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I measured the barometric pressure over 4 days and I obtained the next image: enter image description here

The Y axis is the pressure in hPa and the X axis is the time (4 days)

I think it is very interesting the fact that the boiling and freezing temperature of water change periodically due these barometric pressure changes. This is according to Water's Phase Diagram:

enter image description here

So, I was thinking to make a plot of how the boiling and freezing temperature of water change over the day, but I don't know how to describe those red lines as a function of temperature with respect pressure. The freezing red line could be described as a simple linear function but I don't know about the boiling red line .. Should I use Interpolation? Even so, do you know any reference with a table of Water's Phase Diagram?

Also, maybe this should be another question .. But, why the barometric pressure oscillates in that way?

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    $\begingroup$ The changes in pressure you are seeing are not very big (supported by our general experience that the boiling and freezing point of water do not change much over the course of a day), so I expect that a linear approximation will work just fine for both curves $\endgroup$ – By Symmetry Oct 2 at 12:53
  • $\begingroup$ @BySymmetry - depends how big a mountain you drive up during the day! $\endgroup$ – Jon Custer Oct 2 at 13:11
  • $\begingroup$ The vapor pressure of water as a function of saturation temperature and pressure are found in the steam tables. However, the Clausius-Clapeyron equation for water should be adequate for these purposes. For melting, the melting temperature is very insensitive to pressure. It only changes by 0.01 C over a pressure change of about 1 bar. $\endgroup$ – Chet Miller Oct 2 at 14:25
  • $\begingroup$ Atmospheric tides driven by differential solar heating of the air cause those oscillations. $\endgroup$ – Ben51 Oct 2 at 15:22
  • $\begingroup$ Yes, but I don't understand why atmospheric tides goes up, then goes down just a little, then up again, and then goes down .. and specifically in those hours .. I mean, is not like temperature .. $\endgroup$ – Delfin Oct 2 at 20:40

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