Reversal of Heliospheric Magnetic Field Polarity: Theoretical Model

A simple analytical model of the reversal of the heliospheric magnetic field is suggested. The shape of the heliospheric current sheet is found for each instant of time using a kinematic approximation. Calculation results are illustratively presented in graphic and animated forms, showing a 3-D dynamic picture of the reversal of the heliospheric magnetic field throughout a 22-year solar cycle.     

Systematically Asymmetric Heliospheric Magnetic Field: Evidence for a Quadrupole Mode and Non-Axisymmetry with Polarity Flip-Flops

Recent studies of the heliospheric magnetic field (HMF) have detected interesting, systematic hemispherical and longitudinal asymmetries which have a profound significance for the understanding of solar magnetic fields. The in situ HMF measurements since the 1960s show that the heliospheric current sheet (HCS) is systematically shifted (coned) southward during solar minimum times, leading to the concept of a bashful ballerina. While temporary shifts can be considerably larger, the average HCS shift (coning) angle is a few degrees, less than the 7.2^∘ tilt of the solar rotation axis. Recent solar observations during the last two solar cycles verify these results and show that the magnetic areas in the northern solar hemisphere are larger and their intensity weaker than in the south during long intervals in the late declining to minimum phase. The multipole expansion reveals a strong quadrupole term which is oppositely directed to the dipole term. These results imply that the Sun has a symmetric quadrupole S0 dynamo mode that oscillates in phase with the dominant dipole A0 mode. Moreover, the heliospheric magnetic field has a strong tendency to produce solar tilts that are roughly opposite in longitudinal phase. This implies is a systematic longitudinal asymmetry and leads to a “flip-flop” type behaviour in the dominant HMF sector whose period is about 3.2 years. This agrees very well with the similar flip-flop period found recently in sunspots, as well as with the observed ratio of three between the activity cycle period and the flip-flop period of sun-like stars. Accordingly, these results require that the solar dynamo includes three modes, A0, S0 and a non-axisymmetric mode. Obviously, these results have a great impact on solar modelling.     

宇宙磁场中的中微子

本文讨论了有质量的Dirac粒子在宇宙磁场中的演化。宇宙磁场使空间度规出现各向异性。通过求解Dirac方程,得到了中微子在宇宙磁场中的表观磁矩。     

Small-scale Gradients and Large-scale Diffusion of Charged Particles in the Heliospheric Magnetic Field

We present a simple spin-evolution model that predicts that rapidly rotating accreting neutron stars will be confined mainly to a narrow range of spin frequencies: P=1.5-5 ms. This is in agreement with current observations of neutron stars in both the low-mass X-ray binaries and the millisecond radio pulsars. The main ingredients in the model are (1) the instability of r-modes above a critical spin rate, (2) the thermal runaway that is due to the heat released as viscous damping mechanisms counteract the r-mode growth, and (3) a revised estimate of the strength of the dissipation that is due to the presence of a viscous boundary layer at the base of the crust in an old and relatively cold neutron star. We discuss the gravitational waves that are radiated during the brief r-mode-driven spin-down phase. We also briefly touch on how the new estimates affect the predicted initial spin periods of hot young neutron stars.     

Effects of the Sector Structure of the Interplanetary Magnetic Field on Galactic Cosmic Ray Anisotropy

We study the effects of the sector structure of the interplanetary magnetic field (IMF) on the Galactic cosmic ray (GCR) anisotropy at solar minimum by using Global Network neutron monitor data. The hourly neutron monitor data for 1976 were averaged for the positive (+) and negative (–) IMF sectors (+ and – correspond to the antisolar and solar directions of magnetic field lines, respectively) and then processed by the global survey method. We found that the magnitude of the GCR anisotropy vector is larger in the positive IMF sector and that the phase shifts toward early hours. The derived GCR components A _r, A , and A for the different + and – sectors are then used to calculate the angle ( 46°) between the IMF lines and the Sun–Earth line, the solar wind velocity U ( 420 km/s), the ratio of the perpendicular (K ) and parallel (K _||) diffusion coefficients K /K _|| = ( 0.33), and other parameters that characterize the GCR modulation in interplanetary space.     

Magnetic Flux Imbalance of the Solar and Heliospheric Magnetic Fields

A comparative analysis of solar and heliospheric magnetic fields in terms of their cumulative sums reveals cyclic and long-term changes that appear as a magnetic flux imbalance and alternations of dominant magnetic polarities. The global magnetic flux imbalance of the Sun manifests itself in the solar mean magnetic field (SMMF) signal. The north – south asymmetry of solar activity and the quadrupole mode of the solar magnetic field contribute the most to the observed magnetic flux imbalance. The polarity asymmetry exhibits the Hale magnetic cycle in both the radial and azimuthal components of the interplanetary magnetic field (IMF). Analysis of the cumulative sums of the IMF components clearly reveals cyclic changes in the IMF geometry. The accumulated deviations in the IMF spiral angle from its nominal value also demonstrate long-term changes resulting from a slow increase of the solar wind speed over 1965 – 2006. A predominance of the positive IMF B _z with a significant linear trend in its cumulative signal is interpreted as a manifestation of the relic magnetic field of the Sun. Long-term changes in the IMF B _z are revealed. They demonstrate decadal changes owing to the 11/22-year solar cycle. Long-duration time intervals with a dominant negative B _z component were found in temporal patterns of the cumulative sum of the IMF B _z .     

Magnetic and Velocity Shear Driven Instabilities in the Heliospheric Plasma

We have addressed the problem of combined magnetic and velocity shear driven instabilities in the context of the heliospheric plasma. New high-order numerical methods have been used to analyze the instability dynamics of the heliospheric current-sheet interacting with the structure determined by the slow component of the solar wind on the solar equatorial plane above the helmet streamers. Preliminary results are presented.     

Non-Linear Amplification of a Magnetic Field Driven by Cosmic Ray Streaming

One dimensional numerical results of the non-linear interaction between cosmic rays and a magnetic field are presented. These show that cosmic ray streaming drives large amplitude Alfvénic waves. The cosmic ray streaming energy is very efficiently transfered to the perturbed magnetic field of the Alfvén waves. Thus a magnetic field of interstellar values, assumed in models of supernova remnant blast wave acceleration, would not be appropriate in the region of the shock. The increased magnetic field reduces the acceleration time and so increases the maximum cosmic ray energy, which may provide a simple and elegant resolution to the highest energy galactic cosmic ray problem were the cosmic rays themselves provide the fields necessary for their acceleration. This revised version was published online in July 2006 with corrections to the Cover Date.     

Long-Term Modulation of Galactic Cosmic Rays in the Heliosphere by Curvature of the Interplanetary Magnetic Field

Long-term changes of the GCR intensity in the heliosphere were analysed making use of records of cosmogenic isotopes abundances (¹⁰Be and ¹⁴C) in natural archives and neutron monitor data. These data contain information about short-term, 11-year, 22-year, centennial and two-centennial cycles of solar activity. A mechanism to explain the long-term modulation of GCR due to changes in the curvature of the interplanetary magnetic field, resulting from changes in solar activity, is suggested.     

Milestones in the Observations of Cosmic Magnetic Fields

Magnetic fields are observed everywhere in the universe. In this review, we concentrate on the observational aspects of the magnetic fields of Galactic and extragalactic objects. Readers can follow the milestones in the observations of cosmic magnetic fields obtained from the most important tracers of magnetic fields, namely, the star-light polarization, the Zeeman effect, the rotation measures (RMs, hereafter) of extragalactic radio sources, the pulsar RMs, radio polarization observations, as well as the newly implemented sub-mm and mm polarization capabilities. The magnetic field of the Galaxy was first discovered in 1949 by optical polarization observations. The local magnetic fields within one or two kpc have been well delineated by starlight polarization data. The polarization observations of diffuse Galactic radio background emission in 1962 confirmed unequivocally the existence of a Galactic magnetic field. The bulk of the present information about the magnetic fields in the Galaxy comes from anal     

Understanding the Behavior of the Heliospheric Magnetic Field and the Solar Wind During the Unusual Solar Minimum Between Cycles 23 and 24

The properties of the heliospheric magnetic field and the solar wind were substantially different in the unusual solar minimum between Cycles 23 and 24: the magnetic-field strength was substantially reduced, as were the flow properties of the solar wind, such as the mass flux. Explanations for these changes are offered that do not require any substantial reconsideration of the general understandings of the behavior of the heliospheric magnetic field and the solar wind that were developed in the minimum of Cycle 22?–?23. Solar-wind composition data are used to demonstrate that there are two distinct regions of solar wind: solar wind likely to originate from the stalk of the streamer belt (the highly elongated loops that underlie the heliospheric current sheet), and solar wind from outside this region. The region outside the streamer-stalk region is noticeably larger in the minimum of Cycle 23?–?24; however, the increased area can account for the reduction in the heliospheric magnetic-field strength in this minimum. Thus, the total magnetic flux contained in this region is the same in the two minima. Various correlations among the solar-wind mass flux and coronal electron temperature inferred from solar-wind charge states were developed for the Cycle 22?–?23 solar minimum. The data for the minimum of Cycle 23?–?24 suggest that the correlations still hold, and thus the basic acceleration mechanism is unchanged in this minimum.     

The Origin of Highest Energy Cosmic Rays and Cosmic Magnetic Fields

We summarize the status of the search for the origin of the highest energy cosmic rays. We briefly mention several competing proposals, such as supersymmetric particles, Gamma Ray Bursts also giving rise to energetic protons, interacting high energy neutrinos and cosmological defects, and then concentrate on the possibilities of the propagation of these particles, assuming that they are charged. The distribution of arrival directions of the highest energy particles on the sky ought to reflect the source distribution as well as propagation history. The present status can be summarized as inconclusive. If we were able to confirm any particular theory these particles beyond 10²⁰eV may be turned into tools of high energy physics. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Tilt of the Magnetic Polarity Axis in Active Regions with Different Polarity Separation and Flux

In this paper, 203 bipolar active regions, in which bipolar magnetic fields are dominant, were chosen from the data set of photospheric vector magnetograms observed at Huairou Solar Observing Station in Beijing during 1988–1996. We calculated the tilts of the magnetic polarity axis in these active regions and investigated the dependence of the tilt on physical quantities such as polarity separation, total flux and the relationship between total flux and polarity separation, total area of active regions.The results are as follows:(1) The active regions with large tilt angle have smaller magnetic polarity separations.(2) The active regions with large tilt angle have smaller fluxes.(3) The active regions with large flux have larger polarity separations.(4) The active regions with large area have larger fluxes.These results will possibly provide new information about the nature and dynamic behavior of magnetic flux tubes forming active regions beneath the photosphere.     

Particle Acceleration by a Time-Varying Electric Field in Merging Magnetic Fields

Traditional models for particle acceleration by magnetic reconnection in solar flares assumed a constant electric field in a steady reconnecting magnetic field. Although this assumption may be justified during the gradual phase of flares, the situation is different during the impulsive phase. Observed rapid variations in flare emissions imply that reconnection is non-steady and a time-varying electric field is present in a reconnecting current sheet. This paper describes exploratory calculations of charged particle orbits in an oscillating electric field present either at a neutral plane or a neutral line of two-dimensional magnetic field. A simple analytical model makes it possible to explain the effects of particle trapping and resonant acceleration previously noted by Petkaki and MacKinnon in a numerical simulation. As an application, electron acceleration to X-ray generating energies in impulsive solar flares is discussed within the context of the model.     

宇宙微波背景辐射的观测和理论

介绍了有关宇宙微波背景辐射（ＣＢＲ）观测和理论研究的最新进展。叙述了基于ＣＯＢＥ卫星的观测宇宙学,包括对背景辐射谱,各向异性的观测结果及其理论意义;并系统介绍了ＣＢＲ各向异性形成的种种机制;展望了下一代宇宙微波背景探测器（ＭＡＰ和ＰＬＡＮＣＫ）的科学目标和主要技术参数。     

Temperature of the Cosmic Microwave Background Radiation in Conformal Cosmology

A scheme is proposed for explaining the origin of the observed temperature of the cosmic microwave background (relict) radiation in which this radiation is treated as a product of the decay of primordial vector bosons in the framework of the Hoyle-Narlikar conformal cosmology.     

从微波爆发的精细结构谱估算粒子能量及磁场位形

本文采用荷兰Ｄｗｉｎｇｌｏｏ射电天文台的多通道频谱仪（４－８ＧＨｚ）所观测到的一种典型的精细结构事例（ＴｙｐｅＨａｎｄ）来证实源区存在小尺度磁场结构以及电子的短时标加速过程．进一步根据实测和理论分析估算电子的平均速度大约为光速的十分之一，微磁流管直径大约为６００ｋｍ．以及在短时标（０．１ｓ）加速过程中电子能量密度的演化．由此可见，在射电精细结构的动态频谱中含有极其丰富的物理信息，对太阳耀斑机制的理解具有重要意义．