首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 35 毫秒
1.
Due to the relatively high stream densities involved, collective interactions with the ambient plasma are likely to be important for the electrons producing solar hard X-ray bursts. In thick- and thin-target bremsstrahlung models the most relevant process is limitation of the invoked electron beams by ion sound wave generation in the neutralizing reverse current established in the atmosphere. For the thick target model it is shown that typical electron fluxes are near the maximum permitted by stability of the reverse current so that ion-sound wave generation may be the process which limits the electron injection rate. On the other hand the chromospheric reverse current is sufficient to supply the large total number of electrons which have to be accelerated in the corona. For the thin target the low density of the corona severely limits the possible reverse current so that the maximum upward flux of fast electrons is probably much too small to explain X-ray bursts but compatible with observations of interplanetary electrons.A distinct class of model postulates a small number of electrons confined by resonant scattering in a dense coronal slab surrounding a current sheet with continuous stochastic acceleration offsetting collisional losses. The energetic aspects of such a situation described by Hoyng (1975) are developed here by addition of equations describing the slab geometry in terms of electron diffusion by whistler scattering and of the collisional damping of the accelerating Langmuir waves. Solution of these equations results in values for the fieldB(70–350 G), densityn 0(2–5 × 1012 cm –3), slab dimensions (1018 km2 × 0.3–3 km) and relative Langmuir energy density (10–3 – 10–2) required to produce the observed range of bursts. It is pointed out, however, that there may be no real gain in electron number requirements since the fast electrons in the emitting slab would be constantly swept out along with the frozen-in plasma as dissipation proceeds so that a large total number of electrons is still required. It could in fact be that just such a coronal region is the injection mechanism for the thick-target model.On leave from Department of Astronomy, University of Glasgow, Scotland.  相似文献   

2.
Here we complete an energy balance analysis of a double impulsive hard X-ray flare. From spatial observations, we deduce both flares probably occur in the same loop within the resolution of the data. For the first flare, the energy in the fast electrons (assuming a thick-target model) is comparable to the convective up-flow energy, suggesting that these are related successive modes of energy storage and transfer. The total energy lost through radiation and conduction, 2.0 × 1028 erg, is comparable to the energy in fast electrons 2.5 × 1028 erg. For the second flare, the energy in the fast electrons is more than one order of magnitude greater than the energy of the convective up-flow. Total energy losses are within a factor of two lower than the calculated fast electron energy. We interpret the observations as showing that the first flare occurred in a small loop with fast electrons heating the chromosphere and resulting in chromospheric evaporation increasing the density in the loop. For the second flare most of the heating occurred at the electron acceleration site. The two symmetrical components of the Ca xix resonance line and a high velocity down-flow of 115 km s –1 observed at the end of the second hard X-ray burst are consistent with the flare eruption (reconnection) region being high in the flare loop. The estimated altitude of the acceleration site is 5500 km above the photosphere.  相似文献   

3.
The discrepancy between the observed apparent acceleration of the Moon in longitude (1) and the actual lunar laser ranging data (3), (4) is of the order of ~ 9 × 10–23 rad s–2. It cannot be explained by the rms errors in (1) and (3), (4); processes connected with the internal Earth's dynamics and accelerating the Earth in its rotation might be responsible for the phenomenon, leading to the decreasing of the principal moment of the Earth's inertia ~ – 3.2 × 1029m2 kg cy–1.  相似文献   

4.
By processing 494 observations of Comet Harrington–Abell, we obtained a unified system of elements that includes its turn around the Sun during which it closely approached Jupiter to a minimum distance of 0.037 AU in 1974. A study of the cometary orbit before and after the approach showed that, probably, at the approach of the comet to Jupiter, apart from the well-known gravitational perturbations, its motion was affected by an additional force. An improvement of the cometary orbit by assuming that an additional acceleration inversely proportional to the square of the distance to Jupiter exists in its motion yielded the following values: (4.57 ± 0.42) × 10–10 and (–7.20 ± 0.42) × 10–10 AU day–2 for the radial and transversal acceleration components, respectively. As a plausible explanation of the changes in the cometary orbit, we additionally considered a model based on the hypothesis of partial disintegration of the cometary nucleus. The parameter that characterizes the instant displacement of the center of inertia along the jovicentric radius vector was estimated to be –1.83 ± 0.75 km. Based on a unified numerical theory of cometary motion, we determined the nongravitational parameters using Marsden's model for two periods: A 1 = (11.68 ± 1.74) × 10–10 AU day–2, A 2 = (0.53 ± 0.0357) × 10–10 AU day–2 for 1975–1999 and A 1 = (5.92 ± 5.86) × 10–10 AU day–2, A 2 = (0.08 ± 0.028) × 10–10 AU day–2 for 1955–1969, under the assumption that the nongravitational acceleration changed at the approach of the comet to Jupiter.  相似文献   

5.
Based on the observed dependence of the mean charge of several elements (C, O, Ne, Mg, Si and Fe) on energy for the gradual event of 6 November 1997 we deduce plasma parameters in the accelerating site. This is done in the framework of a charge-consistent acceleration model which incorporates ionisation and recombination processes during heavy ion energization by a parallel shock wave. To obtain good fits to observations we have to assume for the product of the characteristic acceleration time and number density T q ac N (3–10) ×109 s cm–3 and temperature T=106 K of a plasma where all the elements under consideration originated.  相似文献   

6.
Numerical integration of particle trajectories is performed to evaluate the statistical acceleration coefficients D TT for 1 to 100 MeV protons in a solar wind corotating interaction region (CIR) seen at 2.5 and 5.0 AU. Acceleration is followed in the solar wind reference frame and is due to random wave-particle interactions and to random drift motion in moderate scale field gradients. D TT due to the first effect reaches a peak value of 4 × 10 –7 MeV2 s–1 post shock at 10 MeV at 2.5 AU consistent with estimates based both upon cyclotron resonance and transit time damping theory. D TT from the second effect is less well established but is of the order of 10–7 MeV2 s–1 at 10 MeV, 5 AU. A comparison is made between the time constant for statistical acceleration within this CIR and estimates for diffuse shock acceleration and adiabatic deceleration. All three time constants are of the same order, but deceleration is faster than shock acceleration which in turn is faster than statistical acceleration.  相似文献   

7.
In a previous paper Lyttleton (1976) has shown that the apparent secular accelerations of the Sun and Moon, as given by de Sitter, can be largely explained if the Earth is contracting at the rate required by the phase-change hypothesis for the nature of the core. More reliable values for these accelerations have since become available which warrant a redetermination of the various effects concerned on the basis of constantG, and this is first carried out in the present paper. The lunar tidal couple, which is the same whetherG is changing or not, is found to be (4.74±0.38)×1023 cgs, about three-quarters that yielded by the de Sitter values, while within the theory the Moon would take correspondingly longer to reach close proximity to the Earth at about 1.5×109 years ago.The more accurate values of the accelerations enable examination to be made of the effects that a decreasingG would have, and it is shown that a valueG/G=–3×10–11 yr–1 can be weakly satisfied compared with the close agreement found on the basis of constantG, while a value as large numerically asG/G=–6×10–11 yr–1 seems to be definitely ruled out. On the iron-core model, an intrinsic positive component of acceleration of the angular velocity cannot be reconciled at all with the secular accelerations even for constantG, and far less so ifG is decreasing at a rate suggested by any recent cosmological theory.ItG=0, the amount of contraction available for mountain-building would correspond to a reduction of surface area of about 49×106 km2 and a volume to be redistributed of 160×109 km3 if the time of collapse were 2.5×109 years ago. For earlier times, the values are only slightly reduced. IfG/G=–3×10–11 yr–1, the corresponding values are 44×106 km2 and 138×109 km3 for collapse at –2.5×109 yr, and not importantly smaller at 38×106 km2 and 122×109 km3 for collapse at –4.5×109 yr. Any of these values would suffice to account in order of magnitude for all the eras of mountain-building. An intense brief period of mountain-building on an immense scale would result from the Ramsey-collapse at whatever time past it may have occurred.  相似文献   

8.
The long-period perturbations in the orbit of Lageos satellite due to the earth's albedo have been found using a new analytical formalism. The earth is assumed to be a sphere whose surface diffusely reflects sunlight according to Lambert's law. Specular reflection is not considered. The formalism is based on spherical harmonics; it produces equations which hold regardless of whether the terminator is seen by the satellite or not. Specializing in the case of a realistic zonal albedo shows that Lageos' orbital semimajor axis changes periodically by only about a centimeter and the eccentricity by two parts in 105. The longitude of the node increases secularly by about 6×10–4 arc sec yr–1. The effect considered here can explain neither the secular decay of 1.1 mm day–1 in the semimajor axis nor the observed along-track variations in acceleration of order 2×10–12 ms–2.  相似文献   

9.
S. W. Kahler 《Solar physics》1984,90(1):133-138
In the second phase acceleration process the close time coincidence between the gradual hard X-ray burst and the type II shock wave is presumed due to shock acceleration of the electrons producing the gradual phase burst. We point out that recent studies of gradual hard X-ray bursts place the source heights well below the heights of 2–10 × 105 km traversed by the shock. Gradual phase energetic electrons therefore cannot be accelerated in the shock but must be produced elsewhere. We propose the loop systems of long decay X-ray events (LDEs) as the sites of the gradual phase electron production.  相似文献   

10.
The most conspicuous effects of non-gravitational forces in the Earth-Moon system are the accelerations of the Earth's spin and of the Moon's mean angular velocity. Evidence indicates that the present acceleration of the Moon is between –20 and –52 s of arc per century per century and that the present average acceleration of the Earth is between –5 and –23 parts in 109 per century. Over the past 2000 yr, the average for the Moon has been about –42 s per century per century and for the Earth has been about –28 parts in 109 per century; these values are probably correct within 10%. Evidence that does not involve any assumptions about the present values shows strongly that there was a square wave in the accelerations that lasted from about 700–1300, and that the accelerations were different by a factor of perhaps 5 during the time of this wave from what they were at neighboring times.An effect that seems to be changing the obliquity of the ecliptic has been reported in recent literature, on the basis of data obtained within the past century. The effect amounts to about 1/4 s of arc per century if it is real. Older data are not accurate enough to give information about an effect this small.There are no satisfactory explanations of the accelerations. Existing theories of tidal friction are quite inadequate.Paper presented at the AAAS Symposium on the Early History of the Earth and Moon in Philadelphia on 28 December 1971.  相似文献   

11.
Energetic particle (0.1 to 100 MeV protons) acceleration is studied by using high resolution interplanetary magnetic field and plasma measurements at 1 AU (HEOS-2) and at 5 AU (Pioneer 10). Energy changes of a particle population are followed by computing test particle trajectories and the energy changes through the particle interaction with the time varying magnetic field. The results show that considerable particle acceleration takes place throughout the interplanetary medium, both in the corotating interaction regions (CIR) (5 AU), and in quiet regions (1 AU). Although shocks may contribute to acceleration we suggest statistical acceleration within the CIRs is sufficient to explain most energetic particle observations (e.g., McDonaldet al., 1975; Barnes and Simpson, 1976).The first and second order statistical acceleration coefficients which include transit time damping and Alfvén resonance interactions, are found to be well represented byD T 8.5×10–6 T 0.5 MeV s–1 andD TT 4×10–6 T 1.5 MeV2 s–1 at 5 AU.By comparison, Fisk's estimates (1976), based on quasi-linear theory for transit-time damping, gaveD TT 5×10–7 T MeV2 s–1 at 1 AU.  相似文献   

12.
In a closed expanding-contracting Universe, matter will be subject to an inward acceleration large enough to prevent perpetual expansion. A closed Universe must also perform a simple harmonic motion, which might consist either of one single cycle or of an infinite series of oscillations about a central point. It is the purpose of this study to find the rate ofa 0, the cosmic acceleration, from which the gravitational constantG can be determined. It will be shown from Ampère's equation and Planck's radiation law that it is possible to derivea 0=7.623×10–12 ms–2, a value which also conforms with the uncertainty principle. The relationship betweena 0 and electromagnetic radiation is based on the concept that charges (such as electrons) must emit radiation while accelerating. The rate ofa 0 yields a universal gravitational constant ofG=6.645×10–11 N m2 kg–2.  相似文献   

13.
It is known that the observed secular accelerations of the Sun and Moon are not consistent with the tidal interactions of the Earth with the Sun and Moon. Following Dicke, the hypothesis of variable constant of gravity is adopted and expressions for the accelerations are derived. It is shown that if the theoretical ratio of the acceleration is equated the observed one, a unique value for —/G can be calculated. Adopting the accelerations obtained by Fotheringham, Newton, Muller and Stephenson, and Stephenson, it is found that — /G ranges from 1.4 × 10–11 to 3.3 × 10–11 yr–1. This estimate is consistent with the one based upon the comparison of the lunar accelerations measured with respect to atomic and ephemis times.  相似文献   

14.
An ASCA observation of the Jovian impact of the comet Shoemaker-Levy 9 is reported. Four impacts of H, L, Q1 and R were observed and four impacts of B, C, G, and Q2 were observed within 60 minutes after their impacts. No significant flaring of X-ray emission was observed. Upper limit X-ray fluxes of 90 % confidence level, averaged 5 minutes just after the impacts, were 2.4 × 10–13 erg sec–1 cm–2, 3.5 × 10–13 erg sec–1 cm–2, 1.6 × 10–13 erg sec–1 cm–2 and 2.9 × 10–13 erg sec–1 cm–2 for the impacts of H, L, Q1 and R, respectively, in the 0.5(0.7 for H and Q1)–10 keV energy range. However, a hint of X-ray enhancement around Jupiter from July 17 to July 19 was detected with about 2 6 × 10–14 erg sec–1 cm–2 in the 0.5–10 keV energy range.  相似文献   

15.
A magnetospheric boundary and its associated standing-shock wave for the earth are scaled down in size to apply to Mars. A suggestion by the Mariner-IV experimenters that their magnetometer may have detected a Martian shock at 0123 UT (earth) on July 15, 1965, is accepted. The scaling procedure used previously in the case of the Mariner-II flyby of Venus on December 14, 1962, as well as in the present case of Mars is repeated but with a different model. We propose a magnetospheric boundary for the earth, which is based on a maximum radius of 22 R E suggested by Imp-1 magnetometer data. We further suggest a low value (1.2) of the adiabatic exponent, . In addition we propose the use of the interplanetary magnetoacoustic Mach number, M*, which is a combination of both Alfvén and ordinary gasdynamic Mach numbers. Our choice of values for these parameters is not unique since many such combinations exist which will show good agreement with observation. For example, the ratio of the Martian dipole moment to that for the earth is found to be 2.1 × 10–4 by our application of the hypersonic analog. This value compares very closely with 3 × 10–4 deduced as an upper bound by the Mariner-IV investigators. The present synthesis is presented as an independent calculation based on the above theoretical considerations, together with the experimenters' probable observation of a Martian shock wave.Since this paper was submitted for publication, theoretical calculations of the steady-state average magnetic induction in the transition region for an interplanetary field oriented at several angles to the velocity vector have been published by A. Y. Alksne, Planetary Space Science 15 (1967), 239–245. As anticipated in the text above, the magnitudes are slightly changed, but the polarities are significantly different.Formerly the Central Radio Propagation Laboratory of the National Bureau of Standards.  相似文献   

16.
In this article, our previous Hamiltonian theory for the rotation of an Earth whose elastic mantle is deformed by rotation and linisolar attraction is applied to the study of the secular acceleration of the Earth's rotation. Since it is a result of the inelasticity, the theory is extended to include a phase lag. So, we obtain, in a theoretical way, a value of –5.6 × 10–22 rd sec–2, which agrees perfectly with the latest observational results.  相似文献   

17.
Yasnov  L.V.  Bogod  V.M.  Fu  Q.  Yan  Y. 《Solar physics》2003,215(2):343-355
Based on spectral observations of active region NOAA 8545 on 19 May 1999, we describe the processes responsible for non-thermal long-lasting radio emission and for narrow-band non-drifting bursts observed at the same time. Non-thermal long-lasting radio emission consisted of two components: short-duration (1–2 s) microbursts with fluxes about 0.001 s.f.u. and continuum emission with growing spectrum in the range of 1000–2000 MHz. Energetic electrons continuously existed in the active region for more than 2.2 hours. The nature and parameters of microbursts were discussed by Bogod, Mercier, and Yasnov (2001). Here we consider the continuum source nature. It is shown that the model, taking into account the cyclotron loss-cone instability of hot electrons and the generation of plasma waves at the upper hybrid frequency, may explain the observed continuum source parameters. For the narrow-band non-drifting bursts we consider two models: the first taking into account an excitation of weak shock waves across the magnetic field and the second with an excitation of the upper hybrid waves under the double plasma resonance. Continuum source parameters are close to the last model. Our estimations for the magnetic field strength are as follows: H=120–126 G, which is valid for the region where the electron density of background plasmas n=(1.4–1.9) ×109 cm–3; H=180–190 G for the region where n=(3.0–4.3) ×109 cm–3; H=290 G for the region where n e=2.5×1010 cm–3; and H=350 G for the region where n e=3.5×1010 cm–3. The speed of the fast electrons is about 0.10–0.14 c.  相似文献   

18.
In a closed gravitationally-bound Universe we are subject to an inward accelerationa 0. One consequence of this acceleration is that matter will radiate and create a black-body spectrum throughout the Universe. Using the valuea 0=7.623×10–12 ms–2 and a radiation formula from a previously-described cosmological model (Wåhlin, 1981), we obtain a black-body temperature of 2.766 K.  相似文献   

19.
The lifetime of massive X-ray binaries is about 2–5×105 yr, close to the nuclear time scale. The lifetime of nonmassive X-ray binaries close to the thermal one is about 0.5–1×107 yr. Massive systems may be conserved at supernova explosion, the probability of the conservation of nonmassive systems being 1–3×10–3.  相似文献   

20.
In this paper the solar neutron and white-light flare is studied on the basis of radioastronomical observations. It is shown that the 3 June, 1982 flare had an impulsive character. A strong shock wave (M A 2.9) was observed unusually soon after the impulsive phase of the flare. The radio spectrum of this event shows that the primary acceleration process probably occurred in the region with an electron density of n e = 4.4 × 1015 m–3. The pulsations of the type IV radio burst, observed 15 min after the mass ejection process, manifest the reconnection process in the post-flare stage.Proceedings of the Workshop on Radio Continua during Solar Flares, held at Duino (Trieste), Italy, 27–31 May, 1985.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号