The ET measurement from local PWS, such as in my case a Tempest, seems to not have a cap on how high the Solar Radiation measurements affect the et calculation.
How I arrived at this suspicion of a bug? I did a hard reset on my Tempest components. My Tempest typically will read ultra high measurements on the first day but will calibrate itself within a day or so. I think this is a known phenomena. Here is an example on the daily measurement.
This sensor measurement seems to affect the ET shown here:
I was able to reproduce, closely that number. The issue is, not sure if this is by design or a development decision, that the solar radiation measurement isn’t being so called “clamped”.
Technically, and please feel free to correct, solar radiation cannot go above what is called a full clear sky day. To be formal, can’t go above Equation 36 in the FAO56 paper (unless probably there is some extreme space weather event). Therefore, some sort of checking of this needs to happen.
How I reproduce this is that I have my own local version of the calculation based on the FAO paper in Python. The way I clamp is through the following snippit:
With the particular day with the high solar radiation reading, if I switch the r_s with max instead of min, I will be able to reproduce the high Et reading, not exactly though but close.
This is unusual but still in my opinion a potential bug.