Length-of-day and sunspot number data for the study of quasi-decadal Earth's rotation variations

This dataset contains the length-of-day (ΔLOD) and sunspot-number time series used in the study of quasi-decadal variations in Earth's rotation. The ΔLOD dataset is an annually sampled long-term series spanning 1799.5-2026.5. It was constructed by combining the historical yearly ΔLOD series formerly distributed by the IERS Earth Orientation Product Centre with the modern IERS EOPC04 series. The daily EOPC04 observations from 1962/01 to 2026/07 were low-pass filtered and resampled annually before being merged with the historical record. The sunspot dataset contains the yearly mean total sunspot number, version 2.0, spanning 1700.5-2025.5. The original sunspot observations were obtained from the World Data Center SILSO, Royal Observatory of Belgium, and are provided here in the annually sampled form used in the analysis.