause widespread rain, snowfall, and squally weather across large geographical areas between Pakistan and Northeast India.
These systems caused hailstorms in northern Maharashtra, and heavy rainfall in Tamil Nadu.
“Frequent and higher numbers of western disturbances are associated with La Niña,” D Sivanand Pai, head, Climate Monitoring and Services at IMD, Pune said. At present, moderate intensity La Niña conditions — which manifests itself as cooler than normal sea surface temperatures in the equatorial Pacific Ocean — are prevailing.
After a western disturbance crosses India, cold winds from the far north of the country penetrate to lower latitudes, and can reach up to even Telangana and Maharashtra, leading to colder weather, and sometimes to cold wave conditions.
Back-to-back western disturbances separated by 10 days earlier this month caused a prolonged cold spell in Jammu and Kashmir, Punjab, Haryana, Rajasthan, Himachal Pradesh, Uttar Pradesh, Delhi, and Bihar between January 11 and 20.
“The presence of low-lying clouds and the availability of moisture along the Indo-Gangetic plains made it favourable for cold day conditions and the additional chill factor experienced during the day time. This was the longest and most intense spell of the season so far,” Jenamani said.
This has also been a rather wet winter.
Precipitation, mostly in the form of snow, is common during winter over Jammu and Kashmir, Ladakh, Uttarakhand, and Himachal Pradesh. Light to moderate intensity rainfall is also commonly seen during winters in neighbouring regions of North India.
This January, however, has seen widespread rain across the central, northwestern, northern, eastern, and northeastearn regions of India.
As many as 24 states or Union Territories have recorded rainfall varying from excess to large excess this month. The only exceptions have been Arunachal Pradesh (minus 26 per cent), Mizoram (minus 43 per cent), Goa (minus 44 per cent), Karnataka (minus 80 per cent), Kerala (minus 76 per cent) and Lakshadweep (minus 99 per cent).
January has been significantly wet over Delhi, Odisha, Madhya Pradesh, Uttar Pradesh, Uttarakhand, Haryana, Punjab, Chhattisgarh, Himachal Pradesh, Jammu and Kashmir, Ladakh, and Rajasthan, taking the all-India rainfall figure to 38.1 mm so far, which is 196 per cent above normal.
Delhi is witnessing the wettest January in 122 years. The national capital’s monthly rainfall recorded at the Safdarjung (88.2 mm) and Palam (110 mm) stations are already 72 per cent and 99 per cent above normal respectively.
Other states and Union Territories with large surpluses of rainfall during this month include Uttarakhand (102.3 mm), Chandigarh (207.7 mm), Himachal Pradesh (170 mm), Jammu and Kashmir (165.8 mm), and Punjab (104.6 mm).
The winter has been less foggy than normal.
Yes. December and January are known for the formation of dense fog across North India. Delhi in December normally witnesses 278 hours of fog — during which visibility falls below 1,000 metres — over 26 days, but December 2021 saw only 75 hours of fog spread over 22 days. This was the lowest for December since 1982.
In January too, the national capital remained affected by fog for 252 hours against a normal of 292 hours — the lowest since 2008.
IMD officials said the ongoing winter has recorded the lowest fog hours since 1991-92 over Delhi. Conditions for the development of fog are not forecast for the rest of January.
Strong northern and north-westerly winds have been dominant during the past six weeks. This winter saw an unusual duststorm reaching parts of Gujarat, Maharashtra, and Delhi over the last weekend. The strong winds associated with the duststorm originated above Saudi Arabia, and picked up local dust along its course from the desert regions of Afghanistan and Pakistan.
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