Andrew C. Vastano

Sea surface motion over an anticyclonic eddy on the Oyashio Front

Abstract NOAA-6 AVHRR (11-μm band) satellite images for 20 and 21 May 1981 have been used with an interactive computer algorithm to calculate surface flow components from displacement of surface pattern features and elapsed time. The results give estimates of speed and direction for motion along the Oyashio Front and over an anticyclonic eddy between the First and Second Oyashio Intrusions. Speeds of 54 cm/s were detected along the Oyashio thermal ridge. On the periphery of the eddy, speeds in the order of 25 cm/s were present while, nearer the center, motion at 14 cm/s was indicated. A composite picture of flow vectors overlayed on the image for 20 May infers streamline flow characteristics for the surface motion and shows surface isolation of the eddy from the Tohoku area to the south.

Sea Surface Topography Estimation with Infrared Satellite Imagery

Abstract Sea surface flow derived from displacements of surface patterns in sequential NOAA-6 AVHRR (11 micron band) satellite images yield coherent nonuniform distributions of velocity vectors, An analytic representation of flow over the region of the distribution is obtained by performing a least-squares regression analysis for coefficients of a streamfunction expansion that is expressed in terms of trigonometric bash functions. Sea surface topography is estimated with the streamfunction by employing a geostrophic approximation. An application is made to a portion of the Oyashio Frontal Zone in the northwestern Pacific that includes the First and Second Oyashio Intrusions and an anticyclonic eddy. A horizontal map of a local rotational perturbation property is calculated for this region as a further example of the use of the streamfunction analysis.

Perturbations to the Gulf Stream by Atlantis II Seamount

Abstract In a search for a natural occurrence of Taylor-column effects, salinity-temperature-depth (STD) observations were made in the Gulf Stream as it passed over Atlantis II Seamount. Although the stream path changed markedly during the course of the observations, one 5-day set of stations seems to provide a quasi-synoptic picture of the flow. Maps, based on this subset, of potential temperature at eight levels between 200 and 3500 m show deflections and distortions of isotherms near the seamount, and warm-core and cold-core eddies in its lee. The eddies are probably a consequence of the recent incursion of the Stream onto the seamount, while the other features seem qualitatively intelligible in terms of existing Taylor-column theory. From the data available, however, it is not possible to tell with certainty if there was a region of closed streamlines just above the seamount.

Satellite observations of the Texas Current

Abstract The Texas Current is a transient, nearshore element of shelf circulation in the northwestern Gulf of Mexico that can arise and be modified in response to riverine, estuarine, oceanic and atmospheric forcing. Nearly a 600 km reach along the inner Texas shelf is affected by the Currents physical processes. AVHRR imagery and satellite-tracked drifters provide observations of Texas Current realizations. Analyses relate each forcing mechanism with recurrent coastal flow patterns. The Currents response and the evolution of associated spatial and temporal variability imply its potential as a primary agent for advective redistribution and turbulent mixing on the inner shelf.

Sea Surface Flow Estimation with Infrared and Visible Imagery

Abstract Sequential Nimbus-7 CZCS infrared and visible images obtained on orbits 3157 and 3171 during 9–10 June 1979 have been used to derive sea surface flow from advective sea surface pattern displacements and elapsed time. Individual analyses with infrared (11 microns) and visible blue/yellow ratio (0.443 and 0.550 microns) pairs of images yielded coherent velocity distributions over an oceanic region near Georges Bank. A composite of eighty flow vectors illustrates a seaward diversion of cold surface water off Northeast Channel, Gulf of Maine by a northeastward intrusion of Gulf Stream water along the continental slope. These results demonstrate that instances arise when infrared and visible surface pattern changes can be used jointly to compose flow regimes. A sea surface topography map derived from the composite vector distribution has a range of 20 cm and an expected repeatability of 0.39 cm.

Satellite observations of surface circulation in the northwestern Gulf of Mexico during March and April 1989

Abstract Six Argos-reported drifters drogued to a depth of 2.7 m produced eight trajectories over the Texas-Louisiana Shelf and the adjacent oceanic waters of the northwestern Gulf of Mexico from 7 March to 29 April 1989. Launched by United States Coast Guard aircraft and Texas A & M Universitys R.V. Gyre, the trajectories span the shelf from the vicinity of Barataria Bay, Louisiana to the southern reaches of Padre Island near Port Isabel, Texas. Two tracks demonstrate cross-slope and cross-shelf motion northward from the central western Gulf toward Louisiana. These two drifters join three others to define a coastal current flow westward from near the Mississippi delta to Galveston and then southwestward along the Texas coast. Two other trajectories indicate a relatively low-energy mid-shelf regime over the northwestern portion of the outer continental shelf. Five drifter groundings locate a convergence in the nearshore and littoral flows on the Texas coast between Matagorda Peninsula and southern Padre Island. Strong wind-driven events in the northwestern Gulf demonstrate instances of coherent shelf response over 7° of longitude and 3° of latitude. Infrared satellite imagery indicates the regional context and structure of the spatial scales of Gulf of Mexico surface circulation.

Comparison of satellite and drifter surface flow estimates in the northwestern Gulf of Mexico

Abstract A comparison of flow observations has been made with drifting buoys and infrared satellite images for northwestern Gulf of Mexico surface waters during the interval from 10 March to 23 April, 1989. Each drifter was drogued to a depth of 2.7 m and reported four-nine positions along its trajectory every 24 h through the NOAA satellite Argos data collection system. Corresponding flow observations were computed from sequential infrared imagery obtained by Advanced Very-High Resolution Radiometer (AVHRR) on the same satellites. Vector estimates of advective motion were extracted from surface temperature pattern displacements between images paired at 24 and 12 h intervals without knowledge of the drifter trajectories. Twenty-two blind test cases at 24 h intervals formed the data base for examining the relative accuracy between trajectories simulated with satellite flow estimates and those obtained with the drifters. The comparison of actual and computed velocities for 24 h displacements resulted in a counterclockwise regression angle of simulated to actual velocities of −1.7°, a standard error in estimates of simulated speeds from actual speeds of 5.5 cm s −1 for actual speeds in the range from 0 to 60 cm s −1 , and a regression complex coefficient of determination ( ρ 2 ) of 0.936. The study indicates a convergence of results for the satellite image and Argos drifter methods of surface flow estimation and a combined capacity to investigate inertial range circulation variability.