Assessment of the U.S. Outer Continental Shelf Environmental Studies Program I. Physical Oceanography (1990) / Chapter Skim
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3 Regional Oceanography and Evaluation of the Regional Studies Program and Washington Office Generic Programs
3 Regional Oceanography and Evaluation of the Regional Studies Program and Washington Office Generic Programs
Pages 53-94
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From page 53... ...
continental margins the Alaska, Pacific, Gulf of Mexico, and Atlantic regions and evaluates the adequacy and applicability of the ESP physical oceanographic studies carried out uncier the auspices of each regional office. In Alaska, much of the research was carried out by NOAA's Outer Continental Shelf Environmental Assessment Program under an interagency agreement with MMS.
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This maximum current precedes the maximum winter winds by several months. An important role of the alongshore winds, which cause coastal downwelling, is to trap the fresh water along the coast even after being transported hundreds of kilometers from the source.
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o me, ll al o it 8 o _ _ 55 -.1 ~ WN at\\ O o <: o Y °_ CO J o J ~5 .
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The absence of the strong cyclonic wind field in summer permits relaxation of onshore Ekman transport and cessation of coastal downwelling. This allows the onshore intrusion of denser water over the continental shelf bottom.
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Mean flow over the shelf is described qualitatively by the dynamic topography, with some low-frequency pulses driven by weather systems. From more than 20 record-years of direct current measurements on the southeast Bering Sea shelf, three mean and low-frequency current regimes have been identified.
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From page 60... ...
The hydrographic structure on the shelf, which seems little influenced by the slow mean flow, tends to be formed by the boundary inputs from insolation, cooling, melting ice, freezing, and river runoff, as well as lateral exchange with bordering oceanic water masses. Three distinct shelf hydrographic domains and an oceanic domain can be defined, delineated by water depths and separated by fronts that generally parallel the isobaths (see, e.g., Coachman, 1986~: 1.
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From page 61... ...
North of the strait, the Gulf of Anadyr water and Bering Sea water tend to combine and flow northward at 0.15 to 0.2 m/s, splitting around Herald Shoal so that some water goes straight into the Arctic Ocean through Hope Canyon and some turns eastward along the outer shelf of the Beaufort Sea. The Alaskan coastal water also flows along the Alaskan coast, gaining fresher, cooler water from Kotzebue Sound and flowing at speeds of 0.25 to 0.30 m/s along Point Hope, Cape Lisburne, and Icy Cape toward Barrow and the Beaufort Sea beyond.
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This flow seems to be trapped along the outer continental shelf and slope and centered at a depth of 40 to 50 m. Bering Sea water can be traced at least as far as Barter Island.
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Some of this variability has been related to E1 Nino events as well as to atmospheric variability in the North Pacific. Evaluation of MMS-funded Research in the Alaska Region Synopsis Gulf of Alaska From the mid-1970s into the 1980s, data from nearly 130 current-meter moorings were collected on the Gulf of Alaska continental shelf supported by hundreds of current, temperature,
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From page 64... ...
Additional information was sought to assist in prediction of oil movement at the marginal ice edge as well as spilled oil motion in sea ice. The primary modeling efforts were three-dimensional, time-dependent, layered circulation models to predict circulation as well as to provide oil-spill trajectories.
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Sea-surface temperature, wind direction, and air temperatures showed similar variations and seem to be related to North Pacific atmospheric variability as well as ENSO variability. The Bering Sea slope circulation also has not been addressed very much under OCSEAP.
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10 and 11) is characterized by a narrow continental shelf.
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REGIONAL OCEANOGRAPHY AND EVALUATION OF STUDIES PROMS i j (~ / ~ClffSCE~' Cry se 2000 m ~ hi.
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study of the coastal wind field along the west coast of North America for two summers, 1981 and 1982, and the intervening winter using measured winds and geostrophic winds calculated from the FNOC atmospheric pressure analyses. Halliwell and Allen found that: Summer wind fluctuations are driven primarily by the interaction between two relatively stationary pressure systems, the North Pacific subtropical high and the southwest U.S.
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From 450N to 48°N, north of the maximum seasonal wind stress signal, the seasonal cycles of currents (midshelf at 450N and shelf break at 48°N) reach their greatest magnitudes.
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throughout the summer over most of the Pacific coast. Since upwelling introduces nutrients to the euphoric zone, the process is of interest as well to biological oceanographers and fisheries scientists.
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the front tends to remain stationary (i.e., not retreat toward the coast) , and the nearsurface warming near shore is dominated bar alongshore advection (Send et al., 1987~.
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REGIOI~4L OCEANOGRAPHYAND EVALUATION OF STUDIES PROGRAMS FIGURE 12 Jets, squirts, and eddies off the California coast. Source: Mark Abbott and Ted Strub.
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The California Shelf Circulation Model is based on a well-known general circulation model (Blumberg and Mellor, 1983~. The model is the same three-dimensional, time-dependent model that has been used in the Gulf of Mexico, the mid-Atlantic and south Atlantic bights, and the Santa Barbara Channel.
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was used; however, boundary conditions were specified by current meters (~16 moorings) instead of CTM.
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Predicted current amplitudes are smaller by at least a factor of two than those observed in the Santa Barbara Channel, probably because of the way the contractor filtered the boundary conditions. Given the above reported inadequacies, the Physical Oceanography Panel believes that MMS puts too much faith in the results of modeling studies.
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From page 79... ...
In general, the gulf waters consist of three distinct water masses: subtropical underwater, antarctic intermediate water, and North Atlantic deep water. The subtropical underwater enters the gulf from the Caribbean at depths of 200 to 500 m and is found throughout the eastern portion of the gulf.
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The extent of penetration of the Loop Current into the Gulf of Mexico has been studied extensively. At times the Loop Current has been observed to extend northward into the gulf as far as the Louisiana and west Florida continental shelves (Huh et al., 1981~.
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observational program-the Gulf of Mexico Physical Oceanography Field Study designed to study physical oceanographic processes in the Gulf of Mexico. The focus during the first 2 years and the fourth year of the observational program was the eastern Gulf of Mexico.
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The two off-shelf moorings were at water depths of 1,700 and 3,400 m and consisted of five and six current meters, respectively. The configuration of this mooring array was such that it provided information primarily on across-shelf motions that occur at large scales.
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It is intended to provide insight on shelf circulation processes and the effects of the larger-scale gulf circulation processes. Evaluation of Observational Studies The MMS-funded, 5-year physical oceanography observational program was adequate to study the large-scale circulation of the Gulf of Mexico.
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Thus, although MMS has been supporting a physical oceanographic observational program that was adequate to describe some aspects of the general circulation of the Gulf of Mexico, the focus of this program was on circulation features that are of minor importance to the needs of programs designed to perform oil-spill risk-analysis assessments. In summary, the MMS physical oceanography program was designed to look at space and time scales that are too large to be of use for oil-spill risk-assessment analysis.
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Furthermore, the accuracy of the density fields that go into the geostrophic calculation will determine the reliability of the derived circulation. Also, the shelf circulation models might not account for such climatological variations as timing in the maximum river runoff and changes in wind patterns, which can vary from year to year.
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From page 86... ...
There are strong southwestward currents in the slope water and the shelf with, again, strong variability associated with winds, tides, and offshore meandering of the Gulf Stream, mesoscale eddies, and Gulf Stream rings. For MMS planning purposes the Atlantic region is divided into the north Atlantic, mid-Atlantic, and south Atlantic subregions (Figs.
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~ATLANTIC ,r~-~ CANAD^ 1 1 (, ~ ~ In.._ ~ UNITED {'~ em-. STATES N\\ ~ \ ATLANTIC (a 'a ~REGIO N FIGURE 15 North Atlantic planning area of the Atlantic region.
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. ~ FIGURE 17 South Atlantic planning area of the Atlantic region.
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Anticyclonic events are less frequent, but again the storms follow storm tracks lying in the Mid-Atlantic Bight north of Cape Hatteras. In an average year, 5 (Florida)
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. Georges Bank lies off Cape Cod, separating the Gulf of Maine from the slope water, with most of the water exchange occurring through the Great South Channel and Northeast Channel.
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Hydrographic data provided tracers of water masses, including river runoff, and indicated the occurrence of strong wind mixing, upwelling, and injection of water onto the shelf from Gulf Stream frontal eddies. Surface satellite imagery was also used to observe and describe eddy
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. Dynalysis first produced a characteristic tracing model CTM, which neglects advection in the momentum and turbulent energy/length scale equations.
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Another study, proposed in the Regional Studies Plan for FY 1989, which requires study of nearsurface physical oceanographic processes, is assessing the use of satellite-tracked surface buoys in simulating the movement of spilled oil in the marine environment. According to the material available, the physical oceanographic studies completed under the WO of the ESP address areas of real concern and have been completed with quality products in a timely manner.
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