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1
López-Carbonell, M., A. Moret et M. Nadal. « Changes in Cell Ultrastructure and Zeatin Riboside Concentrations in Hedera helix, Pelargonium zonale, Prunus avium, and Rubus ulmifolius Leaves Infected by Fungi ». Plant Disease 82, no 8 (août 1998) : 914–18. http://dx.doi.org/10.1094/pdis.1998.82.8.914.
Texte intégralRésumé :
Ultrastructural alterations in epidermal and mesophyll cells and variations in endogenous zeatin riboside (ZR) concentrations were studied in leaves of Hedera helix, Pelargonium zonale, Pru-nus avium, and Rubus ulmifolius infected by Colletotrichum trichellum, Puccinia pelargonii-zonalis, Cercospora circumscissa, and Phragmidium violaceum, respectively. Infected tissues showed a marked increase in vesicles, myelin-like structures, and electron-dense bodies associated with plasma membranes. The main changes to the chloroplast included thylakoid swelling and disruption of the chloroplast envelope. The ZR content of the green islands was always higher than that of the yellow, senescent parts of the same leaves; the highest levels of ZR were observed in the green areas of infected Prunus avium (462.2 pmol g-1 fresh weight [FW]) and Rubus ulmifolius (441.6 pmol g-1 FW), followed by Pelargonium zonale (263.8 pmol g-1 FW) and Hedera helix (219.8 pmol g-1 FW); the yellow zones of the same leaves had lower ZR contents (78.3, 73.9, 73.6, and 18.1 pmol g-1 FW, respectively). The green islands had almost the same ZR content as the controls (green healthy leaves). These results suggest a relationship between ultrastructural alterations and ZR content of these plant species (blackberry, cherry, English ivy, geranium) in reacting to this type of biotic stress and could confirm the role of cytokinins as senescence-delaying hormones.
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Gerber, Edwin P., et Geoffrey K. Vallis. « A Stochastic Model for the Spatial Structure of Annular Patterns of Variability and the North Atlantic Oscillation ». Journal of Climate 18, no 12 (15 juin 2005) : 2102–18. http://dx.doi.org/10.1175/jcli3337.1.
Texte intégralRésumé :
Abstract Meridional dipoles of zonal wind and geopotential height are found extensively in empirical orthogonal function (EOF) analysis and single-point correlation maps of observations and models. Notable examples are the North Atlantic Oscillation and the so-called annular modes (or the Arctic Oscillation). Minimal stochastic models are developed to explain the origin of such structure. In particular, highly idealized, analytic, purely stochastic models of the barotropic, zonally averaged zonal wind and of the zonally averaged surface pressure are constructed, and it is found that the meridional dipole pattern is a natural consequence of the conservation of zonal momentum and mass by fluid motions. Extension of the one-dimensional zonal wind model to two-dimensional flow illustrates the manner in which a local meridional dipole structure may become zonally elongated in EOF analysis, producing a zonally uniform EOF even when the dynamics is not particularly zonally coherent on hemispheric length scales. The analytic system then provides a context for understanding the existence of zonally uniform patterns in models where there are no zonally coherent motions. It is also shown how zonally asymmetric dynamics can give rise to structures resembling the North Atlantic Oscillation. Both the one- and two-dimensional results are manifestations of the same principle: given a stochastic system with a simple red spectrum in which correlations between points in space (or time) decay as the separation between them increases, EOF analysis will typically produce the gravest mode allowed by the system’s constraints. Thus, grave dipole patterns can be robustly expected to arise in the statistical analysis of a model or observations, regardless of the presence or otherwise of a dynamical mode.
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Cash, Benjamin A., Paul J. Kushner et Geoffrey K. Vallis. « Zonal Asymmetries, Teleconnections, and Annular Patterns in a GCM ». Journal of the Atmospheric Sciences 62, no 1 (1 janvier 2005) : 207–19. http://dx.doi.org/10.1175/jas-3361.1.
Texte intégralRésumé :
Abstract The influence of zonally asymmetric boundary conditions on the leading modes of variability in a suite of atmospheric general circulation models is investigated. The set of experiments consists of nine model configurations, with varying degrees and types of zonal asymmetry in their boundary conditions. The structure of the leading EOF varies with the zonal asymmetry of the base state for each model configuration. In particular, a close relationship is found between the structure of the EOF and the model storm tracks. An approximately linear relationship is found to hold between the magnitude of the zonal asymmetry of the leading EOF and of the storm tracks in the models. It is shown that this linear relationship extends to the observations. One-point correlation maps centered on the regions where the EOFs reach their maximum amplitude show similar structures for all configurations. These structures consist of a north–south dipole, resembling the observed structure of the North Atlantic Oscillation (NAO). They are significantly more zonally localized than the leading EOF, but do resemble one-point correlation maps and sector EOFs calculated for a simulation with zonally symmetric boundary conditions. Thus, the leading EOF for each simulation appears to represent the longitudinal distribution of zonally localized NAO-like patterns. This longitudinal distribution appears to be tied to the distribution of high-frequency eddies, as represented by the storm tracks. A detailed momentum budget for each case confirms that high-frequency eddies play a crucial role in producing the NAO-like patterns. Other dynamical processes also play an important role, but vary with the details of the simulation.
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Helfrich, Karl R., et Joseph Pedlosky. « Time-dependent isolated anomalies in zonal flows ». Journal of Fluid Mechanics 251 (juin 1993) : 377–409. http://dx.doi.org/10.1017/s0022112093003453.
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A theory is developed for time-dependent coherent structures in a marginally stable atmospheric zonal flow. The coherent structures have the form of solitary waves travelling in the zonal direction. Analytical solutions are found for stationary solitary waves but these are shown to be always unstable. The instability manifests itself either as a fission of the structure subsequently emitting two oppositely directed travelling solitary waves or as an implosion in which the structure becomes increasingly more narrow and intense. Which of the two occurs depends sensitively on initial conditions. These solitary waves are stable in head-on collisions only if their joint zonally integrated amplitude is less than a critical value; otherwise, the implosion instability occurs. General initial conditions can give rise to solitary waves which either split, implode, or break down to form a train of nonlinear wave packets. A scenario for the birth and decay of isolated disturbances is given, utilizing the slow parametric transit of the marginal stability curve of the background zonal flow.
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Wedi, Nils P., et Piotr K. Smolarkiewicz. « A Nonlinear Perspective on the Dynamics of the MJO : Idealized Large-Eddy Simulations ». Journal of the Atmospheric Sciences 67, no 4 (1 avril 2010) : 1202–17. http://dx.doi.org/10.1175/2009jas3160.1.
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Abstract The 30–60-day intraseasonal atmospheric oscillation in the equatorial atmosphere, the Madden–Julian oscillation (MJO), is most visible in its signature of outgoing longwave radiation and associated convective centers. Diabatic processes related to tropical convection and two-way atmosphere–ocean interaction are hence generally believed to be crucial in explaining the origin of the MJO phenomenon. However, reliable deterministic forecasting of the MJO in global circulation models and understanding its mechanism remains unsatisfactory. Here a different approach is taken, where the hypothesis is tested that eastward-propagating MJO-like structures originate fundamentally as a result of nonlinear (dry) Rossby wave dynamics. A laboratory-scale numerical model is constructed, where the generation of solitary structures is excited and maintained via zonally propagating meanders of the meridional boundaries of a zonally periodic β plane. The large-eddy simulations capture details of the formation of solitary structures and of their impact on the convective organization. The horizontal structure and the propagation of anomalous streamfunction patterns, a diagnostic typically used in tracing the equatorial MJO, are similar to archetype solutions of the Korteweg–deVries equation, which extends the linear shallow water theory—commonly used to explain equatorial wave motions—to a weakly nonlinear regime for small Rossby numbers. Furthermore, the characteristics of the three-dimensional laboratory-scale numerical results compare well with observed features of the equatorial MJO and thus the study provides indirect evidence of the basic principles underlying the wave-driven eastward propagation of the MJO.
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SEVGİLİ, HASAN, DENİZ ŞİRİN, KLAUS-GERHARD HELLER et MİCHÈLE LEMONNIER-DARCEMONT. « Review of the Poecilimon (Poecilimon) zonatus species group and description of new species from Turkey with data on bioacoustics and morphology (Orthoptera : Phaneropterinae) ». Zootaxa 4417, no 1 (3 mai 2018) : 1. http://dx.doi.org/10.11646/zootaxa.4417.1.1.
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The aim of this study is to conduct a detailed taxonomic revision of the Poecilimon (Poecilimon) zonatus species-group (Orthoptera: Phaneropterinae) using both morphology and bioacoustics. Two new species (Poecilimon (Poecilimon) salmani, P. (P) azizsancar) and one new subspecies (P. (P) zonatus datca) are described. Based on the data, we conclude that the species complex can be separated into two subgroups (P. tauricola and P. zonatus). Within the P. zonatus subgroup, song structures indicate P. variicercis as basal branch since producing two syllable types is possibly a derived character. From both, from bioacoustics and morphology, it is concluded that the relationships between species of the group are as follows: P. tauricola subgroup (P. tauricola + P. azizsancar) + P. zonatus subgroup (P. variicercis + (P. varicornis + (P. zonatus zonatus+P. zonatus datca)) + (P. salmani+P. vodnensis)))). Except for two species (P. vodnensis and P. varicornis), the other species of the group are all distributed in Anatolia. P. vodnensis is known only from Macedonia, whereas, P. varicornis has been recorded only from Syria and Lebanon. We assume that the group originated from an Anatolian ancestral stock and expanded its distribution to the Balkans through Taurus Way and Dardanelles. Other ancestral populations may have also spread in the north-south directions through the appropriate steppe corridors in the Anatolian Diagonal Mountains and in its vicinity.
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Hall, Nicholas M. J., George N. Kiladis et Chris D. Thorncroft. « Three-Dimensional Structure and Dynamics of African Easterly Waves. Part II : Dynamical Modes ». Journal of the Atmospheric Sciences 63, no 9 (1 septembre 2006) : 2231–45. http://dx.doi.org/10.1175/jas3742.1.
Texte intégralRésumé :
Abstract A primitive equation model is used to study the linear normal modes of the African easterly jet (AEJ). Reanalysis data from the summertime mean (June–September; JJAS) flow is used to provide zonally uniform and wavy basic states. The structure and growth rates of modes that grow over West Africa on these basic states are analyzed. For zonally uniform basic states, the modes resemble African easterly waves (AEWs) as in many previous studies, but they are quite baroclinic and surface intensified. For wavy basic states the modes have a longitudinal structure determined by the AEJ. They have a surface-intensified baroclinic structure upstream and a deep barotropic structure downstream, as confirmed by energy conversion diagnostics. These modes look remarkably similar to the composite easterly wave structures found by the authors in a companion paper. The similarity extends to the phase relationship of vertical velocity with streamfunction, which resembles OLR composites, suggesting a dynamical influence on convection. Without damping, the mode for the wavy basic state has a growth rate of 0.253 day−1. With a reasonable amount of low-level damping this mode is neutralized. It has a period of 5.5 days and a wavelength of about 3500 km. Further results with monthly mean basic states show slight variations, as the wave packet essentially follows displacements of the jet core. Experiments focused on specific active and passive years for easterly waves (1988 and 1990) do not yield significantly different results for the modes. These results, and in particular, the stability of the system, lead to the conclusion that barotropic–baroclinic instability alone cannot explain the initiation and intermittence of AEWs, and a finite-amplitude initial perturbation is required.
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Adames, Ángel F., et John M. Wallace. « On the Tropical Atmospheric Signature of El Niño ». Journal of the Atmospheric Sciences 74, no 6 (24 mai 2017) : 1923–39. http://dx.doi.org/10.1175/jas-d-16-0309.1.
Texte intégralRésumé :
Abstract The linear atmospheric signature of ENSO, obtained by regressing fields of geopotential height Z, wind, vertical velocity, and rainfall upon the Niño-3.4 sea surface temperature (SST) index, is partitioned into zonally symmetric and eddy components. The zonally symmetric component is thermally forced by the narrowing and intensification of the zonally averaged equatorial rain belt during El Niño and mechanically forced by the weakening of the upper-tropospheric equatorial stationary waves and their associated flux of wave activity. The eddy component of the ENSO signature is decomposed into barotropic (BT) and baroclinic (BC) contributions, the latter into first and second modal structures BC1 and BC2, separable functions of space (x, y), and pressure p, using eigenvector analysis. BC1 exhibits a nearly equatorially symmetric planetary wave structure comprising three dumbbell-shaped features suggestive of equatorial Rossby waves, with out-of-phase wind and geopotential height perturbations in the upper and lower troposphere. BC1 and BT exhibit coincident centers of action. In regions of the tropics where the flow in the climatological-mean stationary waves is cyclonic, BT reinforces BC1, and vice versa, in accordance with vorticity balance considerations. BC1 and BT dominate the eddy ENSO signature in the free atmosphere. Most of the residual is captured by BC2, which exhibits a shallow, convergent boundary layer signature forced by the weakening of the equatorial cold tongue in SST. The anomalous boundary layer convergence drives a deep convection signature whose upper-tropospheric outflow is an integral part of the BC1 contribution to the ENSO signature.
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Pilette, Daniel. « Les acteurs de zonage et leurs pratiques ». Cahiers de géographie du Québec 22, no 57 (12 avril 2005) : 393–420. http://dx.doi.org/10.7202/021411ar.
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Divers intervenants assument la responsabilité de l'évolution du zonage municipal, lequel se concrétise par des amendements apportés au règlement de zonage de base. L'article rend compte d'une enquête, menée dans les villes de Longueuil, Brossard et Boucherville, et visant à éclairer la situation et les intérêts des divers acteurs impliqués dans le processus du zonage en soulignant les mécanismes d'interaction. Il tente aussi de préciser les effets des amendements du point de vue de l'utilisation effective du sol urbain. Enfin, il rend compte des diverses perceptions du zonage en tant qu'instrument de contrôle et des opinions des intervenants face aux structures décisionnelles et consultatives en matière d'aménagement urbain.
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Magnusdottir, Gudrun, et Chia-Chi Wang. « Intertropical Convergence Zones during the Active Season in Daily Data ». Journal of the Atmospheric Sciences 65, no 7 (1 juillet 2008) : 2425–36. http://dx.doi.org/10.1175/2007jas2518.1.
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Abstract Synoptic-scale variability of vorticity structures in the lower troposphere of the tropics is analyzed in 23 yr of daily averaged high-resolution reanalysis data. The vorticity structures can be divided into zonally elongated vorticity strips, classified as intertropical convergence zones (ITCZs), and more localized maxima, termed westward-propagating disturbances. A composite of such variability is presented for the east to central Pacific and for the east Atlantic/Africa region, both in summer. The composite in the east Pacific is zonally elongated and ITCZ-like, propagating westward over a number of days before dissipating. The spatial structure of the vorticity strip shows the characteristic cyclonic tilt into the latitudinal direction with time that is also seen in modeling experiments. The composite over the Atlantic/Africa region shows two active regions that are correlated on synoptic time scales. The disturbances in the southern region are better developed and longer lasting, even though the time and space scales are smaller than over the east Pacific. Overall, variability over the Atlantic is consistent with variability due to African easterly waves. The double ITCZ in spring in the east Pacific is different from the few earlier studies available. It is stronger south of the equator and located at 10°S, which is farther poleward than earlier studies have indicated. The northern branch that is weak in comparison is located at 5°N. The two branches of the double ITCZ tend to appear in tandem on the 2-week time scale.
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Golebiowska, Aleksandra A., et Syam P. Nukavarapu. « Bio-inspired zonal-structured matrices for bone-cartilage interface engineering ». Biofabrication 14, no 2 (25 février 2022) : 025016. http://dx.doi.org/10.1088/1758-5090/ac5413.
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Abstract Design and development of scaffold structures for osteochondral (OC) interface regeneration is a significant engineering challenge. Recent efforts are aimed at recapitulating the unique compositional and hierarchical structure of an OC interface. Conventional scaffold fabrication techniques often have limited design control and reproducibility, and the development of OC scaffolds with zonal hierarchy and structural integrity between zones is especially challenging. In this study, a series of multi-zonal and gradient structures were designed and fabricated using three-dimensional bioprinting. We developed OC scaffolds with bi-phasic and tri-phasic configurations to support the zonal structure of OC tissue, and gradient scaffold configurations to enable smooth transitions between the zones to more closely mimic a bone-cartilage interface. A biodegradable polymer, polylactic acid, was used for the fabrication of zonal/gradient scaffolds to provide mechanical strength and support OC function. The formation of the multi-zonal and gradient scaffolds was confirmed through scanning electron microscopy imaging and micro-computed tomography scanning. Precisely controlled hierarchy with tunable porosity along the scaffold length established the formation of the bio-inspired scaffolds with different zones/gradient structure. In addition, we also developed a novel bioprinting method to selectively introduce cells into desired scaffold zones of the zonal/gradient scaffolds via concurrent printing of a cell-laden hydrogel within the porous template. Live/dead staining of the cell-laden hydrogel introduced in the cartilage zone showed uniform cell distribution with high cell viability. Overall, our study developed bio-inspired scaffold structures with structural hierarchy and mechanical integrity for bone-cartilage interface engineering.
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Du, Yin, Zhiqing Xie, Ning Wang, Qian Miao et Lingling Zhang. « Influence of Zonal Variation of the Subtropical Westerly Jet on Rainfall Patterns and Frequency of Heavy Precipitation Events over East Asia ». Journal of Climate 35, no 20 (15 octobre 2022) : 3011–26. http://dx.doi.org/10.1175/jcli-d-21-0872.1.
Texte intégralRésumé :
Abstract Understanding the effects of zonal variation of the East Asian subtropical westerly jet (EAWJ) on spatial features of heavy precipitation events requires characterization of the shape, orientation, position, and scale of both the EAWJ and rain belts. Applying a rotating calipers algorithm, jet-axis tracking, wavelet analysis, and K-means clustering algorithm, spatial structures of both the EAWJ and rain belts were quantified for each heavy rainfall event lasting 3 days (3-day-HRE) in 1983–2020. The results reveal that approximately 90% of the EAWJs related to 3-day-HREs had a statistically significant wave structure of ∼6000–12 000 km over East Asia and the North Pacific. These EAWJs had tilted, wavy, and flat patterns and strongly affected the position, orientation, and spatial scales of the 3-day-HRE rain belts by modifying the vapor transport trajectory and vertical rising motions. All types of EAWJ had an orientation similar to that of the rain belts and an average distance to the rain belts of ∼500–1500 km at 105°–125°E and ∼500 km at 125°E–180°. Correspondingly, the rain belts of 3-day-HREs had the largest frequency over eastern China and southern Japan. Zonally asymmetric Rossby waves arising from the land–sea thermal contrast, atmospheric diabatic heating, and topography dominantly contributed to the formation of a meandering or flat EAWJ. A zonally oscillating trough–ridge system, featuring an equivalent barotropic structure with large geopotential height anomalies reaching the lower troposphere, weakens or blocks vapor transport and is ultimately responsible for the strongly varying spatial scales and orientations of rain belts. Significance Statement A solid theoretical basis that variations in the EAWJ intimately covary with the location and orientation of rain belts means that understanding the relationships between the EAWJ’s zonal variations and the spatial features of monsoonal rain belts is conducive to better predicting the weather and climate over East Asia. We quantitatively explored the effects of EAWJ zonal variations on the position, orientation, and scale of rain belts and found that a tilted, wavy, or relatively flat pattern of the EAWJ strongly affected the rain belt spatial features by modifying the vapor transport trajectory. A zonally oscillating trough–ridge system, featuring an equivalent barotropic structure throughout the troposphere, is responsible for the varying spatial scale of rain belts.
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O’Kane, Terence J., Didier P. Monselesan, James S. Risbey, Illia Horenko et Christian L. E. Franzke. « Research Article. On memory, dimension, and atmospheric teleconnections ». Mathematics of Climate and Weather Forecasting 3, no 1 (1 janvier 2017) : 1–27. http://dx.doi.org/10.1515/mcwf-2017-0001.
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AbstractUsing reanalysed atmospheric data and applying a data-driven multiscale approximation to non-stationary dynamical processes, we undertake a systematic examination of the role of memory and dimensionality in defining the quasi-stationary states of the troposphere over the recent decades. We focus on the role of teleconnections characterised by either zonally-oriented wave trains or meridional dipolar structures. We consider the impact of various strategies for dimension reduction based on principal component analysis, diagonalization and truncation.We include the impact of memory by consideration of Bernoulli, Markovian and non-Markovian processes. We a priori explicitly separate barotropic and baroclinic processes and then implement a comprehensive sensitivity analysis to the number and type of retained modes. Our results show the importance of explicitly mitigating the deleterious impacts of signal degradation through ill-conditioning and under sampling in preference to simple strategies based on thresholds in terms of explained variance. In both hemispheres, the results obtained for the dominant tropospheric modes depend critically on the extent to which the higher order modes are retained, the number of free model parameters to be fitted, and whether memory effects are taken into account. Our study identifies the primary role of the circumglobal teleconnection pattern in both hemispheres for Bernoulli and Markov processes, and the transient nature and zonal structure of the Southern Hemisphere patterns in relation to their Northern Hemisphere counterparts. For both hemispheres, overfitted models yield structures consistent with the major teleconnection modes (NAO, PNA and SAM), which give way to zonally oriented wavetrains when either memory effects are ignored or where the dimension is reduced via diagonalising. Where baroclinic processes are emphasised, circumpolar wavetrains are manifest.
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Song, Jie, Wen Zhou, Xin Wang et Chongyin Li. « Zonal Asymmetry of the Annular Mode and Its Downstream Subtropical Jet : An Idealized Model Study ». Journal of the Atmospheric Sciences 68, no 9 (1 septembre 2011) : 1946–73. http://dx.doi.org/10.1175/2011jas3656.1.
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Abstract This study investigates linkages between the zonal asymmetry of the annular mode (AM) zonal pattern and the subtropical jet (STJ) over its downstream regions of the storm track by using an idealized model. Observational analyses show that the AM zonal patterns are more zonally asymmetric during days when the STJ downstream of the storm track is unusually strong, and vice versa. In the idealized model, the STJ downstream of the storm track is varied by introducing an additional zonally localized tropical heating. The model’s AM variability exhibits a nearly zonally uniform structure when there is no or only weak tropical heating. However, the signatures of the AM are locally strengthened in the heating sector; thus, the AM zonal pattern is zonally asymmetric when the tropical heating is large enough to create a strong STJ. The model results also show that the percentage of the variance explained by the AM, the persistence of the AM index, and the intensity of eddy feedback are also increased when the tropical heating becomes stronger. It is argued herein that the zonal asymmetry of the AM pattern is caused by the zonal asymmetry of the anomalous synoptic eddy forcing projecting on the AM, which is primarily due to the zonal asymmetry of the variations of the storm track between the nonheating and heating sectors.
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Fogt, Ryan L., Julie M. Jones et James Renwick. « Seasonal Zonal Asymmetries in the Southern Annular Mode and Their Impact on Regional Temperature Anomalies ». Journal of Climate 25, no 18 (6 avril 2012) : 6253–70. http://dx.doi.org/10.1175/jcli-d-11-00474.1.
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Abstract The Southern Hemisphere annular mode (SAM) is the dominant mode of climate variability in the extratropical Southern Hemisphere. Representing variations in pressure and the corresponding changes to the circumpolar zonal flow, it is typically thought of as an “annular” or ringlike structure. However, on seasonal time scales the zonal symmetry observed in the SAM in monthly or annual mean data is much less marked. This study further examines the seasonal changes in the SAM structure and explores temperature signals across the Southern Hemisphere that are strongly tied to the asymmetric SAM structure. The SAM asymmetries are most marked in the Pacific sector and in austral winter and spring, related to changes in the jet entrance and exit regions poleward of 30°S. Depending on the season, the asymmetric SAM structure explains over 25% of the variance in the overall SAM structure and has strong connections with ENSO or zonal wavenumber 3. In austral summer and autumn the SAM has been becoming more zonally symmetric, especially after 1980, perhaps tied to changes in anthropogenic forcing. Across the Pacific sector, including the Antarctic Peninsula, temperature variations are strongly tied to the asymmetric SAM structure, while temperatures across East Antarctica are more strongly tied to the zonally symmetric SAM structure. The results suggest that studies examining the climate impacts of the SAM across the Southern Hemisphere need to consider the seasonal variations in the SAM structure as well as varying impacts between its positive and negative polarity to adequately describe the underlying relationships.
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Haqq-Misra, Jacob, Sukyoung Lee et Dargan M. W. Frierson. « Tropopause Structure and the Role of Eddies ». Journal of the Atmospheric Sciences 68, no 12 (1 décembre 2011) : 2930–44. http://dx.doi.org/10.1175/jas-d-11-087.1.
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Abstract This paper presents a series of dynamical states using an idealized three-dimensional general circulation model with gray radiation and latent heat release. Beginning with the case of radiative–convective equilibrium, an eddy-free two-dimensional state with zonally symmetric flow is developed, followed by a three-dimensional state that includes baroclinic eddy fluxes. In both dry and moist cases, it is found that the deepening of the tropical tropospheric layer and the shape of the extratropical tropopause can be understood through eddy-driven processes such as the stratospheric Brewer–Dobson circulation. These results suggest that eddies alone can generate a realistic tropopause profile in the absence of moist convection and that stratospheric circulation is an important contributor to tropopause structure.
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Poyrazoglu, Gokturk. « Determination of Price Zones during Transition from Uniform to Zonal Electricity Market : A Case Study for Turkey ». Energies 14, no 4 (15 février 2021) : 1014. http://dx.doi.org/10.3390/en14041014.
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In the electricity market, different pricing models can be applied to increase market competitiveness. Different electricity systems use different market structures. Uniform marginal pricing, zonal marginal pricing, and nodal marginal pricing methods are commonly used market structures. For markets wishing to move from a uniform pricing structure to a more competitive zonal pricing structure, the determination of price zones is critical for achieving a competitive market that generates accurate price signals. Three different pricing zone detection algorithms are analyzed in this paper including the k-means clustering and queen/rook spatially constraint clustering. Finally, the results of a case study for the Turkish electricity system are shared to compare each method.
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Inozemtsev, V. I. « On the Structure of Zonal Spherical Functions on Symmetric Spaces of Negative Curvature of Type AII ». Nelineinaya Dinamika 15, no 2 (2019) : 179–86. http://dx.doi.org/10.20537/nd190207.
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Kiladis, George N., Katherine H. Straub et Patrick T. Haertel. « Zonal and Vertical Structure of the Madden–Julian Oscillation ». Journal of the Atmospheric Sciences 62, no 8 (1 août 2005) : 2790–809. http://dx.doi.org/10.1175/jas3520.1.
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Abstract A statistical study of the three-dimensional structure of the Madden–Julian oscillation (MJO) is carried out by projecting dynamical fields from reanalysis and radiosonde data onto space–time filtered outgoing longwave radiation (OLR) data. MJO convection is generally preceded by low-level convergence and upward motion in the lower troposphere, while subsidence, cooling, and drying prevail aloft. This leads to moistening of the boundary layer and the development of shallow convection, followed by a gradual and then more rapid lofting of moisture into the middle troposphere at the onset of deep convection. After the passage of the heaviest rainfall, a westerly wind burst region is accompanied by stratiform precipitation, where lower tropospheric subsidence and drying coincide with continuing upper tropospheric upward motion. The evolution of the heating field leads to a temperature structure that favors the growth of the MJO. The analysis also reveals distinct differences in the vertical structure of the MJO as it evolves, presumably reflecting changes in its vertical heating profile, phase speed, or the basic-state circulation that the MJO propagates through. The dynamical structure and the evolution of cloud morphology within the MJO compares favorably in many respects with other propagating convectively coupled equatorial waves. One implication is that the larger convective envelopes within the Tropics tend to be composed of more shallow convection along their leading edges, a combination of deep convection and stratiform rainfall in their centers, and then a preponderance of stratiform rainfall along their trailing edges, regardless of scale or propagation direction. While this may ultimately be the factor that governs the dynamical similarities across the various wave types, it raises questions about how the smaller-scale, higher-frequency disturbances making up the MJO conspire to produce its heating and dynamical structures. This suggests that the observed cloud morphology is dictated by fundamental interactions with the large-scale circulation.
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Samuha, Shmuel, Yaakov Krimer et Louisa Meshi. « Strategies for full structure solution of intermetallic compounds using precession electron diffraction zonal data ». Journal of Applied Crystallography 47, no 3 (29 mai 2014) : 1032–41. http://dx.doi.org/10.1107/s1600576714009200.
Texte intégralRésumé :
Owing to the individuality of intermetallic compounds, they are regarded as a special class of materials. As such, there is a need to develop a step-by-step methodology for solution of their structure. The current paper adapts the methodology of structure solution from precession electron diffraction (PED) zonal data for intermetallics. The optimization of PED parameters for structure determination was achieved through the development of the atomic model of a well known Mg17Al12(β) intermetallic phase. It was concluded that the PED acquisition parameters, the number of unique reflections and the quality of the merging process are the most important parameters that directly influence the correctness of a structure solution. The proposed methodology was applied to the structure solution of a highly complex new Mg48Al36Ag16phase, which was recently revealed in the Mg–Al–Ag system. The final atomic model consisted of 152 atoms in the unit cell, distributed over 23 unique atomic positions. The correctness of the atomic model was verified by the reasonability of the interatomic distances and coordination polyhedra formed. It was found that the experimental model of Φ-Al17.1Mg53.4Zn29.5can be assigned as a structure type for the Mg48Al36Ag16phase. The Δ value, which measures the similarity between two structures, was calculated as 0.040.
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Thompson, Andrew F., et Jean-Baptiste Sallée. « Jets and Topography : Jet Transitions and the Impact on Transport in the Antarctic Circumpolar Current ». Journal of Physical Oceanography 42, no 6 (1 juin 2012) : 956–72. http://dx.doi.org/10.1175/jpo-d-11-0135.1.
Texte intégralRésumé :
Abstract The Southern Ocean’s Antarctic Circumpolar Current (ACC) naturally lends itself to interpretations using a zonally averaged framework. Yet, navigation around steep and complicated bathymetric obstacles suggests that local dynamics may be far removed from those described by zonally symmetric models. In this study, both observational and numerical results indicate that zonal asymmetries, in the form of topography, impact global flow structure and transport properties. The conclusions are based on a suite of more than 1.5 million virtual drifter trajectories advected using a satellite altimetry–derived surface velocity field spanning 17 years. The focus is on sites of “cross front” transport as defined by movement across selected sea surface height contours that correspond to jets along most of the ACC. Cross-front exchange is localized in the lee of bathymetric features with more than 75% of crossing events occurring in regions corresponding to only 20% of the ACC’s zonal extent. These observations motivate a series of numerical experiments using a two-layer quasigeostrophic model with simple, zonally asymmetric topography, which often produces transitions in the front structure along the channel. Significantly, regimes occur where the equilibrated number of coherent jets is a function of longitude and transport barriers are not periodic. Jet reorganization is carried out by eddy flux divergences acting to both accelerate and decelerate the mean flow of the jets. Eddy kinetic energy is amplified downstream of topography due to increased baroclinicity related to topographic steering. The combination of high eddy kinetic energy and recirculation features enhances particle exchange. These results stress the complications in developing consistent circumpolar definitions of the ACC fronts.
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Diansky, N. A., et V. A. Bagatinsky. « The thermohaline structure of the North Atlantic waters in different phases of the Atlantic multidecadal oscillation ». Известия Российской академии наук. Физика атмосферы и океана 55, no 6 (21 décembre 2019) : 157–70. http://dx.doi.org/10.31857/s0002-3515556157-170.
Texte intégralRésumé :
The meridional structure of climatic trends and anomalies of potential temperature and salinity in the North Atlantic waters in different periods of the Atlantic Multidecadal Oscillation (AMO) in 19482017 are studied based on the EN4 and WOA2013 objective analyses data. An analysis of these different data sets allowed us to reveal almost identical patterns of variability of the thermohaline fields of the North Atlantic, which increases the reliability of the results. Long-term temperature and salinity trends simulated over the period 19482017 show that warming and salinization of water occur in the upper ~1 km layer of the North Atlantic. On the contrary, cooling and freshening of deep waters are observed, which is associated with the melting of the Greenland ice sheet, transport of fresher waters from the Arctic Ocean, and deepening of these cold and fresher waters into the deeper layers. Composite analysis of the zonally averaged temperature and salinity anomalies of the North Atlantic waters after removing the trends showed that in the warm AMO periods warming and salinization of waters are observed in the upper 1-km layer of the North Atlantic when compared to the cold periods based both on the EN4 and WOA2013 data. Below the 1-km layer, significant regions of cooling and freshening are observed; this distribution is more pronounced in the EN4 data. Analysis of the dynamics of zonally averaged temperature and salinity anomalies in the successive periods associated with the temporal variability of the AMO index revealed that these anomalies propagate along the zonally averaged meridional thermohaline circulation. To show this using the Institute of Numerical Mathematics Ocean Model (INMOM), the stream function of the Atlantic Meridional Overturning Circulation (AMOC) was simulated. It is shown that positive and negative anomalies of both temperature and salinity circulate along the water motion in the AMOC around its core, descending down into the deep ocean layers approximately at 60 N and ascending to the surface at 25 N, replacing each other with a period of about 60 years. It can be assumed that due to this process both the warm and cold phases of the AMO are formed.
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Monahan, Adam H., et John C. Fyfe. « On the Nature of Zonal Jet EOFs ». Journal of Climate 19, no 24 (15 décembre 2006) : 6409–24. http://dx.doi.org/10.1175/jcli3960.1.
Texte intégralRésumé :
Abstract Analytic results are obtained for the mean and covariance structure of an idealized zonal jet that fluctuates in strength, position, and width. Through a systematic perturbation analysis, the leading empirical orthogonal functions (EOFs) and principal component (PC) time series are obtained. These EOFs are built of linear combinations of basic patterns corresponding to monopole, dipole, and tripole structures. The analytic results demonstrate that in general the individual EOF modes cannot be interpreted in terms of individual physical processes. In particular, while the dipole EOF (similar to the leading EOF of the midlatitude zonal mean zonal wind) describes fluctuations in jet position to leading order, its time series also contains contributions from fluctuations in strength and width. No simple interpretations of the other EOFs in terms of strength, position, or width fluctuations are possible. Implications of these results for the use of EOF analysis to diagnose physical processes of variability are discussed.
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Whitehouse, S. G., S. R. Lewis, I. M. Moroz et P. L. Read. « A simplified model of the Martian atmosphere - Part 2 : a POD-Galerkin analysis ». Nonlinear Processes in Geophysics 12, no 5 (17 juin 2005) : 625–42. http://dx.doi.org/10.5194/npg-12-625-2005.
Texte intégralRésumé :
Abstract. In Part I of this study Whitehouse et al. (2005) performed a diagnostic analysis of a simplied model of the Martian atmosphere, in which topography was absent and in which heating was modelled as Newtonian relaxation towards a zonally symmetric equilibrium temperature field. There we derived a reduced-order approximation to the vertical and the horizonal structure of the baroclinically unstable Martian atmosphere, retaining only the barotropic mode and the leading order baroclinic modes. Our objectives in Part II of the study are to incorporate these approximations into a Proper Orthogonal Decomposition-Galerkin expansion of the spherical quasi-geostrophic model in order to derive hierarchies of nonlinear ordinary differential equations for the time-varying coefficients of the spatial structures. Two different vertical truncations are considered, as well as three different norms and 3 different Galerkin truncations. We investigate each in turn, using tools from bifurcation theory, to determine which of the systems most closely resembles the data for which the original diagnostics were performed.
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Baines, Peter G. « The zonal structure of the Hadley circulation ». Advances in Atmospheric Sciences 23, no 6 (décembre 2006) : 869–83. http://dx.doi.org/10.1007/s00376-006-0869-5.
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Kang, In-Sik, Fei Liu, Min-Seop Ahn, Young-Min Yang et Bin Wang. « The Role of SST Structure in Convectively Coupled Kelvin–Rossby Waves and Its Implications for MJO Formation ». Journal of Climate 26, no 16 (6 août 2013) : 5915–30. http://dx.doi.org/10.1175/jcli-d-12-00303.1.
Texte intégralRésumé :
Abstract The dynamics of the Madden–Julian oscillation (MJO) are investigated using an aqua-planet general circulation model (GCM) and a simple one-and-a-half-layer model with a first-baroclinic mode and a planetary boundary layer. The aqua-planet GCM with zonally symmetric SST conditions simulates tropical intraseasonal disturbances with a dominant time scale of about 20 days, which is much faster than that of the observed MJO, although the GCM with realistic surface boundary conditions is shown to reproduce the observed MJO reasonably well. The SST with a broader meridional structure slows down the propagation speed. Several experiments done with various zonally symmetric surface boundary conditions showed that the meridional structure of the SST in fact is a control factor for the propagation characteristics of the MJO. With a simple theoretical model for the MJO, it is shown that the instability of the moist coupled Kelvin–Rossby waves depends on the SST structure, which determines the lower-level moisture field. The SST with a narrow meridional structure prefers to enhance only the fast eastward Kelvin wave, while the broader SST provides enough off-equatorial moisture for the growth of the Rossby component, which couples strongly with the Kelvin component and slows down the eastward modes. The SST influences the coupled Kelvin–Rossby waves through changes in the moist static stability of the free atmosphere and the frictional moisture convergence in the planetary boundary layer. The present results suggest that the essential dynamics of the MJO are rooted in a convectively coupled Kelvin–Rossby wave packet with frictional moisture convergence.
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Gabriel, A., H. Körnich, S. Lossow, D. H. W. Peters, J. Urban et D. Murtagh. « Zonal asymmetries in middle atmospheric ozone and water vapour derived from Odin satellite data 2001–2010 ». Atmospheric Chemistry and Physics 11, no 18 (26 septembre 2011) : 9865–85. http://dx.doi.org/10.5194/acp-11-9865-2011.
Texte intégralRésumé :
Abstract. Stationary wave patterns in middle atmospheric ozone (O3) and water vapour (H2O) are an important factor in the atmospheric circulation, but there is a strong gap in diagnosing and understanding their configuration and origin. Based on Odin satellite data from 2001 to 2010 we investigate the stationary wave patterns in O3 and H2O as indicated by the seasonal long-term means of the zonally asymmetric components O3* = O3-[O3] and H2O* = H2O-[H2O] ([O3], [H2O]: zonal means). At mid- and polar latitudes we find a pronounced wave one pattern in both constituents. In the Northern Hemisphere, the wave patterns increase during autumn, maintain their strength during winter and decay during spring, with maximum amplitudes of about 10–20 % of the zonal mean values. During winter, the wave one in O3* shows a maximum over the North Pacific/Aleutians and a minimum over the North Atlantic/Northern Europe and a double-peak structure with enhanced amplitude in the lower and in the upper stratosphere. The wave one in H2O* extends from the lower stratosphere to the upper mesosphere with a westward shift in phase with increasing height including a jump in phase at upper stratosphere altitudes. In the Southern Hemisphere, similar wave patterns occur mainly during southern spring. By comparing the observed wave patterns in O3* and H2O* with a linear solution of a steady-state transport equation for a zonally asymmetric tracer component we find that these wave patterns are primarily due to zonally asymmetric transport by geostrophically balanced winds, which are derived from observed temperature profiles. In addition temperature-dependent photochemistry contributes substantially to the spatial structure of the wave pattern in O3* . Further influences, e.g., zonal asymmetries in eddy mixing processes, are discussed.
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Markelov, D. A., N. Y. Mineeva, A. P. Akolzin, B. I. Kochurov, M. A. Grigorieva et E. A. Chukmasova. « Geoecological frame of the megalopolis – landscape-zonal standard of sustainable development of geosystems ». Practice of Anticorrosive Protection 24, no 4 (1 décembre 2019) : 34–40. http://dx.doi.org/10.31615/j.corros.prot.2019.94.4-4.
Texte intégralRésumé :
The natural-man-made complex is an interconnected paragenetic geosystem that functions: “natural skeleto – technogenic structures – heat capacity – wind flow – moisture – biological effects – chemical reactions (corrosion) – a cartographic image”. The ghosting characteristics of a natural framework, as a cartographic image of space, serve as indicators and guide marks for making decisions in environmental management in order to protect objects and prevent damage from damaging factors, such as corrosion. Sustainable functioning of the geosystem ensures environmental safety and reliability of any territory and structure. The methodology for assessing the geoecological framework of the territory is substantiated and the analysis of the influence of anthropogenically transformed geosystems is performed. Diagnostics of the ecological state of an object or territory is aimed at establishing a deviation from the “norm”, a typical state of the structure and organization of geosystems. The basis of any diagnosis is the availability of a database of etalons, norms or standards.
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Lin, Pu, Qiang Fu, Susan Solomon et John M. Wallace. « Temperature Trend Patterns in Southern Hemisphere High Latitudes : Novel Indicators of Stratospheric Change ». Journal of Climate 22, no 23 (1 décembre 2009) : 6325–41. http://dx.doi.org/10.1175/2009jcli2971.1.
Texte intégralRésumé :
Abstract Robust stratospheric temperature trend patterns are suggested in the winter and spring seasons in the Southern Hemisphere high latitudes from the satellite-borne Microwave Sounding Unit (MSU) measurement for 1979–2007. These patterns serve as indicators of key processes governing temperature and ozone changes in the Antarctic. The observed patterns are characterized by cooling and warming regions of comparable magnitudes, with the strongest local trends occurring in September and October. In September, ozone depletion induces radiative cooling, and strengthening of the Brewer–Dobson circulation (BDC) induces dynamical warming. Because the trends induced by these two processes are centered in different locations in September, they do not cancel each other, but rather produce a wavelike structure. In contrast, during October, the ozone-induced radiative cooling and the BDC-induced warming exhibit a more zonally symmetric structure than in September, and hence largely cancel each other. However, the October quasi-stationary planetary wavenumber 1 has shifted eastward from 1979 to 2007, producing a zonal wavenumber-1 trend structure, which dominates the observed temperature trend pattern. Simulated temperature changes for 1979–2007 from coupled atmosphere–ocean general circulation model (AOGCM) experiments run for the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4) are compared with the observations. In general, the simulated temperature changes are dominated by zonally symmetric ozone-induced radiative cooling. The models fail to simulate the warming in the southern polar stratosphere, implying a lack of the BDC strengthening in these models. They also fail to simulate the quasi-stationary planetary wave changes observed in October and November.
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Xu, Xiaobiao, Peter B. Rhines et Eric P. Chassignet. « On Mapping the Diapycnal Water Mass Transformation of the Upper North Atlantic Ocean ». Journal of Physical Oceanography 48, no 10 (octobre 2018) : 2233–58. http://dx.doi.org/10.1175/jpo-d-17-0223.1.
Texte intégralRésumé :
AbstractDiapycnal water mass transformation is the essence behind the Atlantic meridional overturning circulation (AMOC) and the associated heat/freshwater transports. Existing studies have mostly focused on the transformation that is forced by surface buoyancy fluxes, and the role of interior mixing is much less known. This study maps the three-dimensional structure of the diapycnal transformation, both surface forced and mixing induced, using results of a high-resolution numerical model that have been shown to represent the large-scale structure of the AMOC and the North Atlantic subpolar/subtropical gyres well. The analyses show that 1) annual mean transformation takes place seamlessly from the subtropical to the subpolar North Atlantic following the surface buoyancy loss along the northward-flowing upper AMOC limb; 2) mixing, including wintertime convection and warm-season restratification by mesoscale eddies in the mixed layer and submixed layer diapycnal mixing, drives transformations of (i) Subtropical Mode Water in the southern part of the subtropical gyre and (ii) Labrador Sea Water in the Labrador Sea and on its southward path in the western Newfoundland Basin; and 3) patterns of diapycnal transformations toward lighter and denser water do not align zonally—the net three-dimensional transformation is significantly stronger than the zonally integrated, two-dimensional AMOC streamfunction (50% in the southern subtropical North Atlantic and 60% in the western subpolar North Atlantic).
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Roundy, Paul E. « Regression Analysis of Zonally Narrow Components of the MJO ». Journal of the Atmospheric Sciences 71, no 11 (29 octobre 2014) : 4253–75. http://dx.doi.org/10.1175/jas-d-13-0288.1.
Texte intégralRésumé :
Abstract Recent works have demonstrated that eastward-propagating features smaller than zonal wavenumber 3 but with spatial structures similar to those of the Madden–Julian oscillation (MJO) frequently develop over the Indo-Pacific warm pool. These signals are characterized by periods shorter than 4 weeks, but since they occur as part of a spectral peak of the MJO, they might be characterized by similar physics. These zonally narrow features occur at any phase of traditionally defined 30–60-day MJO events, but they occur most frequently in its active convective phase. This work presents a linear regression analysis based on filtering in the wavenumber–frequency domain to compare such signals with traditionally defined MJOs and 15–30 m s−1, convectively coupled Kelvin waves. Results show that the trough collocated with the easterly wind anomaly extends westward into the region of lower-tropospheric westerly wind and deep convection in the zonally narrow slow signals and MJOs. The fast Kelvin waves have a ridge anomaly collocated with the westerly wind anomaly. The zonally narrow slow signals and MJOs include a warm anomaly in the boundary layer west of the deep convection that is absent in fast Kelvin waves. Results suggest that MJO dynamics are not confined to the 30–60-day band and that time scales as short as 2 weeks could be considered in wavenumber–frequency diagnostics for the MJO.
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Krivenko, S. V. « RESEARCH OF THE ZONAL STRUCTURE OF SINTERING LAYER ». Izvestiya Visshikh Uchebnykh Zavedenii. Chernaya Metallurgiya = Izvestiya. Ferrous Metallurgy 59, no 8 (1 janvier 2016) : 581–86. http://dx.doi.org/10.17073/0368-0797-2016-8-581-586.
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Liu, L. Q., L. L. Kang et J. Z. Wu. « Zonal structure of unbounded external-flow and aerodynamics ». Fluid Dynamics Research 49, no 4 (5 juillet 2017) : 045508. http://dx.doi.org/10.1088/1873-7005/aa79d0.
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Itoh, K., K. Hallatschek, S. Toda, H. Sanuki et S. I. Itoh. « Coherent Structure of Zonal Flow and Nonlinear Saturation ». Journal of the Physical Society of Japan 73, no 11 (novembre 2004) : 2921–23. http://dx.doi.org/10.1143/jpsj.73.2921.
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Scott, Richard K., et David G. Dritschel. « The structure of zonal jets in geostrophic turbulence ». Journal of Fluid Mechanics 711 (20 septembre 2012) : 576–98. http://dx.doi.org/10.1017/jfm.2012.410.
Texte intégralRésumé :
AbstractThe structure of zonal jets arising in forced-dissipative, two-dimensional turbulent flow on the $\ensuremath{\beta} $-plane is investigated using high-resolution, long-time numerical integrations, with particular emphasis on the late-time distribution of potential vorticity. The structure of the jets is found to depend in a simple way on a single non-dimensional parameter, which may be conveniently expressed as the ratio ${L}_{\mathit{Rh}} / {L}_{\varepsilon } $, where ${L}_{\mathit{Rh}} = \sqrt{U/ \ensuremath{\beta} } $ and ${L}_{\varepsilon } = \mathop{ (\varepsilon / {\ensuremath{\beta} }^{3} )}\nolimits ^{1/ 5} $ are two natural length scales arising in the problem; here $U$ may be taken as the r.m.s. velocity, $\ensuremath{\beta} $ is the background gradient of potential vorticity in the north–south direction, and $\varepsilon $ is the rate of energy input by the forcing. It is shown that jet strength increases with ${L}_{\mathit{Rh}} / {L}_{\varepsilon } $, with the limiting case of the potential vorticity staircase, comprising a monotonic, piecewise-constant profile in the north–south direction, being approached for ${L}_{\mathit{Rh}} / {L}_{\varepsilon } \ensuremath{\sim} O(10)$. At lower values, eddies created by the forcing become sufficiently intense to continually disrupt the steepening of potential vorticity gradients in the jet cores, preventing strong jets from developing. Although detailed features such as the regularity of jet spacing and intensity are found to depend on the spectral distribution of the forcing, the approach of the staircase limit with increasing ${L}_{\mathit{Rh}} / {L}_{\varepsilon } $ is robust across a variety of different forcing types considered.
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Popp, M., et N. J. Lutsko. « Quantifying the Zonal-Mean Structure of Tropical Precipitation ». Geophysical Research Letters 44, no 18 (28 septembre 2017) : 9470–78. http://dx.doi.org/10.1002/2017gl075235.
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Drbohlav, Hae-Kyung Lee, et Bin Wang. « Horizontal and Vertical Structures of the Northward-Propagating Intraseasonal Oscillation in the South Asian Monsoon Region Simulated by an Intermediate Model* ». Journal of Climate 20, no 16 (15 août 2007) : 4278–86. http://dx.doi.org/10.1175/jcli4244.1.
Texte intégralRésumé :
Abstract The structures and mechanism of the northward-propagating boreal summer intraseasonal oscillation (BSISO) in the southern Asian monsoon region are simulated and investigated in a three-dimensional intermediate model (3D model). The horizontal structure of the intraseasonal variability in the 3D model depicts the Kelvin–Rossby wave–type disturbance, which may or may not produce the northward-propagating disturbance in the Indian Ocean, depending on the seasonal-mean background winds. Two experiments are conducted in order to identify what characteristic of seasonal-mean background can induce the northwestward-tilted band in the Kelvin–Rossby wave, whose overall eastward movement gives the impression of the northward propagation at a given longitude. When the prescribed boreal summer mean winds are excluded in the first experiment, the phase difference between the barotropic divergence tendency and convection disappears. Consequently, the Rossby wave–type convection forms a zonally elongated band. As a result, the northward propagation of convection at a given longitude disappears. When the easterly vertical shear is introduced in the second experiment, the horizontal and the vertical structures of BSISO become similar to that of the northward-propagating one. The reoccurrence of the northwestward-directed convective band and the phase difference between the barotropic divergence tendency and the convection suggest that the summer mean zonal winds in the boreal Indian summer monsoon region are a critical condition that causes the horizontal and vertical structures of northward-propagating BSISO in the southern Asian monsoon region.
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Shepherd, M. G., et T. Tsuda. « Large-scale planetary disturbances in stratospheric temperature at high-latitudes in the Southern Summer Hemisphere ». Atmospheric Chemistry and Physics Discussions 8, no 4 (27 août 2008) : 16409–44. http://dx.doi.org/10.5194/acpd-8-16409-2008.
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Abstract. The global structure and propagation of large-scale (periods >5 days) waves in the Southern Hemisphere summer (December 2006–February 2007) at 60° S–75° S latitude are examined using temperature data from GPS radio occultation measurements by COSMIC/FORMOSAT 3 satellite constellation from 10 to 40 km altitude. Spectral analysis has revealed eastward propagating planetary scale perturbations with wavenumbers 1 and 2 and periods of 10-, 16- and 23 days, zonally symmetric waves with the same periods and stationary waves with wavenumber 1 and 2. The presence of the zonally symmetric waves is interpreted as an indication of the coupling of the stationary and traveling waves. The results obtained show a very dynamically active Antarctic summer stratosphere. The novel aspect of the work is in the use of the GPS COSMIC data providing multiple local times each day, thus allowing large-scale wave analysis at high Southern latitudes and revealing planetary wave activity not normally observed in summer, but more consistent with late winter and spring conditions in the stratosphere.
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Falessi, Matteo Valerio, et Fulvio Zonca. « Transport theory of phase space zonal structures ». Physics of Plasmas 26, no 2 (février 2019) : 022305. http://dx.doi.org/10.1063/1.5063874.
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Ming, Alison, Peter Hitchcock et Peter Haynes. « The Response of the Lower Stratosphere to Zonally Symmetric Thermal and Mechanical Forcing ». Journal of the Atmospheric Sciences 73, no 5 (15 avril 2016) : 1903–22. http://dx.doi.org/10.1175/jas-d-15-0294.1.
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Abstract The response of the atmosphere to zonally symmetric applied heating and mechanical forcing is considered, allowing for the fact that the response may include a change in the wave force (or “wave drag”). A scaling argument shows that an applied zonally symmetric heating is effective in driving a steady meridional circulation provided that the wave force (required to satisfy angular momentum constraints) is sufficiently sensitive to changes in the mean flow in the sense that the ratio is large, where K is a measure of the sensitivity of the wave force; α, N, and f are the radiative damping rate, buoyancy frequency, and Coriolis parameter, respectively; and and are the horizontal and vertical length scales of the heating, respectively. Furthermore, in the “narrow heating” regime where this ratio is large, the structure of the meridional circulation response is only weakly dependent on the details of the wave force. The scaling arguments are verified by experiments in a dry dynamical circulation model. Consistent with the scaling prediction, the regime does not apply when the width of the imposed heating is increased. The narrow-heating regime is demonstrated to be relevant to the double peak in tropical lower-stratospheric upwelling considered in a companion paper, supporting the hypothesis that this feature is radiatively driven. Similar arguments are applied to show that a narrow zonally symmetric applied mechanical forcing is primarily balanced by a change in wave force. This provides an explanation for the recently identified compensation between resolved and parameterized waves in driving modeled trends in the Brewer–Dobson circulation.
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Brochero Bustamante, Carlos Esteban, Francisco Fabian Carrascal Perez, Yesith Montero Cantillo et Isueh Arenas Rubio. « Inventory of insect pests and pathogens present in a cashew crop <i>Anacardium occidentale </i>L. in Caribia research center, zona bananera, Magdalena ». Temas Agrarios 28, no 2 (23 décembre 2023) : 208–19. http://dx.doi.org/10.21897/8mnqgh69.
Texte intégralRésumé :
The purpose of this work was to identify pests and diseases associated to cashew crop in Caribia research center of Agrosavia. For 24 months, a monthly monitoring of the different structures of the plant was carried out and the arthropods found to cause damage were collected, as well as tissue samples with symptoms or signs of any disease. Eleven species of pest insects were identified, grouped into seven families and four orders. In addition, six pathogens that caused diseases in different tree structures were identified. Of the phytosanitary problems found, Leptoglossus zonatus Dallas (Hemiptera: Coreidae) and anthracnose are reported as the most relevant for this crop.
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Ring, Michael J., et R. Alan Plumb. « Forced Annular Mode Patterns in a Simple Atmospheric General Circulation Model ». Journal of the Atmospheric Sciences 64, no 10 (1 octobre 2007) : 3611–26. http://dx.doi.org/10.1175/jas4031.1.
Texte intégralRésumé :
Abstract Previous studies using simplified general circulation models have shown that “annular modes” arise as the dominant mode of variability. A simple GCM is used here to explore to what extent these modes are also the preferred response of the system to generic forcing. A number of trials are conducted under which the model is subjected to an artificial, zonally symmetric angular momentum forcing, and the climatologies of these trials are compared to that of the control. The forcing location is varied among the several trials. It is found that the changes in the model’s climatology are generally annular mode–like, as long as the imposed forcing projects strongly upon the annular modes of the unforced model. The role of changes to the eddy–zonal flow feedback versus the action of direct forcing is also considered through the use of a zonally symmetric version of the model. It is found that the direct responses to forcing are insufficient to capture either the strength or the structure of the annular mode responses. Instead, the changes in eddy fluxes are needed to produce the correct responses.
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Mioc, V. « The zonal satellite problem. III Symmetries ». Serbian Astronomical Journal, no 165 (2002) : 1–8. http://dx.doi.org/10.2298/saj0265001m.
Texte intégralRésumé :
The two-body problem associated with a force field described by a potential of the form U =Sum(k=1,n) ak/rk (r = distance between particles, ak = real parameters) is resumed from the only standpoint of symmetries. Such symmetries, expressed in Hamiltonian coordinates, or in standard polar coordinates, are recovered for McGehee-type coordinates of both collision-blow-up and infinity-blow-up kind. They form diffeomorphic commutative groups endowed with a Boolean structure. Expressed in Levi-Civita?s coordinates, the problem exhibits a larger group of symmetries, also commutative and presenting a Boolean structure.
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Nigam, Sumant. « On the Structure of Variability of the Observed Tropospheric and Stratospheric Zonal-Mean Zonal Wind ». Journal of the Atmospheric Sciences 47, no 14 (juillet 1990) : 1799–813. http://dx.doi.org/10.1175/1520-0469(1990)047<1799:otsovo>2.0.co;2.
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Masunaga, Ryusuke, Hisashi Nakamura, Bunmei Taguchi et Takafumi Miyasaka. « Processes Shaping the Frontal-Scale Time-Mean Surface Wind Convergence Patterns around the Kuroshio Extension in Winter ». Journal of Climate 33, no 1 (1 janvier 2020) : 3–25. http://dx.doi.org/10.1175/jcli-d-19-0097.1.
Texte intégralRésumé :
AbstractHigh-resolution satellite observations and numerical simulations have revealed that climatological-mean surface wind convergence and precipitation are enhanced locally around the midlatitude warm western boundary currents (WBCs) with divergence slightly to their poleward side. While steep sea surface temperature (SST) fronts along the WBCs have been believed to play an important role in shaping those frontal-scale atmospheric structures, the mechanisms and processes involved are still under debate. The present study explores specific daily scale atmospheric processes that are essential for shaping the frontal-scale atmospheric structure around the Kuroshio Extension (KE) in winter, taking advantage of a new product of global atmospheric reanalysis. Cluster analysis and case studies reveal that a zonally extending narrow band of surface wind convergence frequently emerges along the KE, which is typically observed under the surface northerlies after the passage of a developed synoptic-scale cyclone. Unlike its counterpart around the cyclone center and associated cold front, the surface convergence tends to be in moderate strength and more persistent, contributing dominantly to the distinct time-mean convergence/divergence contrast across the SST front. Accompanying ascent and convective precipitation, the band of convergence is a manifestation of a weak stationary atmospheric front anchored along the SST front or generation of a weak meso-α-scale cyclone. By reinforcing the ascent and convergence, latent heating through convective processes induced by surface convergence plays an important role in shaping the frontal-scale atmospheric structure around the KE.
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Simpson, Isla R., Michael Blackburn, Joanna D. Haigh et Sarah N. Sparrow. « The Impact of the State of the Troposphere on the Response to Stratospheric Heating in a Simplified GCM ». Journal of Climate 23, no 23 (1 décembre 2010) : 6166–85. http://dx.doi.org/10.1175/2010jcli3792.1.
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Abstract Previous studies have made use of simplified general circulation models (sGCMs) to investigate the atmospheric response to various forcings. In particular, several studies have investigated the tropospheric response to changes in stratospheric temperature. This is potentially relevant for many climate forcings. Here the impact of changing the tropospheric climatology on the modeled response to perturbations in stratospheric temperature is investigated by the introduction of topography into the model and altering the tropospheric jet structure. The results highlight the need for very long integrations so as to determine accurately the magnitude of response. It is found that introducing topography into the model and thus removing the zonally symmetric nature of the model’s boundary conditions reduces the magnitude of response to stratospheric heating. However, this reduction is of comparable size to the variability in the magnitude of response between different ensemble members of the same 5000-day experiment. Investigations into the impact of varying tropospheric jet structure reveal a trend with lower-latitude/narrower jets having a much larger magnitude response to stratospheric heating than higher-latitude/wider jets. The jet structures that respond more strongly to stratospheric heating also exhibit longer time scale variability in their control run simulations, consistent with the idea that a feedback between the eddies and the mean flow is both responsible for the persistence of the control run variability and important in producing the tropospheric response to stratospheric temperature perturbations.
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Ujiie, Masumi. « Zonal structure of the Orikabe plutonic complex, Kitakami mountains. » JOURNAL OF MINERALOGY, PETROLOGY AND ECONOMIC GEOLOGY 84, no 7 (1989) : 226–42. http://dx.doi.org/10.2465/ganko.84.226.
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Gutzler, David S. « Vertical Structure and Interannual Variability of Tropical Zonal Winds ». Journal of Climate 3, no 7 (juillet 1990) : 741–50. http://dx.doi.org/10.1175/1520-0442(1990)003<0741:vsaivo>2.0.co;2.
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Smolyakov, A. I., P. H. Diamond et M. Malkov. « Coherent Structure Phenomena in Drift Wave–Zonal Flow Turbulence ». Physical Review Letters 84, no 3 (17 janvier 2000) : 491–94. http://dx.doi.org/10.1103/physrevlett.84.491.
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Adamczyk, Joanna, et Dirk Tiede. « ZonalMetrics - a Python toolbox for zonal landscape structure analysis ». Computers & ; Geosciences 99 (février 2017) : 91–99. http://dx.doi.org/10.1016/j.cageo.2016.11.005.
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