Updates to VPD calculation

[yixin98]

Description

Updates to function vpdefil: use different functions to calculate saturation vapor pressure for ice VS liquid. The old scripts always use ice saturation vapor pressure, and this will introduce errors in the calculation of VPD.

Types of changes

• Hot fix (emergential bug fix to make ED2 run again)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Other (fix or feature that would cause existing functionality to change)

Testing :

• All new and existing tests passed.

[mpaiao]

Thanks for catching this @yixin98!

[xiangtaoxu]

Thanks, Yixin. @mpaiao do we know how old is this bug? I wonder how much it might have amplified midday suppression in previous simulations...

[mpaiao]

It is probably very old @xiangtaoxu, but as far as I remember, vpd is a purely diagnostic variable in ED2. The only reason I added it was because we cannot back calculate average VPD from the other averaged variables, as the relation between VPD and other variables is very non-linear.

[xiangtaoxu]

Ah. That's right. Good to know!