The Global Mode‐1 S 2 Internal Tide

The global mode‐1 S 2 internal tide is observed using sea surface height (SSH) measurements from four satellite altimeters: TOPEX/Poseidon, Jason‐1, Jason‐2, and Geosat Follow‐On. Plane wave analysis is employed to extract three mode‐1 S 2 internal tidal waves in any given 250 km by 250 km window, which are temporally coherent over a 20 year period from 1992 to 2012. Depth‐integrated energy and flux of the S 2 internal tide are calculated from the SSH amplitude and a conversion function built from climatological hydrographic profiles in the World Ocean Atlas 2013. The results show that the S 2 and M 2 internal tides have similar spatial patterns. Both S 2 and M 2 internal tides originate at major topographic features and propagate over long distances. The S 2 internal tidal beams are generally shorter, likely because the relatively weaker S 2 internal tide is easily overwhelmed by nontidal noise. The northbound S 2 and M 2 internal tides from the Hawaiian Ridge are observed to travel over 3500 km across the Northeast Pacific. The globally integrated energy of the mode‐1 S 2 internal tide is 7.8 PJ (1 PJ = 10 15 J), about 20% that of M 2 (36.4 PJ). The histogram of S 2 to M 2 SSH ratios peaks at 0.4, consistent with the square root of their energy ratio. In terms of SSH, S 2 is greater than M 2 in ≈ 10% of the global ocean and ≥50% of M 2 in about half of the global ocean.