The Moon’s tidal potential is slightly asymmetric, giving rise to so-called third-degree ocean tides, which are small and never before observed on a global scale. High-precision satellite altimeters have collected sea level records for almost three decades, providing a massive database from which tiny, time-coherent signals can be extracted. Here, four third-degree tides are mapped: one diurnal, two semidiurnal, and one terdiurnal. Aside from practical benefits, such as improved tide prediction for geodesy and oceanography, the new maps reveal unique ways the ocean responds to a precisely known, but hitherto unexplored, force. An unexpected example involves the two semidiurnals, where the smaller lunar force is seen to generate the larger ocean tide, especially in the South Pacific. An explanation leads to new information about an ocean normal mode that spatially correlates with the third-degree astronomical potential. The maps also highlight previously unknown shelf resonances in all three tidal bands.

月球的潮汐能力略有不对称，导致了所谓的三度海洋潮汐，这些潮汐很小，而且从未在全球范围内观测到。高精度卫星高度计已经收集了近三十年的海平面记录，提供了一个庞大的数据库，可以从中提取微小的时间相干信号。在这里，绘制了四个三级潮汐：一个昼间，两个半昼间和一个昼间。除了实际的好处，例如改进了对大地测量和海洋学的潮汐预报外，新地图还揭示了海洋对精确已知但迄今尚未探索的力量做出反应的独特方式。一个意外的例子涉及两个半日，其中较小的月球力产生较大的海洋潮汐，特别是在南太平洋。一种解释导致了有关海洋正态模式的新信息，该信息在空间上与三级天文潜力相关。这些图还突出显示了所有三个潮带中以前未知的架子共振。