Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session U14: Geophysical Fluid Dynamics: Air-Sea Interaction |
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Chair: Fabrice Veron, University of Delaware Room: 141 |
Tuesday, November 22, 2022 8:00AM - 8:13AM |
U14.00001: Laboratory experiments on air-sea interaction dynamics for shoaling waves. Fabio Addona, Tetsu Hara, Fabrice Veron When the surface wave field is in local equilibrium with wind forcing, the air-sea transfer coefficients can be expressed as a function of a reference wind speed only. However, such conditions are generally not present in the ocean and exchanges of mass, momentum, gases, etc., at the air-water interface are strongly influenced by sea state conditions. Recent studies show that surface roughness is significantly modified in coastal waters, as shoaling waves slow down and steepen. In particular, an enhancement of the drag coefficient (up to 55%) has been observed for shoaling waves compared to deep water conditions. A correct parametrization of the air-sea transfer coefficients requires detailed knowledge of air-water boundary conditions and it is crucial to obtain reliable high-resolution atmosphere-wave-ocean models. To fulfill this gap, we performed detailed laboratory measurements of the airflow above shoaling waves. The 2D+time measurements allowed us to retrieve the velocity field as a function of the wave phase. In turn, we estimate the relative partition between wave, turbulent, and viscous stresses, and show the phase-dependent turbulent kinetic energy, vorticity, and pressure fields during the shoaling process. |
Tuesday, November 22, 2022 8:13AM - 8:26AM |
U14.00002: How does salinity influence submicron aerosol production? Lena Dubitsky, Dale Stokes, Grant B Deane, James Bird When bubbles are created by breaking ocean waves, they burst and create a shower of droplets which contribute to sea spray aerosols. Submicron-sized droplets in the atmosphere play a key role in cloud properties and formation, which subsequently affects the climate. However, many aspects of predicting the number and size of submicron drops emitted from a bursting bubble remain unclear. It has been documented that submicron droplet production increases with salinity, which has been attributed to bubble coalescence inhibition. We experimentally show that submicron drop production increases with salinity even when using a salt that does not affect bubble coalescence. Additionally, the peak droplet formation diameter decreases with higher salinity, consistent with a changing bubble cap film thickness. This size shift suggests that bubble coalescence is not the only mechanism by which salinity affects submicron droplet production. As a result, salinity likely impacts the submicron aerosol production flux near melting glaciers or other environments with large salinity variations, even if bubble coalescence is negligible. |
Tuesday, November 22, 2022 8:26AM - 8:39AM |
U14.00003: Vignettes of the Fog and Turbulence in Marine Atmosphere (Fatima) 2022 Field Campaign Harindra J Fernando, Edward Creegan, Clive Dorman, Sasa Gabersek, Ismail Gultepe, Eric Pardyjak, Qing Wang In a comprehensive field campaign conducted during 01-31 July 2022, the key drivers in the formation, maturation, and dissipation (i.e., lifecycle) of marine fog were studied, particularly the role of atmospheric turbulence. Momentum, temperature, humidity, and aerosol inhomogeneities of large-scale weather systems cascade down to the smallest (Kolmogorov) scale of atmospheric turbulence (~ 1mm), and the fog droplets form around hygroscopic aerosols of size ~ 100 nm embedded therein, the physicochemical properties of which also play an important role. The massive Fatima field campaign was based on (i) an isolated narrow (1km x 40km) island – Sable Island - located in the North Atlantic Ocean south of Grand Banks and proximity to continental shelf break in a region where cold Labrador and warm Gulf Stream waters osculate, and (ii) the research vessel R/V Atlantic Condor that traversed the area, which also deployed a suite of autonomous surface crafts. All measurement platforms were instrumented in unprecedented proportions by dozens of investigators, with novel and conventional instruments that probed from ~ 1000 km synoptic to ~ 100 nm microphysical scales of the atmosphere as well as upper ~ 250 m of the ocean, supplemented by studies on bio-chemo-physical properties of aerosol nuclei. A brief overview of the Fatima-2022 field campaign will be given in this presentation. |
Tuesday, November 22, 2022 8:39AM - 8:52AM |
U14.00004: Near Surface Dynamics of Inertial Droplets Produced by Wind Forced Mechanical Breaking Waves Robert D Jaquette, David H Richter, Fabrice Veron
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Tuesday, November 22, 2022 8:52AM - 9:05AM |
U14.00005: Measurements of bubbles, drops, and dry aerosol particles in laboratory experiments on spray generation by bubble bursting Megan T Mazzatenta, Baptiste Neel, Martin A Erinin, Luc Deike Bubbles entrained by breaking waves rise to the ocean surface, where they reside before bursting and releasing droplets into the atmosphere. The ejected aerosols affect the climate, motivating study of the controlling parameters behind bubble bursting at the ocean surface. To investigate the effect of salinity on spray production, experiments were conducted in a 50x50x60 cm3 bubbling tank filled with solutions of artificial seawater with salt concentrations ranging from 1.3 to 42 g/L. Combined measurements of bulk bubbles, surface bubbles, drops, and dry aerosol particles were made at each salinity level. Cases were run for bubbles rising in both quiescence and turbulent flow, where turbulence leads to bubble breakup in the bulk and a broad size distribution of bubbles rising to the surface. Bulk and surface bubbles were captured using planar shadowgraph techniques, while drops were imaged with an in-line holographic system and a shadowgraph technique with a telecentric lens. Dry particles were measured using a scanning mobility particle sizer. We discuss resulting distributions of sizes and volumes of the bubbles, drops, and particles and links between the different measurements and the production mechanisms. |
Tuesday, November 22, 2022 9:05AM - 9:18AM |
U14.00006: Large Eddy Simulation of Droplet Transport Near Real Multispectral Waves Kyle D Rocha-Brownell, Sarah E Wells, Kee Horng Seh, Martin A Erinin, Luc Deike, Robert D Jaquette, Fabrice Veron, David H Richter Functions governing the generation of spray and aerosols at the sea surface are often estimated using the so-called flux profile method. Previous work has suggested that this simplified method is insufficient to capture the effects of surface waves, particularly where the advected spray droplets have significant inertia. The focus of this project is to further investigate the sensitivity of droplet dispersion to varying their initial inertia, velocity, and surface wave modes. Large-eddy simulations with inertial Lagrangian particles are used to resolve the turbulent transport of spray droplets in curvilinear coordinates above real wave tank data. The wave was obtained from the University of Delaware Air Sea Interaction Lab and is used as the dynamic bottom boundary of the simulation. The number of modes used to represent the wave is varied across different computational runs. During the simulation individual droplet characteristics are measured over these boundaries. A statistical analysis is performed on the resulting data with a focus on probability distributions of droplet characteristics at time of creation and destruction for each wave configuration. The effect varying initial droplet momentum and wave modes has on droplet dispersion is examined and discussed. |
Tuesday, November 22, 2022 9:18AM - 9:31AM |
U14.00007: Three-dimensional measurements of air entrainment and enhanced bubble transport during wave breaking Daniel Ruth, Baptiste Neel, Martin A Erinin, Megan T Mazzatenta, Robert D Jaquette, Fabrice Veron, Luc Deike We experimentally investigate the depth distributions and dynamics of air bubbles entrained by breaking waves in a wind-wave channel. The forcing frequency of the wavemaker and the speed of the wind above the water surface are varied independently in order to achieve a range of breaking wave conditions. Bubbles are imaged with both a high-resolution camera, which provides information on their depths, and a two-camera stereo tracking system, which provides three-dimensional bubble trajectories and velocities. |
Tuesday, November 22, 2022 9:31AM - 9:44AM |
U14.00008: Numerical simulation of sea spray turbulent transport at the marine boundary layer Kee Horng Seh, Kyle D Rocha-Brownell, Sarah E Wells, William Bruch, Jacques Piazzola, David H Richter In this study, we perform large-eddy simulations (LES) combined with Lagrangian particle tracking to investigate the turbulent flow and transport of spray droplets over realistic waves at the lower boundary. We prescribe spatial wave data as the lower boundary condition, which is obtained by transforming the temporal data from a wind-wave tank experiment at the Pytheas Institute in France. The sea spray generation function (SSGF) introduced by this experimental study is implemented into the droplet-laden LES model. The SSGF creates a wide range of low to intermediate inertia droplets at the water surface. It is estimated using the flux profile method, where the droplet concentrations are measured at a fixed height to estimate spray fluxes at the surface by assuming a vertical concentration profile shape. We aim to verify if the method is adequate at the wave boundary layer. LES are performed for a shear velocity of 1.01 m/s corresponding to a 10-meter wind speed 20 m/s. We compare the droplet concentration profiles from our model with experimental results. Alongside the Eulerian scheme, we discuss the findings from the droplets and wave-induced turbulence statistics, which give us insights into the transport of spray droplets and how this relates to droplet dispersion theories. |
Tuesday, November 22, 2022 9:44AM - 9:57AM |
U14.00009: Langmuir Turbulence in Upper Ocean Boundary Layer William Anderson, Ching-Wen Tseng A large-eddy simulation (LES) model is used to investigate the characteristics of Langmuir turbulence (LT) in the upper ocean boundary layer by solving the grid-filtered Craik-Leibovich (CL) equations. Different parameterizations of LT are measured in an LES model. We have set up models with imposed aerodynamic stresses and bathymetric drag in the upper ocean boundary layer to understand the relative influences of surface wind stress, and Stokes drift velocity, on the structural variations of Langmuir cells (LC). The model applies an improvement to the turbulence structure, scale, and the entrainment buoyancy flux in the ocean surface boundary layer. The structure of LC is dominantly affected by non-uniform turbulent Langmuir number. Associated with this are downwind surface convergence zones adjacent to divergence zones that are rotated, corresponding to the latitude of local conditions. The horizontal scale of the Langmuir cells expands with depth. In the turbulent OBL, Langmuir cells have irregular patterns with finite correlation scales in space and time that depends on different conditions. |
Tuesday, November 22, 2022 9:57AM - 10:10AM |
U14.00010: The effects of temperature and surfactants on secondary droplets generated by the impact of raindrops on a water surface Xinan Liu, Xiguang Zhang, James H Duncan The effects of temperature and surfactants on the secondary droplets generated by the impact of raindrops on a deep-water pool are studied experimentally in an artificial rain facility. A rain generator, consisting of an open-surface rectangular tank with an array of 360 hypodermic needles attached to its bottom, is mounted 2.2 m above a water pool. Secondary droplets are generated as water droplets from the rain generator impact the water surface of the pool. In this study, the temperature of the water in the rain generator was varied from room temperature (about 24 oC) to 4 oC (where water has its highest density) and the concentration of surfactant, Triton X-100, in the water pool was varied from 0 to about mol/l, corresponding to surface tension ranging from 73 to 30 mN/m. Both the diameters and trajectories of the droplets are measured with a cinematic digital in-line holographic technique set at various heights above the pool’s water surface. It is found that the diameters and velocities of the secondary droplets in the rain field change considerably with the temperature of the raindrops and the surface tension of the water in the pool. The effects of water properties on the dynamics of secondary droplets are explored. |
Tuesday, November 22, 2022 10:10AM - 10:23AM |
U14.00011: Gravity currents in the cabbeling regime Andrew P Grace, Marek Stastna, Kevin G Lamb, Andrea Scott Recently, the understanding of the dynamics of flows beneath ice cover has garnered much interest in the geophysical fluid dynamics community. Much focus has gone into characterizing vertical flows beneath ice and their impact on lake dynamics, while less has gone into characterizing the impact of horizontal flows beneath ice. The study of horizontal flows under ice cover is still in its relative infancy, but we know they can play a major role in the transport of nutrients, as well as impacting CML temperature. In this talk, we describe one such example of the interactions of horizontal flows and vertical flows induced from freshwater cabbeling (the mixing of parcels with equal density but different temperature). This talk presents numerical simulations of the evolution of freshwater gravity currents (canonical examples of horizontal density driven flows) where intruding and ambient temperatures are on different sides of the temperature of maximum density. A setup like this might occur in the springtime from a riverine inflow, or by differential heating in littoral regions of a lake. We will highlight how the initial intrusion flows along the upper surface of the domain and mixes with ambient water, and due to cabbeling, generates a coherent bottom current. We will introduce a control parameter (essentially the inverse of the non-dimensional temperature of maximum density), which is key to the evolution of the system, and we will show how the maximum horizontal extent of the initial intrusion varies with it. We show that for some cases, the maximum extent of the initial intrusion controls some of the important characteristics of the coherent bottom current. Finally, we will highlight some of the key characteristics (head height and temperature distribution) of the bottom current. |
Tuesday, November 22, 2022 10:23AM - 10:36AM |
U14.00012: Self-resonances in uniformly stratified uniform shear flow. Lima Biswas, Priyanka Shukla Internal waves (IWs), propagating inside the stably stratified system, are a significant component of ocean mixing and energy redistribution among ocean layers. This talk presents resonance interactions among primary IWs and their second harmonics, i.e., self-resonances. A self-resonance occurs when the resonating primary (km, ωm) wave and its second harmonic (kr, ωr) satisfy kr ± 2km = 0 and ωr ± 2 ωm = 0, where k’s and ω's are the wavenumber and frequency, respectively. A prototypical scenario exhibiting self-resonances among IWs in a uniformly stratified uniform shear flow in a finite depth two-dimensional vertically bounded channel is considered. Such resonances are not possible in a uniformly stratified media without shear. The existence of self-resonances for different buoyancy frequencies is shown by solving the linear wave dispersion relation. After identifying the resonating modes, the amplitude equations are derived for analyzing the stability of such modes. The effect of shear rate and stratification on the self-resonances is addressed by varying the Richardson number, i.e., the squared ratio of the buoyancy frequency and shear rate. This study will help understand the role of stratification and shear in generating self-resonances among IWs. |
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