What is apparent temperature?
Apparent temperature (wind chill) – determines the condition that the thermal sensation will occur under given weather conditions, or simply the difference between the air temperature and the temperature sensation.
Several factors such as air temperature, wind force, humidity and rainfall can affect the feeling of temperature.
The main factor influencing the feeling of temperature is wind.
Each of us has experienced a situation where, for example, in winter, being too warmly dressed, additionally making some effort, sweating. Then a gust of wind was enough to intensify the feeling of chill. This sensation cannot be taken lightly as it can lead to hypothermia and even frostbite.
Wind, whether it's a gale or just a draft, removes warm air from the surface of the skin, allowing for better cooling through evaporation when sweating.
The feeling of temperature has more to do with heat loss than with the actual air temperature. The heat loss factor is defined as the perceived temperature really only for the sake of simplicity.
Such an approach, however, may lead to mistakes, for example in the preparation of appropriate clothes during, for example, a trip to the mountains. For example: the air temperature is 5 ° C and the wind speed is 50 km / h, then the cooling temperature will be -1°C. However, due to the higher ambient temperature, this will not lead to frostbite.
Temperature sensation is also a very subjective value, influenced by many different factors such as body hair, warming fluids and of course individual natural regulation of body temperature.
However, research has shown that we can predict the effect of wind on perceived temperature
Curiosity
The concept of perceived temperature was first introduced by Paul Allman Siple and Charles Passel in the 1940s. It was the result of their observation regarding the freezing of water in the vessel during scientific research in Antarctica. This observation showed that the time after which the water froze depended on its initial temperature, ambient temperature and wind speed.
How to calculate the perceived temperature?
Like most factors influencing modern life, we can present the temperature and temperature sensation using formulas resulting from empirical research. However, none of them gives satisfactory results in the whole range of variability of atmospheric conditions.
In our calculator we used the most popular formula
$$ T_{wc}=13,12+0,6215\cdot T_{a}-11,37\cdot v^{0,16}+0,3965 \cdot T_{a}\cdot v^{0,16}$$
where:
Twc - wind chill temperature
Ta - air temperature in degrees Celsius,
v - wind speed in km/h
However, even this formula also does not apply in all conditions, because e.g. when the wind speed is below 1.34 m/s, it would lead to the calculation of a positive temperature sensation coefficient. This is due to the insulating effect of the air layer on the skin, which remains warm under constant conditions and does not cool down. This means that this formula and others only become applicable at wind speeds above 5 km/h.