The Global Mode‐1 S2 Internal Tide

Abstract The global mode‐1 S2 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 S2 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 S2 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 S2 and M2 internal tides have similar spatial patterns. Both S2 and M2 internal tides originate at major topographic features and propagate over long distances. The S2 internal tidal beams are generally shorter, likely because the relatively weaker S2 internal tide is easily overwhelmed by nontidal noise. The northbound S2 and M2 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 S2 internal tide is 7.8 PJ (1 PJ = 1015 J), about 20% that of M2 (36.4 PJ). The histogram of S2 to M2 SSH ratios peaks at 0.4, consistent with the square root of their energy ratio. In terms of SSH, S2 is greater than M2 in 10% of the global ocean and ≥50% of M2 in about half of the global ocean.