Ionospheric Joule dissipation as a damping mechanism for high latitude ULF pulsations: Observational evidence     

K.H. Glaßmeier  H. Volpers  W. Baumjohann 《Planetary and Space Science》1984,32(11):1463-1466

On 9 January 1979 an SI-excited pulsation event was observed by the Scandinavian Magnetometer Array. The pulsation period shows a clear variation with latitude which suggests decoupled oscillations of individual magnetic field shells. The pulsation amplitudes exhibit an e-fold decay with the damping rate γ varying both in longitudinal and latitudinal directions. Assuming Joule heating in the ionosphere as the dominant damping mechanism (and thus γ ～ Σ^?1_p) approximate height-integrated Pedersen conductivity profiles were calculated which fit well with previously observed Σ_p distributions. This is interpreted as observational evidence for ionosopheric Joule dissipation as the major damping mechanism for high-latitude ULF-pulsations.  相似文献   

Theorie des Triftstromes und der virtuellen Reibung im Meer     

W. Krauß 《Ocean Dynamics》1965,18(5):193-210

Zusammenfassung Entsprechend der Reynoldsschen Konzeption werden die virtuellen Reibungskr?fte berechnet. Die Orbitalbewegungen der Oberfl?chen- und internen Wellen stellen die st?rksten Abweichungen vom mittleren Strom dar. Der auf diesen Bewegungen basierende Reynoldssche Spannungstensor wird aus dem Gleichungssystem (12) bis (14) ermittelt. Formale L?sungen sind (25) bis (28), wennW(z) aus (24) für beliebigeū(z) bekannt ist. Für Oberfl?chenwellen reduziert sich (24) auf (29) mit der N?herungsl?sung (34). Hieraus folgen (37) und (38). Absch?tzung der Integrale führt für Wellen endlicher Kamml?nge auf (55), woraus die Reibungskr?fte (56) bis (58) folgen. Station?re mittlere Str?mungen sind dann durch (61) beschreibbar. μ, gegeben durch (62), wird in Anlehnung an die bestehende Nomenklatur als “virtueller Reibungskoeffizient” bezeichnet. Er ist durch die Parameter des Seeganges bestimmt. Im Gegensatz zu V. W. Ekman werden Triftstr?me durch (67) bis (69) mit den L?sungen (71), (72) bzw. (73), (74) beschrieben. Aus dem sinusoidalen Verlauf der Reibungskoeffizienten (62) folgt eine Streifenstruktur des Triftstromes, wie sie Abb. 3 in Zuordnung zum Seegang zeigt. Die Geschwindigkeitsverteilung eines Streifens ist in Abb. 2 wiedergegeben. Eine Rechtsablenkung analog zur Ekman-Spirale tritt nicht auf; der Strom setzt stets in Richtung des Windes. Durch Messungen in der Ostsee mit Rhodamin wurde die theoretisch zu erwartende Streifenbildung für verschiedene Windgeschwindigkeiten qualitativ nachgewiesen (Abb. 4 und Tafeln 8 und 9).

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The theory of the drift current and the virtual friction in the sea

Summary According to the Reynolds' procedure, the “turbulent” stresses due to surface and internal waves are computed. Starting from Eqs. (12) to (14) for linear internal and surface waves we get the solutions (25) to (28) withW(z) as a solution of (24) for arbitrary mean currents. For surface waves, (24) reduces to (29) with the approximate solution (34). From this follow (37) and (38). Estimating the integrals, we get (55) for waves of finite crests. From this follow (56) to (58) for the frictional forces due to waves. Stationary mean currents are then described by (61). The coefficient (62) is called “eddy viscosity”. It depends on the wave parameters. In contrast to Ekman's theory, drift currents are described by (67) to (69) with the solutions (71), (72) or (73), (74). Due to the sinusoidal shape of the eddy viscosity coefficients (62) the drift current has a band structure. This structure is shown in Fig. 3. The current distribution within a band is shown in Fig. 2. The current runs always in the direction of the wind, a deflection to the right due to Coriolis force is not observed. The forming of bands has been tested by Rhodamin. The results are in qualitative agreement with the theory (Fig. 4 and Plates 8 and 9).

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La théorie du courant de dérive et du frottement virtuel en mer

Résumé Les forces de frottement virtuelles sont calculées d'après la conception de Reynolds. Les mouvements périodiques dans la couche de surface et les ondes internes constituent les écarts les plus importants par rapport au courant moyen. Le tenseur de Reynolds qui prend pour base ces mouvements, est obtenu au moyen du système d'équations (12) à (14). Les solutions obtenues sont (25) à (28) lorsqu'on conna?tW(z) au moyen de (24) pour desū(z) quelconques. Pour les ondes de surface, (24) se réduit à (29) avec la solution approchée (34); les solutions (37) et (38) s'en déduisent. De l'évaluation de l'intégrale on déduit (55) pour des ondes d'une longueur de crête finie et on en tire les forces de frottement (56) à (58). Des courants moyens stationnaires peuvent alors être décrits au moyen de (61). μ, donné par (62) est appelé ?coefficient de frottement virtuel? suivant les dénominations admises et il est déterminé par les paramètres des vagues. Contrairement à V. W. Ekman les courants de dérive sont décrits par (67) à (69) avec les solutions (71), (72) ou encore (73), (74). Du fait de la forme sinuso?dale prise par les coefficients de frottement (62) le courant de dérive se présente sous forme de bandes comme le montre la fig. 3 d'après l'état de la mer. La fig. 2 indique la distribution des vitesses dans une bande. On ne constate pas de déviation vers la droite analogue à celle de la spirale d'Ekman: le courant suit toujours la direction du vent. Des mesures effectuées en mer Baltique avec de la rhodamine ont confirmé quantitativement la formation des bandes théoriquement prévisibles pour différentes vitesses de vent (fig. 4 et planches 8 et 9).

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Hierzu Tafeln 8 und 9  相似文献   

Interngefüge der Kalifeldspate in einem Ötztaler Gneis     

H. Gruß 《Mineralogy and Petrology》1955,5(3):231-241

Ohne ZusammenfassungMit 18 Gefügediagrammen.  相似文献   

A review of pollutants in the sea-surface microlayer (SML): a unique habitat for marine organisms     

Wurl O  Obbard JP 《Marine pollution bulletin》2004,48(11-12):1016-1030

Boundary layers between different environmental compartments represent critical interfaces for biological, chemical and physical processes. The sea-surface microlayer (uppermost 1-1000 microm layer) forms the boundary layer interface between the atmosphere and ocean. Environmental processes are controlled by the SML, and it is known to play a key role in the global distribution of anthropogenic pollutants. Due to its unique chemical composition, the upper organic film of the SML represents both a sink and a source for a range of pollutants including chlorinated hydrocarbons, organotin compounds, petroleum hydrocarbons, polycyclic aromatic hydrocarbons (PAH) and heavy metals. These pollutants can be enriched in the SML by up to 500 times relative to concentrations occurring in the underlying bulk water column. The SML is also a unique ecosystem, serving as an important habitat for fish eggs and larvae. Concentration ranges and enrichment factors of pollutants in the SML in different areas of the world's oceans have been critically reviewed, together with available toxicity data for marine biota found within the SML. Overall, the SML is highly contaminated in many urban and industrialized areas of the world, resulting in severe ecotoxicological impacts. Such impacts may lead to drastic effects on the marine food web and to fishery recruitment in coastal waters. Studies of the toxicity of fish eggs and larvae exposed to the SML contaminants have shown that the SML in polluted areas leads to significantly higher rates of mortality and abnormality of fish embryos and larvae.  相似文献   

Characterization of Compass M-1 signals   总被引：7，自引：4，他引：3  

André Hauschild  Oliver Montenbruck  Jean-Marie Sleewaegen  Lennard Huisman  Peter J. G. Teunissen 《GPS Solutions》2012,16(1):117-126

An analysis of observations from China’s first medium earth orbit satellite Compass M-1 is presented, with main focus on the first orbit and clock solution for this satellite. The orbit is computed from laser ranging measurements. Based on this orbit solution, the apparent clock offset is estimated using measurements from two GNSS receivers, which allow Compass tracking. The analysis of the clock solutions reveals unexpectedly high dynamics in the pseudorange and carrier-phase observations. Furthermore, carrier-to-noise density ratio, pseudorange noise, and multipath are analyzed and compared to GPS and GIOVE. The results of the clock analysis motivate further research on the signals of the geostationary satellites of the Compass constellation.  相似文献   

Critical distances: Comparing measures of spatial accessibility in the riverine landscapes of Peruvian Amazonia     

Maria Salonen  Tuuli ToivonenJean-Michel Cohalan  Oliver T. Coomes 《Applied geography (Sevenoaks, England)》2012,32(2):501-513

Quantitative measures of accessibility are increasingly used in land cover change modeling and in assessing human pressure on the environment. In riverine Amazonia the significance of physical accessibility for biodiversity, land use patterns and economic livelihoods is widely acknowledged, but attempts to quantify accessibility in practice have been few in number. In this study we compare different distance- and frequency-based measures of spatial accessibility and develop a quantitative model of accessibility patterns for the north-eastern Peruvian Amazonia where rivers form the core of the transportation network. We model accessibility between the rural areas of the Loreto region and the capital city of Iquitos, using different distance algorithms in a geographic information system, and complement the distance model with information on river boat frequencies and transport capacities. Patterns of accessibility are visualized in terms of potential production zones for different types of agricultural and non-timber forest products.This study demonstrates how results from different accessibility measures vary considerably. The mean Euclidean distance to Iquitos is almost 270 km, the mean network distance nearly 760 km and the mean travel time 70 h. Observed network distances from validation points to Iquitos are on average 1.6 times longer than Euclidean distances, and for the whole study area, the average ratio between modeled network distances and Euclidean distances is 3.1. The correlation between network distances and time distances is very strong, but time distances are relatively shorter along the major channels where boat traffic is considerably faster than along narrow, tightly meandering rivers. Measures of boat frequency and transport capacity show that availability of transport possibilities is highly varying across the region. These measures provide insights into the ’thickness’ of trade, indicating the level of market integration for riverine settlements. We conclude that quantifying accessibility in an environment like Peruvian Amazonia requires measures that take into account the spatial structure and dynamic nature of the riverine transportation network. Time as a unit of distance provides the most relevant measure of accessibility in the Amazonian context, where many human actions and traditional livelihoods are controlled by travel times between the regional core and the hinterland.  相似文献   

Monte Carlo Markov Chain parameter estimation in semi-analytic models of galaxy formation     

Bruno M. B. Henriques  Peter A. Thomas  Seb Oliver  Isaac Roseboom 《Monthly notices of the Royal Astronomical Society》2009,396(1):535-547

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Tidal effects and the environment dependence of halo assembly     

Oliver Hahn  Cristiano Porciani  Avishai Dekel  C. Marcella Carollo 《Monthly notices of the Royal Astronomical Society》2009,398(4):1742-1756

We explore a possible origin for the puzzling anti-correlation between the formation epoch of galactic dark-matter haloes and their environment density. This correlation has been revealed from cosmological N -body simulations and is in conflict with the extended Press–Schechter model of halo clustering. Using similar simulations, we first quantify the straightforward association of an early formation epoch with a reduced mass-growth rate at late times. We then find that a primary driver of suppressed growth, by accretion and mergers, is tidal effects dominated by a neighbouring massive halo. The tidal effects range from a slowdown of the assembly of haloes due to the shear along the large-scale filaments that feed the massive halo to actual mass loss in haloes that pass through the massive halo. Using the restricted three-body problem, we show that haloes are prone to tidal mass loss within 1.5 virial radii of a larger halo. Our results suggest that the dependence of the formation epoch on environment density is a secondary effect induced by the enhanced density of haloes in filaments near massive haloes where the tides are strong. Our measures of assembly rate are particularly correlated with the tidal field at high redshifts   z ∼ 1  .  相似文献   

Time damping of non-adiabatic MHD slow and thermal waves in a prominence medium: Effect of a background flow     

M. Carbonell  R. Oliver  J.L. Ballester 《New Astronomy》2009,14(3):277-284

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Origin of fault domains and fault-domain boundaries (transfer zones and accommodation zones) in extensional provinces: Result of random nucleation and self-organized fault growth     

Roy W. Schlische  Martha Oliver Withjack   《Journal of Structural Geology》2009,31(9):910

In many extensional provinces, large normal faults dip in the same direction forming fault domains. Features variously named transfer faults, transfer zones, and accommodation zones (hereafter non-genetically referred to as fault-domain boundaries) separate adjacent fault domains. Experimental modeling of distributed extension provides insights on the origin, geometry, and evolution of these fault domains and fault-domain boundaries. In our scaled models, a homogeneous layer of wet clay or dry sand overlies a latex sheet that is stretched orthogonally or obliquely between two rigid sheets. Fault domains and fault-domain boundaries develop in all models in both map view and cross-section. The number, size, and arrangement of fault domains as well as the number and orientation of fault-domain boundaries are variable, even for models with identical boundary conditions. The fault-domain boundaries in our models differ profoundly from those in many published conceptual models of transfer/accommodation zones. In our models, fault-domain boundaries are broad zones of deformation (not discrete strike-slip or oblique-slip faults), their orientations are not systematically related to the extension direction, and they can form spontaneously without any prescribed pre-existing zones of weakness. We propose that fault domains develop because early-formed faults perturb the stress field, causing new nearby faults to dip in the same direction (self-organized growth). As extension continues, faults from adjacent fault domains propagate toward each another. Because opposite-dipping faults interfere with one another in the zone of overlap, the faults stop propagating. In this case, the geometry of the domain boundaries depends on the spatial arrangement of the earliest formed faults, a result of the random distribution of the largest flaws at which the faults nucleate.  相似文献