Difference between revisions of "Physical constants"

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= Global Physical Constants in GEOS-Chem =
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== Overview ==
  
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In GEOS-Chem v10-01 and prior versions, physical parameters (e.g. pi) were defined in multiple locations within GEOS-Chem. In some cases, the parameters were defined with different values or precisions. In an effort to improve accuracy, consistency, and transparency within GEOS-Chem, the GEOS-Chem Support Team is working towards implementing usage of a single set of global parameters everywhere. Updates made per version, starting with v11-01f, are described on this wiki page.
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<span style="color:green">'''''This update was validated with [[GEOS-Chem_v11-01_benchmark_history#v11-01f|1-month benchmark simulation v11-01f]] and [[GEOS-Chem_v11-01_benchmark_history#v11-01f-geosfp-Run0|1-year benchmark simulation v11-01f-geosfp-Run0]]. This version was approved on 16 Apr 2016.'''''</span>
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== For Developers ==
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For v11-01e and prior versions, global constants are stored in <tt>/Headers/CMN_GCTM_mod.F</tt>. For v11-01f and later versions, global constants are stored in <tt>/Headers/physconstants.F</tt>. A complete list of parameters in both files are in the next section of this wiki page.
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We encourage developers to take advantage of the physical parameters available by including the following use statements in routines or modules:
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*v11-01e and prior versions: '''USE CMN_GCTM_MOD'''
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*v11-01f and later versions: '''USE PHYSCONSTANTS'''
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== Physical Constants Available ==
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<span style="color:orange">'''''This update will be validated with [[GEOS-Chem_v11-01_benchmark_history#v11-01f|1-month benchmark simulation v11-01f]]</span>
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In v11-01f, we made the following changes:
 
In v11-01f, we made the following changes:
 
*Changed the name of the global physical parameter file from <tt>/Headers/CMN_GCTM_mod.F</tt> to <tt>/Headers/physconstants.F</tt>
 
*Changed the name of the global physical parameter file from <tt>/Headers/CMN_GCTM_mod.F</tt> to <tt>/Headers/physconstants.F</tt>
 
*Updated all files in <tt>GeosCore</tt> to use physical parameters in <tt>/Headers/physconstants.F</tt>
 
*Updated all files in <tt>GeosCore</tt> to use physical parameters in <tt>/Headers/physconstants.F</tt>
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*Added Boltzmann's constant and standard atmosphere to <tt>/Headers/physconstants.F</tt>
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*Added Boltzmann's constant and standard atmosphere to global physical parameters available
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*Adjusted physical parameter values in HEMCO to use values matching those in <tt>/Headers/physconstants.F</tt>
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*Adjusted hard-coded physical parameter values in HEMCO to match global physical parameter values  
 
*Adjusted molar gas constant value in <tt>/GeosUtil/henry_mod.F</tt> to match value in <tt>/Headers/physconstants.F</tt>
 
*Adjusted molar gas constant value in <tt>/GeosUtil/henry_mod.F</tt> to match value in <tt>/Headers/physconstants.F</tt>
 
*Adjusted values of some global physical parameters to match [http://physics.nist.gov/cuu/Constants/bibliography.html NIST, 2014] values
 
*Adjusted values of some global physical parameters to match [http://physics.nist.gov/cuu/Constants/bibliography.html NIST, 2014] values
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|Not Included
 
|Not Included
 
|'''461.0'''
 
|'''461.0'''
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|legacy (<tt>comode_loop_mod.F</tt>)
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|legacy
  
 
|-valign="top"
 
|-valign="top"
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|molecules/kg
 
|molecules/kg
 
|AVO / 28.9644e-3
 
|AVO / 28.9644e-3
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|'''AVO / AIRMW'''
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|'''AVO / ( AIRMW * 1e-3 )'''
 
|N/A
 
|N/A
  
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|100 divided by acceleration due to gravity
 
|100 divided by acceleration due to gravity
 
|g0_100
 
|g0_100
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|s<sup>2/m
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|s<sup>2</sup>/m
 
|100. / g0
 
|100. / g0
 
|100. / g0
 
|100. / g0
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|Dry air gas constant divided by the acceleration due to gravity
 
|Dry air gas constant divided by the acceleration due to gravity
 
|Rdg0
 
|Rdg0
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|J s<sup>/K/kg/m
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|J s<sup>2</sup>/K/kg/m
 
|Rd / g0
 
|Rd / g0
 
|Rd / g0
 
|Rd / g0
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*Values for pi and the radius of the earth are also defined in <tt>/GeosUtil/regrid_a2a_mod.F90</tt> and values for the molar gas constant and standard atmosphere are also defined in <tt>/GeosUtil/henry_mod.F</tt>. 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 <tt>/Headers/physconstants.F</tt> and therefore does not have access to global parameters defined in that file. This design may change in a future version.
 
*Values for pi and the radius of the earth are also defined in <tt>/GeosUtil/regrid_a2a_mod.F90</tt> and values for the molar gas constant and standard atmosphere are also defined in <tt>/GeosUtil/henry_mod.F</tt>. 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 <tt>/Headers/physconstants.F</tt> and therefore does not have access to global parameters defined in that file. This design may change in a future version.
  
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--[[User:Lizzie Lundgren|Lizzie Lundgren]] ([[User talk:Lizzie Lundgren|talk]]) 20:44, 12 January 2016 (UTC)
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--[[User:Lizzie Lundgren|Lizzie Lundgren]] ([[User talk:Lizzie Lundgren|talk]]) 20:44, 12 January 2016 (UTC)<br>--[[User:Bmy|Bob Yantosca]] ([[User talk:Bmy|talk]]) 15:34, 30 March 2016 (UTC)

Latest revision as of 20:12, 13 July 2023

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)

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