First, what is the apparent temperature (felt temperature)?
Before discussing the influence of wind speed on the felt temperature it would be useful to have a better understanding of what we are talking about, right? So let's start with an update on the weather. When we talk about air temperature or temperature under shelter, we are talking about the temperature measured with a thermometer or a probe placed 1.5 metres above the ground, inside an open-air shelter, well protected from the wind and the weather.
But the reality is often different, precisely because of the winds and the weather. On the one hand, the physiological perception of temperature varies from person to person, but on the other hand, it varies according to atmospheric conditions.
As you know, a dry, calm, and sunny 20 degrees does not feel at all the same as 20 degrees with strong wind and rain. The weather is important, especially in the United Kingdom where the climate is varied (but less so than in the northernmost regions of the world). With a strong northerly wind, the felt temperature changes dramatically!
The feeling of cold is therefore reinforced when the wind joins the party, even with the same temperature. The higher the wind speed, the greater the cooling.
Does wind speed affect the felt temperature?
So we've just answered that big question: yes, the felt temperature changes according to the wind's speed. Let's go into a little more detail about this weather phenomenon that occurs in the United Kingdom and around the world.
Besides, it doesn't matter which way the wind blows, it's the speed that counts.
The wind speed, therefore, changes the actual temperature, which is called the felt temperature. But this is a common term, the real name of this phenomenon is wind chill.
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What is wind chill?
More importantly, does wind chill have anything to do with wind turbines? Apart from the association with wind, not really…
The wind chill is the correct term, better known in popular parlance as the felt temperature. It is simply the sensation of cold that the wind causes on a living organism that radiates heat (like your body), while there is no change in the actual air temperature.
The principle is physical and rather simple, but not obvious: when there is no wind, a thin layer of warm air moistened by the body forms on the surface of the skin. But this small insulating protection is perpetually blown away when it's windy!
Without this layer, our skin is then directly in contact with colder and drier air.* The consequences? The skin gradually dries out as it warms the air to restore this balance… which immediately cools our body (this requires a lot of energy). So that's why, is the principle now clear to you? It's no coincidence that you feel cold when the wind starts to blow.
By now you know that wind chill has nothing to do with a wind turbine, but is the name given to the effect of the wind on the felt temperature. Is the direction of the wind as important as the wind speed?
And does the direction of the wind have an impact on the temperature in the United Kingdom?
It is common to hear that the north wind brings cold weather to the United Kingdom and other neighbouring countries. But is it true that winds coming from this direction cause the temperature, or at least the felt temperature, to drop?
As we have seen above, regardless of the direction of the wind, the wind (unless it is hot) lowers the apparent temperature compared to the "official" temperature. North winds, which are generally colder than other winds, have the effect of making this wind chill even colder. In the United Kingdom, this occurs often. But in Canada, for example, it's much worse because the temperature is lower in winter and the wind can blow very fast!
But the wind from another direction, from the east, west, or south, will also have a cooling effect. The only exception is when the wind temperature is higher than the air temperature.
How is wind chill measured?
Measuring the apparent temperature is not straightforward but it is possible to calculate wind chill. To do this, meteorologists have developed a wind chill index using an empirical mathematical relationship illustrated in the form of a table known to any good meteorologist.
This table takes into account two main variables, air temperature, and wind speed, precisely to evaluate the effects of the latter on the former.
This measure is mostly used in regions with a very harsh climate, such as Canada and in very northern locations, but it can also be applied in some places in the United Kingdom. It is important to know that the lower the temperature, the more the wind reinforces the feeling of cold.
The impact that wind has on temperature is measured with the wind index (again, nothing to do with a wind turbine), which is a number without units. Let's use an example: if the temperature is 0°C and the wind blows at 40 km/h, the wind chill index will be -6°C. In concrete terms, this means that the apparent temperature will be -6°C without wind.
You may have guessed it, but now you understand the principle: wind speed (no matter its direction) has a strong influence on the felt temperature of the human body. The stronger the wind, the colder it feels. So take into account how windy it is when thinking about what you should wear! And why not start measuring the weather data to make sure you don't make a mistake?
