scholarly journals Recent advances in coronal heating

2015 ◽  
Vol 373 (2042) ◽  
pp. 20140269 ◽  
Author(s):  
Ineke De Moortel ◽  
Philippa Browning
Keyword(s):  
Numerical Modelling ◽  
Heat Source ◽  
Thermal Conduction ◽  
Solar Surface ◽  
Coronal Heating ◽  
Future Research ◽  
Small Scale ◽  
The Sun ◽  
Physical Processes ◽  
Outer Atmosphere

The solar corona, the tenuous outer atmosphere of the Sun, is orders of magnitude hotter than the solar surface. This ‘coronal heating problem’ requires the identification of a heat source to balance losses due to thermal conduction, radiation and (in some locations) convection. The review papers in this Theo Murphy meeting issue present an overview of recent observational findings, large- and small-scale numerical modelling of physical processes occurring in the solar atmosphere and other aspects which may affect our understanding of the proposed heating mechanisms. At the same time, they also set out the directions and challenges which must be tackled by future research. In this brief introduction, we summarize some of the issues and themes which reoccur throughout this issue.

scholarly journals Solar structure and evolution

2021 ◽  
Vol 18 (1) ◽  
Author(s):  
Jørgen Christensen-Dalsgaard
Keyword(s):  
Solar Surface ◽  
Solar Neutrinos ◽  
Solar Interior ◽  
Stellar Structure ◽  
The Sun ◽  
Physical Processes ◽  
Solar Evolution ◽  
Internal Properties ◽  
Atmospheric Phenomena

AbstractThe Sun provides a critical benchmark for the general study of stellar structure and evolution. Also, knowledge about the internal properties of the Sun is important for the understanding of solar atmospheric phenomena, including the solar magnetic cycle. Here I provide a brief overview of the theory of stellar structure and evolution, including the physical processes and parameters that are involved. This is followed by a discussion of solar evolution, extending from the birth to the latest stages. As a background for the interpretation of observations related to the solar interior I provide a rather extensive analysis of the sensitivity of solar models to the assumptions underlying their calculation. I then discuss the detailed information about the solar interior that has become available through helioseismic investigations and the detection of solar neutrinos, with further constraints provided by the observed abundances of the lightest elements. Revisions in the determination of the solar surface abundances have led to increased discrepancies, discussed in some detail, between the observational inferences and solar models. I finally briefly address the relation of the Sun to other similar stars and the prospects for asteroseismic investigations of stellar structure and evolution.

scholarly journals What scatter-hoarding animals have taught us about small-scale navigation

2010 ◽  
Vol 365 (1542) ◽  
pp. 901-914 ◽  
Author(s):  
Kristy L. Gould ◽  
Debbie M. Kelly ◽  
Alan C. Kamil
Keyword(s):  
Future Research ◽  
Small Scale ◽  
The Sun ◽  
Scatter Hoarding ◽  
Geometric Properties ◽  
Cue Use ◽  
Unique System ◽  
Spatial Locations

Many animals use cues for small-scale navigation, including beacons, landmarks, compasses and geometric properties. Scatter-hoarding animals are a unique system to study small-scale navigation. They have to remember and relocate many individual spatial locations, be fairly accurate in their searching and have to remember these locations for long stretches of time. In this article, we review what is known about cue use in both scatter-hoarding birds and rodents. We discuss the importance of local versus global cues, the encoding of bearings and geometric rules, the use of external compasses such as the Sun and the influence of the shape of experimental enclosures in relocating caches or hidden food. Scatter-hoarding animals are highly flexible in how and what they encode. There also appear to be differences in what scatter-hoarding birds and rodents encode, as well as what scatter-hoarding animals in general encode compared with other animals. Areas for future research with scatter-hoarding animals are discussed in light of what is currently known.

scholarly journals A contemporary view of coronal heating

2012 ◽  
Vol 370 (1970) ◽  
pp. 3217-3240 ◽  
Author(s):  
Clare E. Parnell ◽  
Ineke De Moortel
Keyword(s):  
Magnetic Field ◽  
Recent Progress ◽  
Coupled System ◽  
Coronal Heating ◽  
The Sun ◽  
Key Factors ◽  
Computing Power ◽  
Heating Mechanism ◽  
Outer Atmosphere ◽  
The Magnetic Field

Determining the heating mechanism (or mechanisms) that causes the outer atmosphere of the Sun, and many other stars, to reach temperatures orders of magnitude higher than their surface temperatures has long been a key problem. For decades, the problem has been known as the coronal heating problem, but it is now clear that ‘coronal heating’ cannot be treated or explained in isolation and that the heating of the whole solar atmosphere must be studied as a highly coupled system. The magnetic field of the star is known to play a key role, but, despite significant advancements in solar telescopes, computing power and much greater understanding of theoretical mechanisms, the question of which mechanism or mechanisms are the dominant supplier of energy to the chromosphere and corona is still open. Following substantial recent progress, we consider the most likely contenders and discuss the key factors that have made, and still make, determining the actual (coronal) heating mechanism (or mechanisms) so difficult.

scholarly journals Our dynamic sun: 2017 Hannes Alfvén Medal lecture at the EGU

2017 ◽  
Vol 35 (4) ◽  
pp. 805-816 ◽  
Author(s):  
Eric Priest
Keyword(s):  
Magnetic Fields ◽  
Magnetic Energy ◽  
Active Regions ◽  
Particle Energy ◽  
Space Environment ◽  
Small Scale ◽  
The Sun ◽  
Strong Shear ◽  
Outer Atmosphere ◽  
Mass Ejection

Abstract. This lecture summarises how our understanding of many aspects of the Sun has been revolutionised over the past few years by new observations and models. Much of the dynamic behaviour of the Sun is driven by the magnetic field since, in the outer atmosphere, it represents the largest source of energy by far. The interior of the Sun possesses a strong shear layer at the base of the convection zone, where sunspot magnetic fields are generated. A small-scale dynamo may also be operating near the surface of the Sun, generating magnetic fields that thread the lowest layer of the solar atmosphere, the turbulent photosphere. Above the photosphere lies the highly dynamic fine-scale chromosphere, and beyond that is the rare corona at high temperatures exceeding 1 million degrees K. Possible magnetic mechanisms for heating the corona and driving the solar wind (two intriguing and unsolved puzzles) are described. Other puzzles include the structure of giant flux ropes, known as prominences, which have complex fine structure. Occasionally, they erupt and produce huge ejections of mass and magnetic fields (coronal mass ejections), which can disrupt the space environment of the Earth. When such eruptions originate in active regions around sunspots, they are also associated with solar flares, in which magnetic energy is converted to kinetic energy, heat and fast-particle energy. A new theory will be presented for the origin of the twist that is observed in erupting prominences and for the nature of reconnection in the rise phase of an eruptive flare or coronal mass ejection.

Detection of Small-Scale Dynamics in the Emission Corona

1994 ◽  
Vol 144 ◽  
pp. 487-490 ◽  
Author(s):  
V. Rušin ◽  
M. Minarovjech
Keyword(s):  
Solar Surface ◽  
High Time ◽  
Small Scale ◽  
The Sun ◽  
Coronal Line ◽  
Short Term ◽  
Line Intensities ◽  
Different Types

AbstractHigh-time records of green (530.3 ran) and red (637.4 nm) coronal line intensities display many occasional short-term variations of different types (oscillations in the range from 5 s to 5 min, non-periodic small or abrupt brightness observed in the line or both in the line and background). The distribution of these features around the Sun is non-uniform, and the amplitude of 5 min oscillations decreases rapidly with the height above the solar surface.

Large-scale coronal heating by the small-scale magnetic field of the Sun

Nature ◽  
10.1038/28108 ◽  
1998 ◽  
Vol 394 (6689) ◽  
pp. 152-154 ◽  
Author(s):  
C. J. Schrijver ◽  
A. M. Title ◽  
K. L. Harvey ◽  
N. R. Sheeley ◽  
Y.-M. Wang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Coronal Heating ◽  
Small Scale ◽  
The Sun

The energy budget in and out of coronal holes

1980 ◽  
Vol 297 (1433) ◽  
pp. 531-540
Keyword(s):  
Solar Wind ◽  
Energy Budget ◽  
Thermal Plasma ◽  
Thermal Conduction ◽  
Solar Surface ◽  
Coronal Holes ◽  
Plasma Pressure ◽  
Energy Requirements ◽  
Physical Processes ◽  
Main Factor

Energy is transmitted into, out of and across the solar atmosphere by such physical processes as radiation, thermal conduction, waves and so forth. Estimates can be made of the magnitudes of some of these and hence an energy budget drawn up for different regions of the atmosphere. In particular it appears that the energy requirements of coronal hole regions of the solar surface are substantially greater than those of other regions. The main factor determining this conclusion is an estimate of the energy required to accelerate the solar wind in regions above coronal holes. Of two possible mechanisms for the acceleration of the solar wind, namely thermal plasma pressure and Alfvén waves, it may be shown that the former places even more severe demands on the energy budget of these regions, whereas the latter is more easily accommodated.

The Interpretation of Solar Spectral Intensities

1988 ◽  
Vol 102 ◽  
pp. 329
Author(s):  
R.W.P. McWhirter
Keyword(s):  
Emission Measure ◽  
Physical Nature ◽  
Atomic Data ◽  
The Sun ◽  
Atomic Properties ◽  
Outer Atmosphere ◽  
Spectral Intensities ◽  
Thin Plasma ◽  
Number Of Authors

The intensity of a specrtal line from an optically thin plasma such as the outer atmosphere of the sun depends on both the atomic properties of the atomic ion responsible for the line and the physical nature of the plasma. In this paper we discuss the various ways in which the measured spectral intensities from the sun are used to discover something about the nature of the sun’s atmosphere. The technique has been referred to as the emission measure method. It has important limitations in terms of the accuracy of the specrtal data as well as the atomic data. We discuss some of these and suggest methods by which they may be assessed. The technique is illustrated by application to real observations from a number of authors.

Small-Scale Deliberation and Mass Democracy: A Systematic Review of the Spillover Effects of Deliberative Minipublics

2021 ◽  
pp. 003232172110072
Author(s):  
Ramon van der Does ◽  
Vincent Jacquet
Keyword(s):  
Systematic Review ◽  
Empirical Evidence ◽  
Empirical Research ◽  
Spillover Effects ◽  
Future Research ◽  
Small Scale ◽  
Long Term Effects ◽  
Current Crisis ◽  
Mass Democracy

Deliberative minipublics are popular tools to address the current crisis in democracy. However, it remains ambiguous to what degree these small-scale forums matter for mass democracy. In this study, we ask the question to what extent minipublics have “spillover effects” on lay citizens—that is, long-term effects on participating citizens and effects on non-participating citizens. We answer this question by means of a systematic review of the empirical research on minipublics’ spillover effects published before 2019. We identify 60 eligible studies published between 1999 and 2018 and provide a synthesis of the empirical results. We show that the evidence for most spillover effects remains tentative because the relevant body of empirical evidence is still small. Based on the review, we discuss the implications for democratic theory and outline several trajectories for future research.

A Critical Review of the Biological Processes in the Chemical Absorption-biological Reduction Integrated System for NO Removal

2021 ◽  
Vol 07 ◽  
Author(s):  
Wei Li
Keyword(s):  
Catalytic Reduction ◽  
Low Cost ◽  
Reduction Process ◽  
Integrated System ◽  
Future Research ◽  
Small Scale ◽  
Biological Processes ◽  
Chemical Absorption ◽  
Biological Reduction ◽  
Biological Reaction

: Exploring low-cost, green and safe technologies to provide an alternative to the conventional selective catalytic reduction process is key to the control of NOx emitted from small-scale boilers and other industrial processes. To meet the demand, the chemical absorption-biological reduction integrated system has been developing recently. chemical absorption-biological reduction integrated system applies Fe(II)EDTA for NO absorption and iron-reducing and denitrifying bacteria for absorbent regeneration. Many studies have focused on the enhancements of mass transfer and biological reaction, among which the biological processes were the rate-limiting steps. This review summarizes the current researches on the biological processes in the CABR system, which focuses on the mechanism and enhancement of biochemical reactions, and provides the possible directions of future research.

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