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1.
Celebrating the diamond jubilee of the Physics Research Laboratory (PRL) in Ahmedabad, India, we look back over the last six decades in solar physics and contemplate on the ten outstanding problems (or research foci) in solar physics:
  1. The solar neutrino problem
  2. Structure of the solar interior (helioseismology)
  3. The solar magnetic field (dynamo, solar cycle, corona)
  4. Hydrodynamics of coronal loops
  5. MHD oscillations and waves (coronal seismology)
  6. The coronal heating problem
  7. Self-organized criticality (from nanoflares to giant flares)
  8. Magnetic reconnection processes
  9. Particle acceleration processes
  10. Coronal mass ejections and coronal dimming
The first two problems have been largely solved recently, while the other eight selected problems are still pending a final solution, and thus remain persistent Challenges for Solar Cycle 24, the theme of this jubilee conference.  相似文献   

2.
Shock remagnetization is a significant mode of alteration of the intensity and direction of magnetization in planetary crustal rocks subjected to the dynamic and thermochemical effects associated with meteorite impact. Shock remagnetization will take place almost instantaneously during and following the transient shock episode, and over longer times depending on residual temperature effects associated with shock heating and the production of impact melt. Remagnetization will follow certain demagnetization effects. The following transitions and residual effects will result in remagnetization of planetary crustal material:
  1. First order reversible crystallographic transitions in bodycentered cubic iron-nickel alloys.
  2. Second order Curie temperature transitions in face-centered cubic iron-nickel alloys.
  3. Shock induced uniaxial anisotropy due to magnetoelasstic coupling of magnetic vectors to the shock wave.
  4. Shock melting of iron containing silicates.
  5. Subsolidus reduction and FeO decomposition.
  6. Partial ther moremanence due to post-shock temperature.
  7. Total thermoremanence due to post-shock temperature.
  8. Production of a superparamagnetic distribution of iron which is sensitive to surface temperature fluctuation.
  9. Thermal effects in metal and alloy phases.
Lunar breccia and soil samples are generally more reduced than crystalline rocks and some of th's reduction is subsolidus probably associated with the transient thermal effects due to meteorite impact in teh porous reglith.  相似文献   

3.
Correlation and spectral analysis of solar radio flux density and sunspot number near the maximum of the sunspot cycle has indicated the existence of
  1. long period amplitude modulation of the slowly varying component (SVC) of radio emission
  2. coronal storage over a period of the order of three solar rotations
  3. fast decay (one solar rotation period or less) of gyromagnetic emissions from radio sources
  4. shift in location of chromospheric sources compared to those of either the upper corona or the photosphere.
  相似文献   

4.
Photoelectric measurements of Doppler shifts of various Fraunhofer lines obtained with the Capri magnetograph were analysed. The height dependence of the supergranular and oscillatory motions, as well as the two dimensional structure of these velocity fields is investigated. The most interesting results are the following:
  1. The oscillatory and supergranular motions are still clearly present in very deep photospheric layers as detected e.g. by means of the Ci line at 5380.3 Å.
  2. Whereas the vertical motions (both of oscillation and supergranulation) increase with height, the horizontal component of the supergranular flow is found to be decreasing slightly.
  3. Aperiodic horizontal motions are observed in the photospheric layers, which are probably connected with the process of excitation of the oscillatory field.
  4. There is no simple way of describing the oscillatory field in terms of independently oscillating ‘cells’, since the two-dimensional pattern changes its appearance drastically already in a fraction of one oscillation period.
  5. The correlation obtained by previous observers between vertical stationary motions, the chromospheric network and magnetic fields in particular is confirmed.
  相似文献   

5.
Based on the developed method of jointly using data on the magnetic fields and brightness of filaments and coronal holes (CHs) at various heights in the solar atmosphere as well as on the velocities in the photosphere, we have obtained the following results:
  • The upward motion of matter is typical of filament channels in the form of bright stripes that often surround the filaments when observed in the HeI 1083 nm line.
  • The filament channels observed simultaneously in Hα and HeI 1083 nm differ in size, emission characteristics, and other parameters. We conclude that by simultaneously investigating the filament channels in two spectral ranges, we can make progress in understanding the physics of their formation and evolution.
  • Most of the filaments observed in the HeI 1083 nm line consist of dark knots with different velocity distributions in them. A possible interpretation of these knots is offered.
  • The height of the small-scale magnetic field distribution near the individual dark knots of filaments in the solar atmosphere varies between 3000 and 20000 km.
  • The zero surface separating the large-scale magnetic field structures in the corona and calculated in the potential approximation changes the inclination to the solar surface with height and is displaced in one or two days.
  • The observed formation of a filament in a CH was accompanied by a significant magnetic field variation in the CH region at heights from 0 to 30000 km up to the change of the predominant field sign over the entire CH area. We assume that this occurs at the stage of CH disappearance.
    •   相似文献   

    6.
    The properties of rapidly changing inhomogeneities visible in the H and K lines above sunspot umbrae are described. We find as properties for these ‘Umbral Flashes’:
    1. A lifetime of 50 sec. The light curve is asymmetrical, the increase is faster than the decrease in brightness.
    2. A diameter ranging from the resolution limit up to 2000 km.
    3. A tendency to repeat every 145 sec.
    4. A ‘proper motion’ of 40 km/sec generally directed towards the penumbra.
    5. A Doppler shift of 6 km/sec.
    6. A magnetic field of 2100 G.
    7. A decrease in this field of 12 G/sec. This decrease is probably related to the flash motion.
    8. At any instant an average of 3–5 flashes in a medium-sized umbra. A weak feature often persists in the umbra after the flash. This post-flash structure initially shows a blue shift, but 100–120 sec after the flash, it shows a rapid red shift just before the flash repeats.
      相似文献   

    7.
    A typical concentric ellipse multiple-arch system was observed in the solar corona during the February 4, 1962 eclipse in New Guinea. The following results have been obtained from analysis of a white-light photograph taken by N. Owaki (see Owaki and Saito, 1967a).
    1. The arches are composed of four equidistant components, elliptical in shape, and almost concentric with a prominence at the common center of the ellipses.
    2. The prominence and arch system appears to be the lower region of a helmet-shaped streamer.
    3. The widths of the arches are observed to increase with height.
    4. Analysis was made in the light of three models for the coronal structures that could lead to the observed arches: (a) rod-like concentrations of electrons; (b) tunnel-shaped elliptical shells of electrons; and (c) dome-like ellipsoidal shells of electrons. Electron densities are derived for the models, and the dome-like model is excluded as a possibility for arch systems exhibiting a coronal cavity.
    5. The scale height in the arch-streamer region is found to be almost the same as that of the K-corona, suggesting equal temperatures, density distributions, etc. in each region.
    6. There is a dark space (a coronal cavity) between the innermost arch and the prominence. The brightness of this cavity is 1/5 that of the adjacent arch. It is 3% brighter than the background corona of the arch-streamer system.
    7. A comparison is made between the deficiency of electrons in the coronal cavity and the excess of electrons in the prominence. It is found that the ratio of the excess to the deficiency lies between 0.9 and 40.
    8. A comparison between the electron efflux from the ‘leaky magnetic bottle’ possibly formed by rod-shaped coronal arches and the electron influx into those arches from the chromosphere leads us to the conclusion that the rod model is probably valid and that spicules appear to be an adequate supply for the electrons observed in the arches. The tunnel model may be valid, but in that case spicules are probably not the sources of the electrons observed in coronal arches.
      相似文献   

    8.
    Coordinates of polar faculae have been measured and processed using daily photoheliograms of the Kislovodsk Station of the Pulkovo observatory with the final goal of studying their latitude distribution during the solar cycles 20–21. The results obtained are as follows:
    1. The first polar faculae emerge immediately after the polarity inversion of the solar magnetic field at the latitudes from 40° to 70° with the average ?-55°.
    2. The zone of the emergence of polar faculae migrates poleward during the period between the neighbouring polarity inversions of the solar magnetic field. This migration is about 20° for 8 years, which corresponds to a velocity of 0.5 m s-1.
    3. The maximum number of polar faculae was reached at the activity minimum (1975–1976).
    4. The last polar faculae were observed in the second half of 1978 at the latitudes from 70° to 80°.
      相似文献   

    9.
    Improving our understanding of the mechanisms that energize the solar wind and heat structures in the solar corona requires the development of empirical methods that can determine the three-dimensional (3D) temperature and density distributions with as much spatial and temporal resolution as possible. This paper reviews the solar rotational tomography (SRT) methods that will be used for 3D reconstruction of the solar corona from data obtained by the next generation of space-based missions such as the Solar and Terrestrial Relations Observatory (STEREO), Solar-B and the Solar Dynamics Observatory (SDO). In the next decade, SRT will undergo rapid advancement on several frontiers of 3D image reconstruction:
    1. Electron density reconstruction from white-light coronagraph images.
    2. Differential emission measure (DEM) reconstruction from EUV images.
    3. Dual-spacecraft (STEREO) observing geometry.
    4. Fusion of data from multiple spacecraft with differing instrumentation.
    5. Time-dependent estimation methods.
    Although the principles described apply to many different wavelength regimes, this paper concentrates on white-light and EUV data. Previous work on all of these subjects is reviewed, and major technical issues and future directions are discussed.  相似文献   

    10.
    The properties of small (< 2″) moving magnetic features near certain sunspots are studied with several time series of longitudinal magnetograms and Hα filtergrams. We find that the moving magnetic features:
    1. Are associated only with decaying sunspots surrounded entirely or in part by a zone without a permanent vertical magnetic field.
    2. Appear first at or slightly beyond the outer edge of the parent sunspot regardless of the presence or absence of a penumbra.
    3. Move approximately radially outward from sunspots at about 1 km s?1 until they vanish or reach the network.
    4. Appear with both magnetic polarities from sunspots of single polarities but appear with a net flux of the same sign as the parent sunspot.
    5. Transport net flux away from the parent sunspots at the same rates as the flux decay of the sunspots.
    6. Tend to appear in opposite polarity pairs.
    7. Appear to carry a total flux away from sunspots several times larger than the total flux of the sunspots.
    8. Produce only a very faint emmission in the core of Hα.
    A model to help understand the observations is proposed.  相似文献   

    11.
    Two-dimensional distributions of kinetic temperature, density and turbulent velocity are obtained for four quiescent prominences observed at the Peruvian eclipse of 12 November, 1966.
    1. The kinetic temperature derived from line widths is around 6000–7000 K in the central part of prominences and rises to 12000K in both edges and possibly in the top of prominences.
    2. The turbulent velocity shows a similar tendency, being 7–9 km/sec in the central part and ≈ 20 km/sec in the outer part. The turbulent velocity also increases slowly towards higher heights in the prominence.
    3. The electron density derived both from the Stark effect and the intensity ratio of the continuous spectra turns out to be about 1010.2–1010.6 cm?3 in the central portion of two prominences.
    4. From the width and the intensity, neutral helium lines are shown to originate in the same region as hydrogen and metallic lines where the kinetic temperature goes down to 6000 K. This indicates that neutral helium is emitted after the ionization due to UV radiation from the corona and the transition region.
      相似文献   

    12.
    This paper is primarily concerned with the questions of models and the mechanisms of radio emission for pulsars, the polarization of this radiation and related topic. For convenience and to provide a more complete picture of the problems involved, a short summary of the data on pulsars is also given. Besides the introduction, the paper contains the following sections:
    1. Some Facts about Pulsars.
    2. The Astrophysical Nature of Pulsars.
    3. Coherent Mechanisms of Radio Emission from Pulsars.
    4. Models of Pulsars: Magnetic, Pulsating White Dwarfs and Neutron Stars.
    5. The Polarization of the Radio Emission from Pulsars.
    6. A Synthesized Model of Pulsars — Magnetic, Pulsating and Rotating Neutron Stars.
    7. Concluding Remarks.
      相似文献   

    13.
    An observational study of maps of the longitudinal component of the photospheric fields in flaring active regions leads to the following conclusions:
    1. The broad-wing Hα kernels characteristic of the impulsive phase of flares occur within 10″ of neutral lines encircling features of isolated magnetic polarity (‘satellite sunspots’).
    2. Photospheric field changes intimately associated with several importance 1 flares and one importance 2B flare are confined to satellite sunspots, which are small (10″ diam). They often correspond to spot pores in white-light photographs.
    3. The field at these features appears to strengthen in the half hour just before the flares. During the flares the growth is reversed, the field drops and then recovers to its previous level.
    4. The magnetic flux through flare-associated features changes by about 4 × 1019 Mx in a day. The features are the same as the ‘Structures Magnétiques Evolutives’ of Martres et al. (1968a).
    5. An upper limit of 1021 Mx is set for the total flux change through McMath Regions 10381 and 10385 as the result of the 2B flare of 24 October, 1969.
    6. Large spots in the regions investigated did not evince flux changes or large proper motions at flare time.
    7. The results are taken to imply that the initial instability of a flare occurs at a neutral point, but the magnetic energy lost cannot yet be related to the total energy of the subsequent flare.
    8. No unusual velocities are observed in the photosphere at flare time.
      相似文献   

    14.
    From a time sequence of high dispersion spectra taken by Evans, the solar fine structures are studied in the Caii infra-red triplet. The Doppler shifts and the intensity fluctuations in different points of the profiles are converted into fluctuations of the model atmosphere. A weighting function method is worked out in that purpose. The theoretical line profiles are computed in non LTE from a program written by Dumont. The results are arranged in two parts:
    1. Low temporal frequencies. A three-column model describes the steady field of temperature, microturbulence and radial velocities fluctuations in the photosphere-chromosphere transition zone.
    2. Oscillations. The propagation of waves is considered in the three above-mentioned columns. The oscillation amplitudes seem statistically larger in the hot column. The vertical phase velocity is very large, even for frequencies higher than the cut-off frequency of acoustic waves. Velocity and temperature fluctuations are connected by different curves of phase-lags and amplitude ratios suggesting a short relaxation time of the temperature fluctuations in the low chromosphere.
      相似文献   

    15.
    We analyze particle acceleration processes in large solar flares, using observations of the August, 1972, series of large events. The energetic particle populations are estimated from the hard X-ray and γ-ray emission, and from direct interplanetary particle observations. The collisional energy losses of these particles are computed as a function of height, assuming that the particles are accelerated high in the solar atmosphere and then precipitate down into denser layers. We compare the computed energy input with the flare energy output in radiation, heating, and mass ejection, and find for large proton event flares that:
    1. The ～10–102 keV electrons accelerated during the flash phase constitute the bulk of the total flare energy.
    2. The flare can be divided into two regions depending on whether the electron energy input goes into radiation or explosive heating. The computed energy input to the radiative quasi-equilibrium region agrees with the observed flare energy output in optical, UV, and EUV radiation.
    3. The electron energy input to the explosive heating region can produce evaporation of the upper chromosphere needed to form the soft X-ray flare plasma.
    4. Very intense energetic electron fluxes can provide the energy and mass for interplanetary shock wave by heating the atmospheric gas to energies sufficient to escape the solar gravitational and magnetic fields. The threshold for shock formation appears to be ～1031 ergs total energy in >20 keV electrons, and all of the shock energy can be supplied by electrons if their spectrum extends down to 5–10 keV.
    5. High energy protons are accelerated later than the 10–102 keV electrons and most of them escape to the interplanetary medium. The energetic protons are not a significant contributor to the energization of flare phenomena. The observations are consistent with shock-wave acceleration of the protons and other nuclei, and also of electrons to relativistic energies.
    6. The flare white-light continuum emission is consistent with a model of free-bound transitions in a plasma with strong non-thermal ionization produced in the lower solar chromosphere by energetic electrons. The white-light continuum is inconsistent with models of photospheric heating by the energetic particles. A threshold energy of ～5×1030 ergs in >20 keV electrons is required for detectable white-light emission.
    The highly efficient electron energization required in these flares suggests that the flare mechanism consists of rapid dissipation of chromospheric and coronal field-aligned or sheet currents, due to the onset of current-driven Buneman anomalous resistivity. Large proton flares then result when the energy input from accelerated electrons is sufficient to form a shock wave.  相似文献   

    16.
    Unique timelapse sequences of Skylab/ATM spectroheliograms reveal the following characteristics of normal (i.e. non-flare) loop structures in the solar atmosphere:
    1. At the 0.5 × 106 K temperature of Ne vii, emission is concentrated into individual spiky structures that project 104–105 km from their magnetic footpoints and live on the order of 30 min.
    2. At the 1.0 × 106 K temperature of Mg ix, the individual spikes are more diffuse, and have greater lengths and longer lifetimes (～ 1.5 hr) than their 0.5 × 106 K counterparts. Perhaps for this reason, more 1.0 × 106 K loops are visible than 0.5 × 106 K loops at any given time.
    3. At the 2.0 × 106 K temperature of Fe xv, emission is confined to a number of relatively diffuse and irregularly shaped features whose collective patterns define closed field volumes in and between active regions. Although the individual features evolve on a time scale of roughly 6 hr, their collective patterns last for several days or more. Unlike the 0.5 × 106 K features, the 2.0 × 106 K features never form as a linear extension along an apparent magnetic field line, but seem to brighten and fade in place.
    These results place severe constraints on theoretical models of coronal heating and mass flow.  相似文献   

    17.
    The Transition Region and Coronal Explorer (TRACE) gave us the highest EUV spatial resolution and the Ramaty High Energy Solar Spectrometric Imager (RHESSI) gave us the highest hard X-ray and gammaray spectral resolution to study solar flares. We review a number of recent highlights obtained from both missions that either enhance or challenge our physical understanding of solar flares, such as:
    1. Multi-thermal Diagnostic of 6.7 and 8.0 keV Fe and Ni lines
    2. Multi-thermal Conduction Cooling Delays
    3. Chromospheric Altitude of Hard X-Ray Emission
    4. Evidence for Dipolar Reconnection Current Sheets
    5. Footpoint Motion and Reconnection Rate
    6. Evidence for Tripolar Magnetic Reconnection
    7. Displaced Electron and Ion Acceleration Sources.
      相似文献   

    18.
    Perturbations of the matter density in a homogeneous and isotropic cosmological model which leads to the formation of galaxies should, at later stages of evolution, cause spatial fluctuations of relic radiation. Silk assumed that an adiabatic connection existed between the density perturbations at the moment of recombination of the initial plasma and fluctuations of the observed temperature of radiation δT/T=δ ?m /3 ?m . It is shown in this article that such a simple connection is not applicable due to:
    1. The long time of recombination;
    2. The fact that when regions withM<1015 M ⊙ become transparent for radiation, the optical depth to the observer is still large due to Thompson scattering;
    3. The spasmodic increase of δ ?m/?m in recombination.
    As a result the expected temperature fluctuations of relic radiation should be smaller than adiabatic fluctuations. In this article the value of δT/T arising from scattering of radiation on moving electrons is calculated; the velocity field is generated by adiabatic or entropy density perturbations. Fluctuations of the relic radiation due to secondary heating of the intergalactic gas are also estimated. A detailed investigation of the spectrum of fluctuations may, in principle, lead to an understanding of the nature of initial density perturbations since a distinct periodic dependence of the spectral density of perturbations on wavelength (mass) is peculiar to adiabatic perturbations. Practical observations are quite difficult due to the smallness of the effects and the presence of fluctuations connected with discrete sources of radio emission.  相似文献   

    19.
    We examine the propagation of Alfvén waves in the solar atmosphere. The principal theoretical virtues of this work are: (i) The full wave equation is solved without recourse to the small-wavelength eikonal approximation (ii) The background solar atmosphere is realistic, consisting of an HSRA/VAL representation of the photosphere and chromosphere, a 200 km thick transition region, a model for the upper transition region below a coronal hole (provided by R. Munro), and the Munro-Jackson model of a polar coronal hole. The principal results are:
    1. If the wave source is taken to be near the top of the convection zone, where n H = 5.2 × 1016 cm?3, and if B ⊙ = 10.5 G, then the wave Poynting flux exhibits a series of strong resonant peaks at periods downwards from 1.6 hr. The resonant frequencies are in the ratios of the zeroes of J 0, but depend on B ⊙, and on the density and scale height at the wave source. The longest period peaks may be the most important, because they are nearest to the supergranular periods and to the observed periods near 1 AU, and because they are the broadest in frequency.
    2. The Poynting flux in the resonant peaks can be large enough, i.e. P ⊙ ≈ 104–105 erg cm?2s?1, to strongly affect the solar wind.
    3. ¦δv¦ and ¦δB¦ also display resonant peaks.
    4. In the chromosphere and low corona, ¦δv ≈ 7–25 kms?1 and ¦δB¦ ≈0.3–1.0 G if P ⊙≈104-105 erg cm?2s?1.
    5. The dependences of ¦δv¦ and ¦δB¦ on height are reduced by finite wavelength effects, except near the wave source where they are enhanced.
    6. Near the base, ¦δB¦ ≈ 350–1200 G if P ⊙ ～- 104–105. This means that nonlinear effects may be important, and that some density and vertical velocity fluctuations may be associated with the Alfvén waves.
    7. Below the low corona most wave energy is kinetic, except near the base where it becomes mostly magnetic at the resonances.
    8. ?0 < δv 2 > v A or < δB 2 > v A/4π are not good estimators of the energy flux.
    9. The Alfvén wave pressure tensor will be important in the transition region only if the magnetic field diverges rapidly. But the Alfvén wave pressure can be important in the coronal hole.
      相似文献   

    20.
    We report the results of the application of our approach to study the behavior of solar activity in the past, where:
  • When reconstructing the variations of solar activity, geomagnetic parameters, and the interplanetary magnetic field in the past we select a sequence of increasing time scales, which can be naturally represented by the potentials of available observational data. We select a total of four time scales: 150–200 years, 400 years, 1000 years, and 10000 years.
  • When constructing the series of each successive (in terms of length) time scale we use the data of the previous time scale as reference data.
  • We abandon, where possible, the series of traditional statistical parameters in favor of the series of physical parameters.
  • When deriving the relations between any parameters of solar activity, geomagnetic disturbance, and the interplanetary magnetic field, we take into account the differential nature of relations on different time scales. To this end, we use the earlier proposed MSR and DPS methods.
  • To verify the resulting reconstructions, we use the “principle of witnesses”, which uses independent (in some cases, indirect) information as initial data.
    •   相似文献   

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