The solar corona during the eclipse of August 1, 2008

A new telescope has been created to investigate the solar corona during eclipses. One lens simultaneously forms three corona images occurring as coronal radiation passes through three polarizers with transmission directions rotated 0°, 60°, and 120° relative to the selected direction; in addition, one image is formed without the polarizer. The telescope was used for solar corona observation during the eclipse of August 1, 2008. We obtained the distributions of polarization brightness, K corona brightness, degree of K corona polarization, and total degree of polarization as well as polarization directions depending on the latitude and radius in the sky plane. Radial distributions of the electron density depending on latitude were calculated. The coronal plasma temperature was determined for different corona structures under the assumption of hydrostatic equilibrium.     

Inactivation Efficiency of Bioaerosols Using Carbon Nanotube Plasma

The purpose of this study was to inactivate indoor bioaerosols using carbon nanotube corona discharge plasma technology. Escherichia coli, Bacillus subtilis, and λ virus bioaerosols were generated using a Collison nebulizer. The effect of various factors, including the flow rate (30, 60, and 90 lpm) and the operating voltages (?1.5, ?3.0, ?4.5, ?6.0, and ?7.5 kV), on bioaerosol reduction was examined. The results indicated that the corona discharge using the carbon nanotube electrodes decreased the threshold voltage of plasma. The inactivation efficiencies of E. coli bioaerosols using the carbon nanotube corona discharge system at discharge voltages of ?1.5, ?3.0, ?4.5, ?6.0, and ?7.5 kV were 57, 61, 71, 93, and 97%, respectively. The corona discharge system using carbon nanotube electrodes had higher bioaerosol inactivation efficiency than the corona discharge system using stainless steel electrodes. The results further demonstrated that the inactivation efficiency decreased with an increasing flow rate. The inactivation efficiencies of E. coli, B. subtilis, and λ virus bioaerosols using carbon nanotube corona discharge plasma were 93, 88, and 81%, respectively.     

日冕物质抛射的数值研究——初态日冕和驱动机制的影响

初态日冕和驱动机制在日冕物质抛射的形成和演化过程中所起的作用是一个引起争论的问题.本文从MHD方程组出发,在不同的初态日冕中,数值模拟了日冕底部新磁通量喷发和热压力扰动两种驱动机制的日冕响应.结果表明,初态日冕和驱动机制对日冕物质抛射的形成及演化都有重要影响.     

Results of Spectral Corona Observations in Solar Activity Cycles 17–24

The results of the work of the global observation network are considered, and a comparative analysis of the data of various coronal observatories is performed. The coronal activity index has been reconstructed for the period 1939–2016 based on the data of various observatories in Kislovodsk system. For this purpose, the corona daily intensity maps from the Sacramento Peak and Lomnický ?tít observatories according to the Solar-Geophysical Data journal have been digitized; they supplement the data of other observatories. The homogeneity and continuity of the corona observations at the Kislovodsk station, including activity cycle 24, is confirmed. Unfortunately, the only observatory at present that continues observation of the spectral corona in Fe XIV 5303 Å and Fe XIV 6374 Å lines is the Kislovodsk astronomical station Mountain Astronomical Station (MAS) of the Central Astronomical Observatory, Russian Academy of Sciences (Pulkovo). The data on the combined corona in 5303 Å line are analyzed. It is shown that there is a high correlation of the intensity index of green corona with solar radiation measurements in the vacuum UV region. Data on the beginning of the new 25th activity cycle in the corona at high latitudes are presented.     

Numerical modelling of spectral sky radiance during a total solar eclipse

Ground-based observations of the spectral sky radiance within the totality region during a total solar eclipse are of significant interest because the contribution from direct and single scattered light from the solar disk is eliminated. In the present paper, we develop a numerical model of the spectral sky radiance during totality, evaluate the contribution of double scattered sunlight to the sky radiance at totality and compare it to solar corona emissions. The results show that the single scattered coronal light is the major contaminant in ground-based observations of the corona, opposite to what was believed before. For observation directions outside the corona the double scattered sun radiation dominates over the single scattered coronal light.     

Onset voltages of atmospheric corona discharges on coniferous trees

In this article, the phenomenon of generation of corona discharges on the tops of trees and plants is described. In the first part of the text, the conditions for generation of this electric field which leads to formation of corona discharge and transfer of electric charge between atmosphere and Earth, are discussed. Experimental results of the onset voltage and its dependence on the discharge parameters are presented. The coincidence between released species from corona burning point and surrounding atmosphere is also discussed. Equation for the calculation of critical intensity of the electric field and onset voltage in dependence on radius of the tip are also discussed and compared with experimental data and equations for current–voltage characteristics are described. The attempt to explain differences between theory and measured data is proposed.     

Studies of the solar corona based on solar eclipse observations at IZMIRAN

From 1945 to 2009, fellows of IZMIRAN participated in 24 expeditions devoted to observations of solar eclipses. The following characteristics of the solar corona were mainly studied: the emission structure, intensity, and polarization; the line and continuous spectra; etc. This paper reviews the most important results, which promoted the development of the present-day concepts of the solar corona structure and physical properties.     

The Flux Tube Tectonics model for coronal heating

An account is presented of the Flux Tube Tectonics model for heating the solar corona, in which a multitude of current sheets are continually forming and dissipating. In addition, a model is summarised for the time-dependent response of the corona to the sudden dissipation of one such current sheet.     

Charged condensation nuclei formed in a room by corona discharge when alternating the polarity of the corona potential and by using alternating corona potential

Summary The content of charged nuclei formed in a room varied by alternating the polarity of a corona device and depended on the period during which the corona of one polarity was switched on. The concentration of charges measured was greater during the negative period than during the positive one, when the action period of corona of one polarity was 30 minutes, but it was the opposite for the period of 5 minutes. When using alternating corona potential of 50 cycles per/sec only positively charged nuclei were established. By using alternating potential the picture was changed when air was blown through the corona device: the content of positively charged nuclei was diminished and negatively charged nuclei were also observed. An air circulation produced by the convection from an electric heater placed below the corona device was sufficient to cause a similar effect.

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Zusammenfassung Der Gehalt an geladenen Kernen, die in einem Raume gebildet wurden, änderte sich beim Wechsel der Polarität einer Koronavorrichtung und hing von der Dauer ab, während der die Koronaentladung einer Polarität eing eschaltet blieb. Die gemessene Konzentration der Ladungen war grösser während der negativen Periode als während der positiven, wenn die Wirkung der Koronaentladung einer Polarität 30 Minuten dauerte, das umgekehrte trat für eine Dauer von 5 Minuten ein. Nur positiv geladene Kerne wurden nachgewiesen, wenn Wechselspannung von 50 Perioden per Sek für die Koronaentladung benutzt wurde. Bei Wechselspannung wurde das Bild geändert, wenn Luft durch die Koronavorrichtung geblasen wurde: Der Gehalt an positiv geladenen Kernen wurde verkleinert und auch negativ geladene Kerne wurden beobachtet. Eine Luftzirkulation, die durch Konvektion von einem elektrischen Heizkörper unterhalb der Koronavorrichtung erzeugt wurde, war genügend, einen ähnlichen Effekt hervorzurufen.

     

Variations in the large-scale polar solar magnetic flux: The average annual series of the Π index in 1858–2006

A long series of the known Π index of the solar corona structure has been proposed. It seems that this index, which characterizes the limb extension of polar coronal plume systems, is of importance because it is related to the large-scale polar solar magnetic flux. Solar corona photographs and drawings during total solar eclipses, collected for 13 solar activity cycles from different sources (78 eclipses), as well as H-alpha map data on the drift of the high-latitude belt of filaments before polarity reversal of the polar magnetic field have been used. Daily solar corona images, obtained on the SOHO spacecraft (using an EIT ultraviolet telescope), have been additionally used.     

Observations of neutral hydrogen in the corona

Measurements of the linear polarization degree (p) of the emission in the inner corona (<1.5 R _⊙) in the green and red continuum ranges are discussed. “Excess p” (Δp = pgreen — pred), which reaches its maximum at 1.2–1.3 R _⊙ (<5%) in the polar regions and 20% within large-scale streamers, is present everywhere in the corona. It has been mentioned that excess p can be explained by the presence of neutral hydrogen in the corona.     

Tangential discontinuities and the optical analogy for stationary fields. VII. Effects of resistivity

Abstract

The relatively large resistivity in the solar photosphere and chromosphere softens the ideal tangential discontinuities of magnetostatic equilibrium into continuous transitions in field direction over scales of 0.1–10 km. This softening is communicated upward at the Alfvén speed into the active solar corona. The degree of softening is a vital part of the theory of magnetic heat input to the active X-ray corona, because the very low resistivity of the coronal gas provides effective dissipation only if the current sheets are reduced to a thickness of 10^?2km.

A close examination of the problem shows that the Alfvén transit time up into the corona is large compared to the characteristic time of 1 sec in which the coronal tangential discontinutities are formed. It also shows that the principal effect of the resistivity is to create a thin surface layer of fluid on adjacent flux bundles, which causes a general drift of the flux but does not directly broaden the current sheets higher up in the field. In fact the motions of the surface layers do not extend upwards beyond the first winding pattern at each end of a coronal loop.

It appears that the photospheric and chromospheric resistivity is without striking consequences for magnetic heating in the corona.     

Seismology of the corona of the Sun

V M Nakariakov and E Verwichte put seismology to work in the study of the solar corona, the hot atmosphere of the Sun.     

Application of the MHD energy principle to magnetostatic atmospheres

Abstract

We apply the MHD energy principle to the stability of a magnetized atmosphere which is bounded below by much denser fluid, as is the solar corona. We treat the two fluids as ideal; the approximation which is consistent with the energy principle, and use the dynamical conditions that must hold at a fluid-fluid interface to show that if vertical displacements of the lower boundary are permitted, then the lower atmosphere must be perturbed as well. However, displacements which do not perturb the coronal boundary can be properly treated as isolated perturbations of the corona alone.     

Evolutionary Changes in the Configuration of the Magnetic Field of the Solar Corona in the Epoch of the Minimum

Geomagnetism and Aeronomy - The evolution of the magnetic configuration in the solar corona is studied. The curvature of the K-corona helmets obtained from an analytical approximation of the...     

Source of Electromagnetic Radiation in Corona and Impedance of the Stationary Magnetic Reconnection Area

Geomagnetism and Aeronomy - A source of high-frequency electromagnetic radiation is formed by energetic particles in the magnetic structures of plasma corona. Energetic particles are formed in the...     

Wave heating of the solar corona and SoHO

A short introduction is given to some wave-heating mechanismsapplicable to the solar corona. Their relevance to the capabilitiesof the SoHO mission is briefly discussed.     

The sound of the Sun

Bill Chaplin and Istvan Ballai review developments in helioseismology – the resonant choir of the Sun – a discipline that now probes the Sun from core to corona.     

Continuous 60-Year Observations of the Spectral Solar Corona at the Mountain Astronomical Station of Pulkovo Observatory

Geomagnetism and Aeronomy - This paper presents observational series of the spectral solar corona obtained with the Small Lyot Coronagraph deployed in 1948 at the Mountain Astronomical Station of...     

The Color of Solar Corona Structures

Geomagnetism and Aeronomy - Two-dimensional distributions of the relative color index (RCI) of the continuous corona spectrum of 1991 and 2006 reveal that the energy distributions in the continuums...