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The Solar Corona: Why It Is Interesting for Us  [PDF]
Boris Somov
Physics , 2013,
Abstract: Strong magnetic fields are of vital importance to the physics of the solar corona. They easily move a rarefied coronal plasma. Physical origin of the main structural element of the corona, the so-called coronal streamers, is discussed. It is shown that the reconnecting current layers inside streamers determine their large-scale structure and evolution, including creation, disruption and recovery. Small-scale (fine) magnetic fields in the photosphere experience random motion. Their reconnection appears to be an important source of energy flux for quiet-corona heating. For active-corona heating, the peculiarities of entropy and magnetoacoustic waves, related to radiative cooling, are significant and should be taken into account in the coronal heating theory.
Solar wind speed theory and the nonextensivity of solar corona  [PDF]
Jiulin Du,Yeli Song
Physics , 2008, DOI: 10.1007/978-3-642-03325-4_10
Abstract: The solar corona is a complex system, with nonisothermal plasma and being in the self-gravitating field of the Sun. So the corona plasma is not only a nonequilibrium system but also a nonextensive one. We estimate the parameter of describing the degree of nonextensivity of the corona plasma and study the generalization of the solar wind speed theory in the framework of nonextensive statistical mechanics. It is found that, when use Chapman's corona model (1957) as the radial distribution of the temperature in the corona, the nonextensivity reduces the gas pressure outward and thus leads a significant deceleration effect on the radial speed of the solar wind.
Modeling Jets in the Corona and Solar Wind  [PDF]
T. Torok,R. Lionello,V. S. Titov,J. E. Leake,Z. Mikic,J. A. Linker,M. G. Linton
Physics , 2015,
Abstract: Coronal jets are transient, collimated eruptions that occur in regions of predominantly open magnetic field in the solar corona. Our understanding of these events has greatly evolved in recent years but several open questions, such as the contribution of coronal jets to the solar wind, remain. Here we present an overview of the observations and numerical modeling of coronal jets, followed by a brief description of "next-generation" simulations that include an advanced description of the energy transfer in the corona ("thermodynamic MHD"), large spherical computational domains, and the solar wind. These new models will allow us to address some of the open questions.
Bright loops in the solar corona  [PDF]
Boris V. Gudiksen,Aake Nordlund
Physics , 2002,
Abstract: The heating of the solar corona and the puzzle of the slender high reaching magnetic loops seen in observations from the Transition Region And Coronal Explorer(TRACE) has been investigated through 3D numerical simulations, and found to be caused by the well observed plasma flows in the photosphere displacing the footpoints of magnetic loops in a nearly potential configuration. It is found that even the small convective displacements cause magnetic dissipation sufficient to heat the corona to temperatures of the order of a million Kelvin. The heating is intermittent in both space and time - at any one height and time it spans several orders of magnitude, and localized heating causes transonic flows along field lines, which explains the observed non-hydrostatic equilibrium of loops that are bright in emission measure.
Kinetic Physics of the Solar Corona and Solar Wind
Marsch Eckart
Living Reviews in Solar Physics , 2006,
Abstract: Kinetic plasma physics of the solar corona and solar wind are reviewed with emphasis on the theoretical understanding of the in situ measurements of solar wind particles and waves, as well as on the remote-sensing observations of the solar corona made by means of ultraviolet spectroscopy and imaging. In order to explain coronal and interplanetary heating, the microphysics of the dissipation of various forms of mechanical, electric and magnetic energy at small scales (e.g., contained in plasma waves, turbulences or non-uniform flows) must be addressed. We therefore scrutinise the basic assumptions underlying the classical transport theory and the related collisional heating rates, and also describe alternatives associated with wave-particle interactions. We elucidate the kinetic aspects of heating the solar corona and interplanetary plasma through Landau- and cyclotron-resonant damping of plasma waves, and analyse in detail wave absorption and micro instabilities. Important aspects (virtues and limitations) of fluid models, either single- and multi-species or magnetohydrodynamic and multi-moment models, for coronal heating and solar wind acceleration are critically discussed. Also, kinetic model results which were recently obtained by numerically solving the Vlasov–Boltzmann equation in a coronal funnel and hole are presented. Promising areas and perspectives for future research are outlined finally.
Influence of corona wind on the convective wheat grain drying course
Sumorek A.,Pietrzyk W.
International Agrophysics , 2001,
Abstract: The convective drying process is widely used despite its very low efficiency. For this reason there are studies searching for a better drying method or agents, which can increase process efficiency. The electric field and accompanying phenomena seem to be the agents that can change the convective drying course. This paper presents test results on convective drying of wheat grain in the electric field and in the ionic (corona) wind. These phenomena accompanying an electric field, can generate electrostriction forces in the drying material (it can cause deformations inside grain) or change heat and mass transfer between the grain surface and the drying medium (the ionic wind). The present study was carried out using an experimental test stand. The test stand allows to generate corona wind with a controlled corona current at constant values of the electric field intensity. Air velocity and temperature were fully stabilised, too. The measurement and recording processes were automated using a personal computer. Comparison between various drying courses recorded, allow to find an electric agent changing convection drying course.
The Extended Solar Cycle Tracked High into the Corona  [PDF]
S. J. Tappin,R. C. Altrock
Physics , 2012, DOI: 10.1007/s11207-012-0133-3
Abstract: We present observations of the extended solar cycle activity in white-light coronagraphs, and compare them with the more familiar features seen in the Fe XIV green-line corona. We show that the coronal activity zones seen in the emission corona can be tracked high into the corona. The peak latitude of the activity, which occurs near solar maximum, is found to be very similar at all heights. But we find that the equatorward drift of the activity zones is faster at greater heights, and that during the declining phase of the solar cycle, the lower branch of activity (that associated with the current cycle) disappears at about 3 Ro. This implies that that during the declining phase of the cycle, the solar wind detected near Earth is likely to be dominated by the next cycle. The so-called "rush to the poles" is also seen in the higher corona. In the higher corona it is found to start at a similar time but at lower latitudes than in the green-line corona. The structure is found to be similar to that of the equatorward drift.
The Absolute Abundance of Iron in the Solar Corona  [PDF]
S. M. White,R. J. Thomas,J. W. Brosius,M. R. Kundu
Physics , 2000, DOI: 10.1086/312673
Abstract: We present a measurement of the abundance of Fe relative to H in the solar corona using a technique which differs from previous spectroscopic and solar wind measurements. Our method combines EUV line data from the CDS spectrometer on SOHO with thermal bremsstrahlung radio data from the VLA. The coronal Fe abundance is derived by equating the thermal bremsstrahlung radio emission calculated from the EUV Fe line data to that observed with the VLA, treating the Fe/H abundance as the sole unknown. We apply this technique to a compact cool active region and find Fe/H = 1.56 x 10^{-4}, or about 4 times its value in the solar photosphere. Uncertainties in the CDS radiometric calibration, the VLA intensity measurements, the atomic parameters, and the assumptions made in the spectral analysis yield net uncertainties of order 20%. This result implies that low first ionization potential elements such as Fe are enhanced in the solar corona relative to photospheric values.
Turbulent Heating in the Solar Wind and in the Solar Corona  [PDF]
Mahendra K. Verma
Physics , 1995,
Abstract: In this paper we calculate the turbulent heating rates in the solar wind using the Kolmogorov-like MHD turbulence phenomenology with Kolmogorov's constants calculated by {\it Verma and Bhattacharjee }[1995b,c]. We find that the turbulent heating can not account for the total heating of the nonAlfv\'enic streams in the solar wind. We show that dissipation due to thermal conduction is also a potential heating source. Regarding the Alfv\'enic streams, the predicted turbulent heating rates using the constants of {\it Verma and Bhattacharjee }[1995c] are higher than the observed heating rates; the predicted dissipation rates are probably overestimates because Alfv\'enic streams have not reached steady-state. We also compare the predicted turbulent heating rates in the solar corona with the observations; the Kolmogorov-like phenomenology predicts dissipation rates comparable to the observed heating rates in the corona [{\it Hollweg, }% 1984], but Dobrowoly et al.'s generalized Kraichnan model yields heating rates much less than that required.
Heating of the Solar Corona by Dissipative Alfven Solitons  [PDF]
K. Stasiewicz
Physics , 2006, DOI: 10.1103/PhysRevLett.99.072001
Abstract: Solar photospheric convection drives myriads of dissipative Alfven solitons (hereinafter called alfvenons) capable of accelerating electrons and ions to energies of hundreds of keV and producing the X-ray corona. Alfvenons are exact solutions of two-fluid equations for a collisionless plasma and represent natural accelerators for conversion of the electromagnetic energy flux driven by convective flows into kinetic energy of charged particles in space and astrophysical plasmas. Their properties have been experimentally verified in the magnetosphere, where they accelerate auroral electrons to tens of keV.
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