The unexpected chill at the fag end of an otherwise warm winter since the past week is the fallout of a cold blast from the Arctic. According to weather scientists from India Meteorological Department (IMD), it is because of a phenomenon called negative (anti-clockwise) Arctic oscillation, which brings blasts of cold Siberian winds to the Indian region.
As a result of this, the entire North India, parts of Central India extending upto Maharashtra besides areas in eastern India are facing cold wave, with temperatures below normal by 3- 6degree celsius. The lowest minimum temperature of 0.7degree celsius was recorded at Chandigarh, besides plains of Punjab and Haryana on Sunday. Cold wave conditions are also likely in certain parts of Vidarbha, Chhattisgarh, Bihar, Jharkhand, Gangetic West Bengal and interior Odisha.
IMD has predicted snow at many places over Western Himalayan region. Rains and thunders-howers are likely at isolated places over adjoining plains.
According to experts in IMD, Arctic oscillation has two phases— positive and negative. During the positive phase, bitterly cold weather remains confined to the Arctic region. However, when this pattern becomes negative, as in the present situation, a reversal of winds takes place and the cold travels southwards. These cold winds have now begun to enter the regions south of the Arctic, including India, resulting in a drop in temperature, they explained.
For a period during the 1970s to mid-1990s, the Arctic Oscillation was found to stay in its positive phase. However, since then it has again alternated between positive and negative, with a record negative phase in the winter of 2009-2010. In the current situation cold winds travelling from Europe and Russia via Afghanistan and Pakistan are making way to northern India. According to weather experts, this is resulting in such bouts of cold spells, in many parts of the country especially in North India.
According to weather scientists, this negative Arctic oscillation that began around a week back is likely to continue for some more time. The winter this year had been unusual, marked by warmer temperatures with few cold spells. In a normal winter, cold spells recur after every 10-15 days, beginning from December. However, this time, cold set in due to heightened activities of strong westerly winds.