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  • 1
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    Observations of the dispersion characteristics and meridional sea level structure of equatorial waves in the Pacific Ocean (2010)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 38 (2008): 1669-1689, doi:10.1175/2007JPO3890.1.
    Description: Spectral techniques applied to altimetry data are used to examine the dispersion relation and meridional sea level structure of wavelike variability with periods of about 20 to 200 days in the equatorial Pacific Ocean. Zonal wavenumber–frequency power spectra of sea surface height, when averaged over about 7°S–7°N, exhibit spectral peaks near the theoretical dispersion curves of first baroclinic-mode equatorial Kelvin and Rossby waves. There are distinct, statistically significant ridges of power near the first and second meridional-mode Rossby wave dispersion curves. Sea level variability near the theoretical Kelvin wave and first meridional-mode Rossby wave dispersion curves is dominantly (but not perfectly) symmetric about the equator, while variability near the theoretical second meridional-mode Rossby wave dispersion curve is dominantly antisymmetric. These results are qualitatively consistent with expectations from classical or shear-modified theories of equatorial waves. The meridional structures of these modes resemble the meridional modes of equatorial wave theory, but there are some robust features of the meridional profiles that were not anticipated. The meridional sea level structure in the intraseasonal Kelvin wave band closely resembles the theoretically expected Gaussian profile, but sea level variability coherent with that at the equator is detected as far away as 11.75°S, possibly as a result of the forced nature of these Kelvin waves. Both first and second meridional-mode Rossby waves have larger amplitude in the Northern Hemisphere. The meridional sea level structure of tropical instability waves closely resembles that predicted by Lyman et al. using a model linearized about a realistic equatorial zonal current system.
    Description: This work was supported in part by the NOAA Climate Prediction Program for the Americas (Grant NA17RJ1223).
    Keywords: Spectral analysis ; Sea level ; Dispersion ; Kelvin waves ; Rossby waves
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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    Barotropic Rossby waves radiating from tropical instability waves in the Pacific Ocean (2011)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2011. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 41 (2011): 1160–1181, doi:10.1175/2011JPO4547.1.
    Description: Tropical instability waves are triggered by instabilities of the equatorial current systems, and their sea level signal, with peak amplitude near 5°N, is one of the most prominent features of the dynamic topography of the tropics. Cross-spectral analysis of satellite altimetry observations shows that there is sea level variability in the Pacific Ocean as far north as Hawaii (i.e., 20°N) that is coherent with the sea level variability near 5°N associated with tropical instability waves. Within the uncertainty of the analysis, this off-equatorial variability obeys the dispersion relation for nondivergent, barotropic Rossby waves over a fairly broad range of periods (26–38 days) and zonal wavelengths (9°–23° of longitude) that are associated with tropical instability waves. The dispersion relation and observed wave properties further suggest that the waves are carrying energy away from the instabilities toward the North Pacific subtropical gyre, which, together with the observed coherence of the sea level signal of the barotropic waves with that of the tropical instability waves, suggests that the barotropic Rossby waves are being radiated from the tropical instability waves. The poleward transport of kinetic energy and westward momentum by these barotropic Rossby waves may influence the circulation in the subtropics.
    Description: Funding for this research came from WHOI’s TropicalResearch Initiative, the Charles D. Hollister Fund for Assistant Scientist Support, the John E. and Anne W. Sawyer Endowed Fund in Special Support of Scientific Staff, and Grant OCE-0845150 from the National Science Foundation.
    Keywords: Barotropic flows ; Rossby waves ; Tropics ; Pacific Ocean ; Instability ; Waves, atmospheric
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
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    Frontal convergence and vertical velocity measured by drifters in the Alboran Sea (2021)
    American Geophysical Union
    Details
    Publication Date: 2022-05-27
    Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(4), (2021): e2020JC016614, https://doi.org/10.1029/2020JC016614.
    Description: Horizontal and vertical motions associated with mesoscale (10–100 km) and submesoscale (1–10 km) features, such as fronts, meanders, eddies, and filaments, play a critical role in redistributing physical and biogeochemical properties in the ocean. This study makes use of a multiplatform data set of 82 drifters, a Lagrangian float, and profile timeseries of temperature and salinity, obtained in a ∼1-m/s semipermanent frontal jet in the Alboran Sea as part of CALYPSO (Coherent Lagrangian Pathways from the Surface Ocean to Interior). Drifters drogued at ∼1-m and 15-m depth capture the mesoscale and submesoscale circulation aligning along the perimeter of fronts due to horizontal shear. Clusters of drifters are used to estimate the kinematic properties, such as vorticity and divergence, of the flow by fitting a bivariate plane to the horizontal drifter velocities. Clusters with submesoscale length scales indicate normalized vorticity ζ/f 〉 1 with Coriolis frequency f and normalized divergence of (1) occurring in patches along the front, with error variance around 10%. By computing divergence from drifter clusters at two different depths, we estimate minimum vertical velocity of (−100 m day−1) in the upper 10 m of the water column. These results are at least twice as large as previous estimates of vertical velocity in the region. Location, magnitude, and timing of the convergence are consistent with behavior of a Lagrangian float subducting in the center of a drifter cluster. These results improve our understanding of frontal subduction and quantify convergence and vertical velocity using Lagrangian tools.
    Description: This research was supported by the Office of Naval Research (ONR) Departmental Research Initiative CALYPSO under program officers Terri Paluszkiewicz and Scott Harper. The authors' ONR grant numbers are as follows: D. R. Tarry, A. Pascual, S. Ruiz and A. Mahadevan N000141613130, S. Essink N000146101612470, P.-M. Poulain N000141812418, T. OÖzgökmen N000141812138, L. R. Centurioni N000141712517 and N00014191269, T. Farrar N000141812431, A. Shcherbina N000141812139 and N000141812420, and E. A. D'Asaro N000141812139.
    Keywords: Alboran Sea ; drifters ; kinematic properties ; Lagrangian float ; submesoscale ; vertical velocity
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 4
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    Long-distance radiation of Rossby Waves from the equatorial current system (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of [publisher] for personal use, not for redistribution. The definitive version was published in Farrar, J. T., Durland, T., Jayne, S. R., & Price, J. F. Long-distance radiation of Rossby Waves from the equatorial current system. Journal of Physical Oceanography, 51(6), (2021): 1947–1966, https://doi.org/10.1175/JPO-D-20-0048.1.
    Description: Measurements from satellite altimetry are used to show that sea surface height (SSH) variability throughout much of the North Pacific Ocean is coherent with the SSH signal of the tropical instability waves (TIWs) that result from instabilities of the equatorial currents. This variability has regular phase patterns consistent with freely propagating barotropic Rossby waves radiating energy away from the unstable equatorial currents, and the waves clearly propagate from the equatorial region to at least 30°N. The pattern of SSH variance at TIW frequencies exhibits remarkable patchiness on scales of hundreds of kilometers, which we interpret as being due to the combined effects of wave reflection, refraction, and interference. North of 40°N, more than 6000 km from the unstable equatorial currents, the SSH field remains coherent with the near-equatorial SSH variability, but it is not as clear whether the variability at the higher latitudes is a simple result of barotropic wave radiation from the tropical instability waves. Even more distant regions, as far north as the Aleutian Islands off of Alaska and the Kamchatka Peninsula of eastern Russia, have SSH variability that is significantly coherent with the near-equatorial instabilities. The variability is not well represented in the widely used gridded SSH data product commonly referred to as the AVISO or DUACS product, and this appears to be a result of spatial variations in the filtering properties of the objective mapping scheme.
    Description: This work was supported by NASA Grants NNX13AE46G, NNX14AM71G, and NNX17AH54G.
    Keywords: Pacific Ocean ; Barotropic flows ; Instability ; Planetary waves ; Rossby waves ; Topographic effects
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 5
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    Another note on Rossby wave energy flux (2020)
    American Meteorological Society
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    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2020. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 50(2),(2020): 531-534, doi:10.1175/JPO-D-19-0237.1.
    Description: Longuet-Higgins in 1964 first pointed out that the Rossby wave energy flux as defined by the pressure work is not the same as that defined by the group velocity. The two definitions provide answers that differ by a nondivergent vector. Longuet-Higgins suggested that the problem arose from ambiguity in the definition of energy flux, which only impacts the energy equation through its divergence. Numerous authors have addressed this issue from various perspectives, and we offer one more approach that we feel is more succinct than previous ones, both mathematically and conceptually. We follow the work described by Cai and Huang in 2013 in concluding that there is no need to invoke the ambiguity offered by Longuet-Higgins. By working directly from the shallow-water equations (as opposed to the more involved quasigeostrophic treatment of Cai and Huang), we provide a concise derivation of the nondivergent pressure work and demonstrate that the two energy flux definitions are equivalent when only the divergent part of the pressure work is considered. The difference vector comes from the nondivergent part of the geostrophic pressure work, and the familiar westward component of the Rossby wave group velocity comes from the divergent part of the geostrophic pressure work. In a broadband wave field, the expression for energy flux in terms of a single group velocity is no longer meaningful, but the expression for energy flux in terms of the divergent pressure work is still valid.
    Description: This work was supported by NASA Grants NNX13AE46G and NNX14AM71G, and National Science Foundation Grant OCE-1336752. We are indebted to Roger Samelson, Joe Pedlosky, and two anonymous reviewers for comments that significantly improved the presentation.
    Description: 2020-08-19
    Keywords: Rossby waves
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 6
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    Drifter observations reveal intense vertical velocity in a surface ocean front (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-03-11
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Tarry, D., Ruiz, S., Johnston, T., Poulain, P., Özgökmen, T., Centurioni, L., Berta, M., Esposito, G., Farrar, J., Mahadevan, A., & Pascual, A. Drifter observations reveal intense vertical velocity in a surface ocean front. Geophysical Research Letters, 49(18), (2022): e2022GL098969, https://doi.org/10.1029/2022gl098969.
    Description: Measuring vertical motions represent a challenge as they are typically 3–4 orders of magnitude smaller than the horizontal velocities. Here, we show that surface vertical velocities are intensified at submesoscales and are dominated by high frequency variability. We use drifter observations to calculate divergence and vertical velocities in the upper 15 m of the water column at two different horizontal scales. The drifters, deployed at the edge of a mesoscale eddy in the Alboran Sea, show an area of strong convergence (urn:x-wiley:00948276:media:grl64766:grl64766-math-0001(f)) associated with vertical velocities of −100 m day−1. This study shows that a multilayered-drifter array can be an effective tool for estimating vertical velocity near the ocean surface.
    Description: This research was supported by the Office of Naval Research (ONR) Departmental Research Initiative CALYPSO under program officers Terri Paluszkiewicz and Scott Harper. The authors' ONR Grant No. are as follows: DT, SR, AM, and AP N000141613130, TMSJ N000146101612470, PP N000141812418, TO N000141812138, LRC N000141712517, and N00014191269, MB and GE N000141812782 and N000141812039, and JTF N000141812431.
    Keywords: Drifters ; Vertical velocity ; Submesoscale ; Kinematic properties ; Fronts ; Alboran Sea
    Repository Name: Woods Hole Open Access Server
    Type: Article
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