Hyderabad: The hour just before the sunrise records the lowest temperature or is the coldest hour of the day, says the Weatherman. Post-sunset, the earth remains warm since it has received solar radiation throughout the day. Gradually it begins to radiate the energy back into the atmosphere. Once the energy is completely radiated, cool dry winds from the Himalayas blowing into Telangana bring the temperature to its lowest or minimum. For example, the coldest hour on Wednesday was recorded between 5.42 am and 6.42 am, before the sunrise.
“During the day, Sun’s rays hit the ground and the Earth receives solar energy. The opposite of this happens post-sunset. This phenomenon is called ‘longwave radiation’.
The earth vertically radiates energy passing through the different layers of the atmosphere.
The emission is a gradual process and takes hours to complete, while the cold and dry wind from north/north-easterly direction presently blowing over Hyderabad begins to flow in from early evening, giving a cooling effect, pointed out Y. K, Reddy, director of Indian Meteorological Depart-ment in Hyderabad.
Meanwhile, a cautionary note: The hotter the day, the cooler the night.
