Warning, /doc/phys_pkgs/streamice.rst is written in an unsupported language. File is not indexed.
view on githubraw file Latest commit 0bad585a on 2022-02-16 18:55:09 UTC
07e785229e dngo*0001 .. _sub_phys_pkg_streamice:
0002
0003 STREAMICE Package
0004 -----------------
0005
0006
0007 Author: Daniel Goldberg
0008
0009 .. _ssub_phys_pkg_streamice_intro:
0010
0011 Introduction
0012 ~~~~~~~~~~~~
0013
0014 Package :filelink:`STREAMICE <pkg/streamice>` provides a dynamic land ice model for MITgcm.
0015 It was created primarily to develop a TAF- and OpenAD-generated ice model adjoint
0016 and to provide synchronous ice-ocean coupling through the :filelink:`SHELFICE <pkg/shelfice>` package.
0017 It solves a set of dynamic equations appropriate for floating ice-shelf
0018 flow as well as ice-stream and slower ice-sheet flow. It has been tested
0019 at the scale of one or several ice streams, but has not been tested at the continental scale.
0020
0021
0022 .. _ssub_phys_pkg_streamice_config:
0023
0024 STREAMICE configuration
0025 ~~~~~~~~~~~~~~~~~~~~~~~
0026
0027 Compile-time options
0028 ^^^^^^^^^^^^^^^^^^^^
0029
0030 :filelink:`pkg/streamice` can be included on at compile
0031 time in the ``packages.conf`` file by adding a line ``streamice`` (see :numref:`using_packages`).
0032
0033 Parts of the :filelink:`pkg/streamice` code can be enabled or disabled at compile time via
0034 CPP flags. These options are set in :filelink:`STREAMICE_OPTIONS.h <pkg/streamice/STREAMICE_OPTIONS.h>`.
0035
0036
0037 .. tabularcolumns:: |\Y{.475}|\Y{.1}|\Y{.45}|
0038 .. table:: CPP flags used by :filelink:`pkg/streamice`.
0039 :name: tab_phys_pkg_streamice_cpp
0040
0041 +-----------------------------------------------+---------+----------------------------------------------------------------------------------------------------------------------+
0042 | CPP Flag Name | Default | Description |
0043 +===============================================+=========+======================================================================================================================+
0044 | :varlink:`STREAMICE_CONSTRUCT_MATRIX` | #define | explicit construction of matrix for Picard iteration for velocity |
0045 +-----------------------------------------------+---------+----------------------------------------------------------------------------------------------------------------------+
0046 | :varlink:`STREAMICE_HYBRID_STRESS` | #undef | use L1L2 formulation for stress balance (default shallow shelf approx.) |
0047 +-----------------------------------------------+---------+----------------------------------------------------------------------------------------------------------------------+
0048 | :varlink:`USE_ALT_RLOW` | #undef | use package array for rLow rather than model |
0049 +-----------------------------------------------+---------+----------------------------------------------------------------------------------------------------------------------+
0050 | :varlink:`STREAMICE_GEOM_FILE_SETUP` | #undef | use files rather than parameters in :varlink:`STREAMICE_PARM03` to configure boundaries |
0051 +-----------------------------------------------+---------+----------------------------------------------------------------------------------------------------------------------+
0052 | :varlink:`ALLOW_PETSC` | #undef | enable interface to PETSc for velocity solver matrix solve |
0053 +-----------------------------------------------+---------+----------------------------------------------------------------------------------------------------------------------+
0054 | :varlink:`STREAMICE_COULOMB_SLIDING` | #undef | enable basal sliding of the form :eq:`coul_eqn` |
0055 +-----------------------------------------------+---------+----------------------------------------------------------------------------------------------------------------------+
0056
0057 .. | :varlink:`STREAMICE_SMOOTH_FLOATATION` | #undef | subgrid parameterization of transition across the grounding line |
0058 .. +-----------------------------------------------+---------+----------------------------------------------------------------------------------------------------------------------+
0059
0060
0061 .. _ssub_phys_pkg_streamice_runtime:
0062
0063 Enabling the package
0064 ^^^^^^^^^^^^^^^^^^^^
0065
0066 Once it has been compiled, :filelink:`pkg/streamice` is switched on/off at run-time by setting :varlink:`useSTREAMICE` to ``.TRUE.`` in file ``data.pkg``.
0067
0068 Runtime parmeters: general flags and parameters
0069 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
0070
0071 Run-time parameters are set in file ``data.streamice`` (read in :filelink:`streamice_readparms.F <pkg/streamice/streamice_readparms.F>`).
0072 General :filelink:`pkg/streamice` parameters are set under :varlink:`STREAMICE_PARM01` as described in :numref:`tab_phys_pkg_streamice_runtimeparms`.
0073
0074
0075 .. tabularcolumns:: |\Y{.3}|\Y{.125}|\Y{.6}|
0076 .. table:: Run-time parameters and default values (defined under :varlink:`STREAMICE_PARM01` namelist)
0077 :name: tab_phys_pkg_streamice_runtimeparms
0078
0079 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0080 | Parameter | Default | Description |
0081 +===========================================+==============================+====================================================================================================================+
0082 | :varlink:`streamice_density` | 910 | the (uniform) density of land ice (kg/m\ :sup:`3`) |
0083 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0084 | :varlink:`streamice_density_ocean_avg` | 1024 | the (uniform) density of ocean (kg/m\ :sup:`3`) |
0085 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0086 | :varlink:`n_glen` | 3 | Glen's Flow Law exponent (non-dim.) |
0087 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0088 | :varlink:`eps_glen_min` | 1e-12 | minimum strain rate in Glen's Law (:math:`\varepsilon_0`, yr\ :sup:`-1`) |
0089 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0090 | :varlink:`eps_u_min` | 1e-6 | minimum speed in nonlinear sliding law (:math:`u_0`, m/yr) |
0091 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0092 | :varlink:`n_basal_friction` | 0 | exponent in nonlinear sliding law (non-dim.) |
0093 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0094 | :varlink:`streamice_cg_tol` | 1e-6 | tolerance of conjugate gradient of linear solve of Picard iteration for velocity |
0095 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0096 | :varlink:`streamice_lower_cg_tol` | TRUE | lower CG tolerance when nonlinear residual decreases by fixed factor |
0097 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0098 | :varlink:`streamice_max_cg_iter` | 2000 | maximum iterations in linear solve |
0099 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0100 | :varlink:`streamice_maxcgiter_cpl` | 0 | as above when coupled with :filelink:`pkg/shelfice` |
0101 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0102 | :varlink:`streamice_nonlin_tol` | 1e-6 | tolerance of nonlinear residual for velocity (relative to initial) |
0103 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0104 | :varlink:`streamice_max_nl_iter` | 100 | maximum Picard iterations in solve for velocity |
0105 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0106 | :varlink:`streamice_maxnliter_cpl` | 0 | as above when coupled with :filelink:`pkg/shelfice` |
0107 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0108 | :varlink:`streamice_nonlin_tol_fp` | 1e-6 | tolerance of relative change for velocity iteration (relative to magnitude) |
0109 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0110 | :varlink:`streamice_err_norm` | 0 | type of norm evaluated for error (:math:`p` in :math:`p`-norm; 0 is :math:`\infty`) |
0111 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0112 | :varlink:`streamice_chkfixedptconvergence`| FALSE | terminate velocity iteration based on relative change per iteration |
0113 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0114 | :varlink:`streamice_chkresidconvergence` | TRUE | terminate velocity iteration based on residual |
0115 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0116 | :varlink:`streamicethickInit` | FILE | method by which to initialize thickness (``FILE`` or ``PARAM``) |
0117 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0118 | :varlink:`streamicethickFile` | :kbd:`' '` | thickness initialization file, in meters (rather than parameters in :varlink:`STREAMICE_PARM03`) |
0119 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0120 | :varlink:`streamice_move_front` | FALSE | allow ice shelf front to advance |
0121 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0122 | :varlink:`streamice_calve_to_mask` | FALSE | if :varlink:`streamice_move_front` TRUE do not allow to advance beyond :varlink:`streamice_calve_mask` |
0123 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0fbff46b46 dngo*0124 | :varlink:`STREAMICE_use_log_ctrl` | FALSE | specify :math:`C` and :math:`B` via their logarithm rather than square root |
0125 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
07e785229e dngo*0126 | :varlink:`streamicecalveMaskFile` | :kbd:`' '` | file to initialize :varlink:`streamice_calve_mask` |
0127 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0128 | :varlink:`streamice_diagnostic_only` | FALSE | do not update ice thickness (velocity solve only) |
0129 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0130 | :varlink:`streamice_CFL_factor` | 0.5 | CFL factor which determine maximum time step for thickness sub-cycling |
0131 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0132 | :varlink:`streamice_adjDump` | 0.0 | frequency (s) of writing of adjoint fields to file (TAF only) |
0133 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0134 | :varlink:`streamicebasalTracConfig` | UNIFORM | method by which to initialize basal traction (``FILE`` or ``UNIFORM``) |
0135 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0136 | :varlink:`streamicebasalTracFile` | :kbd:`' '` | basal trac initialization file (see :ref:`ssub_phys_pkg_streamice_units` for units) |
0137 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0138 | :varlink:`C_basal_fric_const` | 31.71 | uniform basal traction value (see :ref:`ssub_phys_pkg_streamice_units` for units) |
0139 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0140 | :varlink:`streamiceGlenConstConfig` | UNIFORM | method by which to initialize Glen's constant (``FILE`` or ``UNIFORM``) |
0141 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0142 | :varlink:`streamiceGlenConstFile` | :kbd:`' '` | Glen's constant initialization file (see :ref:`ssub_phys_pkg_streamice_units` for units) |
0143 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0144 | :varlink:`B_glen_isothermal` | 9.461e-18 | uniform Glen's constant value (see :ref:`ssub_phys_pkg_streamice_units` for units) |
0145 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0146 | :varlink:`streamiceBdotFile` | :kbd:`' '` | file to initialize time-indep melt rate (m/yr) |
0147 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0148 | :varlink:`streamiceBdotTimeDepFile` | :kbd:`' '` | file to initialize time-varying melt rate (m/yr), based on :varlink:`streamice_forcing_period` |
0149 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0150 | :varlink:`streamiceTopogFile` | :kbd:`' '` | topography initialization file (m); requires #define :varlink:`USE_ALT_RLOW` |
0151 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0152 | :varlink:`streamiceHmaskFile` | :kbd:`' '` | :varlink:`streamice_hmask` initialization file; requires #define :varlink:`STREAMICE_GEOM_FILE_SETUP` |
0153 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0bad585a21 Navi*0154 | :varlink:`streamiceuFaceBdryFile` | :kbd:`' '` | :varlink:`streamice_ufacemask_bdry` initialization file; requires #define :varlink:`STREAMICE_GEOM_FILE_SETUP` |
07e785229e dngo*0155 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0bad585a21 Navi*0156 | :varlink:`streamicevFaceBdryFile` | :kbd:`' '` | :varlink:`streamice_vfacemask_bdry` initialization file; requires #define :varlink:`STREAMICE_GEOM_FILE_SETUP` |
07e785229e dngo*0157 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0158 | :varlink:`streamiceuMassFluxFile` | :kbd:`' '` | mass flux at :math:`u`-faces init. file (m\ :sup:`2`\ /yr); requires #define :varlink:`STREAMICE_GEOM_FILE_SETUP` |
0159 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0160 | :varlink:`streamicevMassFluxFile` | :kbd:`' '` | mass flux at :math:`v`-faces init. file (m\ :sup:`2`\ /yr); requires #define :varlink:`STREAMICE_GEOM_FILE_SETUP` |
0161 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0162 | :varlink:`streamiceuFluxTimeDepFile` | :kbd:`' '` | time-depend. mass flux at :math:`u`-faces file (m\ :sup:`2`\ /yr); |
0163 | | | requires #define :varlink:`STREAMICE_GEOM_FILE_SETUP` |
0164 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0165 | :varlink:`streamicevFluxTimeDepFile` | :kbd:`' '` | time-depend. mass flux at :math:`v`-faces file (m\ :sup:`2`\ /yr); |
0166 | | | requires #define :varlink:`STREAMICE_GEOM_FILE_SETUP` |
0167 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0168 | :varlink:`streamiceuNormalStressFile` | :kbd:`' '` | calving front normal stress parm along :math:`u`-faces (non-dim.; see :ref:`ssub_streamice_boundary_stress`) |
0169 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0170 | :varlink:`streamicevNormalStressFile` | :kbd:`' '` | calving front normal stress parm along :math:`v`-faces (non-dim.; see :ref:`ssub_streamice_boundary_stress`) |
0171 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0172 | :varlink:`streamiceuShearStressFile` | :kbd:`' '` | calving front normal stress parm along :math:`u`-faces (non-dim.; see :ref:`ssub_streamice_boundary_stress`) |
0173 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0174 | :varlink:`streamicevShearStressFile` | :kbd:`' '` | calving front normal stress parm along :math:`v`-faces (non-dim.; see :ref:`ssub_streamice_boundary_stress`) |
0175 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0176 | :varlink:`streamiceuNormalTimeDepFile` | :kbd:`' '` | time-dependent version of :varlink:`streamiceuNormalStressFile` |
0177 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0178 | :varlink:`streamicevNormalTimeDepFile` | :kbd:`' '` | time-dependent version of :varlink:`streamicevNormalStressFile` |
0179 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0180 | :varlink:`streamiceuShearTimeDepFile` | :kbd:`' '` | time-dependent version of :varlink:`streamiceuShearStressFile` |
0181 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0182 | :varlink:`streamicevShearTimeDepFile` | :kbd:`' '` | time-dependent version of :varlink:`streamicevShearStressFile` |
0183 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0184 | :varlink:`streamice_adot_uniform` | 0 | time/space uniform surface accumulation rate (m/yr) |
0185 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0186 | :varlink:`streamice_forcing_period` | 0 | file input frequency for streamice time-dependent forcing fields (s) |
0187 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0188 | :varlink:`streamice_smooth_gl_width` | 0 | thickness range parameter in basal traction smoothing across grounding line (m) |
0189 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0190 | :varlink:`streamice_allow_reg_coulomb` | FALSE | use regularized Coulomb sliding :eq:`coul_eqn`. Requires :varlink:`STREAMICE_COULOMB_SLIDING` CPP option. |
0191 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0fbff46b46 dngo*0192 | :varlink:`STREAMICE_vel_ext` | FALSE | over-ride velocity calculation with binary file |
0193 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0194 | :varlink:`STREAMICE_vel_ext` | FALSE | over-ride velocity calculation with binary file, with velocities applied directly to C-grid. |
0195 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0196 | :varlink:`STREAMICE_uvel_ext_file` | FALSE | file to initialise `x`-velocity component (m/a) |
0197 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0198 | :varlink:`STREAMICE_vvel_ext_file` | FALSE | file to initialise `y`-velocity component (m/a) |
0199 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
07e785229e dngo*0200
0201 .. _ssub_phys_pkg_streamice_domain_setup:
0202
0203 Configuring domain through files
0204 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
0205
0206 The :varlink:`STREAMICE_GEOM_FILE_SETUP` CPP option allows versatility in defining the domain.
0207 With this option, the array :varlink:`streamice_hmask` must be initialized through a file (:varlink:`streamiceHmaskFile`)
0208 as must :varlink:`streamice_ufacemask_bdry` and :varlink:`streamice_vfacemask_bdry`
0209 (through :varlink:`streamiceuFaceBdryFile` and :varlink:`streamicevFaceBdryFile`)
0210 as well as :varlink:`u_flux_bdry_SI` and :varlink:`v_flux_bdry_SI`, volume flux at the boundaries,
0211 where appropriate (through :varlink:`streamiceuMassFluxFile` and :varlink:`streamicevMassFluxFile`).
0212 Thickness must be initialized through a file as well (:varlink:`streamicethickFile`); :varlink:`streamice_hmask`
0213 is set to zero where ice thickness is zero, and boundaries between in-domain and out-of-domain cells
0214 (according to :varlink:`streamice_hmask`) are no-slip by default.
0215
0216 When using this option, it is important that for all internal boundaries,
0217 :varlink:`streamice_ufacemask_bdry` and :varlink:`streamice_vfacemask_bdry` are -1
0218 (this will not be the case if :varlink:`streamiceuFaceBdryFile` and :varlink:`streamicevFaceBdryFile` are undefined).
0219
0220 In fact, if :varlink:`streamice_hmask` is configured correctly, :varlink:`streamice_ufacemask_bdry`
0221 and :varlink:`streamice_vfacemask_bdry` can be set uniformly to -1, UNLESS there are no-stress or
0222 flux-condition boundaries in the domain. Where :varlink:`streamice_ufacemask_bdry` and :varlink:`streamice_vfacemask_bdry`
0223 are set to -1, they will be overridden at (a) boundaries where :varlink:`streamice_hmask` changes from 1 to -1
0224 (which become no-slip boundaries), and (b) boundaries where :varlink:`streamice_hmask` changes from 1 to 0 (which become calving front boundaries).
0225
0226 An example of domain configuration through files can be found in :filelink:`verification/halfpipe_streamice`.
0227 By default, :filelink:`verification/halfpipe_streamice` is compiled with :varlink:`STREAMICE_GEOM_FILE_SETUP` undefined,
0228 but the user can modify this option. The file :filelink:`verification/halfpipe_streamice/input/data.streamice_geomSetup`
0229 represents an alternative version of :filelink:`verification/halfpipe_streamice/input/data.streamice`
0230 in which the appropriate binary files are specified.
0231
0232 Configuring domain through parameters
0233 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
0234
0235 For a very specific type of domain the boundary conditions and initial thickness can be set
0236 via parameters in ``data.streamice``.
0237 Such a domain will be rectangular. In order to use this option, the :varlink:`STREAMICE_GEOM_FILE_SETUP` CPP flag should be undefined.
0238
0239 There are different boundary condition types (denoted within the parameter names) that can be set:
0240
0241 - ``noflow``: :math:`x`- and :math:`y`-velocity will be zero along this boundary.
0242
0243 - ``nostress``: velocity normal to boundary will be zero; there will be no tangential stress along the boundary.
0244
0245 - ``fluxbdry``: a mass volume flux is specified along this boundary, which becomes a boundary condition
0246 for the thickness advection equation (see :ref:`ssub_phys_pkg_streamice_eqns`). Velocities will be zero.
0247 The corresponding parameters :varlink:`flux_bdry_val_NORTH`, :varlink:`flux_bdry_val_SOUTH`,
0248 :varlink:`flux_bdry_val_EAST` and :varlink:`flux_bdry_val_WEST` then set the values.
0249
0250 - ``CFBC``: calving front boundary condition, a Neumann condition based on ice thickness and bed depth,
0251 is imposed at this boundary (see :ref:`ssub_phys_pkg_streamice_eqns`).
0252
0253 Note the above only apply if there is dynamic ice in the cells at the boundary in question.
0254 The boundary conditions are then set by specifying the above conditions over ranges of each
0255 (north/south/east/west) boundary. The division of each boundary should be exhaustive and the ranges should not overlap.
0256 Parameters to initialize boundary conditions (defined under :varlink:`STREAMICE_PARM03` namelist) are listed in :numref:`tab_phys_pkg_streamice_domainparms`.
0257
0258 .. table:: Parameters to initialize boundary conditions (defined under :varlink:`STREAMICE_PARM03` namelist)
0259 :name: tab_phys_pkg_streamice_domainparms
0260
0261 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0262 | Parameter | Default | Description |
0263 +===========================================+==============================+====================================================================================================================+
0264 | :varlink:`min_x_noflow_NORTH` | 0 | western limit of no-flow region on northern boundary (m) |
0265 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0266 | :varlink:`max_x_noflow_NORTH` | 0 | eastern limit of no-flow region on northern boundary (m) |
0267 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0268 | :varlink:`min_x_noflow_SOUTH` | 0 | western limit of no-flow region on southern boundary (m) |
0269 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0270 | :varlink:`max_x_noflow_SOUTH` | 0 | eastern limit of no-flow region on southern boundary (m) |
0271 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0272 | :varlink:`min_y_noflow_EAST` | 0 | southern limit of no-flow region on eastern boundary (m) |
0273 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0274 | :varlink:`max_y_noflow_EAST` | 0 | northern limit of no-flow region on eastern boundary (m) |
0275 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0276 | :varlink:`min_y_noflow_WEST` | 0 | southern limit of no-flow region on western boundary (m) |
0277 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0278 | :varlink:`max_y_noflow_WEST` | 0 | northern limit of no-flow region on eastern boundary (m) |
0279 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0280 | :varlink:`min_x_nostress_NORTH` | 0 | western limit of no-stress region on northern boundary (m) |
0281 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0282 | :varlink:`max_x_nostress_NORTH` | 0 | eastern limit of no-stress region on northern boundary (m) |
0283 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0284 | :varlink:`min_x_nostress_SOUTH` | 0 | western limit of no-stress region on southern boundary (m) |
0285 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0286 | :varlink:`max_x_nostress_SOUTH` | 0 | eastern limit of no-stress region on southern boundary (m) |
0287 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0288 | :varlink:`min_y_nostress_EAST` | 0 | southern limit of no-stress region on eastern boundary (m) |
0289 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0290 | :varlink:`max_y_nostress_EAST` | 0 | northern limit of no-stress region on eastern boundary (m) |
0291 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0292 | :varlink:`min_y_nostress_WEST` | 0 | southern limit of no-stress region on western boundary (m) |
0293 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0294 | :varlink:`max_y_nostress_WEST` | 0 | northern limit of no-stress region on eastern boundary (m) |
0295 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0296 | :varlink:`min_x_fluxbdry_NORTH` | 0 | western limit of flux-boundary region on northern boundary (m) |
0297 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0298 | :varlink:`max_x_fluxbdry_NORTH` | 0 | eastern limit of flux-boundary region on northern boundary (m) |
0299 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0300 | :varlink:`min_x_fluxbdry_SOUTH` | 0 | western limit of flux-boundary region on southern boundary (m) |
0301 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0302 | :varlink:`max_x_fluxbdry_SOUTH` | 0 | eastern limit of flux-boundary region on southern boundary (m) |
0303 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0304 | :varlink:`min_y_fluxbdry_EAST` | 0 | southern limit of flux-boundary region on eastern boundary (m) |
0305 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0306 | :varlink:`max_y_fluxbdry_EAST` | 0 | northern limit of flux-boundary region on eastern boundary (m) |
0307 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0308 | :varlink:`min_y_fluxbdry_WEST` | 0 | southern limit of flux-boundary region on western boundary (m) |
0309 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0310 | :varlink:`max_y_fluxbdry_WEST` | 0 | northern limit of flux-boundary region on eastern boundary (m) |
0311 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0312 | :varlink:`min_x_CFBC_NORTH` | 0 | western limit of calving front condition region on northern boundary (m) |
0313 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0314 | :varlink:`max_x_CFBC_NORTH` | 0 | eastern limit of calving front condition region on northern boundary (m) |
0315 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0316 | :varlink:`min_x_CFBC_SOUTH` | 0 | western limit of calving front condition region on southern boundary (m) |
0317 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0318 | :varlink:`max_x_CFBC_SOUTH` | 0 | eastern limit of calving front condition region on southern boundary (m) |
0319 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0320 | :varlink:`min_y_CFBC_EAST` | 0 | southern limit of calving front condition region on eastern boundary (m) |
0321 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0322 | :varlink:`max_y_CFBC_EAST` | 0 | northern limit of calving front condition region on eastern boundary (m) |
0323 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0324 | :varlink:`min_y_CFBC_WEST` | 0 | southern limit of calving front condition region on western boundary (m) |
0325 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0326 | :varlink:`max_y_CFBC_WEST` | 0 | northern limit of calving front condition region on eastern boundary (m) |
0327 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0328 | :varlink:`flux_bdry_val_SOUTH` | 0 | volume flux per width entering at flux-boundary on southern boundary (m\ :sup:`2`\ /a) |
0329 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0330 | :varlink:`flux_bdry_val_NORTH` | 0 | volume flux per width entering at flux-boundary on southern boundary (m\ :sup:`2`\ /a) |
0331 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0332 | :varlink:`flux_bdry_val_EAST` | 0 | volume flux per width entering at flux-boundary on southern boundary (m\ :sup:`2`\ /a) |
0333 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0334 | :varlink:`flux_bdry_val_WEST` | 0 | volume flux per width entering at flux-boundary on southern boundary (m\ :sup:`2`\ /a) |
0335 +-------------------------------------------+------------------------------+--------------------------------------------------------------------------------------------------------------------+
0336
0337
0338 .. _ssub_phys_pkg_streamice_descr:
0339
0340 Description
0341 ~~~~~~~~~~~
0342
0343 .. _ssub_phys_pkg_streamice_eqns:
0344
0345 Equations Solved
0346 ^^^^^^^^^^^^^^^^
0347
0348 The model solves for 3 dynamic variables: :math:`x`-velocity
0349 (:math:`u`), :math:`y`-velocity (:math:`v`), and thickness (:math:`h`).
0350 There is also a variable that tracks coverage of fractional cells,
0351 discussed in :ref:`ssub_phys_pkg_streamice_advance`.
0352
0353 By default the model solves the "shallow shelf approximation" (SSA) for
0354 velocity. The SSA is appropriate for floating ice (ice shelf) or ice
0355 flowing over a low-friction bed (e.g., Macayeal (1989) :cite:`Macayeal:89`). The SSA consists
0356 of the :math:`x`-momentum balance:
0357
0358 .. math::
0359 \partial_x(h\nu(4\dot{\varepsilon}_{xx}+2\dot{\varepsilon}_{yy})) +
0360 \partial_y(2h\nu\dot{\varepsilon}_{xy}) - \tau_{bx} = \rho g h \frac{\partial s}{\partial x}
0361 :label: mom_x
0362
0363 the :math:`y`-momentum balance:
0364
0365 .. math::
0366 \partial_x(2h\nu\dot{\varepsilon}_{xy}) +
0367 \partial_y(h\nu(4\dot{\varepsilon}_{yy}+2\dot{\varepsilon}_{xx})) - \tau_{by} =
0368 \rho g h \frac{\partial s}{\partial y}
0369 :label: mom_y
0370
0371 where :math:`\rho` is ice density, :math:`g` is gravitational acceleration, and :math:`s` is surface elevation. :math:`\nu`,
0372 :math:`\tau_{bi}` and :math:`\dot{\varepsilon}_{ij}` are ice viscosity, basal drag, and the strain rate tensor, respectively, all explained below.
0373
0374 From the velocity field, thickness evolves according to the continuity
0375 equation:
0376
0377 .. math::
0bad585a21 Navi*0378 h_t + \nabla \cdot(h\vec{u}) = \dot{a}-\dot{b}
07e785229e dngo*0379 :label: adv_eqn
0380
0381 Where :math:`\dot{b}` is a basal mass balance (e.g., melting due to
0382 contact with the ocean), positive where there is melting. This is a field that can be specified through a file. At the moment surface mass
0383 balance :math:`\dot{a}` can only be set as uniform. Where ice is grounded,
0384 surface elevation is given by
0385
0386 .. math:: s = R + h
0387
0388 where :math:`R(x,y)` is the bathymetry, and the basal elevation
0389 :math:`b` is equal to :math:`R`. If ice is floating, then the assumption
0390 of hydrostasy and constant density gives
0391
0392 .. math:: s = (1-\frac{\rho}{\rho_w}) h,
0393
0394 where :math:`\rho_w` is a representative ocean density, and
0395 :math:`b=-(\rho/\rho_w)h`. Again by hydrostasy, floation is assumed
0396 wherever
0397
0398 .. math:: h \leq -\frac{\rho_w}{\rho}R
0399
0400 is satisfied. Floatation criteria is stored in :varlink:`float_frac_streamice`,
0401 equal to 1 where ice is grounded, and equal to 0 where ice is floating.
0402
0403 The strain rates :math:`\varepsilon_{ij}` are generalized to the case of
0404 orthogonal curvilinear coordinates, to include the "metric" terms that
0405 arise when casting the equations of motion on a sphere or projection on
0406 to a sphere (see :ref:`para_phys_pkg_seaice_discretization`).
0407 Thus
0408
0409 .. math::
0410 \begin{aligned}
0411 \dot{\varepsilon}_{xx} = & u_x + k_1 v, \notag \\
0412 \dot{\varepsilon}_{yy} = & v_y + k_1 u, \notag \\
0413 \dot{\varepsilon}_{xy} = & \frac{1}{2}(u_y+v_x) + k_1 u + k_2 v. \notag \end{aligned}
0414
0415 :math:`\nu` has the form arising from Glen's law
0416
0417 .. math::
0418 \nu =
0419 \frac{1}{2}A^{-\frac{1}{n}}\left(\dot{\varepsilon}_{xx}^2+\dot{\varepsilon}_{yy}
0420 ^2+\dot{\varepsilon}_{xx}\dot{\varepsilon}_{yy}+\dot{\varepsilon}_{xy}^2+\dot{
0bad585a21 Navi*0421 \varepsilon}_{\min}^2\right)^{\frac{1-n}{2n}}
07e785229e dngo*0422 :label: visc_eqn
0423
0424 though the form is slightly different if a hybrid formulation is used.
0425
0426 Whether :math:`\tau_b` is nonzero depends on whether the floatation
0427 condition is satisfied. Currently this is determined simply on an
0428 instantaneous cell-by-cell basis (unless subgrid interpolation is used),
0429 as is the surface elevation :math:`s`, but possibly this should be
0430 rethought if the effects of tides are to be considered.
0431 :math:`\vec{\tau}_b` has the form
0432
0433 .. math::
0bad585a21 Navi*0434 \vec{\tau}_b = C (|\vec{u}|^2+u_{\min}^2)^{\frac{m-1}{2}}\vec{u}.
07e785229e dngo*0435 :label: tau_eqn
0436
0437 Again, the form is slightly different if a hybrid formulation is to be
0438 used, and the velocity refers to sliding velocity (:math:`u_b`).
0439
0440 An alternative to the above "power law" sliding parameterization can be used by
0441 defining the :varlink:`STREAMICE_COULOMB_SLIDING` CPP option and setting
0442 :varlink:`streamice_allow_reg_coulomb` to ``.TRUE.``:
0443
0444 .. math::
0445 \vec{\tau}_b = C\frac{|u|^{m}N}{2\left[C^{1/m}|u|+(0.5N)^{1/m}\right]^{m}}u^{-1}\vec{u}
0446 :label: coul_eqn
0447
0448 where :math:`u` is shorthand for the regularized norm in :eq:`tau_eqn` (or for :math:`u_b` if a hybrid formulation is used).
0449 :math:`m` is the same exponent as in :eq:`tau_eqn`. :math:`N` is effective pressure:
0450
0451 .. math::
0452 N = \rho g (h - h_f),
0453 :label: eff_press
0454
0455 with :math:`h_f` the floatation thickness
0456
0457 .. math::
0bad585a21 Navi*0458 h_f = \max\left(0,-\frac{\rho_w}{\rho}R\right),
07e785229e dngo*0459
0460 where :math:`R` is bed elevation. This formulation was used in the MISMIP+ intercomparison tests :cite:`asay-davis:16`.
0461 :eq:`eff_press` assumes complete hydraulic connectivity to the ocean throughout
0462 the domain, which is likely only true within a few tens of kilometers of the
0463 grounding line. With this sliding relation, Coulomb sliding is predominant near the grounding line, with
0464 the yield strength proportional to height above floatation. Further inland sliding transitions to
0465 the power law relation in :eq:`tau_eqn`.
0466
0467 The momentum equations are solved together with appropriate boundary
0468 conditions, discussed below. In the case of a calving front boundary
0469 condition (CFBC), the boundary condition has the following form:
0470
0471 .. math::
0472 (h\nu(4\dot{\varepsilon}_{xx}+2\dot{\varepsilon}_{yy}))n_x +
0473 (2h\nu\dot{\varepsilon}_{xy})n_y = \frac{1}{2}g \left(\rho h^2 - \rho_w
0474 b^2\right)n_x
0475 :label: cfbc_x
0476
0477 .. math::
0478 (2h\nu\dot{\varepsilon}_{xy})n_x +
0479 (h\nu(4\dot{\varepsilon}_{yy}+2\dot{\varepsilon}_{xx}))n_y = \frac{1}{2}g
0480 \left(\rho h^2 - \rho_w b^2\right)n_y.
0481 :label: cfbc_y
0482
0483 Here :math:`\vec{n}` is the normal to the boundary, and :math:`b`
0484 is ice base.
0485
0486 Hybrid SIA-SSA stress balance
0487 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
0488
0489 The SSA does not take vertical shear stress or strain rates (e.g.,
0490 :math:`\sigma_{xz}`, :math:`\partial u/\partial z`) into account.
0491 Although there are other terms in the stress tensor, studies have found
0492 that in all but a few cases, vertical shear and longitudinal stresses
0493 (represented by the SSA) are sufficient to represent glaciological flow.
0494 :filelink:`pkg/streamice` can allow for representation of vertical shear, although the
0495 approximation is made that longitudinal stresses are depth-independent.
0496 The stress balance is referred to as "hybrid" because it is a joining of
0497 the SSA and the "shallow ice approximation" (SIA), which accounts
0498 only for vertical shear. Such hybrid formulations have been shown to be
0499 valid over a larger range of conditions than SSA (Goldberg 2011) :cite:`goldberg:2011`.
0500
0501 In the hybrid formulation, :math:`\overline{u}` and
0502 :math:`\overline{v}`, the depth-averaged :math:`x-` and :math:`y-`
0503 velocities, replace :math:`u` and :math:`v` in :eq:`mom_x`, :eq:`mom_y`, and :eq:`adv_eqn`, and gradients
0504 such as :math:`u_x` are replaced by :math:`(\overline{u})_x`. Viscosity
0505 becomes
0506
0507 .. math::
0508 \nu =
0509 \frac{1}{2}A^{-\frac{1}{n}}\left(\dot{\varepsilon}_{xx}^2+\dot{\varepsilon}_{yy}
0510 ^2+\dot{\varepsilon}_{xx}\dot{\varepsilon}_{yy}+\dot{\varepsilon}_{xy}^2+\frac{1
0bad585a21 Navi*0511 }{4}u_z^2+\frac{1}{4}v_z^2+\dot{\varepsilon}_{\min}^2\right)^{\frac{1-n}{2n}}
07e785229e dngo*0512
0513 In the formulation for :math:`\tau_b`, :math:`u_b`, the horizontal
0514 velocity at :math:`u_b` is used instead. The details are given in Goldberg (2011)
0515 :cite:`goldberg:2011`.
0516
0517 .. _ssub_phys_pkg_streamice_advance:
0518
0519 Ice front advance
0520 ^^^^^^^^^^^^^^^^^
0521
0522 By default all mass flux across calving boundaries is considered lost. However, it is possible to account
0523 for this flux and potential advance of the ice shelf front. If :varlink:`streamice_move_front` is TRUE, then a partial-area formulation is used.
0524
0525 The algorithm is based on Albrecht et al. (2011) :cite:`Albrecht:2011`. In this scheme,
0526 for empty or partial cells adjacent to a calving front, a **reference** thickness
0bad585a21 Navi*0527 :math:`h_{\rm ref}` is found, defined as an average over the thickness
07e785229e dngo*0528 of all neighboring cells that flow into the cell. The total volume input over a time step
0529 is added to the volume of ice already in the cell, whose partial area coverage is then updated
0530 based on the volume and reference thickness. If the area coverage reaches 100% in a time step,
0531 then the additional volume is cascaded into adjacent empty or partial cells.
0532
0533 If :varlink:`streamice_calve_to_mask` is TRUE, this sets a limit to how far the front can
0534 advance, even if advance is allowed. The front will not advance into
0535 cells where the array :varlink:`streamice_calve_mask` is not equal to 1. This mask must
0536 be set through a binary input file to allow the front to advance past its initial position.
0537
0538 No calving parameterization is implemented in :filelink:`pkg/streamice`. However,
0539 front advancement is a precursor for such a development to be added.
0540
0541 .. _ssub_phys_pkg_streamice_units:
0542
0543 Units of input files
0544 ^^^^^^^^^^^^^^^^^^^^
0545
0546 The inputs for basal traction (:varlink:`streamicebasalTracFile`, :varlink:`C_basal_fric_const`)
0547 and ice stiffness (:varlink:`streamiceGlenConstFile`, :varlink:`B_glen_isothermal`) require specific units.
0548 For ice stiffness (`A` in :eq:`visc_eqn`), :math:`B=A^{-1/n}` is specified; or, more accurately,
0549 its square root :math:`A^{-1/(2n)}` is specified (this is to ensure positivity of `B` by squaring the input).
0550 The units of :varlink:`streamiceGlenConstFile` and :varlink:`B_glen_isothermal` are
0551 :math:`\mathrm{Pa}^{1/2}\ \mathrm{yr}^{1/(2n)}`
0552 where :math:`n` is :varlink:`n_glen`.
0553
0554 :varlink:`streamicebasalTracFile` and :varlink:`C_basal_fric_const` initialize the basal traction
0555 (`C` in :eq:`tau_eqn`). Again :math:`C^{1/2}` is directly specified rather than `C` to ensure positivity. The units are
0556 :math:`\mathrm{Pa}^{1/2} (\mathrm{m }\ \mathrm{yr}^{-1})^{n_b}`
0557 where :math:`n_b` is :varlink:`n_basal_friction`.
0558
0559 Numerical Details
0560 ~~~~~~~~~~~~~~~~~
0561
0562 .. figure:: figs/stencil.*
0563 :width: 50%
0564 :align: center
0565 :alt: STREAMICE stencil
0566 :name: figstencil
0567
0568 Grid locations of thickness (`h`), velocity (`u,v`), area, and various masks.
0569
0570 .. figure:: figs/mask_cover.*
0571 :width: 50%
0572 :align: center
0573 :alt: STREAMICE masks
0574 :name: figmask_cover
0575
0576 Hypothetical configuration, detailing the meaning of thickness and velocity
0577 masks and their role in controlling boundary conditions.
0578
0579 The momentum balance is solved via iteration on viscosity (Goldberg 2011 :cite:`goldberg:2011`). At each iteration,
0580 a linear elliptic differential equation is solved via a finite-element method using bilinear basis functions.
0581 The velocity solution "lives" on cell corners, while thickness "lives" at cell centers (:numref:`figstencil`).
0582 The cell-centered thickness is then evolved using a second-order slope-limited finite-volume scheme,
0583 with the velocity field from the previous solve. To represent the flow of floating ice, basal stress
0584 terms are multiplied by an array :varlink:`float_frac_streamice`, a cell-centered array which determines
0585 where ice meets the floation condition.
0586
0587 The computational domain of :filelink:`pkg/streamice` (which may be smaller than the array/grid as
0588 defined by :filelink:`SIZE.h <model/inc/SIZE.h>` and :filelink:`GRID.h <model/inc/GRID.h>`)
0589 is determined by a number of mask
0590 arrays within :filelink:`pkg/streamice`. They are
0591
0592 - :math:`hmask` (:varlink:`streamice_hmask`): equal to 1 (ice-covered), 0
0593 (open ocean), 2 (partly-covered), or -1 (out of domain)
0594
0595 - :math:`umask` (:varlink:`streamice_umask`): equal to 1 (an "active" velocity
0596 node), 3 (a Dirichlet node), or 0 (zero velocity)
0597
0598 - :math:`vmask` (:varlink:`streamice_vmask`): similar to umask
0599
0600 - :math:`ufacemaskbdry` (:varlink:`streamice_ufacemask_bdry`): equal to -1
0601 (interior face), 0 (no-slip), 1 (no-stress), 2 (calving stress
0602 front), or 4 (flux input boundary); when 4, then
0603 :varlink:`u_flux_bdry_SI` must be initialized, through binary or parameter
0604 file
0605
0606 - :math:`vfacemaskbdry` (:varlink:`streamice_vfacemask_bdry`): similar to
0607 :math:`ufacemaskbdry`
0608
0609 :math:`hmask` is defined at cell centers, like :math:`h`. :math:`umask`
0610 and :math:`vmask` are defined at cell nodes, like velocities.
0611 :math:`ufacemaskbdry` and :math:`vfacemaskbdry` are defined at cell
0bad585a21 Navi*0612 faces, like velocities in a C-grid - but unless one sets
07e785229e dngo*0613 ``#define`` :varlink:`STREAMICE_GEOM_FILE_SETUP` in
0614 :filelink:`STREAMICE_OPTIONS.h <pkg/streamice/STREAMICE_OPTIONS.h>`,
0615 the values are only relevant at the boundaries of the grid.
0616
0617 The values of :math:`umask` and :math:`vmask` determine which nodal
0618 values of :math:`u` and :math:`v` are involved in the solve for
0619 velocities. These masks are not configured directly by the user, but are re-initialized based
0620 on :varlink:`streamice_hmask`, :varlink:`streamice_ufacemask_bdry` and :varlink:`streamice_vfacemask_bdry`
0621 at each time step. :numref:`figmask_cover`
0622 demonstrates how these values are set in various cells.
0623
0624 With :math:`umask` and :math:`vmask` appropriately initialized, subroutine
0625 :filelink:`streamice_vel_solve.F <pkg/streamice/streamice_vel_solve.F>` can proceed rather generally.
0626 Contributions are only evaluated if :math:`hmask=1` in a given cell, and a given nodal
0627 basis function is only considered if :math:`umask=1` or :math:`vmask=1`
0628 at that node.
0629
0630
0631 Additional Features
0632 ~~~~~~~~~~~~~~~~~~~
0633
0634 .. Grounding line parameterization
0635 .. ###############################
0636
0637 .. Representing grounding line movement (change of boundary between grounded and floating ice) is problematic in ice sheet models due to the high resolution required. It has been found that sub-grid treatment of the grounding line can partially alleviate this requirement (Gladstone et al, 2011). STREAMICE implements a simple "smoothing" of the floatation condition. By default, ``float_frac_streamice`` is equal to 0 in cells that satisfy the floatation condition, and 1 elsewhere. If the compile option ``STREAMICE_SMOOTH_FLOATATION2`` is defined, then the array varies smoothly between 0 and 1 in cells where :math:`|h-h_f| < w_{smooth}/2`, where
0638
0639 .. .. math::
0640
0641 .. h_f = -\frac{\rho}{\rho_w}R
0642
0643 .. and :math:`w_{smooth}` is specified by ``streamice_smooth_gl_width``. This modification then smooths the transition from grounded to floating ice with respect to basal stress. It is found that this parameterisation is necessary in order to achieve grounding line reversibility in the MISMIP3D intercomparison experiment (Pattyn et al, 2013).
0644
0645 PETSc
0646 ^^^^^
0647
0648 There is an option to use PETSc for the matrix solve component of the velocity solve,
0649 and this has been observed to give a 3- or 4-fold improvement in performance over the
0650 inbuilt conjugate gradient solver in a number of cases. To use this option, the CPP option :varlink:`ALLOW_PETSC` must be defined,
0651 and MITgcm must be compiled with the ``-mpi`` flag (see :numref:`build_mpi`).
0652 However, often a system-specific installation of PETSc is required.
0653 If you wish to use PETSc with :filelink:`pkg/streamice`, please contact the author.
0654
0655 .. _ssub_streamice_boundary_stress:
0656
0657 Boundary Stresses
0658 ^^^^^^^^^^^^^^^^^
0659
0660 The calving front boundary conditions :eq:`cfbc_x` and :eq:`cfbc_y` are intended for ice fronts bordering open ocean.
0661 However, there may be reasons to apply different Neumann conditions at these locations, e.g., one might want to
0662 represent force associated with ice melange, or to represent parts of the ice shelf that are not resolved,
0663 as in Goldberg et al. (2015) :cite:`Goldberg:2015`. The user can then modify these boundary conditions in the form
0664
0665 .. math::
0666 (h\nu(4\dot{\varepsilon}_{xx}+2\dot{\varepsilon}_{yy}))n_x +
0667 (2h\nu\dot{\varepsilon}_{xy})n_y = \frac{1}{2}g \left(\rho h^2 - \rho_w
0668 b^2\right)n_x + \sigma n_x + \tau n_y
0669
0670 .. math::
0671 (2h\nu\dot{\varepsilon}_{xy})n_x +
0672 (h\nu(4\dot{\varepsilon}_{yy}+2\dot{\varepsilon}_{xx}))n_y = \frac{1}{2}g
0673 \left(\rho h^2 - \rho_w b^2\right)n_y + \sigma n_y + \tau n_x
0674
0675 In these equations, :math:`\sigma` and :math:`\tau` represent normal and shear stresses at the boundaries of cells.
0676 They are not specified directly, but through coefficients :math:`\gamma_{\sigma}` and :math:`\gamma_{\tau}`:
0677
0678 .. math::
0679 \sigma = \frac{1}{2}g \left(\rho h^2 - \rho_w
0680 b^2\right)\gamma_{\sigma}
0681
0682 .. math::
0683 \tau = \frac{1}{2}g \left(\rho h^2 - \rho_w
0684 b^2\right)\gamma_{\tau}
0685
0686 :math:`\gamma_{\sigma}` is specified through :varlink:`streamiceuNormalStressFile`, :varlink:`streamicevNormalStressFile`,
0687 :varlink:`streamiceuNormalTimeDepFile`, :varlink:`streamicevNormalTimeDepFile` and :math:`\gamma_{\tau}`
0688 is specified through :varlink:`streamiceuShearStressFile`, :varlink:`streamicevShearStressFile`,
0689 :varlink:`streamiceuShearTimeDepFile`, and :varlink:`streamicevShearTimeDepFile`.
0690 Within the file names, the ``u`` and ``v`` determine whether the values are specified
0691 along horizontal (:math:`u`-) faces and vertical (:math:`v`-) faces. The values will only
0692 have an effect if they are specified along calving front boundaries (see :ref:`ssub_phys_pkg_streamice_domain_setup`).
0693
0694 Adjoint
0695 ~~~~~~~
0696
0697 The STREAMICE package is adjointable using both TAF (Goldberg et al. 2013 :cite:`goldberg_heimbach:2013`)
0698 and OpenAD (Goldberg et al. 2016 :cite:`goldberg_openad_fixed:2016`). In OpenAD, the fixed-point method of
0699 :cite:`christianson:94` is implemented, greatly reducing the memory requirements and also improving performance when PETSc is used.
0700
0701 Verification experiments with both OpenAD and TAF are located in the :filelink:`verification/halfpipe_streamice` (see below).
0702
0703 Key Subroutines
0704 ~~~~~~~~~~~~~~~
0705
0706 Top-level routine: :filelink:`streamice_timestep.F <pkg/streamice/streamice_timestep.F>` (called from :filelink:`model/src/do_oceanic_phys.F`)
0707
0708 ::
0709
0710 CALLING SEQUENCE
0711 ...
0712 streamice_timestep (called from DO_OCEANIC_PHYS)
0713 |
0714 |-- #ifdef ALLOW_STREAMICE_TIMEDEP_FORCING
0715 | STREAMICE_FIELDS_LOAD
0716 | #endif
0717 |
0718 |--#if (defined (ALLOW_STREAMICE_OAD_FP))
0719 | STREAMICE_VEL_SOLVE_OPENAD
0720 | #else
0721 | STREAMICE_VEL_SOLVE
0722 | |
0723 | |-- STREAMICE_DRIVING_STRESS
0724 | |
0725 | | [ITERATE ON FOLLOWING]
0726 | |
0727 | |-- STREAMICE_CG_WRAPPER
0728 | | |
0729 | | |-- STREAMICE_CG_SOLVE
0730 | | #ifdef ALLOW_PETSC
0731 | | STREAMICE_CG_SOLVE_PETSC
0732 | | #endif
0733 | |
0734 | |-- #ifdef STREAMICE_HYBRID_STRESS
0735 | STREAMICE_VISC_BETA_HYBRID
0736 | #else
0737 | STREAMICE_VISC_BETA
0738 | #endif
0739 |
0740 |-- STREAMICE_ADVECT_THICKNESS
0741 | |
0742 | |-- STREAMICE_ADV_FRONT
0743 |
0744 |-- STREAMICE_UPD_FFRAC_UNCOUPLED
0745 |
0746
0747
0748 STREAMICE diagnostics
0749 ~~~~~~~~~~~~~~~~~~~~~
0750
0751 Diagnostics output is available via the diagnostics package (:ref:`outp_pack`). Available output fields are summarized in the
0752 following table:
0753
0754 .. code-block:: text
0755
0756 ----------------------------------------------------------------------------
0757 <-Name->|Levs| mate |<- code ->|<-- Units -->|<- Tile (max=80c)
0758 ----------------------------------------------------------------------------
0759 SI_Uvel | 1 | |UZ L1|m/a |Ice stream x-velocity
0760 SI_Vvel | 1 | |VZ L1|m/a |Ice stream y-velocity
0761 SI_Thick| 1 | |SM L1|m |Ice stream thickness
0762 SI_area | 1 | |SM L1|m^2 |Ice stream cell area coverage
0763 SI_float| 1 | |SM L1|none |Ice stream grounding indicator
0764 SI_hmask| 1 | |SM L1|none |Ice stream thickness mask
0765 SI_usurf| 1 | |SM L1|none |Ice stream surface x-vel
0766 SI_vsurf| 1 | |SM L1|none |Ice stream surface y-vel
0767 SI_ubase| 1 | |SM L1|none |Ice stream basal x-vel
0768 SI_vbase| 1 | |SM L1|none |Ice stream basal y-vel
0769 SI_taubx| 1 | |SM L1|none |Ice stream basal x-stress
0770 SI_tauby| 1 | |SM L1|none |Ice stream basal y-stress
0771 SI_selev| 1 | |SM L1|none |Ice stream surface elev
0772
0773 Experiments and tutorials that use streamice
0774 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
0775
0776 The :filelink:`verification/halfpipe_streamice` experiment uses :filelink:`pkg/streamice`.
0777
0778 .. other references
0779
0780 .. Gladstone, Payne and Cornford (2010). Parameterising the grounding line in flow-line ice sheet models. The Cryosphere, 4, 605–619.
0781
0782 .. Pattyn, F. and others (2013). Grounding-line migration in plan-view marine ice-sheet models: results of the ice2sea MISMIP3d intercomparison. J of Glaciology, 59 (215), 410-422
