In winter, the temperature experienced drops sharply when you are exposed to the wind compared to a place under shelter. An impression due to thermal convection, which also applies to the fan.
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The temperatures indicated in the bulletins weather report are considered sheltered, in the absence of wind and Sun. However, a real measured temperature of -5 ° C translates into a perceived temperature of -10 ° C with a wind of 20 km / h and down to -16 ° C for a wind of 60 km / h. This increased feeling of cold called “wind chill” is due to the Thermal transfer through convection. When you are outside in cold weather, an exchange of heat occurs between the skin surface and the thin layer ofair in contact with this surface. As your skin is around 35 ° C, it will heat the air around it. As the heat exchange is proportional to the temperature difference between the two bodies, the transfer becomes weaker and weaker as the air around the skin heats up.
The perceived temperature drops by several degrees in the presence of wind
But in the presence of wind, the air moves quickly so that the air warmed by the skin is constantly replaced by cold air. The skin thus releases a maximum of heat permanently, the temperature difference remaining significant. It’s exactly the principle of a fan, which continually moves the mass of air so that “new” cold air comes into contact with the skin.
More and more often, weather forecasts incorporate this notion of ” felt temperature »Taking into account the wind. There is nothing scientific about it, however; this is an estimate used especially in regions with a harsh climate to alert the public to preventive measures to be taken against damage caused by cold (frostbite, hypothermia …). Wind chill can be limited by wearing insulated clothing or multiple layers of clothing, which trap heated air and thus retain heat.
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