Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session A5: Geophysical Fluid Dynamics: Air-sea Interaction |
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Sponsoring Units: DFD GPC Chair: James Duncan, University of Maryland Room: B113 |
Sunday, November 20, 2016 8:00AM - 8:13AM |
A5.00001: Air-sea exchange from bubble-induced jetting: How viscous forces suppress droplet production from small bubbles Elena Flynn, Peter Walls, James Bird When a bubble ruptures in the ocean, it frequently produces a jet that releases aerosols into the atmosphere. The number of jet drops ejected is important because droplets may contain sea salt and other cloud condensation nuclei. It is generally accepted that the smallest bubbles produce the largest number of jet drops. However, if the bubble is sufficiently small, viscosity prevents droplet production altogether. Here we investigate the number of jet drops produced by small bubbles. Using a combination of high-speed microscopy, similitude, and numerical simulations, we quantify the extent that viscous forces inhibit this droplet production. [Preview Abstract] |
Sunday, November 20, 2016 8:13AM - 8:26AM |
A5.00002: Numerical investigation of wind over two progressive waves Tao Cao Wind-wave interaction is important in many applications and critical for the fundamental understanding of the wind-wave growth mechanism. It has been found in present study that the growth of short wave is suppressed in the presence of long waves, which is called the sheltering effect. In the present study, we have carried out a direct numerical simulation (DNS) of wind over two surface waves to improve the understanding of the sheltering effect. We have observed that the sheltering effect on the short wave strongly depends on the wave age of the long wave, thus the wave growth rate of the long wave. For the slow and fast long waves, the magnitude of wave growth rate of the short wave is significantly reduced compared with the cases with short wave only. But for the intermediate long wave, this reduction is relatively small. Based on the DNS data, the budget of energy conservation in the wave boundary layer is analyzed in detail. [Preview Abstract] |
Sunday, November 20, 2016 8:26AM - 8:39AM |
A5.00003: Numerical study of airflow over breaking waves. Zixuan Yang, Lian Shen We present direct numerical simulation (DNS) results on airflow over breaking waves. Air and water are simulated as a coherent system. The initial condition for the simulation is a fully-developed turbulent airflow over strongly-forced steep waves. The airflow is driven by a shear stress at the top. The effects of the initial wave steepness and wave age are studied systematically. Because wave breaking is an unsteady process, we use ensemble averaging of a large number of runs to obtain turbulent statistics. Simulation results show that the airflow above does not see the wave trough during wave breaking. Vortex structures at different stages of wave breaking are analyzed based on a linear stochastic estimation method. It is found that the wave breaking alters the pattern of vortex structures. [Preview Abstract] |
Sunday, November 20, 2016 8:39AM - 8:52AM |
A5.00004: Observations of Equatorial Kelvin Waves and their Convective Coupling with the Atmosphere/Ocean Surface Layer Patrick Conry, H. J. S. Fernando, Laura Leo, Byron Blomquist, Vincent Amelie, Nelson Lalande, Ed Creegan, Chris Hocut, Ben MacCall, Yansen Wang, S. U. P. Jinadasa, Chien Wang, Lik-Khian Yeo Intraseasonal disturbances with their genesis in the equatorial Indian Ocean (IO) are an important component of global climate. The disturbances, which include Madden-Julian Oscillation and equatorial Kelvin and Rossby waves in the atmosphere and ocean, carry energy which affects El Ni\~{n}o, cyclogenesis, and monsoons. A recent field experiment in IO (\underline {ASIRI-RAWI}) observed disturbances at three sites across IO with arrays of instruments probing from surface layer to lower stratosphere. During the field campaign the most pronounced planetary-scale disturbances were Kelvin waves in tropical tropopause layer. In Seychelles, quasi-biweekly westerly wind bursts were documented and linked to the Kelvin waves aloft, which breakdown in the upper troposphere due to internal shear instabilities. Convective coupling between waves' phase in upper troposphere and surface initiates rapid (turbulent) vertical transport and resultant wind bursts at surface. Such phenomena reveal linkages between planetary-scale waves and small-scale turbulence in the surface layer that can affect air-sea property exchanges and should be parameterized in atmosphere-ocean general circulation models. [Preview Abstract] |
Sunday, November 20, 2016 8:52AM - 9:05AM |
A5.00005: A dynamic framework for subgrid-scale parametrization of mesoscale eddies in geophysical flows Omer San, Romit Maulik This study puts forth a modular dynamic subgrid-scale modeling framework for large eddy simulation of quasigeostrophic turbulence based upon minimizing the errors between structural and functional subgrid-scale models. The approximate deconvolution procedure (AD) is used to estimate the free modeling parameters for the eddy viscosity coefficient parameterized in space and time using the Smagorinsky and Leith models. The novel idea here is to estimate the modeling parameters using the AD method rather than a test filter. The proposed model is applied to a wind-driven quasigeostrophic four-gyre ocean circulation problem, which is a standard prototype of more realistic ocean dynamics. Results show that the proposed model captures the quasi-stationary ocean dynamics and provides the time averaged four-gyre circulation patterns. Taking into account for local resolved flow characteristics, the model dynamically provides higher eddy viscosity values for lower resolutions. Furthermore, our first step in the numerical assessment for solving the quasigeostrophic turbulence problem addresses the intimate relationship between the eddy viscosity coefficients and the numerical resolution employed by the quasigeostrophic models. [Preview Abstract] |
Sunday, November 20, 2016 9:05AM - 9:18AM |
A5.00006: Dynamical properties of breaking waves: dissipation, air entrainment and spray generation Nick Pizzo, Luc Deike, W. Kendall Melville, Stephanie Popinet Wave breaking in the ocean is of fundamental importance in order to quantify wave dissipation and air-sea interaction, including gas and momentum exchange, and to improve parametrization for ocean-atmosphere exchange in weather and climate models. Here, we present 2D and 3D direct numerical simulations of breaking waves, compared with laboratory measurements. The dissipation due to breaking in the 2D and 3D simulations is found to be in good agreement with experimental observations and inertial-scaling arguments [1,2]. We discuss the transition from a 2D to a 3D flow during breaking. We present a model for air entrainment and bubble statistics that describes well the experimental and numerical data, and is based on turbulent fragmentation of the bubbles and a balance between buoyancy forces and viscous dissipation [2]. Finally we discuss the generation of large drops during the impact and splashing process. [1] Deike, L., Popinet, S., and Melville, W.K. 2015. Journal of Fluid Mechanics. vol 769, p541-569.[2] Deike, L., Melville, W.K., and Popinet, S. 2016. Journal of Fluid Mechanics. vol 801, p91- 129. [Preview Abstract] |
Sunday, November 20, 2016 9:18AM - 9:31AM |
A5.00007: A Laboratory Study of a Water Surface in Response to Rainfall Ren Liu, Xinan Liu, James Duncan The shape of a water surface in response to the impact of raindrops is studied experimentally in a 1.22-m-by-1.22-m water pool with a water depth of 0.3 m. Simulated raindrops are generated by an array of 22-gauge hypodermic needles that are attached to the bottom of an open-surface water tank. The tank is connected to a 2D translation stage to provide a small-radius horizontal circular or oval motion to the needles, thus avoiding repeated drop impacts at the same location under each needle. The drop diameter is about 2.6 mm and the height of the water tank above the water surface of the pool is varied from 1 m to 4.8 m to provide different impact velocities. The water surface features including stalks, crowns and ring waves are measured with a cinematic laser-induced- fluorescence (LIF) technique. It is found that the average stalk height is strongly correlated to the impact velocities of raindrops and the phase speeds of ring waves inside the rain field are different from that measured outside the rain field. [Preview Abstract] |
Sunday, November 20, 2016 9:31AM - 9:44AM |
A5.00008: Instabilities in Non-Boussinesq Density Stratified Long and Narrow Lakes Anirban Guha, Mihir Shete We have discovered a new type of instability that can potentially occur in density stratified long and narrow lakes. The non-Boussinesq air-water interface plays a major role in this instability mechanism. A two layered lake driven by wind is considered; in such wind driven scenarios circulation sets up in each layer of the lake. The flow is assumed to be two dimensional, inviscid and incompressible. A surface gravity wave exists on the interface between air and water while an interfacial gravity wave exists on the interface between the two water layers (interface between warm and cold water). The resonant interactions between these two waves under a suitable doppler shift gives rise to normal mode growth rates leading to instability. We verify these claims analytically by piecewise linear velocity and density profiles. Furthermore we also use a realistic velocity and density profiles that are smooth and perform a linear stability analysis using a non-Boussinesq Taylor-Goldstein equation solver. We find that the normal mode instabilities are instigated by realistic wind velocities. [Preview Abstract] |
Sunday, November 20, 2016 9:44AM - 9:57AM |
A5.00009: Seasonal variability of atmospheric surface layer characteristics and weather pattern in Qatar Dhrubajyoti Samanta, Way Lee Cheng, Reza Sadr Qatar's economy is based on oil and gas industry, which are mostly located in coastal regions. Therefore, better understanding of coastal weather, characteristics of surface layer and turbulence exchange processes is much needed. However, the turbulent atmospheric layer study in this region is severely limited. To support the broader aim and study long term precise wind information, a micro-meteorological field campaign has been carried out in a coastal location of north Qatar. The site is based on a 9 m tower, installed at Al Ghariya in the northern coast of Qatar, equipped with three sonic anemometers, temperature-humidity sensor, radiometer and a weather station. This study shows results based on the period August 2015 to July 2016. Various surface layer characteristics and modellings coefficients based on Monin Obukhov similarity theory is studied for the year and seasonal change is noted. Along with the seasonal variabilities of different weather parameters also observed. We hope this long term field observational study will be very much helpful for research community especially for modelers. In addition, two beach and shoreline monitoring cameras installed at the site could give first time information on waves and shoreline changes, and wind-wave interaction in Qatar. [Preview Abstract] |
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