Lagrangian three-dimensional transport and dispersion by submesoscale currents at an upper-ocean front

Abstract. This work is aimed at identifying the origin of fine-scale features on the sea surface in synthetic aperture radar (SAR) imagery with the help of in-situ measurements as well as numerical models (presented in a companion paper). We are interested in natural and artificial features starting from the horizontal scale of the upper ocean mixed layer, around 30–50 m. These features are often associated with three-dimensional upper ocean dynamics. We have conducted a number of studies involving in-situ observations in the Straits of Florida during SAR satellite overpass. The data include examples of sharp frontal interfaces, wakes of surface ships, internal wave signatures, as well as slicks of artificial and natural origin. Atmospheric processes, such as squall lines and rain cells, produced prominent signatures on the sea surface. This data has allowed us to test an approach for distinguishing between natural and artificial features and atmospheric influences in SAR images that is based on a co-polarized phase difference filter.

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Quasigeostrophic Diagnosis of Mixed Layer Dynamics Embedded in a Mesoscale Turbulent Field

Journal of Physical Oceanography ◽

10.1175/jpo-d-14-0178.1 ◽

2016 ◽

Vol 46 (1) ◽

pp. 275-287 ◽

Cited By ~ 6

Author(s):

Cédric P. Chavanne ◽

Patrice Klein

Keyword(s):

Surface Layer ◽

High Resolution ◽

Mixed Layer ◽

Finite Thickness ◽

Vertical Mixing ◽

Three Dimensional ◽

Upper Ocean ◽

Surface Mixed Layer ◽

Deep Interior ◽

Quasigeostrophic Model

AbstractA quasigeostrophic model is developed to diagnose the three-dimensional circulation, including the vertical velocity, in the upper ocean from high-resolution observations of sea surface height and buoyancy. The formulation for the adiabatic component departs from the classical surface quasigeostrophic framework considered before since it takes into account the stratification within the surface mixed layer that is usually much weaker than that in the ocean interior. To achieve this, the model approximates the ocean with two constant stratification layers: a finite-thickness surface layer (or the mixed layer) and an infinitely deep interior layer. It is shown that the leading-order adiabatic circulation is entirely determined if both the surface streamfunction and buoyancy anomalies are considered. The surface layer further includes a diabatic dynamical contribution. Parameterization of diabatic vertical velocities is based on their restoring impacts of the thermal wind balance that is perturbed by turbulent vertical mixing of momentum and buoyancy. The model skill in reproducing the three-dimensional circulation in the upper ocean from surface data is checked against the output of a high-resolution primitive equation numerical simulation.

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Langmuir turbulence and filament frontogenesis in the oceanic surface boundary layer

Journal of Fluid Mechanics ◽

10.1017/jfm.2019.655 ◽

2019 ◽

Vol 879 ◽

pp. 512-553 ◽

Cited By ~ 1

Author(s):

Peter P. Sullivan ◽

James C. McWilliams

Keyword(s):

Boundary Layer ◽

Surface Waves ◽

Momentum Flux ◽

Shear Instability ◽

Small Scale ◽

Upper Ocean ◽

Surface Boundary ◽

Langmuir Turbulence ◽

Filament Axis ◽

Submesoscale Currents

Submesoscale currents, small-scale turbulence and surface gravity waves co-exist in the upper ocean and interact in complex ways. To expose the couplings, the frontogenetic life cycle of an idealized cold dense submesoscale filament interacting with upper ocean Langmuir turbulence is investigated in large-eddy simulations (LESs) based on the incompressible wave-averaged equations. The simulations utilize large domains and fine meshes with $6.4\times 10^{9}$ grid points. Case studies are made with surface winds or surface cooling with waves oriented in across-filament (perpendicular) or down-filament (parallel) directions relative to the two-dimensional filament axis. The currents $u$, $v$ and $w$ are aligned with the across-filament, down-filament and vertical directions, respectively. Frontogenesis is induced by across-filament Lagrangian secondary circulations in the boundary layer, and it is shown to be strongly impacted by surface waves, in particular the propagation direction relative to the filament axis. In a horizontally heterogeneous boundary layer, surface waves induce both mean and fluctuating Stokes-drift vortex forces that modify a linear, hydrostatic turbulent thermal wind (TTW) approximation for momentum. Down-filament winds and waves are found to be especially impactful, they significantly reduce the peak level of frontogenesis by fragmenting the filament into primary and secondary down-welling sites in a broad frontal zone over a width ${\sim}500~\text{m}$. At peak frontogenesis, opposing down-filament jets $\langle v\rangle$ overlie each other resulting in a vigorous vertical shear layer $\unicode[STIX]{x2202}_{z}\langle v\rangle$ with large vertical momentum flux $\langle v^{\prime }w^{\prime }\rangle$. Filament arrest is induced by a lateral shear instability that generates horizontal momentum flux $\langle u^{\prime }v^{\prime }\rangle$ at low wavenumbers. The turbulent vertical velocity patterns, indicative of coherent Langmuir cells, change markedly across the horizontal domain with both across-filament and down-filament winds under the action of submesoscale currents.

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The three-dimensional structure of an upper ocean vortex in the tropical Pacific Ocean

Nature ◽

10.1038/383610a0 ◽

1996 ◽

Vol 383 (6601) ◽

pp. 610-613 ◽

Cited By ~ 99

Author(s):

Pierre J. Flament ◽

Sean C. Kennan ◽

Robert A. Knox ◽

Pearn P. Niiler ◽

Robert L. Bernstein

Keyword(s):

Pacific Ocean ◽

Three Dimensional ◽

Tropical Pacific ◽

Dimensional Structure ◽

Upper Ocean ◽

Tropical Pacific Ocean ◽

Three Dimensional Structure ◽

The Tropical Pacific

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Enhanced Wind-Driven Downwelling Flow in Warm Oceanic Eddy Features during the Intensification of Tropical Cyclone Isaac (2012): Observations and Theory

Journal of Physical Oceanography ◽

10.1175/jpo-d-14-0176.1 ◽

2015 ◽

Vol 45 (6) ◽

pp. 1667-1689 ◽

Cited By ~ 36

Author(s):

Benjamin Jaimes ◽

Lynn K. Shay

Keyword(s):

Mixed Layer ◽

Numerical Models ◽

Three Dimensional ◽

Ocean Warming ◽

Sea Surface ◽

Upper Ocean ◽

Ekman Pumping ◽

Flow Strength ◽

Oceanic Mixed Layer ◽

Oceanic Eddy

AbstractTropical cyclones (TCs) typically produce intense oceanic upwelling underneath the storm’s center and weaker and broader downwelling outside upwelled regions. However, several cases of predominantly downwelling responses over warm, anticyclonic mesoscale oceanic features were recently reported, where the ensuing upper-ocean warming prevented significant cooling of the sea surface, and TCs rapidly attained and maintained major status. Elucidating downwelling responses is critical to better understanding TC intensification over warm mesoscale oceanic features. Airborne ocean profilers deployed over the Gulf of Mexico’s eddy features during the intensification of tropical storm Isaac into a hurricane measured isothermal downwelling of up to 60 m over a 12-h interval (5 m h−1) or twice the upwelling strength underneath the storm’s center. This displacement occurred over a warm-core eddy that extended underneath Isaac’s left side, where the ensuing upper-ocean warming was ~8 kW m−2; sea surface temperatures >28°C prevailed during Isaac’s intensification. Rather than with just Ekman pumping WE, these observed upwelling–downwelling responses were consistent with a vertical velocity Ws = WE − Rogδ(Uh + UOML); Ws is the TC-driven pumping velocity, derived from the dominant vorticity balance that considers geostrophic flow strength (measured by the eddy Rossby number Rog = ζg/f), geostrophic vorticity ζg, Coriolis frequency f, aspect ratio δ = h/Rmax, oceanic mixed layer thickness h, storm’s radius of maximum winds Rmax, total surface stresses from storm motion Uh, and oceanic mixed layer Ekman drift UOML. These results underscore the need for initializing coupled numerical models with realistic ocean states to correctly resolve the three-dimensional upwelling–downwelling responses and improve TC intensity forecasting.

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Upper ocean response to two collocated typhoons

Ocean Science Discussions ◽

10.5194/osd-10-2255-2013 ◽

2013 ◽

Vol 10 (6) ◽

pp. 2255-2292

Author(s):

D. B. Baranowski ◽

P. J. Flatau ◽

S. Chen ◽

P. G. Black

Keyword(s):

Temperature Anomaly ◽

Three Dimensional ◽

Upper Ocean ◽

Precursor State ◽

Argo Float ◽

Current Decay ◽

High Repetition ◽

Ocean Response ◽

Oceanic Response ◽

Upper Ocean Response

Abstract. The atmospheric wind stress forcing and the oceanic response are examined for the period between 15 September 2008 and 6 October 2008, during which two typhoons, Hagupit and Jangmi passed through the same region of the Western Pacific at Saffir–Simpson intensity categories one and three, respectively. A three-dimensional oceanic mixed layer model is compared against the remote sensing observations as well as high repetition Argo float data. Numerical model simulations suggested that magnitude of the cooling caused by the second typhoon, Jangmi, would have been significantly larger if the ocean had not already been influenced by the first typhoon, Hagupit. It is estimated that the temperature anomaly behind Jangmi would have been about 0.4 °C larger in both cold wake and left side of the track. The numerical simulations suggest that the magnitude and position of Jangmi's cold wake depends on the precursor state of the ocean as well as lag between typhoons. Based on sensitivity experiments we show that temperature anomaly difference between "single typhoon" and "two typhoons" as well as magnitude of the cooling strongly depends on the value of inertial current decay time parameter. Thus, the magnitude of the observed cooling depends also on the amount of kinetic energy in the upper ocean. This paper indicates that studies of ocean-atmosphere tropical cyclone interaction will benefit from denser, high repetition Argo float measurements.

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