118,290 research outputs found
Millennial Variability in an Idealized Ocean Model: Predicting the AMOC Regime Shifts
No full textA salient feature of paleorecords of the last glacial interval in the North Atlantic is pronounced millennial variability, commonly known as Dansgaard–Oeschger events. It is believed that these events are related to variations in the Atlantic meridional overturning circulation and heat transport. Here, the authors formulate a new low-order model, based on the Howard–Malkus loop representation of ocean circulation, capable of reproducing millennial variability and its chaotic dynamics realistically. It is shown that even in this chaotic model changes in the state of the meridional overturning circulation are predictable. Accordingly, the authors define two predictive indices which give accurate predictions for the time the circulation should remain in the on phase and then stay in the subsequent off phase. These indices depend mainly on ocean stratification and describe the linear growth of small perturbations in the system. Thus, monitoring particular indices of the ocean state could help predict a potential shutdown of the overturning circulation
Primorella zhankurganica Tolokonnikova & Fedorov 2022, sp. nov.
No full textPrimorella zhankurganica sp. nov. Figs 4A–F, Table 5 Holotype. SibGIU 12/28 (section with five colony fragments). Material. SibGIU 12/23.1 (micro-CT). Description. Thin branched colonies. Autozooecial wall 0.02 mm thick in endozone. Diaphragms in the autozooecia absent. Oval autozooecial apertures arranged in diagonal rows; 2 apertures per 1 mm along colony length, 3 diagonally. Autozooecia budding from the central axis at low angles, sharply bending in the exozone and intersecting the colony surface at angles of 80–90°. Abundant aktinotostyles in the walls of the exozone, arranged in regular rows between apertures on the colony surface, displaying distinct core with radially arranged small spines, stellate in cross section. Comparison. Primorella zhankurganica sp. nov. differs from P. variata Tolokonnikova, 2015 from the upper Tournaisian of Kurgan region of Russia (Tolokonnikova 2015) in narrower colonies (0.70–0.80 mm vs. 0.67–1.05 mm in P. variata), abundant aktinotostyles (22–24 around each aperture vs 10–16 in P. variata) and smaller apertures (0.07–0.08x 0.16–0.20 mm vs. 0.01–0.12x 0.17–0.22 mm in P. variata). Stratigraphical and geographical ranges. Orgalysay Formation, Mississippian (upper Tournaisian); Karatau, Zhankurgan outcrop, Kazakhstan.Published as part of Tolokonnikova, Zoya A. & Fedorov, Petr V., 2022, Late Devonian-early Carboniferous bryozoans from Zhankurgan (Greater Karatau, Kazakhstan) - taxonomy and palaeobiogeographical implications, pp. 252-264 in Zootaxa 5196 (2) on page 259, DOI: 10.11646/zootaxa.5196.2.6, http://zenodo.org/record/722454
Vadim Fedorov - Biography and Work
No full textBakalářská práce je věnována životu a tvorbě ruského spisovatele Vadima Nikolajeviče Fedorova, žijícímu v České republice.
Cílem bakalářské práce bylo charakterizovat rysy poetiky a tvorby V. N. Fedorova.
Při psaní bakalářské práce byly použity následující metody: popisná, biografická, srovnávací a historická.
Na základě výzkumu je možné shrnout následující závěry:
V. N. Fedorov je typickým zástupcem moderní mužské prózy, pro kterou jsou v dnešní době charakteristické tradiční maskulinita (silný muž a slabá žena) a běžné hrdinství.
Představa hrdiny vznikající při čtení povídek V. N. Fedorova je zcela v souladu s popisovaným typem ruského muže: pracovitý, zpravidla věrný, ochraňující svou milovanou, pečující, pozorný, jednoduchý v komunikaci, nezaujatý atd.
Typy žen V. N. Fedorova v povídkách jsou různorodé: potvora, hysterka, nána, vypočítavá, hýřivá, rozkošná kráska, žena s ocelovým charakterem, silná duchem, atd.
Hlavním tématem povídek je téma vztahu mezi muži a ženami, nejběžnějšími motivy - nevěra, mužské a ženské chtíče.
Stylistika povídek V. N. Fedorova se vyznačuje stručností uměleckých prostředků a syntaxe - úsečností a neúplností vět. Jazyk hlavních postav je moderní a plný žargonů, obsahuje nejen slang, urážlivá slova, ale také mat.
Ráz a styl psaní V. N. Fedorova spisovatele odpovídají této době, a to především komunikaci na internetu na sociálních sítích. Proto jsou povídky autora čtivé, dynamické, čas v nich je prchající, témata jsou koncentrovaná a stlačená, příběhy jsou jednoduché, počet hlavních postav je minimalizován.
Spisovatel se současně zabývá propagací své tvorby a podnikání s nemovitostmi.
Dělá vše samostatně, přes internet, rozmisťuje informace na speciálních stránkách a v sociálních sítích. Sociální síť je pro autora nejen místem k propagaci jeho tvorby a umístění reklamy v oblasti nemovitostí, ale také platformou pro objasnění tvůrčího procesu, osobního života, projevy politických a ideologických názorů, literárních preferencí, stejně tak jako způsob komunikace se čtenářem, získání zpětné vazby.ObhájenoBachelor's thesis is devoted to the study of biography and work of the Russian writer Vadim Nikolayevich Fedorov, who lives in the Czech Republic.
The aim of the work was to reveal the peculiarities of poetics and problems of
V. N. Fedorov's work.
During the study the following methods were used: descriptive, biographical, historical, structural.
The following conclusions were made:
V. N. Fedorov is a bright representative of modern men's prose, which today is characterized by: traditional masculinity (a strong man and a weak woman) and domestic heroism.
The image of the hero that emerges when reading V. N. Feodorov's stories align with the typical Russian man: hardworking, generally faithful,protect and defend his beloved, caring, careful, simple in communication, selfless, etc.
Types of women in the stories of V. N. Feodorov are diverse: bitch, hysterical, fool, mercenary, promiscuous, a charming beauty, a strong-minded, hardy spirit etc.
The central theme of the stories is the relationship between man and woman, the most common motifs are unfaithfulness, male and female lust.
The writing style of V. N. Fedorov's stories are distinguished by the laconic use of artistic means, and syntax - truncation and incompleteness of sentences. The language of the characters is modern and jargonized, containing not only slang, but swear words, as well as filthy words.
The character and writing style of the writer corresponds and are up-to-date with nowadays, especially communication on the Internet, more specifically on social networks. Therefore, the author's stories are readable, dynamic, the timeline is fast-paced, the plots are concentrated and compressed, the stories are simple, the number of characters is minimalized.
The writer is simultaneously engaged in advertising of his works and real estate business. He does it on his own, through the Internet, posting information on special websites and social networks. The social network has become not only a place for the author to promote his work and advertise in real estate, but also a platform for consecration on his creative process, personal life, political and ideological views, literary preferences, as well as a way to communicate with readers and receive feedback
Excitation of SST anomalies in the eastern equatorial Pacific by oceanic optimal perturbations
No full textA generalized stability analysis is used to explore the excitation of sea-surface temperature anomalies in the eastern equatorial Pacific by optimal initial perturbations in temperature and salinity within an ocean general circulation model. We find perturbations that can efficiently modify the SST of the Nino3 region with an approximately 9-month delay. The time interval between the end of March and mid-April is particularly favorable for these perturbations to cause subsequent changes in the eastern equatorial Pacific. This sensitivity is related to two critical factors: during the boreal spring Equinox the heat content of the western equatorial Pacific reaches its seasonal maximum, whereas the zonal winds along the equator relax.The optimal initial anomalies in temperature and salinity have a complex spatial structure extending between 20ºS and 20ºN. This large meridional extent of the anomalies allows for a strong focusing effect - signals from different locations reach the eastern equatorial Pacific simultaneously thus generating a strong transient warming in a relatively small region. Ocean adjustment to the optimal perturbations involves a basin-size Rossby wave that propagates westward and induces a large-scale anomalous eastward advection along the equator, which acts on the mean east-west temperature gradient and gradually warms SST in the east. At the same time, a continuum of Kelvin waves are being excited, which reduce the thermocline slope along the equator and deepen the thermocline in the eastern equatorial Pacific. Thus, the Rossby wave and Kelvin waves work constructively to generate the transient warming of the Nino3 SST. An idealized model with two variables is formulated to illustrate these ideas and, in particular, show the importance of zonal advection feedback for the amplitude and duration of the transient warming. Ultimately, this study highlights the importance of non-normal dynamics for generating an efficient transient growth of SST anomalies in the tropical Pacific even in the absence of coupled ocean-atmosphere interactions
Stability of the Atlantic meridional overturning circulation and stratification in a zonally averaged ocean model: Effects of freshwater flux, Southern Ocean winds, and diapycnal diffusion
No full textThe Atlantic Meridional Overturning Circulation (AMOC) is a crucial component of the global climate system. In this study, using a zonally averaged ocean model, we reexamine the sensitivity of this circulation, and ocean density structure in general, to several types of external forcing. The basin of the model extends from northern high latitudes to Antarctica and includes an implicit representation of a circumpolar channel in the South, and ocean circulation is driven by surface buoyancy fluxes and wind forcing. In contrast to earlier two-dimensional studies of the AMOC, our approach involves a careful treatment of the residual mean circulation (comprising the Eulerian-mean and eddy-induced flows), which is especially important for the Southern Ocean dynamics. Using boundary conditions consistent with present-day observations the model reproduces realistic ocean stratification and meridional overturning. The structure, intensity, and stability of the overturning are then extensively studied using three control parameters: the strength of westerly wind stress over the Southern Ocean, the magnitude of freshwater fluxes imposed on the northern Atlantic, and ocean diapycnal diffusivity. In a realistic parameter range, we estimate the AMOC sensitivity to changes in the Southern Ocean winds on the order of 1 Sv per 20% increase in the wind stress. The overturning also increases with diapycnal diffusivity, but the dependence is weaker than in the absence of the winds. The model can undergo a shutdown of the overturning (subject to a hysteresis) when either the freshwater forcing gradually increases or the wind stress decreases. The hysteresis loop disappears for large values of isopycnal diffusivity. Changes in the AMOC intensity are accompanied by changes in the volume transport of the Antarctic Circumpolar Current. Specifically, the AMOC collapse leads to a strengthening of this transport. Ultimately, our calculations produce stability maps for the steady states of the meridional overturning circulation and provide a general framework that potentially can be used to compare different models, or to understand past abrupt climate changes related to reorganization of the AMOC
The Leading, Interdecadal Eigenmode of the Atlantic Meridional Overturning Circulation in a Realistic Ocean Model
No full textVariations in the strength of the Atlantic meridional overturning circulation (AMOC) are a major potential source of decadal and longer climate variability in the Atlantic. This study analyzes continuous integrations of tangent linear and adjoint versions of an ocean general circulation model [Océan Parallélisé (OPA)] and rigorously shows the existence of a weakly damped oscillatory eigenmode of the AMOC centered in the North Atlantic Ocean and controlled solely by linearized ocean dynamics. In this particular GCM, the mode period is roughly 24 years, its e-folding decay time scale is 40 years, and it is the least-damped oscillatory mode in the system. Its mechanism is related to the westward propagation of large-scale temperature anomalies in the northern Atlantic in the latitudinal band between 30° and 60°N. The westward propagation results from a competition among mean eastward zonal advection, equivalent anomalous westward advection caused by the mean meridional temperature gradient, and westward propagation typical of long baroclinic Rossby waves. The zonal structure of temperature anomalies alternates between a dipole (corresponding to an anomalous AMOC) and anomalies of one sign (yielding no changes in the AMOC). Further, it is shown that the system is nonnormal, which implies that the structure of the least-damped eigenmode of the tangent linear model is different from that of the adjoint model. The “adjoint” mode describes the sensitivity of the system (i.e., it gives the most efficient patterns for exciting the leading eigenmode). An idealized model is formulated to highlight the role of the background meridional temperature gradient in the North Atlantic for the mode mechanism and the system nonnormality.<br/
Unstable AMOC during glacial intervals and millennial variability: The role of mean sea ice extent
No full textA striking feature of paleoclimate records is the greater stability of the Holocene epoch relative to the preceding glacial interval, especially apparent in the North Atlantic region. In particular, strong irregular variability with an approximately 1500 yr period, known as the Dansgaard–Oeschger (D–O) events, punctuates the last glaciation, but is absent during the interglacial. Prevailing theories, modeling and data suggest that these events, seen as abrupt warming episodes in Greenland ice cores and sea surface temperature records in the North Atlantic, are linked to reorganizations of the Atlantic Meridional Overturning Circulation (AMOC). In this study, using a new low-order ocean model that reproduces a realistic power spectrum of millennial variability, we explore differences in the AMOC stability between glacial and interglacial intervals of the 100 kyr glacial cycle of the Late Pleistocene (1 kyr=1000 yr1 kyr=1000 yr). Previous modeling studies show that the edge of sea ice in the North Atlantic shifts southward during glacial intervals, moving the region of the North Atlantic Deep Water formation and the AMOC also southward. Here we demonstrate that, by shifting the AMOC with respect to the mean atmospheric precipitation field, such a displacement makes the system unstable, which explains chaotic millennial variability during the glacials and the persistence of stable ocean conditions during the interglacials
Nikolaj Fedorov i russkaja tradicija platonizma
No full textGünther H. Nikolaj Fedorov i russkaja tradicija platonizma. Studia Russica. 2015;14((V čest´ jubileja Any Chan):155-161
Optimal excitation of AMOC decadal variability: Links to the subpolar ocean
No full textThis study describes the excitation of variability of the Atlantic Meridional Overturning Circulation (AMOC) by optimal perturbations in surface temperature and salinity. Our approach is based on a generalized stability analysis within a realistic ocean general circulation model, which extends the conventional linear stability analysis to transient growth. Unlike methods based on singular value decomposition, our analysis invokes an optimization procedure using Lagrangian multipliers, which is a more general approach allowing us to impose relevant constraints on the perturbations and use linear measures of the AMOC (meridional volume and heat transports).We find that the structure of the optimal perturbations is characterized by anomalies in surface temperature or salinity centered in the subpolar regions of the North Atlantic off the east coasts of Greenland and Canada, south of the Denmark Strait. The maximum impact of such perturbations on the AMOC is reached after 7–9 yr. This is a robust result independent of the perturbations type, the optimization measures, the model surface boundary conditions, or other constraints. The transient growth involves the following mechanism: after the initial (positive) surface density perturbation reaches the deep ocean, it generates a cyclonic geostrophic flow that extracts a zonally-varying temperature anomaly from the mean temperature field in the upper ocean. In turn, the anomalous zonal temperature gradient induces, by thermal wind balance, a northward flow in the upper ocean and a southward flow in the deep ocean, thus strengthening the AMOC. Subsequently, the transient growth gives way to a decaying oscillation corresponding to a damped oceanic eigenmode with a period of about 24 yr. This mode is controlled by westward-propagating large-scale “thermal” Rossby waves, modifying the density field in the North Atlantic and hence the AMOC. Simple estimates show that realistic changes in salinity or temperature in the upper ocean (such as those due to the Great Salinity Anomaly) can induce AMOC variations of several Sverdups via this mechanism, or 10–20% of the mean overturning. An idealized model is formulated to investigate the transient growth and highlight the role of mean convection in communicating surface density anomalies to the deep ocean
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