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 Parameters below for the list of options and Scalar time-series for the full list of supported time-series.

Note

Similarly to the snapshot-saving code (section 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 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.)

Parameters

  1. append (false) If true, append to the scalar time series output file.

  2. buffer_size (10000) Number of scalar diagnostic time-series records to hold in memory before writing to disk. (PISM writes this many time-series records to reduce I/O costs.) Send the USR2 signal to flush time-series.

  3. filename Name of the file to save scalar time series to. Leave empty to disable reporting scalar time-series.

  4. times List or range of times defining reporting time intervals.

  5. variables Requested scalar (time-series) diagnostics. Leave empty to save all available diagnostics.

Comments

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. 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:

    \[ \begin{align}\begin{aligned}\mathtt{ice\_volume\_glacierized}\, \mapsto\, &(\mathtt{ice\_volume\_glacierized\_shelf},\\&\phantom{(}\mathtt{ice\_volume\_glacierized\_grounded}),\end{aligned}\end{align} \]

    while

    \[ \begin{align}\begin{aligned}\mathtt{ice\_area\_glacierized}\, \mapsto\, &(\mathtt{ice\_area\_glacierized\_shelf},\\&\phantom{(}\mathtt{ice\_area\_glacierized\_grounded})\end{aligned}\end{align} \]

    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 ice. Thus there is another splitting:

    \[ \begin{align}\begin{aligned}\mathtt{ice\_volume\_glacierized} \mapsto &(\mathtt{ice\_volume\_glacierized\_cold},\\&\phantom{(}\mathtt{ice\_volume\_glacierized\_temperate})\end{aligned}\end{align} \]

    and

    \[ \begin{align}\begin{aligned}\mathtt{ice\_area\_glacierized}\, \mapsto\, &(\mathtt{ice\_area\_glacierized\_cold\_base},\\&\phantom{(}\mathtt{ice\_area\_glacierized\_temperate\_base}).\end{aligned}\end{align} \]
  • 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 [107] and constants­.global_ocean_area). This follows the definition used in the SeaRISE project [3].

  • 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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