Physical constants

Prior and updated values of global physical constants used in GEOS-Chem are listed in the table below. These constants are located in the source code file Headers/physconstants.F90.

Physical Constants in GEOS-Chem

Parameter	Variable name	Units	Value
Avogadro’s Number	AVO	particles/mol	6.022140857e+23 [1]
Acceleration due to gravity at earth’s surface	g0	m/s2	9.80665 [1]
Pi	PI	unitless	3.14159265358979323 [2]
Molar gas constant	RSTARG	J/K/mol	8.3144598 [1]
Standard atmosphere	ATM	Pa	101325 [1]
Boltzmann’s constant	BOLTZ	J/K	1.38064852e-23 [1]
Von Karman’s constant	VON_KARMAN	unitless	0.4 [2]
Radius of earth	Re	m	6.375e+6 [2]
Dry air gas constant	Rd	J/K/kg	287.0 [2]
Water vapor gas constant	Rv	J/K/kg	461.0 [2]
Molecular weight of dry air	AIRMW	g/mol	28.97 [2]
Molecular weight of water	H2OMW	g/mol	18.016 [2]
Scale height of the atmosphere	SCALE_HEIGHT	m	7600 [2]
Molecules dry air per kg dry air	XNUMOLAIR	molecules/kg	AVO / (AIRMW * 1e-3) [2]
100 divided by acceleration due to gravity	g0_100	s2/m	100.0 / g0 [2]
Pi divided by 180	PI_180	unitless	PI / 180.0 [2]
Dry air gas constant divided by acceleration due to gravity	Rdg0	J s2/K/kg/m	Rd / g0 [2]

Notes

[1] (1,2,3,4,5)

Taken from NIST CODATA Fundamental Physical Constants (2014)

[2] (1,2,3,4,5,6,7,8,9,10,11,12)

Legacy usage in GEOS-Chem versions prior to v11-01