Delhi registered an unprecedented 52.9 degrees Celsius on May 29, while Rajasthan's Churu hit a blistering 50.5 degrees Celsius in what's turning out to be one of the hottest summers for North India. But have you wondered how weather offices worldwide record minimum and maximum temperatures?
Reports of even higher temperatures often raise questions about the accuracy of official recordings.
How exactly these temperatures are measured
Radhey Shyam Sharma, the Director of the Jaipur Meteorological Centre, said that official temperature recordings are not surface temperatures but the air temperature 1.25 metres above the ground. This distinction is important. Surfaces, like sand or metal, can heat up more rapidly under direct sunlight, leading to higher readings than the actual air temperature.
“If we measure the temperature of any surface in the afternoon -- whether it be sand, any metallic body, the metallic part of a vehicle's body, or even of a road's surface-- the sunlight makes the temperature of these surfaces rise faster in the afternoon, and compared to the air temperature these (surface) temperatures will be reported higher,” Mr Sharma said.
How meteorological centres measure these temperatures accurately
They use four specialised thermometers kept in a wooden box (known as the Stevenson Screen), positioned about four feet above the ground.
The Stevenson screen is a white box with openings to let air flow through. These boxes are placed facing north, which helps us get the most accurate temperature readings without being affected too much by sunlight or shade. These thermometers are covered from direct sunlight to prevent external influences and to make sure the readings are precise.
Among the four thermometers, the dry bulb thermometer measures the ambient air temperature directly, while the wet bulb thermometer tracks relative humidity. One thermometer records the day's maximum temperature, while another records the minimum overnight temperature.
These practices are internationally accepted and followed by weather offices worldwide and data recorded using these specifications is considered authentic by weather scientists.