The Capital will have to bear the heat for some more days before it’s drenched in the rain. This year the Met Department has forecasted an above normal monsoon, which is expected to hit the capital between June end and the first week of July. The Met predictions almost always fit correctly while not many would know how and where this is actually done. Have you ever wondered how the temperature is measured and monitored in the city? The HT south Delhi team decided to visit one of the met department observatories in Safdarjung which generally remains busy during extreme weather conditions.
An iconic British-era building leads you into a well-ventilated large round lobby with heavy wooden doors and benches at the Safdarjung Airport terminal. The two-storey building is the Indian Meteorological Department’s surface observatory from where data for Delhi’s weather is collected. The building with high ceilings was the first Met office set up in the city during the British regime in the 1900s and continues to serve the purpose. The building is now maintained by the Airports Authority of India (AAI).
The entry to the building premises has a rectangular green patch, which houses the manual observatory with mercury thermometers set up inside wooden boxes to gauge the minimum and maximum temperatures and relative humidity levels. Over the years, automatic systems have come up with computer screens flashing the wind and cloud movements, however, the weathermen still rely on the manual mercury barometers for more accurate readings.
“For measuring temperature and rainfall, there are both manual and automatic systems. However, the manual readings are more accurate. This is because the automatic systems have a scope of error as it has bi-metals, which can contract and expand during different weather conditions,” said Group Captain R Vishen, Regional Meteorological Centre, IMD.
A cylindrical vessel with a funnel is the manual rain gauge while the electronic funnel is placed right next to it. Besides, one can spot a long rod with electronic censors fitted into it, called the Automatic Weather Station (AWS), which is connected to a satellite and flashes weather updates directly on the Met website.
“Decades ago, when there were no computers to make the long trigonometric equation calculations or study the wind movements on screen, all the work was done manually. We used to have long rolls of charts and maps with everyday readings with which the assessments were made for making the forecast. It used to be a cumbersome task and would take hours to collate data from all the regional centres across the country, which is now available at a click,” said Vishen.
The weather assessment and analysis, he said, is now done through numerical weather production systems. “Earlier, forecasting for the whole of northern India was done at Safdarjung. But with more technology and limited space for equipment, we shifted the rest of the systems to the IMD campus on Lodhi Road, while the manual observatory is still there from where forecast for city is done. There is another upper air observatory at Aya Nagar, to measure the upper winds,” said Anand K Sharma, deputy director general of meteorology, IMD.
Your daily Delhi weather forecast is done on the basis of the data collected from the Safdarjung observatory. The wind measuring mechanisms are placed atop the building, observations from which are taken to issue warnings about squalls or major weather disturbances, which may result in loss of life and property.
“The two most important readings for conducting the forecast are taken twice a day within a gap of twelve hours -- at 5.30 in the morning and at the same time in the evening,” said Ravindra Sethi, assistant meteorologist at Safdarjung.
During rainfall, observations from the rain gauge are noted at every hour and are reported every three hours to be updated to the regional centres. “My kids and even relatives keep asking me about how the weather is going to be for the day. If there is a thunderstorm or a squall taking shape, I inform them beforehand. We send instant updates on the IMD website and SMSes as well during such situations,” said Sethi, who has been with the Met department for over 25 years.
The building still has systems such as thermographs (gives the temperature for each time) and anemograph (to measure atmospheric pressure) connected to the rooftop systems, which are functional from the British rule, a metal chip inside reads : Made in London, 1930.
“Atmospheric pressure is the most important observation on the basis which the wind patterns, affecting the weather, are calculated. We have recently got installed digital barometers as well, but we also take readings from the manual thermographs every day, as there is a difference in accuracy in the digital systems. The old-time equipment is serviced every year,” added Sethi.