Physical constants

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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)