Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session A28: Geophysical Fluid Dynamics: Oceanographic I |
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Chair: Hussein Aluie, University of Rochester Room: 152A |
Sunday, November 19, 2023 8:00AM - 8:13AM |
A28.00001: Energy Spectra and Cascades in the Global Ocean Hussein Aluie, Benjamin Storer, Michele Buzzicotti, Hemant Khatri, Stephen Griffies Our understanding of the ocean's spatial scales and their coupling has been derived mostly from Fourier analysis in small "representative" regions, typically a few hundred kilometers in size, that cannot capture the vast dynamic range at planetary scales. We perform a coarse-graining scale-analysis on data from satellites and reanalysis to probe a range of spatial scales spanning more than three orders of magnitude, including both mesoscales and planetary scales. We present a truly global kinetic energy (KE) wavenumber spectrum, as well as the first analysis of the cascade across this entire range of scales. This provides us with the first estimates of the global amount of energy that is transferred by the KE cascade, as well as the scale-dependent depth structure of the oceanic KE spectrum and cascade. I will discuss some of the key findings, including the cascade's seasonality, its scale-locality, its arrest, and the atmospheric imprint. |
Sunday, November 19, 2023 8:13AM - 8:26AM |
A28.00002: A new method to diagnose turbulent cascade rates in mesoscale ocean systems and planetary atmospheres Brodie Pearson, Cassidy Wagner, Jenna Pearson, Natalie Rodriguez, Sarah Alshenaiber, Baylor Fox-Kemper Energy is supplied to Earth at the planetary scale by solar heating. Much of this energy becomes kinetic energy and ultimately arrives at small scales where it is dissipated by molecular processes. Turbulence plays a key role in the Earth system, "cascading" this energy and other properties (e.g., enstrophy) from one scale to another through non-linear advection, facilitating the movement of energy from planetary to dissipative scales. Despite the important role of turbulent cascades in the ocean, cascade rates are notoriously hard to measure due to sparse data and inhomogeneity. |
Sunday, November 19, 2023 8:26AM - 8:39AM |
A28.00003: Locating convergent filaments from dilation rate fields obtained using Gaussian Process Regression H. M. Aravind, Tamay M Ozgokmen, Michael Allshouse Lagrangian convergence in the ocean is identified using the metric dilation rate, the time average of divergence over a particle trajectory. Trajectories of drifter triads over a finite time interval can be used to estimate dilation rates in the absence of accurate high-resolution velocity fields. However, this method yields area-averaged estimates that are sparse, limiting the ability to accurately identify features with large aspect ratios like convergent submesoscale filaments. While these filaments can play an outsized role in the surface flow field, measuring its strength and shape directly with drifters requires accurately releasing drifters on and near the filament. To circumvent these issues, we compute point-wise dilation rate fields from velocity fields reconstructed using Gaussian Process Regression (GPR) to analyze sparse drifter trajectories. The uncertainties in velocity reconstruction obtained from the GPR method, averaged along particle trajectories, locate Lagrangian confidence regions that are applicable both to synthetic trajectories and the dilation rate field. The method is first tested on an analytic system, before being applied to the drifter data from the Lagrangian Submesoscale Experiment in 2016 to locate convergent filaments. |
Sunday, November 19, 2023 8:39AM - 8:52AM |
A28.00004: Estimating turbulent lengthscales in stratified mixing events from limited measurements Alexis K Kaminski, Jason Olsthoorn Stratified turbulent mixing events play an important role in oceanic flows. However, direct measurement of their associated fluxes is difficult, necessitating the use of turbulent mixing parameterizations. One approach in parameterizing mixing has been to calculate various lengthscales characterizing the state of the stratified turbulent flow, and then to use relationships between these scales to infer the relevant fluxes — an approach which has seen some success when applied to numerical simulations and some observational datasets. However, when dealing with observational data, several additional challenges arise, including not knowing the specific mechanism driving the turbulent mixing and having limited data throughout the flow domain (for instance, isolated profiles). In this work, we subsample direct numerical simulations of both scouring and overturning stratified turbulent mixing events to mimic oceanographic measurements and compute lengthscales from the limited data. We explore how well profile-based estimates characterize the state of the flow and quantify the impact of limited data on the computed fluxes. |
Sunday, November 19, 2023 8:52AM - 9:05AM |
A28.00005: A physics-based explanation for the existence of Stokes drift Raphael Benamran, Aidan Blaser, Luc Lenain, Bia Villas Bôas, Nicholas Pizzo The particle trajectories in irrotational, incompressible, inviscid deep-water surface gravity waves are open, leading to a net drift in the direction of wave propagation known as the Stokes Drift. This is responsible for catalysing surface wave-induced mixing in the ocean, and is essential to the transport of marine debris and generation of Langmuir circulation. |
Sunday, November 19, 2023 9:05AM - 9:18AM |
A28.00006: Impacts of ocean mixing on the Winter Mixed Layer under Sea Ice in the Weddell Sea: Insights from a Large Eddy Simulation Ankit Bhadouriya, Bishakhdatta Gayen, Alessandro Silvano, Alberto N Garabato Sea ice form a dynamic interface between the ocean and atmosphere in polar regions, significantly influencing global climate patterns and marine ecosystems. Winter-mixed layers under sea ice in the Southern Ocean (SO) undergo complex interactions between the atmosphere and the ocean. During the ice formation months (June-September), brine rejection and near-freezing surface temperature make the water column relatively weakly stratified as warm and saline deep water sits right under the cold, fresh, mixed layer (ML) and is susceptible to convective instabilities. We have conducted convection resolving large eddy simulation (LES) to model the ML growth during the winter and characterize the mixing. LES results are compared with observational data and agree well with the ML properties. The results show the rapid deepening of ML during the earlier phase of winter due to high conductive heat flux through thin sea ice, which assists faster sea-ice growth that triggers a high rate of ML deepening owing to large brine rejection. The later stage leads to a slower rate of sea ice formation by reduced conductive heat flux resulting in slower ML deepening. Simulation shows that fine-scale turbulent eddies are crucial in redistributing heat and salt within the ML during sea-ice formation phases and play a vital role in ML dynamics and sea-ice growth. The data from the present study will also indicate improvements required in the parameterization used in large-scale ocean and climate models for the SO. |
Sunday, November 19, 2023 9:18AM - 9:31AM |
A28.00007: Large-eddy simulations of ship channel and shallow bay interactions under wind and wave forcings Mahdi Farsi, Meng Li, John Breier, Scott A Socolofsky, Di Yang Many embayments around Gulf of Mexico, e.g., Corpus Christi Bay and Galveston Bay, feature a shallow barrier-island type bay with a deep artificial ship channel. In these embayment systems, the river and tidal flows are weak and the mixing and transport are dominated by the effects of wind- and wave-driven flows. The interaction between wind and waves causes the generation of Langmuir turbulence (i.e., the combination of large coherent Langmuir circulations and small-scale turbulence), which can induce considerable transport of salinity, nutrient, and sediment between the bay and the ship channel. Langmuir circulations also exhibit noticeable change of intensity as they travel over the ship channel region, which further complicates the channel–bay interaction. In this work, the dynamics of Langmuir turbulence in the channel–bay coupled system is modeled using large-eddy simulation (LES). A suite of LES cases is performed to cover different wind and wave conditions, based on which the material exchanges between the shallow bay and the deep shape channel are quantified. |
Sunday, November 19, 2023 9:31AM - 9:44AM |
A28.00008: Unlocking Landsat's Potential to Explain the Longest Series of Sea Surface Temperature Ashfaq Ahmed, Baylor Fox-Kemper, Daniel Wexler, Monica M Wilhelmus Landsat satellites play an important role in effectively tracking and documenting oceanographic changes within estuaries resulting from natural and anthropogenic events. Long-term Sea Surface Temperature (SST) records from high-resolution Landsat images offer valuable insights into estuarine productivity and climatological characteristics. Our study utilized in-situ corrected multi-satellite Landsat data and tide gauges to investigate the SST variability and tidal forcing over 39 years in Narragansett Bay and neighboring Mt. Hope Bay. Pattern recognition techniques like Empirical Orthogonal Function decomposition revealed that the seasons account for up to 89% of the variabilities. Annual temperature trends exhibited discernible increases in the bays. The upper bay showed greater sensitivity to SST changes than the lower bay, influenced by the bay's bathymetry. Additionally, signal-to-noise ratio analysis underscored the robustness of Landsat imagery in capturing tidal signatures, particularly during low tides. In the future, we aim to further our understanding of the complex dynamics of other estuaries and inform decision-making processes in coastal management and conservation. |
Sunday, November 19, 2023 9:44AM - 9:57AM |
A28.00009: Topographic internal waves in the presence of barotropic and baroclinic forcings SAI SAANDEEP SAMPATIRAO, Michael Allshouse, Hanut Vemulapalli, Manikandan Mathur Bottom topography are known to profoundly impact internal wave activity in the ocean. Barotropic tides interact with bottom topography like continental shelves and deep ocean ridges to generate internal tides, which can propagate far from their sources. These far-propagating internal tides can further interact with bottom topography present along their paths, where internal tide generation by local barotropic forcing is already in place. In this combined analytical and numerical study, we investigate how internal wave generation or scattering at topographic sites is affected by the presence of both barotropic and baroclinic forcings. Specifically, we study the effects of the amplitude ratio and phase difference between the two forcings, height ratio and criticality of the topography, and the stratification profile, A modal decomposition analysis of the wave fields indicates that even relatively weak baroclinic (barotropic) forcing can significantly affect the efficiency of generation (scattering) of internal waves. Sub- and super- critical topographies are both studied. |
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