The main field campaign of the Inner Shelf Departmental Research Initiative was conducted in the section of coast near Point Sal, California in September-October 2017 to better understand the dynamic ...processes that occur along the inner shelf. Internal solitary waves (ISWs) are ubiquitous in the synthetic aperture radar (SAR) satellite images and will be the focus of this paper. The scale invariant feature transform (SIFT) is used as a tool to track ISWs between unique pairs of COSMO-SkyMed SAR images acquired about 24 minutes apart. ISW velocities are estimated using the SIFT matched keypoints between image pairs. Combining this method with instantaneous velocity estimates from the two individual images, based on an ISW amplitude retrieval algorithm previously developed, we can extend our abilities to study ISWs from space and our understanding of ISW dynamics in the California inner shelf region.
Using a combination of models and observations, the US Office of Naval Research Flow Encountering Abrupt Topography (FLEAT) initiative examines how island chains and submerged ridges affect open ...ocean current systems, from the hundreds of kilometer scale of large current features to the millimeter scale of turbulence. FLEAT focuses on the western Pacific, mainly on equatorial currents that encounter steep topography near the island nation of Palau. Wake eddies and lee waves as small as 1 km were observed to form as these currents flowed around or over the steep topography. The direction and vertical structure of the incident flow varied over tidal, inertial, seasonal, and interannual timescales, with implications for downstream flow. Models incorporated tides and had grids with resolutions of hundreds of meters to enable predictions of flow transformations as waters encountered and passed around Palau's islands. In addition to making scientific advances, FLEAT had a positive impact on the local Palauan community by bringing new technology to explore local waters, expanding the country's scientific infrastructure, maintaining collaborations with Palauan partners, and conducting outreach activities aimed at elementary and high school students, US embassy personnel, and Palauan government officials.
The present work is an observational analysis of the small-scale variations induced by Chesapeake Bay outflow on coastal surface circulation off Virginia. The variation in freshwater discharge into ...Chesapeake Bay is investigated as a triggering mechanism for local coastal jets. While it is known that an extra amount of freshwater received from the tributaries will lead to an increased total outflow, the effect on the outflow surface signature (the upper meter) has not been extensively explored. Our analysis is based on surface currents, wind data, and freshwater discharge records. The surface currents were derived from two high-frequency Doppler radars deployed on the Virginia coast during September and October 1996 and 1997. The wind data were obtained from a nearby weather Coastal-Marine Automated Network station, and the freshwater discharge data were from the U.S. Geological Survey stations located at the mouth of each tributary. The freshwater discharge into the bay observed during 1996 decreased from 4200 to 1000 m3/s in 10 days, while for the 1997 period it varied between 500 and 5500 m3/s in 1 week. The present analysis shows that sudden variations of freshwater flux will drive the plume further offshore before its normal southward turning, in the same way upwelling-favorable winds do as reported in all the available literature of the area. Strong freshwater variations on weekly scales are then shown to be an important factor in determining the extent of the surface plume displacement and the fate of the shelf currents or jets.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
From September 30 to October 14, 1993, and from May 18 to June 13, 1994, ocean surface currents along the inshore boundary of the Florida Current were measured using a land‐based ocean surface ...current radar (OSCR) deployed along the Florida Keys. A dual‐station OSCR mapped the current fields at 20‐min intervals with a horizontal resolution of 1.2 km over a 30×44 km domain using the high‐frequency (HF, 25.4 MHz) mode. An upward looking, narrowband acoustic Doppler current profiler (ADCP) was moored in 150 m of water seaward of the shelf break concurrently sampling the three‐dimensional current vector between 15 and 130 m at 30‐min intervals. Regression analyses between surface and subsurface currents at 15 m depth from the ADCP indicated biases of 3–12 cm s−1 and slopes of O(0.8–1). Root‐mean‐square differences were about 18 cm s−1 because of a 15‐m‐depth separation between the two measurements, and bulk current shears were O(10−3 s−1) in the Florida Current where maximum velocities exceeded 150 cm s−1 between 40 and 70 m. Surface tidal currents were 2–10 cm s−1 in the diurnal and semidiurnal bands and revealed fine‐scale variability in the tidal ellipses due to topographical variations. Differences in the tidal current amplitudes between the surface and 15 m ranged from 1 to 3 cm s−1 in these constituents and explained more of the current variance with depth. During the second experiment a submesoscale surface feature was detected along the shelf break and progressed eastward at a rate of about 30 cm s−1. This feature was embedded in the near‐inertial wave band where the local inertial period was ≈29 hours that may have been forced by an abrupt change in the wind direction. This transient feature was trapped and advected along the inshore edge of the Florida Current where the anticyclonic vorticity of the subinertial flow shifted the frequency of the nearinertial motions by a few percent of f. These energetic near‐inertial currents of 15–20 cm s−1 had horizontal and vertical wavelengths of 40 km and 50–100 m, respectively.
The Arabian Sea is characterized by an annually reversing circulation influenced by strong monsoon winds. The southwest monsoon that occurs during summer drives a northward boundary current along the ...coast of Somalia. During the winter monsoon, the southward flowing Somali Current merges with the northward flowing East African Coastal Current to form the eastward flowing South Equatorial Counter Current. This pattern shifts during the summer monsoon as the East African Coastal Current feeds the reversing Somali Current. Part of this northward flow retroflects from the coast at about 4°N to form the Southern Gyre while the remaining flow continues north past the Gulf of Aden or detaches at about 10°N to form the Great Whirl. Sentinel-1 synthetic aperture radar (SAR) data were acquired over the Somali Current in 2016 during the summer and winter monsoons. The Somali Current along the coast, the Southern Gyre and the Great Whirl are well developed at the time of the summer acquisition. The covariability of the atmospheric boundary layer and sea surface temperature was observed at high resolution over the Western Arabian Sea. Wind stress curl derived from the SAR data show the effects of the cold upwelled water and the Somali Current on the wind speed. Significant organized large eddies (OLEs) are also observed east of the Somali Current. During the winter monsoon, the Somali Current, Southern Gyre and Great Whirl are absent. The wind stress curl computed from the SAR data confirm this and do not show distinct circulation patterns or OLEs.
Using a combination of models and observations, the US Office of Naval Research Flow Encountering Abrupt Topography (FLEAT) initiative examines how island chains and submerged ridges affect open ...ocean current systems, from the hundreds of kilometer scale of large current features to the millimeter scale of turbulence. FLEAT focuses on the western Pacific, mainly on equatorial currents that encounter steep topography near the island nation of Palau. Wake eddies and lee waves as small as 1 km were observed to form as these currents flowed around or over the steep topography. The direction and vertical structure of the incident flow varied over tidal, inertial, seasonal, and interannual timescales, with implications for downstream flow. Models incorporated tides and had grids with resolutions of hundreds of meters to enable predictions of flow transformations as waters encountered and passed around Palau’s islands. In addition to making scientific advances, FLEAT had a positive impact on the local Palauan community by bringing new technology to explore local waters, expanding the country’s scientific infrastructure, maintaining collaborations with Palauan partners, and conducting outreach activities aimed at elementary and high school students, US embassy personnel, and Palauan government officials.
Directional distribution of the wind vectors observed by the ERS‐I active microwave instrument (AMI) scatterometer over the global oceans is investigated to examine effects of errors in the ...geophysical model function used to retrieve the wind vectors from backscattering measurements. Three scatterometer data products, together with wind data derived from two operational meteorological analysis models, are analyzed and compared with each other for a period of 2 months. Frequency distributions of the wind directions relative to the midbeam looking direction are calculated in bins of 10°. It is found that scatterometer‐derived wind vectors may exhibit systematic directional preference relative to the antenna beams in comparison with those of the model winds. This artificial directivity is considered to be caused by imperfections in the model function used to retrieve the wind vectors. Dependencies of the directional distributions on incidence angle and wind speed are also discussed for each data products. The distribution, of wind directions is very sensitive to the errors in the model function and can be used as an effective measure of self‐consistency to validate the model function and retrieved wind vectors.
The design and implementation on a Small Waterline Area Twin Hull (SWATH) vessel of a complete system for measuring the directional distribution of wind waves and the concomitant fluctuations of air ...pressure and wind speed immediately above them are described. Data taken with the system on board the Canadian Coast Guard Ship Frederick G. Creed during the 1999 Shoaling Waves Experiment (SHOWEX) are used to calculate the wave-supported fluxes of momentum and energy between the air and the sea.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
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