Prerequisites

1. Download the Simulation Data

Download the simulation data from Zenodo. The files are compatible with SWAN version 41.45.

After unzipping, the folder structure should look like this:

SWAN_TerraNovaBayPolynya_files/
  ├── Tp_from_satellite_swangrid/
  └── swan/
       ├── input/
       ├── S0/
       └── S2_f5/

2. Select the Required Files

For this tutorial, you only need the following:

• The input/ folder (wind, ice concentration, and grid data)
• .swn input files from S0/ and S2_f5/ (one per polynya event)

The S0/ and S2_f5/ folders also contain large output files (.mat, .dat, .sp1, .sp2). Do not copy these. Only the .swn files are required for each simulation.

The Tp_from_satellite_swangrid folder contains satellite-derived peak periods and directions, interpolated onto the SWAN grid. These were used in the original study to validate and calibrate the model (bias, RMSD, spectral tail comparisons), but are not required for this tutorial.

3. Organize the tutorial/ Folder

Create a new directory named tutorial/ and copy only the required files into it. Your structure should look like this:

tutorial
   |
   + polynya
      |
      + S0
      |  |
      |  + polynya2D_20161005.swn
      |  |  
      |  + polynya2D_20161024.swn
      |  |
      |  ...
      |  |
      |  + polynya2D_20201019.swn
      |
      |
      + S2_f5
      |  |
      |  + polynya2D_20161005.swn
      |  |  
      |  + polynya2D_20161024.swn
      |  |
      |  ...
      |  |
      |  + polynya2D_20201019.swn
      |
      + input
         |
         + Aice0_20161005_dx200.dat 
         |
         ...
         |
         + wnd_20211007_10m.dat

4. Modify Each .swn File

Before running any scripts, you need to edit each .swn input file in both the S0/ and S2_f5/ folders to prevent a known Fortran runtime issue.

In each .swn file, look for a line that starts with:

SPECOUT 'COMPGRID' SPEC1D ABS '20211007.sp1'

and comment it out by adding an exclamation mark (!) at the beginning:

!SPECOUT 'COMPGRID' SPEC1D ABS '20211007.sp1'

This modification avoids a common Fortran runtime error that can occur when SWAN attempts to output large spectral files over the full computational grid.

Folder Overview

Here's what each subfolder in tutorial/polynya contains:

• swan/input: Grid definitions, wind fields, and ice concentration maps for 10 polynya events. These are the raw fields for your SWAN simulations.
• swan/S0: Input files for the open water baseline scenario (S0). These runs include only wind-forced waves, with no ice effects.
• swan/S2_f5: Input files for the full ice-influenced scenario (S2_f5), which included frazil/grease effects and applies ice and a power-law exponent of 5 are applied.

All required data is now in place. Next, let's prepare the Python script to run the baseline S0 scenario.