6.33. imogen.nml

This file contains three namelists called IMOGEN_ONOFF_SWITCH, IMOGEN_RUN_LIST and IMOGEN_ANLG_VALS_LIST. Values from this section are only used if IMOGEN is enabled. This is done via the following switch: 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 uses the netcdf read functions in JULES to load the driving data. The required driving data is specific humidity (kg/kg), precipitation (kg/m2/s), wind speed (m/s), incoming shortwave radiation (W/m2), incoming longwave radiation (W/m2), air temeprature (K) and diurnal range of air temperature (K). IMOGEN also needs grid_area read in via JULES_LATLON.

The meteorological driving data used for IMOGEN are at monthly resolution. IMOGEN requires a monthly climatology and then can use either anomalies from that climatology (anlg set to FALSE and anom set to TRUE) or spatial patterns of changes in each meteorological driving variable per degree of global temperature change (anlg set to TRUE and anom set to TRUE). Patterns can be derived at the required spatial resolution using ESMValTool <https://esmvaltool.org/>.

IMOGEN still reads the 1d data from ascii files within the code - this will change in the near future.

See also

References:

  • Huntingford, C. and P. M. Cox (2000), An analogue model to derive additional climate change scenarios from existing GCM simulations, Climate Dynamics 16(8): 575-586. https://doi.org/10.1007/s003820000067

  • Huntingford, C., et al. (2010), IMOGEN: an intermediate complexity model to evaluate terrestrial impacts of a changing climate, Geoscientific Model Development 3(2): 679-687. https://doi.org/10.5194/gmd-3-679-2010

  • Comyn-Platt, E., et al. (2018), Carbon budgets for 1.5 and 2 C targets lowered by natural wetland and permafrost feedbacks, Nature Geoscience 11(8): 568-573. https://doi.org/10.1038/s41561-018-0174-9

  • Zelazowski, P., et al. (2018), Climate pattern-scaling set for an ensemble of 22 GCMs–adding uncertainty to the IMOGEN version 2.0 impact system, Geoscientific Model Development 11.2: 541-560. https://doi.org/10.5194/gmd-11-541-2018

6.33.1. IMOGEN_ONOFF_SWITCH namelist members

IMOGEN_ONOFF_SWITCH::l_imogen
Type

logical

Default

F

Switch for IMOGEN.

TRUE

IMOGEN is used to generate meteorological forcing data and drive JULES.

FALSE

No effect.

Note

If IMOGEN is enabled, at most only z1_tq_vary, z1_tq_in, z1_uv_in, z1_tq_file and z1_tq_var_name are used from the JULES_DRIVE namelist.

6.33.2. 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_radf
Type

character

Default

None

If used, file containing non-CO2 radiative forcing values.

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

IMOGEN_RUN_LIST::nyr_non_co2
Type

integer

Default

21

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

IMOGEN_RUN_LIST::file_scen_co2_ppmv
Type

character

Default

None

If used, file containing CO2 concentration (ppmv).

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_radf
Type

logical

Default

T

If TRUE, include adjustments to non-CO2 radiative forcing.

IMOGEN_RUN_LIST::l_drive_with_global_temps
Type

logical

Default

F

If TRUE, use imogen to provide jules forcing based on the global mean temperature change and the climate patterns.

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:

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::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.

6.33.3. IMOGEN_ANLG_VALS_LIST namelist members

IMOGEN_ANLG_VALS_LIST::diff_frac_const_imogen
Type

real

Default

0.4

IMOGEN uses this instead of diff_frac_const

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::file_patt
Type

character

Default

None

Netcdf file containing the patterns. It should be monthly data (12 months total) with the dimension ‘imogen_drive’ representing time.

IMOGEN_ANLG_VALS_LIST::file_clim
Type

character

Default

None

Netcdf file containing initialising climatology. It should be monthly data (12 months total) with the dimension ‘imogen_drive’ representing time.

IMOGEN_ANLG_VALS_LIST::file_base_anom
Type

character

Default

None

Netcdf files containing prescribed anomalies. There should be one for each year and should be in the form ‘file_base_anom’ followed by ‘year’ (4 digits) and ‘.nc’