trestarting.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 --- trestarting.rst (2692B) --- 1 .. include:: ../../global.txt 2 3 Initialization from a saved model state 4 --------------------------------------- 5 6 "Initialization" has the specific, simple meaning in PISM that option ":opt:`-i`" was 7 used. If a previous PISM run has saved a NetCDF file using ":opt:`-o`" then that file will 8 contain complete initial conditions for continuing the run. The output file from the last 9 run can be loaded with ":opt:`-i`": 10 11 .. code-block:: none 12 13 pisms -eisII A -y 100 -o foo.nc 14 pisms -eisII A -i foo.nc -y 100 -o bar.nc 15 16 As noted verification tests (section :ref:`sec-verif`) and simplified-geometry experiments 17 (section :ref:`sec-simp`) do not need input files at all because they initialize from 18 formulas in the source code. They can, however, be continued from saved model states using 19 :opt:`-i`. Specifying the simplified geometry experiment or verification test *is*, 20 however, necessary if the run is to continue with the climate inputs for that experiment 21 or test. For example, based on the above ``pisms`` runs, it is valid to do 22 23 .. code-block:: none 24 25 pismr -i foo.nc -y 100 -o bar.nc 26 27 but the climate and other parameters use PISM default values, and thus are not 28 (necessarily) the values specified in EISMINT II. 29 30 As a technical note about saved states, a PISM run with :opt:`-stress_balance ssa` also 31 saves the last SSA velocities to the output file in variables :var:`u_ssa` and 32 :var:`v_ssa`. The presence of these velocities adds efficiency in restarting because an 33 initial estimate speeds up the solution of the SSA stress balance equations. If you want 34 to use :opt:`-i` but also ignore these velocities then set 35 :config:`stress_balance.ssa.read_initial_guess` to *false*. 36 37 .. _sec-i-format: 38 39 ``-i`` file format 40 ^^^^^^^^^^^^^^^^^^ 41 42 PISM produces CF-1.5 compliant NetCDF files. The easiest way to learn the output format 43 *and* the :opt:`-i` format is to do a simple run and then look at the metadata in the 44 resulting file, like this: 45 46 .. code-block:: none 47 48 pisms -eisII A -y 10 -o foo.nc 49 ncdump -h foo.nc | less 50 51 Note that variables in the output file have a ``pism_intent`` attribute. When 52 ``pism_intent`` is ``diagnostic``, the variable can be deleted from the file without 53 affecting whether PISM can use it as a :opt:`-i` input file. Variables with 54 ``pism_intent`` is ``model_state``, by contrast, must be present when using :opt:`-i`. 55 56 The automatically-produced :var:`time` variable has a ``units`` attribute like ``"seconds 57 since 1-1-1"`` because the CF metadata conventions require a reference date. 58 59 .. FIXME: double-check the statement below 60 61 By default PISM ignores this reference date except when it is used in unit conversions 62 based on a calendar (see below).