Ray Richard D
NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.
Sci Adv. 2020 Nov 25;6(48). doi: 10.1126/sciadv.abd4744. Print 2020 Nov.
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.
月球的潮汐势略有不对称，从而产生了所谓的三阶海洋潮汐，这种潮汐规模较小，此前从未在全球范围内被观测到。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，从中可以提取微小的、时间连贯的信号。在此，绘制了四种三阶潮汐图：一种日潮、两种半日潮和一种三日潮。除了实际益处，如改进大地测量学和海洋学的潮汐预测外，这些新地图还揭示了海洋对一种精确已知但此前未被探索的力作出反应的独特方式。一个意想不到的例子涉及两种半日潮，在这种情况下，较小的月球引力却产生了较大的海洋潮汐，尤其是在南太平洋。一种解释带来了关于一种海洋简正模的新信息，该简正模在空间上与三阶天文势相关。这些地图还突出显示了所有三个潮汐带中以前未知的陆架共振。
