6.28. imogen.nml

This file contains two namelists called IMOGEN_RUN_LIST and IMOGEN_ANLG_VALS_LIST. Values from this section are only used if IMOGEN is enabled (i.e. l_imogen = TRUE).

Since IMOGEN calculates the forcing for an entire year at once, an IMOGEN run must have a start time of 00:00:00 on the 1st of January for some year.

IMOGEN is currently restricted to run only on the HadCM3LC grid, i.e. there are 96 x 56 grid cells where each cell has size 3.75 degrees longitude by 2.5 degrees latitude with no Antarctica. This means that:

• nx = 96 and ny = 56.

IMOGEN also uses its own I/O, so it expects IMOGEN specific files in a different format to JULES - this may change in the future. Examples of IMOGEN input files can be found in the data provided to run the ‘rose stem’ test suites on supported platforms (e.g. JASMIN).

6.28.1. IMOGEN_RUN_LIST namelist members

IMOGEN_RUN_LIST::co2_init_ppmv

Type:real Default:286.085

Initial CO2 concentration (ppmv).

IMOGEN_RUN_LIST::file_scen_emits

Type:character Default:None

If used, file containing CO2 emissions.

This file is expected to be in a specific format - see the IMOGEN example.

IMOGEN_RUN_LIST::file_non_co2_vals

Type:character Default:None

If used, file containing non-CO2 values.

This file is expected to be in a specific format - see the IMOGEN example.

IMOGEN_RUN_LIST::file_scen_co2_ppmv

Type:character Default:None

If used, file containing CO2 values.

This file is expected to be in a specific format - see the IMOGEN example.

IMOGEN_RUN_LIST::ch4_init_ppbv

Type:real Default:774.1

Initial CH4 concentration (ppbv).

Only if land_feed_ch4 = TRUE.

IMOGEN_RUN_LIST::yr_fch4_ref

Type:real Default:2000

Year for reference wetland CH4 emissions and atmospheric CH4 decay rate, i.e. fch4_ref, tau_ch4_ref & ch4_ppbv_ref.

Only if land_feed_ch4 = TRUE.

IMOGEN_RUN_LIST::ch4_ppbv_ref

Type:real Default:1751.02

Reference atmosphere CH4 concentration at yr_fch4_ref (ppbv).

Only if land_feed_ch4 = TRUE.

IMOGEN_RUN_LIST::tau_ch4_ref

Type:real Default:8.4

Lifetime of CH4 in atmosphere at yr_fch4_ref (years). Value used in Gedney et al. (2004) S3 (Table 1) from TAR, Table 4.3 (subscript d).

Only if land_feed_ch4 = TRUE.

IMOGEN_RUN_LIST::fch4_ref

Type:real Default:180.0

Reference wetland CH4 emissions for reference year yr_fch4_ref (Tg CH4/yr).

Only if land_feed_ch4 = TRUE.

IMOGEN_RUN_LIST::file_ch4_n2o

Type:character Default:None

File containing the CH4 and N2O atmos concs. The number of years in this file is defined by nyr_ch4_n2o. This file is expected to be an ascii file with three columns: the first column is the year, the second column is the CH4 concentration (ppbv) and the third column is the N2O concentration (ppbv). There is one row for each year and no header.

Only if land_feed_ch4 = TRUE.

IMOGEN_RUN_LIST::nyr_ch4_n2o

Type:integer Default:241

Number of years of CH4 and N2O data in file_ch4_n2o.

Only if land_feed_ch4 = TRUE.

IMOGEN_RUN_LIST::anlg

Type:logical Default:T

If TRUE, then use the GCM analogue model.

IMOGEN_RUN_LIST::anom

Type:logical Default:T

If TRUE, then incorporate anomalies.

IMOGEN_RUN_LIST::c_emissions

Type:logical Default:T

If TRUE, CO2 concentration is calculated.

IMOGEN_RUN_LIST::include_co2

Type:logical Default:T

If TRUE, include adjustments to CO2 values.

IMOGEN_RUN_LIST::include_non_co2

Type:logical Default:T

If TRUE, include adjustments to non-CO2 values.

IMOGEN_RUN_LIST::land_feed_co2

Type:logical Default:F

If TRUE, include land CO2 feedbacks on atmospheric CO2.

IMOGEN_RUN_LIST::land_feed_ch4

Type:logical Default:F

If TRUE, include wetland CH4 feedbacks on atmospheric CH4. Prescribed CH4 concentrations assume a non-varying natural wetland CH4 component. However, when land_feed_ch4 = TRUE the constant wetland CH4 emissions are perturbed using the anomaly in modelled natural wetland CH4 emission. The methane emissions are calculated for the diagnosed wetland area when l_top = TRUE. These are accumulated and passed to IMOGEN.

To ensure consistency with the observed atmospheric CH4 growth rate the model needs to be calibrated to produce fch4_ref TgCh4 per year (default 180) for the year yr_fch4_ref (default 2000). This is done by calibrating q10_ch4 (either q10_ch4_cs, q10_ch4_npp, q10_ch4_resps, depending on whether cs, npp or resps is defined as the substrate by ch4_substrate) and const_ch4 (either const_ch4_cs, const_ch4_npp, const_ch4_resps, again depending on whether cs, npp or resps is defined as the substrate by ch4_substrate). The calibration can be carried out as discussed in Comyn-Platt et al. (2018) and needs to be checked before proceeding because the model won’t necessarily produce the correct values by default.

For wetland CH4 feedbacks values for the following: fch4_ref, tau_ch4_ref, ch4_ppbv_ref, yr_fch4_ref, ch4_init_ppbv, file_ch4_n2o, and nyr_ch4_n2o are also required.

See also

References:

• Gedney, N., Cox, P. M. & Huntingford, C. Climate feedback from wetland methane emissions. Geophys. Res. Lett. 31, L20503 (2004).
• Comyn-Platt E, Hayman G, Huntingford C, Chadburn SE, Burke EJ, Harper AB, Collins WJ, Webber CP, Powell T, Cox PM, Gedney N. Carbon budgets for 1.5 and 2 C targets lowered by natural wetland and permafrost feedbacks. Nature geoscience. 2018 Aug;11(8):568.

IMOGEN_RUN_LIST::ocean_feed

Type:logical Default:F

If TRUE, include ocean feedbacks on atmospheric CO2.

IMOGEN_RUN_LIST::nyr_emiss

Type:integer Default:241

Number of years of emission data in file.

IMOGEN_RUN_LIST::file_points_order

Type:character Default:None

File containing the mapping of IMOGEN global grid points onto IMOGEN land points (different from the JULES land points).

IMOGEN_RUN_LIST::initialise_from_dump

Type:logical Default:F

Indicates how the IMOGEN prognostic variables will be initialised.

TRUE

Use a dump file (specified in dump_file below) from a previous run with IMOGEN to initialise the IMOGEN prognostics.

FALSE

IMOGEN will handle the initialisation of its prognostics internally.

IMOGEN_RUN_LIST::dump_file

Type:character Default:None

The name of the dump file to initialise from.

Only used if initialise_from_dump = TRUE.

6.28.2. IMOGEN_ANLG_VALS_LIST namelist members

IMOGEN_ANLG_VALS_LIST::q2co2

Type:real Default:3.74

Radiative forcing due to doubling CO2 (W m^-2).

IMOGEN_ANLG_VALS_LIST::f_ocean

Type:real Default:0.711

Fractional coverage of the ocean.

IMOGEN_ANLG_VALS_LIST::kappa_o

Type:real Default:383.8

Ocean eddy diffusivity (W m^-1 K^-1).

IMOGEN_ANLG_VALS_LIST::lambda_l

Type:real Default:0.52

Inverse of climate sensitivity over land (W m^-2 K^-1).

IMOGEN_ANLG_VALS_LIST::lambda_o

Type:real Default:1.75

Inverse of climate sensitivity over ocean (W m^-2 K^-1).

IMOGEN_ANLG_VALS_LIST::mu

Type:real Default:1.87

Ratio of land to ocean temperature anomalies.

IMOGEN_ANLG_VALS_LIST::t_ocean_init

Type:real Default:289.28

Initial ocean temperature (K).

IMOGEN_ANLG_VALS_LIST::nyr_non_co2

Type:integer Default:21

Number of years for which non-co2 forcing is prescribed.

IMOGEN_ANLG_VALS_LIST::dir_patt

Type:character Default:None

Directory containing the patterns.

Files in this directory are expected to be in a specific format - see the IMOGEN example.

IMOGEN_ANLG_VALS_LIST::dir_clim

Type:character Default:None

Directory containing initialising climatology.

Files in this directory are expected to be in a specific format - see the IMOGEN example.

IMOGEN_ANLG_VALS_LIST::dir_anom

Type:character Default:None

Directory containing prescribed anomalies.

Files in this directory are expected to be in a specific format - see the IMOGEN example.

IMOGEN_ANLG_VALS_LIST::file_non_co2

Type:logical Default:F

If true, then non-CO2 radiative forcings are contained within a file.