Length of Day Variability and Climate Indicators: Insights from ENSO Events

The interplay between the length of day (LOD) and the El Niño–Southern Oscillation (ENSO) has been investigated in geophysical research since the 1980s. LOD, defined as the negative time derivative of UT1-UTC, is intrinsically linked to the Earth Rotation Angle (ERA), a fundamental Earth Orientation Parameter (EOP).

ENSO, a dominant climate mode in the tropical eastern Pacific, substantially influences tropical and subtropical regions. Extreme ENSO episodes are associated with significant hydroclimatic anomalies across multiple regions, including severe droughts and floods. These events evolve over extended incubation periods, during which interannual fluctuations in LOD and the angular momentum of the atmosphere (AAM), ocean (OAM), and lithosphere/hydrogeosphere (HAM) are modulated by complex ocean–atmosphere interactions.

Key manifestations of ongoing climate change, such as rising global temperatures and sea levels, are strongly modulated by ENSO. Interannual variability in global mean sea surface temperature (GMST) and global mean sea level (GMSL) further reflects Earth's rotational dynamics changes.

This study aims to elucidate the interannual (2–8 years) couplings between LOD, AAM, OAM, HAM, and selected climate indices, including the Southern Oscillation Index (SOI), Oceanic Niño Index (ONI), GMST, and GMSL. The influence of these climate signals on LOD from 1976 to 2024 will be assessed using advanced semblance analysis, exploring multiple methodological variants based on the continuous wavelet transform to capture correlations across both temporal and spectral domains.

A detailed understanding of these interactions enhances our knowledge of Earth’s dynamic system, informs geophysical modeling efforts, and improves the precision of applications that rely on accurate timekeeping and measurements of Earth’s rotational behaviour.