Biogeochemistry

Biogeochemistry#

Biogeochemistry in CESM#

Biogeochemistry features have been available since CESM1.0 and are on by default in CESM2.0.

Three components of CESM have biogeochemistry features:

CAM

  • CO\(_{2}\) constituents in CAM that use the land and ocean fluxes of CO\(_{2}\) as surface boundary conditions.

  • CAM passes CO\(_{2}\) to the coupler for land and ocean flux computations.

  • The CO\(_{2}\) consitutients are coupled with radiation computations.

POP

  • Includes the MARBL ecosystem library in CESM2.0

CLM

  • Features covered elsewhere [LINK]

Coupled BGC Compsets#

Terminology

  • BGC CO\(_{2}\): what is used by surface components

  • RAD CO\(_{2}\): what is used by the atmospheric radiative code

  • Diagnostic CO\(_{2}\): prescribed atmospheric CO\(_{2}\) concentrations. (E.g. constant, read from file, 1% ramp, etc.)

  • Prognostic CO\(_{2}\): predicted atmospheric CO\(_{2}\) concentrations. Atmospheric consitutent is computed from surface CO\(_{2}\) fluxes.

B1850, BHIST

  • Compset long name has BCG%BDRD

  • Coupled model, BGC & RAD CO\(_{2}\) are diagnostic

B1850_BPRP, BHIST_BPRP

  • Shortnames introduced in CESM2.1.1

  • Compset long name has BGC%BPRP

  • Coupled model, BGC & RAD CO\(_{2}\) are prognostic

Ocean Specific BGC Compsets#

C1850ECO

  • Ocean alone, 1850 aerosols, normal year forcing

G1850ECO

  • Ocean and sea ice, 1850 aerosols, normal year forcing

G1850ECOIAF

  • Ocean and sea ice, 1850 aerosols, interannually varying forcing

These can be found by using the following command in the same directory as create_newcase

./query_config --compsets pop

BGC Initial Conditions#

Coupled BDRD compsets

  • BDRD is default RUN_REFCASE set for f09_g17 or f19_g17 resolution experiments

  • Provided initial conditions were spun-up with f09_g17 resolution model. Note that the carbon cycle is not as well balanced in f19_g17 resolution experiments as it is with f09_g17 resolution.

Coupled BPRP compsets

  • PBRP is the default RUN_REFCASE set for f09_g17

Ocean alone or Ocean-ice compsets

  • Initial conditions are provided but are not spun up.

BGC env*xml variables#

CCSM_BGC

  • Controls which CO\(_{2}\) fields are exchanged between CESM components.

bgc_settings

Figure: CCSM_BGC settings.

  • CO2A: land only or ocean only runs.

  • CO2B: atmosphere-land runs. Ocean and fossil fuel CO\(_{2}\) fluxes are read for m a file.

  • CO2C: fully coupled runs.

CCSM_CO2_PPMV

  • Constant CO\(_{2}\) reference value used in some configurations.

OCN_CO2_TYPE or LND_CO2_TYPE

  • Controls CO\(_{2}\) used by ocean and land components.

  • Constant, prognistic, diagnostic.

OCN_TRACER_MODULES

  • Controls which ocean tracers are used.

  • Ocean ecosystem model is called ecosys.

BGC units and sign conventions#

bgc_units

Figure: BGC units and sign conventions.

  • CAM variables CO2, CO2_LND, CO2_OCN, CO2_FF all have units of (kg CO2)/(kg dry air). Note that these are not typical units for carbon cycle modelers. To convert to ppmv multipy by 1.0e6*28.966/44.0 . 28.966 is the molecular weight of dry air and 44.0 is the molecular weight of CO\(_{2}\).

  • Same quantity in different CESM component output has: different names, different units, different sign conventions (for fluxes).

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