In the early days of 2023, Delhi and other parts of northwest India found themselves amidst a severe cold wave. With temperatures plummeting to a chilling record of 1.9 degrees Celsius on January 8th, it marks the second-lowest minimum temperature noted in January over the past 15 years. The region experienced harsh cold day conditions induced by fog and low cloud cover, where temperatures remained considerably lower than normal in areas like Delhi, Punjab, Haryana, Chandigarh, Himachal Pradesh, Rajasthan, Uttar Pradesh and Madhya Pradesh.
What is Triggering this Cold Wave?
The cold wave that gripped north India can be attributed to a combination of various factors. According to the India Meteorological Department (IMD), the large-scale fog cover prevalent over the region was one of the primary reasons for colder than average temperatures in January 2023. Not only did the fog last for extended durations but it also obstructed sunlight from reaching the Earth’s surface, thereby altering the radiation balance.
Foggy Mornings and Nights
Although foggy or cloudy nights usually result in warmer weather conditions, continual fog persistence for two to three days led to cooling even at night. Factors such as light winds and high moisture content near the land surface contribute towards forming a dense layer of fog over substantial portions of the Indo-Gangetic plains in the morning.
The Influence of Westerly Winds
The absence of any significant impact of western disturbances in the region gave rise to cold northwesterly winds that further contributed to the reduction in temperatures. Westerly and northwesterly winds with speeds ranging from 5 to 10 kmph in the afternoons have also been a notable factor in the temperature drop.
Understanding a Cold Wave
A cold wave can be defined as a sudden decrease in temperature within a 24-hour period that demands significantly enhanced protection for agriculture, industry, commerce, and social activities. In the context of plains, a cold wave announcement is made when the minimum temperature drops to 10 degrees Celsius or below, and falls by 4.5 degrees Celsius or more than normal for two consecutive days.
India’s Core Cold Wave Zone
The ‘core cold wave zone’ in India comprises Punjab, Himachal Pradesh, Uttarakhand, Delhi, Haryana, Rajasthan, Uttar Pradesh, Gujarat, Madhya Pradesh, Chhattisgarh, Bihar, Jharkhand, West Bengal, Odisha, and Telangana.
Causes of Cold Wave in India
A cold wave can occur due to several reasons such as the absence of cloud cover in the region that traps outgoing infrared radiation. Another cause is snowfall in the upper Himalayas, which results in blowing cold winds towards the region.
About the India Meteorological Department
Founded in 1875, the India Meteorological Department (IMD) falls under the jurisdiction of the Ministry of Earth Sciences of the Government of India. The primary responsibility of IMD lies in meteorological observations, weather forecasting, and seismology.