太阳10cm波爆发与共生的硬X射线耀斑中精细结构的分析

利用日本“Ｙｏｈｋｏｈ”卫星的资料及北京天文台２８４０ＭＨｚ的射电观测资料,对１９９２年６月７日的太阳爆发事件进行了分析,结果表明,在这次爆发的脉冲相期间存在着大小两种时间尺度的脉动分量,大尺度的脉动周期约为３０ｓ,小尺度脉动周期为１－４ｓ。利用硬Ｘ射线成像观测结果,发现大尺度的脉动与硬Ｘ射线源区的一系列变化相对应。文中给出了一个环－环相互作用的ＭＨＤ振荡调制物理图像。     

Nitrate in the Greenland ice sheet in the years following the 1908 tunguska event

The Tunguska event on 30 June 1908 has been subjected to much speculation within different fields of research. Publication of the results of the 1961 expedition to the Tunguska area (Florensky, 1963) supports that a cometary impact caused the event. Based on this interpretation, calculations of the impactor energy release and explosion height have been reported by Ben-Menahem (1975), and velocity, mass, and density of the impactor by Petrov and Stulov (1975). Park (1978) and Turco et al., 1981, Turco et al., 1982, used these numbers to calculate a production of ca. 30 × 10⁶ tons of NO during atmospheric transit. This paper presents a high-resolution study of nitrate concentration in the Greenland ice sheet in ca. 10 years covering the Tunguska event. No signs of excess nitrate are found in three ice cores from two different sites in Greenland in the years following the Tunguska event. By comparing these results with results for other aerosols generally found in the ice, the lack of excess NO₃^? following the Tunguska event can be interpreted as indicating that the impactor nitrate production calculated by Park (1978) and Turco et al., 1981, Turco et al., 1982 are 1–2 orders of magnitude too high. To explain this it is suggested, from other lines of reasoning, that the impactor density determined by Petrov and Stulov (1975) probably is too low.     

Platinum group element abundances in a peat layer associated with the Tunguska event, further evidence for a cosmic origin

We have measured excesses of Pd, Rh, Ru, REE, Co, Sr, and Y in a peat column from the Northern peat bog of the 1908 Tunguska explosion site. Earlier, in this peat column the presence of an Ir anomaly at the event layers (30- depth) has been found (Planet Space Sci. 48 (1998) 179). In these layers, Pd, Rh, Ru, Co, Sr, and Y show pronounced anomalies of a factor 4-7 higher than the background value. In the event layers there are also good correlations between the siderophile platinum group elements (Pd, Rh, Ru) and Co, indicators of cosmic material, which imply they might have the same source, i.e. the Tunguska explosive body. The patterns of CI-chondrite-normalized REE in the event layers are much flatter than those in normal peat layers and different from those in the nearby traps. Furthermore, in these layers the patterns of CI-chondrite-normalized PGEs and the element ratios (e.g. C/Pd, C/Rh, and between some siderophile elements) give evidence that the Tunguska explosive body was more likely a comet, although we cannot exclude the possibility that the impactor could be a carbonaceous asteroid. We have estimated the total mass of a solid component of the explosive body up to 10³-10⁶ tons.     

Tectonic and kinematic study of a strike-slip zone along the southern margin of Central Ovda Regio, Venus: Geodynamical implications for crustal plateaux formation and evolution

The tectonic system of the southern margin of Central Ovda Regio, a crustal plateau which straddles Venus equator, has been interpreted as a dextral strike-slip array, on the basis of evidence clearly identifiable, as are Riedel fracture patterns of different scales, en échelon folds and brittle strike-slip faults. This transcurrent regime developed two main shear belts (Inner and Outer, on respectively thicker and thinner crust), whose minimum dextral displacement has been estimated in 30-50 km. Since the up or downwelling models for plateau formation cannot easily explain tectonic shears of this magnitude along their margins, an alternative hypothesis has been built, which stands on the proposed collisional belt which could form Ovda northern border (King et al., 1998, Lunar Planet. Sci. Conf. 29, Abstract 1209; Tuckwell and Ghail, 2002, Lunar Planet. Sci. Conf. 33, Abstract 1566). Within this framework, the shear would represent a transcollisional transcurrent zone, similar to the strike-slip zones produced in the foreland of the Himalayas-Tibet collision front. Eastern Ovda would be an independent area of thickened crust, pushed to the SSE by the northern collision, with the deformation concentrated at its margins, and experiencing a shear strain on its southern margin. None of the data, however, either supports nor helps to discard theoretical subduction events as a cause of the collision. On the contrary, image relationships could be interpreted as evidence that the main shear deformation took place during the last global resurfacing event on the planet.     

New evidence for a volcanically, tectonically, and climatically active Mars

Geological analysis of Mars imagery supports the hypothesis that the planet has been the site of recent (<?10 Ma) volcanic and tectonic processes and glacier flow, and makes most likely previous suggestions of continuing endogenic and exogenic activity. Tectonic structures which deform very slightly cratered (at MOC scales) surfaces of Tharsis Montes and surrounding regions seem to attest to active tectonism (both extensional and transcurrent) on Mars. Exogenic processes in this region, such as a glacial origin for the aureole deposits on the northwestern flanks of the Tharsis Montes shield volcanoes, are supported by new data. The very recent age of these structures could be the first direct confirmation that drastic changes in obliquity are modulating the martian climate, such that an increase in obliquity would result in equatorial glaciers taking the place of the receding polar ice caps. If this and other concurring research is extended and confirmed, the ‘alive Mars’ which would emerge would constitute a most appealing place for exobiology and comparative planetology.     

No iridium anomaly after the 1908 Tunguska impact: Evidence from a Greenland ice core

Abstract— We have determined the abundances of Ir and other elements by neutron activation analysis on annual dust samples from an ice core from Site B in the Crête region in central Greenland covering the years 1905–1914. Iridium was detected in all samples, but we found no excess Ir above the background in the years following the Tunguska event. The lack of an Ir anomaly in the years after the Tunguska impact combined with the knowledge of the energy released during the impact and our present knowledge about stratospheric transport implies either a very low Ir content of the impactor or an exceptionally high geocentric velocity for the impactor.     

The nature of the Tunguska meteorite

Abstract— Arguments in favor of the cometary origin of the Tunguska meteorite are adduced along with reasons against the asteroidal hypothesis. A critical analysis is given for the hypotheses by Sekanina (1983) and Chyba et al. (1993). On the basis of the azimuth and inclination of the trajectory of the Tunguska body with plausible values of the geocentric velocity, the semimajor axis of the orbit and its inclination to the ecliptic plane are calculated for this body. It is noted that the theory of the disintegration of large bodies in the atmosphere put forward by Chyba et al. (1993) is crude. Applying more accurate theories (Grigoryan, 1979; Hills and Goda, 1993) as well as taking into account the realistic shape of the body yield for the cometary body lower disruption heights than obtained by Chyba et al. Numerical simulations carried out by Svettsov et al. agree well with the cometary hypothesis and the analytical calculations based on Grigoryan's theory. The asteroidal hypothesis is shown not to be tenable: the complete lack of stony fragments in the region of the catastrophe, cosmochemical data (in particular, the results of an isotope analysis), and some other information contradict this hypothesis. It is shown that stony fragments that would have originated in the explosive disruption of the Tunguska body would not be vaporized by the radiation of the vapor cloud nor as a result of their fall to the Earth's surface.     

THE TUNGUSKA EVENT AND THE METEORS WITH TERMINAL FLARES

The comparison of the Tunguska body explosion with the effect of terminal flares of meteors and fireballs leads us to the conclusion that these events are of a similar nature but differ only by their scale. We consider that the dynamics of progressive breaking and evaporation of meteoric bodies during their entry into the terrestrial atmosphere could explain the terminal burst. An extremely porous body model for the Tunguska meteorite was analysed and rejected as unsatisfactory. The realistic values of the initial velocity (～30 km/sec) and of the inclination angle for the Tunguska's trajectory (5–15°) give orbital elements not in contradiction with the cometary origin of the Tunguska body.     

Solar proton events during solar cycles 19, 20, and 21

Solar proton events have been studied for over thirty years and a great deal of lore has grown around them. It is the purpose of this paper to test some of this lore against the actual data. Data on solar proton events now exist for the period from 1956 to 1985 during which time 140 events took place in which the event integrated fluxes for protons of energy > 30 MeV was larger than 10⁵ particles cm^-2. We have studied statistical properties of event integrated fluxes for particles with energy > 10 MeV and for particles with energy > 30 MeV. Earlier studies based on a single solar cycle had resulted in a sharp division of events into ordinary and anomalously large events.Two such entirely separate distributions imply two entirely separate acceleration mechanisms, one common and the other very rare. We find that the sharp division is neither required nor justified by this larger sample. Instead the event intensity forms a smooth distribution for intensities up to the largest observed implying that any second acceleration mechanism cannot be rare. We have also studied the relation of event sizes to the sunspot number and the solar cycle phase. We find a clear bimodal variation of annual integrated flux with solar cycle phase but no statistically significant tendency for the large events to avoid sunspot maximum. We show there is almost no relation between the maximum sunspot number in a solar cycle and the solar cycle integrated flux. We also find that for annual sunspot numbers greater than 35 (i.e., non-minimum solar cycle conditions) there is no relation whatsoever between the annual sunspot numbers and annual integrated flux.     

Determination of intrinsic mode and linear mode coupling in solar microwave bursts

An explicit equation of the propagational angle of microwave emission between the line-of-sight and the local magnetic field is newly derived based on the approximated formulae of nonthermal gyrosynchrotron emission (Dulk and Marsh in Astrophys. J. 259, 350, 1982). The existence of the solution of propagational angle is clearly shown under a series of typical parameters in solar microwave observations. It could be used to determine the intrinsic mode and linear mode coupling in solar microwave bursts by three steps. (1) The mode coupling may happen only when the angle approximately equals to 90 degrees, i.e., when the emission propagates through the quasi-transverse region (Cohen in Astrophys. J. 131, 664, 1960). (2) The inversion of polarization sense due to the weakly mode coupling takes place only when the transition frequency defined by Cohen (1960) is larger than the frequency of microwave emission, and an observable criterion of the weakly mode coupling in flaring loops was indicated by the same polarization sense in the two footpoints of a flaring loop (Melrose and Robinson in Proc. Astron. Soc. Aust. 11, 16, 1994). (3) Finally, the intrinsic mode of microwave emission is determined by the observed polarization and the calculated direction of local magnetic field according to the general plasma dispersion relation, together with the mode coupling process. However, a 180-degree ambiguity still exists in the direction of longitudinal magnetic field, to produce an uncertainty of the intrinsic mode. One example is selected to check the feasibility of the method in the 2001 September 25 event with a loop-like structure nearby the central meridian passage observed by Nobeyama Radio Heliograph and Polarimeters. The calculated angle in one footpoint (FP) varied around 90^° in two time intervals of the maximum phase, which gives a direct evidence of the emission propagating through a quasi-transverse region where the linear mode coupling took place, while, the angle in another FP was always smaller than 90^° where the mode coupling did not happen. Moreover, the right-circular sense at 17 GHz was always observed in both two FPs during the event, which supports that the transition frequency should be larger than 17 GHz in the first FP together with strong magnetic field of over 2000 Gauses in photosphere, where the weakly coupled case should happen. Moreover, there are two possibilities of the intrinsic mode in the two FPs due to the 180-degree ambiguity. (1) The emission of extraordinary (X) mode from the first FP turns to the ordinary (O) mode in the two time intervals of the maximum phase, while, the X-mode is always emitted from the second FP. (2) The inversion from O-mode to X-mode takes place in the first FP, while the O-mode keeps in the second FP. If the magnetic polarities in photosphere and corona are coincident in this event, the intrinsic mode belongs to the second case.     

Cenozoic sediment distribution and tectonic movements in the Faroe region

A complex history of Cenozoic vertical movements in the Faroe region has been revealed from interpretation of geophysical and geological data, mainly offshore reflection seismic data, side-scan images, shallow cores, and onshore mapping. The history comprises several phases of tectonic disturbances observed at different scales. On the eastern margin of the Faroe Platform a late Eocene–early Oligocene phase of doming of the Faroe Platform has caused a postdepositional tilting of Eocene strata along the southern margin of the platform; a mid-Miocene phase of compressional tectonics is evidenced on seismic transects as gentle anticlines and associated reverse faults; and possible Pliocene uplift of the Faroe Islands is indicated by a progradational wedge of sediments deposited on the eastern Faroe Platform. At the continental margin/slope north of the Faroe Platform, reflection seismic data imaging the postbasalt sedimentary strata indicate three distinct tectonic events phases in the Eocene–Oligocene, Miocene and Pliocene, respectively. In contrast to the Faroe Platform the Faroe–Shetland Channel was characterised by more or less continuous subsidence dominated throughout the Cenozoic. During the Eocene, sediments deposited in the Faroe–Shetland Channel was mostly derived from a source area on the British shelf.     

Atmospheric ionization and cosmic rays: studies and measurements before 1912

The discovery of cosmic rays, a milestone in science, was based on the work by scientists in Europe and the New World and took place during a period characterized by nationalism and lack of communication. Many scientists that took part in this research a century ago were intrigued by the penetrating radiation and tried to understand the origin of it. Several important contributions to the discovery of the origin of cosmic rays have been forgotten; historical, political and personal facts might have contributed to their substantial disappearance from the history of science.     

Electrolysis in space and fate of Phaethon

A new process of the energy accumulation in icy bodies (e.g., planetary satellites, cometary nuclei) is advanced which is applicable for space conditions: namely, the volumetric electrolysis of the ice containing foreign inclusions. The electrolysis takes place when the electric current, generated by virtue of the body's movement in the external magnetic field (planetary magnetospheres, the solar wind field, etc.) flows through the body.The cosmogonical concept which treats the Sun-Jupiter system as a limiting case of a close binary star, together with the known data on mass, composition and space distribution of asteroids, allows one to assume the initial existence between Mars and Jupiter of a Moon-like planet enriched with ices and allied by its parameters to the Galilean satellites (mainly Ganymede and Callisto). If this planet was affected by the ancient solar wind with during 10⁹ yr, it could have accumulated the energy sufficient for its explosion.The process considered seems able to explain, from a unified point of view, a large number of phenomena — such as the burst activity of comets, a considerable hydrogen excess in their tails, a noticeable long-period comet perihelia orientation toward the solar apex, the existence of asteroidal families and the separation of asteroids by their chemical composition into two main groups, the Tunguska event, etc.     

Measurement and analysis of magnetic field variation during a class 2b flare

We report a digital analysis of high-time-resolution videomagnetograms taken during a class 2b flare that occurred at 60° east. The data were obtained at the Big Bear Observatory and calibrated by a Mt. Wilson magnetogram. Changes of weak magnetic fields (less than 100 G) with an amplitude from 30 to 100% have been detected over 55% of the optical flare region, apparently taking place at the initial phase of the flare. Statistical considerations suggest a real flare association with most of these changes.H observations show that large changes took place over the footpoints of heavily inclined structures like penumbral fibrils, while smaller changes took place over the plage region. An apparent polarity reversal was found at the feet of erupted fibrils.Based on force-free field calculations these changes can be reasonably explained as a transformation of the current-carrying fields to potential fields which produced large changes in the field line inclination and rotation.Visiting Associate, Summer 1977.     

Hα Surges Initiated by Newly-emerging Satellite Magnetic Fields

On July 22, 2011 and in the active region NOAA 11259 there ap- peared the event of the ejection of solar atmospheric Hα surges. According to the full-disc Hα observations of the Big Bear Solar Observatory in United States, three consecutive surges at one and the same place in the north of the main spot of the active region were discovered. The trajectories of these three surges exhib- ited the ?gure of straight lines, and their integral con?guration is like an inverted Eiffel Tower. The ?rst two surges are quite similar, and in each of them there appeared two bright points in the northern part of the main spot. After several minutes, the surges appeared in the midst of bright points. When the bright- ness of the bright points attained the maximum value, the surges spouted out from the midst of bright points. And after reaching the maximum altitude, they quickly vanished. Before the ejection of the third surge took place, no bright points appeared. Besides, its maximal altitude is merely one half of that of the ?rst two surges. Via a comparison with the SDO/HMI (Solar Dynamics Obser- vatory/Helioseismic and Magnetic Imager) data of radial magnetic ?elds, it is found that in more than one hour before the appearance of the ?rst surge there emerged bipolar magnetic ?elds in the region of ejection. Besides, in several min- utes before the ejection of each Hα surge the magnetic ?uxes of positive polarity diminished. Via our analysis it is found that there appeared reconnections be- tween the newly emerging satellite magnetic ?elds and the preexisting magnetic ?elds in the spot, and this caused the continuous ejections of Hα surges.     

Comment on “Evidence for a very high carbon/iridium ratio in the Tunguska impactor” by K. L. Rasmussen,H. J. F. Olsen,R. Gwozdz and E. M. Kolesnikov

Abstract— We discuss possible evidence for a dilution of ¹⁴C caused by the Tunguska impact event, proposed by Rasmussen et al. (1999). The results presented in that paper and other available information do not support this hypothesis.     

Trajectory and orbit of the Tunguska meteorite revisited

Abstract— A critical survey is presented of all determinations of the azimuth and inclination of the Tunguska meteorite's trajectory based either on eyewitness testimonies or on the mathematical treatment of the forest-leveling field in the area of the catastrophe. The eyewitness testimonies collected in the neighborhood of the Nizhnyaya Tunguska River indicate the most probable azimuth of the trajectory projection to be 104° from the north to the east, which is close to the most recent azimuth estimate from the forest-leveling field, 99°. For the most part of the trajectory, its inclination could not exceed 15°. However, it is seen from aerodynamic calculations that the combined action of the gravity field and a nonzero aerodynamic lift could increase the inclination to 40° as the end of the trajectory was approached. Meteoroid orbits are calculated for a broad family of trajectories with azimuths ranging from 99° (Fast et al, 1976) to 137° (Krinov, 1949) and geocentric velocities ranging from 25 to 40 km/s. Orbits with large azimuth values (120° and larger) are shown to belong to the asteroidal type. They are succeeded by the orbits of short-period and long-period comets, whereas very small azimuth values and large geocentric velocities correspond to the region of hyperbolic orbits. Certain restrictions on the possible trajectory azimuths and geocentric velocities of the Tunguska body are imposed by this study.     

The world's most famous meteor shower picture

Summary The world's most famous meteor shower picture (Fig. 1) is of the storm that took place in the early morning of Wednesday, 13 November 1833. The picture was, however, produce 54 years after the event, being first published in April 1888. It had a biblical origin and was only taken over by the astronomers in the mid 1920s. The artist was the Swiss painter Karl Jauslin and the engraver was Adolf Völlmy.     

Continuous energy injection at numerous bright points during soft X-ray flare enhancement

The common assumption that a single volume of plasma produces X-ray emission during solar flares is difficult to reconcile with the very complex structure observed in H spectroheliograms. Nevertheless such a model has been considered reasonably adequate because the rapid rise and slow decay of emission has approximately the form expected when a plasma volume, isolated thermally from its surroundings, is heated quickly in the early stages of the event.Data presented in this paper show that a number of secondary peaks in intensity are usually observed throughout the soft X-ray emission. These can be explained by a model in which the X-ray emission comes from many relatively short-lived volumes of hot plasma. It appears that the lifetime of each such region is about five minutes, while the H spectroheliograms suggest that they are spaced throughout the extended region of activity. The relatively long period of flare activity arises because new volumes of plasma appear as others decay. Since each of these regions has to be energized during its development it is concluded that energy is released throughout the period of the X-ray flare.On leave of absence from the Mullard Space Science Laboratory, University College London WC1E-6BT.     

Two ‘negative bursts’ with moving filaments, 19 May 1969

The event of 1969 May 19, 1430 UT included a flare, radio burst, and an active dark flocculus (ADF) or moving filament described by Vorpahl (1973) and a microwave negative burst superposed on a gradual rise and fall, described by Covington (1973). He found the interpretation of a second decrease at 2010 UT to be ambiguous in the absence of complete information. The second decrease is found here to be part of a series of events that parallels that of the earlier negative burst. Each decrease is superposed on a long-enduring burst that begins simultaneously with the eruption of a prominence near the equator at east limb and each is preceded by an ADF seen in H in a nearby active region. The similarity of these sequences strengthens the interpretation of the second event as a negative burst. The prominence eruptions, while not directly related to the negative bursts, add to a number of other signs of rapid changes in the large-scale structure of magnetic fields in the complex of active regions where the events took place.