Saving time series of scalar diagnostic quantities

It is also possible to save time-series of certain scalar diagnostic quantities using a combination of the options -ts_file, -ts_times, and -ts_vars. For example,

pismr -i foo.nc -y 1e4 -o output.nc -ts_file time-series.nc \
      -ts_times 0:1:1e4 -ts_vars ice_volume_glacierized,ice_area_glacierized_grounded

will run for 10000 years, saving total ice volume and grounded ice area to time-series.nc yearly. See tables Table 28 for the list of options and Scalar time-series for the full list of supported time-series.

Note that, similarly to the snapshot-saving code (section Saving re-startable snapshots of the model state), this mechanism does not affect adaptive time-stepping. Here, however, PISM will save exactly the number of time-series records requested.

Omitting the -ts_vars option makes PISM save all available variables listed in Scalar time-series. Because scalar time-series take minimal storage space, compared to spatially-varying data, this is usually a reasonable choice. Run PISM with the -list_diagnostics option to see the list of all available time-series.

If the file foo.nc, specified by -ts_file foo.nc, already exists then by default the existing file will be moved to foo.nc~ and the new time series will go into foo.nc. To append the time series onto the end of the existing file, use option -ts_append.

PISM buffers time-series data and writes it at the end of the run, once 10000 values are stored, or when an -extra_file is saved, whichever comes first. Sending an USR1 (or USR2) signal to a PISM process flushes these buffers, making it possible to monitor the run. (See section Signals, to control a running PISM model for more about PISM’s signal handling.)

Table 28 Command-line options controlling saving scalar time-series
Option Description
-ts_file Specifies the file to save to.
-ts_times Specifies times to save at as a MATLAB-style range \(a:\Delta t:b\), a comma-separated list, or a keyword (hourly, daily, monthly, yearly). See section Saving time series of spatially-varying diagnostic quantities.
-ts_vars Comma-separated list of variables. Omitting this option is equivalent to listing the all variables.
-ts_append Append time series to file if it already exists. No effect if file does not yet exist.

Besides the above information on usage, here are comments on the physical significance of several scalar diagnostics:

  • For each variable named ..._flux, positive values mean ice sheet mass gain.
  • PISM reports ice volume, ice mass, and several other quantities for “glacierized” areas. These quantities do not include contributions from areas where the ice thickness is equal to or below the value of the configuration parameter output.ice_free_thickness_standard (in meters). Corresponding quantities without the suffix do include areas with a thin, “seasonal” ice cover.
  • Ice volume and area are computed and then split among floating and grounded portions: ice_volume_glacierized \(\mapsto\) (ice_volume_glacierized_shelf, ice_volume_glacierized_grounded) while ice_area_glacierized \(\mapsto\) (ice_area_glacierized_shelf, ice_area_glacierized_grounded). The volumes have units \(m^3\) and the areas have units \(m^2\).
  • The thermodynamic state of the ice sheet can be assessed, in part, by the amount of cold or temperate (“temp”) ice. Thus there is another splitting: ice_volume_glacierized \(\mapsto\) (ice_volume_glacierized_cold, ice_volume_glacierized_temperate) and ice_area_glacierized \(\mapsto\) (ice_area_glacierized_cold_base, ice_area_glacierized_temperate_base).
  • The sea level rise potential sea_level_rise_potential is the increase in sea level (in meters) that would result from melting all the grounded ice not displacing sea water and distributing the corresponding fresh water volume uniformly over the entire global ocean (\(362.5 \cdot 10^6\, km^2\), see [97]). This follows the definition used in the SeaRISE project [55].
  • Fields max_diffusivity and max_hor_vel relate to PISM time-stepping. These quantities appear in per-time-step form in the standard output from PISM (i.e. at default verbosity). max_diffusivity determines the length of the mass continuity sub-steps for the SIA stress balance (sub-)model. max_hor_vel determines the CFL-type restriction for mass continuity and conservation of energy contributions of the SSA stress balance (i.e. sliding) velocity.

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