Physical constants
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Overview
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)