Find in Library

<p>Satellite altimetry provides a unique technique for observing the sea surface height (SSH) signature of internal tides from space. Previous studies have constructed empirical internal tide models for the four largest constituents M<span class="inline-formula">₂</span>, S<span class="inline-formula">₂</span>, K<span class="inline-formula">₁</span>, and O<span class="inline-formula">₁</span> by satellite altimetry. Yet no empirical models have been constructed for minor tidal constituents. In this study, we observe mode-1 N<span class="inline-formula">₂</span> internal tides (the fifth largest constituent) using about 100 satellite years of SSH data from 1993 to 2019. We employ a recently developed mapping procedure that includes two rounds of plane wave analysis and a two-dimensional bandpass filter in between. The results show that mode-1 N<span class="inline-formula">₂</span> internal tides have millimeter-scale SSH amplitudes. Model errors are estimated from background internal tides that are mapped using the same altimetry data but with a tidal period of 12.6074 h (N<span class="inline-formula">₂</span> minus 3 min). The global mean error variance is about 25 % that of N<span class="inline-formula">₂</span>, suggesting that the mode-1 N<span class="inline-formula">₂</span> internal tides can overcome model errors in some regions. We find that the N<span class="inline-formula">₂</span> and M<span class="inline-formula">₂</span> internal tides have similar spatial patterns and that the N<span class="inline-formula">₂</span> amplitudes are about 20 % of the M<span class="inline-formula">₂</span> amplitudes. Both features are determined by the N<span class="inline-formula">₂</span> and M<span class="inline-formula">₂</span> barotropic tides. The mode-1 N<span class="inline-formula">₂</span> internal tides are observed to propagate hundreds to thousands of kilometers in the open ocean. The globally integrated N<span class="inline-formula">₂</span> and M<span class="inline-formula">₂</span> internal tide energies are 1.8 and 30.9 PJ, respectively. Their ratio of 5.8 % is larger than the theoretical value of 4 % because the N<span class="inline-formula">₂</span> internal tides contain relatively larger model errors. Our mode-1 N<span class="inline-formula">₂</span> internal tide model is evaluated using independent satellite altimetry data in 2020 and 2021. The results suggest that the model can make internal tide correction in regions where the model variance is greater than twice the error variance. This work demonstrates that minor internal tidal constituents can be observed using multiyear multi-satellite altimetry data and dedicated mapping techniques.</p>