Delhi and other parts of north India are bracing for near cold wave conditions
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Over the past two days, the minimum temperature has risen by close to four degrees, up to 10.4 degrees Celsius, but a forecast from the India Meteorological Department (IMD) shows it is expected to fall again.
After a brief rise in night time temperatures, Delhi is bracing for another phase of near cold wave conditions in the coming days.
The dip in temperature
- One of the main reasons is snowfall in high altitude areas north of Delhi, including places in Jammu and Kashmir, Himachal Pradesh, and Uttarakhand.
- Cold winds blowing from these areas lower temperature across northwest India every winter, including Delhi.
- Snowfall has occurred frequently in high altitude areas since November 15 this year, which explains the drop in minimum temperature in Delhi in the following days.
- This snowfall occurred under the influence of a Western Disturbance — an extra-tropical storm associated with rainfall, fog and snow in northern India — which also brought sudden showers and cloudy skies to Delhi on November 15.
- When skies are cloudy, there is comparatively less solar radiation during day time, which lowers maximum temperatures.
- This is also clear by the sudden three-degree drop in maximum temperature in Delhi on November 17 and 18, from 29.1 degrees Celsius to 26 degrees Celsius.
- However, cloudy skies increase the minimum or night time temperature as they hinder radiation from earth to the atmosphere at night.
- Clear skies have the opposite effect, which can be noted in the gradual reduction in minimum temperature recorded in Delhi after November 16 as the cloud cover moved away — from 16 degrees Celsius to 6.3 degrees Celsius on November 23, which was five degrees below normal for this time of the year.
- A cold wave is declared when there’s a significant drop in minimum or night time temperature.
- A reason behind this below-normal drop in temperatures is also explained by the climate pattern La Niña, which has developed this year, according to a statement issued by the World Meteorological Organisation (WMO) on October 29.
- The large-scale cooling of the ocean-surface temperatures in the central and eastern equatorial Pacific Ocean, coupled with changes in the tropical atmospheric circulation, namely winds, pressure and rainfall.