Last edition: 05/28/20 16:23:00 by stefryn

The PI is responsible to closely follow the progress of the action, and especially to contact NEMO project manager if the delay on preview (or review) are longer than the 2 weeks expected.

  1. Summary
  2. Description
  3. Implementation
  4. Preview
  5. Tests
  6. Review


Action SI3-10_EAP_rheology
PI(S) Stefanie Rynders
Digest Add new module icedyn_rhg_eap.F90 with similar structure to the existing icedyn_rhg_evp.F90 module to include EAP rheology as an option in SI3.
Branch source:/NEMO/branches/{YEAR}/dev_r{REV}_{ACTION_NAME}
Previewer(s) Andrew Coward
Reviewer(s) Clement Rousset?
Ticket #2325


Current EVP rheology assumes ice is isotropic, but observations show linear kinematic features (LKF) which are sign of anisotropic behaviour. Elastic anisotropic plastic (EAP) rheology has been developed by UCL to address this shortcoming (refs 1-3 theoretical development, refs 4-5 for implementation in CICE). It is routinely used in CICE simulations and shows more realistic LKF patterns.

The IMMERSE project has a milestone and deliverable to implement EAP rheology in SI3.


Development cautions

  • EAP used in CICE with explicit solver, hasn't been tested with implicit solver (check CICE manual)
  • EAP hasn't been used with adaptive solver (Kimmritz) ' stability unknown ' not used for now
  • EAP hasn't been used with Lemieux landfast ice changes ' stability unknown ' not used for now
  • need 8 functions, though coding rules say it is to be avoided
  • all recycled CICE code will need to be rewritten to match NEMO coding conventions.

Module list

modules to be changed:


new module


Code modifications

EAP code based on Heorton et al. 2018 implementation in CICE


This is the main rheology module, contains two subroutines: ice_dyn_rhg and ice_dyn_rhg_init. Some placeholders for EAP rheology already defined

The subroutine ice_dyn_rhg does timing and conservation checks, calls the rheologies (select case pattern) and calls the writing of restart files

The subroutine ice_dyn_rhg_init reads the rheology parameters from the namelist and writes to the log

no namelist parameters needed for eap specifically, need to use nn_evp and rn_relast for the subcycling


  • select case parameter np_rhg_EAP to choose EAP rheology, defined on line 35 to be uncommented
  • namelist parameter to be added for EAP after line 38
LOGICAL ::   ln_rhg_EAP       ! EAP rheology
  • np_rhg_EAP used to switch on eap rheology on line 139 to be uncommented
  • namelist parameter to be added in line 112
NAMELIST/namdyn_rhg/  ln_rhg_EVP, ln_aEVP, rn_creepl, rn_ecc , nn_nevp, rn_relast, ln_rhg_EAP
  • line of log output to be added for eap, proposed after line 133 ?
WRITE(numout,*) '      rheology EAP (icedyn_rhg_eap)                        ln_rhg_EAP = ', ln_rhg_EAP
  • to be added USE statement, after line 18
USE icedyn_rhg_eap ! sea-ice: EAP rheology
  • to be added CASE option, after line 82
CASE ( np_rhgEAP)
      CALL ice_dyn_rhg_eap( kt, stress1_i, stress2_i, stress12_i, shear_i, divu_i, delta_i )
  • to be added call to restart file writing in ice_dyn_rhg, after line 86
IF( ln_rhg_EAP )   CALL rhg_eap_rst( 'WRITE', kt )
  • to be added call to restart file reading in ice_dyn_rhg_init, after line 142
IF( ln_rhg_EAP  )   CALL rhg_eap_rst( 'READ' )  !* read or initialize all required files


new module to be added

The structure will be the same as icedyn_rhg_evp.F90, with some code and extra functions added The subroutine ice_dyn_rhg_eap contains the stress calculation and momentum balance and subcycling

  • compute mask at F point: no changes needed
  • compute ice, snow mass + ice strength: initialisation of variables to be added: uses 8 functions for the variables w1, w2, s11kr, s12kr, s22r, s11ks, s12ks, s22ks
  • keep landfast ice option, but test later unsure whether extra tensile strength will be stable hasn't been used with EAP in other models
  • compute terms of momentum equation: wind/ocean stress, mass terms, coriolis term: no changes needed
  • solve momentum equation iteratively: use Bouillon option (more stable), possibly test Kimmritz option later
  • insert stress update: insert structure tension evolution (stepa subroutine), line 688 unsure whether this will be stable with implicit solver instead of explicit one →ask Harry (note in stepa says it is implicit, clarify)
  • calls calc_ffrac 4 times, 4 corners of cell and average: ( warning: s11, s22 not defined on same point as s12 in SI3 need 4 corners, check?)
  • calculate delta, shear, divergence for redistribution: no changes needed
  • diagnostics: add output of anisotropy with iom_put calls need to define fields in xml files
  • The subroutine rhg_eap_rst: add structure tensor components (anistropy) restart writing/reading variables a11_1, a11_2, a11_3, a11_4 and a12_1, a12_2, a12_3, a12_4; pay attention to order of reads 8 functions for yield surface lookup table inside functions everything scalar
  • calc_ffrac subroutine? uses stresses and anisotropy tensor (both defined on corners), but inside function everything scalar - separate subroutine will not be needed if only one grid point is enough


The first advection module, containing tracers: add anisotropy tracer


The second advection module, containing tracers: add anisotropy tracer


1) Wilchinsky, A.V. and Feltham, D.L. A continuum anisotropic model of sea-ice dynamics. Proc. R. Soc. Lond. A, 460(2047): 2105-2140, July 2004. doi: 10.1098/rspa.2004.1282 .

2) Wilchinsky, A.V. and Feltham, D.L. Dependence of Sea Ice Yield-Curve Shape on Ice Thickness. J. Phys. Oceanogr., 34(12): 2852-2856, 2004. doi: 10.1175/JPO2667.1

3) Wilchinsky, A.V. and Feltham, D.L. Modelling the rheology of sea ice as a collection of diamond-shaped floes. J. Nonnewton. Fluid Mech., 138(1): 22-32, September 2006. doi: 10.1016/j.jnnfm.2006.05.001.

4) Tsamados, M.; Feltham, D. L., and Wilchinsky, A. V. Impact of a new anisotropic rheology on simulations of Arctic sea ice. J. Geophys. Res., 118 (1):91-107, January 2013. doi: 10.1029/2012JC007990.

5) Heorton, H. D. B. S. and Feltham, D. L. and Tsamados, M. Stress and deformation characteristics of sea ice in a high-resolution, anisotropic sea ice model. Phil. Trans. R. Soc. A, 376(2129), 2018. doi: 10.1098/rsta.2017.0349

Test case

We will use the ice_adv2d testcase modified to examine the effect of the rheology by imposing different controlled boundary conditions. The approach is inspired by the idealised simulations in Heorton et al. 2018.

Documentation updates

Section on EAP rheology to be included SI3 reference manual section 3 : ice dynamics.


Since the preview step must be completed before the PI starts the coding, the previewer(s) answers are expected to be completed within the two weeks after the PI has sent the request to the previewer(s).
Then an iterative process should take place between PI and previewer(s) in order to find a consensus

Possible bottlenecks:

  • the methodology
  • the flowchart and list of routines to be changed
  • the new list of variables wrt coding rules
  • the summary of updates in literature

Once an agreement has been reached, preview is ended and the PI can start the development into his branch.

update: EAP rheology has an impact on the closing rate for ridging/rafting. Currently this is hardcoded appropriate for EVP in icedyn_rdgrft.F90. An option will be added in icedyn_rdgrft.F90 to use EAP rate instead. update 2: Current implementation in CICE ignores the impact of advection on the anisotropy. Initial implementation in SI3 will do the same, so no extra tracer is needed for now. This can be reasessed later.


Once the development is done, the PI should complete the tests section below and after ask the reviewers to start their review.

This part should contain the detailed results of SETTE tests (restartability and reproducibility for each of the reference configuration) and detailed results of restartability and reproducibility when the option is activated on specified configurations used for this test

Regular checks:

  • Can this change be shown to produce expected impact (option activated)?
  • Can this change be shown to have a null impact (option not activated)?
  • Results of the required bit comparability tests been run: are there no differences when activating the development?
  • If some differences appear, is reason for the change valid/understood?
  • If some differences appear, is the impact as expected on model configurations?
  • Is this change expected to preserve all diagnostics?
  • If no, is reason for the change valid/understood?
  • Are there significant changes in run time/memory?

The test case is called ICE_RHEO, included in the development branch in the tests folder. It is based on the ice_adv2d test case, but with some differences in the forcing and boundary conditions, see the usrdef files in the MY_SRC directory. There is no single verification value, rather the intention is to examine the deformation patterns caused by different rheologies, which can be compared to those in Heorton et al. 2018 (CICE-based). The rheologies are EVP vs EAP, but it could be used for other future rheology options too.

Current status: there is still an issue preventing to reproduce Harry's results, probably in the boundary conditions, which I need to recheck with him.

Convergence of the velocities can be checked with code from changeset 12741 which is not yet incorporated in this branch.


A successful review is needed to schedule the merge of this development into the future NEMO release during next Merge Party (usually in November).


  • Is the proposed methodology now implemented?
  • Are the code changes in agreement with the flowchart defined at preview step?
  • Are the code changes in agreement with list of routines and variables as proposed at preview step?
    If, not, are the discrepancies acceptable?
  • Is the in-line documentation accurate and sufficient?
  • Do the code changes comply with NEMO coding standards?
  • Is the development documented with sufficient details for others to understand the impact of the change?
  • Is the project literature (manual, guide, web, …) now updated or completed following the proposed summary in preview section?


Is the review fully successful? If not, please indicate what is still missing

Once review is successful, the development must be scheduled for merge during next Merge Party Meeting.

Last modified 2 months ago Last modified on 2020-05-28T16:23:00+02:00