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  • 1
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    Submesoscale processes at shallow salinity fronts in the Bay of Bengal : observations during the winter monsoon (2018)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. 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 48 (2018): 479-509, doi:10.1175/JPO-D-16-0283.1.
    Description: Lateral submesoscale processes and their influence on vertical stratification at shallow salinity fronts in the central Bay of Bengal during the winter monsoon are explored using high-resolution data from a cruise in November 2013. The observations are from a radiator survey centered at a salinity-controlled density front, embedded in a zone of moderate mesoscale strain (0.15 times the Coriolis parameter) and forced by winds with a downfront orientation. Below a thin mixed layer, often ≤10 m, the analysis shows several dynamical signatures indicative of submesoscale processes: (i) negative Ertel potential vorticity (PV); (ii) low-PV anomalies with O(1–10) km lateral extent, where the vorticity estimated on isopycnals and the isopycnal thickness are tightly coupled, varying in lockstep to yield low PV; (iii) flow conditions susceptible to forced symmetric instability (FSI) or bearing the imprint of earlier FSI events; (iv) negative lateral gradients in the absolute momentum field (inertial instability); and (v) strong contribution from differential sheared advection at O(1) km scales to the growth rate of the depth-averaged stratification. The findings here show one-dimensional vertical processes alone cannot explain the vertical stratification and its lateral variability over O(1–10) km scales at the radiator survey.
    Description: S. Ramachandran acknowledges support from the National Science Foundation through award OCE 1558849 and the U.S. Office of Naval Research, Grants N00014-13-1-0456 and N00014-17- 1-2355. A. Tandon acknowledges support from the U.S. Office of Naval Research, Grants N00014-13-1-0456 and N00014-17-1-2355. J. T. Farrar and R. A. Weller were supported by the U.S. Office of Naval Research, Grant N00014-13-1-0453, to collect the UCTD data and process theUCTD and shipboard meteorological data. J. Nash, J. Mackinnon, and A. F. Waterhouse acknowledge support from the U. S. Office of Naval Research, Grants N00014-13-1-0503 and N00014-14-1-0455. E. Shroyer acknowledges support from the U. S. Office of Naval Research, Grants N00014-14-10236 and N00014-15- 12634. A. Mahadevan acknowledges support fromthe U. S. Office of Naval Research, Grant N00014-13-10451. A. J. Lucas and R. Pinkel acknowledge support from the U. S. Office of Naval Research, Grant N00014-13-1-0489.
    Description: 2018-08-26
    Keywords: Indian Ocean ; Baroclinic flows ; Potential vorticity ; Fronts ; Monsoons ; Oceanic mixed layer
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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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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  • 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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    Decomposition of vertical velocity for nutrient transport in the upper ocean (2019)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2019. 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 49(6), (2019): 1561-1575, doi:10.1175/JPO-D-19-0002.1.
    Description: Within the pycnocline, where diapycnal mixing is suppressed, both the vertical movement (uplift) of isopycnal surfaces and upward motion along sloping isopycnals supply nutrients to the euphotic layer, but the relative importance of each of these mechanisms is unknown. We present a method for decomposing vertical velocity w into two components in a Lagrangian frame: vertical velocity along sloping isopycnal surfaces and the adiabatic vertical velocity of isopycnal surfaces . We show that , where is the isopycnal slope and is the geometric aspect ratio of the flow, and that accounts for 10%–25% of the total vertical velocity w for isopycnal slopes representative of the midlatitude pycnocline. We perform the decomposition of w in a process study model of a midlatitude eddying flow field generated with a range of isopycnal slopes. A spectral decomposition of the velocity components shows that while is the largest contributor to vertical velocity, is of comparable magnitude at horizontal scales less than about 10 km, that is, at submesoscales. Increasing the horizontal grid resolution of models is known to increase vertical velocity; this increase is disproportionately due to better resolution of , as is shown here by comparing 1- and 4-km resolution model runs. Along-isopycnal vertical transport can be an important contributor to the vertical flux of tracers, including oxygen, nutrients, and chlorophyll, although we find weak covariance between vertical velocity and nutrient anomaly in our model.
    Description: MAF was supported by a National Defense Science and Engineering Graduate Fellowship and AM by NSF OCE-I434788. The authors thank Glenn Flierl and Ruth Curry for helpful conversations, and three anonymous reviewers for comments that improved the manuscript.
    Description: 2020-06-11
    Keywords: Baroclinic flows ; Mesoscale processes ; Small scale processes ; Subgrid-scale processes ; Vertical motion
    Repository Name: Woods Hole Open Access Server
    Type: Article
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