! This code is part of RRTM for GCM Applications - Parallel (RRTMGP)
!
! Contacts: Robert Pincus and Eli Mlawer
! email: rrtmgp@aer.com
!
! Copyright 2015-, Atmospheric and Environmental Research,
! Regents of the University of Colorado, Trustees of Columbia University. All right reserved.
!
! Use and duplication is permitted under the terms of the
! BSD 3-clause license, see http://opensource.org/licenses/BSD-3-Clause
! -------------------------------------------------------------------------------------------------
!> ## Physical and mathematical constants used in RRTMGP gas optics calculation
!>
!> If the host model in which RRTGMP is embedded has defined these constants elsewhere
!> the model definitions can be used instead by renaming. For example,
!> ```use mo_model_constants, only k_boltz => boltzman_k, ...```
!> where the syntax is local_name => original_name
!> and all the local names need to be defined
!
!> "Constants" specific to the earth's atmosphere should also be made consistent with the
!> host model but may be changed in a call to init_constants(), normally at initialization
! -------------------------------------------------------------------------------------------------
module mo_gas_optics_constants
use mo_rte_kind, only: wp
public
! -----------------------------------------
! Physical constants, 2018 SI defintion of metric system
! doi:10.1088/1681-7575/aa950a (see also https://www.nist.gov/si-redefinition/meet-constants)
! Boltzmann constant [J/K] = [(kg m^2)/(K s^2)]
real(wp), parameter :: k_boltz = 1.380649e-23_wp
! molecular weight of water [kg/mol]
real(wp), parameter :: m_h2o = 0.018016_wp
! Avogadro's number [molec/mol]
real(wp), parameter :: avogad = 6.02214076e23_wp
! Universal gas constant [J/(mol K)]
real(wp), parameter :: R_univ_gconst = avogad * k_boltz
! -----------------------------------------
!
! Constants specific to the earth's atmosphere -- changeable in init() because they
! might be different on e.g. other planets
! molecular weight of dry air [kg/mol]
real(wp), protected :: m_dry = 0.028964_wp
! Gravity at Earth's surface [m/s2]
real(wp), protected :: grav = 9.80665_wp
! Specific heat at constant pressure for dry air [J/(K kg)]
real(wp), protected :: cp_dry = 1004.64_wp
contains
! -----------------------------------------
subroutine init_constants(gravity, mol_weight_dry_air, heat_capacity_dry_air)
real(wp), optional, intent(in) :: gravity, mol_weight_dry_air, heat_capacity_dry_air
!! Planetary and atmospheric values used by RRTMGP in computing gas optical properties
!! Default values reflect modern Earth but these can be changed using this routine
if(present(gravity)) grav = gravity
if(present(mol_weight_dry_air)) m_dry = mol_weight_dry_air
if(present(heat_capacity_dry_air)) cp_dry = heat_capacity_dry_air
end subroutine init_constants
! -----------------------------------------
end module mo_gas_optics_constants
