Contact:  Bruce Wyman
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Change History: WebCVS Log

Constants are defined as real parameters, except for PI and RADIAN, which are calculated in constants_init to promote consistency and accuracy among various compilers.

Constants are accessed through the "use" statement.

fms_mod

constants_init:

Initialization routine. The purpose of this routine is initialize the value of PI and RADIAN, and to write the version and tag name information to the log file.

Name	Type	Value	Units	Description
RADIUS	real	6371.e3	m	radius of the earth
OMEGA	real	7.292e-5	1/s	rotation rate of the planet (earth)
GRAV	real	9.80	m/s^2	acceleration due to gravity
RDGAS	real	287.04	J/kg/deg	gas constant for dry air
KAPPA	real	2./7.	---	RDGAS / CP_AIR
CP_AIR	real	RDGAS/KAPPA	J/kg/deg	specific heat capacity of dry air at constant pressure
CP_OCEAN	real	3989.24495292815	J/kg/deg	specific heat capacity taken from McDougall (2002) "Potential Enthalpy ..."
RHO0	real	1.035e3	kg/m^3	average density of sea water
RHO0R	real	1.0/RHO0	m^3/kg	reciprocal of average density of sea water
RHO_CP	real	RHO0*CP_OCEAN	J/m^3/deg	(kg/m^3)*(cal/kg/deg C)(joules/cal) = (joules/m^3/deg C)
RVGAS	real	461.50	J/kg/deg	gas constant for water vapor
DENS_H2O	real	1000.	kg/m^3	density of liquid water
HLV	real	2.500e6	J/kg	latent heat of evaporation
HLF	real	3.34e5	J/kg	latent heat of fusion
HLS	real	2.834e6	J/kg	latent heat of sublimation
TFREEZE	real	273.16	degK	temp where fresh water freezes
WTMAIR	real	2.896440E+01	AMU	molecular weight of air
WTMH2O	real	1.801534E+01	AMU	molecular weight of water
WTMO3	real	47.99820E+01	AMU	molecular weight of ozone
DIFFAC	real	1.660000E+00	---	diffusivity factor
SECONDS_PER_DAY	real	8.640000E+04	seconds	seconds in a day
AVOGNO	real	6.023000E+23	atoms/mole	Avogadro's number
PSTD	real	1.013250E+06	dynes/cm^2	mean sea level pressure
PSTD_MKS	real	101325.0	Newtons/m^2	mean sea level pressure
REARTH	real	6.356766E+08	cm	radius of the earth
RADCON	real	((1.0E+02*GRAV)/(1.0E+04*CP_AIR))*SECONDS_PER_DAY	deg sec/(cm day)	factor used to convert flux divergence to heating rate in degrees per day
RADCON_MKS	real	(GRAV/CP_AIR)*SECONDS_PER_DAY	deg sec/(m day)	factor used to convert flux divergence to heating rate in degrees per day
O2MIXRAT	real	2.0953E-01	---	mixing ratio of molecular oxygen in air
RHOAIR	real	1.292269	kg/m^3	reference atmospheric density
ALOGMIN	real	-50.0	---	minimum value allowed as argument to log function
FREZDK	real	273.16	deg K	melting point of water
STEFAN	real	5.6734e-8	W/m^2/deg^4	Stefan-Boltzmann constant
VONKARM	real	0.40	---	Von Karman constant
PI	real	4.0*ATAN(1.0)	---	ratio of circle circumference to diameter
RADIAN	real	180.0/PI	---	degrees per radian
C2DBARS	real	1.e-4	dbars	converts rho*g*z (in mks) to dbars: 1dbar = 10^4 (kg/m^3)(m/s^2)m
KELVIN	real	273.15	---	degrees Kelvin at zero Celsius
EPSLN	real	1.0e-40	---	a small number to prevent divide by zero exceptions

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Constants have been declared as type REAL, PARAMETER.

The value a constant can not be changed in a users program. New constants can be defined in terms of values from the constants module using a parameter statement.<br><br>

The name given to a particular constant may be changed.<br><br>

Constants can be used on the right side on an assignment statement (their value can not be reassigned).

As PI is calculated, it cannot be a parameter variable. Do not assign a new value to PI.

EXAMPLE

    use constants_mod, only:  TFREEZE, grav_new => GRAV
    real, parameter :: grav_inv = 1.0 / grav_new
    tempc(:,:,:) = tempk(:,:,:) - TFREEZE
    geopotential(:,:) = height(:,:) * grav_new

1. Renaming of constants.

2. Additional constants.

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