<p>It’s a set routine every morning at the Safdarjung Meteorological Office in south Delhi where assistant meteorologist Y N Prasad takes the temperature readings.<br /><br /></p>.<p>The maximum temperature is always recorded in the evening, at 4.30 pm, and the minimum in the morning, always at 6.20 am.<br /><br />Prasad explains why.<br /><br />“The maximum and minimum temperatures lies between radiation and re-radiation. When the sun gives out radiation to earth, it’s called solar radiation. When the earth emits heat, it is known as re-radiation.<br /><br />“When solar radiation is about to end and re-radiation is about to begin, then we get the maximum temperature at 4.30 pm. When solar radiation is about to begin and re-radiation is about to end, we get the minimum temperature at 6.20 am.”<br /><br />The thermometer is placed in the shade, away from direct sunlight. The box housing it is designed to ensure air gets to the thermometer.<br /><br />Humidity is calculated by the combination of two thermometers – dry thermometer and wet thermometer, explains Prasad.<br /><br />“Our centre also provides vital information to Safdarjung airport,” he says. <br /><br />Visibility information<br /><br />“Aviation requires weather forecast in loading and unloading the aircraft. Plus, the visibility information is very important.”<br /><br />“We have a ‘two-type barometer’ that gives QAP – the station-level pressure, which is required for landing of an aircraft – and after getting QAP we derive QNH, the mean sea level pressure, which is essential for take off,” he adds. <br /><br />“We have a digital barometer also and a self-recording instrument that catches any errors in the readings.”<br /><br />At Aya Nagar, the Met office floats a balloon which records the temperature and wind direction 16 km above ground. <br /><br />Prasad gives an equation from his 30-year experience. <br /><br />“If the humidity is high, the dew difference between yesterday and today is more. Then definitely there will be a change in weather.” He means it will turn worse.<br /></p>
<p>It’s a set routine every morning at the Safdarjung Meteorological Office in south Delhi where assistant meteorologist Y N Prasad takes the temperature readings.<br /><br /></p>.<p>The maximum temperature is always recorded in the evening, at 4.30 pm, and the minimum in the morning, always at 6.20 am.<br /><br />Prasad explains why.<br /><br />“The maximum and minimum temperatures lies between radiation and re-radiation. When the sun gives out radiation to earth, it’s called solar radiation. When the earth emits heat, it is known as re-radiation.<br /><br />“When solar radiation is about to end and re-radiation is about to begin, then we get the maximum temperature at 4.30 pm. When solar radiation is about to begin and re-radiation is about to end, we get the minimum temperature at 6.20 am.”<br /><br />The thermometer is placed in the shade, away from direct sunlight. The box housing it is designed to ensure air gets to the thermometer.<br /><br />Humidity is calculated by the combination of two thermometers – dry thermometer and wet thermometer, explains Prasad.<br /><br />“Our centre also provides vital information to Safdarjung airport,” he says. <br /><br />Visibility information<br /><br />“Aviation requires weather forecast in loading and unloading the aircraft. Plus, the visibility information is very important.”<br /><br />“We have a ‘two-type barometer’ that gives QAP – the station-level pressure, which is required for landing of an aircraft – and after getting QAP we derive QNH, the mean sea level pressure, which is essential for take off,” he adds. <br /><br />“We have a digital barometer also and a self-recording instrument that catches any errors in the readings.”<br /><br />At Aya Nagar, the Met office floats a balloon which records the temperature and wind direction 16 km above ground. <br /><br />Prasad gives an equation from his 30-year experience. <br /><br />“If the humidity is high, the dew difference between yesterday and today is more. Then definitely there will be a change in weather.” He means it will turn worse.<br /></p>
