Search Results

You are looking at 1 - 10 of 10 items for

  • Author or Editor: Andrew C. Vastano x
  • Refine by Access: All Content x
Clear All Modify Search
Joyce E. Scemitz and Andrew C. Vastano

Abstract

The mixing and entrainment processes present in a cyclonic ring are investigated by means of a parametric model which is fitted to serial temperature data for a North Atlantic ring. The physical model assumes an axially symmetric ring in which the temperature is presumed to be governed bywhere KA and KZ are the horizontal and vertical eddy diffusivity coefficients and JT) is the (r,z) Jacobian of the transverse streamfunction ψ and the temperature T. Data from two cruises during the 1967 observation of a ring by the Woods Hole Oceanographic Institution provided estimates of the derivatives of the temperature. Regression analysis was used to determine the coefficients for polynomial representations of ψ(r,z) for selected combinations of Kh and Kz. The study indicates upper bounds on the order of magnitude for the diffusivities (Kh,Kz)=(105,10) cm2 s−1 based upon near-minimum least-squares error estimates from the regression analysis. An important result is that little differentiation exists between a purely advective entrainment regime and those regimes including both entrainment and diffusion; i.e., the entrainment circulation appears to be the dominant mechanism in the temporal changes of the ring for a time scale of at least two months. The results provide streamline patterns for the transverse flow from the surface to 1000 m depth consistent with isotherm movement and changes in the ring water masses.

Full access
Joyce E. Schmitz and Andrew C. Vastano

Abstract

An entrainment and diffusion model has been applied to successive observations of a decaying Gulf Stream cyclonic ring to investigate changes in the streamline pattern as the ring moved from deep water onto Blake Plateau. Entrainment of water into the ring core is the dominant feature in each field of streamlines. The decay process measured in terms of the time required to replace the ring volume indicates an approximately linear decrease of renewal time as the ring moves into shallow water.

Full access
Andrew C. Vastano and Denise E. Hagan

Abstract

The North American Slope and Gulf Stream components that constitute the initial water masses within a cyclonic ring can combine with Sargasso Sea water to generate Western North Atlantic Water (WNAW) common to the main anticyclonic gyre in the Sargasso Sea. Evidence from the 1967 ring survey indicates that warm, saline water from above mixes with cooler, fresher water from below to produce WNAW in the region of the mid-thermocline (7–12°C). At mid-thermocline depths, WNAW can be traced along σt surfaces from the ring center to the Sargasso Sea. Vertical stability conditions support the mixing concept. Distributions of the zooplankton species Nematoscelis megalops found for the 1975–76 Ring D survey can be interpreted as indicating mixing and detrainment through the mid-thermocline region.

Full access
Andrew C. Vastano and George E. Owens

Abstract

The acoustic properties of a cyclonic Gulf Stream ring have been studied with field data and ray computations. Cyclonic rings represent relatively low sound velocity regions with large horizontal gradients of sound velocity embedded in the Sargasso Sea. Ray computations have shown the development of deep sound-channel-axis propagation from a near-surface source within a cyclonic ring.

Full access
Joyce E. Schmitz and Andrew C. Vastano

Abstract

The parametric model used by Schmitz and Vastano (1975) to investigate a Gulf Stream cyclonic ring has been applied to successive observations of a Gulf of Mexico anticyclonic ring. Coefficients for a polynomial representation of the transverse streamfunction ψ(r,z) were determined for pairs of eddy diffusivity coefficients. Using the minimum least-squares error residual as a criterion, the best flow pattern for the ring occurred for (Kh,Kz)=(106,0) cm2 s−1. The total transverse transport through the ring was found to be an order of magnitude larger than that found in the Gulf Stream cyclonic ring.

Full access
Andrew C. Vastano and Robert O. Reid

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.

Full access
Gerald T. Hebenstreit, Eddie,N. Bernard, and Andrew C. Vastano

Abstract

A finite-difference numerical model based on the classical linear long-wave equations has been developed to study the tsunami response of multiple-island systems. The first application of this model was to the Hawaiian Islands. Early results were satisfactory. However, one drawback to the model was the use, at the outer open boundaries of the basin, of a radiation condition which allowed only wave energy approaching the boundary at a normal angle to pass out of the basin without reflection. Recently, an improved boundary condition has been employed which takes into account the radial propagation of scattered waves near the boundary. The earlier model tests were repeated using this new condition. The major features of the results remained relatively unchanged. Certain secondary features of the response. which had made analysis of model results quite complicated, were either eliminated or greatly reduced.

Full access
Andrew C. Vastano, Joyce E. Schmitz, and Denise E. Hagan

Abstract

Eight cruises over a 10-month period in the North Atlantic have provided the Cyclonic Ring Experiment with observations of two rings. Life histories, structure and structural changes have been studied with emphasis on the effects of Stream interaction and spindown processes. Ring AL was generated in September 1976 with a central water mass composed of Slope and anticyclonic ring waters. Ring BOB separated from the Stream in March 1977 with a Shelf and Slope Water core. Both rings had a 7-month lifetime, interacted with the Gulf Stream and were regenerated. The Stream interaction altered the core structures, and in the case of BOB, cruise observations show significant changes in ring size and shape. BOB's spatial extent decreased with interaction and increased during spindown while eccentricity of the ring behaved in an opposite manner.

Full access
Andrew C. Vastano, Stephen E. Borders, and Ruth E. Wittenberg

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.

Full access
Denise E. Hagan, Donald B. Olson, Joyce E. Schmitz, and Andrew C. Vastano

Abstract

Field observations provide a data base that supports a comparison of ring structures in terms of the background Sargasso Sea environment. Five ring surveys, three from the 1967 sequence, a big baby ring and ring AL, were selected for this study. Anomalies of temperature, salinity, transport potential energy density, heat content and sound velocity have been examined using a reference which closely approximates Iselin's characteristic T-S relation for the western gyre.

The results for the 1967 sequence demonstrate an initial reduction in anomaly strengths followed by strong ring stability. Comparison of two different rings, possibly equal in age, show the effect of the initial water mass conditions on anomaly strengths. Comparison of a cyclonic ring and the big baby ring reveals similar anomaly strengths and sizes in the same geographical region for rings that are assumed to be two and eleven months in age, respectively. This suggests that big baby rings can initially represent more intense perturbations to the Sargasso Sea than cyclonic ring counterparts.

Full access