Climate (once again), Humidity

Thu, 17 Nov 2005 14:35:52 PST
Humidity is expressed in many ways all of which refer to the amount of water vapor (a gas) in the air.  When the air becomes saturated, it means that it can hold no more of this gas and the excess will condense and coalesce against a solid object such as glass or leaves (the dew point) or become fog when suspended and eventually rain.  Relative humidity is the ratio of water vapor in the air to the amount of water vapor that would be needed for saturation.

Two independant factors determine the changes in relative humidity; temperature and available moisture.  When temperature rises, and the water vapor remains constant, the relative humidity drops.  If you come home to a cold, damp house and turn up the heat, you feel much more comfortable not only because of the temperature, but of the lower relative humidity.  The same "feel" occurs if at a constant temperature you change the humidity either up or down by removing or putting more water vapor into the air by misting or having a source of water available to evaporate.  When you take a hot shower, the temperature in the bathroom rises slightly, but the available water vapor goes sky high.

For those plants that require periods of dry weather, I have very little success due to my inability to lower the humidity as well as soil moisture adequately even when not exposed to rain (Ponerorchis).  Conversely, Crinums do beautifully as does Oxalis pes-caprae.  This is due to the ability or inability of plants with specific requirements to transpire their internal moisture content because of my high relative humidity.

Rodger was right when he described 95% relative humidity at 95F as a steambath, and to add to that I would say 99% relative humidity at 45F in San Francisco would be a fogbath and it is colder than a dog's nose in a snow storm!

Also, water vapor is a greenhouse gas adding to global warming.

Gary in Hilo, HI, where it is rains everyday, and in the winter it rains all day.  
23C/75F, relative humidity 80%, but the trade winds makes it comfortable.

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