Early Warning Signals for Regime Transition in the Stable Boundary Layer: A Model Study     

I. G. S. van Hooijdonk  A. F. Moene  M. Scheffer  H. J. H. Clercx  B. J. H. van de Wiel 《Boundary-Layer Meteorology》2017,162(2):283-306

The evening transition is investigated in an idealized model for the nocturnal boundary layer. From earlier studies it is known that the nocturnal boundary layer may manifest itself in two distinct regimes, depending on the ambient synoptic conditions: strong-wind or overcast conditions typically lead to weakly stable, turbulent nights; clear-sky and weak-wind conditions, on the other hand, lead to very stable, weakly turbulent conditions. Previously, the dynamical behaviour near the transition between these regimes was investigated in an idealized setting, relying on Monin–Obukhov (MO) similarity to describe turbulent transport. Here, we investigate a similar set-up, using direct numerical simulation; in contrast to MO-based models, this type of simulation does not need to rely on turbulence closure assumptions. We show that previous predictions are verified, but now independent of turbulence parametrizations. Also, it appears that a regime shift to the very stable state is signaled in advance by specific changes in the dynamics of the turbulent boundary layer. Here, we show how these changes may be used to infer a quantitative estimate of the transition point from the weakly stable boundary layer to the very stable boundary layer. In addition, it is shown that the idealized, nocturnal boundary-layer system shares important similarities with generic non-linear dynamical systems that exhibit critical transitions. Therefore, the presence of other, generic early warning signals is tested as well. Indeed, indications are found that such signals are present in stably stratified turbulent flows.  相似文献   

Metasomatic events recorded in ultramafic xenoliths from the Hyblean area (Southeastern Sicily, Italy)     

Vittorio Scribano  Marco Viccaro  Renato Cristofolini  Luisa Ottolini 《Mineralogy and Petrology》2009,95(3-4):235-250

Three types of ultramafic xenoliths from the Hyblean area (Sicily) show prime evidence for mantle metasomatism, namely: 1) Spinel-facies depleted harzburgite veined by phlogopite-bearing clinopyroxenite; 2) Amphibole-bearing harzburgite; and 3) Al-spinel websterite. (2) and (3) exhibit glassy pockets having respectively mugearitic and basanitic compositions, but a little amount of glass with low Ca and very low alkalis in (2). Glasses generally show trace element distributions consistent with the partial melting of pargasite-dominated mineral assemblages. Abundant Ca-Mg-carbonate globules immersed in these glassy pockets testify to immiscibility between silicate and carbonatite melts. Silicate melts and hydrous-silicate supercritical fluids, which underwent phase separation during fluxing throughout the semi-brittle lithospheric mantle, may account for such metasomatizing processes. The nature and abundance of some fluid-mobile elements in glasses and hydrous minerals (especially the Ca-poor glass, with B?=?59 ppm, Li?=?27 ppm, Ba?=?700 ppm and phlogopite, with Ba?=?8,465 ppm, Sr?=?260 ppm, F?=?5,700 ppm) suggest that some hydrous fluids may derive from hydrothermally altered oceanic crust. Conversely, metasomatizing silicate melts probably have a deep-seated origin. These results confirm previous suggestions on the key role of mantle metasomatism in the origin of some alkaline Hyblean magmas.  相似文献   

Modelling a cohesive‐frictional debris flow: an experimental,theoretical, and field‐based study     

Fabio Vittorio De Blasio  Hedda Breien  Anders Elverhøi 《地球表面变化过程与地形》2011,36(6):753-766

The rheology of debris flows is difficult to characterize owing to the varied composition and to the uneven distribution of the components that may range from clay to large boulders, in addition to water. Few studies have addressed debris flow rheology from observational, experimental, and theoretical viewpoints in conjunction. We present a coupled rheological‐numerical model to characterize the debris flows in which cohesive and frictional materials are both present. As a first step, we consider small‐scale artificial debris flows in a flume with variable percentages of clay versus sand, and measure separately the rheological properties of sand–clay mixtures. A comparison with the predictions of a modified version of the numerical model BING shows a reasonable agreement between measurements and simulations. As application to a field case, we analyse a recent debris flow that occurred in Fjærland (Western Norway) for which much information is now available. The event was caused by a glacial lake outburst flood (GLOF) originating from the failure of a moraine ridge. In a previous contribution (Breien et al., Landslides, 2008 , 5: 271–280) we focused on the hydrological and geomorphological aspects. In particular we documented the marked erosion and reported the change in sediment transport during the event. In contrast to the laboratory debris flows, the presence of large boulders and the higher normal pressure inside the natural debris flow requires the introduction of a novel rheological model that distinguishes between mud‐to–clast supported material. We present simulations with a modified BING model with the new cohesive‐frictional rheology. To account for the severe erosion operated by the debris flow on the colluvial deposits of Fjærland, we also suggest a simple model for erosion and bulking along the slope path. Numerical simulations suggest that a self‐sustaining mechanism could partly explain the extreme growth of debris flows running on a soft terrain.  相似文献   

HTP2₁/c–C2/c phase transition and kinetics of Fe²⁺–Mg order–disorder of an Fe-poor pigeonite: implications for the cooling history of ureilites     

Matteo Alvaro  Fernando Cámara  M. Chiara Domeneghetti  Fabrizio Nestola  Vittorio Tazzoli 《Contributions to Mineralogy and Petrology》2011,162(3):599-613

A natural Ca-poor pigeonite (Wo₆En₇₆Fs₁₈) from the ureilite meteorite sample PCA82506-3, free of exsolved augite, was studied by in situ high-temperature single-crystal X-ray diffraction. The sample, monoclinic P2₁/c, was annealed up to 1,093°C to induce a phase transition from P2₁/c to C2/c symmetry. The variation with increasing temperature of the lattice parameters and of the intensity of the b-type reflections (h + k = 2n + 1, present only in the P2₁/c phase) showed a displacive phase transition P2₁/c to C2/c at a transition temperature T _Tr = 944°C, first order in character. The Fe–Mg exchange kinetics was studied by ex situ single-crystal X-ray diffraction in a range of temperatures between the closure temperature of the Fe–Mg exchange reaction and the transition temperature. Isothermal disordering annealing experiments, using the IW buffer, were performed on three crystals at 790, 840 and 865°C. Linear regression of ln k _D versus 1/T yielded the following equation: ln k_\textD = - 3717( ±416)/T(K) + 1.290( ±0.378);    (R² = 0.988) \ln \,k_{\text{D}} = - 3717( \pm 416)/T(K) + 1.290( \pm 0.378);\quad (R^{2} = 0.988) . The closure temperature (T _c) calculated using this equation was ∼740(±30)°C. Analysis of the kinetic data carried out taking into account the e.s.d.'s of the atomic fractions used to define the Fe–Mg degree of order, performed according to Mueller’s model, allowed us to retrieve the disordering rate constants C ₀ K _dis⁺ for all three temperatures yielding the following Arrhenius relation: ln( C₀ K_\textdis ⁺ ) = ln K₀ - Q/(RT) = 20.99( ±3.74) - 26406( ±4165)/T(K);    (R² = 0.988) \ln \left( {C_{0} K_{\text{dis}}^{ + } } \right) = \ln \,K_{0} - Q/(RT) = 20.99( \pm 3.74) - 26406( \pm 4165)/T(K);\quad (R^{2} = 0.988) . An activation energy of 52.5(±4) kcal/mol for the Fe–Mg exchange process was obtained. The above relation was used to calculate the following Arrhenius relation modified as a function of X _Fe (in the range of X _Fe = 0.20–0.50): ln( C₀ K_\textdis ⁺ ) = (21.185 - 1.47X_\textFe ) - \frac(27267 - 4170X_\textFe )T(K) \ln \left( {C_{0} K_{\text{dis}}^{ + } } \right) = (21.185 - 1.47X_{\text{Fe}} ) - {\frac{{(27267 - 4170X_{\text{Fe}} )}}{T(K)}} . The cooling time constant, η = 6 × 10⁻¹ K⁻¹ year⁻¹ calculated on the PCA82506-3 sample, provided a cooling rate of the order of 1°C/min consistent with the extremely fast late cooling history of the ureilite parent body after impact excavation.  相似文献   

Depositional processes on oceanic island shelves – Evidence from storm‐generated Neogene deposits from the mid‐North Atlantic     

Ricardo P. Meireles  Rui Quartau  Ricardo S. Ramalho  Ana C. Rebelo  José Madeira  Vittorio Zanon  Sérgio P. Ávila 《Sedimentology》2013,60(7):1769-1785

Oceanic islands – such as the Azores in the mid‐North Atlantic – are periodically exposed to large storms that often remobilize and transport marine sediments along coastlines, and into deeper environments. Such disruptive events create deposits – denominated tempestites – whose characteristics reflect the highly dynamic environment in which they were formed. Tempestites from oceanic islands, however, are seldom described in the literature and little is known about storm‐related sediment dynamics affecting oceanic island shelves. Therefore, the geological record of tempestite deposits at oceanic islands can provide invaluable information on the processes of sediment remobilization, transport and deposition taking place on insular shelves during and after major storms. In Santa Maria Island (Azores), a sequence of Neogene tempestite deposits was incorporated in the island edifice by the ongoing volcanic activity (thus preserved) and later exposed through uplift and erosion. Because it was overlain by a contemporary coastal lava delta, the water depth at the time of deposition could be inferred, constituting an excellent case‐study to gain insight on the still enigmatic processes of insular shelf deposition. Sedimentological, palaeontological, petrographic and palaeo‐water depth information allowed the reconstruction of the depositional environment of these sediments. The sequence typifies the characteristics of a tempestite (or successive tempestites) formed at ca 50 m depth, in a steep, energetic open insular shelf, and with evidence for massive sediment remobilization from the nearshore to the middle or outer shelf. The authors claim that cross‐shelf transport induced by storm events is the main process of sediment deposition acting on steep and narrow shelves subjected to high‐energetic environments, such as the insular shelves of open‐sea volcanic islands.  相似文献   

临界转换的早期预警信号   总被引：1，自引：0，他引：1  

Marten Scheffer  George Sugihara  Jordi Bascompte  Victor Brovkin  Vasilis Dakos  Hermann Held  Max Rietkerk  李迎春  闫伟  蒋长胜 《国际地震动态》2009,(9):1-14

从生态系统到金融市场和气候在内的很多复杂动力系统,都会有临界点,在这样的点上系统可能会发生突变,从而演变到一个对立的动力模式上。在这样的临界点到达之前对其进行预测极为困难,但是现在,不同科学领域的研究工作表明,普遍性的早期预警信号有迹可循。对一系列不同类型的系统来说,这些信号会指示是否正在趋近一个临界阈值。  相似文献   

Sicilian serpentinite xenolihs conaining abioic organics wih nanodiamond clusers ans key model for prebioic processes     

Sergei K.Simakov  Vittorio Scribano  Nikolai N.Mel'Nik  Germana Barone 《地学前缘(英文版)》2021,12(1):255-263

Rock fragments from the deepest parts of a buried hydrothermal system belonging to the Mesozoic Tethys Oceanentered as xenoliths in a Miocenic diatreme. hence b...  相似文献   

Facies and Late Triassic fossils in the Roisan zone,Austroalpine Dent Blanche and Mt Mary-Cervino nappe system,NW Alps     

Gloria Ciarapica  Leonsevero Passeri  Franco Bonetto  Giorgio Vittorio Dal Piaz 《Swiss Journal of Geoscience》2016,109(1):69-81

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Sulla portata di un corso d'acqua dedotta dalla profondita' critica     

Prof. Dr. Ing. Vittorio Baggi 《Pure and Applied Geophysics》1942,4(1):106-110

Riassunto Con riferimenti pratici l'A. dimostra come i valori delle portate di fiumi e torrenti dedotti dalle formule relative alla pendenza critica e profondità critica risultano troppo discordi dal vero allorchè non sono soddisfatte tutte le ipotesi dalle quali derivano le formule.

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Zusammenfassung Der Verf. zeigt an Hand von sicheren Beobachtungsdaten, dass die Ergiebigkeitswerte von Flüssen und Bächen welche sich aus der Formeln der kritischen Gefälle und Tiefe ableiten lassen viel zu sehr von der Wirklichkeit abweichen können wenn die Annahmen welche für jene Formeln zugrundegelegt wurden nicht befriedigt sind.

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Sull'impiego dei gravimetri in terreni montagnosi     

Ing. Vittorio Scheffer 《Pure and Applied Geophysics》1941,3(1):194-199

Riassunto L'A. riferisce sugli accorgimenti da tener presente nell' impiego e specialmente nel trasporto dei gravimetri in terreni montagnosi: con riguardo ai metodi adottati nei rilievi da lui diretti nell'Appennino tosco-emiliano.

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Zusammenfassung Die Transportmöglichkeiten des Gravimeters und seiner Ausrüstung bei einer detaillierten Messung im Gebirge. Beschreibung einer Messmethode, welche von der geophysikalischen Abteilung der Società Petrolifera Italiana in den toscoemilianischen Appeninen mit gutem Erfolg angewendet wurde. Schweremesser und Ausrüstung wurden dabei auf Maultieren transportiert.

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