Simulation of Lagrangian Drifters in the Labrador Sea

N0001496WR3005

Numerical Simulation of Drifter Response to Labrador Sea Convection

Approved for public release; distribution is unlimited.This report describes numerical simulation of two types of idealized drifters: pure Lagrangian drifters and the isobaric drifters. A large-eddy (LES) model was used to predict the fully-turbulent non-hydrostatic evolution of the oceanic flow fields that are typical of the Labrador Sea. The LES simulation indicates that either free or forced convection may dominate, depending upon the magnitudes of the wind stress and the net surface heat fluxed out of the ocean surface. Free convection predominates in the winter regimes of the periphery of the polar seas, especially in the very deeply-convecting regions of open water adjacent to marginal ice zones. Forced convection is more dominant in the stable ice-covered regions of the polar seas experiencing strong wind-stirring and kinetic energy exchange with the ice. Forced convection may be an important precursor to free convection, and the organized cells of forced convection may help dilate the ice field to enhance heat and buoyancy exchange between the OPBL and the atmosphere

Nonhydrostatic Modeling of West Florida Shelf Flow

LONG-TERM GOALS: The long range scientific goal of the Oceanic Planetary Boundary Layer (OPBL) Laboratory is to understand the role of the OPBL in the coupled exchange of energy, momentum and mass between the upper ocean and the atmosphere (and the cryosphere).Document Number: N0001401WR2039

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http://archive.org/details/determinationofc00gallN

Surface Heating and Patchiness in the Coastal Ocean off Central California During a Wind Relaxation Event

The difference between the temperature of the ocean at 4-cm and 2-m depth was continuously monitored during a cruise to the coastal transition zone off Point Arena, California (38°58′N, 123°45′W), during June 1987. The two temperatures were coincident most of the time but diverged during one nearshore leg of the cruise where large temperature differences (ΔT) of up to 4.7°C were observed between the 4-cm and 2-m sensors, in areas which were separated by regions where the two temperatures were coincident as usual. The spatial scale of this “patchy” thermal structure was about 5–10 km. The Naval Postgraduate School mixed layer model (Garwood, 1977) was used to simulate the near surface stratification when forced by the observed wind stress, surface heating, and optical clarity of the water. The model produced a thin strongly stratified surface layer at stations where exceptionally high turbidity was observed but did not produce such features otherwise. This simple model could not explain the horizontal patchiness in the thermal structure, which was likely due to patchiness in the near-surface chlorophyll distributions or to submesoscale variability of the surface wind stress.This is the publisher's version of record. The original submission is copyrighted by American Geophysical Union and can be found here: http://www.agu.org

Metal artifact suppression at the hip: diagnostic performance at 3.0 T versus 1.5 Tesla

PurposeThis work aimed to compare the diagnostic performance of a metal artifact suppression sequence (MAVRIC-SL) for imaging of hip arthroplasties (HA) at 1.5 and 3 Tesla (T) field strength.MethodsEighteen patients (10 females; aged 27-74) with HA were examined at 3.0 and 1.5 T within 3 weeks. The sequence protocol included 3D-MAVRIC-SL PD (coronal), 3D-MAVRIC-SL STIR (axial), FSE T1, FSE PD and STIR sequences. Anatomical structures and pathological findings were assessed independently by two radiologists. Artifact extent and technical quality (image quality, fat saturation and geometric distortion) were also evaluated. Findings at 1.5 and 3.0 T were compared using a Wilcoxon signed rank test.ResultsWhile image quality was better at 1.5 T, visualization of anatomic structures and clinical abnormalities was not significantly different using the two field strengths (p > 0.05). Fat suppression and amount of artifacts were significantly better at 1.5 T (p  < 0.01). Inter- and intra-reader agreement for different anatomic details, image quality and visualization of abnormalities ranged from k = 0.62 to k = 1.00.ConclusionMAVRIC-SL at 1.5 T had a comparable diagnostic performance when compared MAVRIC-SL at 3.0 T; however, the higher field strength was associated with larger artifacts, limited image quality and worse fat saturation

An oceanic mixed layer model capable of simulating cyclic states

Reprinted from Journal of Physical Oceanography, Vol.7, No.3, May 1977.The article of record as published may be found at http://journals.ametsoc.org/doi/abs/10.1175/1520-0485%281977%29007%3C0455%3AAOMLMC%3E2.0.CO%3B2A new one-dimensional bulk model of the mixed layer of the upper ocean is presented . An entrainment hypothesis dependent upon the relative distribution of turbulent energy between horizontal and vertical components is offered as a plausible mechanism for governing both entrainment and layer retreat. This model has two properties not previously demonstrated: (i) The fraction of wind-generated turbulent kinetic energy partitioned to potential energy increase by means of mixed layer deepening is dependent upon layer stability, H*=h/L, as measured by the ratio of mixed layer depth h to Obukhov length L. This results in a modulation of the mean entrainment rate by the diurnal heating and cooling cycle. (ii) Viscous dissipation is enhanced for increased values of Ro−1= hf/u*, where f is the Coriolis parameter and u*. the friction velocity for the water. This enables a cyclical steady state to occur over an annual period by limiting maximum layer depth. A nondimensional framework used to present the general solution also suggests a basis for model comparison and data analysis.NOAA’s Environmental Research Laboratories and by NOAA’s GATE OfficeOffice of Naval Research under ONR Contract N000147TWRTOO42-NROS3-275-5.N0001477WR70024Approved for public release; distribution is unlimited

Numerical Ocean Prediction Models -- Goal for the 1980s

The article of record as published may be found at http://dx.doi.org/10.1175/1520-0477(1980)0612.0.CO;2This paper is based on a seminar presented at the Geophysical Fluid Dynamics Laboratory, Princeton, N.J., on 3 November 1979.Based on the experience of numerical weather prediction during the 1950s and 1960s as a model, a case is presented for the development of an ocean prediction capability during the 1980s. Examples selected from recent research at the Naval Postgraduate School are used to illustrate some aspects of the theoretical background, representation of physical processes, observational support systems, and the justification for a first-generation ocean prediction system.The research described here was sponsored by the Office of Naval Research, Ocean Science Branch, under contract number NR083-275, N00014-79- WR-90020 and by the Naval Oceanographic Research and Development Activity (Code 320) under contract number N68462-79-WR-90029

First-generation numerical ocean prediction models : goal for the 1980's

This report is based on a talk presented at the Geophysical Fluid Dynamics Laboratory, Princeton, NJ during November 1979.Using the experience of numerical weather prediction during the 1950's and 1960's as a model, a case is presented for development during the 1980's of an ocean prediction capability. Examples selected from recent research at the Naval Postgraduate School are used to illustrate some aspects of the theoretical background, representation of physical processes, observational-support systems and the justification for a first-generation ocean prediction systemPrepared for: Naval Ocean Research and Development Activity Office of Naval Research, Ocean Science and Technologyhttp://archive.org/details/firstgenerationn00elsbN