Namelist configuration discussion meeting

We are progressing towards the configuration stage of the ACCESS-OM3 0.25deg, and as such, it’s crucial to discuss the namelist options and parameterisations.

To streamline this process, we propose organising an online meeting to collectively review and discuss the namelists. While we may not finalise all options during this session, it will serve as a valuable starting point in our configuratioin journey.

Meeting details:

We welcome anyone interested in contributing this discussion. Together we can make informed decisons and progress efficiently towards our objectives.


Thanks @minghangli - we’ll be focusing on MOM6 parameters for this meeting, right?

Yes, specifically for discussing MOM6 parameters during this meeting.

The discussion starting point should be MOM_input in the 1deg_jra55do_ryf configuration of MOM6-CICE6, which is the most up to date.

  • MOM_input includes only non-default parameters
  • MOM_parameter_doc.all shows every parameter in this configuration (including defaults not explicitly specified in MOM_input)

A draft note serves as a starting point for discussion. The content of the notes is organised in the same order as the comparison across different configs. And the order of the comparison table aligns with MOM_parameter_doc.all.

Two comparison tables are provided at the moment,

  1. MOM6-CICE6_0.25deg-1deg-1deg-AK_reorder
    (1.1) MOM6-CICE6_0.25deg_ryf_ml/MOM_input,
    (1.2) MOM6-CICE6_1deg_jra55do_ryf/MOM_input (original),
    (1.3) MOM6-CICE6_1deg_jra55do_ryf_andrew/MOM_input (this is the latest version located here)

  2. panan-om4_025-MOM6-CICE6_0.25deg
    (2.1) mom6-panan/MOM_input,
    (2.2) mom6-om4-025/MOM_input,
    (2.3) MOM6-CICE6_0.25deg_ryf_ml/MOM_input


  • Just for clarification,

    • (1.2) presents the original parameters aligned with MOM_parameter_doc.all. Following a sanity check, all parameters in the original version are included in (1.2), including default ones at this stage.
    • (1.3) reflects the latest MOM6-CICE6/1deg_jra55do_ryf input file after aligning parameters with MOM_parameter_doc.all. While there are minor discrepancies between (1.2) and (1.3), only non-default parameters are included in (1.3). However, three parameters are absent in (1.3). This inconsistency arises because MOM_parameter_doc.all does not encompass “all” parameters!!!
  • The three missing non-default parameters are listed at the end of (1.1).

! === module MOM_entrain_diffusive ===
                                              ! "default = 5
                                              ! The maximum number of iterations that may be used to
                                              ! calculate the interior diapycnal entrainment."
                                              ! "[m] default = 2.683281572999748E-05
                                              ! The tolerance with which to solve for entrainment values."
! === module MOM_mixed_layer ===
HMIX_MIN = 2.0
                                              ! "[m] default = 0.0
                                              ! The minimum mixed layer depth if the mixed layer depth
                                              ! is determined dynamically."
  • The comparison table is ordered consistently with each input file, facilitating convenient comparison.

Great, thanks @minghangli - I’ve now flagged that MOM_parameter_doc bug here MOM_parameter_doc_* incomplete · Issue #121 · COSIMA/access-om3 · GitHub

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The ACCESS-OM2 MOM5 config is probably not much use for MOM6, but for what it’s worth, here are tables of the ACCESS-OM2 1deg and 0.25deg MOM5 parameters and their differences. Discussion of these choices is given in the draft tech report.

MOM_input in the 1deg_jra55do_ryf configuration of MOM6-CICE6 is still closely based on the CESM gmom_jra config (see differences).

This table shows how it differs from our MOM6 global and panantarctic configs, and from mom6-examples.

Some of these are not actually differences, since MOM_input in the 1deg_jra55do_ryf configuration of MOM6-CICE6 omits defaults.

Meeting notes (this is a wiki - please edit!)

existing cosima mom6 came from mom6 examples from om4 0.25° but with some changes

Adele: should we get the GFDL OM5 param? Steve says we should use their mixing parameters which they have carefully tuned (see MOM6 science testing · Issue #96 · COSIMA/access-om3 · GitHub) - Adele to follow up - GFDL OM5 parameters are here.

Adele: dttherm:dt ratio was only 2 for regional due to boundary issues but could presumably be increased for global

Dougie: WOMBAT has hard-coded 900s timestep for ecology - can be configurable in generic tracers

leave HFREEZE set to 10m (default) so we calculate freeze/melt potential

MINIMUM_DEPTH - changes land mask - set to zero so we control minimum depth via

CHANNEL_CONFIG set to none

nk set to 75 at both 1° and 0.25° to match ACCESS-OM2-01 - use KDS75 z* - test hybrid adaptive coords later; initial target is something as robust as we can, eg for CMIP7

look in more detail at DTFREEZE_DP = -7.75E-08 - differs from default 0 and would be redundant if we used TFREEZE_FORM = “TEOS10” - should we move to TEOS10 for EOS as well?

do we want to save diagnostics on a lower resolution horizontal grid?

USE_MEKE: calculates evolution of mesoscale EKE budget and uses it to tune eddy parameterisation - something we should test; until we do that we should leave as-is or turn off - see 1deg_jra55do_ryf: Address MOM warnings · Issue #13 · COSIMA/MOM6-CICE6 · GitHub

RESOLN_SCALED_KH, KHTH - leave on at both 1° and 0.25°

leave KHTH parameters as they are for mow, but needs testing - important to test if they came from NCAR as may not have been tested

TIDES - turn off, and all associated parameters

Lateral viscosity, smag etc - try using same values as ACCESS-OM2

mixed layer restratification - not very sensitive to these params so use the same as access-om2 for consistency

use KPP with existing for now but test EPBL for future configs (ask Wilton - he’s done some testing)

use pressure-dependent frazil

pen_sw_* - match access-om2 shortwave penetration if we can, and test/compare - may have bearing on WOMBAT - Dougie to do with Pearse - what about WOMBAT-mid shortwave attenuation? is that still planned? - might change

use neutral diffusion at both 1° and 0.25° - is this done the same way as in mom5? - to test

RESTART_CONTROL - try using default (1)

OCEAN_SURFACE_STAGGER = “A” - needed for NUOPC to avoid remapping in mediator

LATENT_HEAT_FUSION - make sure this matches CICE - add to list of cross-component tests

ADJUST_NET_SRESTORE_TO_ZERO = True - matches access-om2

ADJUST_NET_FRESH_WATER_TO_ZERO = True - matches access-om2


FLUXCONST = 0.11 matches access-om2 piston velocity

RESTORE_SALINITY - to investigate - can we have salinity restoring via salt flux in OM3? I guess we want a water flux in CM3?

GUST_CONST - leave as-is for now

MAX_ENT_IT and TOLERANCE_ENT - set to default - see MOM_parameter_doc_* incomplete · Issue #121 · COSIMA/access-om3 · GitHub

HMIX_MIN - add to MOM_input and leave as 2.0 - see MOM_parameter_doc_* incomplete · Issue #121 · COSIMA/access-om3 · GitHub


RESTART_CHECKSUMS_REQUIRED = True - needed for repro testing, leave as default

all OBC params irrelevant


PRANDTL_TURB = 1.0 (default)



Jump over EPBL for now

leave TIMEUNIT = 8.64E+04 (default)


DIAG_COORDS - want both zstart and rho2

BAD_VAL_SS*_MAX/MIN - should work out why it crashes with default values Sudden crashes with excessive SSH · Issue #55 · COSIMA/access-om3 · GitHub

Summary of Tests we should run:

  1. Hybrid and/or Adaptive vertical coordinates (vs default z*)
  2. The Equation of State - switch to Roquet formulation??
  3. Can we output diagnostics at subsampled resolution??
  4. MEKE to tune eddy parameterisation.
  5. KHTH & neutral diffusion
  6. Smagorinsky lateral viscosity - move towards OM2 values?
  7. EPBL vs KPP
  8. SW penetration scheme - pen_sw_*
  10. Salinity restoring fluxconst

Note that some of these tests will require longer (10-20 year) simulations.


Discussion here on which EOS to use from Bob: Should we use TEOS-10? · mom-ocean/MOM6 · Discussion #1592 · GitHub

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