A ‘magnetospheric’ scenario of the solar flare in a quadrupole magnetic configuration

An attempt is made to impart a constructive character to the concept of the solar flaremagnetospheric substorm analogy. An idealized scheme for a two-ribbon solar flare in the originally closed magnetosphere of the active region is discussed. The basis is formed by a terrestrial substorm scenario with two active phases (Mishin et al., 1992). While a quadrupole magnetic configuration turns out to be a solar analog of the Earth's magnetosphere. A physical mechanism that sustains the preflare storage phase, is provided by an instability like a stretching instability of the closed geomagnetotail. The storage process is attributed to the emergence into the corona of closed magnetic flux lines in adjacent (to the location of the would-be flare) regions. The flare flash-phase is determined by the change-over of the stretching instability to a disruption instability of a nonstationary (not neutral) current sheet inside the storage zone. The final recovery phase corresponds to the wellknown Pneuman-Kopp model.     

The existence of a ‘gap’ in the evolutionary sequence of pulsars

A replot of period derivative against period is done for about 300 pulsars, and the main features of the plot are discussed. The significance of a gap in this plot is reexamined and the existence of pulsars with nulling and subpulse drifting behaviour below this gap is pointed out. The implications of this for pulsar evolution are also discussed.     

Turbulence properties in the solar convection envelope： properties of the overshooting regions

We apply the turbulent convection model (TCM) to investigate properties of tur-bulence in the solar convective envelope, especially in overshooting regions. The results show TCM gives negative turbulent heat flux uγ′T′in overshooting regions, which is sim-ilar to other nonlocal turbulent convection theories. The turbulent temperature fluctuation T′T′shows peaks in overshooting regions. Most important, we find that the downward overshooting region below the base of the solar convection zone is a thin cellular layer filled with roll-shaped convective cells. The overshooting length for the temperature gradi-ent is much shorter than that for element mixing because turbulent heat flux of downward and upward moving convective cells counteract each other in this cellular overshooting region. Comparing the models' sound speed with observations, we find that raking the convective overshooting into account helps to improve the sound speed profile of our nonlocal solar models. Comparing the p-mode oscillation frequencies with observations,we validated that increasing the diffusion parameters and decreasing the dissipation pa-rameters of TCM make the p-mode oscillation frequencies of the solar model be in betteragreement with observations.     

Polarization of ULF waves in the earth’s magnetosphere

Conditions for the realization of ULF waves with different polarization are formulated and verified with the use of observational data from the spacecrafts which performed measurements in the earth’s magnetosphere. It is shown that the conditions formulated are in good agreement with observed wave parameters.     

Non-thermal processes during the ‘build-up’ phase of solar flares and in absence of flares

Hard X-ray and radio observations lead to the conclusion that production of non-thermal electrons is a common phenomenon of the active Sun. A preliminary analysis of three hard X-ray bursts observed with the OGO-5 satellite and the radio observations reported in the literature indicates that non-thermal particles are present in the flare region prior to the impulsive (flash) phase and also during the gradual rise and fall (GRF) bursts which are usually explained in terms of purely thermal radiation. The principal difference between the non-thermal electrons observed before the flash phase and during the flash phase appears to be in their total number rather than in the hardness of their energy spectrum. This indicates that the basic characteristics of the two acceleration processes are probably similar although the total energy converted into non-thermal electrons is considerably larger in the flash phase than in the build-up phase. Transient absorbing H features and filament activations are discussed in terms of their ability to produce energetic particle events and magnetic energy release.Presently at the Space Sciences Laboratory, University of California, Berkeley and Institute of Plasma Research, Stanford University, Stanford, California.     

On ‘bimodality of the solar cycle’ and the duration of cycle 21

The period-growth dichotomy of the solar cycle predicts that cycle 21, the present solar cycle, will be of long duration (>133 mo), ending after July 1987. Bimodality of the solar cycle (i.e., cycles being distributed into two groups according to cycle length, based on a comparison to the mean cycle period) is clearly seen in a scatter diagram of descent versus ascent durations. Based on the well-observed cycles 8–20, a linear fit for long-period cycles (being a relatively strong inverse relationship that is significant at the 5% level and having a coefficient of determination r ² 0.66) suggests that cycle 21, having an ascent of 42 mo, will have a descent near 99 mo; thus, cycle duration of about 141 mo is expected. Like cycle 11, cycle 21 occurs on the downward envelope of the sunspot number curve, yet is associated with an upward first difference in amplitude. A comparison of individual cycle, smoothed sunspot number curves for cycles 21 and 11 reveals striking similarity, which suggests that if, indeed, cycle 21 is a long-period cycle, then it too may have an extended tail of sustained, low, smoothed sunspot number, with cycle 22 minimum occurring either in late 1987 or early 1988.     

Preferred longitudes of sunspot groups and high-speed solar wind streams: Evidence for a ‘solar memory’

Correlation analysis of the mean longitude distribution of sunspot groups (taken from the Greenwich Photoheliographic Results) and high-speed solar wind streams (inferred from the C9 index for geomagnetic disturbances) with the Bartels rotation period P = 27.0 days shows anti-correlation for individual cycles.In particular, the longitudes of post-maximum stable streams of cycle 18 and 19 are well anticorrelated with the preferred longitudes of sunspot groups during the maximum activity periods of these cycles. This is further analyzed using the daily Zürich sunspot number, R, between 1932 and 1980, which reveals a conspicuous similarity of cycle 18 and 19 as well as cycle 20 and 21.We conclude that there is a solar memory for preferred longitudes of activity extending at least over one, probably two cycles (i.e. one magnetic cycle of 22 years). We conjecture that this memory extends over longer intervals of time as a long-term feature of solar activity.     

Pitch angle scattering of solar particles: Comparison of ‘particle’ and ‘field’ approach

In the quasi-linear theory of pitch angle scattering the power spectrum of magnetic field fluctuations is related to the shape of the pitch angle diffusion coefficient D(), the absolute value of the mean free path , and the rigidity dependence of the mean free path (R). We discuss these relations in detail during the solar particle event of 11 April, 1978 which was observed on HELIOS-2 at a distance of 0.49 AU from the Sun. Magnetic field measurements obtained during the time of the event are used as a basis for the layer model in which the method of particle trajectories in an actually measured field is used to simulate pitch angle diffusion. The values of D() and based on the trajectory simulation for 100 MeV protons (field approach) are compared with results obtained from solar proton data (particle approach) and with predictions from quasi-linear theory based on the additional assumption of the slab model for magnetic field fluctuations (QLT approach). The time of the event is characterized by a high level of field fluctuations, the observed mean free path of about 0.03 AU for 100 MeV protons is smaller than the average value near 1 AU. Results from the field and particle approaches agree surprisingly well. The remaining difference in the mean free path of about a factor of 2 could be due to tangential discontinuities which are measured by the magnetometer, but not seen by the real particles traveling along the average field. The results from the field and QLT approaches based on the same set of magnetic field measurements differ by about a factor of 4. One of the reasons for this discrepancy is that the conditions for resonance scattering are only marginally valid. In addition, the wave vectors representing Alfvén-type fluctuations may not be totally field aligned. This deviation from the slab model would cause an increase of the theoretically predicted mean free path and lead to better agreement with the other two approaches.     

The Formation of MgI 4571 Å in the solar atmosphere

The two-dimensional equation of transfer is solved for the case of locally-controlled source function (LTE) and radiationally-controlled ionization. Horizontal fluctuations in electron temperature and macroscopic velocity fields are superposed on the basic one-dimensional model (cf. Altrock and Cannon, 1972). Output intensities are compared with observed rms intensity fluctuations and spatially-averaged intensities in Mg i 4571 Å. We find that at least one model (with a height-independent temperature fluctuation T/T=±0.02 in the range 0h450 km) can predict the magnitude of the intensity fluctuations in both the continuum and 4571 Å. The asymmetry of the line can be explained by adding a height-independent, temperature-correlated flow of amplitude 1 to 2 km s^–1. The relationship between these results and other multi-dimensional analyses is discussed.On leave from Department of Applied Mathematics, University of Sydney, Sydney, Australia.     

Polarization effects in RATAN-600 solar observations in the “Southern sector with a flat reflector” mode

We report the results of numerical simulations of the instrumental signal in the Stokes V channel of circular polarization as observed by RATAN-600 radio telescope operating in the “Southern sector with a flat reflector” mode. Our simulations are based on an improved algorithm of the beam pattern computation that takes into account diffraction in the space between the telescope mirrors. The computations cover a wide range of wavelengths in the case of a focused antenna and in the presence of aberrations. We analyze the structure and properties of the element M ₄₁ of the Mueller matrix and of the parasite signal from the solar disk in various cases of the antenna irradiation. We estimate the differences between the left- and right-polarization power-beam patterns of the telescope. We report the computed M ₁₁ and M ₄₁ elements for the case of observation of the right- and left-polarized radiation at different points of the focal line of the secondary mirror, and analyze their variations as a function of a number of parameters, including, in particular, the shift applied to correct the displacement of scans.     

The excitation of the iron Kα feature in solar flares

We evaluate the relationship between the hard X-ray photon spectrum and the flux of iron K emission in a thick-target electron bombardment model. Results are presented for various power-law hard X-ray spectra. We then apply these results to two events observed with the Hard X-Ray Burst Spectrometer and the K channel of the X-Ray Polychromator Bent Crystal Spectrometer on the Solar Maximum Mission satellite. For one of the events, on 29 March, 1980, at 09:18 UT, the K flux predicted for a thick-target non-thermal process is significant compared to the background fluorescent component, and the data are indeed consistent with an enhancement of the predicted amount. For the other event, on 14 October, 1980 at 06:09 UT, the hard X-ray spectrum is so steep that no significant Ka flux is predicted for this process, and no enhancement is seen. We conclude that the agreement between the predicted K flux and the observed magnitude of the K enhancement above the fluorescent background at the time of the large hard X-ray bursts lends support to a thick-target non-thermal interpretation of impulsive hard X-ray emission in solar flares.     

Is the ‘superhot’ hard x-ray component in solar flares consistent with a thermal source?

It has been shown by Brown and Emslie (1988) that any optically thin thermal bremsstrahlung source must emit an energy spectrumL () (keV s^–1 keV^–1) which has the property that higher derivatives alternate in sign, i.e., (–) ^j L(^j)() > 0 for allj. In this short note, we apply this test to the superhot component discussed by Linet al. (1981) in order to determine whether a strictly thermal interpretation of this component is valid. We find that all statistically significant higher derivatives do indeed have the correct sign; this strengthens the identification of this component as due to a thermal source.Presidential Young Investigator.     

F stars: Evidence for ‘two-dimensional’ age-metallicity relation and a new light on the enrichment history of the solar neighbourhood

From theuvby photometry and proper motions for about 5500 nearby F stars we have found the following: (i) F stars, taken in narrow ranges of metallicity, show at [Fe/H]<0 rather distinct cut-off in their distribution along the Main Sequence (MS) at the blue side, which is suggested to be an indication for the MS turn-off in stellar groups of fixed metallicity; (ii) the corresponding turn-off age from theoretical isochrones strongly correlates with the mean peculiar velocity of the turn-off stars; (iii) the sub-groups of stars of different colours have essentially the same mean peculiar velocity at low metallicity, but at high metallicity the velocities of the red subgroups are much larger than those of the blue ones. We argue that these properties of F stars lead to a two-dimensional age-metallicity relation with the following main features: (i) a very large spread of metal abundance for old stars, (ii) narrowing of the metallicity range toward younger ages, (iii) increase of mean metallicity toward younger ages. This AMR seems to require a major revision of current models of the chemical evolution of the Galaxy: it suggests that the spatial distribution of metal abundance in the interstellar medium was initially highly inhomogeneous, the inhomogeneities being smoothed out and the mean metallicity being increased as the time went on.We also find an evidence for the evolution of the gaseous matter, from which the open clusters are formed, to be somehow decoupled from the evolution of the overall ISM.     

‘Crossing’ method for studying the turbulence in solar and stellar atmospheres

A new crossing method for the study of turbulent velocities in solar and stellar photospheres is considered. The method does not need knowledge of the abundance and oscillator strengths for determining the microturbulent velocity, if the macroturbulent velocity is adopted; or it allows investigation of the micro- and macro-velocities simultaneously, if the abundance and oscillator strengths are known. Using the crossing method for 200 lines of neutral iron we obtain microturbulent velocities for a large range of depths in the solar photosphere. The distribution of macroturbulent velocities with depth is also investigated. The total velocity field calculated from the obtained micro- and macro-velocities agrees with previous results from independent methods. This demonstrates the reliability of using the crossing method for separate determination of the micro- and macroturbulent velocities in solar and stellar atmospheres.     

On one mechanism for the generation of a reverse solar wind shock in the magnetosheath in front of the Earth’s magnetosphere

A possible mechanism for the generation of a reverse fast shock in the magnetosheath in the solar wind flow around the Earth’s magnetosphere is considered. It is shown that such a shock can emerge through the breaking of a nonlinear fast magnetosonic compression wave reflected from the magnetopause toward the bow shock rear. In this case, the magnetopause is represented as a tangential discontinuity with a zero normal magnetic field component at it and the mechanism under consideration is assumed to be secondary with respect to the sudden disturbance of the bow shock-Earth’s magnetosphere system by a nonstationary solar wind shock. A possible confirmation of the process under study by in-situ SC3 experimental observations of the bow shock front motion on the Cluster spacecraft is pointed out.     

The 3410 Å band of the PH molecule in the solar photospheric spectrum

Some weak unidentified solar photospheric lines in the wavelength range: (3400–3465) Å may be due to PH lines of the (0, 0) band of the PH(A ³ _i - X ^{3 -})system. These faint PH molecular lines have resulted an excitation temperature of the order of 4500 K. Using experimental lifetime data for PH in the A ³ _i state, an absorption oscillator strength f ₀₀ = 0.0075 is derived for the 3410 Å band of the PH (A ³ _i - X ^{3 -})system. Accurate line positions, oscillator strength and transition probability for the 4.4 fundamental rotation-vibration band of the PH molecule are obtained. A comparison of positions of some lines of the 4.4 band with those obtained on new tracings of high resolution solar spectra shows many coincidences with weak solar lines.     

Rapid changes in the fine structure of a coronal ‘bright point’ and a small coronal ‘active region’

A coronal bright point is resolved into a pattern of emission which, at any given time, consists of 2 or 3 miniature loops (each 2500 km in diameter and 12 000 km long). During the half-day lifetime of the bright point individual loops evolved on a time scale 6 min. A small ctive region seemed to evolve in this way, but the occasional blurring together of several loops made it difficult to follow individual changes.     

The ‘naked’ singularity in the scalar-tensor gravitation theory

The complete analysis of possible types of non-relativistic and ultra-relativistic motions in the field of the naked singularity of the STGT is given. The problem of the infall of a monochromatic radiation emitter on the naked singularity is studied. In spite of the absence of a freezing effect in the STGT, the naked singularity is not observable, for the brightness of the falling emitter decreases much faster than in the GTR. Atrr _g , the trajectory of particles and light are quite similar to that of the GTR, and due to this fact the naked singularity is observationally indistinguishable from a black hole.     

The origin of the ‘FUN’ anomalies and the high temperature inclusions in the allende meteorite

The discovery of isotopic anomalies in white inclusions of the meteorite Allende has led to fundamental questions concerning the origin of these anomalies and of the white inclusions themselves. An analysis of the FUN anomalies in the inclusions C1 and EK1-4-1 demonstrates that these isotopic anomalies may be decomposed into individual nucleosynthetic components, which have been subjected to separate mass and component fractionations. There is no evidence that any freshlysynthesized material injected into the primitive solar nebula was of abnormal isotopic composition, or that the FUN anomalies were due to an injection of unusual material. Rather, they show the effects of form of interstellar grains whose size or chemistry served as a memory for the nucleosynthetic origins of their constituent atoms. Giant gaseous protoplanets, as described for the early solar nebula by Cameron (1978), are a potential site for achieving both mass and component fractionations, and for producing white inclusions in general.     

On the origin of the azimuthal asymmetry in pole-on protoplanetary disks: The case of LkHα 101

The model of a protoplanetary disk around a star with a low-mass companion (M ₂: M ₁ ≤ 0.1) moving in a circular orbit inclined at a small angle to the disk plane (≤10°) is considered. The SPH method is used to calculate the hydrodynamic flows. The orbital motion of the companion leads to a nonuniform distribution of matter in the disk: a matter-free gap, density waves, and gas flows are formed in it. As a result of perturbations, the inner part of the disk is inclined relative to its periphery and does not coincide with the orbital plane of the companion either. This leads to an anisotropic illumination of the disk by the star and, as a consequence, to the appearance of a large-scale inhomogeneity in the disk image: it has a bright horseshoe-shaped region and a small shadow zone located asymmetrically relative to the line of nodes. An asymmetry of the disk image is clearly seen even when it is viewed pole-on. The orbital motion of the companion does not lead to any synchronous motion of the dark (shadow) and bright regions: they only execute small oscillations relative to some preferential direction. The asymmetric image of the disk around the star LkHα 101 seen nearly pole-on can be reproduced rather accurately within the proposed model. A study of such asymmetric disks opens up new opportunities for the search of massive bodies in the neighborhoods of young stars.