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Near-surface measurements of meridional velocity suggest that wind forcing excites equatorial waves in the biweekly band in the Indian Ocean. The characteristics of these waves in the deep ocean are poorly constrained, and it is unclear how well models capture the deep variability. In this work, biweekly temperature variations in a few low vertical modes in the deep east Indian Ocean are observed using seismically generated sound waves. These so-called T waves are generated by earthquakes off Sumatra and received by a hydrophone station off Diego Garcia. Changes in their travel times reflect temperature-induced sound speed variations in the intervening ocean. Regression analysis indicates that these variations are caused by westward-propagating Yanai waves. A comparison between T-wave data and model output shows generally good consistency in biweekly variations dominated by the first three vertical modes, although the biweekly variance differs by up to a factor of 2 between the data and the models. A similar degree of discrepancy appears in the comparison between the models and deep mooring measurements. These results highlight the potential of using T-wave data to study biweekly Yanai waves in the deep equatorial ocean and to calibrate numerical simulations of the variability they cause.
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Vertical‐Slice Ocean Tomography With Seismic Waves
Abstract Seismically generated sound waves that propagate through the ocean are used to infer temperature anomalies and their vertical structure in the deep East Indian Ocean. TheseTwaves are generated by earthquakes off Sumatra and received by hydrophone stations off Diego Garcia and Cape Leeuwin. Between repeating earthquakes, aTwave's travel time changes in response to temperature anomalies along the wave's path. What part of the water column the travel time is sensitive to depends on the frequency of the wave, so measuring travel time changes at a few low frequencies constrains the vertical structure of the inferred temperature anomalies. These measurements reveal anomalies due to equatorial waves, mesoscale eddies, and decadal warming trends. By providing direct constraints on basin‐scale averages with dense sampling in time, these data complement previous point measurements that alias local and transient temperature anomalies.
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- Award ID(s):
- 2023161
- PAR ID:
- 10409469
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 50
- Issue:
- 8
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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