Jekyll2024-03-05T18:07:59+00:00https://www.pism.io/feed.xmlPISMWebsite for PISM, the Parallel Ice Sheet ModelThe PISM Authorsuaf-pism@alaska.eduPISM 2.1 is out2023-11-27T00:00:00+00:002023-11-27T00:00:00+00:00https://www.pism.io/news/2023/11/27/pism2.1<p>We are pleased to announce the release of PISM v2.1.</p>
<h2 id="notable-changes-compared-to-v20">Notable changes compared to v2.0</h2>
<p>Some of these were included in 2.0.x bug fix releases.</p>
<h3 id="mass-transport">Mass transport</h3>
<ul>
<li>
<p>Added a flux limiter that ensures strict preservation of non-negativity of ice thickness
and therefore mass conservation up to rounding error.</p>
<p>This is a Zalesak-style limiter described in</p>
<p>P. K. Smolarkiewicz, “Comment on “A Positive Definite Advection Scheme Obtained by
Nonlinear Renormalization of the Advective Fluxes”,” Monthly Weather Review, vol. 117,
no. 11, pp. 2626–2632, 1989, doi:
<a href="https://doi.org/10.1175/1520-0493(1989)117<2626:COPDAS>2.0.CO;2">10.1175/1520-0493(1989)117<2626:COPDAS>2.0.CO;2</a>.</p>
<p>Note that this approach (unlike modifications of the discretization of SIA diffusivity
in the Jarosch et al. paper mentioned below) works with <em>all</em> stress balance models.</p>
</li>
<li>
<p><a href="https://github.com/pism/pism/blob/v2.1/examples/bedrock_step/README.md">Implemented a
benchmark</a>
verifying mass conservation in an “isothermal SIA + mass continuity” setup with “rough”
bed topography.</p>
<p>This benchmark is described in</p>
<p>A. H. Jarosch, C. G. Schoof, and F. S. Anslow, “Restoring mass conservation to shallow
ice flow models over complex terrain,” The Cryosphere, vol. 7, no. 1, pp. 229–240, Feb.
2013, doi: <a href="https://doi.org/10.5194/tc-7-229-2013">10.5194/tc-7-229-2013</a>.</p>
</li>
</ul>
<h3 id="isochrone-tracing">Isochrone tracing</h3>
<ul>
<li>Implemented an <a href="https://www.pism.io/docs/manual/modeling-choices/dynamics/age.html#isochronal-layer-tracing">isochronal layer tracing
scheme</a>
(see A. Born and A. Robinson, “Modeling the Greenland englacial stratigraphy,” The
Cryosphere, vol. 15, no. 9, pp. 4539-4556, 2021, doi:
<a href="https://doi.org/10.5194/tc-15-4539-2021">10.5194/tc-15-4539-2021</a>.)</li>
</ul>
<h3 id="surface-processes">Surface processes</h3>
<ul>
<li>Implemented the <a href="https://www.pism.io/docs/climate_forcing/surface.html#diurnal-energy-balance-model-debm-simple">diurnal energy balance model
dEBM-simple</a>
(see M. Zeitz, R. Reese, J. Beckmann, U. Krebs-Kanzow, and R. Winkelmann, “Impact of the
melt-albedo feedback on the future evolution of the Greenland Ice Sheet with
PISM-dEBM-simple,” The Cryosphere, vol. 15, no. 12, pp. 5739-5764, Dec. 2021, doi:
<a href="https://doi.org/10.5194/tc-15-5739-2021">10.5194/tc-15-5739-2021</a>.)</li>
</ul>
<h3 id="atmosphere-forcing">Atmosphere forcing</h3>
<ul>
<li>Added support for 2D precipitation offsets in <code class="language-plaintext highlighter-rouge">-atmosphere ...,delta_P</code>. If the input
file set using <code class="language-plaintext highlighter-rouge">atmosphere.delta_P.file</code> contains a scalar time series <code class="language-plaintext highlighter-rouge">delta_P</code>, use
that as a time-dependent constant-in-space forcing. If the input file contains a 2D
variable <code class="language-plaintext highlighter-rouge">delta_P</code>, use that as a time-and-space-dependent forcing.</li>
<li>Added support for 2D air temperature offsets in <code class="language-plaintext highlighter-rouge">-atmosphere ...,delta_T</code>. If the input
file set using <code class="language-plaintext highlighter-rouge">atmosphere.delta_T.file</code> contains a scalar time series <code class="language-plaintext highlighter-rouge">delta_T</code>, use
that as a time-dependent constant-in-space forcing. If the input file contains a 2D
variable <code class="language-plaintext highlighter-rouge">delta_T</code>, use that as a time-and-space-dependent forcing.</li>
<li>Added support for piecewise-constant temporal interpolation of near-surface air
temperatures in <code class="language-plaintext highlighter-rouge">-atmosphere given</code>: set
<code class="language-plaintext highlighter-rouge">atmosphere.given.air_temperature_interpolation</code> to <code class="language-plaintext highlighter-rouge">piecewise_constant</code>.</li>
</ul>
<h3 id="ocean-forcing">Ocean forcing</h3>
<ul>
<li>Added the ability to use ocean model components implemented in Python (see
<a href="https://github.com/pism/pism/blob/v2.1/examples/python/pism.py"><code class="language-plaintext highlighter-rouge">examples/python/pism.py</code></a>)</li>
</ul>
<h3 id="calving">Calving</h3>
<ul>
<li>Fixed a bug reported by Christian Rodehacke: calving mechanisms should not remove ice at
ice fronts adjacent to isolated patches of ice-free water (see <a href="https://github.com/pism/pism/issues/521">issue
#521</a>).</li>
</ul>
<h3 id="stress-balance">Stress balance</h3>
<ul>
<li>Improved the initial guess of sliding velocity used when the ice front advances by
extrapolating velocity computed by the <code class="language-plaintext highlighter-rouge">SSAFD</code> solver during the previous time step (set
<code class="language-plaintext highlighter-rouge">stress_balance.ssa.fd.extrapolate_at_margins</code> to <code class="language-plaintext highlighter-rouge">false</code> to disable).</li>
</ul>
<h3 id="energy-conservation">Energy conservation</h3>
<ul>
<li>
<p>PISM no longer attempts to correct energy conservation by freezing basal water.</p>
<p>At each time step PISM checks basal enthalpy and if necessary modifies it to ensure
continuity of temperature in each <code class="language-plaintext highlighter-rouge">bedrock+ice</code> column. Sometimes this modification
creates energy; prior to this change PISM attempted to remove an equivalent amount of
energy by modifying the basal melt rate to freeze water stored at the base.</p>
<p>Under some conditions this basal melt rate adjustment <em>created mass</em> by freezing more
water than available and even led to crashes with error messages stating that ice
thickness exceeds <code class="language-plaintext highlighter-rouge">Lz</code>.</p>
</li>
</ul>
<h3 id="input-and-output-diagnostics">Input and output, diagnostics</h3>
<ul>
<li>Added diagnostics <code class="language-plaintext highlighter-rouge">tendency_of_ice_{amount,mass}_due_to_frontal_melt</code> and
<code class="language-plaintext highlighter-rouge">tendency_of_ice_{amount,mass}_due_to_forced_retreat</code>. Renamed diagnostic
<code class="language-plaintext highlighter-rouge">max_sliding_vel</code> to <code class="language-plaintext highlighter-rouge">max_horizontal_vel</code>.</li>
</ul>
<h3 id="bug-fixes">Bug fixes</h3>
<ul>
<li>Added time bounds to scalar forcing files in
<a href="https://github.com/pism/pism/tree/v2.1/examples/std-greenland"><code class="language-plaintext highlighter-rouge">examples/std-greenland</code></a>.</li>
<li>
<p>Fixed a bug in the code ensuring non-negativity of ice thickness. (The old code added
too much ice in an attempt to ensure non-negativity – so much so that sometimes this
caused crashes with error messages stating that ice thickness exceeds <code class="language-plaintext highlighter-rouge">Lz</code>.)</p>
<p>Note that this “projection step” (<code class="language-plaintext highlighter-rouge">ice_thickness = max(tentative_ice_thickness, 0)</code>)
should have no effect now: the flux limiter mentioned above is designed to ensure
non-negativity. We keep this step, however, to maintain the ability to keep track of ice
thickness changes due to conservation errors (if they ever happen).</p>
</li>
<li>Fixed bugs in scalar diagnostics <code class="language-plaintext highlighter-rouge">ice_volume_cold</code> and <code class="language-plaintext highlighter-rouge">ice_volume_temperate</code>.</li>
<li>Use CF-compliant units “<code class="language-plaintext highlighter-rouge">common_years</code>” in forcing files.</li>
</ul>
<h3 id="other">Other</h3>
<ul>
<li>Added <a href="https://github.com/pism/pism/blob/v2.1/CITATION.cff">CITATION.cff</a> to properly
acknowledge all contributions and to make it easier to cite PISM.</li>
<li>Implemented UNO2, UNO3 and a couple of related transport methods (not used, but
available for future use; see J.-G. Li, “Upstream Nonoscillatory Advection Schemes,”
Monthly Weather Review, vol. 136, no. 12, pp. 4709-4729, Dec. 2008, doi:
<a href="https://doi.org/10.1175/2008mwr2451.1">10.1175/2008mwr2451.1</a>.).</li>
<li>Use <code class="language-plaintext highlighter-rouge">realpath()</code> to resolve relative file names. Now configuration parameters ending in
<code class="language-plaintext highlighter-rouge">.file</code>, when saved to output files and in PISM output to <code class="language-plaintext highlighter-rouge">stdout</code>, contain <em>absolute</em>
file names. This will make it easier to reproduce runs based on an output file.</li>
<li>Added support for checkpointing the HTCondor way (see commit
<a href="https://github.com/pism/pism/commit/3740c41df6f35fdf0d7501f96f5cab362f25a24b">3740c41df</a>).</li>
<li>Use <code class="language-plaintext highlighter-rouge">-list_diagnostics all</code> to print the list of all diagnostics, <code class="language-plaintext highlighter-rouge">-list_diagnostics
spatial</code> for 2D and 3D variables, and <code class="language-plaintext highlighter-rouge">-list_diagnostics scalar</code> for scalar time series.</li>
<li>Added code to generate <code class="language-plaintext highlighter-rouge">pism.pc</code> and <code class="language-plaintext highlighter-rouge">pismicebin.pc</code> for use with <code class="language-plaintext highlighter-rouge">pkg-config</code>. This
will make it easier to use PISM as a library (to couple to a GCM, for example).</li>
<li>PISM’s build system uses <code class="language-plaintext highlighter-rouge">pkg-config</code> to look for some of the required libraries.</li>
<li>Refactored utility classes used to store 2D and 3D arrays.</li>
<li>Replaced <code class="language-plaintext highlighter-rouge">examples/searise-antarctica</code> with <code class="language-plaintext highlighter-rouge">examples/antarctica</code> based on <a href="https://doi.org/10.1594/PANGAEA.734145">ALBMAP
v1</a> data. This avoids a dependency on <a href="https://doi.org/10.5281/zenodo.10140224">SeaRISE
data</a> formerly hosted by the University of
Montana.</li>
</ul>The PISM AuthorsWe are pleased to announce the release of PISM v2.1.Congrats to Constantine2023-05-01T00:00:00+00:002023-05-01T00:00:00+00:00https://www.pism.io/news/2023/05/01/patience<p>Dear PISM users and developers</p>
<p>It’s my pleasure to congratulate our software engineer and PISM mastermind Constatine Khroulev to the birth of his son, Alexander (Sasha). Constantine is now on paternity leave and hence I’d like to ask for your patience as answering PISM questions will take longer in the next couple months.</p>
<p>Thank you for your understanding,</p>
<p>Andy</p>The PISM AuthorsDear PISM users and developersJoint GEUS-PIK workshop October 24-25, 20222022-10-26T00:00:00+00:002022-10-26T00:00:00+00:00https://www.pism.io/news/2022/10/26/geus-pik-workshop<p><img src="/img/news/geus-pik-workshop-group-photo-2022.jpg" alt="" title="Group Photo in front of GEUS" width="50%" /></p>
<p style="text-align: center;"><em>Group photo in front of GEUS.</em></p>
<p>Nanna Karlsson and Liam Colgan hosted the first joint GEUS-PIK PISM workshop at GEUS in Copenhagen, DK, October 24-25, 2022.</p>
<p style="text-align: center;"><img src="/img/news/geus-pik-workshop-photo-1-2022.jpg" alt="" title="R. Winkelmann (PIK)" width="50%" /></p>
<p><em>Ricarda Winkelmann <a href="http://www.pik-potsdam.de">(PIK)</a> introducing the concept of tipping points</em></p>
<p>Over 15 reseachers from <a href="https://eng.geus.dk">GEUS</a>, <a href="http://www.pik-potsdam.de">PIK</a>, <a href="https://www.au.dk">Aarhus University</a>, <a href="http://www.dmi.dk">DMI</a> and <a href="https://www.uaf.edu">UAF</a> attendend the first joint GEUS-PIK PISM workshop at GEUS. The participants presented their latest PISM and PISM-adjacent research interspersed with lively discussions which data sets could be used for model initialization, calibrations and validation, how can we detect tipping points, what are the best practices to initialize PISM, and which physical processes are currently missing. The discussions continued during a visit to the GEUS roof where Nanna showed us the GEUS weather station and during the workshop dinner. Many started dreaming about joining field work in Greenland some day.</p>
<p style="text-align: center;"><img src="/img/news/geus-pik-workshop-photo-2-2022.jpg" alt="" width="50%" /></p>
<p>We are all already looking forward to the next joint workshop currently planned for October 2023.</p>
<p>Thank you Liam and Nanna for organizing and hosting the workshop.</p>
<p style="text-align: center;"><img src="/img/news/geus-pik-workshop-dinner-photo-2022.jpg" alt="" title="Group Dinner" width="50%" /></p>
<p><em>Group dinner Monday evening</em></p>The PISM AuthorsPISM 2.0 is out2021-12-03T00:00:00+00:002021-12-03T00:00:00+00:00https://www.pism.io/news/2021/12/03/pism2.0<p>PISM developers have been hard at work to bring you a brand new
version of PISM, packed with new features. After years of development,
PISM finally includes a Blatter solver, warranting a new major
version: PISM 2.0.</p>
<h2 id="notable-changes">Notable changes</h2>
<h3 id="new-logo">New logo</h3>
<p>PISM has a new logo designed by <a href="https://www.pik-potsdam.de/members/garbe/">Julius Garbe</a>.</p>
<p style="text-align: center;"><img src="https://raw.githubusercontent.com/pism/logo/main/png/pism_logo_transp.png" alt="" width="50%" /></p>
<h3 id="new-website">New website</h3>
<p>The new website at <a href="https://www.pism.io/">www.pism.io</a> replaces the
<a href="http://web.archive.org/web/20210812174625/https://pism-docs.org/wiki/doku.php">old version</a>.</p>
<h3 id="stress-balance">Stress balance</h3>
<ul>
<li>Implemented a <a href="http://www.pism.io/docs/manual/modeling-choices/dynamics/blatter.html">FEM solver for the first order
approximation</a>
of the Stokes equations due to Blatter (1995). This solver supports
multigrid preconditioners (see Brown et al 2013) and includes 5
verification test based on manufactured solutions.</li>
<li>Implemented <a href="http://www.pism.io/docs/manual/simplified-geometry/ismip-hom.html">experiments A,B,C,D,E from the ISMIP-HOM
intercomparison</a>.</li>
<li>Fixed the approximation of the driving stress at floating ice margins
in the
<a href="http://www.pism.io/docs/manual/modeling-choices/dynamics/ssa.html">SSA</a>
solver. (This fix was contributed by Ronja Reese and Torsten
Albrecht; see <a href="http://www.pism.io/docs/technical/ssafd-flow-line.html">these
notes</a> for
details.)</li>
</ul>
<h3 id="basal-strength">Basal strength</h3>
<ul>
<li>Implemented regularized Coulomb sliding as in Zoet & Iverson, 2020, A slip law for
glaciers on deformable beds, equation 3.</li>
<li>Assume that in the “ocean” areas the till at the base is saturated with water, i.e. the
till water amount is equal to <code class="language-plaintext highlighter-rouge">hydrology.tillwat_max</code>. This change should improve
grounding line movement and make the basal yield stress modification turned on with
<code class="language-plaintext highlighter-rouge">basal_yield_stress.slippery_grounding_lines</code> unnecessary.</li>
<li>Implemented a mechanism for “optimizing” the till friction angle used by the Mohr-Coulomb
yield stress model. The implementation is based on the code contributed by T. Albrecht.</li>
</ul>
<h3 id="bed-deformation">Bed deformation</h3>
<ul>
<li>The <a href="http://www.pism.io/docs/manual/modeling-choices/subglacier/bed-deformation.html#given-bed-deformation-history">new <code class="language-plaintext highlighter-rouge">-bed_def given</code>
component</a>
reads in a prescribed bed deformation history from a file (e.g. from
a solid-Earth model) relative to a (high-resolution) reference
topography, indicated by configuration parameter
<code class="language-plaintext highlighter-rouge">bed_deformation.given.file</code> and
<code class="language-plaintext highlighter-rouge">bed_deformation.given.reference_file</code>, respectively.</li>
</ul>
<h3 id="calving">Calving</h3>
<ul>
<li>Implemented scaling of calving rates using a time-dependent factor.
Set <code class="language-plaintext highlighter-rouge">calving.rate_scaling.file</code> to the name of the file containing
<code class="language-plaintext highlighter-rouge">frac_calving_rate</code> (units: “1”).</li>
<li><a href="http://www.pism.io/docs/manual/modeling-choices/marine/calving.html#calving-of-thin-floating-ice">Ice thickness
threshold</a>
read in from <code class="language-plaintext highlighter-rouge">calving.thickness_calving.file</code> can be both space- and
time-dependent.</li>
</ul>
<h3 id="fracture-density-model">Fracture density model</h3>
<ul>
<li>Implemented the <a href="http://www.pism.io/docs/manual/modeling-choices/marine/damage.html">fracture
density</a>
growth parameterization due to Borstad et al (equation 4 in <a href="http://doi.org/10.1002/2015GL067365">Borstad
et al, 2016</a>). Code contributed
by T. Albrecht).</li>
</ul>
<h3 id="atmosphere-forcing">Atmosphere forcing</h3>
<ul>
<li>Support <a href="http://www.pism.io/docs/climate_forcing/atmosphere.html#precipitation-scaling">2D precipitation
scaling</a>
in <code class="language-plaintext highlighter-rouge">-atmosphere ...,frac_P</code>. If the input file set using
<code class="language-plaintext highlighter-rouge">atmosphere.frac_P.file</code> contains a scalar time series <code class="language-plaintext highlighter-rouge">frac_P</code>, use
that as a time-dependent constant-in-space forcing. If the input
file contains a 2D variable <code class="language-plaintext highlighter-rouge">frac_P</code>, use that as a
time-and-space-dependent forcing.</li>
<li>Added surface elevation smoothing to the <a href="http://www.pism.io/docs/climate_forcing/atmosphere.html#orographic-precipitation">orographic precipitation
model</a>.
High-frequency modes in the surface elevation that can develop in
runs with evolving ice geometry (consider grounded ice margins) may
cause oscillations in the computed precipitation field (probably due
to the Gibbs phenomenon). These oscillations may result in an even
rougher topography, triggering a feedback loop polluting model
results. Set
<code class="language-plaintext highlighter-rouge">atmosphere.orographic_precipitation.smoothing_standard_deviation</code>
(in meters) to smooth the ice surface elevation to reduce this
effect.</li>
<li>Added <code class="language-plaintext highlighter-rouge">atmosphere.elevation_change.precipitation.temp_lapse_rate</code> to
the <a href="http://www.pism.io/docs/climate_forcing/atmosphere.html#adjustments-using-modeled-change-in-surface-elevation"><code class="language-plaintext highlighter-rouge">-atmosphere ...,elevation_change</code>
modifier</a>.
Now this parameter is used to compute the temperature change <code class="language-plaintext highlighter-rouge">dT</code>
used to scale precipitation by a factor <code class="language-plaintext highlighter-rouge">exp(C * dT)</code> with <code class="language-plaintext highlighter-rouge">C =
atmosphere.precip_exponential_factor_for_temperature</code>. We need a
separate temperature lapse rate parameter to be able to use this
modifier with atmosphere models that include an elevation-dependent
near-surface air temperature parameterizations, e.g. <code class="language-plaintext highlighter-rouge">-atmosphere
pik,elevation_change</code>.</li>
</ul>
<h3 id="ocean-forcing">Ocean forcing</h3>
<ul>
<li>The <a href="http://www.pism.io/docs/climate_forcing/ocean.html#basal-melt-rate-and-temperature-from-thermodynamics-in-boundary-layer">three-equation ocean
model</a>
<code class="language-plaintext highlighter-rouge">-ocean th</code> uses constant salinity (see
<code class="language-plaintext highlighter-rouge">constants.sea_water.salinity</code>) if <code class="language-plaintext highlighter-rouge">salinity_ocean</code> is not present
in the forcing file.</li>
<li>Added a <a href="http://www.pism.io/docs/climate_forcing/ocean.html#scalar-melange-back-pressure-offsets">new ocean
modifier</a>:
<code class="language-plaintext highlighter-rouge">-ocean ...,delta_MBP</code>. This component reads scalar time-dependent
melange pressure offsets (units: Pa) and uses them in the calving
front boundary condition for the SSA.</li>
<li>Adjusted
<a href="http://www.pism.io/docs/climate_forcing/ocean.html#pico">PICO</a>
ocean input average across covered basins, in which the ice shelf
has in fact a connection to the ocean. Large ice shelves spanning
two basins that do not share an ocean boundary are split into two
separate ice shelf instances. (This code was contributed by Torsten
Albrecht.)</li>
<li>Added <code class="language-plaintext highlighter-rouge">sea_level.constant.value</code>. This sets the default sea level
elevation used with <code class="language-plaintext highlighter-rouge">-sea_level constant</code>.</li>
<li>Removed <code class="language-plaintext highlighter-rouge">ocean.always_grounded</code>. Set <code class="language-plaintext highlighter-rouge">sea_level.constant.value</code> to a
large negative value to ensure that all ice is grounded.</li>
<li>Removed <code class="language-plaintext highlighter-rouge">ocean.melange_back_pressure_fraction</code>: it is no longer
needed.</li>
</ul>
<h2 id="input-and-output-diagnostics">Input and output, diagnostics</h2>
<ul>
<li>Added a new <code class="language-plaintext highlighter-rouge">output.format</code> value: <code class="language-plaintext highlighter-rouge">netcdf4_serial</code> and
<code class="language-plaintext highlighter-rouge">output.compression_level</code>. Use <code class="language-plaintext highlighter-rouge">-o_format netcdf4_serial
-output.compression_level N</code> (<code class="language-plaintext highlighter-rouge">N</code> between 1 and 9) to write
compressed NetCDF from rank 0.</li>
<li>Support writing compressed NetCDF in parallel with NetCDF 4.7.4 or newer and HDF5 1.10.3
or newer. Set <code class="language-plaintext highlighter-rouge">output.compression_level</code> to enable compression.</li>
<li>Stop with an error message if some values of a variable read from a file match the
<code class="language-plaintext highlighter-rouge">_FillValue</code> attribute (PISM expects input files to contain data at all grid points
within the domain).</li>
<li>Now PISM stops with an error message if time-dependent forcing data read from a file do
not span the whole length of a simulation. Set <code class="language-plaintext highlighter-rouge">input.forcing.time_extrapolation</code> to
“true” to disable this check.</li>
<li>Removed the configuration parameter <code class="language-plaintext highlighter-rouge">input.forcing.evaluations_per_year</code>. Now
the code evaluates <em>exact</em> values of time averages of time-dependent forcing inputs.</li>
<li>Major improvement in the handling of time-dependent forcing. A file containing periodic
forcing has to contain <em>exactly</em> one period. The start and the length of the period are
derived from time bounds read from this file. This makes it easier to use periodic
forcing and adds supports for arbitrary period lengths. See the manual section about
time-dependent inputs.</li>
<li>All time-dependent forcing files have to contain time bounds.</li>
<li>Now PISM always respects the reference date in input files.</li>
<li>Improved the approximation of the grounding line flux (scalar and 2D diagnostics
<code class="language-plaintext highlighter-rouge">grounding_line_flux</code>): the flux <em>through</em> the grounding line should be zero if its
direction is parallel to the grounding line. Unfortunately this is impossible to achieve
for an arbitrary grounding line shape if the grounding line is approximated by a mask on
a uniform grid (as in PISM). This change improves the approximation for some
combinations of grounding line shapes and grid resolutions. (This issue was reported by
Ronja Reese.)</li>
</ul>
<h3 id="model-time-and-time-stepping">Model time and time stepping</h3>
<ul>
<li>Added a new parameter: <code class="language-plaintext highlighter-rouge">time_stepping.resolution</code>. PISM rounds time step lengths <em>down</em> to
a multiple of this number (default: 1 second). This reduces <a href="https://github.com/pism/pism/issues/407">the influence of rounding
errors on time step lengths</a>.</li>
<li>Command-line options <code class="language-plaintext highlighter-rouge">-y</code>, <code class="language-plaintext highlighter-rouge">-ys</code>, <code class="language-plaintext highlighter-rouge">-ye</code>, <code class="language-plaintext highlighter-rouge">-max_dt</code> and corresponding configuration
parameters use units of <code class="language-plaintext highlighter-rouge">365 days</code> instead of <code class="language-plaintext highlighter-rouge">years</code>. The latter has the meaning of the
mean tropical year, i.e. the constant used to convert from <code class="language-plaintext highlighter-rouge">1/s</code> to <code class="language-plaintext highlighter-rouge">1/year</code>. Use <code class="language-plaintext highlighter-rouge">-y
1000years</code>, etc to reproduce the old behavior.</li>
<li>Fixed a bug in the code managing time step restrictions (this
affected the last time step of runs using <code class="language-plaintext highlighter-rouge">-skip</code> and runs with
<code class="language-plaintext highlighter-rouge">-skip</code> in which <code class="language-plaintext highlighter-rouge">-max_dt</code> is active).</li>
</ul>
<h3 id="other">Other</h3>
<ul>
<li>Added the new command-line option <code class="language-plaintext highlighter-rouge">-refinement_factor N</code>. Use this
to select a regional modeling domain using <code class="language-plaintext highlighter-rouge">-x_range ... -y_range
...</code>, then use a grid that is <code class="language-plaintext highlighter-rouge">N</code> times finer.</li>
<li>Added support for automatic unit conversion in command-line options.
If an option argument is a number PISM assumes that it uses PISM’s
internal units. If it is a number followed by a units string
recognized by UDUNITS it is automatically converted to PISM’s
internal units. For example, the following are equivalent: <code class="language-plaintext highlighter-rouge">-Lz
1000</code>, <code class="language-plaintext highlighter-rouge">-Lz 1000m</code>, <code class="language-plaintext highlighter-rouge">-Lz 1km</code>.</li>
<li>Added a new NetCDF variable <code class="language-plaintext highlighter-rouge">thk_bc_mask</code> prescribing locations
where the ice thickness is kept fixed. This mask is combined with
<code class="language-plaintext highlighter-rouge">vel_bc_mask</code>: we keep ice thickness fixed at all the locations
where the sliding (usually SSA) velocity is fixed.</li>
<li>Renamed NetCDF variables <code class="language-plaintext highlighter-rouge">bc_mask</code> to <code class="language-plaintext highlighter-rouge">vel_bc_mask</code> and <code class="language-plaintext highlighter-rouge">u_ssa_bc</code>
and <code class="language-plaintext highlighter-rouge">v_ssa_bc</code> to <code class="language-plaintext highlighter-rouge">u_bc</code> and <code class="language-plaintext highlighter-rouge">v_bc</code>.</li>
<li>Removed the <code class="language-plaintext highlighter-rouge">pisms</code> executable. Run <code class="language-plaintext highlighter-rouge">pismr -eisII X</code> to run
<a href="http://www.pism.io/docs/manual/simplified-geometry/eismint-2.html">EISMINT-II</a>
experiment <code class="language-plaintext highlighter-rouge">X</code>.</li>
<li><code class="language-plaintext highlighter-rouge">fill_missing_petsc.py</code> uses homogeneous Neumann BC at domain boundaries.</li>
<li>Added optional arguments <code class="language-plaintext highlighter-rouge">time_units</code> and <code class="language-plaintext highlighter-rouge">calendar</code> to
<code class="language-plaintext highlighter-rouge">PISM.util.prepare_output()</code> in the Python bindings.</li>
</ul>The PISM AuthorsPISM developers have been hard at work to bring you a brand new version of PISM, packed with new features. After years of development, PISM finally includes a Blatter solver, warranting a new major version: PISM 2.0.Version 1.22020-02-13T00:00:00+00:002020-02-13T00:00:00+00:00https://www.pism.io/news/2020/02/13/version1.2<p>We are pleased to announce the release of the Parallel Ice Sheet Model
(PISM) v1.2.</p>
<p>Compared to v1.1, the new version includes</p>
<ul>
<li>modifications required by ISMIP6 experiments,</li>
<li>the frontal melt parameterization by Rignot et al (https://doi.org/10.1002/2016GL068784),</li>
<li>the orographic precipitation following Smith and Barstad, <em>A linear theory of orographic precipitation</em> (2004),</li>
<li>the ability to use <a href="https://ncar.github.io/ParallelIO/">NCAR ParallelIO</a> for better I/O performance,</li>
<li>numerous bug fixes and minor improvements.</li>
</ul>
<p>Please see <a href="https://github.com/pism/pism/blob/v1.2/CHANGES.rst">the change
log</a> for a
complete list.</p>The PISM AuthorsWe are pleased to announce the release of the Parallel Ice Sheet Model (PISM) v1.2.MPI-M Hamburg, Germany: open postdoc for coupled atmosphere-ocean-ice sheet model2020-02-05T00:00:00+00:002020-02-05T00:00:00+00:00https://www.pism.io/news/2020/02/05/postdocmpim2020<p>The Max Planck Institute for Meteorology (MPI-M) contributes to the BMBF
project “From the Last Interglacial to the Anthropocene: Modeling a
Complete Glacial Cycle” <a href="https://www.palmod.de/">(PalMod,
www.palmod.de)</a>, which aims at
simulating the climate from the peak of the last interglacial up to the
present using comprehensive Earth System Models. Phase II of this
project has an open position Postdoctoral Scientist (W073). The
successful candidate will be part of a local team performing and
analysing long-term transient simulations covering the last glacial and
the transition into the Holocene with an interactively coupled
atmosphere-ocean-ice sheet model. Additionally, the candidate will
contribute to the continued development of this model. The model system
consists of the MPI-Earth system model, the ice sheet model PISM, and
the solid-earth model VILMA.</p>
<p>For further information regarding the job description, please contact
Uwe Mikolajewicz (uwe.mikolajewicz(at)mpimet.mpg.de). Do not forward
your application to this email address; see links at the <a href="http://web.archive.org/web/20201025135956/https://mpimet.mpg.de/en/institute/opportunities/mpim-w073/">official
announcement</a>.</p>The PISM AuthorsThe Max Planck Institute for Meteorology (MPI-M) contributes to the BMBF project “From the Last Interglacial to the Anthropocene: Modeling a Complete Glacial Cycle” (PalMod, www.palmod.de), which aims at simulating the climate from the peak of the last interglacial up to the present using comprehensive Earth System Models. Phase II of this project has an open position Postdoctoral Scientist (W073). The successful candidate will be part of a local team performing and analysing long-term transient simulations covering the last glacial and the transition into the Holocene with an interactively coupled atmosphere-ocean-ice sheet model. Additionally, the candidate will contribute to the continued development of this model. The model system consists of the MPI-Earth system model, the ice sheet model PISM, and the solid-earth model VILMA.AWI PostDoc: Antarctic Ice Sheets in warming climates2020-01-23T00:00:00+00:002020-01-23T00:00:00+00:00https://www.pism.io/news/2020/01/23/postdocawi<p>Dr. Lohmann’s group at <a href="https://www.awi.de/en/">AWI</a> is
seeking a postdoc to work with PISM and the multi-scale Earth system
model AWI-ESM. See</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>https://recruitingapp-5442.de.umantis.com/Vacancies/548/Description/2
</code></pre></div></div>The PISM AuthorsDr. Lohmann’s group at AWI is seeking a postdoc to work with PISM and the multi-scale Earth system model AWI-ESM. SeePISM now uses Slack2019-12-16T00:00:00+00:002019-12-16T00:00:00+00:00https://www.pism.io/news/2019/12/16/slack<p>PISM now has a <a href="https://www.slack.com">Slack</a> workspace. You
can join us via the link <a href="https://join.slack.com/t/uaf-pism/shared_invite/enQtODc3Njc1ODg0ODM5LThmOTEyNjEwN2I3ZTU4YTc5OGFhNGMzOWQ1ZmUzMWUwZDAyMzRlMzBhZDg1NDY5MmQ1YWFjNDU4MDZiNTk3YmE">Slack invite for PISM
Help</a></p>
<p>We hope this will streamline our handling of user questions, and speed
up our response time. Also, the more PISM users sign up, the more we
will be able to help each other out.</p>The PISM AuthorsPISM now has a Slack workspace. You can join us via the link Slack invite for PISM HelpPhD Studentship: Palaeoglaciology of Eurasian Ice Sheets2019-12-05T00:00:00+00:002019-12-05T00:00:00+00:00https://www.pism.io/news/2019/12/05/phdstudentsheffield<p>Dr. Ely’s group at the University of Sheffield is advertising for a PhD
student in paleo-ice sheet modeling, possibly including PISM:
<a href="https://www.jobs.ac.uk/job/BXA408/phd-studentship-palaeoglaciology-of-eurasian-ice-sheets">https://www.jobs.ac.uk/job/BXA408/phd-studentship-palaeoglaciology-of-eurasian-ice-sheets</a></p>The PISM AuthorsDr. Ely’s group at the University of Sheffield is advertising for a PhD student in paleo-ice sheet modeling, possibly including PISM: https://www.jobs.ac.uk/job/BXA408/phd-studentship-palaeoglaciology-of-eurasian-ice-sheetsPISM (and other source codes) go into cold storage2019-12-05T00:00:00+00:002019-12-05T00:00:00+00:00https://www.pism.io/news/2019/12/05/svalbardvault<p>In February they are going to put PISM in the bottom of an old coal mine
in Svalbard:</p>
<p><a href="https://archiveprogram.github.com/">GitHub Archive Program</a>,
with <a href="https://www.youtube.com/watch?v=fzI9FNjXQ0o">video</a>.</p>
<p>But don’t worry. Development continues.</p>The PISM AuthorsIn February they are going to put PISM in the bottom of an old coal mine in Svalbard: