C. P. Escoubert,C. T. Russell,and R. Schmidt (eds.), The Cluster and Phoenix Missions     

Němeček  Zdeněk 《Solar physics》1998,178(2):437-437

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On some problems of the downward continuation of the 5′×5′ mean Helmert gravity disturbance     

W. Sun  P. Vaníček 《Journal of Geodesy》1998,72(7-8):411-420

This research deals with some theoretical and numerical problems of the downward continuation of mean Helmert gravity disturbances. We prove that the downward continuation of the disturbing potential is much smoother, as well as two orders of magnitude smaller than that of the gravity anomaly, and we give the expression in spectral form for calculating the disturbing potential term. Numerical results show that for calculating truncation errors the first 180^∘ of a global potential model suffice. We also discuss the theoretical convergence problem of the iterative scheme. We prove that the 5^′×5^′ mean iterative scheme is convergent and the convergence speed depends on the topographic height; for Canada, to achieve an accuracy of 0.01 mGal, at most 80 iterations are needed. The comparison of the “mean” and “point” schemes shows that the mean scheme should give a more reasonable and reliable solution, while the point scheme brings a large error to the solution. Received: 19 August 1996 / Accepted: 4 February 1998  相似文献   

Model studies of an open-pit mine bottom loaded by artesian water pressure     

J. Trčková 《Environmental Geology》1998,35(4):245-250

 Experimental modelling methods are used for prediction of deformation and groundwater outflows at the bottom of an open-pit mine during the excavation of brown coal. Thermal gas-bearing artesian water exerts an uplift pressure on the impervious subsoil of the coal seam and threatens the stability of the mine bottom. The breakthrough of the mine bottom would seriously affect the groundwater regime and may endanger mining activities. The mining is carried out within the protection zones of the Carlsbad spa springs. Results of model studies are used to determine protective hydrogeological and mining measures for providing the maximum protection for the open-pit mine and the spa springs. Received: 16 August 1996 · Accepted: 9 June 1997  相似文献   

Point source radiation in inhomogeneous anisotropic structures     

Ivan Pšenčík  Telesson Neves Teles 《Pure and Applied Geophysics》1996,148(3-4):591-623

The ray formulae for the radiation from point sources in unbounded inhomogeneous isotropic as well as anisotropic media consist of two factors. The first one depends fully on the type and orientation of the source and on the parameters of the medium at the source. We call this factor the directivity function. The second factor depends on the parameters of the medium surrounding the source and this factor is the well-known geometrical spreading. The displacement vector and the radiation pattern defined as a modulus of the amplitude of the displacement vector measured on a unit sphere around the source are both proportional to the ratio of the directivity function and the geometrical spreading.For several reasons it is desirable to separate the two mentioned factors. For example, there are methods in exploration seismics, which separate the effects of the geometrical spreading from the observed wave field (so-called true amplitude concept) and thus require the proposed separation. The separation also has an important impact on computer time savings in modeling seismic wave fields generated by point sources by the ray method. For a given position in a given model, it is sufficient to calculate the geometrical spreading only once. A multitude of various types of point sources with a different orientation can then be calculated at negligible additional cost.In numerical examples we show the effects of anisotropy on the geometrical spreading, the directivity and the radiation pattern. Ray synthetic seismograms due to a point source positioned in an anisotropic medium are also presented and compared with seismograms for an isotropic medium.  相似文献   

A possible relation between geomagnetic activity and winter air surface temperatures in Prague     

Josef Pýcha  Pavel Hejda  Josef Bochníček 《Studia Geophysica et Geodaetica》1992,36(4):329-337

Summary A possible relation between the 10-day geomagnetic activity, solar activity and temperatures as measured at the meteorological station Prague - Klementinum in 1932–1975 was sought. It was found that: 1) Kp correlates with the surface temperature in Prague substantially better than Wolf's number R. 2) The correlation between Kp and the surface air temperature is not very close, but is significant at the level p=0.9! 3) If the QBO phase is taken into account, the correlations for the January and February decades of the years 1956–1975 improve as in [27] (van Loon, Labitzke).  相似文献   

Superposition of Variscan ductile shear deformation on pre-Variscan mantled gneiss structure (Catherine dome,Erzgebirge, Bohemian massif)     

Bedřich Mlčoch  Karel Schulmann 《International Journal of Earth Sciences》1992,81(2):501-513

Three tectonometamorphic events have been recognized in the crystalline rocks of the Catherine mantled gneiss Dome (CD) in the central Erzgebirge. The first tectonometamorphic event is characterized by the acquisition of a S1–S2 metamorphic foliation, development of F2 isoclinal partly syn-schistose folding and intrusion of early synkinematic granites. P-T conditions correspond to higher amphibolite facies metamorphism and culminate in anatexis. A diapiric intrusion of Cambro-Ordovician muscovite-biotite porphyritic granite has verticalized the S2 foliation and is responsible for the genesis of the classical mantled gneiss dome. Oblate strain and orthorhombic diffuse c-axis patterns are typical of the marginal parts of the dome.The whole rock sequence was subsequently affected by westward oriented heterogeneous Variscan ductile shearing under the conditions reaching amphibolite fades. A strongly non-coaxial deformation has partly overprinted the earlier fabrics in anatectic orthogneiss and produced augen-orthogneiss from porphyritic granite in the central part of the CD dome. Prolate to plane strain fabrics, oblique quartz c-axis patterns and a widespread occurrence of S-C fabrics are the most characteristic features of this phase.

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Zusammenfassung Im Kristallin des Katherinenberg mantled gneiss dome im mittleren Erzgebirge wurde eine dreiphasige tektono-metamorphe Entwicklungsgeschichte nachgewiesen.Das alte Stadium stellt bereits eine polyphase Entwicklung dar. Es wird durch die Anlage eines penetrativen metamorphen Lagenbaus (syn D₁ — syn D₂), durch F₂ früh Isoklinalfalten, sowie durch die Intrusion frühkinematischer z. T. anatektischer Granite charakterisiert. PT-Daten belegen amphibolitfazielle Bedingungen, die lokal zu Anatexis führen.Diapirartige Intrusionen kambro-ordovische, porphyrische Zweiglimmergranite bewirkten eine sehr unterschiedliche z. T. subvertikale Raumlage der regionalmetamorphen Einheiten. Diese Intrusionen des zweiten Stadiums sind verantwortlich für die Entstehung des eigentlichen mantled gneiss dome. Oblat Gefüge und diffuse Kreuzgürtel-Verteilungen der Quarz c-Achsen sind typisch für die Randbereiche dieses Gneisdomes.Während des jüngsten Stadiums prägen bzw. überprägen westvergente duktile Scherprozesse bei Bedingungen der niedriggradigen Amphibolitfazies die Gefüge. Schiefgürtel-Verteilungen der Quarz c-Achsen und S-C Gefüge charakterisieren diese jüngste, variszische Phase.

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Résumé Trois événements tectono-métamorphiques ont été reconnus dans les roches cristallines du dôme de gneiss coiffé de Catherine (Erzgebirge oriental). Le premier de ces événements est caractérisé par l'acquisition d'une foliation S_1–2, le développement de plis isoclinaux F₂ partiellement synschisteux et l'intrusion de granites syntectoniques précoces. Les conditions (P, T) correspondent au facies supérieur des amphibolites et atteignent l'anatexie. L'intrusion diapirique d'un granite à deux micas cambro-ordovicien a verticalisé la foliation S_1–2 et est responsable de la genèse du dôme de gneiss coiffé. Une déformation par aplatissement et des fabriques orthorhombiques diffuses des axes c du quartz caractérisent les zones marginales du dôme.L'ensemble des terrains a été ensuite affecté par un cisaillement ductile varisque hétérogène à vergence ouest, dans les conditions du facies inférieur des amphibolites. Une déformation fortement noncoaxiale a transposé partiellement les structures précoces des orthogneiss anatectiques et a transformé les granites porphyriques de la partie centrale du dôme de Catherine en orthogneiss oeillés. Cette phase est caractérisée par des fabriques obliques pour les axes c du quartz et par de fréquentes structures s-c.

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- . (S₁), f₁ . , . , /, - , S₁ , - . . , , , . - S — .

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Pressure drag on the Dinaric Alps during the ALPEX SOP     

V. Tutiš  B. Ivančan-Picek 《Meteorology and Atmospheric Physics》1991,47(1):73-81

Summary During the ALPEX SOP (March–April, 1982), microbarographic measurements were conducted on the Northern Adriatic as a part of research on the Bora. In this paper the measured pressure field around the Dinaric Alps is used to compute the total pressure drag vectors using Archimedes law.The 3-hourly temporal variations of these drag vectors is examined for different synoptic events. During the anticyclonic calm weather period at the end of March and beginning of April there is evidence of a divrnal drag variation. Regardless of magnitude, the pressure drag vectors seem to be aligned almost perpendicular to the main mountain ridge. During synoptic scale flow developments the drag direction change usually appears steady and slow (1–2 days). However during an exceptionally strong frontal passage (8/9 April) this time scale was much shorter (3–6 hours). The maximae of the pressure drag during SOP are always connected with Bora periods and the magnitudes of the drag values indicate that during these events there is a major sink of atmospheric momentum over the Dinaric Alpine region.With 11 Figures  相似文献   

Book reviews     

V. Karas  J. Horáček  John Dyson 《Astrophysics and Space Science》1991,179(2):335-337

The dispersive characteristic of hydromagnetic surface waves along a plasma-plasma interface when the upper fluid moves with a uniform velocity is discussed. The region of propagation of these waves is shifted above or below depending on whether the basic velocity (uniform)U0.  相似文献   

Lower hybrid resonance spherics     

J. Bošková  F. Jiříček  E. E. Titova  T. A. Yakhnina 《Studia Geophysica et Geodaetica》1990,34(3):269-277

Summary After a fractional-hop whistler, a trace of limited frequency range with somewhat higher dispersion, markedly growing when approaching the lower cutoff frequency, is frequently observed on spectrograms of broadband VLF measurements made by satellites moving in the outer ionosphere. This phenomenon, which we have called LHR spheric, has been studied on VLF measurements made by the Interkosmos-14 satellite in the height range of 500–1700 km. The results show that LHR spherics are created by the same mechanism as LHR whistlers that sometimes appear after ducted whistlers. In this event, it is a part of the electromagnetic energy radiated by a lightning flash which, on passing trough the ionosphere, has been transformed to quasi-electrostatic resonance waves. They reach the satellite in the same way as whistler-mode waves. Transformation of a part of the energy radiated by a lightning flash to electrostatic quasi-resonance waves is possible in the ionosphere due to the scattering of the original whistler wave on small-scale turbulence.  相似文献   

Short Note: Strain invariants     

Petr Vaníček  Erik W. Grafarend  Mustafa Berber 《Journal of Geodesy》2008,82(4-5):263-268

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