Physical constants

Physical Constants Available

This update was validated with 1-month benchmark simulation v11-01f and 1-year benchmark simulation v11-01f-geosfp-Run0. This version was approved on 16 Apr 2016.

In v11-01f, we made the following changes:

• Changed the name of the global physical parameter file from /Headers/CMN_GCTM_mod.F to /Headers/physconstants.F
• Updated all files in GeosCore to use physical parameters in /Headers/physconstants.F
• Added Boltzmann's constant and standard atmosphere to global physical parameters available
• Adjusted hard-coded physical parameter values in HEMCO to match global physical parameter values
• Adjusted molar gas constant value in /GeosUtil/henry_mod.F to match value in /Headers/physconstants.F
• Adjusted values of some global physical parameters to match NIST, 2014 values

Prior and updated values of global physical constants in /Headers/physconstants.F are listed in the table below. All values use flexible precision and are therefore double-precision unless compiling with single-precision enabled. Parameters in v11-01f that are different than in previous versions, either due to different values or because they were previously not included, are in bold.

Parameter	Description	Units	Prior to v11-01f	v11-01f	Source
Avogadro's Number	AVO	particles/mol	6.022e+23	6.022140857e+23	NIST, 2014
Acceleration due to gravity at earth's surface	g0	m/s2	9.8	9.80665	NIST, 2014
Pi	PI	unitless	3.14159265358979323	3.14159265358979323	legacy
Molar gas constant	RSTARG	J/K/mol	8.31450	8.3144598	NIST, 2014
Standard atmosphere	ATM	Pa	Not Included	101325	NIST, 2014
Boltzmann's constant	BOLTZ	J/K	Not Included	1.38064852e-23	NIST, 2014
Von Karman's constant	VON_KARMAN	Unitless	0.4	0.4	legacy
Radius of earth	Re	m	6.375e+6	6.375e+6	legacy
Dry air gas constant	Rd	J/K/kg	287.0	287.0	legacy
Water vapor gas constant	Rv	J/K/kg	Not Included	461.0	legacy
Molecular weight of dry air	AIRMW	g/mol	28.97	28.97	legacy
Molecular weight of water	H2OMW	g/mol	18.016	18.016	legacy
Scale height of the atmosphere	SCALE_HEIGHT	m	7600	7600	legacy
Molecules dry air per kg dry air	XNUMOLAIR	molecules/kg	AVO / 28.9644e-3	AVO / ( AIRMW * 1e-3 )	N/A
100 divided by acceleration due to gravity	g0_100	s2/m	100. / g0	100. / g0	legacy
Pi divided by 180	PI_180	unitless	PI / 180.	PI / 180.	legacy
Dry air gas constant divided by the acceleration due to gravity	Rdg0	J s2/K/kg/m	Rd / g0	Rd / g0	legacy

Important Notes:

• Physical parameters are still hard-coded in several places within HEMCO. Using a single set of global physical parameters in HEMCO will be in a future HEMCO version update.
• Values for pi and the radius of the earth are also defined in /GeosUtil/regrid_a2a_mod.F90 and values for the molar gas constant and standard atmosphere are also defined in /GeosUtil/henry_mod.F. These definitions remain so that the HEMCO standalone software has access to them. In the current version of HEMCO, the HEMCO standalone does not download /Headers/physconstants.F and therefore does not have access to global parameters defined in that file. This design may change in a future version.

--Lizzie Lundgren (talk) 20:44, 12 January 2016 (UTC)
--Bob Yantosca (talk) 15:34, 30 March 2016 (UTC)