Overview

This repository contains the access/auscom fork of cice5 used in the ACCESS-ESM1.6 and ACCESS-OM2. It was forked from https://github.com/CICE-Consortium/CICE-svn-trunk/ which in turn captured the trunk from the subversion (svn) repository of the Los Alamos Sea Ice Model, CICE, including release tags through version 5.1.2.

ACCESS-ESM1.6 related code came from https://code.metoffice.gov.uk/trac/cice/browser/main/branches/pkg/Config/vn5.1.2_GSI8.1_package_branch/cice?order=name&rev=334#source (MOSRS account required)

More recent versions are found in the CICE and Icepack repositories, which are maintained by the CICE Consortium.

There is PDF documentation(DOI) available for CICE 5.1.2, however some changes were made to this fork to support coupling with ACCESS-OM2 and ACCESS-ESM1.6, Parallel IO, ERA5 Forcing, BGC modelling and for other updates. Some of these changes are described in the ACCESS-OM2 Technical Report.

Build Systems

We recommend and support using CMake to build cice5, however the Makefile build is kept in this repository for any legacy models still using these files.

Three drivers are supported by the CMake build, selected with CICE_DRIVER:

CICE_DRIVER	Used by	Coupling
auscom (default)	ACCESS-OM2	OASIS3-MCT + libaccessom2
access	ACCESS-ESM1.6	OASIS3-MCT
cice	standalone / testing	none

Grid size, block decomposition and task count

The global grid size and the block decomposition are both chosen at run time, in the domain_nml group of the namelist (cice_in.nml for the auscom and access drivers, ice_in otherwise). A single executable can therefore be run at any resolution and any number of MPI tasks, without rebuilding:

&domain_nml
    nprocs       = 24        ! must equal the MPI task count
  , nx_global    = 360       ! global grid size, i
  , ny_global    = 300       ! global grid size, j
  , block_size_x = 15        ! block size in i, excluding ghost cells
  , block_size_y = 300       ! block size in j, excluding ghost cells
  , max_blocks   = -1        ! -1 => derive from the actual distribution
/

Notes:

This runtime specification for domain grids, nprocs, block sizes, and max blocks, was backported from CICE6 in this CICE5 PR; please refer to CICE6 docs for details on the namelist parameters.

• block_size_x and block_size_y need not divide nx_global/ny_global evenly — the decomposition is padded — but choosing sizes that do avoids wasted work.
• max_blocks = -1 is the recommended setting. Each task sets it to the number of blocks that task actually owns, once the distribution has been built, so it is exact and needs no guessing. It is a per-task value: an uneven distribution gives different tasks different max_blocks, and each allocates only what it needs. The minimum and maximum across tasks are reported to the diagnostic log. Setting it explicitly still works, and still aborts if a task turns out to need more blocks than that; a value larger than necessary only wastes memory.
• There is nothing to tune for the roundrobin, sectrobin and sectcart distributions. They build an internal blockIndex work array before the per-task block count is known, so it is sized from an estimate and grown on demand if that estimate is too small; no run can fail because of it. cartesian, rake and spacecurve do not use that array at all.
• The values in effect are echoed to the ice diagnostic log under Domain Information.
• The ESM (access) driver requires max_blocks == 1, i.e. exactly one block per task, because its atmosphere coupling unpacks directly into block index 1. It aborts at startup otherwise. The OM2 (auscom) driver has no such restriction.

nx_global, ny_global, block_size_x and block_size_y are required in domain_nml; max_blocks may be given or left at -1 to be derived. The build has no grid or block settings at all — the old -DNXGLOB, -DNYGLOB, -DBLCKX, -DBLCKY and -DMXBLCKS macros and their CICE_* CMake variables are gone. Since nothing about the domain is baked into the executable, it is simply cice_<driver>.exe.

Upgrading an existing namelist: a domain_nml that relied on the compiled-in values must now spell out nx_global, ny_global, block_size_x and block_size_y. Use the values the build previously passed via -D; the run aborts at startup with a message naming the missing setting if any is absent.

Note that the vertical and tracer dimensions (NICECAT, NICELYR, NSNWLYR, the tracer counts) are still compile-time.

Useful links

• Wiki: https://github.com/CICE-Consortium/CICE-svn-trunk/wiki

  Information about the CICE model prior to version 6 including how to obtain the code

• Version Index: https://github.com/CICE-Consortium/CICE-svn-trunk/wiki/CICE-Versions-Index-(older)

  Numbered CICE releases prior to version 6.

• Resource Index: https://github.com/CICE-Consortium/About-Us/wiki/Resource-Index

  List of resources for information about the Consortium and its repositories as well as model documentation, testing, and development.