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Miscellaneous Debris => Weather sensors, design, analysis, discussion, home brew => Tech Corner => Humidity => Topic started by: SLOweather on March 22, 2016, 02:09:30 PM
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For my weather station project, I've been looking for the equation for this and found several references. Here's one:
From http://maxwellsci.com/print/rjaset/v6-2984-2987.pdf
(http://www.sloweather.com/blog/2016/160322rh1.jpg)
the expanded formula containing all of the intermediate equations is:
(http://www.sloweather.com/blog/2016/160322rh2.jpg)
For the intermediate stuff, see the source PDF.
That will be fun to program!
Interestingly, a lot of sources use the mean barometric pressure of 1013.25024 mb instead of the current local reading. I think I'll build that equation in Excel and then see how much difference the BP makes.
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Interestingly, a lot of sources use the mean barometric pressure of 1013.25024 mb instead of the current local reading. I think I'll build that equation in Excel and then see how much difference the BP makes.
Also, might the pressure be "absolute" rather than a sea-level pressure?
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Also, might the pressure be "absolute" rather than a sea-level pressure?
The reference cited says:
When P is the mean atmospheric pressure (assumed to be 1013.25024 mb)...
Emphasis mine... I have seen other references with the same assumption, including one, I believe, from the NWS.
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I think what they're doing there with that assumption is to reduce it down to a simpler calculation.
In physics the absolute pressure at the location would be used, but perhaps it doesn't make much difference in the meteorological world.