[mpas-developers] updates to mpas_constants.F

[Michael Duda]

Hi, Folks.

As part of a merge of changes from the atmos_physics branch to the
trunk, I'd like to update the shared module mpas_constants.F to include
the gas constant for water vapor plus a derived parameter equal to
Rv/Rd.  Additionally, a couple of constants that were previously defined
explicitly are now defined in terms of other constants; specifically:

old code:
   real (kind=RKIND), parameter :: cv = 716.  ! cp - rgas
   real (kind=RKIND), parameter :: cvpm = -.71385842 ! -cv/cp

new code:
   real (kind=RKIND), parameter :: cv      = cp - rgas
   real (kind=RKIND), parameter :: cvpm    = -cv/cp

Finally, I've added some comments describing the constants. Attached is
the mpas_constants.F that I'm proposing to commit to the trunk. I
realize there's a potential debate here as to whether we shouldn't have
a core-specific constants module, but for now, I'd like to avoid that
and make a small update to what currently exists.

Unless there are any objections or suggestions for improvement, I'll
plan to commit the new mpas_constants.F tomorrow.

Thanks,
Michael
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module mpas_constants

   use mpas_kind_types

   real (kind=RKIND), parameter :: pii     = 3.141592653589793   ! Pi
   real (kind=RKIND), parameter :: a       = 6371229.0           ! spherical Earth radius [m]
   real (kind=RKIND), parameter :: omega   = 7.29212e-5          ! angular rotation rate of the Earth [s-1]
   real (kind=RKIND), parameter :: gravity = 9.80616             ! acceleration due to gravity [m s-2]
   real (kind=RKIND), parameter :: rgas    = 287.0               ! gas constant for dry air [J kg-1 K-1]
   real (kind=RKIND), parameter :: rv      = 461.6               ! gas constant for water vapor [J kg-1 K-1]
   real (kind=RKIND), parameter :: rvord   = rv/rgas             ! 
   real (kind=RKIND), parameter :: cp      = 1003.0              ! specific heat of dry air at constant pressure [J kg-1 K-1]
   real (kind=RKIND), parameter :: cv      = cp - rgas           ! specific heat of dry air at constant volume [J kg-1 K-1]
   real (kind=RKIND), parameter :: cvpm    = -cv/cp              !
   real (kind=RKIND), parameter :: prandtl = 1.0                 ! Prandtl number


   contains

   subroutine dummy()

   end subroutine dummy

end module mpas_constants