multimelt provides three types of “services”. (1)It can produce masks of the different circum-Antarctic ice shelves and geometric properties on each ice shelf level (neede for the pdifferent parameterisations). (2) It computes mean profiles of temperature and salinity in front of the ice shelves in given domains of interest. (3) It computes 2D and 1D metrics related to basal melt of ice shelves.

The procedure to create the masks and box and plume characteristics is shown in the notebook prepare_mask_example.ipynb. The steps are also explained more in detail in Preparing masks to identify ice shelf and main ice shelf characteristics around Antarctica, Preparing the box characteristics and Preparing the plume characteristics.

The procedure to compute and format the input temperature (T) and salinity (S) profiles from 2D fields is shown in the notebook T_S_profiles_per_ice_shelf.ipynb. The steps are also explained more in detail in prepare_prof. !BE CAREFUL! If your 2D fields are in conservative temperature and absolute salinity, do not forget to convert them with the script conversion_CTtoPT_SAtoSP.ipynb.

The procedure to compute melt rates from temperature and salinity profiles is shown in the notebook compute_melt_example.ipynb. The steps are also explained more in detail in prod_melt.

How to run (2) : Preparing the input profiles

Conversion from conservative temperature to potential temperature and from absolute salinity to practical salinity

Input data

Currently, most of the functions of multimelt are tailored for circum-Antarctic model output from NEMO, the Nucleus for European Modelling of the Ocean [NEMO Team, 2019], interpolated to a south polar stereographic grid (EPSG:3031). However, it can be used for other models/grids if the variable names are changed accordingly either in the functions or the model’s output (requires a bit of digging).

The conversion script conversion_CTtoPT_SAtoSP.ipynb needs these files as input:

  • file_mask: file containing the depth information of your depth coordinate, for each x/y pair if it is not constant (we will assume that it is approximately constant and take a mean over all x/y pairs at each depth level)

  • file_isf: file containing masks created earlier with multimelt.create_isf_mask_functions.create_mask_and_metadata_isf()

  • file_TS_orig: 3D field of conservative temperature, absolute salinity and sea-surface temperature for just one time step

  • ts_files: 3D fields of conservative temperature and absolute salinity for all time steps (can be several files), they need to contain the 3D potential temperature votemper, the 3D practical salinity vosaline, and the 2D sea-surface temperature sosst

Running

Use the notebook conversion_CTtoPT_SAtoSP.ipynb.

Output

The resulting netcdf file contains the following variables:

  • theta_ocean: 3D field of potential temperature

  • salinity_ocean: 3D field of practical salinity

Prepare input temperature and salinity profiles averaged over given domains in front of the ice shelves

Input data

Currently, most of the functions of multimelt are tailored for circum-Antarctic model output from NEMO, the Nucleus for European Modelling of the Ocean [NEMO Team, 2019], interpolated to a south polar stereographic grid (EPSG:3031). However, it can be used for other models/grids if the variable names are changed accordingly either in the functions or the model’s output (requires a bit of digging).

The input profiles are currently computed averaged over five domains: within 10, 25, 50 and 100 km of the ice-shelf front on the continental shelf, and offshore (for bathymetry deeper than the continental shelf).

The computation script T_S_profiles_per_ice_shelf.ipynb (1) calculates the distance to the ice front for the small domain in front of the ice shelf and (2) takes the ocean points at a given distance of the ice front and averages over them.It needs these files as input:

Running

Use the notebook T_S_profiles_per_ice_shelf.ipynb.

Output

The main result is the netcdf 'T_S_mean_prof_corrected_km_contshelf_and_offshore_1980-2018.nc' containing profiles of theta_ocean and salinity_ocean averaged over different domains in front of the ice shelf (currently: within 10, 25, 50 and 100 km of the ice-shelf front on the continental shelf, and offshore for bathymetry deeper than the continental shelf).

It produces several temporary netcdf files needed in case the script crashes but that can be deleted afterwards:

  • 'dist_to_ice_front_only_contshelf_oneFRIS.nc'

  • 'mask_offshore_oneFRIS.nc'

  • 'ds_sum_for_mean_contshelf.nc'

  • 'T_S_mean_prof_corrected_km_contshelf_1980-2018.nc'

  • 'ds_sum_for_mean_offshore.nc'

  • 'T_S_mean_prof_corrected_km_offshore_1980-2018.nc'