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1.
Solar activity behaviour on the eve of the Maunder minimum may provide important information on the period of further suppression of sunspot population. We analyse sunspot positions and areas in the 1630s extracted from rare drawings published by Pierre Gassendi in Opera Omnia. This work was published in two different editions, the first in Lyon and the second almost 70 years later in Florence. The drawings published in Lyon are found to be slightly different from those published in Florence, which produces a discrepancy in the position of spots of a few degrees, while sunspot group areas may differ by a factor of two. We reveal that the orientation of the drawings in the book is not always the same as might be seen in the telescope. We conjecture that the time of Gassendi’s observations covers the beginning of a new Schwabe cycle in the southern hemisphere. The differential rotation rate in the 1630s is also assessed and discussed.  相似文献   

2.
Carol S. Breed 《Icarus》1977,30(2):326-340
Geomorphic features in the Hellespontus region, Mars, were compared with dunes of the crescentic ridge type in numerous terrestrial sand seas quantitatively by dimensional analysis of dune lengths, widths, and wavelengths. Mean values for the Hellespontus dunes are close to mean values derived from measurements of all sampled terrestrial sand seas. Terrestrial analogs of form and areal distribution of the Hellespontus dunes are shown by comparison of scale ratios derived from the measurements. Dunes of similar form occur in South West Africa, in Pakistan, in the southeastern Arabian peninsula, in the Sahara, in eastern USSR and northern China, and in western North America. Terrestrial analogs closest to form and areal distribution of the Hellespontus dunes are in the Kara Kum Desert, Turkmen SSR, and in the Ala Shan (Gobi) Desert, China.  相似文献   

3.
Long-wave energy emitted by the Earth-atmosphere into space is characterized by changes in power over time that always lag behind the changes in power of the absorbed solar radiation due to slow variation in enthalpy of the Earth-atmosphere system. Long-term variation of the solar energy radiation absorbed by the Earth remains uncompensated by the energy radiated into space over the interval of time that is determined by the thermal inertia. The basic state of the climate system is when the debit and credit sides in the Earth’s global annual mean energy budget (including the air and water envelopes) are almost always unbalanced. The annual mean balance of the heat budget of the Earth-atmosphere over a long time period will reliably define the behavior and magnitude of the energy excess accumulated by the Earth or energy deficit to allow us to determine adequately and to predict beforehand the trend and amplitude of the forthcoming climate change using the prognosis of variations in the total solar irradiance (solar constant). The decrease in solar constant has been observed since the early 1990s. The Earth as a planet will have a negative balance in the energy budget in the future as well, because the Sun is entering the decline phase of the bicentennial luminosity changes. This will lead to a drop in temperature in approximately 2014. The increase in albedo and decrease in greenhouse gas concentration in the atmosphere will result in the additional decrease in absorbed portion of the solar energy and reduced greenhouse effect. The additional drop in temperature exceeding the effect of decreased solar constant can occur as a result of successive feedback effects. A deep bicentennial minimum in solar constant is to be anticipated in 2042 ± 11 and the 19th Little Ice Age (for the last 7500 years) may occur in 2055 ± 11.  相似文献   

4.
The effect of mass balance variations on changes in surface elevation of the Greenland ice sheet is examined in connection with the rise in sea level that will be caused by increased melting. Changes in surface elevation of several metres (of either sign) can occur in the ablation area of the ice sheet over a period of a few years as a result of random ablation forcing without being evidence of change in mean climate. Similar, but smaller, changes can occur in the accumulation area due to accumulation forcing. The ablation area of the ice sheet probably thickened from the mid-1970s to the mid-1980s as a result of lower ablation in that period but thinned again in the late 1980s as a result of higher ablation then. There is no evidence of any present trend of increased melting. Future climate warming will involve an accelerated thinning of the ablation area that could be detected in 1–2 decades against the background of natural fluctuations in surface elevation.  相似文献   

5.
Abstract– The Siljan impact structure in Sweden is the largest confirmed impact structure in Western Europe. Despite this, the structure has been poorly studied in the past, and detailed studies of shock metamorphic features in the target lithologies are missing. Here, we present the results of a detailed systematic search for shock metamorphic features in quartz grains from 73 sampled localities at Siljan. At 21 localities from an area approximately 20 km in diameter located centrally in the structure, the orientations of 2851 planar deformation feature sets in 1179 quartz grains were measured. Observations of shatter cones outside of the zone with shocked quartz extend the total shocked area to approximately 30 km in diameter. The most strongly shocked samples, recording pressures of up to 20 GPa, occur at the very central part of the structure, and locally in these samples, higher pressures causing melting conditions in the affected rocks were reached. Pressures recorded in the studied samples decrease outwards from the center of the structure, forming roughly circular envelopes around the proposed shock center. Based on the distribution pattern of shocked quartz at Siljan, the original transient cavity can be estimated at approximately 32–38 km in diameter. After correcting for erosion, we conclude that the original rim to rim diameter of the Siljan crater was somewhere in the size range 50–90 km.  相似文献   

6.
EUV and X-ray images of the Sun are used as tracers of the magnetic field structure in the Solar atmosphere in order to study the existence of currents in active regions. Criteria are suggested for comparing the data with theoretical extrapolations of magnetic field lines above the level of magnetograph observations. Analysis of the data presented in conjunction with force-free field calculations suggests the existence of currents flowing in opposite directions in nearby sets of loops in the active regions shown. Some simple qualitative implications of opposed current structures are suggested.  相似文献   

7.
We present the results of study of the ionized gas velocity fields in 28 nearby (systemic velocity below 1000 km s?1) dwarf galaxies. The observations were made at the 6-m BTA telescope of the SAO RAS with the scanning Fabry-Perot interferometer in the Hα emission line. We were able to measure regular circular rotation parameters in 25 galaxies. As a rule, rotation velocities measured in HII are in a good agreement with the data on the HI kinematics at the same radii. Three galaxies reveal position angles of the kinematic axis in the HII velocity fields that strongly (tens of degrees) differ from the measurements in neutral hydrogen at large distances from the center or from the orientation of the major axis of optical isophotes. The planes of the gaseous and stellar disks in these galaxies most likely do not coincide. Namely, in DDO99 the gaseous disk is warped beyond the optical radius, and in UGC3672 and UGC8508 the inclination of orbits of gas clouds varies in the inner regions of galaxies. It is possible that the entire ionized gas in UGC8508 rotates in the plane polar to the stellar disk.  相似文献   

8.
The temporal variation of the horizontal velocity in sub-surface layers beneath three different types of active region is studied using the technique of ring diagrams. In this study, we select active regions (ARs) 10923, 10930, 10935 from three consecutive Carrington rotations: AR 10930 contains a fast-rotating sunspot in a strong emerging active region while other two have non-rotating sunspots with emerging flux in AR 10923 and decaying flux in AR 10935. The depth range covered is from the surface to about 12 Mm. In order to minimize the influence of systematic effects, the selection of active and quiet regions is made so that these were observed at the same heliographic locations on the solar disk. We find a significant variation in both components of the horizontal velocity in active regions as compared to quiet regions. The magnitude is higher in emerging-flux regions than in the decaying-flux region, in agreement with earlier findings. Further, we clearly see a significant temporal variation in depth profiles of both zonal and meridional flow components in AR 10930, with the variation in the zonal component being more pronounced. We also notice a significant influence of the plasma motion in areas closest to the rotating sunspot in AR 10930, while areas surrounding the non-rotating sunspots in all three cases are least affected by the presence of the active region in their neighborhood.  相似文献   

9.
The analysis of the transition from the large-scale fluid regime to the short-scale kinetic range of wavelengths in the development of the turbulent cascade of energy is nowadays subject of fervent discussion in the space plasmas scientific community. We make use of Hybrid Vlasov-Maxwell simulations where the full kinetic dynamics of ions is taken into account, while electrons are treated as a fluid. We investigate the development of turbulence in the solar wind, in 1D-3V phase space configuration and in the frequency range across the ion cyclotron frequency. These simulations allow for the analysis of the role of kinetic effects in the short-scale region of the energy spectra in the direction parallel to the background magnetic field. Our numerical results show the presence of a significant electrostatic activity at small wavelengths, triggered by the resonant interaction of ions with longitudinal waves. Our model does not allow to take into account the evolution of the turbulent spectra in the plane perpendicular to the ambient field, due to limited dimensionality in phase space. On the other hand, this model permits to isolate and study the possibility of transferring the electromagnetic large-scale energy on the small-scale kinetic electrostatic component of the spectrum. Peculiar features observed in the spacecraft data in the solar wind are qualitatively reproduced within the hybrid-Vlasov model, such as the generation of perpendicular temperature anisotropy and accelerated longitudinal beams of ions in the distribution of particle velocities as well as the appearance of a marked peak of electrostatic activity in the short-scale termination of the turbulent spectra.  相似文献   

10.
We applied the method of the short time Lyapunov indicators to the planar circular and to the planar elliptic restricted three-body problem in order to study the structure of the phase space in some selected regions. In the circular case we computed the short-time averages of the stretching numbers to distinguish between regular and chaotic domains of the phase space. The results obtained in this way are in good agreement with the corresponding Poincaré's surface of sections. Using the short time Lyapunov indicators we determined the detailed structure of the phase space in the semi-major axis-eccentricity plane of the test particle both in the circular and in the elliptic restricted problem (in the latter case for some values of the eccentricities of the primaries) and we studied the main features of the phase space.This revised version was published online in October 2005 with corrections to the Cover Date.  相似文献   

11.
A simple model is used to present a unified picture of the polarity pattern of the interplanetary magnetic field observed during the solar cycle. Emphasis in this paper is on the field near solar maximum. The heliographic latitude dependence of the dominant polarity of the interplanetary magnetic field is explained in terms of weak poloidal (dipolar) field sources in the sun's photosphere. Unlike the Babcock theory, the author hypothesizes that the dipolar field exists at equatorial latitudes (0–20°), too, (as well as in polar regions) and that the major source of the interplanetary magnetic field observed near the ecliptic plane is the dipolar field from equatorial latitudes. The polarity of the interplanetary field data taken in 1968 and in the first half of 1969 near solar maximum may possibly be explained in terms of a depression of the dipolar field boundary in space. The effect on the solar wind of the greater activity in the northern hemisphere of the sun that existed in 1968 and in the first half of 1969 is believed responsible for this hypothesized depression, especially near solar maximum, of the plane separating the + and - dipolar polarity below the solar equatorial plane in space. Predictions are made concerning the interplanetary field to be observed near the ecliptic plane in each portion of the next solar cycle.  相似文献   

12.
The plasma mechanism of radio emission in the coronas of late-type stars is shown to be considerably more efficient than that in the solar corona because of the high plasma temperature in their magnetic arches. This is attributable to an increase in the length of plasma-wave conversion into electromagnetic waves and a decrease in the optical depth of collisional wave absorption. Magnetic-arch filamentation results in a decrease in the intensity of the fundamental-tone radio emission and in the relative dominance of the second-harmonic radio emission. The efficiency of the fundamental-tone radio emission increases with plasma density in a coronal arch. The plasma mechanism accounts for the high brightness temperature of the flare radio emission from stars (≥1014 K).  相似文献   

13.
The aim of the present paper will be to introduce a new system of curvilinear coordinateshereafter referred to as Roche coordinates-in which spheres of constant radius are replaced by equipotential surfaces of a rotating gravitational dipole (which consists of two discrete points of finite mass, revolving around their common center of gravity); while the remaining coordinates are orthogonal to the equipotentials. It will be shown that the use of such coordinates offers a new method of approach to the solution of certain problems of particle dynamics (such as, for instance, the construction of certain types of trajectories in the restricted problem of three bodies); as well as of the hydrodynamics of gas streams in close binary systems, in which the equipotential surfaces of their components distorted by axial rotation and mutual tidal interaction constitute essential boundary conditions.Following a general outline of the problem in Section 1, the Roche coordinates associated with the equipotentials of a rotating gravitational dipole will be constructed in the plane case (Section 2), and their geometrical properties discussed. In Section 3, we shall transform the fundamental equations of hydrodynamics to their forms appropriate in the curvilinear Roche coordinates. The metric coefficients of this transformation will be formulated in a closed form in Section 4 in terms of the respective partial derivatives of the potential; while in Section 5 analytic expressions for the Roche coordinates will be given in the orbital plane of the dipole, which are exact as far as the distortion of the equipotential curves from circular form can be described by the second, third and, fourth harmonics.The concluding Section 6 will be devoted to a formulation of the equations of a mass-point in the restricted problem of three bodies in the Roche coordinates. Three special cases will be considered: (a) motion in the neighborhood of the equipotential curves; (b) motion in the direction normal to such curves; and (c) motion in the neighbourhood of the Lagrangian points. It will be shown that motion in one coordinate is possible only in limiting cases which will be enumerated; but twodimensional motions in which one velocity component is very much smaller than the other invite further study.A generalization of the plane Roche coordinates to three dimensions, with application to additional classes of problems, is being postponed for a subsequent paper.  相似文献   

14.
对在1981-2000年世界上所发表的和中国学者所发表的有关恒星与恒星系统的论文作统计发现：此期间世界上这一领域的发展较平稳，而我国的发展快速．这反映了改革开放后，我国基础学科研究大有进展．从各分支所占的比重和发展来看，我国在恒星与恒星系统的研究与世界同期有几乎相同的分布，因此总体上我国在这一领域的发展基本正常．当然有些分支发展较快，如有关超新星及其遗迹、星际介质和恒星形成区、化学丰度的研究等，这和一些较强的研究团组形成有关；在双星研究方面，我国则与世界发展一致，双星研究始终是恒星研究领域的重点；而在世界范围内较突出的关于银河系的研究，在我国却相对较弱．恒星和恒星系统这一研究领域20年的论文数统计显示，我国学者所发表的论文只占世界总论文数的1．3％，虽然在最后5年有大幅上升，但也只占2．0％，这与我国IAU会员数所占比例相比是偏少的．就世界整体而言，恒星领域的研究进展与整个天文学领域相比是较慢的，显然这与一批能做深空探测和高能波段观测的设备投入有关．因此，除了对恒星及恒星系统领域作统计分析外，对整个天文学领域各大分支作分析可能对制定今后我国天文学发展计划更有利。  相似文献   

15.
In this investigation, the polarization transfer equations in terms of the Stokes parameters are derived for electromagnetic waves propagating in an arbitrary direction in an inhomogeneous magnetized plasma. This system of transfer equations is then solved analytically in the case when the magnetized plasma is homogeneous. For simplicity in presentation, the source term in the equation of transfer has been omitted. Transitting to the special case of quasi-longitudinal propagation, the results obtained here are shown to be in agreement to that derived by Zheleznyakov earlier.  相似文献   

16.
We propose an interpretation of the enrichments in volatiles observed in the four giant planets with respect to the solar abundance. It is based on the assumption that volatiles were trapped in the form of solid clathrate hydrates and incorporated in planetesimals embedded in the feeding zones of each of the four giant planets. The mass of trapped volatiles is then held constant with time. The mass of hydrogen and of not trapped gaseous species continuously decreased with time until the formation of the planet was completed, resulting in an increase in the ratio of the mass of trapped volatiles to the mass of hydrogen (Gautier et al., Astrophys. J. 550 (2001) L227). The efficiency of the clathration depends upon the amount of ice available in the early feeding zone. The quasi-uniform enrichment in Ar, Kr, Xe, C, N, and S observed in Jupiter is reproduced because all volatiles were trapped. The non-uniform enrichment observed in C, N and S in Saturn is due to the fact that CH4, NH3, and H2S were trapped but not CO and N2. The non-uniform enrichment in C, N and S in Uranus and Neptune results from the trapping of CH4, CO, NH3 and H2S, while N2 was not trapped. Our scenario permits us to interpret the strongly oversolar sulfur abundance inferred by various modelers to be present in Saturn, Uranus and Neptune for reproducing the microwave spectra of the three planets. Abundances of Ar, Kr and Xe in these three are also predicted. Only Xe is expected to be substantially oversolar. The large enrichment in oxygen in Neptune with respect to the solar abundance, calculated by Lodders and Fegley (Icarus 112 (1994) 368) from the detection of CO in the upper troposphere of the planet, is consistent with the trapping of volatiles by clathration. The upper limit of CO in Uranus does not exclude that this process also occurred in Uranus.  相似文献   

17.
Convection is highly geostrophic in the liquid cores of planets. A three-dimensional Boussinesq model in a plane rotating layer is considered in this study, and an analysis is given of the mechanism of the nonlinear interaction of Fourier waves that results in energy transfer through the spectrum. The structure of the wave triangle is demonstrated to be strongly different on scales smaller (or larger) than those of the leading mode of cyclonic turbulence. The differences in the structure of the triads of the thermal turbulence from that in the Kolmogorov model of homogeneous and isotropic turbulence are shown. The regimes with rotation considered in the study are typical of the modern models of convection and dynamo in the cores of planets, including the Earth.  相似文献   

18.
Turbulent diffusion of magnetic field plays an essential role in the generation of magnetic field in most astrophysical bodies. This paper reviews what can be proved, and what can be believed, about the turbulent diffusion of magnetic field. Observations indicate the dissipation of magnetic field at rates that can be understood only in terms of turbulent diffusion. Theory shows that a largescale weak magnetic field diffuses in a turbulent flow in the same way that smoke is mixed throughout the fluid by the turbulence. The small-scale fields (produced from the large-scale field by the turbulence) are limited in their growth by reconnection of field lines at neutral points, so that the turbulent mixing of field and fluid is not halted by them.Altogether, it appears that the mixing of field and fluid in the observed turbulent motions in the Sun and in the Galaxy is unavoidable. Turbulent diffusion causes decay of the general solar fields in a decade or so, and of the galactic field in 108–109 yr. We conclude that continual dynamo action is implied by the observed existence of the fields.This work was supported in part by the National Aeronautics and Space Administration under Grant NGL 14-001-001.  相似文献   

19.
We investigate the internal structure of clusters of galaxies in high-resolution N -body simulations of four different cosmologies. There is a higher proportion of disordered clusters in critical-density than in low-density universes, although the structure of relaxed clusters is very similar in each case. Crude measures of substructure, such as the shift in the position of the centre-of-mass as the density threshold is varied, can distinguish the two in a sample of just 20 or so clusters; it is harder to differentiate between clusters in open and flat models with the same density parameter. Most clusters are in a quasi-steady state within the virial radius and are well-described by the density profile of Navarro, Frenk & White.  相似文献   

20.
A theoretical study of the influence of propagating acoustic pulses in the solar chromosphere upon the line profiles of the Ca ii resonance and infrared triplet lines has been made. The major objective has been to explain the observed asymmetries seen in the cores of the H and K lines and to predict the temporal behavior of the infrared lines caused by passing acoustic or shock pulses. The velocities in the pulses, calculated from weak shock theory, have been included consistently in the non-LTE calculations. The results of the calculations show that these lines are very sensitive to perturbations in the background atmosphere caused by the pulses. Only minor changes in the line shapes result from including the velocities consistently in the line source function calculations. The qualitative changes in the line profiles vary markedly with the strength of the shock pulses. The observed differences in the K line profiles seen on the quiet Sun can be explained in terms of a spectrum of pulses with different wave-lengths and initial amplitudes in the photosphere.  相似文献   

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