共查询到20条相似文献,搜索用时 15 毫秒
1.
Yue-hua Ma You-wen He Pin-xin Xu Hai-bin Zhao 《Chinese Astronomy and Astrophysics》2008,32(2):186-196
During the first international joint observation of the Leo strong meteor shower, multidisciplinary and multi-media synthetic observation of Leo and Draco strong meteor showers and their catastrophic space weather events were carried out. The comprehensive analysis of the observed and related data of the Leo, Perseus and Draco strong meteor showers obtained for near half a century (from 1957 to 2003) fully verifies that the non-sporadic periodic strong meteor shower may lead to catastrophic space weather events. Preliminary identification is made of the following: the mechanism of formation of strong meteor showers, the law of occurrence of the fbEs abnormal peak and serious safety hazards for astronavigation. Also discussed in this paper are the evolutionary process of cometary dust, the law of occurrence and loss of cosmic dust storm and the mechanism of maintaining cosmic dust in the mid-latitude Es layer. 相似文献
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In this paper we present results from 3D MHD numerical simulations based on the flux tube tectonics method of coronal heating proposed by Priest, Heyvaerts, and Title (2002). They suggested that individual coronal loops connect to the photosphere in many different magnetic flux fragments and that separatrix surfaces exist between the fingers connecting a loop to the photosphere and between individual loops. Simple lateral motions of the flux fragments could then cause currents to concentrate along the separatrices which may then drive reconnection contributing to coronal heating. Here we have taken a simple configuration with four flux patches on the top and bottom of the numerical domain and a small background axial field. Then we move two of the flux patches on the base between the other two using periodic boundary conditions such that when they leave the box they re-enter it at the other end. This simple motion soon causes current sheets to build up along the quasi-separatrix layers and subsequently magnetic diffusion/reconnection occurs. 相似文献
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We derive the transformations to convert the state vector in cartesian coordinates into geometric orbital elements (and conversely
the geometric elements into the state vector) for a test particle moving around an oblate planet. These transformations arise
from the epicyclic theory and are accurate to second order in eccentricity and inclination. This paper is written to be directly
used for computational purposes, such as the numerical study of ring dynamics. 相似文献
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The effects of changes in the space environment on the ISOPHOT photoconductivedetectors over the whole ISO mission were studied using the complete setof responsivity check measurements taken after the curing of the detectors.We found that the responsivity of the Ge-based, low bias voltage far-infrared detectors (P3, C100, and C200) is sensitive to the conditions of the Space Weather.We present evidence that an increased responsivity level (20% – 50%) after curing of the detectors is linked to the onset of geomagnetic storms. TheSi-based, high bias voltage detectors P1, P2 and PHT–SS show only small changesin their responsivity. An exception is the PHT–SL array which shows a similar,but less pronounced behaviour as the FIR detectors. While these relationshave been demonstrated by our study, a detailed physical understanding is still outstanding. The Space Weather dependent scatter of the responsivity,being the photometric scaling factor (conversion from measured photo currentto inband power on the detector), justifies the observing mode design to include frequent monitoring of its actual level. 相似文献
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Marco Belan Sergio de Ponte Silvano Massaglia Daniela Tordella 《Astrophysics and Space Science》2004,293(1-2):225-232
The experiment described here is focussed to the observation of underexpanded, hypersonic turbulent jets. The experiment is relevant to a few aspects concerning the dynamics of astrophysical phenomena such as the Herbig-Haro jets and to the interaction between the large-scale vortices and the system of shocks that determine the spreading and entrainment properties of highly compressible free-flows. A number of orifice jets with a ratio between the stagnation pressure and the ambient pressure of the order 103-104 have been studied by changing the stagnation/ambient density ratio. This has been realized using dissimilar gases in the jet and in the ambient medium: by using He, Ar and air the stagnation/ambient density ratio can be changed by one order of magnitude while keeping fixed the pressure ratio. It has been possible to visualize the near and mid-term evolution of the jets and measure the axial and transversal density distributions. A comparison relevant to the shock waves configuration in between the nozzle exit and the first Mach's disk is shown for an air in air laboratory jet and its numerical simulation. 相似文献
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Georgobiani D Kosovichev AG Nigam R Nordlund Å Stein RF 《The Astrophysical journal》2000,534(2):L139-L142
The ACIS front-illuminated CCDs on board the Chandra X-Ray Observatory were damaged in the extreme environment of the Earth's radiation belts, resulting in enhanced charge transfer inefficiency (CTI). This produces a row dependence in gain, event grade, and energy resolution. We model the CTI as a function of input photon energy, including the effects of detrapping (charge trailing), shielding within an event (charge in the leading pixels of the 3x3 event island protects the rest of the island by filling traps), and nonuniform spatial distribution of traps. This technique cannot fully recover the degraded energy resolution, but it reduces the position dependence of gain and grade distributions. By correcting the grade distributions as well as the event amplitudes, we can improve the instrument's quantum efficiency. We outline our model for CTI correction and discuss how the corrector can improve astrophysical results derived from ACIS data. 相似文献
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Gianluigi Bodo Claudio Zanni Giuseppe Murante Paola Rossi Silvano Massaglia Attilio Ferrari 《Astrophysics and Space Science》2004,293(1-2):247-254
We study, by numerical simulations, the propagation of an axisymmetric supersonic jet in an isothermal King atmosphere and we analyse the evolution of the resulting X-ray properties and their dependence on the jet physical parameters. We show the existence of two distinct regimes of interaction, with strong and weak shocks. In the first case shells of enhanced X-ray emission are to be expected, whereas in the second case we expect deficit of X-ray emission coincident with the cocoon. Analysing the results of our simulations we find that the jet kinetic power is the main parameter controlling the transition between the two regimes. We also discuss, in the same scheme, the ICM heating induced by the jet propagation, considering its effects on the observed relations between the cluster X-ray luminosity and temperature and between cluster entropy and temperature. 相似文献
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Halo coronal mass ejections (HCMEs) are responsible of the most severe geomagnetic storms. A prediction of their geoeffectiveness
and travel time to Earth’s vicinity is crucial to forecast space weather. Unfortunately, coronagraphic observations are subjected
to projection effects and do not provide true characteristics of CMEs. Recently, Michalek (Solar Phys.
237, 101, 2006) developed an asymmetric cone model to obtain the space speed, width, and source location of HCMEs. We applied this technique
to obtain the parameters of all front-sided HCMEs observed by the SOHO/LASCO experiment during a period from the beginning
of 2001 until the end of 2002 (solar cycle 23). These parameters were applied for space weather forecasting. Our study finds
that the space speeds are strongly correlated with the travel times of HCMEs to Earth’s vicinity and with the magnitudes related
to geomagnetic disturbances. 相似文献
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R. F. Coker B. H. Wilde J. M. Foster B. E. Blue P. A. Rosen R. J. R. Williams P. Hartigan A. Frank C. A. Back 《Astrophysics and Space Science》2007,307(1-3):57-62
We have conducted experiments on the Omega laser at the University of Rochester that have produced jets of supersonic Ti impacting
and being deflected by a ball of high density plastic. These mm-sized jets of dense plasma are highly complex, have large
Reynolds numbers, and, given sufficient time and shear, should produce a fully turbulent flow. The experiments are diagnosed
with a point-projection backlighter, resulting in a single image per shot. Simulations of the 3D hydrodynamics capture the
large-scale features of the experimental data fairly well while missing some of the smaller scale turbulent-like phenomena.
This is to be expected given the limited characterization of the targets as well as the finite resolution of the 3D simulations.
If Euler scaling holds, these experiments should model larger astrophysical jets in objects such as HH 110 where an outflow
can be seen colliding with a molecular cloud. However, Euler scaling demands that not only the isothermal internal Mach numbers
of the two systems be similar but also that any dissipative mechanisms, such as radiative cooling or viscous dissipation,
be of equal importance relative to each other. Similar equations of state are required as well. We discuss such issues in
the context of these experiments and simulations. 相似文献
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Studying space weather is an excellent subject for getting people interested in space science in general; therefore, it is being included as part of the education and public outreach activities being organized during the International Heliophysical Year (IHY). The general public find the subject interesting because variation in the space environment, i.e., space weather, can be related to their daily lives. The international organization concerned with space weather is called the International Space Environment Service (ISES). This organization is composed of the World Warning Agency (WWA) and 11 Regional Warning Centers (RWCs). The WWA and RWCs collect, collate, and disseminate space weather information on a regular basis. This report contains history and activities of the ISES. 相似文献
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Xiao-Yan Xu Peng-Fei Chen Cheng Fang Department of Astronomy Nanjing University Nanjing 《中国天文和天体物理学报》2005,5(6):636-644
Observations indicate that solar coronal mass ejections (CMEs) are closely associated with reconnection-favored flux emergence, which was explained in the emerging flux trigger mechanism for CMEs by Chen & Shibata based on numerical simulations. We present a parametric survey of the triggering agent: its polarity orientation, position, and the amount of the unsigned flux. The results suggest that whether a CME can be triggered depends on both the amount and location of the emerging flux, in addition to its polarity orientation. A diagram is presented to show the eruption and non-eruption regimes in the parameter space. The work is aimed at providing useful information for the space weather forecast. 相似文献
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We present results from a global simulation of the interaction of the solar wind with Earth's magnetosphere, ionosphere, and
thermosphere for the Bastille Day geomagnetic storm and compare the results with data. We find that during this event the
magnetosphere becomes extremely compressed and eroded, causing 3 geosynchronous GOES satellites to enter the magnetosheath
for an extended time period. At its extreme, the magnetopause moves at local noon as close as 4.9 R
E to Earth which is interpreted as the consequence of the combined action of enhanced dynamic pressure and strong dayside reconnection
due to the strong southward interplanetary magnetic field component B
z, which at one time reaches a value of −60 nT. The lobes bulge sunward and shield the dayside reconnection region, thereby
limiting the reconnection rate and thus the cross polar cap potential. Modeled ground magnetic perturbations are compared
with data from 37 sub-auroral, auroral, and polar cap magnetometer stations. While the model can not yet predict the perturbations
and fluctuations at individual ground stations, its predictions of the fluctuation spectrum in the 0–3 mHz range for the sub-auroral
and high-latitude regions are remarkably good. However, at auroral latitudes (63° to 70° magnetic latitude) the predicted
fluctuations are slightly too high.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1014228230714 相似文献
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一般认为,Langmuir波(LW)转换为电磁波是太阳Ⅲ型射电爆的产生机制。由电子束流不稳定性可以很容易地激发LW,正向LW和反向LW的相互作用被认为是产生Ⅲ型爆二次谐波的原因,但反向LW的色散方程和产生机制尚未得到充分研究。通过粒子(Particle In Cell,PIC)模拟研究了反向LW的产生机制,发现反向LW不能由电子束流直接激发,其能量基本上是由正向LW散射得到的。然而,电子束流对正向LW的二次谐波有直接放大作用。 相似文献
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The sunspot penumbra is a transition zone between the strong vertical magnetic field area (sunspot umbra) and the quiet Sun.
The penumbra has a fine filamentary structure that is characterized by magnetic field lines inclined toward the surface. Numerical
simulations of solar convection in inclined magnetic field regions have provided an explanation of the filamentary structure
and the Evershed outflow in the penumbra. In this article, we use radiative MHD simulations to investigate the influence of
the magnetic field inclination on the power spectrum of vertical velocity oscillations. The results reveal a strong shift
of the resonance mode peaks to higher frequencies in the case of a highly inclined magnetic field. The frequency shift for
the inclined field is significantly greater than that in vertical-field regions of similar strength. This is consistent with
the behavior of fast MHD waves. 相似文献
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Anthony L. Peratt 《Astrophysics and Space Science》1997,256(1-2):51-75
Advances in the simulation of astrophysical and cosmic plasmas are the direct result of advances in computational capabilities, today consisting of new techniques such as multilevel concurrent simulation, multi-teraflop computational platforms and experimental facilities for producing and diagnosing plasmas under extreme conditions for the benchmarking of simulations. Examples of these are the treatment of mesoscalic plasma and the scaling to astrophysical and cosmic dimensions and the Accelerated Strategic Computing Initiative whose goal is to construct petaflop (1015 floating operations per second) computers, and pulsed power and laser inertial confinement plasmas where megajoules of energy are delivered to highly-diagnosed plasmas. This paper concentrates on the achievements to date in simulating and experimentally producing plasmas scaled to both astrophysical and cosmic plasma dimensions. A previous paper (Part I, Peratt, 1997) outlines the algorithms and computational growth. 相似文献