GEOS-Chem species units
- Species in GEOS-Chem
- Physical properties of GEOS-Chem species
- GEOS-Chem species database
- GEOS-Chem species units
- Adding passive species to GEOS-Chem
- Species indexing in GEOS-Chem
In GEOS-Chem v10-01 and prior versions, GEOS-Chem tracer units are converted between molar mixing ratio and mass per grid box. The conversion between tracer v/v and kg requires grid area which is incompatible with grid-independent high-performance GEOS-Chem. Furthermore, the switch between units is confusing and inconsistently documented. In order to achieve grid-independence and to bring greater clarity to GEOS-Chem, the GEOS-Chem Support Team is working towards implementing consistent area-independent tracer units throughout the model beginning in GEOS-Chem v11-01.
It is important to note a terminology shift with regards to tracers and species starting in GEOS-Chem v11-01. Tracers are referred to as species starting in v11-01g. Prior to GEOS-Chem v11-01, species are stored separately from tracers in fixed units of molecular number density. Starting with v11-01, species and tracers and stored together and therefore all species, advected and not advected, are subject to the new units described in this page.
Our goals are as follows:
- Use mass mixing ratio throughout GEOS-Chem with minimal exceptions
- Remove all uses of kg tracer per grid box
- Remove all uses of grid box area
Because this project touches nearly all parts of GEOS-Chem and is being conducted concurrently with several other development projects, we are working towards these goals in distinct phases.
GEOS-Chem v11-01 and later versions
|Phase 1||v11-01e||Implement area-independent species units
||Approved 04 Jan 2016|
|Phase 2||TBD||Remove area-dependent units in chemistry and diagnostics||On hold until implementation of FlexChem|
|Phase 3||TBD||Remove area-dependent species units remaining in specialty simulations||TBD pending input from 3rd party developers
|Phase 4||TBD||Remove remaining area dependencies, including use of:
Comparison of v10-01 and v11-01
The table below details the v10-01 tracer concentration units versus v11-01 species concentration units in GEOS-Chem along with work status per GEOS-Chem component. Note that in <codeR>v11-01</tt>, unlike in GEOS-Chem v10-01 and prior versions, there are multiple forms of mixing ratio used: dry mass mixing ratio, dry molar mixing ratio, and tracer mass per unit area. GEOS-Chem components that still rely on area-dependent units are in bold.
Terminology note: What we used to call tracers in v10-01 are now referred to as advected species in v11-01 and higher versions.
|Component||v10-01 tracer units||v11-01 species units||Status||Notes|
|Restart files||v/v||v/v dry||Unit update complete|
|GEOS-Chem initialization||kg||kg/kg dry||Unit update complete|
|AIRQNT and SET_H2O_TRAC||kg||kg/kg dry||Unit update complete|
|Two-way nesting||kg||kg||Unit change requires 3rd party developer input|
|Transport||v/v||kg/kg dry||Unit update complete|
|Wet scavenging initialization||v/v||kg/kg dry||Unit update complete|
|Dry deposition||kg||kg/kg dry||Unit update complete|
|HEMCO||kg||kg/kg dry||Unit update complete|
|Mercury emissions||kg||kg||Unit change requires 3rd party developer input|
|Mixing||v/v, kg||v/v dry, kg/m2||Unit update complete|
|Convection||v/v||kg/kg dry||Unit update complete|
|Chemistry||v/v, kg||v/v, kg||Unit change pending FlexChem implementation||Includes all routines called within DO_CHEMISTRY.|
|Wet deposition||kg||kg/m2||Unit update complete|
|TOMAS aerosol microphysics||kg||kg||Unit change requires 3rd party developer input||Collaboration with TOMAS team in progress.|
|Recompute AOD||kg||kg||Unit change pending FlexChem implementation|
|Radiative transfer||kg||kg||Unit change requires 3rd party developer input|
Unit Conversion Locations
v10-01 and prior versions
The table below lists all major instances of tracer concentration unit conversions in GEOS-Chem v10-01 and prior versions. In the table, the symbol -> indicates a one-way conversion while the symbol <-> indicates a local two-way conversion.
|Input||v/v -> kg||copy_STT||restart_mod.F||Convert to kg for initialization after reading v/v from restart file|
|Main||kg -> v/v||--||main.F||Convert to v/v for transport, air quantity update, and wet scavenging initialization|
|Main||v/v -> kg||--||main.F||Convert to kg for dry deposition and phase 2 emissions|
|Main||kg -> v/v||--||main.F||Convert to v/v for mixed layer mixing and cloud convection|
|Main||v/v -> kg||--||main.F||Convert to kg for chemistry, wet deposition, AOD, and RRTMG|
|Output||kg -> v/v||make_restart_file||restart_mod.F||Convert to v/v for writing to restart file|
|Mixing||v/v <-> kg||do_mixing||mixing_mod.F||Convert locally to kg for applying tendencies|
|Chemistry||kg <-> v/v||chemsulfate||sulfate_mod.F||Convert locally to v/v for post-gravitational settling sulfate chemistry|
|Chemistry||kg <-> v/v||do_strat_chem||strat_chem_mod.F||Convert locally to v/v for Linoz and Synoz stratospheric ozone chemistry|
|TOMAS aerosol microphysics||v/v <-> kg||chem_so4_aq||sulfate_mod.F||Convert locally to kg for TOMAS|
|TOMAS aerosol microphysics||v/v <-> kg||compute_F, washout||wetscav_mod.F||Convert locally to kg for TOMAS routines|
|TOMAS aerosol microphysics||v/v <-> kg||checkmn||tomas_mod.F||Convert locally to kg for TOMAS routines|
|Two-way nesting||v/v <-> kg||exchange_global_post, exchange_nested_post||exchange_mod.F||Convert locally to kg to exchange data between coupled runs|
The unit conversions listed above generally use the CONVERT_UNITS routine implemented in dao_mod.F which applies a unit conversion to all tracers and all grid boxes stored in State_Chm%TRACERS. Sometimes tracer unit conversion occurs without use of CONVERT_UNITS, such as conversion from kg to v/v for output in either the restart file or for diagnostics. Diagnostics-related conversions are not included in the table above.
The table below lists all major instances of tracer concentration unit conversions that are incorporated into GEOS-Chem v11-01. In the table, the symbol -> indicates a one-way conversion while the symbol <-> indicates a local two-way conversion. All components of GEOS-Chem not included in the table now use tracer concentration units kg/kg dry.
|Unit change complete||Area-independent|
|Input||v/v dry -> kg/kg dry||copy_STT||restart_mod.F||Convert to kg/kg dry after reading from restart file|
|Output||kg/kg dry -> v/v dry||make_restart_file||restart_mod.F||Convert to v/v dry for writing to restart file|
|Mixing||kg/kg dry <-> v/v dry||do_mixing||mixing_mod.F||Use v/v dry to preserve legacy usage in PBL mixing NOTE: We may update units to mass mixing ratio in the future|
|Mixing||v/v dry <-> kg/m2||do_tend||mixing_mod.F||Convert locally to kg/m2 for applying tendencies|
|Wet deposition||kg/kg dry <-> kg/m2||wetdep, wetdep_merra||wetscav.F||Use kg/m2 to to enable column-wise calculations|
|Mercury emissions||kg/kg dry <-> kg||emissmercury||mercury_mod.F||Convert locally to kg for mercury emissions not yet in HEMCO|
|Update pending FlexChem||Area-dependent|
|Chemistry||kg/kg dry <-> kg||do_chemistry||chemistry_mod.F||Convert locally to kg for chemistry|
|Chemistry||kg/kg dry <-> kg||aerosol_conc||aerosol_mod.F||Convert locally to kg for aerosol chemistry|
|Chemistry||kg <-> v/v dry||do_strat_chem||strat_chem_mod.F||Preserve use of v/v dry for Linoz and Synoz stratospheric ozone chemistry|
|Chemistry||kg/kg dry <-> kg||calc_ste||strat_chem_mod.F||Convert locally to kg for stratosphere-to-troposphere exchange flux|
|Chemistry||kg <-> v/v dry||chemsulfate||sulfate_mod.F||Preserve use of v/v dry for sulfate chemistry|
|Developer input needed||Area-dependent|
|Two-way nesting||kg/kg dry <-> kg||exchange_global_post, exchange_nested_post||exchange_mod.F||Convert locally to kg to exchange data between coupled runs|
|TOMAS aerosol microphysics||v/v dry <-> kg||chem_so4_aq||sulfate_mod.F||Convert locally to kg for TOMAS routines|
|TOMAS aerosol microphysics||kg/kg dry <-> kg||emisscarbontomas||carbon_mod.F||Convert locally to kg for TOMAS routines|
|TOMAS aerosol microphysics||kg/kg dry <-> kg||emisssulfatetomas||sulfate_mod.F||Convert locally to kg for TOMAS routines|
|TOMAS aerosol microphysics||kg/kg total <-> kg||washout||wetscav_mod.F||Convert locally to kg for TOMAS routines|
|TOMAS aerosol microphysics||kg/m2 <-> kg||washout||wetscav_mod.F||Convert locally to kg for TOMAS routines|
|TOMAS aerosol microphysics||kg/kg dry <-> kg||aero_diaden||tomas_mod.F||Convert locally to kg for TOMAS routines|
|TOMAS aerosol microphysics||kg/m2 <-> kg||aqoxid||tomas_mod.F||Convert locally to kg for TOMAS routines|
|Radiative transfer||kg/kg dry <-> kg||do_rrtmg_rad_transfer||rrtmg_rad_transfer_mod.F||Convert locally to kg for RRTMG|
Special Unit Conversion Considerations
Updating Air Quantities
Special care must be taken to conserve tracer mass when updating air quantities. If tracer concentrations are in mixing ratio (e.g. v/v or kg/kg) then the mixing ratio must be updated when the air mass changes in order to prevent false tracer mass sources or sinks. In GEOS-Chem v10-01, air quantities were updated while tracer concentrations were kg/grid box, making a mixing ratio update unnecessary. In GEOS-Chem v11-01, however, the primary tracer concentration unit is mixing ratio.
To facilitate the preservation of mass balance, the dao_mod.F routine AIRQNT now contains the functionality of updating tracer mixing ratio when air quantities are updated. AIRQNT is called every time pressure and/or specific humidity changes and now accepts a logical argument indicating whether or not to update mixing ratio. If tracer units are in kg/m2 then updating mixing ratio is unnecessary.
As part of the implementation of this change, we discovered that specific humidity changes during non-local PBL mixing but air quantities are not immediately updated. With the implementation of new tracer units, this caused differences between v11-01e and previous versions. A fix to call AIRQNT within non-local PBL mixing is now included in non-local PBL mixing. Note, however, that an existing but possibly unrelated issue where tracer mass is not conserved in non-local PBL mixing remains unresolved.