Winter is back, it is correspondingly cold. Tomorrow, Saturday, the breeze will also come, and with it, it will feel even colder. The wind chill factor comes into play. What's it all about?
Wind and temperature
The combination of wind and air temperature has a different influence on our well-being depending on the season. In the heat of summer, for example, the breeze is quite welcome in this country, as it makes high temperatures more bearable. Wind also increases the evaporation rate – and this not only for open water surfaces and the ground, but also for the human body. He regulates his temperature balance via his skin and sweating. What feels good in summer can turn into the opposite in winter at low temperatures! This is where the wind chill factor comes into play. It is an attempt to quantify the heat loss of the human body in different wind and temperature conditions. In 1941, polar explorers Paul Siple and Charles F. Passel were commissioned by the U.S. Armed Forces to conduct experiments in this regard. At first, these experiments had a laboratory character and were not very much oriented towards everyday human conditions. Over the years, these experiments and calculations were adapted, which made the matter even more complex in some cases.
In fact, the wind chill factor cannot be equated 1:1 with the perceived temperature, but it is a crucial part of it. It is an approximate measure of heat loss from human skin. In order to improve everyday use, it is given as a temperature value. When there is no wind or very little wind, a flat parcel of warmer and moistened air forms over the skin; this can be held in place by the body hair. As wind speed increases, this small layer of warm air is removed and the evaporation rate over the skin increases. This results in a cooling effect. So there is a difference between the real temperature measurement on a dry thermometer and the temperature felt by a person in reality. This difference increases with increasing wind speed.
Fig. 1: Increasing temperature difference with increasing wind speed ; Source: MeteoNews AG
The wind chill factor is defined only for temperatures below 10 degrees and wind speeds of 1.34 m/s and higher. In the meantime, good tables and calculation tools are available on the Internet that make this effect quantifiable. For example, an air temperature of 5 degrees at a wind speed of 50 km/h is perceived as -1 degree. But of course this does not mean that it is -1 degrees! There is still no frostbite (since the real temperature is positive), but very much hypothermia. With frosty temperatures and much wind then however also the danger of frostbite increases – this first at the places exposed to the wind such as the face (in particular noses, cheeks and ears). In the normal everyday life of a person in Switzerland, cold and wind are mostly only an unpleasant combination, one speaks then for example of a "biting" Bise. However, for people who work outdoors for longer periods of time, this already poses a considerable health risk and places increased demands on clothing. Not only thermal protection, but also wind protection is important!
Fig. 2: Wind chill effect, influence of the wind on the perceived temperature; Source: MeteoNews AG
It can become life-threatening in mountain sports, for example. With great effort and wet sweaty clothing, the reserves in case of an accident or sudden change of weather are not too large. The immediate priority here is protection from the wind, which is why a windproof jacket and a rescue blanket should always be carried. In trail running, this is even mandatory for competitions and is controlled accordingly.
Fig. 3: Sometimes life-saving in extreme situations - a rescue blanket; Source: free source
To stay with mountain sports: Here it also shows that the wind chill factor is only an approximation. In the calculations, sea level is assumed as the basis. With altitude, however, the air density decreases and with it its heat capacity, which reduces the effect. This is not taken into account. However, this is not supposed to be accurate to the decimal point anyway. The biggest variable in the resulting felt temperature is the human being anyway. A large overweight man with a lot of body fat will react differently than a lean high performance athlete or a small woman. Greasy body and face creams improve cold protection, and a beard also makes a difference.
So or so – who wants, can feel starting from tomorrow this effect at the own body more exactly on the tooth. The winter temperature level will be joined by the breeze. It will pick up during the day tomorrow and blow moderately in the afternoon with gusts of 30 to 40 km/h, at Lake Geneva it will even be strong with peaks of 50 to 60 km/h. With temperatures around freezing point, you'll want to find a sheltered corner!
