Exploring the North Atlantic Ocean on floppy disks

Data from four floppy disks found in the zip fileA selection of hydrographic station data in the Atlantic between 8°S and 70°N is packed on four 5 1/4" floppy disks. Sample utility programs for reading and plotting the data are also on the disks. We present this computer atlas in preliminary form for use by students and professionals, in the belief that easy access to this valuable historical data will be educational and stimulating.Funding was provided by the Office of Naval Research under contract Number N00014-84-C-0134, and the National Science Foundation through grant Number OCE86-13810

Geothermal Heating and its Influence on the Meridional Overturning Circulation

The effect of geothermal heating on the meridional overturning circulation is examined using an idealized, coarse-resolution ocean general circulation model. This heating is parameterized as a spatially uniform heat flux of 50 mW m-2 through the (flat) ocean floor, in contrast with previous studies that have considered an isolated hotspot or a series of plumes along the mid-Atlantic ridge. The equilibrated response is largely advective: a deep perturbation of the meridional overturning cell on the order of several Sv is produced, connecting with an upper-level circulation at high latitudes, allowing the additional heat to be released to the atmosphere. Risingmotion in the perturbation deep cell is concentrated near the equator. The upward penetration of this cell is limited by the thermocline, analogous to the role of the stratosphere in limiting the upward penetration of convective plumes in the atmosphere. The magnitude of the advective response is inversely proportional to the deep stratification; with a weaker background meridional overturning circulation and a less stratified abyss, the overturning maximum of the perturbation deep cell is increased. This advective response also cools the low-latitude thermocline. The qualitative behavior is similar in both a single hemisphere and double hemisphere configuration.The anomalous circulation driven by geothermal fluxes is more substantial than previously thought. We are able to understand the structure and strength of the response in the idealized geometry and further extend these ideas to explain the results of Adcroft et al. [2001], where the impact of geothermal heating was examined using a global configuration

BMI and EAT-26, predictors for low BMD?

The primary purpose of this study was to characterize bone mineral density (BMD) in healthy adult females in the Southern United States. A secondary purpose was to determine to what extent age, race, body mass index (BMI), and disordered eating contribute to BMD status. Age ranged from 25 to 50 years (39.8 ± 8.5). Race was classified into Caucasian or non-Caucasian. BMI was 28.97 ± 7.85 (kg/m2). The Eating Attitudes Test (EAT-26) was used to identify disordered eating characteristics. The Alara MetriScan was used to assess BMD values. Regression results showed that the linear combination of three independent variables—age, race, and BMI—predicted 34.5% of the variance in BMD, R2 = .345, R2 adj = .334, F(3, 170) = 29.87, p < .001. The strongest predictor of low BMD was Caucasian race

Capture of particles of dust by convective flow

Interaction of particles of dust with vortex convective flows is under theoretical consideration. It is assumed that the volume fraction of solid phase is small, variations of density due to nonuniform distribution of particles and those caused by temperature nonisothermality of medium are comparable. Equations for the description of thermal buoyancy convection of a dusty medium are developed in the framework of the generalized Boussinesq approximation taking into account finite velocity of particle sedimentation. The capture of a cloud of dust particles by a vortex convective flow is considered, general criterion for the formation of such a cloud is obtained. The peculiarities of a steady state in the form of a dust cloud and backward influence of the solid phase on the carrier flow are studied in detail for a vertical layer heated from the sidewalls. It is shown that in the case, when this backward influence is essential, a hysteresis behavior is possible. The stability analysis of the steady state is performed. It turns out that there is a narrow range of governing parameters, in which such a steady state is stable.Comment: 14 pages, 10 figures, published in Physics of Fluid

Turbulence in a free surface

We report an experimental and numerical study of turbulent fluid motion in a free surface. The flow is realized experimentally on the surface of a tank filled with water stirred by a vertically oscillating grid positioned well below the surface. Particles floating on the surface are used to visualize the flow. The effect of surface waves appears to be negligible. The flow is unconventional in that it is confined to two dimensions but does not have squared vorticity as a conservation law, that it is not divergence free and that it inherits scaling features of the mean square velocity differences S_2(R) and the vorticity fluctuations Omega(R) from the bulk 3-d turbulence.Comment: 4 pages, 4 Postscript figure

Statistical mechanics of Fofonoff flows in an oceanic basin

We study the minimization of potential enstrophy at fixed circulation and energy in an oceanic basin with arbitrary topography. For illustration, we consider a rectangular basin and a linear topography h=by which represents either a real bottom topography or the beta-effect appropriate to oceanic situations. Our minimum enstrophy principle is motivated by different arguments of statistical mechanics reviewed in the article. It leads to steady states of the quasigeostrophic (QG) equations characterized by a linear relationship between potential vorticity q and stream function psi. For low values of the energy, we recover Fofonoff flows [J. Mar. Res. 13, 254 (1954)] that display a strong westward jet. For large values of the energy, we obtain geometry induced phase transitions between monopoles and dipoles similar to those found by Chavanis and Sommeria [J. Fluid Mech. 314, 267 (1996)] in the absence of topography. In the presence of topography, we recover and confirm the results obtained by Venaille and Bouchet [Phys. Rev. Lett. 102, 104501 (2009)] using a different formalism. In addition, we introduce relaxation equations towards minimum potential enstrophy states and perform numerical simulations to illustrate the phase transitions in a rectangular oceanic basin with linear topography (or beta-effect).Comment: 26 pages, 28 figure

Sensitivity of the Atlantic meridional overturning circulation to South Atlantic freshwater anomalies

The sensitivity of the Atlantic Meridional Overturning Circulation (AMOC) to changes in basin integrated net evaporation is highly dependent on the zonal salinity contrast at the southern border of the Atlantic. Biases in the freshwater budget strongly affect the stability of the AMOC in numerical models. The impact of these biases is investigated, by adding local anomaly patterns in the South Atlantic to the freshwater fluxes at the surface. These anomalies impact the freshwater and salt transport by the different components of the ocean circulation, in particular the basin-scale salt-advection feedback, completely changing the response of the AMOC to arbitrary perturbations. It is found that an appropriate dipole anomaly pattern at the southern border of the Atlantic Ocean can collapse the AMOC entirely even without a further hosing. The results suggest a new view on the stability of the AMOC, controlled by processes in the South Atlantic. <br/

Turbulence and passive scalar transport in a free-slip surface

We consider the two-dimensional (2D) flow in a flat free-slip surface that bounds a three-dimensional (3D) volume in which the flow is turbulent. The equations of motion for the two-dimensional flow in the surface are neither compressible nor incompressible but strongly influenced by the 3D flow underneath the surface. The velocity correlation functions in the 2D surface and in the 3D volume scale with the same exponents. In the viscous subrange the amplitudes are the same, but in the inertial subrange the 2D one is reduced to 2/3 of the 3D amplitude. The surface flow is more strongly intermittent than the 3D volume flow. Geometric scaling theory is used to derive a relation between the scaling of the velocity field and the density fluctuations of a passive scalar advected on the surface.Comment: 11 pages, 10 Postscript figure

Beyond the Fokker-Planck equation: Pathwise control of noisy bistable systems

We introduce a new method, allowing to describe slowly time-dependent Langevin equations through the behaviour of individual paths. This approach yields considerably more information than the computation of the probability density. The main idea is to show that for sufficiently small noise intensity and slow time dependence, the vast majority of paths remain in small space-time sets, typically in the neighbourhood of potential wells. The size of these sets often has a power-law dependence on the small parameters, with universal exponents. The overall probability of exceptional paths is exponentially small, with an exponent also showing power-law behaviour. The results cover time spans up to the maximal Kramers time of the system. We apply our method to three phenomena characteristic for bistable systems: stochastic resonance, dynamical hysteresis and bifurcation delay, where it yields precise bounds on transition probabilities, and the distribution of hysteresis areas and first-exit times. We also discuss the effect of coloured noise.Comment: 37 pages, 11 figure

Incidence and impact of postoperative pancreatic fistula after minimally invasive and open distal pancreatectomy

BACKGROUND: Previous studies reported a higher rate of postoperative pancreatic fistula after minimally invasive distal pancreatectomy compared to open distal pancreatectomy. It is unknown whether the clinical impact of postoperative pancreatic fistula after minimally invasive distal pancreatectomy is comparable with that after open distal pancreatectomy. We aimed to compare not only the incidence of postoperative pancreatic fistula, but more importantly, also its clinical impact. METHODS: This is a post hoc analysis of a multicenter randomized trial investigating a possible beneficial impact of a fibrin patch on the rate of clinically relevant postoperative pancreatic fistula (International Study Group for Pancreatic Surgery grade B/C) after distal pancreatectomy. Primary outcomes of the current analysis are the incidence and clinical impact of postoperative pancreatic fistula after both minimally invasive distal pancreatectomy and open distal pancreatectomy. RESULTS: From October 2010 to August 2017, 252 patients undergoing distal pancreatectomy were randomized, and data of 247 patients were available for analysis: 87 minimally invasive distal pancreatectomy and 160 open distal pancreatectomies. The postoperative pancreatic fistula rate after minimally invasive distal pancreatectomy was significantly higher than that after open distal pancreatectomy (28.7% vs 16.9%, P = .029). More patients were discharged with an abdominal surgical drain after minimally invasive distal pancreatectomy compared to open distal pancreatectomy (30/87, 34.5% vs 26/160, 16.5%, P = .001). In patients with postoperative pancreatic fistula, additional percutaneous catheter drainage procedures were performed less often (52% vs 84.6%, P = .012), with fewer drainage procedures (median [range], 2 [1-4] vs 2, [1-7], P = .014) after minimally invasive distal pancreatectomy. CONCLUSION: In this post hoc analysis, the postoperative pancreatic fistula rate after minimally invasive distal pancreatectomy was higher than that after open distal pancreatectomy, whereas the clinical impact was less