At a time when (extreme) temperature is a subject that goes far beyond elevator conversations, a debate arises time and again: how much can you trust the thermometers spread across urban roads?
This is because it is not uncommon to come across equipment that presents different temperatures, whether between digital clocks separated by a few blocks of distance, or by official measurement, published by the National Institute of Meteorology (Inmet).
The teacher Fernando Lang da Silveira from the Physics Institute of the Federal University of Rio Grande do Sul (UFRGS), explained how this equipment operates, and this already helps to answer.
“Air temperature measurements are made by meteorological stations, such as those from Inmet, which provide official data. These measures comply with a series of universally used criteria”, explains Lang.
He emphasizes that, for this, it is not enough to have good thermometers that are properly calibrated.
“As the objective is to measure air temperature, the thermometers must be in a meteorological shelter”, says the UFRGS professor. These shelters, in general, are white, “to minimize the absorption of thermal energy”.
They are also installed approximately 1.5 meters above the ground and have shutters, which allows natural air circulation inside, where the measuring equipment is located. All of this, as you can see, is very different from what we see in street thermometers.
According to Professor Lang da Silveira, street equipment has a thermocouple-type temperature sensor, “in which the temperature measurement is the result of an electrical signal coming from the sensor”, he explains.
And the caveat is: the sensors are accurate, but the temperature they capture is that of the sensor itself.
“At meteorological stations, thermometers are located in a special shelter, which aims to ensure that the temperature recorded is as close as possible to the temperature of the atmospheric air.”
“Two digital clocks in close proximity can provide very different temperature measurements. It is easy to imagine that if one is in the shade and the other under direct sunlight – or if one is in a more ventilated place than the other – they will register different temperatures”, says Lang.
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In short, street sensors capture “a ‘real’ temperature, but for the reasons stated above it is not a reliable measure of the atmospheric air temperature”, he says.
“Thermal sensation estimates involve factors other than temperature, such as relative humidity and wind speed.”
Source: CNN Brasil

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