Finding vapor pressure deficit at leaf surface and leaf net photosynthesis

[nick]

Hi, I want to write out VPD at leaf surface and leaf net photosynthesis. Specifically D and An in equation 9.1 of the tech note:

I see part of this equation getting solved at line 4135 if PhotosynthesisMod.F90 where there is a sunlit version of An being used, but I don't see D. Could someone point me to where this is being calculated or used? I assume I could derive D from esat_tv and eair used in this module, but want to be sure.

Thanks.

 

[nick]

Ok I figured this out. I didn't look at section 9.6 on the numerical implementation of the above equation 9.1 as a quadratic. And I see D=(ei - ea)/1000 and when using the Medlyn model, in the code this is rh_can = max((esat_tv(p) - ceair), 50._r8) * 0.001_r8
whereas for Ball-Berry this is rh_can = ceair / esat_tv(p)