Dust particle and solar radiation     

J. Klačka  J. Kaufmannová 《Earth, Moon, and Planets》1993,61(1):63-65

Influence of the solar radiation (electromagnetic and corpuscular - solar wind) on the motion of the interplanetary dust particle is investigated. The ratio time of inspiralling toward the Sun: time of inspiralling neglecting the change of mass of the particle is presented as a function of initial eccentricities.  相似文献   

The role of bathymetry and directional wave conditions on observed crescentic bar dynamics     

Rinse L. de Swart  Francesca Ribas  Gonzalo Simarro  Jorge Guillén  Daniel Calvete 《地球表面变化过程与地形》2021,46(15):3252-3270

Nearshore sandbars are important features in the surf zone of many beaches because they strongly influence the mean circulation and evolving morphology. Due to variations in wave conditions, sandbars can experience cross-shore migration and vary in shape from alongshore uniform (shore-parallel) to alongshore rhythmic (crescentic). Sandbar dynamics have been studied extensively, but existing observational studies usually do not quantify the processes leading to crescentic bar formation and straightening. This study analyses the dynamics of crescentic bar events at the fetch-limited beach of Castelldefels (northwestern Mediterranean Sea, Spain) using 7.5 years of hourly time-exposure video images and detailed wave conditions. The results show that, despite the generally calm wave conditions, the sandbars were very dynamic in the cross-shore and longshore directions. They often migrated rapidly offshore during storms (up to 70 m in one day) and more slowly onshore during post-storm conditions. Crescentic bars were often present at the study site (48% of the time), but only when the sandbar was at least 10 m from the shoreline. They displayed a large variability in wavelengths (100–700 m), alongshore migration speeds (0–50 m/day) and cross-shore amplitudes (5–20 m). Wavelengths increased for larger bar–shoreline distances and the alongshore migration speeds were strongly correlated with the alongshore component of the radiation stresses. Crescentic patterns typically developed during low–medium energetic waves with limited obliquity ( $\theta \lesssim 20$° at 10 m depth), while bar straightening occurred during medium–high energetic waves with strong oblique angles of incidence ( $\theta \gtrsim 15$°). Overall, this study provides further proof for the important role of wave direction in crescentic bar dynamics and highlights the strong dependence of crescentic bar development on the initial bathymetric configuration.  相似文献   

A multifractal analysis of lidar measured water vapour     

J. E. Pinzón  C. E. Puente  M. B. Parlange  W. Eichinger 《Boundary-Layer Meteorology》1995,76(4):323-347

Accurate and fast-response measurements of space-time observations of specific humidity were made above a drying land surface at the University of California at Davis, using the Los Alamos water Raman-lidar. In an attempt to quantify the space-time intermittency features of turbulent flows in the lower atmosphere, a multifractal analysis of these water vapour measurements was performed. The structure of the specific humidity, (x, t), was analyzed quantifying a scalar gradient measure both in time and space, for all possible one-dimensional cuts, i.e. and . The results confirm the multifractal nature of this scalar gradient measure (a type of scalar dissipation rate) and show that humidity measurements at fixed times (x) are more intermittent (e.g. have less entropy dimension) than those at fixed locations in space (t). Similar multifractal behaviour of the spatial data, with and without a transformation from the observed wind velocities, supports the validity of Taylor's hypothesis for the studied fields.  相似文献   

Geochemical and structural evolution of micas in the Rožná and Dobrá Voda pegmatites,Czech Republic     

P. Černý  R. Chapman  J. Staně  M. Nová  H. Baadsgaard  M. Rieder  M. Kavalová  L. Ottolini 《Mineralogy and Petrology》1995,55(1-3):177-201

Summary The chemistry, structural parameters, polytypism, optical properties and Rb-Sr isotopes were examined in 11 to 60 samples of biotite, muscovite and lepidolite from the pegmatites at Roná (the type locality of lepidolite; 323 ± 4Ma) and Dobrá Voda (306 ± 9Ma) in western Moravia. At both localities, early endocontact biotite is followed inwards by muscovite and lepidolite, which is concentrated in and around the core. At Roná, a 1M lepidolite follows after 2M₁ muscovite but all later generations of lepidolite are 2M₂, close to Tri₅₀ Ply₅₀ and in part associated with muscovite 2M₁. At Dobrá Voda, all lepidolite types are 1M and free of muscovite, and the late varieties approximate Tri₃₀ Ply₇₀. At both localities, a trend of increasing HF is indicated during the progress of mica crystallization, culminating in precipitation of topaz. Polytypism of lepidolite is not correlatable with any compositional or growth feature, or their combination. Throughout the mica crystallization, Rb/Cs decreases but K/Rb becomes reversed after an initial decrease. Boron is partitioned preferentially into muscovite (up to 1.10 wt.% B₂O₃) but Be, Zn, Mn and Sc are enhanced in lepidolite. A slight increase in Fe, Ba and Cl in the last generation of lepidolite might be possibly due to mixing of residual pegmatite fluids with metamorphic pore solutions.

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Geochemische und strukturelle Entwicklung der Glimmer in den Pegmatiten von Roná und Dobrá Voda, Tschechische Republik

Zusammenfassung In 11 bis 60 Proben von Biotit, Muskovit und Lepidolith aus den Pegmatiten von Roná (Typlokalität des Lepidoliths; 323 ± 9 Ma) in Westmähren wurden Chemie, Struktur-parameter, Polytypie, optische Eigenschaften und Rb-Sr-Isotopie untersucht. An beiden Lokalitäten wird früher Biotit an Endokontakten nach Innen von Muskovit und Lepidolith gefolgt, letzterer ist in und um den Kern konzentriert. In Roná folgt 1M-Lepidolith auf 2M₁-Muskovit, aber alle späteren Lepidolithgenerationen sind 2M₂, nahe Tri₅₀Ply₅₀ und zum Teil mit 2M₁-Muskovit vergesellschaftet. In Dobrá Voda sind alle Lepidolithe vom Typ 1M und frei von Muskovit, die späten Varietäten kommen Tri₅₀Ply₅₀ nahe. An beiden Lokalitäten ist während des Fortschreitens der Glimmerkristallisation eine Tendenz von steigendem HF angezeigt, die in der Ausfällung von Topas ihren Höhepunkt findet. Die Polytypie des Lepidoliths kann nicht mit irgendeiner Eigenheit der Zusammensetzung oder des Wachstums korreliert worden, auch nicht mit einer Kombination von diesen. Während der ganzen Glimmerkristallisation nimmt Rb/Cs ab, aber die Tendenz von K/Rb ändert sich nach anfänglichem Abfall. Das Bor verteilt sich bevorzugt auf den Muskovit (bis zu 1.10 Gew. -% B₂O₃), aber die Be-, Zn-, Mn- und Sc-Gehalte sind im Lepidolith erhöht. Ein leichter Ansteig von Fe, Ba und Cl in der letzten Lepidolithgeneration könnte vielleicht durch eine Mischung von pegmatitischen Restlösungen mit metamorphen Porenlösungen verursacht sein.

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With 9 Figures  相似文献   

A topological approach to understand a multiple-loop solar flare     

L. G. Bagalá  C. H. Mandrini  M. G. Rovira  P. Démoulin  J. C. Hénoux 《Solar physics》1995,161(1):103-121

We analyze the UV and X-ray data obtained by the SMM satellite for the flare starting at 02:36 UT on November 12, 1980 in AR 2779. From a detailed revision of the Ov emission, we find that the observations are compatible with energy being released in a zone above the magnetic inversion line of the AR intermediate bipole. This energy is then transported mainly by conduction towards the two distant kernels located in the AR main bipole. One of these kernels is first identified in this paper. Accelerated particles contribute to the energy transport only during the impulsive phase.We model the observed longitudinal magnetic field by means of a discrete number of subphotospheric magnetic poles, and derive the magnetic field overall topology. As in previous studies of chromospheric flares, the Ov kernels are located along the intersection of the computed separatrices with the photosphere. Especially where the field-line linkage changes discontinuously, these kernels can be linked in pairs by lines that extend along separatrices. Our results agree with the hypothesis of magnetic energy released by magnetic reconnection occurring on separatrices.  相似文献   

Kleť minor planet discovery frequency by months (comparison)     

J. Tichá  M. Tichý  Z. Moravec 《Earth, Moon, and Planets》1995,68(1-3):579-583

Abstrakt The Kle search programme for minor planets using 0,63m Maksutov camera of Kle Observatory was begun in 1977 as a long-term project continuing up to the present day. The discovery frequency according to seasons in the year shows multiple differences between particular months.The comparison with the number of observing nights and obtained search plates; weather conditions and other influences will be discussed. The Kle minor planet discovery frequency also will be compared with the data base of all numbered minor planets.  相似文献   

A multivariate statistical and geostatistical study on the geochemistry of allochtonous karst bauxite deposits in Hungary     

Bárdossy  George  Kovács  Ó. 《Natural Resources Research》1995,4(2):138-153

A geochemical evaluation of the Szc-Halimba-Kisld area, Hungary, covering an area of more than 200 km² is presented using different statistical and geostatistical methods. The study area is a representative example of allochtonous karst bauxite accumulation. The three groups of deposits studied here have been explored and mined since 1950. Several thousand boreholes have been drilled, and bauxite cores were analyzed for the five main chemical components. A total of 80,000 pleces of analytical data were processed, followed by a geological examination of borehole logs and of mining excavations.The quantitative geochemical evaluation of the data set led to both geochemical and practical results: The geochemical behavior of the allochtonous, clastic karst bauxite deposits differs essentially from that of the autochtonous and parautochtonous ones, as well as that of the lateritic bauxite deposits. The deposits of the study area can be split into several subsequent geochemical-sedimentological units, each representing an event of bauxite transport and accumulation. Clear regional patterns can be revealed in the composition of these units. The geostatistically measured chemical variability of the geochemical units is rather different, the lowest units showing the smallest variability. The interrelations of the main chemical components are weaker and more irregular in the studied deposits than in the autochtonous lateritic bauxite deposits. Additional local genetic features, such as transport routes, can be delineated by the methods applied. Within each deposit, local changes of chemical composition and of its variability can be determined more precisely. These results can be used in bauxite prospecting and exploration, because areas of high or low bauxite quality can be predicted.  相似文献   

On the discrepancy between the magnetic D-component and the overhead horizontal current at high-latitudes     

L. Jalonen  T. Nygrén 《Planetary and Space Science》1979,27(7):1027-1032

The discrepancy between the overhead E-region current and the magnetic D-component is studied using data obtained by the Chatanika incoherent scatter radar (L = 5.6). The F-region horizontal current is estimated to be too small to cause the observed D-deflection. Also, the assumption that the magnetic effects of the Pedersen and field-aligned currents cancel each other on the ground is shown to be inadequate to solve the problem. The significance of the inclination angle in the data analysis and the importance of the field-aligned current sheets are discussed.  相似文献   

A model of the origin of the Jovian ring     

E. Grün  G. Morfill  G. Schwehm  T.V. Johnson 《Icarus》1980,44(2):326-338

Starting with the assumption that the micron-sized particles which make up the bright Jovian ring are fragments of erosive collisions between micrometeoroid projectiles and large parent bodies, a physical model of the ring is calculated. The physics of high-velocity impacts leads to a well-defined size distribution for the ejecta, the optical properties of which can be compared with observation. This gives information on the ejecta material (very likely silicates) and on the maximum size of the projectiles, which turns out to be about 0.1 μm. The origin of these projectiles is discussed, and it is concluded that dust particles ejected in volcanic activity from Io are the most likely source. The impact model leads quite naturally to a distribution in ejecta sizes, which in turn determines the structure of the ring. The largest ejecta form the bright ring, medium-sized ejecta form a disk extending all the way to the Jovian atmosphere, and the small ejecta form a faint halo, the structure of which is dominated by electromagnetic forces. In addition to the Io particles, interaction with interplanetary micrometeoroids is also considered. It is concluded that μm-sized ejecta from this source have ejection velocities which are several orders of magnitude too large, and thus cannot contribute significantly to the observed bright ring. However, the total mass ejection rate is significant. Destruction of these ejecta by the Io particles may provide additional particles for the halo.  相似文献   

Motions in the solar atmosphere associated with the white light flare of 11 July 1978     

L. Dezső  Lidia Gesztelyi  L. Kondás  Ágnes Kovács  S. Rostás 《Solar physics》1980,67(2):317-338

Series of white light heliograms and oft- and on-band H filtergrams have been obtained, with an average spatial resolution of 1, to study the flare active McMath region 15403 on 11 July, 1978. A great number of accurate heliographic positions were determined for the umbrae, the white light flare patches and several bright H flare knots, as well as along the principal zero filament and an arch prominence. Using the measured heliographic coordinates of these objects their motions could be analyzed in some detail. The velocities of several different objects could be deduced from the coordinates. Since the heliocentric angle of the region was about 45°, the variation in apparent heliographic coordinates also enabled some variations in heights to be determined.It is pointed out that the flare when fully developed, consisted almost entirely of loops. The zero filament which was activated prior to the flare ran between two umbrae of common penumbra and opposite polarity, one belonging to an old, the other to a new spot group. The white light flare developed on both sides of the filament where it passed between these two umbrae; it was also the place where the flare started. Observational evidence appears to indicate that the erupted filament re-formed from below.An indication has been found that there was a link between the motion of some umbrae and the major flare occurrence.  相似文献