## Changes since 0.6 (February 13, 2014)

### Improvements
  - Implement the three-equation parameterization of the sub-shelf
    energy and salt flux balance described in *Holland D. and Jenkins
    A.*, **Modeling thermodynamic ice-ocean interactions at the base
    of an ice shelf**, Journal of Physical Oceanography, 1999
  - Allow time and space-dependent PDD temperature standard deviation.
    See [#179](https://github.com/pism/pism/issues/179).
  - Implement a parameterization of the standard deviation of the
    near-surface air temperature use by the PDD model: `Sigma = a*T + b`,
    where `T` is the mean-annual air temperature. See
    [#265](https://github.com/pism/pism/issues/265).
  - Check the range of ice thickness during regridding and
    bootstrapping.
  - Save CTS (cold-temperate transition surface field) when `-o_size
    big` is set. See [#262](https://github.com/pism/pism/issues/262).
  - Allow starting a run with `-hydrology routing` from a result of a
    run with `-hydrology null` (set basal water amount "`bwat`" to a
    default value if not found in an input file).
  - The Temperature Index surface mass balance (PDD) model supports
    non-contiguous updates (and the `-surface ...,cache` modifier).
  - Add the `-timestep_hit_multiples X` command-line option. See
    [#254](https://github.com/pism/pism/issues/254).

### Documentation and the build system
  - Update Cray XK6 installation instructions. See
    [#240](https://github.com/pism/pism/issues/240).
  - Update Debian installation instructions.
  - Support Mac OS X 10.9.x.
  - Remove the undocumented Storglaciaren example from the User's Manual.
  - Update subglacial strength documentation.

### Bug fixes, etc
  - Fix RACMO mass balance missing value in the `std-greenland` example.
    This significantly improves the modeled extent of the Greenland ice
    sheet in the examples shown in the Getting Started section of the
    User's Manual.  The figures in this section are all updated.
  - Add `IceModelVec2T::init_constant()` (allows using `IceModelVec2T`
    to store a field that is constant in both time and space; used by
    the PDD model).
  - Fixes in the PDD model: Fix the snow depth reset code;
    sub-intervals consistent with the interpolation scheme; fix
    initialization message (repeatable vs non-repeatable case).
  - Update lists of variables to save in PISM output files. See
    [#264](https://github.com/pism/pism/issues/264).
  - Standard out ice area and volume reporting consistent with
    saved scalar time-series.
  - Read `Href` from an input file during bootstrapping.
  - Minor improvements in model initialization code.
  - `IceGrid::kBelowHeight()` calls `MPI_Abort()`.
  - Fix a bug in `IceModelVec3Custom`.
  - Avoid re-reading periodic climate forcing data.
  - Fix a bug in the automatic vertical grid extension code.
  - Fix a bug in the code processing `-ts_times`, `-extra_times`
    command-line options: make sure that `-extra_times a:delta:b` saves
    diagnostic quantities at time b.
  - Now `-energy none` runs expect to find enthalpy, not temperature,
    in an input file.
  - Fix a bug in the `-part_redist` (redistribution of residual ice
    thickness in the sub-grid calving front position parameterization).
  - Fix a crash when reading a variable with missing "units" attribute.
  - Minor fix in `PISMRoutingHydrology`.
  - `-surface_given_period X` takes an integer X.
  - Minor fix in the discharge flux reporting code.
  - Fix a bug in `-ocean ...,cache` and `-surface ...,cache`.

## Changes from 0.5 (around May 18, 2012) to 0.6

### Basal strength and basal hydrology
  - A significant change to the model physics for till: effective
	pressure in till is now computed by empirically-based (and exponential)
	formula from [`Tulaczyketal2000`] relating amount in till to effective
	pressure.
  - New mass-conserving subglacial hydrology model.

### Marine ice sheet modeling
  - Implement a parameterization of the melange back pressure as a
	part of the stress boundary condition at the ice shelf front.
  - Implement fracture density model and fracture-induced ice
    softening (see [`AlbrechtLevermann2012`]).
  - Parameterization of the sub-grid position of the grounding line and
    related improvements (see [`Feldmannetal2014`,`Gladstoneetal2012`]).
  - MISMIP3D example (see [`MISMIP3d2013`]), grounding line reversibility.
  - Fixes related to the handling of the grounding line (i.e. driving stress, etc)
  - Use an implementation of a serial two-scan connected-component
    algorithm to identify icebergs.
  - Report cumulative discharge (calving) flux as a 2D field.

### Climate inputs and ocean inputs
  - `PISMSurfaceModel` returns climatic mass balance in `[kg m-2 s-1]`
  - Remove `pclimate`; add the `-test_climate_models` option.
  - `-part_grid` extended to grounded marine termini.
  - Require time bounds in time-dependent climate forcing.
  - Improve the PDD scheme. (Keeps track of the snow depth during the year
    to choose PDD factors but does not model multi-year snow cover.)
  - Implement the 3-equation sub-shelf melt parameterization (see
    [`Hellmer1998`]).
  - Implement caching surface and ocean models `-ocean ...,cache` and
    `-surface ...,cache`. (Update boundary inputs every X years but
    include interannual variability.)
  - Remove `EISMINT-Greenland`.

### Inverse modeling
  - Inverse modeling tools *are* a part of the release now.

### Energy
  - New bootstrapping heuristic filling ice temperature at depth from surface
    mass balance (if available).
  - Allow "regridding" enthalpy from files containing ice temperature
    and liquid water fraction.
  - Allow cold flow laws in the enthalpy mode and GPBLD in the cold
    mode (same as Paterson-Budd).
  - Corrected basal boundary condition in the enthalpy system.

### Usability
  - Implement poor man's parallel I/O, with compression
  - Ensure "continuity" in time of reported cumulative diagnostic fields.
  - Let the user precisely specify the dates corresponding to the run (`-time_file`).
  - Many more diagnostic quantities; use `-list_diagnostics` to see.
  - PISM keeps track of options and parameters that were set but were not used.
  - Use projection info to compute latitude and longitude bounds.
	(Reduces post-processing needed to work with PISM's output.)

### Miscellaneous
  - Improve mass conservation and mass transport.
  - New validation example based on laboratory experiment with xanthan gum.
    Uses millimeter grid spacing and shows configurability of PISM.
  - Implement a "constant 2D velocity" stress balance object (for testing and
    prescribing sliding)

### Under the hood
  - Improve the build system.
  - Switch to PETSC 3.3 or 3.4, stop supporting 3.2.
  - Switch to [UDUNITS-2](http://www.unidata.ucar.edu/software/udunits/).
  - Require [FFTW-3](http://www.fftw.org) to build PISM.
  - Use [CalCalcs](http://meteora.ucsd.edu/~pierce/calcalcs/) for proper calendar support.
  - Remove the Debian [meta-] package.
  - Clean up command-line options selecting sub-models (calving,
    stress balance, energy, basal yield stress).
  - Better `SSAFD` recovery logic; save model state on failure.
  - Use non-zero initial guess in the SSAFD KSP solver.
  - Improved basal yield stress code.

## Changes from 0.4 (around June 1, 2011) to 0.5

  - Switch to PETSc 3.2
  - Move to github.com
  - Add regional modeling tools: pismo, Python tools
  - Improve the IceFlowLaw class by moving physical constants out of it
  - Implement `-o_format [netcdf4_parallel, pnetcdf]`
  - Implement `-o_order [xyz, yxz, zyx]`
  - Implement `-e_age_coupling`
  - Improved the implementation of PISM's basal yield stress model
  - Separated flow laws used in SIA and SSA code. New command-line
    options: `-sia_e`, `-ssa_e`. New config. parameters:
    `sia_enhancement_factor`, `ssa_enhancement_factor`
  - Fixed `-topg_to_phi`: now it takes 4 numbers (no special value in the ocean)
  - `-pdd_annualized` implemented, and recommended for degree-day scheme usage
  - Flush time-series when `-extra_files` are written
  - Improved documentation (mostly climate forcing code)
  - Improved climate forcing code and its interface (in particular:
    consistent command-line options)
  - Fixed numerous bugs
  - Improved regridding code
  - Implemented temperature-dependent conductivity and specific heat capacity of ice
  - Model time is in seconds
  - PISM uses time bounds, both in reporting code and code using forcing data
  - Reported rates of change are computed as average rates over
    reporting intervals, by differencing cumulative quantities
  - Reporting: daily, monthly, yearly
  - Added support for the Gregorian calendar
  - PISM uses Proj.4 to compute latitudes, longitudes, and cell areas
  - Implemented `-tauc_to_phi`
  - Updated and improved modeling examples
  - Removed the pgrn executable; all whole-Greenland examples use pismr
  - Removed the EISMINT-Ross example and the pross executable
  - Inverse modeling tools (not part of the release)