WRF formulation of saturation vapor pressure

[yhwong]

Hello,

I am trying to figure out how WRF computes saturation vapor pressure (which is used to calculate relative humidity) but couldn't seem to find it in the WRF documentation. I read somewhere that the constants svp1, svp2 and svp3 in module_model_constants.F should be used for the computation of saturation vapor pressure (e_s). However, I am not sure how is the calculation actually done. My questions:

1. What are the constants svp1, svp2, and svp3?
2. How is saturation vapor pressure (e_s) calculation in WRF? Does it depend on the different schemes (e.g. microphysics scheme)?

Thank you very much for any insight you can provide!

 

[Ming Chen]

svp1, svp2 and svp3 are constants for saturation vapor pressure calculation. The first two variables are dimensionless and svp3 has the unit of K.

The algorithm to compute saturate water vapor pressure is

ES=svp1*exp(svp2*(T-svpt0)/(T-svp3))

Note that the value of svp1 can be specified to either 611.2 or 0.6112. The unit of ES will change accordingly.

 

[Jayanti pal]

What are those constants? are those available with model output? what is svp0?

 

[Ming Chen]

These are constant variables and they are not included in wrfout files.