在寒冷天氣下, 空氣較潮濕會否讓人感覺較冷, 還沒有明確結論. 唯一可以肯定的是風的效應最明顯, 因此我們常聽到的都是風寒效應和相關的指標(例如美國所採用的), 並沒有考慮空氣的濕度.
也的確有不少人指出空氣較潮濕可能令人感覺較冷, 其原因則眾說紛云, 有些純綷考慮人體和空氣之間的熱傳播, 亦有些是考慮衣服在潮濕環境下的保暖功能.
至於先前曾提及的 NET 指數, 是有考慮了濕度的作用. 但從下圖所見(取自天文台 r444), 濕度的影響亦不是很大. 例如當溫度為 10 度時, 在靜風下, 30% 和 90% 的 NET 數值看不到有何分別. 風大至 10 米秒時, 90% 的 NET 才比 30% 的 NET 低 3 至 4 度.
google 一下, 則找到約是 1 年前的網上討論, 個人認為頗具代表性:
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Environment Canada has studied this alleged effect. They have not been able to find an appreciable link between cooling rates (for humans exposed to the air) of relatively humid cold air and relatively dry cold air. There have been many supposed factors put forward in this forum that Environment Canada has ruled out as contributing to the phenomenon. First: evaporation is not a factor. Water vapour is already a gas; it doesn't need more energy to evaporate. Second: condensation is not a factor. The human skin surface is warmer than winter air, therefor water vapour will not condense on the skin. As for heat capacity, thermal conductivity etc., these are atmospheric variables that do change in different conditions. However, these variable have not been proven to account for the significant "wet cold" phenomenon many people claim to exist. So what causes it? So far, nothing has been proven, but there are a few good guesses that have been put forward.
1) In many areas during the winter, high humidity conditions often co-exist with some kind of precipitation. Any kind of liquid water (mist, fog whatever) coming in contact with the skin, in conjunction with cold temps is obviously going to feel cold. This is a no-brainer, but it is important to stress the different effects of water vapour and liquid water.
2) Probably most important: in the winter, high humidity almost always occurs during overcast conditions. Under heavy cloud cover, the earth's surface receives only diffuse sunlight. In these conditions, a person is not likely feel the radiant heat of the sun. Even in the winter and at high latitudes, direct sunlight can warm surfaces on which it shines. Even on the Canadian prairie, during a January cold snap, where temps can drop below -30 Celcius, finding a sunny spot out of the wind makes a big difference if you're trying to stay warm.
Also, keep in mind that there is no scientific measurement for the "wet cold" phenomenon. There is a measurement for low temps and high wind: the wind-chill effect. This is a predictable, observable phenomenon that both people and instruments can detect. There is also a measurement for high temps and high humidity: the humidex. Again, this is predictable and observable.
Canadians are weather fanatics, and to match their fervor, they have a government service (Environment Canada) that provides them with almost every possible weather fact observable. Canadians have been clamoring for a "wet cold" measurement, but Environment Canada can't find anything to give.
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就是說一些加拿大人都認為濕度越高, 天氣越凍, 但"加拿大環境局"並沒有找到任何關連, 並排除了一些民眾提出的原因. 即使"濕凍"存在, 也可能不是受空氣的濕度影響.
至於大風對室內氣溫的影響, 則又好像較少提及. 例如今天溫度上升了, 但留在室內好像也很冷, 是否偏東風下市區風速較大, 慘透入屋的能力較強? 又或者風較大容易將整棟大廈的熱帶走? 其實有個室內溫度計就會一清二楚了.
