tmask.rst - pism - [fork] customized build of PISM, the parallel ice sheet model (tillflux branch)
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       tmask.rst (1860B)
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            1 .. include:: ../../../global.txt
            2 
            3 .. _sec-floatmask:
            4 
            5 Flotation criterion, mask, and sea level
            6 ----------------------------------------
            7 
            8 The most basic decision about marine ice sheet dynamics made internally by PISM is whether
            9 a ice-filled grid cell is floating. That is, PISM applies the "flotation criterion"
           10 :cite:`Winkelmannetal2011` at every time step and at every grid location to determine whether
           11 the ice is floating on the ocean or not. The result is stored in the ``mask`` variable.
           12 The ``mask`` variable has ``pism_intent`` = ``diagnostic``, and thus it does *not* need to
           13 be included in the input file set using the ``-i`` option.
           14 
           15 The possible values of the ``mask`` are given in :numref:`tab-maskvals`. The mask
           16 does not *by itself* determine ice dynamics. For instance, even when ice is floating (mask
           17 value ``MASK_FLOATING``), the user must turn on the usual choice for ice shelf dynamics,
           18 namely the SSA stress balance, by using options :opt:`-stress_balance ssa` or
           19 :opt:`-stress_balance ssa+sia`.
           20 
           21 .. list-table:: The PISM mask, in combination with user options, determines the dynamical
           22                 model.
           23    :name: tab-maskvals
           24    :header-rows: 1
           25    :widths: 1,1
           26 
           27    * - Mask value
           28      - Meaning
           29 
           30    * - 0 = ``MASK_ICE_FREE_BEDROCK``
           31      - ice free bedrock 
           32 
           33    * - 2 = ``MASK_GROUNDED``
           34      - ice is grounded 
           35 
           36    * - 3 = ``MASK_FLOATING``
           37      - ice is floating (the SIA is never applied; the SSA is applied if the ``ssa`` or
           38        ``ssa+sia`` stress balance model is selected
           39 
           40    * - 4 = ``MASK_ICE_FREE_OCEAN``
           41      - ice-free ocean 
           42 
           43 Assuming that the geometry of the ice is allowed to evolve (which can be turned off by
           44 option ``-no_mass``), and assuming an ocean exists so that a sea level is used in the
           45 flotation criterion (which can be turned off by option :opt:`-dry`), then at each time
           46 step the mask will be updated.