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Author : Steven Alderson

ticket : #942

Branch : dev_r3337_NOCS10_ICB


Description

Implement Martin & Adcroft's scheme for calving and drifting of icebergs (Ocean Modeling 34, 2010).

Icebergs represent a propagating source of freshwater, which may be far removed from near land point runoff which has been traditionally used to represent iceberg influence.

In this scheme icebergs are represented as lagrangian particles which propagate and decay according to momentum and mass balance equations. Each particle in the code actually represents a group of icebergs of the same size (so reducing the computational effort of tracking individual icebergs). Ten classes are defined by default, having different masses, lengths and members. Input is via an input ice flux array on the model grid. Ice accumulates over time at the flux points until enough is formed to create an iceberg in at least one class. (Alternatively, there is a test mode where a fully formed iceberg can be released instantaneously in a box at the beginning of a run.) Icebergs are assigned a unique set of numbers as an identifier. In the MPP case with jpnij processors, modulo arithmetic jpnij is used to force uniqueness. For long runs with many processors this necessitates the use of an identifier made from multiple integers.

As the icebergs propagate they break up either reducing to freshwater or ice bits (which are assumed to carry on with their parent iceberg and thus delay melting). The freshwater is returned to an array on the model grid and thence to the emp arrays. Both input and output iceberg arrays are written to the NEMO mean files. Iceberg trajectories can also be output along with properties along track, to their own NETCDF files. They are written in creation order separately from each processor and so must be unpacked.

New OPA_SRC files

ICB/icb_oce.F90

Declarations of icebergs types and variables. Icebergs are described by a new FORTRAN TYPE which is a linked list of icebergs.

ICB/icbclv.F90

Routines which convert calving flux into ice available for calving in each iceberg class.

ICB/icbdia.F90

Extensive diagnostic information can be produced. This module accumulates data for release at intervals determined by namelist variables.

ICB/icbdyn.F90

Module to handle momentum equation describing iceberg propagation.

ICB/icbini.F90

Initialisation routines.

ICB/icblbc.F90

Routines to deal with lateral boundaries: east-west cyclic condition, north fold and also MPP exchanges.

ICB/icbrst.F90

Write out restart files

ICB/icbrun.F90

Top level routine to call iceberg routines in the correct order

ICB/icbthm.F90

Module to calculate mass balance of icebergs

ICB/icbtrj.F90

Deal with iceberg trajectory output files

ICB/icbutl.F90

Various utility routines

Modified OPA_SRC files

DIA/diawri.F90

added extra output for iceberg gridded files

DYN/dynspg_flt.F90 LBC/lbclnk.F90 LBC/lib_mpp.F90 SOL/solmat.F90 SOL/solsor.F90

All of the above five routines have been modified because of the need to perform boundary exchange on arrays inside the iceberg code independently of jpr2di, jpr2dj. This requires the halo size to be explicitly passed to lbc_lnk_e.

SBC/sbc_oce.F90

Add ln_icebergs declaration

SBC/sbcmod.F90

Perform timestepping of icebergs from here.

nemogcm.F90

Initialise and finalise iceberg code.

Limitations and Future Improvements

  • Currently the heat flux associated with melting icebergs is not accounted for.
  • Netcdf output is coded with low level library calls and should be rewritten where possible using IOM.
  • An MPP run with jpni=1 is not currently allowed, because the east-west cyclical exchange has not been tested in this case.
  • Allow for the thickness of icebergs in calculating the forces impinging on them.

Sample

Test icebergs are introduced into a box in Drake Passage at the start of a years run of ORCA2. The first image is from a run starting from rest on January 1st. All icebergs are from the single largest class. The longest lived survives for just over 6 months.

The next result is from one starting from rest on June 1st. All other parameters remain the same. Here the longest lived iceberg survives for 8 months.


Testing

Testing could consider (where appropriate) other configurations in addition to SETTE].

SETTE Tested'''YES'''
Other model configurations'''YES'''
Processor configurations tested[ WORCA2LIMPIS_16, WORCA2LIMPIS_LONG ]
If adding new functionality please confirm that the
New code doesn't change results when it is switched off
and ''works'' when switched on
'''YES'''

Code has been tested with gfortran (gcc 4.5.3). There were problems compiling with key_agrif using gcc 4.3.1 (not related to this branch).

Bit Comparability

Does this change preserve answers in your tested standard configurations (to the last bit) ?'''YES'''
Does this change bit compare across various processor configurations. (1xM, Nx1 and MxN are recommended)'''YES (2x8, 4x4'''
Is this change expected to preserve answers in all possible model configurations?'''YES'''
Is this change expected to preserve all diagnostics?
,,''Preserving answers in model runs does not necessarily imply preserved diagnostics. ''
'''YES'''

If you answered '''NO''' to any of the above, please provide further details:

  • Which routine(s) are causing the difference?
  • Why the changes are not protected by a logical switch or new section-version
  • What is needed to achieve regression with the previous model release (e.g. a regression branch, hand-edits etc). If this is not possible, explain why not.
  • What do you expect to see occur in the test harness jobs?
  • Which diagnostics have you altered and why have they changed?Please add details here……..

System Changes

Does your change alter namelists?'''NO '''
Does your change require a change in compiler options?'''NO '''

If any of these apply, please document the changes required here…….


Resources

''Please ''summarize'' any changes in runtime or memory use caused by this change……''


IPR issues

Has the code been wholly (100%) produced by NEMO developers staff working exclusively on NEMO?'''NO '''
  • Based on a code kindly supplied by Adcroft and Martin.
Last modified 8 years ago Last modified on 2012-05-10T08:53:14+02:00

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