Three-dimensional global simulation of multiple ICMEs’ interaction and propagation from the Sun to the heliosphere following the 25–28 October 2003 solar events

This study performs simulations of interplanetary coronal mass ejection (ICME) propagation in a realistic three-dimensional (3D) solar wind structure from the Sun to the Earth by using the newly developed hybrid code, HAFv.2+3DMHD. This model combines two simulation codes, Hakamada–Akasofu–Fry code version 2 (HAFv.2) and a fully 3D, time-dependent MHD simulation code. The solar wind structure is simulated out to 0.08 AU (18 Rs) from source surface maps using the HAFv.2 code. The outputs at 0.08 AU are then used to provide inputs for the lower boundary, at that location, of the 3D MHD code to calculate solar wind and its evolution to 1 AU and beyond. A dynamic disturbance, mimicking a particular flare’s energy output, is delivered to this non-uniform structure to model the evolution and interplanetary propagation of ICMEs (including their shocks). We then show the interaction between two ICMEs and the dynamic process during the overtaking of one shock by the other. The results show that both CMEs and heliosphere current sheet/plasma sheet were deformed by interacting with each other.     

民法精神的复兴与中国的现代化

市场经济就是法制经济。中国对市场经济的历史选择，意味着中国法律体系的构建必须以源于罗马法的民法为主导。本文从法理和中西法律传统的比较中，阐释了培养民法的意识，强化民法的基本理念，树立人文主义的民法精神对中国迈向物质和精神现代化具有深远的意义。     

Characterization of Solar Coronal Holes and Plumes Using Spectroscopic Diagnostic Techniques Applied to SOHO/CDS Observations

Results from a series of SOHO/Coronal Diagnostic Spectrometer (CDS) observations of coronal holes and plumes are presented, including analysis of a low-latitude plume observed in August 1996. Spectroscopic diagnostic techniques using the CHIANTI atomic database are applied to derive the plasma parameters: electron density, temperature, and element abundances. The results are compared with quiet sun values. Coronal electron densities in the holes are found to be about 2 × 10⁸ cm^-3, a factor of two to three lower than in the quiet sun. The plasma thermal distribution exhibits differences between coronal holes, the quiet sun and plumes. For example, the peak of the emission in coronal holes is at a lower temperature (T ⋍ 8 × 10⁵ K) than in the quiet sun (T ⋍ 1 × 10⁶ K), while plumes are cooler (T ⋍ 7.6 × 10⁵ K) and show a different distribution, closer to an isothermal state. This revised version was published online in June 2006 with corrections to the Cover Date.     

Nonthermal Radiation Mechanisms

In this paper we review the possible radiation mechanisms for the observed non-thermal emission in clusters of galaxies, with a primary focus on the radio and hard X-ray emission. We show that the difficulty with the non-thermal, non-relativistic Bremsstrahlung model for the hard X-ray emission, first pointed out by Petrosian (Astrophys. J. 557, 560, 2001) using a cold target approximation, is somewhat alleviated when one treats the problem more exactly by including the fact that the background plasma particle energies are on average a factor of 10 below the energy of the non-thermal particles. This increases the lifetime of the non-thermal particles, and as a result decreases the extreme energy requirement, but at most by a factor of three. We then review the synchrotron and so-called inverse Compton emission by relativistic electrons, which when compared with observations can constrain the value of the magnetic field and energy of relativistic electrons. This model requires a low value of the magnetic field which is far from the equipartition value. We briefly review the possibilities of gamma-ray emission and prospects for GLAST observations. We also present a toy model of the non-thermal electron spectra that are produced by the acceleration mechanisms discussed in an accompanying paper Petrosian and Bykov (Space Sci. Rev., 2008, this issue, Chap. 11).     

Mixing in Stars and the Evolution of the 3He Abundance

We first recall the observational and theoretical facts that constitute the so-called 3He problem. We then review the chemical anomalies that could be related to the destruction of 3He in red giants stars. We show how a simple consistent mechanism can lead to the destruction of 3He in low mass stars and simultaneously account for the low 12C/13C ratios and low lithium abundances observed in giant stars of different populations. This process should both naturally account for the recent measurements of 3He/H in galactic HII regions and allow for high values of 3He observed in some planetary nebulae. We propose a simple statistical estimation of the fraction of stars that may be affected by this process.     

Shortcomings of the Standard Solar Model

The SSM, invented in early nineteen sixties, remains a useful construction. There are now much larger number of its predictions that may be compared with observations than when it was first introduced. Seismic sounding based on oscillations frequencies provides the best test of the physical input for modelling stellar evolution. The results of the test must be viewed as a support for the standard theory of stellar evolution. However, significant differences in the sound-speed, photospheric He abundance, and other parameters between the Sun and the current models remain. Shortcomings in the EOS and in treatment of convection have been revealed. The differences in the sound-speed in the radiative interior may be explained by small opacity errors but other explanations are possible. Results of seismic sounding support the idea that the element mixing in the outer part of the radiative interior occurred during a significant fraction of the Sun's life. Such mixing is considered as a possible explanation of the deficit of lithium. The shortcomings of SSM cannot explain the deficits of measured neutrino fluxes. This revised version was published online in June 2006 with corrections to the Cover Date.     

The relationship between inductive electric field and flares

We observationally deduce the inductive electric field in the photosphere for the first time from the horizontal velocities computed by local correlation tracking (LCT) technique and the vector magnetic fields derived from vector magnetograms. We study the relationship between E and powerful flares (X-class) of four active regions (ARs): NOAA 10720, 10486, 9077 and 8100. It is found that the kernels of flares are roughly located near the inversion lines where maxima of E are observed. Our results show that E relates to the accumulation of non-potentiality in the photosphere and the transportation of non-potentiality from the photosphere to the corona.     

Solar Nebula Magnetohydrodynamics

The dynamical state of the solar nebula depends critically upon whether or not the gas is magnetically coupled. The presence of a subthermal field will cause laminar flow to break down into turbulence. Magnetic coupling, in turn, depends upon the ionization fraction of the gas. The inner most region of the nebula (≲0.1 AU) is magnetically well-coupled, as is the outermost region (≳10 AU). The magnetic status of intermediate scales (∼1 AU) is less certain. It is plausible that there is a zone adjacent to the inner disk in which turbulent heating self-consistently maintains the requisite ionization levels. But the region adjacent to the active outer disk is likely to be magnetically ``dead.' Hall currents play a significant role in nebular magnetohydrodynamics. Though still occasionally argued in the literature, there is simply no evidence to support the once standard claim that differential rotation in a Keplerian disk is prone to break down into shear turbulence by nonlinear instabilities. There is abundant evidence—numerical, experimental, and analytic—in support of the stabilizing role of Coriolis forces. Hydrodynamical turbulence is almost certainly not a source of enhanced turbulence in the solar nebula, or in any other astrophysical accretion disk. This revised version was published online in June 2006 with corrections to the Cover Date.     

Standard Solar Composition

We review the current status of our knowledge of the chemical composition of the Sun, essentially derived from the analysis of the solar photospheric spectrum. The comparison of solar and meteoritic abundances confirms that there is a very good agreement between the two sets of abundances. They are used to construct a Standard Abundance Distribution. This revised version was published online in June 2006 with corrections to the Cover Date.     

The ultraviolet view of the Magellanic Clouds from GALEX: A first look at the LMC source catalog

The Galaxy Evolution Exporer (GALEX) has performed unprecedented imaging surveys of the Magellanic Clouds (MC) and their surrounding areas including the Magellanic Bridge (MB) in near-UV (NUV, 1771-2831 Å) and far-UV (FUV, 1344-1786 Å) bands at 5^″$5^{″}$ resolution. Substantially more area was covered in the NUV than FUV, particularly in the bright central regions, because of the GALEX FUV detector failure. The 5σ$\sigma$ depth of the NUV imaging varies between 20.8 and 22.7 (ABmag). Such imaging provides the first sensitive view of the entire content of hot stars in the Magellanic System, revealing the presence of young populations even in sites with extremely low star-formation rate surface density like the MB, owing to high sensitivity of the UV data to hot stars and the dark sky at these wavelengths.