If you want to know whether (or weather, heh) it's comfortable or not to have a morning jog or go on a weekend hiking trip – stick with that term. The higher the dew point is, the more moisture that is in the air. Now that you know the formulas for dew point and humidity, you may wonder, what is the difference between those two terms?ĭew point is an accurate measurement of the moisture content in the air. It is merely the water content in the air, expressed in grams per cubic meter:Ībsolute humidity = m / V, where m is the mass of water vapor, and V is the volume of the air and water vapor mixture.įor saturated air at 30 ☌ (86 ☏), the absolute humidity in the atmosphere ranges from ~0 to 30 grams per cubic meter.ĭid you notice that the formulas don't take the temperature into consideration? To understand this definition, you also need to know the meaning of absolute humidity. Or, expressed differently, the relative humidity is the ratio of the water vapor pressure Pw to the saturation water vapor pressure Pws at the given temperature: relative_humidity = 100% × current absolute humidity / max absolute humidity, at current temperature.In other words, it's the amount of moisture in the air compared to what the air can maximally "hold" at that temperature: It is the ratio of the current absolute humidity to the maximum absolute humidity possible for the current temperature. This calculator strongly suggests me to replace the dew point with the dew point/frost point known parameter when I want to calculate the humidity for a dew point of -40.Relative humidity is expressed as a percentage. There is a number of dew point/humidity calculators, for example: Michell Humidity Calculator (this is one of the manufacturers of dew point sensors). Some other people can confuse these concepts. This is more correct, right? Is it necessary to edit the article, or in fact these two definitions do not contradict each other (and why, if so)? The frost point for a given parcel of air is always higher than the dew point, as breaking the stronger bonding between water molecules on the surface of ice compared to the surface of liquid water requires a higher temperature. The frost point is similar to the dew point in that it is the temperature to which a given parcel of humid air must be cooled, at constant atmospheric pressure, for water vapor to be deposited on a surface as ice crystals without undergoing the liquid phase (compare with sublimation). Am I right?Īt the end of the article, there is another definition that contradicts the previous one: In any case, I think this definition is not entirely correct, because the dew point is below frost point when the value is below zero. When the temperature is below the freezing point of water, the dew point is called the frost point, as frost is formed via deposition rather than condensation to form dew.ĭo I understand correctly that they are talking about the dew point temperature (which called frost point if it is below zero, regardless of the current real gas temperature), not about the real temperature of the gas at which this dew point is measured? The dew point is the temperature to which air must be cooled to become saturated with water vapor. Good day! I found the definition of dew point and frost point somewhat odd on wikipedia.
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