More Like this

1. A Multiagency Experiment on Internal Wave Energy, Mixing, and Interactions and Their Representation in Global Ocean Models and Operational Forecasts

   https://doi.org/10.1175/BAMS-D-24-0174.1  

   Buijsman, Maarten C; Waterhouse, Amy F; Zaron, Edward D; Yadidya, Badarvada; Xu, Chengzhu; Whitley, Victoria; Wenegrat, Jacob O; Wang, Jinbo; Wallcraft, Alan J; Varma, Dheeraj; et al (January 2026, Bulletin of the American Meteorological Society)

   McPhaden, Michael (Ed.)

   Abstract As part of a National Oceanographic Partnership Program (NOPP) project, seven teams—comprising investigators from universities, federal laboratories, and industry—are collaboratively investigating the generation, propagation, and dissipation of internal waves in the global ocean using complementary, state-of-the-art observations and model simulations. Internal waves, generated by the interaction of tides, winds, and mean flows, permeate the ocean and influence its physical state. Internal waves transport scalar and vector properties—both geographically and across scales—and contribute to irreversible mixing, modulate acoustic propagation, and complicate the identification of subinertial (e.g., geostrophic) flows in observations. For these reasons, accurately representing internal waves in global ocean forecast models is a high priority. The collaborations reported here are improving the understanding of the internal wave life cycle and enhancing model skill in simulating it. Three observational teams are collecting in situ data using 1) redeployable moored arrays that resolve internal waves from multiple directions, 2) global deployments of profiling floats that measure internal wave energy fluxes, shear, and mixing, and 3) high-resolution arrays that focus on bottom boundary layer processes. Four modeling teams are guiding the design and placement of these observation platforms and are using the collected observations to 1) improve internal wave representation and dissipation in ocean models, 2) conduct high-resolution process studies, and 3) implement data assimilation in idealized, regional, and global simulations. These efforts are further supported by high-resolution sea surface height measurements from the new Surface Water and Ocean Topography (SWOT) satellite, which provide context for in situ observations and improve ocean forecasting systems. Significance StatementA collaboration among scientists from U.S. universities, national laboratories, and industry is advancing our understanding and prediction of internal waves in the global ocean. These waves—characterized by vertical scales of tens to hundreds of meters and horizontal scales of tens to hundreds of kilometers—play a critical role in maritime commerce, naval operations, and ocean circulation. The team integrates novel observational approaches, including internal wave–resolving moored arrays, ship-of-opportunity float deployments, bottom boundary layer–distributed sensor networks, and satellite wide-swath altimetry, with cutting-edge global, regional, and process-model simulations. Together, these efforts are improving the representation of internal wave processes in ocean models and enhancing their predictive capabilities for operational forecasts. 

   more » « less
2. Fiber‐Optic Observations of Internal Waves and Tides

   https://doi.org/10.1029/2023JC019980  

   Williams, E. F.; Ugalde, A.; Martins, H. F.; Becerril, C. E.; Callies, J.; Claret, M.; Fernandez‐Ruiz, M. R.; Gonzalez‐Herraez, M.; Martin‐Lopez, S.; Pelegri, J. L.; et al (September 2023, Journal of Geophysical Research: Oceans)

   Abstract Although typically used to measure dynamic strain from seismic and acoustic waves, Rayleigh‐based distributed acoustic sensing (DAS) is also sensitive to temperature, offering longer range and higher sensitivity to small temperature perturbations than conventional Raman‐based distributed temperature sensing. Here, we demonstrate that ocean‐bottom DAS can be employed to study internal wave and tide dynamics in the bottom boundary layer, a region of enhanced ocean mixing but scarce observations. First, we show temperature transients up to about 4 K from a power cable in the Strait of Gibraltar south of Spain, associated with passing trains of internal solitary waves in water depth <200 m. Second, we show the propagation of thermal fronts associated with the nonlinear internal tide on the near‐critical slope of the island of Gran Canaria, off the coast of West Africa, with perturbations up to about 2 K at 1‐km depth and 0.2 K at 2.5‐km depth. With spatial averaging, we also recover a signal proportional to the barotropic tidal pressure, including the lunar fortnightly variation. In addition to applications in observational physical oceanography, our results suggest that contemporary chirped‐pulse DAS possesses sufficient long‐period sensitivity for seafloor geodesy and tsunami monitoring if ocean temperature variations can be separated. 

   more » « less
3. Pantropical Indo-Atlantic temperature gradient modulates multi-decadal AMOC variability in models and observations

   https://doi.org/10.1038/s41612-023-00489-x  

   Ferster, Brady S; Borchert, Leonard F; Mignot, Juliette; Menary, Matthew B; Cassou, Christophe; Fedorov, Alexey V (December 2023, npj Climate and Atmospheric Science)

   Abstract Interconnections between ocean basins are recognized as an important driver of climate variability. Recent modeling evidence suggests that the North Atlantic climate can respond to persistent warming of the tropical Indian Ocean sea surface temperature (SST) relative to the rest of the tropics (rTIO). Here, we use observational data to demonstrate that multi-decadal changes in pantropical ocean temperature gradients lead to variations of an SST-based proxy of the Atlantic Meridional Overturning Circulation (AMOC). The largest contribution to this temperature gradient-AMOCconnection comes from gradients between the Indian and Atlantic Oceans. TherTIOindex yields the strongest connection of this tropical temperature gradient to theAMOC. Focusing on the internally generated signal in three observational products reveals that an SST-basedAMOCproxy index has closely followed low-frequency changes ofrTIOtemperature with about 26-year lag since 1870. Analyzing the pre-industrial control simulations of 44 CMIP6 climate models shows that theAMOCproxy index lags simulated mid-latitudeAMOCvariations by 4 ± 4 years. These model simulations reveal the mechanism connectingAMOCvariations to pantropical ocean temperature gradients at a 27 ± 2 years lag, matching the observed time lag in 28 out of the 44 analyzed models. rTIO temperature changes affect the North Atlantic climate through atmospheric planetary waves, impacting temperature and salinity in the subpolar North Atlantic, which modifies deep convection and ultimately the AMOC. Through this mechanism, observed internalrTIOvariations can serve as a multi-decadal precursor ofAMOCchanges with important implications forAMOCdynamics and predictability. 

   more » « less
4. Genesis and Propagation of Low‐Frequency Abyssal T ‐Waves

   https://doi.org/10.1029/2024JC021518  

   Shen, Zhichao; Wu, Wenbo; Callies, Jörn (October 2024, Journal of Geophysical Research: Oceans)

   Abstract AbyssalT‐waves are seismo‐acoustic waves originating from abyssal oceans. Unlike subduction‐zone‐generated slopeT‐waves which are generated through multiple reflections between the sea surface and the gently dipping seafloor, the genesis of abyssalT‐waves cannot be explained by the same theory. Several hypotheses, including seafloor scattering, sea surface scattering, and internal‐wave‐induced volumetric scattering, have been proposed to elucidate their genesis and propagation. The elusive mechanism of abyssalT‐waves, particularly at low‐frequencies, hinders their use to quantify ocean temperatures through seismic ocean thermometry (SOT) and estimate oceanic earthquake parameters. Here, using realistic geophysical and oceanographic data, we first conduct numerical simulations to compare synthetic low‐frequency abyssalT‐waves under different hypotheses. Our simulations for the Romanche and Blanco transform faults suggest seafloor scattering as the dominant mechanism, with sea surface and internal waves contributing marginally. Short‐scale bathymetry can significantly enhance abyssalT‐waves across a broad frequency range. Also, observedT‐waves from repeating earthquakes in the Romanche, Chain, and Blanco transform faults exhibit remarkably high repeatability. Given the dynamic nature of sea surface roughness and internal waves, the highly repeatableT‐wave arrivals further support the seafloor scattering as the primary mechanism. The dominance of seafloor scattering makes abyssalT‐waves useable for constraining ocean temperature changes, thereby greatly expanding the data spectrum of SOT. Our observations of repeating abyssalT‐waves in the Romanche and Chain transform faults could provide a valuable data set for understanding Equatorial Atlantic warming. Still, further investigations incorporating high‐resolution bathymetry are warranted to better model abyssalT‐waves for earthquake parameter estimation. 

   more » « less
5. Observations of coherent transverse wakes in shoaling nonlinear internal waves

   https://doi.org/10.1175/JPO-D-21-0059.1  

   Lucas, Andrew J.; Pinkel, Robert (March 2022, Journal of Physical Oceanography)

   Abstract Space- and time-continuous seafloor temperature observations captured the three-dimensional structure of shoaling nonlinear internal waves (NLIWs) off of La Jolla, California. NLIWs were tracked for hundreds of meters in the cross- and along-shelf directions using a fiber optic Distributed Temperature Sensing (DTS) seafloor array, complemented by an ocean-wave-powered vertical profiling mooring. Trains of propagating cold-water pulses were observed on the DTS array inshore of the location of polarity transition predicted by weakly nonlinear internal wave theory. The subsequent evolution of the temperature signatures during shoaling was consistent with that of strongly nonlinear internal waves with a large Froude number, highlighting their potential to impact property exchange. Unexpectedly, individual NLIWs were trailed by a coherent, small-scale pattern of seabed temperature variability as they moved across the mid- and inner shelf. A kinematic model was used to demonstrate that the observed patterns were consistent with a transverse instability with an along-crest wavelength of ∼10 m – a distance comparable to the cross-crest width of the wave-core – and with an inferred amplitude of several meters. The signature of this instability is consistent with the span-wise vortical circulations generated in three-dimensional direct numerical simulations of shoaling and breaking nonlinear internal waves. The coupling between the small-scale transverse wave-wake and turbulent wave-core may have an important impact on mass, momentum, and tracer redistribution in the coastal ocean. 

   more » « less