Consulta: subjectFacets:"Instability"
Registros recuperados: 24
Data/hora: 02/06/2024 02:50:48

Instability of a two-step Rankine vortex in a reduced gravity QG model
Provedor de dados: 5
Autores: Perrot, Xavier; Carton, Xavier.
We investigate the stability of a steplike Rankine vortex in a one-active-layer, reduced gravity, quasi-geostrophic model. After calculating the linear stability with a normal mode analysis, the singular modes are determined as a function of the vortex shape to investigate short-time stability. Finally we determine the position of the critical layer and show its influence when it lies inside the vortex.
Tipo: Text
Palavras-chave: Vortex dynamics; Instability; Normal/Singular modes; Critical layer.
Ano: 2014
URL: http://archimer.ifremer.fr/doc/00202/31360/31183.pdf

Instabilites sous-marine etudiees par submersibles
Provedor de dados: 5
Autores: Savoye, Bruno.
Sediment instability appears to be important as a part of global sedimentary budget. Among the various types of sedimentary instabilities, submarine slides are probably the most spectacular and the hardest to study and predict, although their consequences on human and industrial marine activities can be dramatic. IFREMER is conducting a research project on this topic. An area off Nice (France) has been particularly studied because of its recent activity. Mapping and instability area detection have been carried out. With the possibility of direct interactive observation and highly accurate submarine in -situ operation, the submersible is an extremely efficient tool for sediment studies, but diving purposes have to be precisely defined to provide useful...
Tipo: Text
Palavras-chave: Sediments; Instability; Sedimentology; Sedimentary structures; Ocean floor; Marine technology; Geology; Submersibles; Unmanned vehicles.
Ano: 1990
URL: http://archimer.ifremer.fr/doc/1990/acte-1150.pdf

Seasonal Mesoscale and Submesoscale Eddy Variability along the North Pacific Subtropical Countercurrent
Provedor de dados: 5
Autores: Qiu, Bo; Chen, Shuiming; Klein, Patrice; Sasaki, Hideharu; Sasai, Yoshikazu.
Located at the center of the western North Pacific Subtropical Gyre, the Subtropical Countercurrent (STCC) is not only abundant in mesoscale eddies, but also exhibits prominent submesoscale eddy features. Output from a 1/30 degrees high-resolution OGCM simulation and a gridded satellite altimetry product are analyzed to contrast the seasonal STCC variability in the mesoscale versus submesoscale ranges. Resolving the eddy scales of &gt;150 km, the altimetry product reveals that the STCC eddy kinetic energy and rms vorticity have a seasonal maximum in May and April, respectively, a weak positive vorticity skewness without seasonal dependence, and an inverse (forward) kinetic energy cascade for wavelengths larger (shorter) than 250 km. In contrast, the...
Tipo: Text
Palavras-chave: Circulation/ Dynamics; Eddies; Instability; Mesoscale processes; Observational techniques and algorithms; Altimetry; Models and modeling; Ocean models; Variability; Seasonal variability.
Ano: 2014
URL: http://archimer.ifremer.fr/doc/00245/35588/34142.pdf

A Persistent Deep Anticyclonic Vortex in the Rockall Trough Sustained by Anticyclonic Vortices Shed From the Slope Current and Wintertime Convection
Provedor de dados: 5
Autores: Smilenova, Angelina; Gula, Jonathan; Le Corre, Mathieu; Houpert, Loïc; Reecht, Yves.
Tipo: Text
Palavras-chave: Mesoscale eddy; Eddy merger; Instability; Potential vorticity transformations; Topographic effects; Water masses mixing; Rockall Trough.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00655/76734/77881.pdf

The Role of Curvature in Modifying Frontal Instabilities. Part II: Application of the Criterion to Curved Density Fronts at Low Richardson Numbers
Provedor de dados: 5
Autores: Buckingham, Christian; Gula, Jonathan; Carton, Xavier.
We continue our study of the role of curvature in modifying frontal stability. In Part I, we obtained an instability criterion valid for curved fronts and vortices in gradient wind balance (GWB): Φ′ = L′q′ &lt; 0, where L′ and q′ are the nondimensional absolute angular momentum and Ertel potential vorticity (PV), respectively. In Part II, we investigate this criterion in a parameter space representative of low-Richardson-number fronts and vortices in GWB. An interesting outcome is that, for Richardson numbers near 1, anticyclonic flows increase in q′, while cyclonic flows decrease in q′, tending to stabilize anticyclonic and destabilize cyclonic flow. Although stability is marginal or weak for anticyclonic flow (owing to multiplication by L′), the...
Tipo: Text
Palavras-chave: Eddies; Fronts; Instability; Ocean circulation; Potential vorticity; Frontogenesis/frontolysis; Vortices; Angular momentum.
Ano: 2021
URL: https://archimer.ifremer.fr/doc/00677/78919/81286.pdf

Contributions of Atmospheric Stochastic Forcing and Intrinsic Ocean Modes to North Atlantic Ocean Interdecadal Variability
Provedor de dados: 5
Autores: Arzel, Olivier; Huck, Thierry.
Atmospheric stochastic forcing associated with the North Atlantic Oscillation (NAO) and intrinsic ocean modes associated with the large-scale baroclinic instability of the North Atlantic Current (NAC) are recognized as two strong paradigms for the existence of the Atlantic Multidecadal Oscillation (AMO). The degree to which each of these factors contribute to the low-frequency variability of the North Atlantic is the central question in this paper. This issue is addressed here using an ocean general circulation model run under a wide range of background conditions extending from a super-critical regime where the oceanic variability spontaneously develops in the absence of any atmospheric noise forcing to a damped regime where the variability requires some...
Tipo: Text
Palavras-chave: Instability; Rossby waves; Climate variability; Interdecadal variability; Multidecadal variability; North Atlantic Oscillation.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00599/71138/69452.pdf

On the unsteady steepening of short gravity waves near the crests of longer waves in the absence of generation or dissipation
Provedor de dados: 5
Autores: Peureux, Charles; Ardhuin, Fabrice; Guimarães, Pedro Veras.
The wave action equation provides a general framework that has been applied to the conservative hydrodynamic interactions between short and long surface waves. So far, only a limited range of solutions have been investigated. Here we show that the wave action equation predicts that groups of short waves propagating over long monochromatic waves are unstable. We demonstrate theoretically and numerically a new ratchet‐type instability that progressively condenses short wave action around the long wave crests due to the correlation of phase speed and action fluctuations. This instability is of particular interest because it may lead to a higher probability of breaking for short waves propagating in directions within ±35 degrees of the dominant waves...
Tipo: Text
Palavras-chave: Instability; Modulation; Wind waves.
Ano: 2021
URL: https://archimer.ifremer.fr/doc/00661/77318/83369.pdf

The Role of Curvature in Modifying Frontal Instabilities. Part I: Review of Theory and Presentation of a Nondimensional Instability Criterion
Provedor de dados: 5
Autores: Buckingham, Christian; Gula, Jonathan; Carton, Xavier.
In this study, we examine the role of curvature in modifying frontal stability. We first evaluate the classical criterion that the Coriolis parameter f multiplied by the Ertel potential vorticity (PV) q is positive for stable flow and that instability is possible when this quantity is negative. The first portion of this statement can be deduced from Ertel’s PV theorem, assuming an initially positive fq. Moreover, the full statement is implicit in the governing equation for the mean geostrophic flow, as the discriminant, fq, changes sign. However, for curved fronts in cyclogeostrophic or gradient wind balance (GWB), an additional term enters the discriminant owing to conservation of absolute angular momentum L. The resulting expression, (1 + Cu)fq &lt; 0 or...
Tipo: Text
Palavras-chave: Instability; Ocean dynamics; Potential vorticity; Turbulence; Frontogenesis/frontolysis; Fronts; Vortices; Angular momentum.
Ano: 2021
URL: https://archimer.ifremer.fr/doc/00677/78920/81288.pdf

The vertical structure of open-ocean submesoscale variability during a full seasonal cycle
Provedor de dados: 5
Autores: Erickson, Zachary K; Thompson, Andrew F; Callies, Jörn; Yu, Xiaolong; Naveira Garabato, Alberto; Klein, Patrice.
Submesoscale dynamics are typically intensified at boundaries and assumed to weaken below the mixed layer in the open ocean. Here, we assess both the seasonality and the vertical distribution of submesoscale motions in an open ocean region of the northeast Atlantic. Second-order structure functions, or variance in properties separated by distance, are calculated from submesoscale-resolving ocean glider and mooring observations, as well as a 1/48° numerical ocean model. This data set combines a temporal coverage that extends through a full seasonal cycle, a horizontal resolution that captures spatial scales as small as 1 km, and vertical sampling that provides near-continuous coverage over the upper 1000 m. While kinetic and potential energies undergo a...
Tipo: Text
Palavras-chave: Instability; Mixing; Small scale processes; Buoy observations; Profilers; Oceanic.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00592/70388/68470.pdf

Optimal Perturbations of an Oceanic Vortex Lens
Provedor de dados: 5
Autores: Meunier, Thomas; Menesguen, Claire; Carton, Xavier; Le Gentil, Sylvie; Schopp, Richard.
The stability properties of a vortex lens are studied in the quasi geostrophic (QG) framework using the generalized stability theory. Optimal perturbations are obtained using a tangent linear QG model and its adjoint. Their fine-scale spatial structures are studied in details. Growth rates of optimal perturbations are shown to be extremely sensitive to the time interval of optimization: The most unstable perturbations are found for time intervals of about 3 days, while the growth rates continuously decrease towards the most unstable normal mode, which is reached after about 170 days. The horizontal structure of the optimal perturbations consists of an intense counter-shear spiralling. It is also extremely sensitive to time interval: for short time...
Tipo: Text
Palavras-chave: Vortex lenses; Intrathermocline eddies; Instability; Optimal perturbations.
Ano: 2018
URL: https://archimer.ifremer.fr/doc/00454/56605/58297.pdf

Mesures geotechniques par grand fond
Provedor de dados: 5
Autores: Cochonat, Pierre; Dansy, G; Leduc, Bernard; Meunier, Jacques; Harmegnies, Francois; Floury, L.
The mechanical behaviour of sediments is usually studied from laboratory core analyses which do not take into account the real state of in-situ stresses. Therefore, the aimed purpose is presently to determine the in-situ geotechnical properties which mainly depend on the relationship between fine-grained particles and intergranular fluids. At IFREMER, these achievements have been pursued in the framework of 2 scientific program: "Nodules and Sedimentary Processes and Instability on Slopes, for which surficial measurements were conducted on selected seafloor targets usually pre-defined from high resolution geophysical data." 2 kinds of instrumentation were developed in correlation to 2 different strategies of handling at sea. There is the instrumentation of...
Tipo: Text
Palavras-chave: Submarine cables; Deep sea mining; Offshore equipment; Geotechnology; Submersibles; Sedimentary structures; Sedimentology; Ferromanganese nodules; Instability; Marine technology; Sediments; Ocean floor; Deep water.
Ano: 1990
URL: http://archimer.ifremer.fr/doc/1990/acte-1157.pdf

Ageostrophic instability in rotating, stratified interior vertical shear flows
Provedor de dados: 5
Autores: Wang, Peng; Mcwilliams, James C.; Menesguen, Claire.
The linear instability of several rotating, stably stratified, interior vertical shear flows (U) over bar (z) is calculated in Boussinesq equations. Two types of baroclinic, ageostrophic instability, AI1 and AI2, are found in odd-symmetric (U) over bar (z) for intermediate Rossby number (R-0). AI1 has zero frequency; it appears in a continuous transformation of the unstable mode properties between classic baroclinic instability (BCI) and centrifugal instability (CI). It begins to occur at intermediate R-0 values and horizontal wavenumbers (k, l) that are far from l = 0 or k = 0, where the growth rate of BCI or CI is the strongest. AI1 grows by drawing kinetic energy from the mean flow, and the perturbation converts kinetic energy to potential energy. The...
Tipo: Text
Palavras-chave: Baroclinic flows; Instability; Waves in rotating fluids.
Ano: 2014
URL: http://archimer.ifremer.fr/doc/00211/32230/30753.pdf

Influence of Reynolds number and forcing type in a turbulent von Karman flow
Provedor de dados: 5
Autores: Saint-michel, Brice; Dubrulle, B.; Marie, Louis; Ravelet, F.; Daviaud, F.
We present a detailed study of a global bifurcation occuring in a turbulent von Karman swirling flow. In this system, the statistically steady states progressively display hysteretic behaviour when the Reynolds number is increased above the transition to turbulence. We examine in detail this hysteresis using asymmetric forcing conditions-rotating the impellers at different speeds. For very high Reynolds numbers, we study the sensitivity of the hysteresis cycle-using complementary particle image velocimetry and global mechanical measurements-to the forcing nature, imposing either the torque or the speed of the impellers. New mean states, displaying multiple quasi-steady states and negative differential responses, are experimentally observed in torque...
Tipo: Text
Palavras-chave: Turbulence; Instability; Negative response; Symmetry.
Ano: 2014
URL: http://archimer.ifremer.fr/doc/00204/31503/29904.pdf

Study of the stability of a large realistic cyclonic eddy
Provedor de dados: 5
Autores: De Marez, Charly; Meunier, Thomas; Morvan, Mathieu; L’hégaret, Pierre; Carton, Xavier.
We investigate the stability of a composite cyclone representative of Arabian Sea eddies using a high resolution primitive equation model. We observe that the eddy is unstable with respect to a mixed barotropic/baroclinic instability, leading to the growth of an azimuthal mode 2 perturbation. The latter deforms the eddy, which eventually evolves into a tripole after about 4 months of simulation. The presence of a critical level for the most unstable mode generates sharp fronts in the surface mixed layer where the Rossby number is large. These fronts then become unstable, and this generates submesoscale cyclones and filaments. Near these fronts, diapycnal mixing occurs, causing the potential vorticity to change sign locally, and symmetric instability to...
Tipo: Text
Palavras-chave: Mesoscale; Eddy; Instability; Submesoscale; Vortex.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00598/70967/69196.pdf

The Internal Generation of the Atlantic Ocean Interdecadal Variability
Provedor de dados: 5
Autores: Arzel, Olivier; Huck, Thierry; Colin De Verdiere, Alain.
Numerical simulations of a realistic ocean general circulation model forced by prescribed surface fluxes are used to study the origin and structure of intrinsic interdecadal variability of the ocean circulation. When eddy-induced turbulent diffusivities are low enough, spontaneous oscillations of the Atlantic meridional overturning circulation (AMOC) with periods O(20) yr and amplitude O(1) Sv (1 Sv ≡ 106 m3 s−1) emerge. The transition from the steady to the oscillatory regime is shown to be consistent with a supercritical Hopf bifurcation of the horizontal Peclet number. Adding atmospheric thermal damping is shown to have a very limited influence on the domain of existence of intrinsic variability. The spatial structure of the mode consists of a dipole of...
Tipo: Text
Palavras-chave: Instability; Meridional overturning circulation; Ocean circulation; Planetary waves; Climate variability; Multidecadal variability.
Ano: 2018
URL: https://archimer.ifremer.fr/doc/00464/57522/59708.pdf

A MEZŐGAZDASÁGI JÖVEDELMEK STABILITÁSA
Provedor de dados: 31
Autores: Lamfalusi,   Ibolya.
A mezőgazdasági jövedelmek stabilitásának megteremtése mindenkor az ag-rárpolitika fontos törekvése. A mezőgazdaságból élőknek a termelői jövedelem nagysága és alakulása meghatározza a gazdálkodói életszínvonal minőségét. Az EU országok jövedelemstabilitási mutatóival összevetve a magyar mezőgazda-ságét meg¬állapítható, hogy a hazai gazdálkodók helyzete igen kedvezőtlen. Az ágazatban mind a nominális értéken vett jövedelem stabilitása, mind pedig a jövedelem re¬ál¬értéke kedvezőtlenül alakult. A reáljövedelem 1998 és 2005 között egyetlen évben sem érte el az 1998. évi 80%-át, sőt 2003-ban 50%-nál kevesebb volt.  A mezőgazdasági termelés jövedelemstabilitását a mezőgazdasági kibocsátás kiegyensúlyozottsága határozza meg alapvetően. A kibocsátás már magában...
Tipo: Journal Article
Palavras-chave: Jövedelem; Stabilitás; Instabilitás; EU; Mezőgazdaság; Income; Stability; Instability; EU; Rural economy; Agricultural and Food Policy; Community/Rural/Urban Development; Production Economics.
Ano: 2007
URL: http://purl.umn.edu/57674

Pourquoi et comment l’instabilité est-elle une caractéristique structurelle des marchés agricoles?
Provedor de dados: 31
Autores: Boussard,   Jean-Marc.
Agricultural price volatility is "bad". But where does it come from? Remedies are completely different for "endogenous" or "exogenous" fluctuations. The recent crisis seems to indicate that exogenous remedies have been applied to endogenous fluctuations.
Tipo: Conference Paper or Presentation
Palavras-chave: Instability; Agricultural policy; Development; Fluctuations; Quotas; Cobweb; Insurance.; Agricultural and Food Policy; Industrial Organization; Political Economy; Production Economics; Public Economics; B5; D4; D6; D8; N5; O1.
Ano: 2007
URL: http://purl.umn.edu/44424

Diversity, Globalisation and Market Stability
Provedor de dados: 31
Autores: Lasselle,   Laurence; Svizzero,   Serge; Tisdell,   Clement A.
Tipo: Working or Discussion Paper
Palavras-chave: Diversity; Globalisation; Heterogeneity of Behaviour; Instability; Environmental Economics and Policy; Financial Economics.
Ano: 2001
URL: http://purl.umn.edu/90501

Diversity of Communities and Economic Development: An Overview
Provedor de dados: 31
Autores: Ranis,   Gustav.
This paper reviews the literature on the impact of ethnic diversity on economic development. Ethnically polarized societies are less likely to agree on the provision of public goods and more likely to engage in rent seeking activities  providing lower levels of social capital. Initial conditions are important determinants of adverse development outcomes.  The role of decentralization, democracy and markets as potential remedies are discussed.  The paper then presents a number of preliminary hypotheses on the relationship between diversity and instability in order to stimulate future research.
Tipo: Working or Discussion Paper
Palavras-chave: Africa; Diversity; Economic Growth; Instability; Institutional and Behavioral Economics; International Development; Political Economy; O11; O40; O43; O55.
Ano: 2011
URL: http://purl.umn.edu/115713

Instability, Supply Response and Insurance in Oilseeds Production in India
Provedor de dados: 31
Autores: Pandey,   L.M.; Kumar,   Sant; Mruthyunjaya.
Yield and price instability and covariate risks have been examined for major oilseeds, viz. groundnut, rapeseed/mustard, sunflower and soybean, in selected states of India using time series data. Risk behaviour and effects of price and price risk on production have been analyzed in a rational expectations framework. The study has also estimated social gains from yield and revenue insurance in oilseeds. While instabilities in yield, prices and gross return have shown mixed responses, covariate risks have increased. The results of econometric analysis have indicated that the expected prices and price risk are important determinants of oilseeds production. Price elasticities of oilseed production have been found to vary between 0.26 and 0.88 and price risk...
Tipo: Journal Article
Palavras-chave: Oilseeds; Instability; Covariate risks; Rational expectation; Production response; Risk effect; Insurance market; Social benefits; Agricultural and Food Policy.
Ano: 2005
URL: http://purl.umn.edu/58464

ON THE EXISTENCE OF STABLE EQUILIBRIA IN AGRICULTURE
Provedor de dados: 31
Autores: Goetz,   Stephan J.
Problems of instability and disequilibrium in U.S. agriculture are synthesized within a single conceptual framework.  Agricultural and non-agricultural sector offer curves are used to illustrate why it may not be feasible to achieve and maintain equilibrium and price stability in U.S. agriculture.  Empirical evidence on resource disequilibrium and instability in the ratio of prices paid and received by farmers is presented.
Tipo: Journal Article
Palavras-chave: Instability; Disequilibrium; Offer curves; U.S. agriculture; Policy; Demand and Price Analysis.
Ano: 1993
URL: http://purl.umn.edu/15207

Diversity of Communities and Economic Development: An Overview
Provedor de dados: 31
Autores: Ranis,   Gustav.
This paper reviews the literature on the impact of ethnic diversity on economic development. Ethnically polarized societies are less likely to agree on the provision of public goods and more likely to engage in rent seeking activities  providing lower levels of social capital. Initial conditions are important determinants of adverse development outcomes.  The role of decentralization, democracy and markets as potential remedies are discussed.  The paper then presents a number of preliminary hypotheses on the relationship between diversity and instability in order to stimulate future research.
Tipo: Working or Discussion Paper
Palavras-chave: Africa; Diversity; Economic Growth; Instability; International Development; O11; O40; O43; O55.
Ano: 2009
URL: http://purl.umn.edu/54531

A Measure to Compare Matchings in Marriage Markets
Provedor de dados: 31
Autores: Biermann,   Florian M.
In matching markets the number of blocking pairs is often used as a criterion to compare matchings. We argue that this criterion is lacking an economic interpretation: In many circumstances it will neither reflect the expected extent of partner changes, nor will it capture the satisfaction of the players with the matching. As an alternative, we set up two principles which single out a particularly “disruptive” subcollection of blocking pairs. We propose to take the cardinality of that subset as a measure to compare matchings. This cardinality has an economic interpretation: the subset is a justified objection against the given matching according to a bargaining set characterization of the set of stable matchings. We prove multiple properties relevant for a...
Tipo: Working or Discussion Paper
Palavras-chave: Stable Marriage Problem; Matching; Blocking Pair; Instability; Matching  Comparison; Decentralized Market; Bargaining Set; Environmental Economics and Policy; C0.
Ano: 2011
URL: http://purl.umn.edu/108250

Food security based on the spatial temporal feature of grain production
Provedor de dados: 31
Autores: He,   Yan-fen; Ma,   Chao-qun; Yang,   Hai-juan.
We use the mean value and variation coefficient model to analyze the spatial-temporal feature of grain production in 31 provinces from the year 1980 to 2006.  Time series of grain production is divided into 3 stages according to the average yield and the variation coefficient of grain production in provincial level, which are the lower yield and higher variation stage, the higher yield and lower variation stage and the higher yield and higher variation stage.  We classify the grain production of each province into four types according to the grain production level and the annual variation characteristics: the lower yield and higher variation type, the lower yield and lower variation type, the higher yield and lower variation type and the higher yield and...
Tipo: Thesis or Dissertation
Palavras-chave: Grain production; Spatial-temporal feature; Instability; Food security; China; Agricultural and Food Policy; Crop Production/Industries; Food Consumption/Nutrition/Food Safety; Food Security and Poverty; Resource /Energy Economics and Policy.
Ano: 2009
URL: http://purl.umn.edu/53435