This winter, in many parts of the region, maximum temperatures on some days have been nearly 10°C below normal.
What is a ‘cold day’?
A cold-day condition is said to prevail when the maximum temperature during the day is at least 4.5°C below normal. If the maximum temperature is at least 6.5°C below normal, it is classified as a “severe” cold day.
Why is it so cold this year?
- Low clouds – This extended cold spell has been triggered by Stratus clouds hanging low over a large geographical area stretching all the way from Pakistan to Bangladesh. The north-south width of the Stratus blanket is 500-800 km, affecting all of North India. The formation of such clouds are unique over the Indo-Gangetic Plains, and that these clouds have been observed only since 1997. As these clouds are formed at a height of 300 metres to 400 metres from the surface, they largely block the day’s sunlight, resulting in cold days.
- Western disturbances – Moderate to intense western disturbances, occurring frequently, have contributed to the severe cold over all of North India. Also, the flow of northwesterly winds over Northwest India, at a low height, has increased the chill factor, making days much colder than normal during December. Again, this December has witnessed haze, fog, and rainfall after the passing of each western disturbance, triggering cold weather conditions over large swathes of North India.
- Climate Change – . The unusually cold December this year could just be another instance of extreme climates becoming more frequent, a result of climate change. Across the world, the frequency and intensity of both heatwaves and cold waves have increased over the last several years, and are predicted to increase further. The same is the case with extreme rainfall and drought. This year, India experienced an unusually wet August and September. The amount of rainfall in September was a once-in-a-century event. Scientists say climate change is bringing in greater uncertainty in weather patterns, making them more difficult to predict.
Source – The Indian Express
QUESTION – Each passing winter is witnessing record breaking drops in temperatures of North-West India. Examine the ‘specific’ causes that led to such drastic drop in day-night temperatures in the recent winter season.