What`s happening is that, when the sun comes out, water evaporates, driven by the sun`s heat. Also, the plants give off more water during the day than the night, due to their photosynthesis activity. As I recall from my South Georgia pulp & paper days, maybe those gigantic mosquitoes of yours stir it up, too. (They sure thrive in it!
At any rate, it`s a race between evaporation rate adding water to the atmosphere and the rising air temperature increasing the amount of water that it can hold.
Spoiler alert: For those brave souls who want to venture further, keep on reading. For most of us, this is a good stopping place.
I am attempting to attach an example of a "psychrometric chart"which can be found on the internet at (http://me.queensu.ca/Courses/MECH330/Ps ... ica_SI.pdf
) http://me.queensu.ca/Courses/MECH330/Ps ... ica_SI.pdf
This thing is a diagram of how much water vapor the air can hold at various temperatures. ...nightmarish, huh? This is what us old-timers used to use before computers took over the engineering calculations. (Slide rule, anyone?
) Anyway, the attachment display isn't large enough, so I suggest you download the thing and make it larger in your PDF reader.
Anyway, across the bottom horizontal axis is dry bulb temperature. Let`s say it`s 20 degC out there. If you go vertically along that 20 degree line (constant dry bulb temperature) until you hit the curve (where wet bulb and dry bulb temperature are the same
), that`s 100% humidity. If you haven`t gone cross-eyed yet, note that you can read off how much water is in the air by looking horizontally at the "Humidity Ratio" scale, which is grams of water per kilogram of dry air. This is the heart of the diagram. The rest is just window dressing but, like a well-dressed window display during the holiday season, gives you oh so much more.
Had enough, yet? Now, let`s try heating our 100% humidity saturated air with sunshine. If you could somehow not add any water, you would move horizontally to the right, and you can see that as the temperature goes up, you cross the relative humidity lines, meaning that the relative humidity goes down. We`re going horizontally, meaning that we`re not adding any water, but the ability of the air to hold more water goes up as the temperature increases (and as your eyes start to glaze over
But hang on! There`s nothing to stop pond water and tree water from evaporating and entering the air. Suppose that it`s plenty steamy and there`s plenty of sunshine, which reminds me of a morning in southeast Arkansas where I grew up. Yuk. If water can enter the air freely, meaning that plenty of heat is available, this time we`ll move up along the 100% relative humidity curve, that outer one to the left.
As you add heat (which is symbolized by the enthalpy scale on the far right, but that`s a fancy word, so let`s ignore that!
), temperature rises, as you can see by the (slanted downward to the right) temperature lines that you`re passing by as you go up along that saturation curve. Let`s suppose that the temperature rises to a steamy 25 degC at 100% humidity. The amount of water vapor, grams per kilo of dry air (scale on the right) has gone from about 15 to about 20 grams/kilo of dry air as the swamp water evaporates. (You can juggle the math to see how much heat you had to add to do that, but let`s not go overboard just yet.
Confused yet? But wait! There`s more! There`s reality, up there ahead, just around the bend. (...struggling sounds as guys in white coats enter, wrestle the Duck to the ground, and wrap him in a straight jacket.
) What actually happens is part way between the two cases of (1) temperature going up without adding water vapor, and (2) temperature staying constant with water vapor being (in this case) removed.
Somewhere in between lies "the truth," and it`s determined by how fast water can condense or evaporate, phase of moon and height of tide, and your mother-in-law`s... Well, you get it. The chart shows a static condition called equilibrium, but the real world is dynamic and never quite gets there. As they say on the X Files TV series, the truth is out there somewhere.... And I bet it`s mosquito infested, wherever it is.
Now, back to our regularly-scheduled... AWKKK! Hey! Don`t...
http://me.queensu.ca/Courses/MECH330/Ps ... ica_SI.pdf http://me.queensu.ca/Courses/MECH330/Ps ... ica_SI.pdf