First global observations of third-degree ocean tides.

Area of Science:

• Oceanography
• Geophysics
• Satellite Oceanography

Background:

• The Moon's tidal potential exhibits slight asymmetry, creating subtle third-degree ocean tides previously unobserved globally.
• Long-term, high-precision satellite altimetry data provides a unique resource for detecting and analyzing these faint oceanic signals.

Purpose of the Study:

• To map four distinct third-degree ocean tides (one diurnal, two semidiurnal, one terdiurnal).
• To investigate the ocean's response to this unexplored lunar force and its implications for ocean dynamics.
• To identify previously unknown shelf resonances.

Main Methods:

• Analysis of nearly three decades of high-precision satellite altimeter sea level records.
• Extraction and mapping of small, time-coherent signals corresponding to third-degree tidal components.

Main Results:

• Successfully mapped four third-degree tides: one diurnal, two semidiurnal, and one terdiurnal.
• Observed an unexpected phenomenon where a smaller lunar force generated a larger ocean tide, particularly in the South Pacific.
• Identified a correlation between an ocean normal mode and the third-degree astronomical potential.
• Discovered previously unknown shelf resonances across all three tidal bands.

Conclusions:

• The study provides the first global maps of third-degree ocean tides, enhancing tide prediction for geodesy and oceanography.
• Reveals novel aspects of ocean response to lunar forcing, including an unexpected amplification of semidiurnal tides.
• Offers new insights into ocean normal modes and shelf-sea interactions, advancing our understanding of ocean dynamics.