Results 1 - 10 of 788
Results 1 - 10 of 788. Search took: 0.025 seconds
|Sort by: date | relevance|
[en] We used a picture of the solar granulation and a picture of the 'Bright Umbral-dots' of a sunspot to deduce separately by a Fourier Transform Power Spectrum method the distributions of their spectral densities. Both pictures are taken as a selected part of a large scale picture of the Sunspot. The comparison of their power spectra is discussed, and displays an important difference in the high-frequency part of the spectrum
[fr]Les spectres de puissance par transformee de Fourier optique ont ete effectues sur deux portions d'un meme cliche de tache solaire: (A) une region relativement homogene de la granulation solaire hors de la tache; (B) la region centrale de la tache montrant les points brillants de l'ombre. On en deduit la variation des densites spectrales, pour la granulation, d'une part, et les points brillants situes dans l'ombre, d'autre part. La comparaison de ces spectres montre une difference importante dans la partie haute frequence
[en] A preliminary communication is presented demonstrating the granular appearance of internal parts of all small and great umbras of the large complex September 1974 sunspot group. The 'bright umbral dots' seem to be central positions of the individual granular cells, or even tops of convective elements that may penetrate into visible layers of the umbra. (author)
[en] The article presents the results of a literature analysis of the methods of compaction of materials, analytical and experimental research on the creation of a roller compacting device and the determination of its operation modes, which provides an efficient preliminary compaction of a composite mixture based on technogenic materials. (paper)
[en] For the period 1966-1978, a negative correlation has been found between the mean center-to-center distance of the granules and solar activity as expressed by the Wolff number or by the radio-flux at 2800 MHz. This behaviour results from a global shrinking of the histogram towards small distances when the activity increases
[fr]On trouve, pour la periode 1966-1978, une correlation negative entre la distance moyenne des centres des granules et l'activite solaire exprimee par le nombre de Wolff ou le flux radio a 2800 MHz. Ce comportement resulte d'une contraction d'ensemble de l'histogramme vers les petites distances lorsque l'activite augmente
[en] We address the sensitivity of the Ni I 676.78 nm GONG line and the K I 769.9 nm resonance line to the temperature fluctuations present in the solar granulation. The temperature contrasts due to granulation are probably small in the upper photosphere where the cores of these two helioseismology lines are formed. However, the cores are sensitive also to the granulation temperature contrasts in the deep photosphere, through non-local NLTE effects in their formation. The largest effects are due to the ultraviolet radiation field, which is strongly modulated by the granulation in the deep layers where it escapes and carries these contrasts upwards to the line formation height. We discuss the resulting NLTE mechanisms and their influence on the two lines
[en] We present the results of a Fourier analysis of supergranular velocity fields measured in different heliographic latitudes. The observations were taken with the domeless coude refractor of the Kiepenheuer Institute at Anacapri/Italy. The analysis of two-dimensional power spectra of supergranular velocity fields yields the following main results: We find evidence for a decrease of the mean cell diameter of the supergranulation towards higher latitudes. For the equator belt we determine a mean cell size of 37800 ± 460 km, a minimum value of 33700 ± 330 km is found for latitudes around 450. Towards higher latitudes the cell size seems to increase again. We measure rms.-velocities of 236 ± 4 ms-1, and find no significant variation with latitude
[en] As we approach solar convection simulations that seek to model the interaction of small-scale granulation and supergranulation and even larger scales of convection within the near-surface shear layer (NSSL), the treatment of the boundary conditions and minimization of sub-grid scale diffusive processes become increasingly crucial. We here assess changes in the dynamics and the energy flux balance of the flows established in rotating spherical shell segments that capture much of the NSSL with the Curved Spherical Segment (CSS) code using two different diffusion schemes. The CSS code is a new massively parallel modeling tool capable of simulating 3-D compressible MHD convection with a realistic solar stratification in rotating spherical shell segments.
[en] The long-standing puzzle of reversed-C bisectors of spectral lines is addressed with the tools of the third-signature plot and bisector mapping. The F8 supergiant γ Cyg, which shows strongly reversed bisectors, is analyzed and found to have a monotonic decline in velocities with height in its photosphere, consistent with a convective overshoot region similar to what is seen for stars on the cool side of the granulation boundary. Further, a flux deficit is derived that is not unlike those for stars on the cool side of the granulation boundary, although the γ Cyg flux deficit is wider and peaks at a higher velocity. The reversed-C bisector shape is caused by a combination of a steep decline in velocities with height, as shown in the third-signature plot, with a flux deficit spanning only a fraction of the red wing of the line profiles, in contrast to cooler stars where the deficit extends over most of the red wing. Apparently no unusual velocity fields or other bizarre behaviors are needed to explain the granulation boundary; it stems more simply from the continuous changes of normal convective overshoot across the HR diagram.
[en] We detected 2.8 bright points (BPs) per Mm2 in the quiet Sun with the New Solar Telescope at Big Bear Solar Observatory, using the TiO 705.68 nm spectral line at an angular resolution ∼0.''1 to obtain a 30 minute data sequence. Some BPs formed knots that were stable in time and influenced the properties of the granulation pattern around them. The observed granulation pattern within ∼3'' of knots presents smaller granules than those observed in a normal granulation pattern, i.e., around the knots a suppressed convection is detected. Observed BPs covered ∼5% of the solar surface and were not homogeneously distributed. BPs had an average size of 0.''22, they were detectable for 4.28 minutes on average, and had an averaged contrast of 0.1% in the deep red TiO spectral line.
[en] Many helioseismic measurements suffer from substantial systematic errors. A particularly frustrating one is that time-distance measurements suffer from a large center to limb effect which looks very similar to the finite light travel time, except that the magnitude depends on the observable used and can have the opposite sign. This has frustrated attempts to determine the deep meridional flow in the solar convection zone, with Zhao et al. applying an ad hoc correction with little physical basis to correct the data. In this Letter, we propose that part of this effect can be explained by the highly asymmetrical nature of the solar granulation which results in what appears to the oscillation modes as a net radial flow, thereby imparting a phase shift on the modes as a function of observing height and thus heliocentric angle.