Lagrangian statistics in unforced barotropic flows

We consider the dispersion of particles in potential vorticity (PV)-conserving flows. Because particle drift is preferentially along the mean PV contours, Lagrangian dispersion is strongly anisotropic. If the mean PV field moreover is spatially variable, as when there is topography, the anisotropy is more clearly visible in the dispersion of displacements along and across the mean PV field itself. We examine several numerical examples of unforced barotropic flows; in all cases, this projected dispersion is more anisotropic than that in cartesian (x, y) coordinates. What differs is the rate at which spreading occurs, both along and across contours. The method is applicable to real data, as is illustrated with float data from the deep North Atlantic. The results suggest a preferential spreading along contours of (barotropic) f/H

Representativeness of meridional hydrographic sections in the western South Atlantic

Many studies of the oceanic circulation are based on data collected during quasi-synoptic hydrographic surveys. After spatial averaging, to filter out the effects of mesoscale variability, it is often explicitly or implicitly assumed that the synoptic hydrographic gradients are representative of a quasi-steady mean state. Climatological tracer fields and float data at the depth of the North Atlantic Deep Water in the western South Atlantic (Brazil Basin) support the notion of a quasi-steady mean circulation characterized by alternating bands of primarily zonal flow with meridional scales of several hundreds of km. Visually, the mean circulation appears to dominate three samples of the large-scale meridional-density-gradient field taken between 1983 and 1994. A quantitative comparison reveals, however, that the baroclinic temporal variability of the zonal velocities is of the same magnitude as the mean and is associated with similar spatial scales. The synoptic geostrophic flow field is, therefore, only marginally representative of the mean state. Thus, the data do not support one of the central assumptions of reference-velocity methods, such as linear box-inverse models and the β-spiral, because baroclinic temporal variability renders the equation systems underlying these methods inconsistent. A modal decomposition of the temporally varying baroclinic zonal velocity field in the Brazil Basin indicates that the first two dynamical modes dominate, accounting for ≈90% of the rms velocities. The residual flow field that remains after removing the first two baroclinic modes from the three synoptic samples is dominated by the mean circulation. However, its magnitude is not sufficient to account for the float and tracer observations. Therefore, it is necessary to determine the projection of the mean zonal velocities onto the barotropic and the first two baroclinic modes in order to diagnose fully the mean zonal circulation in the western South Atlantic. There is evidence that the representativeness of synoptic hydrographic sections in other regions may be similarly marginal

An off-shell I.R. regularization strategy in the analysis of collinear divergences

We present a method for the analysis of singularities of Feynman amplitudes based on the Speer sector decomposition of the Schwinger parametric integrals combined with the Mellin-Barnes transform. The sector decomposition method is described in some details. We suggest the idea of applying the method to the analysis of collinear singularities in inclusive QCD cross sections in the mass-less limit regularizing the forward amplitudes by an off-shell choice of the initial particle momenta. It is shown how the suggested strategy works in the well known case of the one loop corrections to Deep Inelastic Scattering.Comment: 25 pages, 3 figure

Unfinished Business: a Review of the Implementation of the Provisions of United Nations General Assembly Resolutions 61/105 and 64/72, Related to the Management of Bottom Fisheries in Areas Beyond National Jurisdiction

In 2006 the General Assembly adopted resolution 61/105, based on a compromise proposal offered by deep-sea fishing nations, which committed States and regional fisheries management organisations [RFMOs] to take specific measures to protect vulnerable marine ecosystems [VMEs] from the adverse impacts of bottom fisheries in the high seas and to ensure the longterm sustainability of deep-sea fish stocks. These measures included conducting impact assessments to determine whether significant adverse impacts[SAIs] to VMEs would occur, managing fisheries to prevent SAIs on VMEs, and closing areas of the high seas to bottom fishing where VMEs are known or likely to occur, unless regulations are in place to prevent SAIs and to manage sustainably deep-sea fish stocks. Based on a review in 2009 of the actions taken by States and RFMOS, the UNGA adoptedresolution 64/72 that reaffirmed resolution 61/105 and strengthened the call for action through committing States, inter alia, to ensure that vessels do not engage in bottom fishing until impact assessments have been carried out and to not authorise bottom fishing activities until the measures in resolutions 64/72 and 61/105 have been adopted andimplemented

Continuity of the four-point function of massive ϕ44\phi_4^4-theory above threshold

In this paper we prove that the four-point function of massive \vp_4^4-theory is continuous as a function of its independent external momenta when posing the renormalization condition for the (physical) mass on-shell. The proof is based on integral representations derived inductively from the perturbative flow equations of the renormalization group. It closes a longstanding loophole in rigorous renormalization theory in so far as it shows the feasibility of a physical definition of the renormalized coupling.Comment: 23 pages; to appear in Rev. Math. Physics few corrections, two explanatory paragraphs adde

Austenite Formation and Manganese Partitioning during Double Soaking of an Ultralow Carbon Medium-Manganese Steel

Double soaking (DS) is a thermal processing route intended to produce austenite–martensite microstructures in steels containing austenite-stabilizing additions and consists of intercritical annealing (primary soaking), followed by heating and brief isothermal holding at an increased temperature (secondary soaking), and quenching. Herein, experimental dilatometry during DS of a medium-manganese (Mn) steel with nominally 7 wt% Mn and an ultralow residual carbon concentration, in combination with phase-field simulations of austenite formation during secondary soaking, is presented. The feasibility of maintaining heterogeneous Mn distributions during DS is demonstrated and insight is provided on the effects of the secondary soaking temperature and prior Mn distribution on the ferrite-to-austenite phase transformation during the secondary soaking portion of the DS treatment

A practical indicator for surface ocean heat and freshwater buoyancy fluxes and its application to the NCEP reanalysis data

The buoyancy flux at the air/sea interface plays a key role in water mass transformation and mixing as it modifies surface water density and in turn drives overturning and enhances stratification. It is the interplay of these two independent heat and freshwater buoyancy flux components that is of central importance when analysing mechanisms of the ocean/atmosphere interaction. Here, a diagnostic quantity (ΘB) is presented that allows to capture the relative contribution of both components on the buoyancy flux in one single quantity. Using NCEP reanalysis of heat and freshwater fluxes (1948–2009) demonstrates that ΘB is a convenient tool to analyse both the temporal and spatial variability of their corresponding buoyancy fluxes. For the global ocean the areal extent of buoyancy gain and loss regions changed by 10%, with the largest extent of buoyancy gain during the 1970–1990 period. In the subpolar North Atlantic, and likewise in the South Pacific, decadal variability in freshwater flux is pronounced and, for the latter region, takes control over the total buoyancy flux since the 1980s. Some of the areal extent time series show a significant correlation with large-scale climate indices

Four-dimensional integration by parts with differential renormalization as a method of evaluation of Feynman diagrams

It is shown how strictly four-dimensional integration by parts combined with differential renormalization and its infrared analogue can be applied for calculation of Feynman diagrams.Comment: 6 pages, late