Global Ocean Associates

Alexandria, VA, United States

Global Ocean Associates

Alexandria, VA, United States
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Buijsman M.C.,University of California at Los Angeles | Buijsman M.C.,Geophysical Fluid Dynamics Laboratory | McWilliams J.C.,University of California at Los Angeles | Jackson C.R.,Global Ocean Associates
Journal of Geophysical Research: Oceans | Year: 2010

The nonhydrostatic Regional Ocean Modeling System is applied to study the effects of thermocline shoaling/deepening, bathymetry, and asymmetric modulated tides on the soliton growth to the west and east of Luzon Strait in the South China Sea and western Pacific Ocean. Luzon Strait comprises a shallow east ridge and a deep west ridge, and its interaction with barotropic tidal currents yields strong westward internal tides that disperse into solitons. Satellite imagery indicates that the westward solitons are more numerous and better defined than the eastward solitons. The model results show that the eastward solitons are 45%, 39%, 28%, and 23% smaller than the westward solitons due to asymmetric modulated barotropic tides at the east ridge, a deeper Pacific Ocean, westward thermocline shoaling related to the Kuroshio current, and internal tide resonance in a double ridge configuration, respectively. Due to the westward location of the Kuroshio, little thermocline deepening occurs east of the east ridge. Hence, the influence of thermocline deepening on counteracting eastward soliton growth is small. The Kuroshio mainly enhances westward soliton growth. The dispersion of internal tides into solitons is governed by the balance between the nonlinearity parameter on the one hand and the nonhydrostatic and Coriolis dispersions on the other. It is shown that this balance favors soliton growth for thermocline shoaling, while it counters it for a deeper ocean. A series of double ridge experiments is performed, in which the distance between the ridges and the height of the west ridge are varied. For a semidiurnal tidal forcing and two Gaussian ridges separated by 100 km, barotropic to baroclinic energy conversion is enhanced at both ridges, causing larger westward internal tides and solitons. The combination of Coriolis forcing, thermocline shoaling, and a double ridge configuration enhances the distinctiveness of the so-called type a and b solitons when a modulated tide occurs. Copyright 2010 by the American Geophysical Union.

Li X.,College Park | Jackson C.R.,Global Ocean Associates | Pichel W.G.,College Park
Geophysical Research Letters | Year: 2013

Internal solitary waves (ISWs) are regularly generated at the Luzon Strait, propagate westward into the South China Sea, and dissipate on the continental shelf after persisting for more than 4 days. The Dongsha Atoll stands in the middle of their propagation path and the incident ISW bifurcates as it interacts with, and passes the atoll. As the two arms meet on the western side of Dongsha, they produce complex patterns from nonlinear internal wave interactions. In this study, new satellite observations are presented that show unusual ISW refraction patterns at the Dongsha Atoll. In these satellite images the incident wave is located on one side of Dongsha, and the portion of the wave closest to the atoll continues to propagate around the atoll circularly, while the remaining portion of the arm continues its westward propagation. The process is adequately modeled using a function relating ISW phase speed to ocean depth. Key Points Unusual IW refraction at Dongsha Atoll is observed by satellite images A conceptual model is implemented to understand the mechanism of IW refraction The rare occurrence of refracted IW at atoll is discussed ©2013. American Geophysical Union. All Rights Reserved.

Jackson C.R.,Global Ocean Associates | Alpers W.,University of Hamburg
Journal of Geophysical Research: Oceans | Year: 2010

A wide variety of oceanic and atmospheric phenomena are often observed in and around the sunglint region on optical images of the sea surface. The appearance of these phenomena depends strongly on the viewing geometry with areas on the sea surface that are rougher (or smoother) than the background appearing as either brighter or darker than the background depending on their position relative to the specular point. To understand these sea surface signature variations, this paper introduces the concept of a critical sensor viewing angle, defined as the sensor zenith angle at which different sea surface roughness variances produce identical sunglint radiance. It is when the imaging geometry transitions through the critical angle that a surface feature goes through a brightness reversal. Knowledge of where this transition takes place is important for properly interpreting the characteristics of the sea surface signature of these phenomena. The theory behind the concept of the critical angle is presented and then applied to sunglint imagery acquired over the ocean from space by the Moderate Resolution Imaging Spectroradiometer onboard NASA's Aqua and Terra satellites. © 2010 by the American Geophysical Union.

Simmons H.,University of Alaska Fairbanks | Chang M.-H.,National Taiwan Ocean University | Chang Y.-T.,National Taiwan University | Chao S.-Y.,University of Cambridge | And 3 more authors.
Oceanography | Year: 2011

Nonlinear internal solitary waves generated within Luzon Strait move westward across the northern South China Sea, refract around Dongsha Atoll, and dissipate on the Chinese continental shelf after a journey of over 500 km lasting more than four days. In the last 10 years a great deal of observational, theoretical, and modeling effort has been directed toward understanding and predicting these solitary waves and their effects on the oceanography of the northern South China Sea. This paper reviews a variety of modeling approaches (two- and three-dimensional, kinematic, hydrostatic, and nonhydrostatic) that have been employed to gain insight into the generation mechanisms and physics of the South China Sea's nonlinear solitary waves with the goal of predicting wave characteristics such as phase speed, amplitude, and arrival time.

Monaldo F.M.,Johns Hopkins University | Li X.,National Oceanic and Atmospheric Administration | Pichel W.G.,National Oceanic and Atmospheric Administration | Jackson C.R.,Global Ocean Associates
Bulletin of the American Meteorological Society | Year: 2014

The capacity to retrieve high-resolution winds from spaceborn synthetic aperture radar (SAR) imagery has matured significantly over the past decade. The retrieved speeds have been shown to have standard deviations of less than 2 m s 1 when compared to buoys and other independent measures. Microwave measurement of winds from space is not new. The wind archives available from scatterometer satellites such as the Quick Scatterometer (QuikSCAT) and Advanced Scatterometer (ASCAT) provide important global data. However, scatterometer data have resolutions from 12 to 50 km. They are less valuable in coastal areas. SAR winds and conventional scatterometer winds are properly seen as complimentary. The multiyear archive of Radarsat-1 data offers the prospect of generating a high-resolution wind data archive.

Garcia-Pineda O.,Florida State University | MacDonald I.R.,Florida State University | Li X.,College Park | Jackson C.R.,Global Ocean Associates | Pichel W.G.,College Park
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing | Year: 2013

We developed a Textural Classifier Neural Network Algorithm (TCNNA) to process Synthetic Aperture Radar (SAR) data to map oil spills. The algorithm processes SAR data and wind model outputs (CMOD5) using a combination of two neural networks. The first neural network filters out areas of the image that do not need to be processed by flagging pixels as oil candidates; the second neural network performs a statistical textural analysis to differentiate between pixels of sea surface with or without floating oil. By combining the two neural networks, we are able to process a full resolution geotiff SAR image (16 bit, ∼ 350 MB) in less than one minute on a conventional PC. The algorithm performs efficiently for all radar incidence angles when wind conditions are above 3 m/s. When low wind conditions are present, the performance of the neural network classification is limited, however the algorithm output allows the user to easily discard any elements of the classification and export the final product as a map of the water covered by oil. The results of this algorithm allowed us to process rapidly all of the images collected by Envisat during the Gulf of Mexico (GOM) Deepwater Horizon (DWH) oil spill event. By normalizing oil detections by the frequency that each area was sampled, we estimate that oil covered a mean daily area of 10,750 km2 (with a total extent of 119,600 km2 of the GOM surface waters), and approximately 1,300 km of the Northern GOM shoreline was threatened by the presence of drifting oil. © 2008-2012 IEEE.

Pichel W.G.,The Center for Satellite Applications and Research | Monaldo F.,Johns Hopkins University | Jackson C.,Global Ocean Associates | Li X.,National Oceanic and Atmospheric Administration | And 2 more authors.
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2011

SAR-derived wind measurements are in the process of being implemented for operational production within NOAA's National Environmental Satellite, Data, and Information Service. For C-band ENVISAT and RADARSAT-1/2 data, the CMOD5 algorithm is being used; for ALOS data, a special L-band wind algorithm is employed. Comparisons of both C-band and L-band winds with ASCAT scatterometer wind measurements show biases of 0.58 m/s or less and standard deviations of 1.31 m/s or less. SAR wind vectors will be stored in a NetCDF4-formatted file and made available in a number of product formats via the NOAA CoastWatch program. © 2011 IEEE.

Jackson C.R.,Global Ocean Associates | Arvelyna Y.,Tokyo University of Marine Science and Technology | Asanuma I.,Tokyo University of Information Sciences
Oceanography | Year: 2011

A study of satellite imagery over the Philippines undertaken as part of the US Office of Naval Research Philippine Straits Dynamics Experiment (PhilEx) found significant high-frequency nonlinear internal wave activity in the waters around the Philippine Archipelago. Along with previously known nonlinear internal wave occurrence in the Sulu Sea and the Sulu Archipelago, the study found new areas of activity near Surigao Strait, within Butuan and Macajalar bays along the northern coast of Mindanao in the southeastern Bohol Sea, in the Samar Sea, and at the shelfbreak at the northern end of the Sulu Sea between Palawan and Panay islands. Signatures in the imagery show that the surface expression of internal waves around the Philippines span a considerable spatial scale, from large solitary waves in the Sulu Sea (10-km scale) to very fine (10-m scale) wave packets found in Butuan Bay. This paper presents examples and discusses the characteristics of the nonlinear internal wave signatures observed in synthetic aperture radar and optical sunglint satellite imagery from around the Philippines. © 2011 by The Oceanography Society.

Tessler Z.D.,Lamont Doherty Earth Observatory | Gordon A.L.,Lamont Doherty Earth Observatory | Jackson C.R.,Global Ocean Associates
Journal of Physical Oceanography | Year: 2012

Observations of early stage, large-amplitude, nonlinear internal waves in the Sulu Sea are presented. Water column displacement and velocity profile time series show the passage of two solitary-like waves close to their generation site. Additional observations of the same waves are made as they propagate through the Sulu Sea basin. These waves of depression have an estimated maximum amplitude of 44 m. Observed wave amplitude and background stratification are used to estimate parameters for both a Korteweg-de Vries (K-dV) and a Joseph wave solution. These analytic model solutions are compared with a fully nonlinear model as well. Model wave half-widths bracket the observed wave, with the Joseph model narrower than the K-dV model. The modal structure of the waves change as they transit northward though the Sulu Sea, with higher mode features present in the southern Sulu Sea, which dissipate by the time the waves reach the north. Observed and modeled energies are roughly comparable, with observed potential energy estimated at 6.5 × 10 7 J m -1, whereas observed kinetic energy is between 4.6 × 10 7 J m -1 and 1.5 × 10 8 J m -1, depending on the integration limits. If this energy remains in the Sulu Sea, an average dissipation rate of 10 -9 W kg -1 is required over its volume, helping to maintain elevated mixing rates. © 2012 American Meteorological Society.

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