CoAuthors

Alford Matthew (Scripps Institution of Oceanography, University of California San Diego, United States); Girton James (Applied Physics Laboratory, University of Washington, Seattle, United States); Rainville Luc (Applied Physics Laboratory, University of Washington, Seattle, United States); Simmons Harper (University of Alaska Fairbanks, United States)

We aim to construct a global internal tide model consisting of 4 principal tidal constituents M2, S2, O1 and K1. Sea-surface height (SSH) measurements from multiple satellite altimeters during 1992–2012 are used (50 satellite-years in total). The results represent a 20-year coherent internal tide field. Two-dimensional plane wave fits in 160-km (M2) or 250-km (S2, O1 and K1) windows are employed to (1) suppress mesoscale contamination by extracting internal tides with both spatial and temporal coherence, and (2) separately resolve internal tides in multiple propagation directions. M2 usually has the strongest SSH signals; however, the contribution of S2, O1 and K1 may be greater in a few regions (e.g., the western Pacific). M2 and S2 have similar, but different, spatial patterns. We will present global maps of the amplitude and phase of each tidal constituent and their superposition.

The generation and propagation of M2 internal tides are discussed in detail. M2 internal tides are mainly generated over topographic features including continental slopes and mid-ocean ridges. Internal tidal beams of 100–300 km width are observed to propagate hundreds to thousands of km. Multi-wave interference is widespread, due to the existence of multiple internal tides at any one site. M2 internal tides propagate across critical latitudes for PSI (28.8 S/N) with little energy loss, consistent with field measurements by MacKinnon et al. (2013). In the eastern Pacific Ocean, M2 internal tides lose significant energy in propagating across the Equator, likely due to the loss of coherence in the varying equatorial jets. In contrast, little energy loss is observed in the equatorial zones in the Atlantic, Indian, and western Pacific oceans. Global integration of the altimetric M2 internal tides yields a lower bound energy of 36 PJ (1 PJ = 10^15 J). The satellite altimetric and field moored M2 internal tides are in fairly good agreement. The M2 internal tides from satellite altimetry and a global eddy-resolving numerical model agree favorably in the central North Pacific.