We explain what thermal sensation is and what factors influence it. In addition, we tell you how it is calculated and how it differs from temperature.
What is thermal sensation?
Thermal sensation or perceived temperature is the degree of cold or heat that the human body perceives in its environment, depending not only on the temperature recorded by the thermometer, but also on environmental factors such as wind speed or ambient humidity.
This perceived temperature or temperature perception is normally expressed in an index published by the meteorological services of each country, to warn citizens that there is a notable discrepancy between the official temperature and the one they will feel when they are outdoors. This index is usually expressed in the ordinary temperature measurement unit, either on the Celsius (°C) or Fahrenheit (°F) scale. In some English-speaking countries, the heat index is used for this purpose in summer and the wind chill in winter. You must read about Halloween once.
The concept of thermal sensation arose in the mid-twentieth century, during World War II, thanks to the experiences of the American explorers Paul A. Siple (1908-1968) and Charles Passel (1915-2002) in Antarctica, where they exposed different bottles of water to the environment and measured the time it took for the liquid to freeze, depending on atmospheric conditions and wind.
His findings on heat loss were used by the US Weather Service, and from there arose the first formula for calculating perceived temperature. From 1960 onwards this formula began to be used regularly in meteorological services around the world and in 2001 it was revised to formulate it again in a more precise way.
Difference between temperature and thermal sensation
In general, temperature is the degree of heat in the atmosphere at a place, which is measured objectively and generally, through the use of thermometers. Temperature depends on factors such as solar radiation and the conservation of atmospheric heat (for example, cloudy days are usually warmer, since there is more energy in the atmosphere).
However, the temperature of a region can be perceived in subjective ways depending on the specific meteorological conditions of each location. Thus, when the wind blows or the atmosphere is humid, the official temperature values can be very different from the degree of cold or heat perceived by people. This second environmental indicator is the thermal sensation or perceived temperature, and it has less to do with the state of the atmosphere, but with the distorting effect that certain meteorological phenomena have on the environment, making it feel colder or warmer than it really is.
Very simply put, temperature is the official degree of heat or cold in the atmosphere; while the thermal sensation is the degree of heat or cold that bodies will experience in said atmosphere due to certain meteorological factors. Maybe you should definitely read about Star of David once.
Factors that influence the thermal sensation
The thermal sensation can be conditioned by meteorological elements, and also by individual bodily factors, such as the metabolic rate of each individual. However, when it comes to proposing an index that is useful for all people, these latter factors are not very useful.
On the other hand, the perceived temperature depends on various factors in winter and summer. During the cold months, the degree of wind intensity is more relevant, which contributes to the decrease in the perceived temperature; In summer, the degree of atmospheric humidity is more important, since the high levels of energy in the atmosphere contribute to creating a stifling sensation.
However, when calculating the thermal sensation in summer, the action of the wind can also be taken into account, as it removes the layers of warm air and allows a greater flow of energy, dissipating the perceived heat.
How is wind chill calculated?
According to most meteorological services, wind chill or perceived temperature is calculated by applying a specific formula designed to reflect the human body’s perception of cold or heat. However, there is no universal formula and meteorological services use the formula that best suits the type of climate in their specific regions.
In the case of Canada and the United States, the calculation formula used during winter (Wind chill) is the following:
St = 13.12 + 0.6215 T – 11.37 V0.16 + 0.3965 V0.16
Where St represents the estimated wind chill, T the ambient temperature expressed in degrees Celsius (°C) and V the wind speed recorded by an anemometer located at a height of 10 meters and expressed in kilometers per hour (km/h).
The trend of these values is expressed in tables such as the following:
St = T + 5 [ (P – 10) / 9 ]
Where St represents the estimated thermal sensation, T the dry air temperature expressed in degrees Celsius (°C) and P the water vapor pressure produced by the ambient humidity, expressed in hectopascals (hPa) or the percentage of relative humidity (%).
