Solar Physics最新文献

Using Type-II radio bursts from Wind/WAVES and the associated coronal mass ejections (CMEs) from SOHO/LASCO, Gopalswamy et al. (2005) found a hierarchical relationship between the wavelength range of the Type-II bursts and the CME kinetic energy. Under ‘DH (Decametric–Hectometric) Type-II bursts’, they have included m (metric)-DH, pure DH, and DH-km (kilometric) bursts. In this work, we consider the pure DH, m-DH, and DH-km subsets separately. We find that CMEs associated with DH-km Type-II bursts have the largest values of average speed, nonhalo width, mass, and halo fraction. CMEs associated with m-DH Type-II bursts have a slightly larger average speed and mass than those causing pure DH Type-II bursts. CMEs associated with m-DH and pure DH Type-II bursts have a slightly lower speed and halo fraction compared to those associated with the combined set of DH Type-II bursts in Gopalswamy et al. (2005), while CMEs causing the DH-km Type-II bursts have even larger values of CME parameters. DH-km Type-II burst-associated CMEs have the largest solar energetic particles (SEPs) association compared to m-DH and pure DH Type-II burst-associated CMEs. The DH-km Type-II burst-associated CMEs’ SEP association is slightly smaller than that of Gopalswamy et al. (2005) m-km Type-II burst-associated CMEs. The CMEs associated with major SEP have a higher average speed than the pure DH and m-DH CMEs but smaller than the DH-km CMEs.

The solar cycle is a complex phenomenon. To comprehensively understand it, we have to study various tracers. The most important component of this complex is the solar dynamo, which is understood as self-excitation of the solar magnetic field in the form of traveling waves somewhere in the convection zone. Along with the solar dynamo, the formation of the solar cycle involves other processes associated with the dynamo but not its necessary part. We review such phenomena that have not yet been explained in terms of dynamo theory. We consider the manifestations of the solar cycle in harmonics of the solar large-scale surface magnetic field, including zonal, sectorial, and tesseral harmonics; analyze their contribution to magnetic energy; and identify phases of the activity cycle using harmonics of different types of symmetry. The universal magnetic scenario of a solar activity cycle does not depend on its number and amplitude. At the beginning of the cycle in the photosphere, the zonal harmonics account for 37 – 42% of the total energy (not 100%, as assumed in simplified descriptions). Sectorial harmonics do not disappear but account for 5 – 10% of the total energy. At this stage, the greatest energy (about 40%) is contained in the tesseral harmonics. As the cycle develops, the relative energy of zonal harmonics gradually decreases, reaching a minimum of 15 – 18% immediately before the onset of the sunspot maximum. The relative energy of sectorial harmonics increases and reaches a maximum (60 – 65%) somewhat later than the calendar date of the sunspot maximum. A particular feature of the tesseral harmonics is that their relative energy index changes in a much narrower range and never falls below 40%, even at the cycle minimum. This is due to active regions and nonglobal magnetic fields. Tesseral harmonics may be formed in shallow subphotospheric layers.

Since I have lived a rather ordinary life, my focus will center on what I have studied, with only exceptional personal matters being discussed. Nevertheless, rather new ideas are presented in Section 6.2 on the flare theory and in Section 9 on the mechanism of the 22-year solar cycle. These ideas have been included in light of my 90 years of age, hoping that someone will further develop them if they are deemed valid.

Coronal holes (CHs) are large-scale, low-density regions in the solar atmosphere that may expel high-speed solar wind streams that incite hazardous, geomagnetic storms. Coronal and solar wind models can predict these high-speed streams, and the performance of the coronal model can be validated against segmented CH boundaries. We present a novel method named Sub-Transition Region Identification of Ensemble Coronal Holes (STRIDE-CH) to address prominent challenges in segmenting CHs using extreme-ultraviolet (EUV) imagery. Ground-based, chromospheric He i 10,830 Å line imagery and underlying Fe i photospheric magnetograms are revisited to disambiguate CHs from filaments and quiet Sun, overcome obscuration by coronal loops, and complement established methods in the community which use space-borne coronal EUV observations. Classical computer vision techniques are applied to constrain the radiative and magnetic properties of detected CHs, produce an ensemble of boundaries, and compile these boundaries in a confidence map that quantifies the likelihood of the CH presence throughout the solar disk. This method is a science-enabling one towards future studies of CH formation and variability from a mid-atmospheric perspective.

Aditya-L1 is the first space-based solar observatory from India, which is studying the Sun and solar wind from the first Lagrangian point (L1) in a halo orbit. Among the seven payloads, four of them are remote sensing and three are in situ ones. The Plasma-Analyzer Package for Aditya (PAPA) is one among the in situ payloads for exploring the composition of the solar wind and its energy distribution (in the range from 0.01 to 3 keV for electrons and 0.01 to 25 keV for ions) continuously throughout the lifetime of the mission. PAPA has two sensors: the Solar-Wind Electron Energy Probe (SWEEP) indented to measure the solar-wind electron flux and the Solar-Wind Ion Composition AnalyzeR (SWICAR) indented to measure the ion flux and composition as a function of direction and energy as well as electrons. Thus, SWEEP measures only electron parameters, whereas SWICAR has two modes of operation – ion mode in which ion parameters are measured and electron mode in which electron parameters are measured. These two modes in SWICAR are mutually exclusive. The payload is unique and the technologies like the high-voltage (± 5 kV DC) programmable power supply and the dual-mode (electrons and ions) detection of particles using a single sensor (SWICAR) are notable first-time developments. Data from PAPA will provide detailed knowledge of the solar-wind conditions with high time resolution. SWICAR will also provide: (1) the elemental composition of solar-wind ions in the mass range of 1 – 60 amu, and (2) the differential energy flux and abundances of dominant ion species. The key parameters such as bulk speed, density, and kinetic temperature of the solar-wind electrons and dominant ion species can be regularly derived. From these, inferences can be made on the coronal temperatures, plasma sources of suprathermal ion populations, and the nature and dynamics of the solar-wind plasma, with the support of models. In this article, the scientific objectives as well as the design aspects of PAPA payload are discussed in detail along with the calibration and first on board observational results.

The first-order effect of Coulomb forces between the charged particles of a plasma is the well-known Debye-Hückel-term. This term represents a negative contribution to the pressure and energy of the gas, which at high densities could overwhelm the ideal gas contributions and make the gas implode into a black hole. However, this fate could be prevented by specific physical mechanisms. We investigate three different mechanisms and analyze their effects on the equation of state and solar models, as well as their physical justifications. We conclude that higher-order Coulomb terms, in combination with quantum diffraction of electrons, provide the needed convergence.

My romantic attraction to the stars started at the age of 11 under the dark Swedish skies. While it was clear from then on that I wanted to be an astronomer, a sequence of chance encounters led me to choose solar physics and embark on an unpredictable path across the globe, including work for my PhD in the USSR about the Sun’s magnetic field, followed by an experiment on a Soviet satellite to record scattering polarization on the Sun. On my first hike in the Rocky Mountains in 1971, I had a chance encounter with my future wife and married 4 months later in Sweden. In 1980, we moved to Switzerland for 43 years. Finally, our geographically scattered family reunited. All of us, sons and grandsons, are now settled in Colorado. My story tells how this unplanned path was intertwined with the search for answers about the nature of solar magnetism.

The solar corona is the prototypical example of a low-density environment heated to high temperatures by external sources. The plasma cools radiatively, and because it is optically thin to this radiation, it becomes possible to model the density, velocity, and temperature structure of the system by modifying the MHD equations to include an energy source term that approximates the local heating and cooling rates. The solutions can be highly inhomogeneous and even multiphase because the well-known linear instability associated with this source term, thermal instability, leads to a catastrophic heating and cooling of the plasma in the nonlinear regime. Here we show that there is a separate, much simpler linear instability accompanying this source term that can rival thermal instability in dynamical importance. The stability criterion is the isochoric one identified by Parker (1953), and we demonstrate that cooling functions derived from collisional ionization equilibrium are highly prone to violating this criterion. If catastrophic cooling instability can act locally in global simulations, then it is an alternative mechanism for forming condensations, and due to its nonequilibrium character, it may be relevant to explaining a host of phenomena associated with the production of cooler gas in hot, low density plasmas.