Air is made up of various gases, including nitrogen, oxygen, and carbon dioxide. It also contains amounts of water vapor that are constantly changing due to the water cycle.
Absolute humidity is the mass of water vapor in a given volume of air, regardless of temperature.
Relative humidity is what appears in the daily weather forecast. Measures the concentration of water vapor in air as a percentage of the maximum it can contain at a given temperature and pressure.
In summer, when we talk about relative humidity, a 30°C day with 20% humidity wouldn’t be the same as a day with 90% humidity.
Moist heat can be unbearable, even dangerous. This is because the greater amount of water vapor present in hot air at higher humidity levels can make it difficult to dissipate excess body heat through sweating. Without this evaporation, you can get very hot very quickly.
The temperature makes a big difference
However, as the temperature decreases, the relationship between water vapor and relative humidity changes.
When the air has cooled enough and the relative humidity is 100%, condensation occurs, which is the process in which vapor turns into a liquid.
These water droplets form the clouds that we see and when the droplets are large and heavy enough, they fall as rain or snow.
So as the air cools, the relative humidity increases.
Therefore, 90% humidity at 25°C and 90% humidity at -10°C will be associated with different amounts of water.
At cold temperatures, even at high relative humidity, there will be much fewer grams of water per kilogram of air.
Therefore, in Canadian winters, the amount of water in a wet cold is exactly the same as in a dry cold.
David Phillips, a climate scientist at Environment and Climate Change Canada, explains that for every kilogram of air at roughly -20°C saturated, there will be only half a gram of extra water.
So there is very little difference, He said.
« So it is clear that if dry air is more comfortable than moist air, it cannot be due to moisture or water. »
There aren’t enough water molecules in this air to conduct heat away from your body, as you can see, it’s negligible., he adds.
This principle was tested and was the subject of a research article published in 1988 (A new window) From Defense Research and Development in Canada
The paper looked at a number of experiments conducted in the 1950s in which people in a laboratory environment were exposed to cold temperatures at different levels of relative humidity.
According to the report,
Researchers [n’ont] No significant difference was found in the physiological responses to high and low humidity.
But why does it feel different?
So, if this popular belief is a myth, why is a cold day on the east coast so cold when a day -30°C in the prairie is more likely?
There are other factors at play, not the humidity in the air. People’s individual tolerance and ability to keep themselves dry also plays a role.
This is why some people need to wear the hat at -2°C in Maritime, but those same people will not need to wear the hat in Edmonton until it reaches -10°C or -15°C.
The wind is sure to make a difference. Today, -15°C in Kingston, Ontario, with winds blowing at 50kph, will be just as cold as a calm day at -30°C in Edmonton or Regina.
The sunlight factor also plays a role, when the humidity is high, there are often more clouds than in a clear, cold winter in the prairie. Little sunshine warms us up a little.
Another factor is clothing. Winter fashion in the prairie tends to be a little different than in Toronto. Obviously, wearing a blazer in a blazer will keep us warmer than lighter clothing.
When it comes to clothing, David Phillips remembers that it’s essential to stay dry to keep warm.
With information from Kristi Klimenhaga.
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