Occurrence of seeding multi-layer clouds in the Arctic from ground-based observations

This data set contains information on the occurrence of cloud layers derived from the combination of radiosonde soundings with coincident cloud radar measurements, following the methodology of Vassel et al. (2019). While the original approach was developed for cloud observations during the MOSAiC campaign, we additionally include data from the ACSE and AO2018 ship campaigns, as well as from long-term monitoring sites at Ny-Ålesund (Svalbard) and Utqiagvik (Alaska). The data set consists of MATLAB .mat files, which are monthly output files (for assumed ice crystal sizes of 100, 200, and 400 micrometers) for each station or campaign. These files are generated by the MATLAB program a_make_MLC_classification_arctic.m availbe at: https://github.com/SEE-GEO/Classification_algorithm_of_multilayer_clouds. The output files are valid only for hexagonal plate ice crystals, as used in the analysis presented in Achtert et al. (2026). However, the calculations can also be repeated assuming other ice crystal habits, such as aggregates, rimed columns, or stellar particles. The .mat output files can be visualized using the MATLAB script a_make_MLC_classification_arctic_several_years_plots.m. Vassel, M., Ickes, L., Maturilli, M., and Hoose, C.: Classification of Arctic multilayer clouds using radiosonde and radar data in Svalbard,Atmos. Chem. Phys., 19, 5111-5126, https://doi.org/10.5194/acp-19-5111-2019, 2019.