It is already known from the 20th century that the angular velocity of the Earth is not fixed but shows some fluctuations. By extension, the length of the day varies over the years. The objective of this study is to evaluate a time series covering the last 61 years (1962–2022) that includes daily variations in the Length of Day. The time series analysis method was the Singular Spectrum Analysis (SSA), from which the trend and twenty of the most significant periodic signals of the series were derived. Next, the least-squares fitting method was applied to these periodic signals and trends to obtain the best estimates of their parameters. Lastly, an investigation was conducted to identify the natural phenomena that appear to cause these variations in the Length of Day, based on the existing literature. The combination of SSA and least-squares fitting proved quite effective for analyzing the specific time series. The results were compared with those of similar studies on the aforementioned problem and showed high agreement.
Pappa et al. (Wed,) studied this question.