2. What is the wind chill effect?
The wind chill effect is often incorrectly equated with perceived temperature. Wind chill describes the sensation of cold and is therefore an element of the perceived temperature.
The wind chill effect describes the difference between the actual, measured temperature and how cold it feels, which is influenced by the cooling effect of the wind. As long as the air temperature is lower than our body temperature, a person will radiate heat. This means that the air around the skin warms up very slightly. We therefore have a warm layer of air on our skin’s surface that warms us up when temperatures are lower. When there is wind, however, this slightly warmer air is blown away. This speeds up the rate of evaporation from the skin. The body has to expend more energy for this, and there is a consequent loss of heat. The stronger the wind blows, the stronger this effect is and the more heat the body loses, thus making us feel cold.
In other words, the stronger the wind, the colder the same air temperature feels. This effect is called wind chill.
3. Quantification and calculation
The cooling effect on the skin caused by the wind can best be described in terms of temperature. This special temperature is called the “wind chill temperature” (WCT). The WCT is the air temperature that, in a standard environment (in shade and with slight air movement), would cause the same rate of heat loss per area of skin exposed to the wind as the actual air temperature would with the influence of the wind.
The definition of WCT was chosen for reasons of comprehensibility, as a temperature is better understood by the general public than a measurement in watts per square metre (in german), for example. It is therefore not a temperature in the true sense of the word, but a measure of the rate of heat loss that is simply expressed in units of temperature.
- Unlike perceived temperature (see above), the WCT does not take air humidity or radiation conditions into consideration.
- Moreover, it is only applicable to temperatures of 10 degrees or less – in other words, to temperatures lower than what we perceive as comfortable.
- WCT is also calculated on the basis of a number of assumptions that are not always true.
- For example, the altitude of the air is assumed to be at sea level. But in the mountains, the air is thinner, which means the heat loss and the wind chill effect are less.
- Additional influencing factors that affect how we perceive temperature (e.g. physical activity, clothing, body size and weight, etc.) are not taken into consideration.
Wind chill formula
WCT is calculated using the wind chill formula:
- W = 13.12 + 0.6215 * T – 11.37 * v 0.16 + 0.3965 * T * v0.16
- T= air temperature [°C], v= wind speed [km/h]
The table below contains several WCT calculations: