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Dohan K.,Earth and Space Research | Maximenko N.,University of Hawaii at Manoa
Oceanography | Year: 2010

The interconnected ocean surface current system involves multiple scales, including basin-wide gyres, fast narrow boundary currents, eddies, and turbulence. To understand the full system requires measuring a range of motions, from thousands of kilometers to less than a meter, and time scales from those that are climate related (decades) to daily processes. Presently, satellite systems provide us with global and regional maps of the ocean surface's mesoscale motion (larger than 100 km). Surface currents are measured indirectly from satellite systems. One method involves using remotely sensed fields of sea surface height, surface winds, and sea surface temperature within a physical model to produce currents. Another involves determining surface velocity from paths of drifting surface buoys transmitted to satellite sensors. Additional methods include tracking of surface features and exploitation of the Doppler shift in radar fields. The challenges for progress include measuring small and fast processes, capturing the vertical variation, and overcoming sensor limitations near coasts. Here, we detail the challenges as well as upcoming missions and advancements in satellite oceanography that will change our understanding of surface currents in the next 10 years. Source

Lagerloef G.,Earth and Space Research
Eos | Year: 2012

Understanding the links between ocean circulation, the global water cycle, and climate variations requires knowledge of ocean surface salinity. NASA's Aquarius satellite mission (http://aquarius.nasa.gov), which monitors the global open ocean surface salinity field, embarked on its science operations phase after completing the in-orbit performance assessment on 1 December 2011. The data (Figure 1) are already showing new and interesting information. © 2012 American Geophysical Union. All Rights Reserved. Source

Dohan K.,Earth and Space Research | Davis R.E.,University of California at San Diego
Journal of Physical Oceanography | Year: 2011

Upper-ocean dynamics analyzed from mooring-array observations are contrasted between two storms of comparable magnitude. Particular emphasis is put on the role of the transition layer, the strongly stratified layer between the well-mixed upper layer, and the deeper more weakly stratified region. The midlatitude autumn storms occurred within 20 days of each other and were measured at five moorings. In the first storm, the mixed layer follows a classical slab-layer response, with a steady deepening during the course of the storm and little mixing of the thermocline beneath. In the second storm, rather than deepening, the mixed layer shoals while intense near-inertial waves are resonantly excited within the mixed layer. These create a large shear throughout the transition layer, generating turbulence that broadens the transition layer. Details of the space-time structure of the frequencies in both short waves and near-inertial waves are presented. Small-scale waves are excited within the transition layer. Their frequencies change with time and there are no clear peaks at harmonics of inertial or tidal frequencies. Wavelet transforms of the inertial oscillations show the evolution as a spreading in frequency, a deepening of the core into the transition layer, and a shift off the inertial frequency. A second near-inertial energy core appears below the transition layer at all moorings coincident with a rapid decay of mixed layer currents. An overall result is that direct wind-generated motions extend to the depth of the transition layer. The transition layer is a location of enhanced wave activity and enhanced shear-driven mixing. © 2011 American Meteorological Society. Source

Gordon A.L.,Lamont Doherty Earth Observatory | Sprintall J.,University of California at San Diego | Ffield A.,Earth and Space Research
Oceanography | Year: 2011

Confined by the intricate configuration of the Philippine Archipelago, forced by the monsoonal climate and tides, responding to the remote forcing from the open Pacific and adjacent seas of Southeast Asia, the internal Philippine seas present a challenging environment to both observe and model. The Philippine Straits Dynamics Experiment (PhilEx) observations reported here provide a view of the regional oceanography for specific periods. Interaction with the western Pacific occurs by way of the shallow San Bernardino and Surigao straits. More significant interaction occurs via Mindoro and Panay straits with the South China Sea, which is connected to the open Pacific through Luzon Strait. The Mindoro/Panay throughflow reaches into the Sulu Sea and adjacent Bohol and Sibuyan seas via the Verde Island Passage and Tablas and Dipolog straits. The deep, isolated basins are ventilated by flow over confining topographic sills that causes upward displacement of older resident water, made more buoyant by vertical mixing, which is then exported to surrounding seas to close the overturning circulation circuit. © 2011 by The Oceanography Society. Source

Lilly J.M.,Earth and Space Research | Olhede S.C.,University College London
IEEE Transactions on Signal Processing | Year: 2010

The generalizations of instantaneous frequency and instantaneous bandwidth to a bivariate signal are derived. These are uniquely defined whether the signal is represented as a pair of real-valued signals or as one analytic and one anti-analytic signal. A nonstationary but oscillatory bivariate signal has a natural representation as an ellipse whose properties evolve in time, and this representation provides a simple geometric interpretation for the bivariate instantaneous moments. The bivariate bandwidth is shown to consist of three terms measuring the degree of instability of the time-varying ellipse: amplitude modulation with fixed eccentricity, eccentricity modulation, and orientation modulation or precession. An application to the analysis of data from a free-drifting oceanographic float is presented and discussed. Copyright © 2010 IEEE. Source

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