tmask.rst - pism - [fork] customized build of PISM, the parallel ice sheet model (tillflux branch) (HTM) git clone git://src.adamsgaard.dk/pism (DIR) Log (DIR) Files (DIR) Refs (DIR) LICENSE --- tmask.rst (1860B) --- 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.