Atlantification index (ATLi) data (and code) for a CMIP6 multi-model ensemble of historical and ssp585 simulations

This folder contains 12 NetCDF files that provide annual time series of the Atlantification index (ATLi) derived from an ensemble of CMIP6 climate simulations, along with an accompanying .R code file detailing the calculations used to obtain ATLi and to identify the position of the Atlantic-Arctic boundary. ATLi measures the relative areal extension of the Atlantic domain in the European Arctic, specifically in the Fram Strait and Barents Sea. This index is introduced and described in the manuscript "Future Atlantification of the European Arctic limited under sustained global warming" by De Rovere et al. (2025), published in Scientific Reports (https://doi.org/10.1038/s41598-025-16161-8). The naming convention for each NetCDF file follows the structure: ATLi_{model}_historical_ssp585_{realization}.nc, where {model} corresponds to the CMIP6 model name (considered models are MPI-ESM1-2-LR, MRI-ESM2-0, MIROC-ES2L, and IPSL-6A-LR), and {realization} indicates the realization code. Each dataset contains two variables: time and annual-mean ATLi time series. ATLi for the ssp585 experiment is concatenated to the corresponding historical ATLi from which the ssp585 experiment is initialized, resulting in annual time series spanning from 1850 to 2100. The R script titled "Cluster_front_ATLi" provides a standardized version of the code performing the following calculations: 1) conduct the cluster analysis used to distinguish between the Atlantic and Arctic domains in the European Arctic 2) identify grid points characterizing the Atlantic front 3) calculate the ATLi index. ATLi index.