Short-term temporal variations of X-ray bright points     

J. T. Nolte  C. V. Solodyna  M. Gerassimenko 《Solar physics》1979,63(1):113-118

Skylab S-054 data have been used to examine the flux from X-ray bright points with 90 s time resolution. There is evidence of a steady heating input, similar to one reported for active region loops. Also observed are impulsive brightenings of bright points and rapid decays which are consistent with a sudden turn-off of the steady heating.  相似文献   

Photoelectric lightcurve and period of rotation of the asteroid 182 Elsa     

A.W. Harris  J.W. Young  F. Scaltriti  V. Zappalà 《Icarus》1980,41(2):316-317

Photoelectric observations on five consecutive nights yield a period of rotation of 80 ± 2 hr with an amplitude of 0.7 magnitude for 182 Elsa, making it the longest period of rotation known to date. 182 Elsa is classed as an S object with a diameter of 48 km.  相似文献   

Io's sodium emission cloud and the voyager 1 encounter     

B.A. Goldberg  Yu. Mekler  R.W. Carlson  T.V. Johnson  D.L. Matson 《Icarus》1980,44(2):305-317

Io's neutral sodium emission cloud was monitored during the period of Voyager 1 encounter from two independent ground-based sites. Observations from Table Mountain Observatory verified the continued existence of the “near-Io cloud” (d < 1.5 × 10⁵ km, for 4πI > 1 kR; R denotes Rayleigh) while those from Wise Observatory showed a deficiency in the weaker emission at greater distances from Io. The sodium cloud has been monitored from both observatories for several years. These and other observations demonstrate that the behavior of the cloud is complex since it undergoes a variety of changes, both systematic and secular, which can have both time and spatial dependencies. The cloud also displays some characteristics of stability. Table Mountain images and high-dispersion spectra (resolution $\text{～0.2}\text{A}\text{?}$) indicate that the basic shape and intensity of the “near cloud” have remained relatively constant at least since imaging observations began in 1976. Wise Observatory low-dispersion spectra (resolution $\text{～1}\text{A}\text{?}$) which have been obtained since 1974 demonstrate substantial variability of the size and intensity of the “far cloud” (d ? 1.5 × 10⁵ km) on a time scale of months or less. Corresponding changes in the state of the plasma associated with the Io torus are suggested, with the period of Voyager 1 encounter represented as a time of unusually high plasma temperature and/or density. Dynamic models of the sodium cloud employing Voyager 1 plasma data provide a reasonable fit to the Table Mountain encounter images. The modeling assumptions of anisotropic ejection of neutral sodium atoms from the leading, inner hemisphere of Io with a velocity distribution characteristic of sputtering adequately explain the overall intensity distribution of the “near cloud”. During the Voyager 1 encounter period there appeared a region of enhanced intensity projecting outward from Io's orbit and inclined to the orbital plane. This region is clearly distinguished from the sodium emission normally aligned with the plane of Io's orbit. The process responsible for this phenomenon is not yet understood. Similar but less pronounced features are also present in several Table Mountain images obtained over the past few years.  相似文献   

A model of the origin of the Jovian ring     

E. Grün  G. Morfill  G. Schwehm  T.V. Johnson 《Icarus》1980,44(2):326-338

Starting with the assumption that the micron-sized particles which make up the bright Jovian ring are fragments of erosive collisions between micrometeoroid projectiles and large parent bodies, a physical model of the ring is calculated. The physics of high-velocity impacts leads to a well-defined size distribution for the ejecta, the optical properties of which can be compared with observation. This gives information on the ejecta material (very likely silicates) and on the maximum size of the projectiles, which turns out to be about 0.1 μm. The origin of these projectiles is discussed, and it is concluded that dust particles ejected in volcanic activity from Io are the most likely source. The impact model leads quite naturally to a distribution in ejecta sizes, which in turn determines the structure of the ring. The largest ejecta form the bright ring, medium-sized ejecta form a disk extending all the way to the Jovian atmosphere, and the small ejecta form a faint halo, the structure of which is dominated by electromagnetic forces. In addition to the Io particles, interaction with interplanetary micrometeoroids is also considered. It is concluded that μm-sized ejecta from this source have ejection velocities which are several orders of magnitude too large, and thus cannot contribute significantly to the observed bright ring. However, the total mass ejection rate is significant. Destruction of these ejecta by the Io particles may provide additional particles for the halo.  相似文献   

On the convective instability of finitely conducting viscous model chromosphere     

V. D. Sankhla  P. K. Bhatia 《Astrophysics and Space Science》1980,68(1):11-18

The convective stability of a simple model chromosphere, consisting of protons, electrons and hydrogen atoms in the ground state, has been studied in the presence of a vertically upward uniform magnetic field to include the effects of FLR, Hall-currents, finite conductivity and ionization. The ionization in the chromosphere is collisional and the recombination is radiative. It is found that the Schwarzchild criterion should necessarily be satisfied for the stability together with the condition thatv > 2v ₀, where is kinematic viscosity andv ₀ is gyroviscosity. Some special cases have also been investigated.  相似文献   

The Martian paleoclimate and enhanced atmospheric carbon dioxide     

R.D. Cess  V. Ramanathan  Tobias Owen 《Icarus》1980,41(1):159-165

Current evidence indicates that the Martian surface is abundant with water presently in the form of ice, while the atmosphere was at one time more massive with a past surface pressure of as much as 1 atm of CO₂. In an attempt to understand the Martian paleoclimate, we have modeled a past CO₂H₂O greenhouse and find global temperatures which are consistent with an earlier presence of liquid surface water, a finding which agrees with the extensive evidence for past fluvial erosion. An important aspect of the CO₂H₂O greenhouse model is the detailed inclusion of CO₂ hot bands. For a surface pressure of 1 atm of CO₂, the present greenhouse model predicts a global mean surface temperature of 294°K, but if the hot bands are excluded, a surface temperature of only 250°K is achieved.  相似文献   

Estimation of coronal magnetic field from razin effect in solar decametric continuum burst     

R. V. Bhonsle  S. S. Degaonkar 《Solar physics》1980,68(2):339-342

A solar flare of importance 1B which occurred at 06:36 UT on April 27, 1979 on the solar disk (N 20, E 16) produced intense radio bursts. The most interesting feature of this event is the observation of a strong continuum radiation (type IV) starting at 06:53 UT and lasting for about 10 min in the decametric range. This continuum radiation displayed sharp low frequency cut-off, which varied from about 40 to 30 MHz in a quasiperiodic manner and could be attributed to Razin effect. The perturbation of this cut-off frequency is interpreted as that induced by the passing MHD shock wave through the region of the trapped energetic electrons. Assuming model electron density values and using the observed cut-off frequency, the magnitude of coronal magnetic field around 2R from Sun center works out to be about 6 G.  相似文献   

Urban-rural migration in the non-Chernozem zone of the RSFSR (with particular reference to Vologda Oblast)     

Alekseyev AI  Danilova IA  Zubarevich NV  Nikulin YI 《Soviet geography》1980,21(5):301-307

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Long term modulation of cosmic rays and inferable electromagnetic state in solar modulating region     

K. Nagashima  I. Morishita 《Planetary and Space Science》1980,28(2):177-194

It is demonstrated that the long term variation in cosmic ray intensity I(t) can be described by an integral equation, , which is derived from a generalization of Simpson's coasting solar wind model. A source function S(t?τ) is given by some appropriate solar activity index at a time t?τ(τ ? 0) and the characteristic functionf(τ)(?0 forτ ? 0) expresses the time dependence of the efficiency of the intensity depression due to solar disturbances represented by S(t ?τ) when the disturbances generated at the solar surface propagate through the modulating region with the solar wind. It is demonstrated further that the equation can be derived from the general diffusion-convection theory on some assumptions, and as a result, the source and characteristic functions can be related to diffusion coefficient and its transition in space. Assuming the sunspot number R (or two activity indices including R) as the source function, the characteristic function f(τ) [or f(τ)'s] is obtained with data of the cosmic ray intensity extended over several decades. Based on the theory, one can obtain from f(τ) the following physical quantities in space, such as the transition and life time of solar disturbances, the boundary of the modulating region, and the radial and time dependences of the diffusion coefficient, radial density gradient and modulated intensity of cosmic rays. Results deduced from the present analysis are consistent with those obtained directly or indirectly by space observations.  相似文献   

Origin of framboidal pyrite in clayey Holocene sediments and in Jurassic black shale in the northwestern part of the Barents Sea     

A. ELVERHØI 《Sedimentology》1977,24(4):591-595

Framboidal pyrite is identified in clayey Holocene sediments in the northwestern part of the Barents Sea, and also in clasts of black Jurassic (?) shale within these sediments. Two types of framboidal pyrite are distinguished. Framboids in the Holocene sediments lack a matrix between the microcrystals whereas the Jurassic specimens have a matrix. In contrast to the rest of the clastic sedimentary material in the area, the framboidal pyrite in the Holocene sediments is not reworked from the underlying Mesozoic rocks, but has formed recently. In some Holocene sediments the microcrystals are well organized and crystal-like faces are developed. The framboidal texture is probably a result of pyrite crystallization. The matrix is concluded to be due to diagenetic alteration and is not a primary feature of the framboidal pyrite.  相似文献