Data files recorded by the analyzer in *.dat format are converted to netCDF format using a python routine. The raw data are then processed using the calibration routines FaVaCal, in use at FARLAB, University of Bergen, Norway. Calibration periods are identified and removed for separate processing with plots and quality evaluation. Water vapour isotope measurements are corrected for the humidity-isotope ratio dependency, as documented by Weng et al., 2020. The complete data processing is described in more detail in the data report for stable water isotope measurements from MASIN aircraft during IGP. The vapour isotope data are joined with the meteorological data from the R/V Alliance obtained during IGP at a 60 s averaging time using the processing tool isofuse. Output from this conversion is stored as one single datafiles (naming: IGP2018_SNOWPACE_Alliance_cruise_data_V3.1_60s.nc; format: netcdf). Results from liquid sample analysis for water isotopes from the R/V Alliance are available in one datafile (naming:IGP2018_SNOWPACE_water_isotope_samples_Alliance.csv, format: csv). Post processing was done by Harald Sodemann (UiB), who also acts as data contact.