!------------------------------------------------------------------------------ ! Module: modmet_constants ! Authors: Marte Voorneveld, RIVM ! Anton Beljaars, KNMI (source parameterization basis) ! Created: June 11 2026 ! Updated: June 11 2026 ! Description: ! This module defines physical and empirical constants used throughout ! the ModMet library. ! Constants and defaults follow the original KNMI routines that formed ! the basis of this package. !------------------------------------------------------------------------------ module modmet_constants implicit none (type, external) public ! Fundamental constants real, parameter :: VONK = 0.4 ! von Karman constant [-] real, parameter :: GRAVITY = 9.8 ! gravitational acceleration [m/s^2] real, parameter :: KELVIN_OFFSET = 273.15 ! offset to convert Celsius to Kelvin [K] real, parameter :: CP_AIR = 1005.0 ! Reference-state constants real, parameter :: TR = KELVIN_OFFSET + 9.85 ! reference temperature [K] (9.85 C) real, parameter :: PRESSURE_REF = 1005.0 ! reference pressure [hPa] real, parameter :: RO = PRESSURE_REF / (2.87 * TR) ! reference density [kg/m^3] ! Thermodynamic constants real, parameter :: LAMBDA = 2465.0 - 2.38 * (10.0 - 15.0) real, parameter :: GAMMA = CP_AIR / (LAMBDA * 0.622) ! psychrometric constant (K/hPa) ! Surface and scheme parameters real, parameter :: ALBEDO = 0.23 ! surface albedo [-] real, parameter :: D1 = 15.0 ! empirical night-scheme constant [-] real, parameter :: ALFA = 1.0 ! Priestley-Taylor day-scheme coefficient [-] real, parameter :: AG = 5.0 ! soil heat transfer coefficient real, parameter :: AL_VEG = 0.23 ! typical albedo for vegetation [-] ! Numerical constants real, parameter :: EPS = 1.0e-6 ! small number for numerical stability real, parameter :: PI = 3.14159265358979323846 real, parameter :: PI180 = 180.0 / PI ! degree/radian conversion factor angle / PI180 real, parameter :: PID2 = PI / 2.0 end module modmet_constants