Code and derived data for: Arctic freeze-onset dates shifted later while their separation narrowed in NSIDC-0747 during 1979–2023

Code, derived annual tables, source-input checksums and publication figures supporting Arctic freeze-onset dates shifted later while their separation narrowed in NSIDC-0747 during 1979–2023. The primary estimand is the geodesic-area-weighted separation between positive early and continuous freeze-onset dates at or north of 60 degrees N. The package includes fixed-domain, concentration/QA, ice-age-week, interval-bound, buoy-event and calendar-lag HAC sensitivity analyses. Raw provider datasets are not included. Software: MIT; author-derived data, figures and documentation: CC BY 4.0; bundled third-party code retains its own MIT licence.