Code and data for 'Four-dimensional variational data assimilation with a sea-ice thickness emulator'

All the codes written to build the datasets, train the emulator and run the 4D--Var minimization are available in nextsim-4dvar-1.

The post-processed dataset for training the emulator are in data/twin_exp. The dataset is based on neXtSIM simulation data and ERA5 forcing data and extracted from the SASIP shared data OpenDAP server:

• The neXtSIM simulations were performed by Gauillaume Boutin and published in the paper "Arctic sea ice mass balance in a new coupled ice–ocean model using a brittle rheology framework" (Boutin et al., 2023) and available as Zenodo dataset (Boutin et al., 2022).
• The forcing data is based on the ERA5 reanalysis dataset published in the paper: "The ERA5 global reanalysis" (Hersbach et al., 2020) and available as dataset from the Copernicus Climate Change Service (C3S, Copernicus Climate Change Service, 2023). The here used forcing data is based on the hourly reanalysis data on single levels and interpolated with nearest neighbors to the curvilinear grid as used in the output from the neXtSIM simulations. 
• The same dataset can then be used to perform 4D-Var minimimzation in twin experiment case
• The folder data/cs2smos contains all post-processed datasets necessary to perform real observations with CS2SMOS
• CS2SMOS retrievals are publicly available here

The neural network weights are included under models.
These neural network weights have been used to generate the results presented in the paper.

References:

Guillaume Boutin, Heather Regan, Einar Ólason, Laurent Brodeau, Claude Talandier, Camille Lique, & Pierre Rampal. (2022). Data accompanying the article "Arctic sea ice mass balance in a new coupled ice-ocean model using a brittle rheology framework" (1.0) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.7277523

Boutin, G., Ólason, E., Rampal, P., Regan, H., Lique, C., Talandier, C., Brodeau, L., and Ricker, R.: Arctic sea ice mass balance in a new coupled ice–ocean model using a brittle rheology framework, The Cryosphere, 17, 617–638, https://doi.org/10.5194/tc-17-617-2023, 2023.

Copernicus Climate Change Service (2023): ERA5 hourly data on single levels from 1940 to present. Copernicus Climate Change Service (C3S) Climate Data Store (CDS), DOI: 10.24381/cds.adbb2d47.

Hersbach H, Bell B, Berrisford P, et al. The ERA5 global reanalysis. Q J R Meteorol Soc. 2020; 146: 1999–2049. https://doi.org/10.1002/qj.3803