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101.
102.
J. van der Plicht B. van Geel S. J. P. Bohncke J. A. A. Bos M. Blaauw A. O. M. Speranza R. Muscheler S. Bjrck 《第四纪科学杂志》2004,19(3):263-269
Accurate chronologies are essential for linking palaeoclimate archives. Carbon‐14 wiggle‐match dating was used to produce an accurate chronology for part of an early Holocene peat sequence from the Borchert (The Netherlands). Following the Younger Dryas–Preboreal transition, two climatic shifts could be inferred. Around 11 400 cal. yr BP the expansion of birch (Betula) forest was interrupted by a dry continental phase with dominantly open grassland vegetation, coeval with the PBO (Preboreal Oscillation), as observed in the GRIP ice core. At 11 250 cal. yr BP a sudden shift to a humid climate occurred. This second change appears to be contemporaneous with: (i) a sharp increase of atmospheric 14C; (ii) a temporary decline of atmospheric CO2; and (iii) an increase in the GRIP 10Be flux. The close correspondence with excursions of cosmogenic nuclides points to a decline in solar activity, which may have forced the changes in climate and vegetation at around 11 250 cal. yr BP. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
103.
An analytical model for the constant-head pumping test is developed for a partially penetrating well that has a finite thickness skin, and intersects a single vertical fracture. In the model, the fracture is fully confined and flow occurs only in the fracture. The model is developed using Laplace transform and finite Fourier transform methods. The model is to be used for analysing well test data from vertically fractured media and for verifying numerical models. Dimensionless curves are used to study the effects of a finite thickness skin and a partially penetrating wellbore. In the presence of a finite thickness skin, or a partially penetrating wellbore, a typical flow response for the constant-head pumping test has three distinct periods of flow corresponding to small-, intermediate- and large-time. Small- and large-time approximations are presented for the model. For tests where the wellbore is fully penetrating, or the partial penetration ratio is known, these approximations can be used to analyse field data. 相似文献
104.
M. A. J. Snijders 《Astrophysics and Space Science》1987,130(1-2):243-254
The 1985 outburst of the bright, recurrent nova RS Oph was almost simultaneously observed at X-ray, UV, optical, IR and radio frequencies at many epochs. The abundances in the ejected shell and the development of the bolometric luminosity as a function of time suggest that the cause of the outburst is a nuclear runaway on a massive white dwarf.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Development, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986. 相似文献
105.
E. F. Arias C. Boucher M. Feissel J. -F. Lestrade 《Astrophysics and Space Science》1991,177(1-2):187-192
The relative orientations of various VLBI celestial reference frames are evaluated on the basis of coordinate differences of common sources. It is shown that an accuracy better than 0.001 can be achieved. Possible regional deformations in the different catalogues are investigated; they are found to reach a few 0.001 in some restricted zones. The application of these studies to the realisation of a combined celestial reference frame consistent with the BIH Terrestrial System is outlined. 相似文献
106.
J. Drimmel 《Meteorology and Atmospheric Physics》1964,14(2):213-217
Zusammenfassung Die bisher ungeklärte Winter-Anomalie der D-Schicht sowie die explosionsartigen Erwärmungen der Hochstratosphäre im Winter können durch Staubpartikel interplanetaren Ursprungs (Meteorströme) hervorgerufen werden. Eine Anlagerung von Elektronen an die Staubteilchen in der Exosphäre bewirkt das Einfangen der kleinsten Partikel durch das erdmagnetische Feld und verhindert so ihr Verglühen in der Ionosphäre. Durch Sedimentation und turbulente Diffusion gelangt der Meteorstaub bis in die Ozonosphäre, wo er oxydiert wird und so eine plötzliche Wärmeentwicklung zur Folge hat. Die angelagerten Elektronen exosphärischen Ursprungs können bei zeitgerechter Photoablösung elektromagnetische Wellen dämpfen und so die Winter-Anomalie der D-Schicht hervorrufen.
Summary The winter-anomaly of the ionospheric D-region for which no sufficient explanation existed up to now, as well as the explosive warming of the high stratosphere in wintertime are possibly caused by dust particles of inter-planetary origin (meteoric showers). The attachment of electrons on the dust particles in the exosphere causes the magnetic field of the earth to catch the smallest particles and so they do not evaporate in the ionosphere. By sedimentation and turbulent diffusion the meteoric dust reaches the ozonosphere where it is oxidized, which is followed by a sudden development of heat. After photo-detachment in due time the formerly attached electrons of exospheric origin are able to damp electro-magnetic waves and by this they cause the winter-anomaly of the D-region.
Résumé L'anomalie de la couche D — inexplicable jusqu'ici — ainsi que les hausses prodigieusement rapides de la température de la haute stratosphère, deux phénomènes particuliers de l'hiver, peuvent être provoquées par des particules de poussière d'origine interplanétaire (courants de météorites). Des électrons adhérant, dans l'exosphère, aux grains de poussière permettent l'entraînement des plus petites particules par le champ magnétique terrestre et empèchent ainsi leur désintégration dans l'ionosphère. Par sédimentation et diffusion turbulente, la poussière cosmique parvient ensuite jusque dans l'ozonosphère où elle est oxydée. Il en résulte alors un dégagement subit de chaleur. Les électrons d'origine exosphérique adhérant à la poussière cosmique peuvent atténuer, s'ils s'en détachent en temps opportun sous l'effet du rayonnement solaire, les ondes électromagnétiques et provoquer ainsi l'anomalie d'hiver de la couche D.相似文献
107.
D. J. Schove 《Pure and Applied Geophysics》1963,55(1):249-261
Summary The geometry of the principal Upper High (near the Indian Occean) in the 300–100 mb layer appears to account for the Southern Oscillation (S.O.), and models of its behaviour are presented. Significant features of these models include the equatorial points of upper convergence (C) and divergence (D), a pressure discontinuity (CNDS) forming «arcs» and an «enclosure» around the high, and, lastly, encircling «crescents» both outside and inside the enclosure. The geography of the seasonal sucession can thus—in a qualitative manner—be interpreted in the light of known wind and contour patterns near the tropopause. With a few general principles, the established empirical rules of long-range forecasting then follow by deduction. The models and the terminology are useful likewise in the interpretation of solar-terrestrial relations and of climatic fluctuations. 相似文献
108.
109.
A spatial statistical method has been developed from the well-known Kriging technique in geostatistics, as a way of providing quantitative comparison between a pair of spatial data sets, and a measure for such a comparison. This residual analysis method is applied to oceanographic data in order to compare Iceland-Faeroes Front (IFF) model predictions against appropriate field observations, with an aim to assess the IFF model performance and its prediction accuracy. The method is also used to evaluate the model-generated dynamical variability within the model predictions, as well as the natural variability within the frontal observations. From the results, it has been found that the IFF model is highly robust, and gives better predictions at depth 150–350 m than elsewhere. Within such a depth (i.e. 250–350 m), there is also evidence to suggest that the main frontal region is most active above the IF Ridge. The natural variability obtained from the observations appears to be comparable to the model-generated dynamical variability after 20 days of integration, indicating a certain degree of accuracy in the model predictions. The method reported in this paper could also be extended for further use in model data assimilation. Thus, the work not only demonstrates how spatial statistics can be applied to oceanographic data, but also opens up new statistical tools for data handling in ocean modelling. 相似文献
110.
The wadic project: A comprehensive field evaluation of directional wave instrumentation 总被引:1,自引:0,他引:1
J. Allender T. Audunson S. F. Barstow S. Bjerken H. E. Krogstad P. Steinbakke L. Vartdal L. E. Borgman C. Graham 《Ocean Engineering》1989,16(5-6)
The results of a comprehensive field trial of nearly all commercially available directional wave measurement systems at the Edda field in the North Sea during winter 1985-86 are presented. The results summarize the accuracy of the principal engineering wave parameters from each system and the dependence on sea state. Limiting factors on system performance and operational problems are also included in the assessment. Overall experience has been good with systems utilizing widely different measurement principles returning consistent results. 相似文献