CICE: the Los Alamos Sea Ice Model Documentation and Software User’s Manual Version 5.1 LA-CC-06-012 Elizabeth C. Hunke, William H. Lipscomb, Adrian K. Turner, Nicole Jeffery, Scott Elliott Los Alamos National Laboratory Los Alamos NM 87545 March 17, 2015 Contents 1 Introduction 3 2 Coupling with other climate model components4 2.1 Atmosphere...........................................6 2.2 Ocean..............................................8 2.3 Variable exchange coefficients.................................9 3 Model components 11 3.1 Tracers............................................. 13 3.1.1 Tracers that depend on other tracers (e.g., melt ponds)................ 14 3.1.2 Ice age......................................... 15 3.1.3 Sea ice biogeochemistry................................ 16 3.1.4 Aerosols........................................ 18 3.1.5 Brine height....................................... 19 3.2 Horizontal transport....................................... 21 3.2.1 Reconstructing area and tracer fields.......................... 22 3.2.2 Locating departure triangles.............................. 24 3.2.3 Integrating fields.................................... 27 3.2.4 Updating state variables................................ 28 3.3 Transport in thickness space.................................. 29 3.4 Mechanical redistribution.................................... 31 3.5 Dynamics............................................ 34 3.5.1 Momentum....................................... 35 3.5.2 Internal stress...................................... 36 3.5.3 Revised approach.................................... 40 3.6 Thermodynamics........................................ 42 3.6.1 Melt ponds....................................... 43 3.6.2 Thermodynamic surface forcing balance........................ 51 1 3.6.3 New temperatures................................... 53 3.6.4 Growth and melting.................................. 63 4 Numerical implementation 64 4.1 Directory structure....................................... 64 4.2 Grid, boundary conditions and masks............................. 68 4.2.1 Grid domains and blocks................................ 69 4.2.2 Tripole grids...................................... 70 4.2.3 Bio-grid......................................... 70 4.2.4 Column configuration................................. 71 4.2.5 Boundary conditions.................................. 71 4.2.6 Masks.......................................... 71 4.3 Initialization and coupling................................... 72 4.4 Choosing an appropriate time step............................... 73 4.5 Model output.......................................... 74 4.5.1 History files....................................... 74 4.5.2 Diagnostic files..................................... 75 4.5.3 Restart files....................................... 75 4.6 Execution procedures...................................... 77 4.7 Performance........................................... 78 4.8 Adding things.......................................... 81 4.8.1 Timers......................................... 81 4.8.2 History fields...................................... 82 4.8.3 Tracers......................................... 82 5 Troubleshooting 83 5.1 Initial setup........................................... 83 5.2 Restarts............................................. 84 5.3 Slow execution......................................... 85 5.4 Debugging hints......................................... 85 5.5 Known bugs........................................... 86 5.6 Interpretation of albedos.................................... 86 5.7 Proliferating subprocess parameterizations........................... 86 Acknowledgments and Copyright 87 Table of namelist options 88 Index of primary variables and parameters 94 General Index 112 Bibliography 116 3 1 Introduction The Los Alamos sea ice model (CICE) is the result of an effort to develop a computationally efficient sea ice component for a fully coupled atmosphere–land global climate model. It was designed to be compatible with the Parallel Ocean Program (POP), an ocean circulation model developed at Los Alamos National Laboratory for use on massively parallel computers [62, 13, 14]. The current version of the model has been enhanced greatly through collaborations with members of the community. CICE has several interacting components: a thermodynamic model that computes local growth rates of snow and ice due to vertical conductive, radiative and turbulent fluxes, along with snowfall; a model of ice dynamics, which predicts the velocity field of the ice pack based on a model of the material strength of the ice; a transport model that describes advection of the areal concentration, ice volumes and other state variables; and a ridging parameterization that transfers ice among thickness categories based on energetic balances and rates of strain. External routines would prepare and execute data exchanges with an external “flux coupler,” which then passes the data to other climate model components such as POP. This model release is CICE version 5.1, available from http://oceans11.lanl.gov/trac/CICE/wiki. It up- dates CICE 5.0, which was released in September 2013: include ice velocity in atm-ice coupling updates (e.g. stress) for high-frequency coupling • allow a variable coefficient for the ice-ocean heat flux • several new namelist options improve flexibility, especially for coupled model configurations: • – ice-ocean heat flux – ‘virtual’ or ‘real’ topo melt pond water – ocean freezing temperature – high-frequency coupling – coupling and computational grids may be different – and more additional software enhancements improve flexibility and compatibility with CESM, Hadley Centre, • and U.S. Navy coupled models new diagnostics and updated documentation • various bug fixes • The previous version, CICE v5.0, includes the following improvements: A method for prognosing sea ice salinity, including improved snow-ice formation • Two new explicit melt pond parameterizations (topo and level-ice) • Sea ice biogeochemistry • Elastic-Anisotropic-Plastic rheology • Improved parameterization of form drag • The “revised EVP” under-damping approach • Gracefully handles the case when an internal layer melts completely • 4 Coupling with other climate model components Gregorian calendar with leap years • Reduced memory and floating-point operations for tracer calculations • Ice and snow enthalpy defined as tracers • New history variables for melt ponds, ridging diagnostics, biogeochemistry and more • Read/write variables on the extended grid, including ghost (halo) cells • Parallelism option via OpenMP threads • Improved parallel efficiency through halo masks and new block distributions • Parallel I/O option via the PIO library • Restarts in binary or netCDF formats • CPP options for categories, layers and tracers • Corrected bugs, particularly for nonstandard configurations. • With so many new parameterizations, we must admit that all combinations have not been tested. Also, different parameterizations for various sub-processes (e.g., snow infiltration by melt or sea water have been introduced as part of the new code options, which need to be unified or pulled out as separate options. Generally speaking, subroutine names are given in italic and file names are boldface in this document. Symbols used in the code are typewritten, while corresponding symbols in this document are in the math font which, granted, looks a lot like italic. A comprehensive index, including a glossary of symbols with many of their values, appears at the end. The organization of this software distribution is described in Section 4.1; most files and subroutines referred to in this documentation are part of the CICE code found in cice/source/, unless otherwise noted. We pronounce the model name as “sea ice,” but there has been a small grass-roots movement underway to alter the model name’s pronunciation from “sea ice” to what an Italian might say, che¯0-cha¯ or “chee-chay.” Others choose to say s¯ıs (English, rhymes with “ice”), ses¯ (French, like “cease”), or she-¯ ¯ı-soo (“Shii-aisu,” Japanese). For more information about the CICE model and its user community, visit the web pages http://oceans11.lanl.gov/trac/CICE/wiki http://oceans11.lanl.gov/trac/CICE/wiki/CiceUsers http://oceans11.lanl.gov/trac/CICE/wiki/CiceCodeModifications http://oceans11.lanl.gov/trac/CICE/wiki/CiceDev 2 Coupling with other climate model components The sea ice model exchanges information with the other model components via a flux coupler. CICE has been coupled into numerous climate models with a variety of coupling techniques. This document is ori- ented primarily toward the CESM Flux Coupler [39] from NCAR, the first major climate model to incorpo- rate CICE. The flux coupler was originally intended to gather state variables from the component models, compute fluxes at the model interfaces, and return these fluxes to the component models for use in the next integration period, maintaining conservation of momentum, heat and fresh water. However, several of these fluxes are now computed in the ice model itself and provided to the flux coupler for distribution to the other components, for two reasons. First, some of the fluxes depend strongly on the state of the ice, and vice versa, Coupling with other climate model components 5 Atmosphere Ocean Provided by the flux coupler to the sea ice model z◦ Atmosphere level height Ffrzmlt Freezing/melting potential U~a Wind velocity Tw Sea surface temperature Qa Specific humidity S Sea surface