 "heatwave")
As the firm grip of sweltering heat grows across India, the Indian Meteorological Department's automatic weather station (AWS) is under scrutiny.
On Wednesday, the 52.9 degree Celsius recorded at Mungeshpur station in Delhi raised eyebrows. The IMD has sent a team to inspect the temperature sensor at Mungeshpur AWS to ensure it is functioning correctly. Similarly, the AWS in Nagpur recorded a whopping 56 degrees Celsius on Thursday.
Two of the four AWS set up by the India Meteorological Department (IMD) in Nagpur recorded unusually high temperatures, exceeding 50 degrees Celsius. The Nagpur AWS, located in the 24-hectare open agriculture field at PDKV in Ramdaspeth, off North Ambazari Road, recorded an astounding 56 degrees Celsius. The AWS at the Regional Meteorological Centre (RMC) in Sonegaon also recorded 54 degrees Celsius.
Meanwhile, the AWS in the fields of the Central Institute of Cotton Research (CICR) at Khapri, off Wardha Road, showed 44 degrees Celsius, and the Ramtek AWS recorded 44 degrees Celsius as well.
This has put the spotlight on automated weather stations.
What are Automatic Weather Stations?
Since its establishment in 1875, the IMD has been documenting various weather parameters such as air temperature, humidity, pressure, precipitation, and wind characteristics at traditional observatories. Currently, the IMD oversees a network of more than 550 surface observatories for weather prediction. Yet, this manual system falls short of providing continuous monitoring, especially for phenomena like cyclones and monsoons.
To address this limitation, the IMD has augmented its network with Automatic Weather Stations (AWS) to minimise human intervention. Starting in the summer of 2022, the IMD has deployed AWS at 15 new locations in Delhi and the NCR region, augmenting weather surveillance alongside the existing manual stations.
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According to data from the Ministry of Earth Sciences, there are presently 795 AWS operational nationwide.
How does the IMD's AWS measure temperature?
AWS automatically records ambient air temperature, relative humidity, precipitation, wind speed, and wind direction on an hourly basis. These stations autonomously collect and transmit weather data, reported in Indian Standard Time (IST) on a 24-hour scale. Ambient air temperature is gauged in degrees Celsius using an electrical resistance thermometer.
The AWS data is relayed to Pune data centre, where the codes are interpreted and uploaded on AWS/ARG Networks portal in real time.
What are the challenges associated with AWS measurements?
Meteorological authorities caution against relying on AWS data during periods of intense heat, as the sensors may malfunction beyond 38 degrees Celsius. AWS sensors are imported from European countries, where the temperatures don't rise as high as in Indian cities.
Beyond a certain temperature threshold, the accuracy of recordings becomes unreliable, exhibiting a positive bias. The expansion of essential elements should ideally follow a linear pattern, but this linearity is compromised at higher temperatures.
Experts also note that improper maintenance and placement of AWS units, such as installing them on rooftops or over concrete structures, can lead to erroneous readings from nearby topography and overheating.
What is the other heat measuring device?
Experts suggest that among the two methods, thermometer-based readings, conducted at locations like the Safdarjung observatory in Delhi, are more dependable due to the nature of the device.
The housing for the thermometer, such as the one at the Safdarjung observatory, is termed a "Stevenson Screen" - a wooden enclosure designed to shield meteorological instruments from precipitation and direct heat radiation while enabling free circulation of air around them.
Dry bulb and wet bulb thermometers within the "Stevenson Screen" are positioned vertically, while maximum and minimum thermometers are placed horizontally. The north-facing opening of the wooden box prevents direct sunlight exposure.
