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1

Viking solar corona experiment  

Microsoft Academic Search

The 1976 Mars solar conjunction resulted in complete occulations of the Viking spacecraft by the sun at solar minimum. During the conjunction period, coherent 3.5- and 13-cm wavelength radio waves from the orbiters passed through the solar corona and were received with the 64-m antennas of the NASA Deep Space Network. Data were obtained within at least 0.3 and 0.8

G. LEONARD Tyler; Joseph P. Brenkle; Thomas A. Komarek; Arthur I. Zygielbaum

1977-01-01

2

Solar Corona Seismology  

NASA Astrophysics Data System (ADS)

The presence of oscillations in solar coronal structures has been known for more than seventy years. Observational reports about the presence of oscillatory motions in solar filaments go back to 1930 while in the case of other coronal structures (loops, plumes, etc) direct evidence has been recently obtained thanks to the detailed observations made by SoHO and TRACE. Due to these satellites, as well as to ground-based observations, evidence of magnetohydrodynamic (MHD) waves in the solar corona has risen dramatically. MHD coronal seismology provides with an indirect path to determine the physical conditions and parameters of the solar corona [coronal magnetic field, transport coefficients (viscosity, resistivity, thermal conductivity, etc.), heating function, filling factors] which are difficult to measure accurately. In essence, it is similar to the acoustic diagnostic of the solar interior (Helioseismology) and to MHD spectroscopy used to determine physical helioseismology parameters of laboratory plasmas. In spite that there are many solar coronal structures in which oscillations have been detected (prominences, loops, plumes, coronal holes, etc.), in the following we will concentrate in prominences and coronal loops trying to summarize part of our current knowledge about their oscillations as well as about the theoretical models developed to explain those oscillations in terms of MHD waves.

Ballester, J. L.

2006-12-01

3

Instabilities in the solar corona  

Microsoft Academic Search

It is shown that both observations and theoretical evidence exists for the presence of high levels of low-frequency plasma turbulence in the solar corona. A rough survey of relevant plasma instabilities is given with emphasis on their applicability to circumstances in the solar corona. It is found that mainly low-frequency waves with frequency up to the electron cyclotron frequency can

J. Rosenberg

1973-01-01

4

Heating of the Solar Corona  

Microsoft Academic Search

This article reviews recent results about physical mechanisms that contribute to heat the solar corona as well as their impact on the energetic balance of the coronal plasma. A general description of the solar corona is given, mainly based on X-ray images and complemented with data from other spectral ranges. The presence of a magnetic field is found to be

D. O. Gomez

1990-01-01

5

The Solar Corona  

NSDL National Science Digital Library

This site describes the corona of the sun from three different points of view. In the first case, the white-light corona is the sight that is visible during total eclipses of the sun as a pearly white crown surrounding the sun and displays a variety of features including streamers, plumes, and loops. The emission line corona is explained on the basis of the extreme heat of the corona and the X-ray corona is described in terms of past and present research projects designed to study it. The site also contains an image for each of the three parts.

Hathaway, David

6

Turbulence in the solar corona  

Microsoft Academic Search

The solar corona has been revealed in the past decade to be a highly dynamic nonequilibrium plasma environment. Both the loop-filled coronal base and the extended acceleration region of the solar wind appear to be strongly turbulent, but direct observational evidence for a cascade of fluctuation energy from large to small scales is lacking. In this paper I will review

Steven R. Cranmer

2007-01-01

7

Waves in the Solar Corona  

Microsoft Academic Search

Waves at all scales ranging in wavelength from the size of a loop (fraction of a solar radius) down to the gyroradii (a few meters) of coronal ions are believed to play a key role in the transport of mechanical energy from the chromosphere to the Sun's corona and wind and through the dissipation of wave energy in the heating

E. Marsch

2004-01-01

8

Turbulence in the Solar Corona  

Microsoft Academic Search

The solar corona has been revealed in the past decade to be a highly dynamic\\u000anonequilibrium plasma environment. Both the loop-filled coronal base and the\\u000aextended acceleration region of the solar wind appear to be strongly turbulent,\\u000abut direct observational evidence for a cascade of fluctuation energy from\\u000alarge to small scales is lacking. In this paper I will review

Steven R. Cranmer

2007-01-01

9

Turbulence in the solar corona  

NASA Astrophysics Data System (ADS)

The solar corona has been revealed in the past decade to be a highly dynamic nonequilibrium plasma environment. Both the loop-filled coronal base and the extended acceleration region of the solar wind appear to be strongly turbulent, but direct observational evidence for a cascade of fluctuation energy from large to small scales is lacking. In this paper I will review the observations of wavelike motions in the corona over a wide range of scales, as well as the macroscopic effects of wave-particle interactions such as preferential ion heating. I will also present a summary of recent theoretical modeling efforts that seem to explain the time-steady properties of the corona (and the fast and slow solar wind) in terms of an anisotropic MHD cascade driven by the partial reflection of low-frequency Alfvén waves propagating along the superradially expanding solar magnetic field. Complete theoretical models are difficult to construct, though, because many of the proposed physical processes act on a multiplicity of spatial scales (from centimeters to solar radii) with feedback effects not yet well understood. This paper is thus a progress report on various attempts to couple these disparate scales.

Cranmer, Steven R.

2007-08-01

10

Waves in the Solar Corona  

NASA Astrophysics Data System (ADS)

Waves at all scales ranging in wavelength from the size of a loop (fraction of a solar radius) down to the gyroradii (a few meters) of coronal ions are believed to play a key role in the transport of mechanical energy from the chromosphere to the Sun's corona and wind and through the dissipation of wave energy in the heating and sustaining of the solar corona. A concise review of new observations and theories of waves in the magnetically confined (loops) as well as open (holes) corona is given with emphasis on energetics and dynamics. Recent remote-sensing solar observations have revealed loop oscillations as expected from MHD theory. These low-frequency oscillations are excited in connection with flares and appear to be strongly damped. Recent analysis of in-situ measurements of ions in fast solar wind and related theory have indicated the importance of pitch-angle scattering of ions in the wave frame as predicted from kinetic plasma theory a microprocess that may hold the key to understand plasma acceleration and heating by damping of high-frequency waves. Evidence obtained from spectroscopy of coronal ions points to cyclotron resonance absorption as a possible cause of the observed emission-line broadenings.

Marsch, E.

2004-01-01

11

F-corona-experiment: Requirements for remote sensing of interplanetary dust  

NASA Astrophysics Data System (ADS)

The near solar dust that produces the brightness of the F corona represents the central region of the interplanetary dust cloud. The structure of the inner dust cloud and the properties of the near solar dust contribute to the understanding of the meteoritic complex and its relation to other constituents of the interplanetary medium. The flux rates of these micrometeorites have to be considered for the concept of near solar missions. To investigate this complex a synoptical observation in different spectral ranges is needed. The concept of the dedicated rocket-borne experiment is outlined.

Mann, Ingrid; Hartwig, Hermann

1991-11-01

12

Solar Corona Seismology  

Microsoft Academic Search

The presence of oscillations in solar coronal structures has been known for more than seventy years. Observational reports about the presence of oscillatory motions in solar filaments go back to 1930 while in the case of other coronal structures (loops, plumes, etc) direct evidence has been recently obtained thanks to the detailed observations made by SoHO and TRACE. Due to

J. L. Ballester

2006-01-01

13

Magnetohydrodynamic modeling of the global solar corona  

Microsoft Academic Search

A three-dimensional magnetohydrodynamic model of the global solar corona is described. The model uses observed photospheric magnetic fields as a boundary condition. A version of the model with a polytropic energy equation is used to interpret solar observations, including eclipse images of the corona, Ulysses spacecraft measurements of the interplanetary magnetic field, and coronal hole boundaries from Kitt Peak He

Zoran Mikic; Jon A. Linker; Dalton D. Schnack; Roberto Lionello; Alfonso Tarditi

1999-01-01

14

Magnetic fields and the solar corona  

Microsoft Academic Search

Coronal magnetic fields calculated by the methods developed in Paper I (Altschuler and Newkirk, 1969) and the empirical description of the solar corona of November 1966 derived in Paper II (Newkirket al., 1970) are combined in order to investigate what connection exists between the magnetic fields and the density structure of the corona.

Gordon Newkirk; Martin D. Altschuler

1970-01-01

15

The heating of the solar corona  

Microsoft Academic Search

The heating of the solar corona has been a fundamental astrophysical issue for over sixty years. Over the last decade in particular, space-based solar observatories (Yohkoh, SOHO and TRACE) have revealed the complex and often subtle magnetic-field and plasma interactions throughout the solar atmosphere in unprecedented detail. It is now established that any energy release mechanism is magnetic in origin

R. W. Walsh; J. Ireland

2003-01-01

16

On Rotation of the Solar Corona  

NASA Astrophysics Data System (ADS)

We have studied the rotation of the solar corona using the images taken at a 9.4 nm wavelength by the AIA 094 instrument on board the Solar Dynamics Observatory (SDO) satellite. Our analysis implies that the solar corona rotates differentially. It appears that ?, the angular rotation velocity of the solar corona, does not only depend on heliographic latitude but is also a function of time, while the nature of the latter dependence remains unclear. Besides measurement errors, deviations ? ? from the mean rotational speed are also caused by proper motion of the observed point source (the tracer) with respect to its surroundings. The spread in ? values at a particular heliographic latitude is a real effect, not caused by measurement errors. Most of the observations carry relative error less than 1 % in ?.

Lorenc, M.; Rybanský, M.; Dorotovi?, I.

2012-12-01

17

Pulsating radio emissions from the solar corona  

Microsoft Academic Search

Three solar outbursts which show pulsating radio emissions at metric waves (239 MHz) are examined. The behaviour of the single frequency, high-time resolution records and the spectral diagrams seem to indicate that such phenomena are peculiar phases of type IV radiation, perhaps connected with absorptions in the solar corona. The spectral analysis of the low-frequency modulation of the emissions show

A. Abrami

1970-01-01

18

A mechanism for heating the solar corona  

Microsoft Academic Search

The high temperatures measured in the solar corona are explained in terms of heating which results from the work done on the plasma by expanding magnetic flux. This theory, which invokes no wave deposition or ohmic heating processes, is consistent with the strongly magnetized, highly variable nature of the solar atmosphere.

1980-01-01

19

Wave heating of the solar corona  

Microsoft Academic Search

The possible role of waves in the heating of the solar corona has been investigated. A dispersion relation has been derived for waves propagating in a homogeneous plasma subject to dissipation by viscosity and thermal conduction. The dissipation mechanisms have been incorporated self-consistently into the equations, and no assumptions about the strength of the damping have been made. Solutions of

Lisa Janice Porter

1994-01-01

20

MHD Shock Heating in Solar Corona Holes  

Microsoft Academic Search

Summary form only given. We report on a one dimensional simulation of plane polarized, large amplitude, Alfven waves traveling upwards through a gravitationally stratified solar corona hole. In the low plasma beta region the waves develop into fast magnetic shocks that reach great heights with little heat dissipation, where they excite large amplitude slow hydrodynamic shocks that deposit sufficient energy

M. A. Huerta; J. A. Orta; G. C. Boynton; J. Lee

2007-01-01

21

Scintillation Effects on Radio Wave Propagation Through Solar Corona  

Microsoft Academic Search

When RF waves pass through the solar corona and solar wind regions close to the Sun, strong scintillation effects appear at their amplitude, frequency and phase, especially in the regions very close to the Sun (less than 4 solar radius). After analyzing recent solar corona conjunction experimental data at S, X and Ka bands, we have developed a group of

C. M. Ho; M. K. Sue; A. Bedrossian; R. W. Sniffin

22

Observations of the White Light Corona from Solar Orbiter and Solar Probe Plus  

NASA Astrophysics Data System (ADS)

The SoloHI instrument on Solar Orbiter and the WISPR instrument on Solar Probe+ will make white light coronagraphic images of the corona as the two spacecraft orbit the Sun. The minimum perihelia for Solar Orbiter is about 60 Rsun and for SP+ is 9.5 Rsun. The wide field of view of the WISPR instrument (about 105 degrees radially) corresponds to viewing the corona from 2.2 Rsun to 20 Rsun. Thus the entire Thomson hemisphere is contained within the telescope's field and we need to think of the instrument as being a traditional remote sensing instrument and then transitioning to a local in-situ instrument. The local behavior derives from the fact that the maximum Thomson scattering will favor the electron plasma close to the spacecraft - exactly what the in-situ instruments will be sampling. SoloHI and WISPR will also observe scattered light from dust in the inner heliosphere, which will be an entirely new spatial regime for dust observations from a coronagraph, which we assume to arise from dust in the general neighborhood of about half way between the observer and the Sun. As the dust grains approach the Sun, they evaporate and do not contribute to the scattering. A dust free zone has been postulated to exist somewhere inside of 5 Rsun where all dust is evaporated, but this has never been observed. The radial position where the evaporation occurs will depend on the precise molecular composition of the individual grains. The orbital plane of Solar Orbiter will gradually increase up to about 35 degrees, enabling a very different view through the zodiacal dust cloud to test the models generated from in-ecliptic observations. In this paper we will explore some of the issues associated with the observation of the dust and will present a simple model to explore the sensitivity of the instrument to observe such evaporations.

Howard, R. A.; Thernisien, A. F.; Vourlidas, A.; Plunkett, S. P.; Korendyke, C. M.; Sheeley, N. R.; Morrill, J. S.; Socker, D. G.; Linton, M. G.; Liewer, P. C.; De Jong, E. M.; Velli, M. M.; Mikic, Z.; Bothmer, V.; Lamy, P. L.

2011-12-01

23

Nanoflare heating of solar and stellar coronae  

NASA Astrophysics Data System (ADS)

A combination of observational and theoretical evidence suggests that much, and perhaps most, of the Sun's corona is heated by small unresolved bursts of energy called nanoflares. It seems likely that stellar coronae are heated in a similar fashion. Nanoflares are here taken to mean any impulsive heating that occurs within a magnetic flux strand. Many mechanisms have this property, including waves, but we prefer Parker's picture of tangled magnetic fields. The tangling is caused by turbulent convection at the stellar surface, and magnetic energy is released when the stresses reach a critical level. We suggest that the mechanism of energy release is the "secondary instability" of electric current sheets that are present at the boundaries between misaligned strands. I will discuss the collective evidence for solar and stellar nanoflares and hopefully present new results from the Solar Dynamics Observatory that was just launched.

Klimchuk, James

24

Solar Corona on 10.21.2010  

NASA Video Gallery

The solar corona on 2010/10/21, observed by SDO’s AIA. The false colors represent images taken with different filters that are sensitive to distinct coronal temperatures: blue for one million degrees, green -1.5 million, and red - 2 million. The movie shows three simultaneous eruptions: one near the center of the disk, and two at opposite sides of the Sun, together spanning over a million miles.

Holly Zell

2010-12-13

25

Locating Current Sheets in the Solar Corona  

Microsoft Academic Search

Current sheets are essential for energy dissipation in the solar corona, in particular by enabling magnetic reconnection.\\u000a Unfortunately, sufficiently thin current sheets cannot be resolved observationally and the theory of their formation is an\\u000a unresolved issue as well. We consider two predictors of coronal current concentrations, both based on geometrical or even\\u000a topological properties of a force-free coronal magnetic field.

J. Büchner

2006-01-01

26

Locating current sheets in the solar corona  

Microsoft Academic Search

Current sheets are essential for energy dissipation in the solar corona, in\\u000aparticular by enabling magnetic reconnection. Unfortunately, sufficiently thin\\u000acurrent sheets cannot be resolved observationally and the theory of their\\u000aformation is an unresolved issue as well. We consider two predictors of coronal\\u000acurrent concentrations, both based on geometrical or even topological\\u000aproperties of a force free coronal magnetic

Joerg Buechner

2007-01-01

27

Nonlinear Plasma Physics of the Solar Corona  

NASA Astrophysics Data System (ADS)

As a tribute to Dennis Papadopoulos, we present a review of some recent ideas in solar coronal plasma physics. In particular we discuss some models of coronal heating, notably the coronal tectonics model, as well as some ideas on the nature of reconnection in three dimensions. In addition, we summarise a model for the time-dependent response of the corona to the sudden dissipation of a current sheet.

Priest, Eric R.

2011-01-01

28

HEATING THE SOLAR X-RAY CORONA  

Microsoft Academic Search

The X-ray corona of the Sun consists of the diffuse X-ray background and the bright X-ray loops (107 erg\\/cm2sec) confined in the strong (100 Gauss) bipolar fields of mag- netic active regions. The bipolar fields are rooted in the solar granules which continually intermix the photo- spheric footpoints of the bipolar fields and progressively interlace the field lines. The intermixing

E. N. Parker

29

Ion Heating in the Solar Corona and Solar Wind  

Microsoft Academic Search

The solar corona is the hot, ionized outer atmosphere of the Sun that expands into interplanetary space as a supersonic solar wind. This tenuous medium is a unique laboratory for the study of magnetohydrodynamics (MHD) and plasma physics with ranges of parameters that are inaccessible on Earth. The last decade has seen significant progress toward identifying and characterizing the processes

Steven Cranmer

2009-01-01

30

Ion Cyclotron Damping in the Solar Corona and Solar Wind  

Microsoft Academic Search

The solar corona is the hot, ionized outer atmosphere of the Sun. Coronal plasma expands into interplanetary space as a supersonic bulk outflow known as the solar wind. This tenuous and unbounded medium is a unique laboratory for the study of kinetic theory in a nearly collisionless plasma, as well as magnetohydrodynamic waves, shocks, and jets. Particle velocity distributions in

Steven R. Cranmer

31

Ion cyclotron damping in the solar corona and solar wind  

Microsoft Academic Search

The solar corona is the hot, ionized outer atmosphere of the Sun. Coronal plasma expands into interplanetary space as a supersonic bulk outflow known as the solar wind. This tenuous and unbounded medium is a unique laboratory for the study of kinetic theory in a nearly collisionless plasma, as well as magnetohydrodynamic waves, shocks, and jets. Particle velocity distributions in

Steven R. Cranmer

2001-01-01

32

Radio seismology of the outer solar corona  

NASA Astrophysics Data System (ADS)

Context. Observed oscillations of coronal loops in extreme ultraviolet (EUV) lines have been successfully used to estimate plasma parameters in the inner corona (<0.2 R0, where R0 is the solar radius). However, coronal seismology in EUV lines fails for higher altitudes because of rapid decrease in line intensity. Aims: We aim to use radio observations to estimate the plasma parameters of the outer solar corona (>0.2 R0). Methods: We used the large Ukrainian radio telescope URAN-2 to observe type IV radio bursts at the frequency range of 8-32 MHz during the time interval of 09:50-12:30 UT on April 14, 2011. The burst was connected to C2.3 flare, which occurred in AR 11190 during 09:38-09:49 UT. The dynamic spectrum of radio emission shows clear quasi-periodic variations in the emission intensity at almost all frequencies. Results: Wavelet analysis at four different frequencies (29 MHz, 25 MHz, 22 MHz, and 14 MHz) shows the quasi-periodic variation of emission intensity with periods of ~34 min and ~23 min. The periodic variations can be explained by the first and second harmonics of vertical kink oscillation of transequatorial coronal loops, which were excited by the same flare. The apex of transequatorial loops may reach up to 1.2 R0 altitude. We derive and solve the dispersion relation of trapped magnetohydrodynamic oscillations in a longitudinally inhomogeneous magnetic slab. The analysis shows that a thin (with width to length ratio of 0.1), dense (with the ratio of internal and external densities of ?20) magnetic slab with weak longitudinal inhomogeneity of the Alfvén speed may trap the observed oscillations. Seismologically estimated Alfvén speed inside the loop at the height of ~1 R0 is ~1000 km s-1. The magnetic field strength at this height is estimated as ~0.9 G. Extrapolation of magnetic field strength to the inner corona gives ~10 G at the height of 0.1 R0. Conclusions: Radio observations can be successfully used for the sounding of the outer solar corona, where EUV observations of coronal loops fail. Therefore, radio seismology of the outer solar corona is complementary to EUV seismology of the inner corona.

Zaqarashvili, T. V.; Melnik, V. N.; Brazhenko, A. I.; Panchenko, M.; Konovalenko, A. A.; Franzuzenko, A. V.; Dorovskyy, V. V.; Rucker, H. O.

2013-07-01

33

Transport of cosmic rays in the solar corona  

Microsoft Academic Search

A model is proposed to explain the transport of energetic protons in the solar corona. The particles are assumed to undergo an enhanced gradient-B drift along thin current sheets separating discontinuous field structures in the corona. These discontinuities may represent the extension into the corona of photospheric granular and supergranular cell boundaries. We have made a quantitative analysis of this

L. A. Fisk; K. H. Schatten

1972-01-01

34

Locating Current Sheets in the Solar Corona  

NASA Astrophysics Data System (ADS)

Current sheets are essential for energy dissipation in the solar corona, in particular by enabling magnetic reconnection. Unfortunately, sufficiently thin current sheets cannot be resolved observationally and the theory of their formation is an unresolved issue as well. We consider two predictors of coronal current concentrations, both based on geometrical or even topological properties of a force-free coronal magnetic field. First, there are separatrices related to magnetic nulls. Through separatrices the magnetic connectivity changes discontinuously. Coronal magnetic nulls are, however, very rare. Second, inspired by the concept of generalized magnetic reconnection without nulls, quasi-separatrix layers (QSL) were suggested. Through QSL the magnetic connectivity changes continuously, though strongly. The strength of the connectivity change can be quantified by measuring the squashing of the flux tubes which connect the magnetically conjugated photospheres. We verify the QSL and separatrix concepts by comparing the sites of magnetic nulls and enhanced squashing with the location of current concentrations in the corona. Due to the known difficulties of their direct observation, we simulated coronal current sheets by numerically calculating the response of the corona to energy input from the photosphere, heating a simultaneously observed Extreme Ultraviolet Bright Point. We did not find coronal current sheets at separatrices but at several QSL locations. The reason is that, although the geometrical properties of force-free extrapolated magnetic fields can indeed hint at possible current concentrations, a necessary condition for current sheet formation is the local energy input into the corona.

Büchner, J.

2006-02-01

35

RADIATIVE HEATING OF THE SOLAR CORONA  

SciTech Connect

We investigate the effect of solar visible and infrared radiation on electrons in the Sun's atmosphere using a Monte Carlo simulation of the wave-particle interaction and conclude that sunlight provides at least 40% and possibly all of the power required to heat the corona, with the exception of dense magnetic flux loops. The simulation uses a radiation waveform comprising 100 frequency components spanning the solar blackbody spectrum. Coronal electrons are heated in a stochastic manner by low coherence solar electromagnetic radiation. The wave 'coherence time' and 'coherence volume' for each component is determined from optical theory. The low coherence of solar radiation allows moving electrons to gain energy from the chaotic wave field which imparts multiple random velocity 'kicks' to these particles causing their velocity distribution to broaden or heat. Monte Carlo simulations of broadband solar radiative heating on ensembles of 1000 electrons show heating at per particle levels of 4.0 x 10{sup -21} to 4.0 x 10{sup -20} W, as compared with non-loop radiative loss rates of {approx}1 x 10{sup -20} W per electron. Since radiative losses comprise nearly all of the power losses in the corona, sunlight alone can explain the elevated temperatures in this region. The volume electron heating rate is proportional to density, and protons are assumed to be heated either by plasma waves or through collisions with electrons.

Moran, Thomas G., E-mail: moran@grace.nascom.nasa.gov [Physics Department, Catholic University of America, 200 Hannan Hall, Washington, DC 20064 (United States) and NASA/GSFC, Code 671, Greenbelt, MD 20771 (United States)

2011-10-20

36

Radiative Heating of the Solar Corona  

NASA Astrophysics Data System (ADS)

We investigate the effect of solar visible and infrared radiation on electrons in the Sun's atmosphere using a Monte Carlo simulation of the wave-particle interaction and conclude that sunlight provides at least 40% and possibly all of the power required to heat the corona, with the exception of dense magnetic flux loops. The simulation uses a radiation waveform comprising 100 frequency components spanning the solar blackbody spectrum. Coronal electrons are heated in a stochastic manner by low coherence solar electromagnetic radiation. The wave "coherence time" and "coherence volume" for each component is determined from optical theory. The low coherence of solar radiation allows moving electrons to gain energy from the chaotic wave field which imparts multiple random velocity "kicks" to these particles causing their velocity distribution to broaden or heat. Monte Carlo simulations of broadband solar radiative heating on ensembles of 1000 electrons show heating at per particle levels of 4.0 × 10-21 to 4.0 × 10-20 W, as compared with non-loop radiative loss rates of ?1 × 10-20 W per electron. Since radiative losses comprise nearly all of the power losses in the corona, sunlight alone can explain the elevated temperatures in this region. The volume electron heating rate is proportional to density, and protons are assumed to be heated either by plasma waves or through collisions with electrons.

Moran, Thomas G.

2011-10-01

37

Ultraviolet spectroscopy of the extended solar corona  

NASA Astrophysics Data System (ADS)

The first observations of ultraviolet spectral line profiles and intensities from the extended solar corona (i.e., more than 1.5 solar radii from Sun-center) were obtained on 13 April 1979 when a rocket-borne ultraviolet coronagraph spectrometer of the Harvard-Smithsonian Center for Astrophysics made direct measurements of proton kinetic temperatures, and obtained upper limits on outflow velocities in a quiet coronal region and a polar coronal hole. Following those observations, ultraviolet coronagraphic spectroscopy has expanded to include observations of over 60 spectral lines in coronal holes, streamers, coronal jets, and solar flare/coronal mass ejection (CME) events. Spectroscopic diagnostic techniques have been developed to determine proton, electron and ion kinetic temperatures and velocity distributions, proton and ion bulk flow speeds and chemical abundances. The observations have been made during three sounding rocket flights, four Shuttle deployed and retrieved Spartan 201 flights, and the Solar and Heliospheric Observatory (SOHO) mission. Ultraviolet spectroscopy of the extended solar corona has led to fundamentally new views of the acceleration regions of the solar wind and CMEs. Observations with the Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO revealed surprisingly large temperatures, outflow speeds, and velocity distribution anisotropies in coronal holes, especially for minor ions. Those measurements have guided theorists to discard some candidate physical processes of solar wind acceleration and to increase and expand investigations of ion cyclotron resonance and related processes. Analyses of UVCS observations of CME plasma properties and the evolution of CMEs have provided the following: temperatures, inflow velocities and derived values of resistivity and reconnection rates in CME current sheets, compression ratios and extremely high ion temperatures behind CME shocks, and three dimensional flow velocities and magnetic field chirality in CMEs. Ultraviolet spectroscopy has been used to determine the thermal energy content of CMEs allowing the total energy budget to be known for the first time. Such spectroscopic observations are capable of providing detailed empirical descriptions of solar energetic particle (SEP) source regions that allow theoretical models of SEP acceleration to be tailored to specific events, thereby enabling in situ measurements of freshly emitted SEPs to be used for testing and guiding the evolution of SEP acceleration theory. Here we review the history of ultraviolet coronagraph spectroscopy, summarize the physics of spectral line formation in the extended corona, describe the spectroscopic diagnostic techniques, review the advances in our understanding of solar wind source regions and flare/CME events provided by ultraviolet spectroscopy and discuss the scientific potential of next generation ultraviolet coronagraph spectrometers.

Kohl, John L.; Noci, Giancarlo; Cranmer, Steven R.; Raymond, John C.

2006-04-01

38

Solar corona expansion and heliospheric current sheet creation  

Microsoft Academic Search

Heliospheric current sheet (CS) creation has been investigated by numerical solution of 3D MHD equations, using the PERESVET code to the problem of solar corona expansion. The dipole magnetic field corresponds to the solar activity minimum, and typical corona parameters are used as initial conditions. Plasma compression, dissipation, thermal conductivity, and gravitation are taken into account. The normal magnetic field

I. M. Podgorny; A. I. Podgorny

2008-01-01

39

The structure of the external corona in solar activity minimum.  

NASA Astrophysics Data System (ADS)

The external corona was observed using the photography method during the total solar eclipse at Mohe on March 9, 1997. The observational data was disposed using the astronomical Video Image Collecting Processing System. The shape and structure of the external corona in solar activity minimum are analysed.

Luo, Baorong; Wang, Feng

40

Nanoflares and the Heating of the Solar Corona  

Microsoft Academic Search

There is a simmering dispute on the heating of the solar corona. Waves or flares that is the question. New observational signatures of the heating process(es) have been revealed by observations of SoHO TRACE Yohkoh and RHESSI. The evidence for heating in the quiet corona active region loops and the solar wind are different and must be distinguished. Prime indications

A. O. Benz

2004-01-01

41

On the evolution of dust in the solar vicinity.  

PubMed

The analysis of interplanetary dust shows that the majority of particles in out-of-ecliptic regions comes from comets and also that near solar dust, in the ecliptic regions, results most probably largely from comets. The intense radiation flux in the solar vicinity is expected to cause strong modifications in the material composition and surface structure of interplanetary dust particles and hence the analysis of near solar dust provides interesting insights into the evolution of meteoritic, especially cometary materials. Because of the lack of in-situ measurements our present knowledge concerning these processes derives from remote sensing, i.e. observations of the solar F-corona. In particular these are observations of albedo, polarization and colour temperature given in terms of average particle properties. For example the analysis of near infra-red F-corona data points to the existence of a strong component of irregularly structured silicate particles, most probably of cometary origin. The data may indicate a subsequent sublimation of different particles or different constituents of the particles. Here we compare particle properties derived from F-corona observations with model calculations of single particle properties and discuss perspectives of future analysis of cometary dust in the interplanetary cloud. PMID:11543534

Mann, I; Mukai, T; Okamoto, H

1995-01-01

42

Magnetohydrodynamic Simulations of the Solar Corona and Solar Wind Using a Boundary Treatment to Limit Solar Wind Mass Flux  

Microsoft Academic Search

Magnetohydrodynamic simulations of the solar corona and solar wind are sensitive to conditions in the sub-Alfvénic plasma at the base of the solar corona because the structure of the simulated solar corona is determined by the pressure balance of the plasma and the magnetic field. Therefore, it is important to construct an adequate boundary treatment for the sub-Alfvénic surface, and

Keiji Hayashi

2005-01-01

43

The Temperature and Density Structure of the Quiet Solar Corona  

NASA Astrophysics Data System (ADS)

The temperature and density structure of the quiet solar corona remains unclear. In this poster, we will present a preliminary analysis of a quiet solar coronal loop structure observed with SOHO and TRACE. After determining the magnetic field structure from potential field extrapolation, we attempt to model this loop using RTV scaling laws with various heating functions. This work is in preparation for a full-scale statistical study of SOHO/TRACE data to determine the structure of the quiet solar corona.

Winebarger, A. R.; Warren, H. P.

2001-05-01

44

Ion Heating in the Solar Corona and Solar Wind  

NASA Astrophysics Data System (ADS)

The solar corona is the hot, ionized outer atmosphere of the Sun that expands into interplanetary space as a supersonic solar wind. This tenuous medium is a unique laboratory for the study of magnetohydrodynamics (MHD) and plasma physics with ranges of parameters that are inaccessible on Earth. The last decade has seen significant progress toward identifying and characterizing the processes that heat the corona and accelerate the solar wind, but the basic physics is still unclear. Some key clues about the mechanisms responsible for energizing the plasma have come from UV spectroscopy of the extended corona (i.e., using a combination of an occulting coronagraph and a spectrometer). There is evidence for preferential acceleration of heavy ions in the fast solar wind, ion temperatures exceeding 100 million K, and marked departures from Maxwellian velocity distributions. These collisionless departures from thermal equilibrium point to specific types of kinetic processes. This presentation reviews the measurements (both telescopic and from `in situ' probes) that constrain theoretical explanations and provides a current survey of the landscape of proposed ideas for ion energization. Many of the suggested processes are related to the dissipation of MHD waves (e.g., ion cyclotron waves), and many involve multiple steps of energy conversion between waves, turbulence, current sheets, and other nonlinear plasma features. A discussion of future measurements that could help to test, refine, and possibly winnow down the list of competing models will also be presented.

Cranmer, Steven

2009-05-01

45

The effect of corona discharge on dust mite and cat allergens  

Microsoft Academic Search

Corona discharge has previously been reported to destroy the house dust mite allergen Der p1. This present paper describes the efficacy of corona discharge to destroy three more clinically important allergens and investigates the factors that affect this process. Using Der p1, Der p2, Der f1 and Fel d1 the allergen reducing efficacies of both negative and positive corona, of

Neil Goodman; John F Hughes

2004-01-01

46

Radio Observations of the Solar Corona During an Eclipse  

NASA Astrophysics Data System (ADS)

We carried out radio observations of the solar corona at 170 MHz during the eclipse of 2008 August 1, from the Gauribidanur observatory located about 100 km north of Bangalore in India. The results indicate the presence of a discrete radio source of very small angular dimension (?15'') in the corona from where the observed radiation originated.

Kathiravan, C.; Ramesh, R.; Barve, Indrajit V.; Rajalingam, M.

2011-04-01

47

Mass and energy flow in the solar chromosphere and corona  

Microsoft Academic Search

Some results of investigations into the mass and energy flow in the solar chromosphere and corona are reviewed. The objective of these investigations is the development of a physical model that will not only account for the physical conditions in the outer atmosphere of the sun but also can be applied to the study of the chromospheres and coronae of

G. L. Withbroe; R. W. Noyes

1977-01-01

48

Collisional damping of surface waves in the solar corona  

Microsoft Academic Search

It has been suggested that surface waves may be able to heat the solar corona. These waves can propagate into the corona and supply the required energies, and because they are linearly compressive they can be dissipated by ion viscosity and electron heat conduction. In this paper the authors evaluate the damping of surface waves by viscosity and heat conduction.

B. E. Gordon; J. V. Hollweg

1983-01-01

49

A study of the composition of the lower solar corona  

Microsoft Academic Search

Some trends in the composition of the lower solar corona due to mixing and diffusion have been examined. Mixing has been treated through plausible inference from the thermal gradient and through analogy with the neutral atmosphere of the earth. These indicate that diffusion may be important in the lower corona. Changes in composition due to pressure and thermal gradients have

M. P. Nakada

1969-01-01

50

Joule heating and anomalous resistivity in the solar corona  

Microsoft Academic Search

Recent radioastronomical observations of Faraday rotation in the solar corona can be interpreted as evidence for coronal currents, with values as large as 2.5×109 Amperes (Spangler, 2007). These estimates of currents are used to develop a model for Joule heating in the corona. It is assumed that the currents are concentrated in thin current sheets, as suggested by theories of

S. R. Spangler

2009-01-01

51

HEATING OF THE SOLAR CORONA BY GRAVITY WAVES  

Microsoft Academic Search

ABS>A new type of hydrodynamic-wave heating is proposed for the solar ; corona. It is shown that internal gravity waves are preferentially generated by ; the convection zone and are easily transmitted to the corona. Acoustic waves ; with frequency characteristic of the photospheric granules cannot be transmitted ; through the reversing layer. The gravity waves are shown to dissipate

William A. Whitaker

1963-01-01

52

Exploring dynamic events in the solar corona  

NASA Astrophysics Data System (ADS)

With the advent of modern computational technology it is now becoming the norm to employ detailed 3D computer models as empirical tools that directly account for the inhomogeneous nature of the Sun-Heliosphere environment. The key advantage of this approach lies in the ability to compare model results directly to observational data and to use a successful comparison (or lack thereof) to glean information on the underlying physical processes. Using extreme ultraviolet waves (EUV waves) as the overarching scientific driver, we apply this observation modeling approach to study the complex dynamics of the magnetic and thermodynamic structures that are observed in the low solar corona. Representing a highly non-trivial effort, this work includes three main scientific thrusts: an initial modeling effort and two EUV wave case-studies. First we document the development of the new Low Corona (LC) model, a 3D time-dependent thermodynamic magnetohydrodynamic (MHD) model implemented within the Space Weather Modeling Framework (SWMF). Observation synthesis methods are integrated within the LC model, which provides the ability to compare model results directly to EUV imaging observations taken by spacecraft. The new model is then used to explore the dynamic interplay between magnetic structures and thermodynamic energy balance in the corona that is caused by coronal heating mechanisms. With the model development complete, we investigate the nature of EUV waves in detail through two case-studies. Starting with the 2008 March 25 event, we conduct a series of numerical simulations that independently vary fundamental parameters thought to govern the physical mechanisms behind EUV waves. Through the subsequent analysis of the 3D data and comparison to observations we find evidence for both wave and non-wave mechanisms contributing to the EUV wave signal. We conclude with a comprehensive observation and modeling analysis of the 2010 June 13 EUV wave event, which was observed by the recently launched Solar Dynamics Observatory. We use a high resolution simulation of the transient to unambiguously characterize the globally propagating front of EUV wave as a fast-mode magnetosonic wave, and use the rich set of observations to place the many other facets of the EUV transient within a unified scenario involving wave and non-wave components.

Downs, Cooper James

53

Magnetic fields and the structure of the solar corona  

Microsoft Academic Search

During the eclipse of 12 November 1966, the solar corona was photographed at an effective wavelength of 6500 Å with an f\\/16, 11.1 cm aperture camera. Reduction of the observations yields coronal radiances and polarizations from 1.4 to 3.5 solar radii. Standard techniques are used for the separation of F and K-coronas, determination of coronal electron densities and temperatures, and

Gordon Newkirk; Robert G. Dupree; Edward J. Schmhl

1970-01-01

54

Next-Generation Model of the Corona and Solar Wind.  

National Technical Information Service (NTIS)

A central goal of solar and space physics is to understand the influence of the sun and its activity on the heliosphere, particularly the space environment near the Earth. A quantitative description of the ambient solar corona and solar wind is key to und...

J. A. Linker

2011-01-01

55

Modelling the Large Scale Structure of the Solar Corona  

NASA Astrophysics Data System (ADS)

We report on recent attempts to find a quantitative description of both the magnetic field and the distribution of plasma in the lower corona that matches the white light images of the K-corona. We use the magnetostatic model of Bogdan and Low and data obtained by the High Altitude Observatory K-Coronameter (1.2 - 2.3 Rsun) and the Solar Maximum Mission Coronameter/Polarimeter (1.5 - 4 Rsun). By varying parameters in the Bogdan and Low model we are able to quantitatively match the general characteristics of the lower corona at solar minimum: power law radial profiles of coronal brightness: enhanced brightness at the equator; uniform density depletion at the pole. Further, we use the best fit model to determine a temperature distribution in the corona and investigate the implications this has for solar wind theory.

Gibson, S.; Bagenal, F.

1992-05-01

56

A study of the composition of the solar corona and solar wind  

Microsoft Academic Search

Effects of diffusion on the composition of the solar corona and solar wind have been examined. Multi-component diffusion equations have been solved simultaneously in attempts to account for the flux of He and heavier elements in the solar wind. Large enhancements of these elements at the base of the assumed isothermal corona appear to be required to give observed fluxes.

M. P. Nakada

1970-01-01

57

Solar aureoles caused by dust, smoke, and haze.  

PubMed

The forward scattering of sunlight by atmospheric aerosols causes a bright glow to appear around the Sun. This phenomenon, the simplest manifestation of the solar corona, is called the solar aureole. Simple methods can be used to photograph the solar aureole with conventional and digital cameras. Aureole images permit both a visually qualitative and an analytically quantitative comparison of aureoles caused by dust, smoke, haze, pollen, and other aerosols. Many hundreds of aureole photographs have been made at Geronimo Creek Observatory in Texas, including a regular time series since September 1998. These images, and measurements extracted from them, provide an important supplement to studies of atmospheric aerosols. PMID:12570271

Mims, Forrest M

2003-01-20

58

Nanoflare heating of solar and stellar coronae  

Microsoft Academic Search

A combination of observational and theoretical evidence suggests that much, and perhaps most, of the Sun's corona is heated by small unresolved bursts of energy called nanoflares. It seems likely that stellar coronae are heated in a similar fashion. Nanoflares are here taken to mean any impulsive heating that occurs within a magnetic flux strand. Many mechanisms have this property,

James Klimchuk

2010-01-01

59

Heating the solar corona by plasma loops  

Microsoft Academic Search

We investigate the heating of the corona via plasma loops. It is shown that it may be possible to maintain the high corona temperatures using plasma loops as conduits. Under certain conditions heat can flow across magnetic fields up temperature gradients, a mechanism that has been previously applied to the heating of plasma loops. A typical conduit loop is hotter

J. M. A. Ashbourn; L. C. Woods

2006-01-01

60

Modeling the large-scale structure of the solar corona  

NASA Astrophysics Data System (ADS)

The aim of this study is to find a quantitative description of both the magnetic field and the distribution of plasma in the lower corona that matches the white light images of the K-corona. The magnetostatic model of Bogdan and Low (1986) and data obtained by the High Altitude Observatory Mark III K-Coronameter stationed at Mauna Loa, Hawaii is used. To start with, the simplest, solar minimum case when the corona is approximately longitudinally symmetric is taken. By varying parameters in the Bogdan and Low model it is possible to quantitatively match the general characteristics of the lower corona at solar minimum: power law radial profiles of coronal brightness; enhanced brightness at the equator; uniform density depletion at the pole.

Bagenal, F.; Gibson, S.

1991-10-01

61

Modeling the large-scale structure of the solar corona  

NASA Astrophysics Data System (ADS)

The aim of this study is to find a quantitative description of both the magnetic field and the distribution of plasma in the lower corona that matches the white light images of the K-corona. We use the magnetostatic model of Bogdan and Low (1986) and data obtained by the High Altitude Observatory Mark III K-Coronameter stationed at Mauna Loa, Hawaii. To start with, we take the simplest, solar minimum case when the corona is approximately longitudinally symmetric. By varying parameters in the Bogdan and Low model we are able to quantitatively match the general characteristics of the lower corona at solar minimum: power law radial profiles of coronal brightness; enhanced brightness at the equator; uniform density depletion at the pole.

Bagenal, F.; Gibson, S.

62

Propagation of Radio Waves in the Corona and Solar Wind  

NASA Astrophysics Data System (ADS)

The solar corona and solar wind are plasmas characterized by large scale MHD structures, waves, and turbulence. These introduce both systematic and random variations in the refractive index which affect the propagation of radio waves. A variety of propagation phenomena occur -- regular refraction; angular, temporal, and spectral broadening; scintillations in amplitude and phase -- widely referred to as scattering phenomena. In this tutorial I review the physical basis of these phenomena and describe a variety of techniques designed to exploit observations of scattering phenomena to deduce properties of the corona and solar wind plasma.

Bastian, T. S.

63

Heating of the solar corona plasma by fast electron streams  

SciTech Connect

The heating of the solar corona above active regions due to the dissipation of plasma turbulence, which is excited by energetic electron streams, is discussed. The efficiency of energy transfer from electron beams to the main plasma is estimated. It is shown that a layer of nonisothermal plasma is formed in the corona above an active region during developed type III noise storms. The role of heat conduction in the process of formation of such a layer is discussed.

Levin, B.N.

1979-11-01

64

Joule heating and anomalous resistivity in the solar corona  

Microsoft Academic Search

Recent radioastronomical observations of Faraday rotation in the solar corona\\u000acan be interpreted as evidence for coronal currents, with values as large as\\u000a$2.5 \\\\times 10^9$ Amperes (Spangler 2007). These estimates of currents are used\\u000ato develop a model for Joule heating in the corona. It is assumed that the\\u000acurrents are concentrated in thin current sheets, as suggested by

Steven R. Spangler

2009-01-01

65

Measurement of the polarization of the solar corona  

NASA Astrophysics Data System (ADS)

The position of the polarization plane in the solar corona during the total eclipse of July 11, 1991 was measured with a rotating polaroid with the axis oriented to the radius at an angle of +/- 45 deg. The polarization plane was everywhere tangential to the solar surface with an accuracy of up to 1 percent.

Kuchmi, S.; Molodenskij, M. M.; Nikol'Skij, G. M.; Filippov, B. P.

1993-06-01

66

Energy Distribution of Heating Processes in the Quiet Solar Corona  

Microsoft Academic Search

We have determined the variations in the emission measure of the solar corona using EUV Imaging Telescope\\/Solar and Heliospheric Observatory observations of iron lines in a quiet region of the Sun. The emission measure is found to vary significantly in at least 85% of all the pixels within 42 minutes. The variations are interpreted as heating events that bring chromospheric

Saem Krucker; Arnold O. Benz

1998-01-01

67

Development of a complex of activity in the solar corona  

Microsoft Academic Search

Skylab observations of the Sun in soft X-rays gave us the first possibility to study the development of a complex of activity in the solar corona during its whole lifetime of seven solar rotations. The basic components of the activity complex were permanently interconnected (including across the equator) through sets of magnetic field lines, which suggests similar connections also below

Robert Howard; Zden?k Švestka

1977-01-01

68

The 2008 August 1 Eclipse Solar-Minimum Corona Unraveled  

NASA Astrophysics Data System (ADS)

We discuss the results stemming from observations of the white-light and [Fe XIV] emission corona during the total eclipse of the Sun of 2008 August 1, in Mongolia (Altaj region) and in Russia (Akademgorodok, Novosibirsk, Siberia). Corresponding to the current extreme solar minimum, the white-light corona, visible up to 20 solar radii, was of a transient type with well pronounced helmet streamers situated above a chain of prominences at position angles 48°, 130°, 241°, and 322°. A variety of coronal holes, filled with a number of thin polar plumes, were seen around the poles. Furthering an original method of image processing, stars up to 12 mag, a Kreutz-group comet (C/2008 O1) and a coronal mass ejection (CME) were also detected, with the smallest resolvable structures being of, and at some places even less than, 1 arcsec. Differences, presumably motions, in the corona and prominences are seen even with the 19 minutes time difference between our sites. In addition to the high-resolution coronal images, which show the continuum corona (K-corona) that results from electron scattering of photospheric light, images of the overlapping green-emission-line (530.3 nm, [Fe XIV]) corona were obtained with the help of two narrow-passband filters (centered on the line itself and for the continuum in the vicinity of 529.1 nm, respectively), each with an FWHM of 0.15 nm. Through solar observations, on whose scheduling and details we consulted, with the Solar and Heliospheric Observatory, Hinode's XRT and SOT, Transition Region and Coronal Explorer, and STEREO, as well as Wilcox Solar Observatory and Solar and Heliospheric Observatory/Michelson Doppler Imager magnetograms, we set our eclipse observations in the context of the current unusually low and prolonged solar minimum.

Pasachoff, J. M.; Rušin, V.; Druckmüller, M.; Aniol, P.; Saniga, M.; Minarovjech, M.

2009-09-01

69

Topological Structure of the Magnetic Solar Corona  

NASA Astrophysics Data System (ADS)

The solar corona is a highly complex and active plasma environment, containing many exotic phenomena such as solar flares, coronal mass ejections, prominences, coronal loops, and bright points. The fundamental element giving coherence to all this apparent diversity is the strong coronal magnetic field, the dominant force shaping the plasma there. In this thesis, I model the 3D magnetic fields of various coronal features using the techniques of magnetic charge topology (MCT) in a potential field. Often the real coronal field has departures from its potential state, but these are so small that the potential field method is accurate enough to pick out the essential information about the structure and evolution of the magnetic field. First I perform a topological analysis of the magnetic breakout model for an eruptive solar flare. Breakout is represented by a topological bifurcation that allows initially enclosed flux from the newly emerging region in my MCT model of a delta sunspot to reconnect out to large distances. I produce bifurcation diagrams showing how this behaviour can be caused by changing the strength or position of the emerging flux source, or the force-free parameter ?. I also apply MCT techniques to observational data of a coronal bright point, and compare the results to 3D numerical MHD simulations of the effects of rotating the sources that underlie the bright point. The separatrix surfaces that surround each rotating source are found to correspond to locations of high parallel electric field in the simulations, which is a signature of magnetic reconnection. The large-scale topological structure of the magnetic field is robust to changes in the method of deriving point magnetic sources from the magnetogram. Next, I use a Green's function expression for the magnetic field to relax the standard topological assumption of a flat photosphere and extend the concept of MCT into a spherical geometry, enabling it to be applied to the entire global coronal magnetic field. I perform a comprehensive study of quadrupolar topologies in this new geometry, producing several detailed bifurcation diagrams. These results are compared to the equivalent study for a flat photosphere. A new topological state is found on the sphere which has no flat photosphere analogue; it is named the dual intersecting state because of its twin separators joining a pair of magnetic null points. The new spherical techniques are then applied to develop a simple six-source topological model of global magnetic field reversal during the solar cycle. The evolution of the large-scale global magnetic field is modelled through one complete eleven-year cycle, beginning at solar minimum. Several distinct topological stages are exhibited: active region flux connecting across the equator to produce transequatorial loops; the dominance of first the leading and then the following polarities of the active regions; the magnetic isolation of the poles; the reversal of the polar field; the new polar field connecting back to the active regions; the polar flux regaining its dominance; and the disappearance of the transequatorial loops.

Maclean, R. C.

2007-12-01

70

Patchy reconnection in the solar corona  

NASA Astrophysics Data System (ADS)

Magnetic reconnection in plasmas, a process characterized by a change in connectivity of field lines that are broken and connected to other ones with different topology, owes its usefulness to its ability to unify a wide range of phenomena within a single universal principle. There are newly observed phenomena in the solar corona that cannot be reconciled with two-dimensional or steady-state standard models of magnetic reconnection. Supra-arcade downflows (SADs) and supra-arcade downflowing loops (SADLs) descending from reconnection regions toward solar post-flare arcades seem to be two different observational signatures of retracting, isolated reconnected flux tubes with irreducible three-dimensional geometries. This dissertation describes work in refining and improving a novel model of patchy reconnection, where only a small bundle of field lines is reconnected across a current sheet (magnetic discontinuity) and forms a reconnected thin flux tube. Traditional models have not been able to explain why some of the observed SADs appear to be hot and relatively devoid of plasma. The present work shows that plasma depletion naturally occurs in flux tubes that are reconnected across nonuniform current sheets and slide trough regions of decreasing magnetic field magnitude. Moreover, through a detailed theoretical analysis of generalized thin flux tube equations, we show that the addition to the model of pressure-driven parallel dynamics, as well as temperature-dependent, anisotropic viscosity and thermal conductivity is essential for self-consistently producing gas-dynamic shocks inside reconnected tubes that heat and compress plasma to observed temperatures and densities. The shock thickness can be as long as the entire tube and heat can be conducted along tube's legs, possibly driving chromospheric evaporation. We developed a computer program that solves numerically the thin flux tube equations that govern the retraction of reconnected tubes. Simulations carried out with this program corroborate our theoretical predictions. A comparison of these simulations with fully three-dimensional magnetohydrodynamic simulations is presented to assess the validity of the thin flux tube model. We also present an observational method based on total emission measure and mean temperature to determine where in the current sheet a tube was reconnected.

Guidoni, Silvina Esther

2011-05-01

71

Nanoflares and the Heating of the Solar Corona  

NASA Astrophysics Data System (ADS)

There is a simmering dispute on the heating of the solar corona. Waves or flares that is the question. New observational signatures of the heating process(es) have been revealed by observations of SoHO TRACE Yohkoh and RHESSI. The evidence for heating in the quiet corona active region loops and the solar wind are different and must be distinguished. Prime indications come from the distribution of temperature and radiation loss in relation to height the correlation of magnetic flux and brightness nanoflares and other fluctuations line broadening and waves. The reported microevents in the quiet regions are about 3 orders of magnitude smaller than microevents reported in active regions. The effects from localized energy release regardless of the energy source must be considered. In particular the reaction of the chromosphere on energy release by evaporation has an important effect on the corona. A further requirement for the heating process is to deposit most of the heat in the low corona but heat the upper corona to even higher temperature. Finally the heating process(es) must be able to account for the coronae of more active stars showing coronal emissions at levels of more than 3 orders of magnitude higher than the Sun

Benz, A. O.

2004-01-01

72

The Solar Corona: Why It Is Interesting for Us  

NASA Astrophysics Data System (ADS)

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.

Somov, B. V.

2013-02-01

73

Reconnection-Driven Alfven (RDA) Waves in the Solar Corona  

NASA Astrophysics Data System (ADS)

The mechanisms for heating the corona and accelerating the solar wind remain active areas of solar and heliospheric research. Currently, two relatively distinct paradigms confront these problems: a waves/turbulence paradigm, and a magnetic reconnection/dissipation paradigm. The fact that magnetic reconnection generates Alfvén waves suggests that the heating of the low-beta corona and the acceleration of the wind are likely the result of both paradigms operating simultaneously. This research aims to unify the two competing viewpoints. We present 3D MHD simulations of magnetic reconnection/dissipation processes in the solar corona that provide a self-consistent mechanism for producing the energy injection spectrum required by the waves/turbulence paradigm. We analyze the simulations to quantify the amount of magnetic energy released in the reconnection process and the material and energy fluxes carried by large-amplitude, nonlinear, reconnection-driven Alfvén (RDA) waves. In addition to isolating the RDA waves, characterizing their physical properties, and investigating their evolution in a low-beta, gravitationally stratified model corona, we examine their time-dependent material and energy outflows and discuss their observable consequences in the corona and inner heliosphere.

Edmondson, J. K.; Lynch, B. J.; DeVore, C. R.; Velli, M.

2011-12-01

74

Solar corona expansion and heliospheric current sheet creation  

NASA Astrophysics Data System (ADS)

Heliospheric current sheet (CS) creation has been investigated by numerical solution of 3D MHD equations, using the PERESVET code to the problem of solar corona expansion. The dipole magnetic field corresponds to the solar activity minimum, and typical corona parameters are used as initial conditions. Plasma compression, dissipation, thermal conductivity, and gravitation are taken into account. The normal magnetic field component is an important feature of the heliospheric CS. The sheet cannot be a neutral one. Current generation is similar to action of a short closed MHD generator. The solar wind temperature is determined by plasma cooling because of plasma expansion and heat conduction from the Sun. In the process of expansion the solar wind is accelerated and achieves the supersonic velocity at a distance of about 3 solar radii. The CS is surrounded by a thick plasma sheet. Plasma velocity is decreased inside the sheet as demonstrated by previous workers.

Podgorny, I. M.; Podgorny, A. I.

2008-02-01

75

Remote sensing measurements of the corona with the Solar Probe  

NASA Astrophysics Data System (ADS)

Remote sensing measurements of the solar corona are indispensable for the exploration of the source and acceleration regions of the solar wind which are inaccessible to in situ plasma, particles and fields experiments. Furthermore, imaging the solar disk and corona from the unique vantage point of the trajectory and the proximity of the Solar Probe spacecraft, will provide the first ever opportunity to explore the small scale structures within coronal holes and streamers from viewing angles and with spatial resolutions never attained before. Imaging will also provide the essential context for the in situ measurements. The scientific advantages of different proposed imagers are summarized here. Both disk and limb observations are recommended. Given the power, weight and telemetry limitations of the Solar Probe, the optimal choice of imagers could not be provided at the time of the workshop. Further concentrated studies were highly recommended.

Rifai Habbal, Shadia; Woo, Richard

1997-01-01

76

Differential rotation of the solar electron corona  

Microsoft Academic Search

Autocorrelation analyses of K-coronameter observations made at Haleakala and Mauna Loa, Hawaii, during 1964–1967 have established average yearly rotation rates of coronal features as a function of latitude and height above the limb. At low latitudes the corona was found to rotate at the same rate as sunspots but at higher latitudes was consistently faster than the underlying photosphere. There

Richard T. Hansen; Shirley F. Hansen; Harold G. Loomis

1969-01-01

77

Heating the Solar Corona by Magnetic Reconnection  

Microsoft Academic Search

Here I review briefly the theory of magnetohydrodynamic reconnection and ask what observational evidence is there that it is heating the corona. In particular, the new directions in which three-dimensional theory for reconnection is heading are outlined. Part of the coronal heating problem has been solved with the identification of reconnection driven by converging flux motions as the key for

E. R. Priest

1999-01-01

78

Heating the Solar Corona by Magnetic Reconnection  

Microsoft Academic Search

Here I review briefly the theory of magnetohydrodynamic reconnection and ask what observational evidence is there that it is heating the corona. In particular, the new directions in which three-dimensional theory for reconnection is heading are outlined. Part of the coronal heating problem has been solved with the identification of reconnection driven by converging flux motions as the key for

E. R. Priest

1998-01-01

79

Occultation of a Radio Star by the Solar Corona  

Microsoft Academic Search

IT has been suggested1 that the radiation from a radio star might be cut off by refraction in the solar corona, even when the angular separation of the sun and the star is several times the angular radius of the visible disk (Rsolar). The existing data on the coronal electron density have been used for predicting the effective radius of

K. E. Machin; F. G. Smith

1952-01-01

80

The cooling of flare produced plasmas in the solar corona  

Microsoft Academic Search

Solar flare X-rays, at energies less than 10 keV, are emitted by hot plasmas located in the corona. Three plasma cooling models are examined in detail. The cooling of the electrons by Coulomb collisions with ions at a lower temperature would require the observed material to occupy very large volumes. Cooling could take place by conduction or by radiation and

J. L. Culhane; J. F. Vesecky; K. J. H. Phillips

1970-01-01

81

Diffusion of heavy ions in the solar corona  

Microsoft Academic Search

The steady-state diffusive motion of ionized atoms (more massive than hydrogen) in the solar corona has been investigated theoretically, with special emphasis on relating the flow velocity and density of these ions to the flow properties of the ionized hydrogen background. The basic approach taken in this study was to regard the ions as 'test particles' interacting with the background

Y. Alloucherie

1970-01-01

82

Gas-magnetic field interactions in the solar corona  

Microsoft Academic Search

It is evident from eclipse photographs that gas-magnetic field interactions are important in determining the structure and dynamical properties of the solar corona and interplanetary medium. Close to the Sun in regions of strong field, the coronal gas can be contained within closed loop structures. However, since the field in these regions decreases outward rapidly, the pressure and inertial forces

G. W. Pneuman; Roger A. Kopp

1971-01-01

83

Mass and energy flow in the solar chromosphere and corona  

Microsoft Academic Search

The work reviews some investigations into the mass and energy flow in the solar chromosphere and corona; the objective of these investigations is the development of a physical model that will not only account for the physical conditions in the outer atmosphere of the sun, but can also be applied to the study of the outer atmospheres of other stars.

G. L. Withbroe; R. W. Noyes

1977-01-01

84

Possible Role of mhd Waves in Heating the Solar Corona  

Microsoft Academic Search

Heating of the solar corona by MHD waves has been investigated. Taking account of dissipation mechanisms self-consistently, a new general dispersion relation has been derived for waves propagating in a homogeneous plasma. Solution of this sixth-order dispersion relation provides information on how the damping of both slow and fast mode waves depends upon the plasma density, temperature, field strength, and

B. N. Dwivedi; V. S. Pandey

2003-01-01

85

Nano?ares and the Heating of the Solar Corona  

Microsoft Academic Search

New observational signatures of the heating process(es) have been revealed by space missions including SoHO, TRACE, Yohkoh, and RHESSI. Evidences for heating in the quiet corona, active region loops, and the solar wind are difierent and must be distinguished. Prime indi- cations come from line broadening and waves, the distribution of temper- ature and radiation loss in relation to height,

Arnold O. Benz

86

A view of solar magnetic fields, the solar corona, and the solar wind in three dimensions  

Microsoft Academic Search

In the last few years it has been recognized that the solar corona and the solar wind are three-dimensional. The deviations from spherical or even cylindrical symmetry are first-order effects, which are important for a basic description and physical understanding of the coronal expansion. Models of coronal magnetic fields are considered along with the characteristics of large-scale solar structure, the

L. Svalgaard; J. M. Wilcox

1978-01-01

87

Long term storage of relativistic particles in the solar corona  

Microsoft Academic Search

A model is presented which shows that large numbers of energetic electrons (0.3-> 10 MeV) and protons (1–30 MeV) can be stored in the solar corona at altitudes around 3 × 105 km for periods in excess of 5 days. Specific reference is made to the time period July 6–16 1968 as an excellent example of energetic solar particle storage.

George M. Simnett; Stephen S. Holt

1971-01-01

88

Seeing the corona with the solar probe plus mission: the wide-field imager for solar probe+ (WISPR)  

NASA Astrophysics Data System (ADS)

The Solar Probe Plus (SPP) mission scheduled for launch in 2018, will orbit between the Sun and Venus with diminishing perihelia reaching as close as 7 million km (9.86 solar radii) from Sun center. In addition to a suite of in-situ probes for the magnetic field, plasma, and energetic particles, SPP will be equipped with an imager. The Wide-field Imager for the Solar PRobe+ (WISPR), with a 95° radial by 58° transverse field of view, will image the fine-scale coronal structure of the corona, derive the 3D structure of the large-scale corona, and determine whether a dust-free zone exists near the Sun. Given the tight mass constrains of the mission, WISPR incorporates an efficient design of two widefield telescopes and their associated focal plane arrays based on novel large-format (2kx2k) APS CMOS detectors into the smallest heliospheric imaging package to date. The flexible control electronics allow WISPR to collect individual images at cadences up to 1 second at perihelion or sum several of them to increase the signal-to-noise during the outbound part of the orbit. The use of two telescopes minimizes the risk of dust damage which may be considerable close to the Sun. The dependency of the Thomson scattering emission of the corona on the imaging geometry dictates that WISPR will be very sensitive to the emission from plasma close to the spacecraft in contrast to the situation for imaging from Earth orbit. WISPR will be the first `local' imager providing a crucial link between the large scale corona and the in-situ measurements.

Vourlidas, Angelos; Howard, Russell A.; Plunkett, Simon P.; Korendyke, Clarence M.; Carter, Michael T.; Thernisien, Arnaud F. R.; Chua, Damien H.; Van Duyne, Peter; Socker, Dennis G.; Linton, Mark G.; Liewer, Paulett C.; Hall, Jeffrey R.; Morrill, Jeff S.; DeJong, Eric M.; Mikic, Zoran; Rochus, Pierre L. P. M.; Bothmer, Volker; Rodman, Jens; Lamy, Philippe

2013-09-01

89

Further Results on the Rotation of the Solar Corona  

NASA Astrophysics Data System (ADS)

Synoptic photoelectric observations of the coronal Fe XIV and Fe X emission lines at 530.3 nm and 637.4 nm, respectively, are analyzed to study the rotational behavior of the solar corona as a function of latitude, height and time. The data used are measurements made with the Sacramento Peak 40-cm coronagraph and Emission-Line Coronal Photometer of the intensity of these lines observed at 1.15 to 1.45 solar radii (Ro) between 1973 (1984 for Fe X) and 2000. An earlier similar temporal-correlation analysis of the Fe XIV data at 1.15 Ro over only one 11-year solar activity cycle (Sime, Fisher and Altrock 1989, Astrophys. J. 336, 454) found suggestions of solar-cycle variations in the differential-rotation and latitude-averaged-rotation patterns that combined the effects of large-scale patterns seen in the white-light corona and smaller-scale patterns seen in chromospheric and photospheric rotation. These results will be tested over the longer epoch now available. In addition, the new 1.15 Ro Fe XIV results will be compared with those at greater heights and with results from the Fe X line and radio frequencies (Vats et al. 2001, Astrophys. J., 548, L87) to form a global picture of solar rotation throughout the corona and over more than two solar cycles.

Altrock, R. C.

2001-12-01

90

Heating the Solar Corona by Magnetic Reconnection  

Microsoft Academic Search

Here I review briefly the theory of magnetohydrodynamic reconnection and ask what observational evidence is there that it\\u000a is heating the corona. In particular, the new directions in which three-dimensional theory for reconnection is heading are\\u000a outlined. Part of the coronal heating problem has been solved with the identification of reconnection driven by converging\\u000a flux motions as the key for

E. R. Priest

1998-01-01

91

Heating of Solar Corona and Acceleration of a Low-Speed Wind by Acoustic Waves Generated in the Corona  

Microsoft Academic Search

We investigate possibilities of solar coronal heating by acoustic waves generated not at the photosphere but in the corona, aiming at heating in the mid- to low-latitude corona where the low-speed wind is expected to come from. Acoustic waves of period tau˜ 100 s are triggered by chromospheric reconnection, which is one model of small scale magnetic reconnection events recently

Takeru Ken Suzuki

2002-01-01

92

The solar wind and the temperature-density structure of the solar corona  

Microsoft Academic Search

The influence of the solar wind on large-scale temperature and density distributions in the lower corona is studied. This influence is most profoundly felt through its effect upon the geometry of coronal magnetic fields since the presence of expansion divides the corona into magnetically ‘open’ and ‘closed’ regions. Each of these regions is governed by entirely different energy transport processes.

G. W. Pneuman

1973-01-01

93

SemiEmpirical 2-D MHD Model of the Solar corona and Solar Wind: Energy Flow in the Corona  

Microsoft Academic Search

We have developed a semi-empirical 2-D MHD model of the solar corona and solar wind for which the major data inputs are white\\u000a light coronagraph data and plasma and magnetic field data from the Ulysses spacecraft. With regard to the white light coronagraph data we have used data from Spartan 201-05 to construct our empirical\\u000a models of the electron density

Ed Sittler; Madhullika Guhathakurta; Ruth Skoug

2001-01-01

94

Aspects of nonlinear magnetohydrodynamics in the solar corona  

NASA Astrophysics Data System (ADS)

The solar corona is structured by the dynamics of plasmas and magnetic fields, which, at the global scales of coronal loops, prominences and helmet streamers may be described by magnetohydrodynamics. Here we will discuss the importance and role of nonlinear interactions both in the heating of the solar corona, which relies on the transfer, storage and dissipation of the mechanical energy present in photospheric motion, and in the acceleration of the slow solar wind above helmet streamers. In the first example, nonlinear interactions including the coupling of coronal magnetic fields to the velocity field and emerging flux through the photosphere determine both the rate of heating and the resulting coronal topology. In the second example, linear resistive instabilities in develop nonlinearly to accelerate plasmoids into the slow wind. Once plasmoids are generated, the melon-seed force due to the overall magnetic field radial gradients is followed using an Expanding Box Model.

Einaudi, G.; Rappazzo, A. F.; Velli, M.; Dahlburg, R. B.

2004-04-01

95

Modelling the large scale structure of the solar corona  

NASA Astrophysics Data System (ADS)

A quantitative description of the large scale structure of magnetic field and density distribution in the coronal plasma is found. The magnetostatic model of Bogdan and Low and white light images from both NASA's Solar Maximum Mission (SMM) Coronagraph/Polarimeter and the High Altitude Observatory Mark 3 (MK3) K coronameter are used. This is an extension of previous work which used only the Mk3 data. The SMM data were considerably less noisy than the Mk3 data for radii higher than about 1.5 solar radii, particularly at mid-to-high latitude. By combining the SMM and Mk3 datasets, a density distribution that matched the white light images of the corona was more accuratly obtained. The model then allows calculation of the magnetic field and plasma characteristics (such as the coronal temperature structure) which are essential for understanding the mechanisms that heat the corona and drive the solar wind.

Gibson, Sarah; Bagenal, F.

1992-11-01

96

Structure and Dynamics of the Solar Corona  

NASA Astrophysics Data System (ADS)

We briefly review several aspects of the quasi-stationary structure of the corona in relation with the helio-sheet and, also, of the more confined by the magnetic field structures, including streamers, loops, jets, plumes and narrow linear rays. Both the temperature and the density structures are tentatively considered. Flows deduced from proper motions analysis are discussed. We did not include CMEs and flares in this presentation but other more radial and possibly highly impulsive beams with flows are discussed. We stress the importance of the variations of the coronal magnetic field and inferred currents in explaining the observed structures.

Koutchmy, S.

97

A new mechanism for heating the solar corona  

NASA Astrophysics Data System (ADS)

The heating of the solar corona to temperatures of the order of 106 K and more is one of the outstanding problems of solar physics. Beside the high temperatures, Soho/UVCS observations have shown that heavy ions in polar corona, like O5+ and Mg9+, are heated more than protons, and that heavy ion heating is more than mass proportional; further, the perpendicular temperatures T? are much larger than parallel temperatures Tparallel . Here we show that the heating of heavy ions can be explained by ion reflection off supercritical quasi-perpendicular collisionless shocks and the subsequent acceleration by the motional electric field E = - (1/c) V × B. The energization due to E is perpendicular to the magnetic field, and is more than mass proportional with respect to protons, because the heavy ion orbit is mostly upstream of the quasi-perpendicular shock foot.

Zimbardo, Gaetano

98

Propagation Of P-modes Into The Solar Corona  

NASA Astrophysics Data System (ADS)

Magneto-hydrodynamic (MHD) wave modes are observed to propagate from the photosphere into the corona. These have the potential to be exploited as an observational tool in an analogous way to the use of acoustic waves in helio/terrestrial seismology. In regions of strong magnetic field p-modes are thought to undergo mode conversion to slow magneto-acoustic waves. New observations are presented of the propagation of these slow magneto-acoustic p-modes into the solar corona along the loops emerging from active regions. The prospects for new observations with STEREO and Solar-B are also discussed. This work is supported through the NASA post doctoral program.

Marsh, Michael

2006-06-01

99

Magnetic fields and the structure of the solar corona  

Microsoft Academic Search

Several different mathematical methods are described which use the observed line-of-sight component of the photospheric magnetic field to determine the magnetic field of the solar corona in the current-free (or potential-field) approximation. Discussed are (1) a monopole method, (2) a Legendre polynomial expansion assuming knowledge of the radial photospheric magnetic field, (3) a Legendre polynomial expansion obtained from the line-of-sight

Martin D. Altschuler; Gordon Newkirk

1969-01-01

100

Rigid and differential rotation of the solar corona  

Microsoft Academic Search

The rotation of the solar corona has been studied using recurrence properties of the green coronal line (5303 Å) for the interval 1947–1970. Short-lived coronal activity is found to show the same differential rotation as short-lived photospheric magnetic field features. Long-lived recurrences show rigid rotation in the latitude interval ±57°.5. It is proposed that at least part of the variability

Ester Antonucci; Leif Svalgaard

1974-01-01

101

ESTIMATING THE ''DARK'' ENERGY CONTENT OF THE SOLAR CORONA  

SciTech Connect

The discovery of ubiquitous low-frequency (3-5 mHz) Alfvenic waves in the solar chromosphere (with Hinode/Solar Optical Telescope) and corona (with CoMP and SDO) has provided some insight into the non-thermal energy content of the outer solar atmosphere. However, many questions remain about the true magnitude of the energy flux carried by these waves. Here we explore the apparent discrepancy in the resolved coronal Alfvenic wave amplitude ({approx}0.5 km s{sup -1}) measured by the Coronal Multi-channel Polarimeter (CoMP) compared to those of the Hinode and the Solar Dynamics Observatory (SDO) near the limb ({approx}20 km s{sup -1}). We use a blend of observational data and a simple forward model of Alfvenic wave propagation to resolve this discrepancy and determine the Alfvenic wave energy content of the corona. Our results indicate that enormous line-of-sight superposition within the coarse spatio-temporal sampling of CoMP hides the strong wave flux observed by Hinode and SDO and leads to the large non-thermal line broadening observed. While this scenario has been assumed in the past, our observations with CoMP of a strong correlation between the non-thermal line broadening with the low-amplitude, low-frequency Alfvenic waves observed in the corona provide the first direct evidence of a wave-related non-thermal line broadening. By reconciling the diverse measurements of Alfvenic waves, we establish large coronal non-thermal line widths as direct signatures of the hidden, or ''dark'', energy content in the corona and provide preliminary constraints on the energy content of the wave motions observed.

McIntosh, Scott W. [High Altitude Observatory, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307 (United States); De Pontieu, Bart, E-mail: mscott@ucar.edu [Lockheed Martin Solar and Astrophysics Lab, 3251 Hanover St., Org. A021S, Bldg. 252, Palo Alto, CA 94304 (United States)

2012-12-20

102

Possible Role of mhd Waves in Heating the Solar Corona  

Microsoft Academic Search

Heating of the solar corona by MHD waves has been investigated. Taking account of dissipation mechanisms self-consistently,\\u000a a new general dispersion relation has been derived for waves propagating in a homogeneous plasma. Solution of this sixth-order\\u000a dispersion relation provides information on how the damping of both slow and fast mode waves depends upon the plasma density,\\u000a temperature, field strength, and

B. N. Dwivedi; V. S. Pandey

2003-01-01

103

Magnetic tornadoes as energy channels into the solar corona.  

PubMed

Heating the outer layers of the magnetically quiet solar atmosphere to more than one million kelvin and accelerating the solar wind requires an energy flux of approximately 100 to 300?watts per square metre, but how this energy is transferred and dissipated there is a puzzle and several alternative solutions have been proposed. Braiding and twisting of magnetic field structures, which is caused by the convective flows at the solar surface, was suggested as an efficient mechanism for atmospheric heating. Convectively driven vortex flows that harbour magnetic fields are observed to be abundant in the photosphere (the visible surface of the Sun). Recently, corresponding swirling motions have been discovered in the chromosphere, the atmospheric layer sandwiched between the photosphere and the corona. Here we report the imprints of these chromospheric swirls in the transition region and low corona, and identify them as observational signatures of rapidly rotating magnetic structures. These ubiquitous structures, which resemble super-tornadoes under solar conditions, reach from the convection zone into the upper solar atmosphere and provide an alternative mechanism for channelling energy from the lower into the upper solar atmosphere. PMID:22739314

Wedemeyer-Böhm, Sven; Scullion, Eamon; Steiner, Oskar; van der Voort, Luc Rouppe; de la Cruz Rodriguez, Jaime; Fedun, Viktor; Erdélyi, Robert

2012-06-27

104

Differential Rotation of the Ultraviolet Corona at Solar Maximum  

NASA Astrophysics Data System (ADS)

Synoptic observations of the O VI 1032 Å spectral line from the UltraViolet Coronagraph Spectrometer (UVCS) telescope on board the Solar and Heliospheric Observatory (SOHO) have been analyzed in order to establish the rotational characteristics of the solar corona in the time interval from 1999 March 18 to 2002 December 31, corresponding to the maximum phase of solar cycle 23. By using autocorrelation analysis techniques, we determined the latitude and time dependence of the coronal rotation rate at a heliocentric distance of 1.6 R sun from the solar equator up to about 15° from the poles. Although the equatorial rotation rate is initially consistent with the coronal synodic rotation period (~27.5 days) inferred in a previous study by Giordano & Mancuso around solar minimum, a systematic and substantial acceleration is observed to occur during the second part of the year 2000, with the equatorial coronal synodic rotation period settling to an average value of 25.7 days in the time interval extending from 2001 August to 2002 April, corresponding to a ~7% increase in coronal rotation rate. It is shown that the coronal magnetic structures rotate much faster at all latitudes, and less differentially, than the underlying small-scale magnetic structures linked to the photospheric plasma. The rotation rate of sunspots is however compatible, at least within ~20° from the solar equator, with the one estimated in the middle corona.

Mancuso, Salvatore; Giordano, Silvio

2011-03-01

105

Alfvénic waves with sufficient energy to power the quiet solar corona and fast solar wind.  

PubMed

Energy is required to heat the outer solar atmosphere to millions of degrees (refs 1, 2) and to accelerate the solar wind to hundreds of kilometres per second (refs 2-6). Alfvén waves (travelling oscillations of ions and magnetic field) have been invoked as a possible mechanism to transport magneto-convective energy upwards along the Sun's magnetic field lines into the corona. Previous observations of Alfvénic waves in the corona revealed amplitudes far too small (0.5?km?s(-1)) to supply the energy flux (100-200?W?m(-2)) required to drive the fast solar wind or balance the radiative losses of the quiet corona. Here we report observations of the transition region (between the chromosphere and the corona) and of the corona that reveal how Alfvénic motions permeate the dynamic and finely structured outer solar atmosphere. The ubiquitous outward-propagating Alfvénic motions observed have amplitudes of the order of 20?km?s(-1) and periods of the order of 100-500?s throughout the quiescent atmosphere (compatible with recent investigations), and are energetic enough to accelerate the fast solar wind and heat the quiet corona. PMID:21796206

McIntosh, Scott W; De Pontieu, Bart; Carlsson, Mats; Hansteen, Viggo; Boerner, Paul; Goossens, Marcel

2011-07-27

106

On the observation of scattered radio emission from sources in the solar corona  

Microsoft Academic Search

The effects of scattering and refraction on radio waves in the solar corona are considered for several different coronal models. By considering a source near the plasma level in a spherically symmetric corona and in a streamer enhancement superimposed on a spherically symmetric corona we obtain results relating to bursts of types I, II and III.

A. C. Riddle

1974-01-01

107

Mars solar wind interaction: Formation of the Martian corona and atmospheric loss to space  

Microsoft Academic Search

A three-dimensional (3-D) atomic oxygen corona of Mars is computed for periods of low and high solar activities. The thermal atomic oxygen corona is derived from a collisionless Chamberlain approach, whereas the nonthermal atomic oxygen corona is derived from Monte Carlo simulations. The two main sources of hot exospheric oxygen atoms at Mars are the dissociative recombination of O2+ between

J. Y. Chaufray; R. Modolo; F. Leblanc; G. Chanteur; R. E. Johnson; J. G. Luhmann

2007-01-01

108

Catastrophic cooling and cessation of heating in the solar corona  

NASA Astrophysics Data System (ADS)

Context. Condensations in the more than 106 K hot corona of the Sun are commonly observed in the extreme ultraviolet (EUV). While their contribution to the total solar EUV radiation is still a matter of debate, these condensations certainly provide a valuable tool for studying the dynamic response of the corona to the heating processes. Aims: We investigate different distributions of energy input in time and space to investigate which process is most relevant for understanding these coronal condensations. Methods: For a comparison to observations we synthesize EUV emission from a time-dependent, one-dimensional model for coronal loops, where we employ two heating scenarios: simply shutting down the heating and a model where the heating is very concentrated at the loop footpoints, while keeping the total heat input constant. Results: The heating off/on model does not lead to significant EUV count rates that one observes with SDO/AIA. In contrast, the concentration of the heating near the footpoints leads to thermal non-equilibrium near the loop top resulting in the well-known catastrophic cooling. This process gives a good match to observations of coronal condensations. Conclusions: This shows that the corona needs a steady supply of energy to support the coronal plasma, even during coronal condensations. Otherwise the corona would drain very fast, too fast to even form a condensation. Movies are available in electronic form at http://www.aanda.org

Peter, H.; Bingert, S.; Kamio, S.

2012-01-01

109

COMPOSITION OF THE SOLAR CORONA, SOLAR WIND, AND SOLAR ENERGETIC PARTICLES  

SciTech Connect

Along with temperature and density, the elemental abundance is a basic parameter required by astronomers to understand and model any physical system. The abundances of the solar corona are known to differ from those of the solar photosphere via a mechanism related to the first ionization potential of the element, but the normalization of these values with respect to hydrogen is challenging. Here, we show that the values used by solar physicists for over a decade and currently referred to as the 'coronal abundances' do not agree with the data themselves. As a result, recent analysis and interpretation of solar data involving coronal abundances may need to be revised. We use observations from coronal spectroscopy, the solar wind, and solar energetic particles as well as the latest abundances of the solar photosphere to establish a new set of abundances that reflect our current understanding of the coronal plasma.

Schmelz, J. T. [Physics Department, University of Memphis, Memphis, TN 38152 (United States); Reames, D. V. [IPST, University of Maryland, College Park, MD 20742 (United States); Von Steiger, R. [ISSI, Hallerstrasse 6, 3012 Bern (Switzerland); Basu, S., E-mail: jschmelz@memphis.edu [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520 (United States)

2012-08-10

110

Formation of suprathermal electron distributions in the quiet solar corona  

NASA Astrophysics Data System (ADS)

Context: Solar wind electron velocity distribution functions (VDFs) show enhanced levels of suprathermal electrons as compared to a Maxwellian distribution. Previous studies show that the suprathermal tails of solar wind VDFs can be fitted by kappa distributions, and that a coronal origin of the suprathermal electrons is possible. Aims: The generation of suprathermal electrons by resonant interaction with whistler waves in the corona is investigated under quiet solar conditions without any flare activity. The magnetic field geometry is that of a closed magnetic loop. The electron-whistler interaction is described within the framework of quasilinear theory, that leads to pitch-angle diffusion of the electrons in the reference frame of the waves. Methods: A study of electron VDFs requires a kinetic description of the electrons. The model used in this paper is based on a numerical solution of the Boltzmann-Vlasov equation for the electrons, considering Coulomb collisions and wave-electron interaction. The waves are assumed to enter the simulation box with a given power-law spectrum, which evolves inside the box due to wave propagation and absorption by the electrons. Starting from a nearly Maxwellian initial electron VDF, the temporal evolution of the VDF is calculated until a final steady state has been reached. Results: The results show that a population of suprathermal electrons develops in a closed coronal loop. The electron VDF can be approximated by a power-law in the energy range of 4-10 keV. The power-law index is in agreement with the solar wind observations. For lower energy, the electrons are thermalized in the dense model coronal loop, and the efficiency of the acceleration mechanism decreases for higher energies. The energy range of the simulation box has to be chosen sufficiently large, and the influence of the loop geometry on the results is also studied. Conclusions: These numerical studies show that the quiet solar corona is capable of producing suprathermal electron VDFs with similar characteristics to those observed in the solar wind. This study is focused on a closed region in the solar corona, but if such an electron population is present in the corona, it should also appear in the solar wind.

Vocks, C.; Mann, G.; Rausche, G.

2008-03-01

111

The Absolute Abundance of Iron in the Solar Corona.  

PubMed

We present a measurement of the abundance of Fe relative to H in the solar corona using a technique that differs from previous spectroscopic and solar wind measurements. Our method combines EUV line data from the Coronal Diagnostic Spectrometer (CDS) on the Solar and Heliospheric Observatory 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&solm0;H=1.56x10-4, 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 approximately 20%. This result implies that low first ionization potential elements such as Fe are enhanced in the solar corona relative to photospheric values. PMID:10813683

White; Thomas; Brosius; Kundu

2000-05-10

112

Atomic Data for Solar Corona Studies  

NASA Astrophysics Data System (ADS)

In recent years due to the increased sophistication of space instrumentation ever more detailed observations of a large variety of coronal structures became available. Nevertheless, thus far no credible model emerged that describes the means by which the solar upper atmosphere is created and maintained. Nevertheless, while interpreting such spectra, some unexpected properties of coronal plasmas were discovered. Although there are many cases where agreements between observations and calculations are found, there are cases were clear discrepancies do exist. I discuss some of the unexpected observational results that were recently discovered, and suggest some observations that if successfully executed could help explain the processes that form and maintain the solar upper atmosphere.

Feldman, Uri

2011-05-01

113

Atomic Data for Solar Corona Studies  

SciTech Connect

In recent years due to the increased sophistication of space instrumentation ever more detailed observations of a large variety of coronal structures became available. Nevertheless, thus far no credible model emerged that describes the means by which the solar upper atmosphere is created and maintained. Nevertheless, while interpreting such spectra, some unexpected properties of coronal plasmas were discovered. Although there are many cases where agreements between observations and calculations are found, there are cases were clear discrepancies do exist. I discuss some of the unexpected observational results that were recently discovered, and suggest some observations that if successfully executed could help explain the processes that form and maintain the solar upper atmosphere.

Feldman, Uri [Artep Inc., 2922 Excelsior Springs Court, Ellicott City, Maryland, 21044 (United States)

2011-05-11

114

Large-scale structure of the solar corona magnetic field  

NASA Astrophysics Data System (ADS)

The configuration of the solar corona magnetic field has been studied. Data on the position of the K-corona emission polarization plane during the solar eclipses of September 21, 1941; February 25, 1952; and August 1, 2008, were used as an indicator of the magnetic field line orientation. Based on an analysis of these data, a conclusion has been made that the studied configuration has a large-scale organization in the form of a cellular structure with an alternating field reversal. The estimated cell size was 61° ± 6° (or 36° ± 2°) in longitude with a latitudinal extension of 40°-50° in the range of visible distances 1.3-2.0 R Sun . A comparison of the detected cellular structure of the coronal magnetic field with synoptic {ie908-1} maps indicated that the structure latitudinal boundaries vary insignificantly within 1.1-2.0 R Sun . The possible causes of the formation of the magnetic field large-scale cellular configuration in the corona and the conditions for the transformation of this configuration into a two-sector structure are discussed.

Merzlyakov, V. L.; Starkova, L. I.

2012-12-01

115

Joule heating and anomalous resistivity in the solar corona  

NASA Astrophysics Data System (ADS)

Recent radioastronomical observations of Faraday rotation in the solar corona can be interpreted as evidence for coronal currents, with values as large as 2.5×109 Amperes (Spangler, 2007). These estimates of currents are used to develop a model for Joule heating in the corona. It is assumed that the currents are concentrated in thin current sheets, as suggested by theories of two dimensional magnetohydrodynamic turbulence. The Spitzer result for the resistivity is adopted as a lower limit to the true resistivity. The calculated volumetric heating rate is compared with an independent theoretical estimate by Cranmer et al. (2007). This latter estimate accounts for the dynamic and thermodynamic properties of the corona at a heliocentric distance of several solar radii. Our calculated Joule heating rate is less than the Cranmer et al estimate by at least a factor of 3×105. The currents inferred from the observations of Spangler (2007) are not relevant to coronal heating unless the true resistivity is enormously increased relative to the Spitzer value. However, the same model for turbulent current sheets used to calculate the heating rate also gives an electron drift speed which can be comparable to the electron thermal speed, and larger than the ion acoustic speed. It is therefore possible that the coronal current sheets are unstable to current-driven instabilities which produce high levels of waves, enhance the resistivity and thus the heating rate.

Spangler, S. R.

2009-06-01

116

Transequatorial Loops in the Solar Corona  

Microsoft Academic Search

Using X-ray coronal images, full-disk longitudinal magnetograms, and vector magnetograms of active regions, we study active regions connected across the solar equator. We survey the Yohkoh data set between 1991 October and 1998 December and find 87 transequatorial loop systems (TLSs). We classify these loops in four different categories and study a separation between regions, their rotation rates, and the

Alexei A. Pevtsov

2000-01-01

117

DIRECT MEASUREMENTS OF MAGNETIC TWIST IN THE SOLAR CORONA  

SciTech Connect

In the present work, we study the evolution of magnetic helicity in the solar corona. We compare the rate of change of a quantity related to the magnetic helicity in the corona to the flux of magnetic helicity through the photosphere and find that the two rates are similar. This gives observational evidence that helicity flux across the photosphere is indeed what drives helicity changes in the solar corona during emergence. For the purposes of estimating coronal helicity, we neither assume a strictly linear force-free field nor attempt to construct a nonlinear force-free field. For each coronal loop evident in extreme ultraviolet, we find a best-matching line of a linear force-free field and allow the twist parameter {alpha} to be different for each line. This method was introduced and its applicability discussed in Malanushenko et al. The object of this study is emerging and rapidly rotating AR 9004 over about 80 hr. As a proxy for coronal helicity, we use the quantity ({alpha}{sub i} L{sub i} /2) averaged over many reconstructed lines of magnetic field. We argue that it is approximately proportional to the 'flux-normalized' helicity H/{Phi}{sup 2}, where H is the helicity and {Phi} is the total enclosed magnetic flux of the active region. The time rate of change of such a quantity in the corona is found to be about 0.021 rad hr{sup -1}, which is comparable with the estimates for the same region obtained using other methods, which estimated the flux of normalized helicity to be about 0.016 rad hr{sup -1}.

Malanushenko, A.; Longcope, D. W. [Department of Physics, Montana State University, Bozeman, MT 59717 (United States); Yusuf, M. H. [Berea College, Berea, KY 40404 (United States)

2011-08-01

118

The EUV Emission in Comet-Solar Corona Interactions  

NASA Astrophysics Data System (ADS)

The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) viewed a comet as it passed through the solar corona on 2011 July 5. This was the first sighting of a comet by a EUV telescope. For 20 minutes, enhanced emission in several of the AIA wavelength bands marked the path of the comet. We explain this EUV emission by considering the evolution of the cometary atmosphere as it interacts with the ambient solar atmosphere. Water ice in the comet rapidly sublimates as it approaches the Sun. This water vapor is then photodissociated, primarily by Ly-?, by the solar radiation field to create atomic H and O. Other molecules present in the comet also evaporate and dissociate to give atomic Fe and other metals. Subsequent ionization of these atoms can be achieved by a number of means, including photoionization, electron impact, and charge exchange with coronal protons and other highly-charged species. Finally, particles from the cometary atmosphere are thermalized to the background temperature of the corona. Each step could cause emission in the AIA bandpasses. We will report here on their relative contribution to the emission seen in the AIA telescopes.

Bryans, P.; Pesnell, W. D.; Schrijver, C. J.; Brown, J. C.; Battams, K.; Saint-Hilaire, P.; Liu, W.; Hudson, H. S.

2011-12-01

119

Oxygen abundance in the Solar Corona  

NASA Astrophysics Data System (ADS)

Solar observations with the satellite instrument UVCS/SOHO (Ultraviolet Coronagraph Spectrometer / Solar and Heliospheric Observatory) have revealed that the Oxygen abundance within large scale closed structures of coronal streamers may be much lower than at photospheric levels. In coronal Oxygen images, this characteristic is seen as relatively dark features in the central part of streamers. Previous analysis, suggest abundance reduction factors of up to an order of magnitude (Raymond et al. 1997, Marocchi et al. 2001, Strachan et al. 2002, Uzzo et al. 2003). Using UVCS observational data in the O+5 lines (Cranmer et al. 1999, Strachan et al. 2002) and own models for the global magnetic coronal structure and solar wind (Vásquez et al. 2003), we develop models for the temperature and outflow velocity of coronal Oxygen ions. Using the Oxygen elemental abundance as a free parameter, we compute the expected emissivity in the O+5 lines and synthesize resulting images, thus considering projection effects in a more detailed fashion than previous studies. We find that, in order to obtain intensity profiles similar to the observed ones, the assumed Oxygen abundances within streamers must be much lower than photospheric values. We estimate the required abundance reduction factors, and find out that these are even lower than previous estimates that do not account in detail for projection effects.

Vásquez, A. M.; Raymond, J. C.

120

Solar Probe Plus exploration of the solar corona and inner heliosphere  

NASA Astrophysics Data System (ADS)

Solar Probe Plus (SPP) will be the first mission to directly explore the sub-Alfvénic corona measuring in-situ the plasma, magnetic fields, electromagnetic waves and energetic particles and imaging the scattered light in the source regions of the heliosphere. Solar Probe Plus objectives are to understand coronal heating and wind acceleration for both slow and fast solar wind streams, determine the structure and dynamics of the plasma and magnetic fields at the sources of the solar wind, and explore the mechanisms that accelerate and transport energetic particles. This talk describes SPP objectives and the measurement strategies to achieve the objectives in detail. It will also illustrate how Solar Probe Plus' investigation of the inner heliosphere will enhance the scientific return of other missions, such as Solar Orbiter (SO): SPP and SO will together provide our most detailed understanding of the processes by which the dynamically interacting plasmas and magnetic fields escape the corona to become the solar wind.

Velli, M. M.; Bale, S.; Fox, N. J.; Howard, R. A.; Kasper, J. C.; Szabo, A.

2011-12-01

121

MHD modeling of the solar corona: Progress and challenges  

NASA Astrophysics Data System (ADS)

The Sun and its activity is the ultimate driver of space weather at Earth. This influence occurs not only via eruptive phenomena such as coronal mass ejections, but also through the structure of the corona itself, which forms the genesis of fast solar wind streams that trigger recurrent geomagnetic activity. Coronal structure also determines the connection of the ambient interplanetary magnetic field to CME-related shocks and impulsive solar flares, and thus controls where solar energetic particles propagate. In this talk we describe both the present state of the art and new directions in coronal modeling for both dynamic and slowly varying phenomena. We discuss the challenges to incorporating these capabilities into future space weather forecasting and specification models. Supported by NASA through the HTP, LWS, and SR&T programs, by NSF through the FESD and CISM programs, and by the AFOSR Space Science program.

Linker, Jon; Mikic, Zoran; Lionello, Roberto; Riley, Pete; Titov, Viacheslav; Torok, Tibor

2012-07-01

122

Field-aligned potential drops in the solar corona  

SciTech Connect

A field-aligned potential drop of {Phi}{sub {parallel}} {le} 100 kV can be produced in the corona due to the loss cone constriction effect on a 0.25 A/m{sup 2} field-aligned current driven by the dynamo process in the photosphere under the condition that N{sub m} {ge} 2 {times} 10{sup 4} cm{sup {minus}3} and B{sub m} {ge} 60 G near the top region of a coronal loop. This condition probably can be satisfied during coronal mass ejections when the coronal loop rises to a height greater than one solar radius. Since coronal mass ejection events are often observed to precede solar flares, the proposed model of field-aligned potential drop can be related to solar flare through coronal mass ejection events. The resulting 100 kV field-aligned potential drop in the corona can accelerate an electron beam to produce nonthermal hard X-ray bursts. The magnetic field produced by the field-aligned current is estimated to be {delta}B(O) {approx} 0.2 T at the foot of an erupting coronal loop. The ratio {beta}B(O)/B{sub o} = 1, which is on the high side, but is probably acceptable for coronal mass ejection events of very large spatial scales.

Kan, J.R.; Lyu, L.H. (Univ. of Alaska, Fairbanks (United States))

1990-04-01

123

Heavy ion reflection and heating by collisionless shocks in polar solar corona  

Microsoft Academic Search

We propose a new model for explaining the observations of preferential heating of heavy ions in the polar solar corona. We consider that a large number of small scale shock waves can be present in the solar corona, as suggested by recent observations of polar coronal jets by the Hinode and STEREO spacecraft. The heavy ion energization mechanism is, essentially,

Gaetano Zimbardo

2011-01-01

124

Heating of the solar corona by the resonant absorption of Alfven waves  

Microsoft Academic Search

An improved method for calculating the resonance absorption heating rate is discussed and the results are compared with observations in the solar corona. To accomplish this, the wave equation for a dissipative, compressible plasma is derived from the linearized magnetohydrodynamic equations for a plasma with transverse Alfven speed gradients. For parameters representative of the solar corona, it is found that

Joseph M. Davila

1987-01-01

125

Heating of the solar corona by dissipative Alfvén solitons.  

PubMed

Solar photospheric convection drives myriads of dissipative Alfvén 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. PMID:16712308

Stasiewicz, K

2006-05-04

126

Dust environment in the outer Solar System  

Microsoft Academic Search

Since the discovery of the first Edgeworth-Kuiper Belt (EKB) object in 1992, more than 600 EKB objects have been discovered so far. Collisions among EKB objects could produce a significant amount of dust in the outer Solar System. Due to interactions with the giant planets, the EKB dust disk has non-uniform distributions in both radial and azimuthal directions. Some of

J.-C. Liou

2003-01-01

127

Dust Accumulation on MER Solar Panels  

NASA Astrophysics Data System (ADS)

HiRISE acquired in March 2011 a color image of the Spirit Mars Exploration Rover from orbit that shows an exceptionally bright reflection from the rover solar panels. HiRISE data combined with laboratory measurements of MER solar cell reflectance provide a method for constraining the thickness of dust on the solar panels. Spirit is the brightest object in the HiRISE scene with a reflectance that is about 3 times higher at 500 nm and about 1.5 times higher at 700 and 850 nm than bright outcrop and soil near the rover. The rover is also less red than these nearby materials and less red than a typical Mars dust spectrum modeled with the same geometry and seen through similar atmospheric conditions as the HiRISE image. Lighting and viewing angles for the HiRISE image of Spirit are close to a specular reflection geometry when factoring in the rover orientation, the sun position, and the location of HiRISE during image acquisition. Laboratory photometric measurements of clean and dust-coated MER solar cells show a strong specular reflection for dust coating thicknesses up to at least 45 micrometers. The specular reflection was not present in the laboratory data when the solar cell was covered with about a 135 micrometer thick layer. The dust used in the experiments consisted of less than 10 micrometer sized particles derived from a palagonitic tephra from Mauna Kea that is spectrally similar to Mars dust. A survey of MER Pancam color images acquired by Spirit and Opportunity also shows several examples of specular reflections from the solar panels. These examples correspond to times when the solar cells were moderately clean to dusty as inferred from the amount of power generated by the cells. Specular reflections in Pancam images have been observed when the solar cell output was only 45% that of a dust-free cell. Spirit HiRISE data indicate that the rover was not covered by an optical thick layer of dust because some of the reflected light must have come from the underlying solar panels. The laboratory and HiRISE data suggest that the Spirit solar panels may have had a dust layer on the order of only 10s of micrometers thick. Further investigation of rover image data sets for the presence or absence of specular reflections as correlated with solar cell power output will yield more quantitative information on the amounts of atmospheric dust accumulation throughout the Spirit and Opportunity missions.

Guinness, E. A.; Arvidson, R. E.; McEwen, A. S.; Cull, S.

2011-12-01

128

Corongraphic Observations and Analyses of The Ultraviolet Solar Corona  

NASA Astrophysics Data System (ADS)

The activities supported under NASA Grant NAG5-613 included the following: 1) reduction and scientific analysis of data from three sounding rocket flights of the Rocket Ultraviolet Coronagraph Spectrometer, 2) development of ultraviolet spectroscopic diagnostic techniques to provide a detailed empirical description of the extended solar corona, 3) extensive upgrade of the rocket instrument to become the Ultraviolet Coronal Spectrometer (UVCS) for Spartan 201,4) instrument scientific calibration and characterization, 5) observation planning and mission support for a series of five Spartan 201 missions (fully successful except for STS 87 where the Spartan spacecraft was not successfully deployed and the instruments were not activated), and 6) reduction and scientific analysis of the UVCS/Spartan 201 observational data. The Ultraviolet Coronal Spectrometer for Spartan 201 was one unit of a joint payload and the other unit was a White Light Coronagraph (WLC) provided by the High Altitude Observatory and the Goddard Space Flight Center. The two instruments were used in concert to determine plasma parameters describing structures in the extended solar corona. They provided data that could be used individually or jointly in scientific analyses. The WLC provided electron column densities in high spatial resolution and high time resolution. UVCS/Spartan provided hydrogen velocity distributions, and line of sight hydrogen velocities. The hydrogen intensities from UVCS together with the electron densities from WLC were used to determine hydrogen outflow velocities. The UVCS also provided O VI intensities which were used to develop diagnostics for velocity distributions and outflow velocities of minor ions.

Kohl, John L.

2000-10-01

129

Development of three-dimensional magnetohydrodynamic model for solar corona and solar wind simulation  

NASA Astrophysics Data System (ADS)

Propagation of coronal mass ejections from solar surface to the Earth magnetosphere is strongly influenced by the conditions in solar corona and ambient solar wind. Thus, reliable simulation of the background solar wind is the primary task toward the development of numerical model for the transient events. In this paper we introduce a new numerical model which has been specifically designed for numerical study of the solar corona and ambient solar wind. This model is based on our recently developed three-dimensional Spherical Coordinate Adaptive Magneto-Hydro-Dynamic (MHD) code (SCA-MHD-3D) [Yuan et al., 2009]. Modifications has been done to include the observed magnetic field at the photosphere as inner boundary conditions. The energy source term together with reduced plasma gamma are used in the nonlinear MHD equations in order to simulate the solar wind acceleration from subsonic speed at solar surface to supersonic speed at the inter-heliosphere region, and the absorbing boundary conditions are used at the solar surface. This model has been applied to simulate the background solar wind condition for several different solar rotations, and comparison between the observation and model output have shown that it reproduces many features of solar wind, including open and closed magnetic fields, fast and slow solar wind speed, sector boundaries, etc.

Yuan, Xingqiu; Trichtchenko, Larisa; Boteler, David

130

Dust Around R Coronae Borealis Stars. II. Infrared Emission Features in an H-poor Environment  

NASA Astrophysics Data System (ADS)

Residual Spitzer/Infrared Spectrograph spectra for a sample of 31 R Coronae Borealis (RCB) stars are presented and discussed in terms of narrow emission features superimposed on the quasi-blackbody continuous infrared emission. A broad ~6-10 ?m dust emission complex is seen in the RCBs showing an extreme H-deficiency. A secondary and much weaker ~11.5-15 ?m broad emission feature is detected in a few RCBs with the strongest ~6-10 ?m dust complex. The Spitzer infrared spectra reveal for the first time the structure within the ~6-10 ?m dust complex, showing the presence of strong C-C stretching modes at ~6.3 and 8.1 ?m as well as of other dust features at ~5.9, 6.9, and 7.3 ?m, which are attributable to amorphous carbonaceous solids with little or no hydrogen. The few RCBs with only moderate H-deficiencies display the classical "unidentified infrared bands (UIRs)" and mid-infrared features from fullerene-related molecules. In general, the characteristics of the RCB infrared emission features are not correlated with the stellar and circumstellar properties, suggesting that the RCB dust features may not be dependent on the present physical conditions around RCB stars. The only exception seems to be the central wavelength of the 6.3 ?m feature, which is blueshifted in those RCBs showing also the UIRs, i.e., the RCBs with the smallest H deficiency.

García-Hernández, D. A.; Kameswara Rao, N.; Lambert, D. L.

2013-08-01

131

DRIVEN WAVES AS A DIAGNOSTICS TOOL IN THE SOLAR CORONA  

SciTech Connect

Detecting the signature of Alfven waves in the solar atmosphere remains an observational challenge. At the same time, it could also be an important key to gaining critical understanding of the solar wind and especially of the near-Earth space weather formation. Here, we investigate the plausibility of using inhomogeneous flow-driven compressional fluctuations as a diagnostics tool for Alfven waves in the solar corona. The nature of the fluctuations driven by transverse Alfven waves in inhomogeneous flows was recently investigated by Kaghashvili et al., and analytical solutions that accurately link driven waves to the Alfvenic driver were found. The novelty of this mechanism is that the analysis of the detected compressional fluctuations can provide a clue about the Alfven waves that are otherwise difficult to detect. We review this physical process in a low-beta approximation relevant to solar coronal conditions and outline basic reasons why it can be one of the major processes that comes about as outflowing plasma emerges from divergent coronal holes. After establishing a quantitative link, we consider an example with coronal hole plasma parameters similar to the ones reported recently where evidence for Alfven waves in solar X-ray jets was discussed. We show how this diagnostics tool can be used to analyze the detected intensity fluctuations.

Kaghashvili, Edisher Kh.; Quinn, Richard A. [Atmospheric and Environmental Research, Inc., 131 Hartwell Avenue, Lexington, MA 02421 (United States); Hollweg, Joseph V., E-mail: ekaghash@aer.co [Space Science Center, University of New Hampshire, Durham, NH 03824 (United States)

2009-10-01

132

No evidence of a circumsolar dust ring from infrared observations of the 1991 solar eclipse  

NASA Astrophysics Data System (ADS)

Large-format IR array detectors are employed to map the solar corona out to large angular distances from the sun during the 1991 eclipse, and the images are used to confirm the absence of a circumsolar dust ring. An HgCdTe-array detector is employed with broadband H, J, and K filters to study wavelengths of 1-2.5 microns. An inhomogeneous structure in the K-corona is noted in the images of the H- and K-band surface brightnesses, and elliptical flattening of the F-corona is cnfirmed. The 2D IR observations are argued to provide unambiguous evidence that no circumstellar dust ring existed during the time of observation. The dynamics of the interplanetary dust particles are theorized to be the product of influences other than or in addition to those described by gravitational-radiation drag calculations. The results suggest that previous detections of dust rings do not necessarily reflect the existence of 'local' coronal dust rings.

Lamy, P.; Kuhn, J. R.; Lin, H.; Koutchmy, S.; Smartt, R. N.

1992-09-01

133

Convective Instability Of The Solar Corona: Why The Solar Wind Blows  

Microsoft Academic Search

Chapman's conductive model of the solar corona is characterized by a temperature varying as r-2\\/7 with heliocentric distance r. The density distribution in this non-isothermal hydrostatic model has a minimum value at 123 RS, and increases with r above that altitude. It is shown that this hydrostatic model becomes convectively unstable above r = 35 RS, where the temperature lapse

Joseph Lemaire

2010-01-01

134

Constant cross section of loops in the solar corona  

NASA Astrophysics Data System (ADS)

Context. The corona of the Sun is dominated by emission from loop-like structures. When observed in X-ray or extreme ultraviolet emission, these million K hot coronal loops show a more or less constant cross section. Aims: In this study we show how the interplay of heating, radiative cooling, and heat conduction in an expanding magnetic structure can explain the observed constant cross section. Methods: We employ a three-dimensional magnetohydrodynamics (3D MHD) model of the corona. The heating of the coronal plasma is the result of braiding of the magnetic field lines through footpoint motions and subsequent dissipation of the induced currents. From the model we synthesize the coronal emission, which is directly comparable to observations from, e.g., the Atmospheric Imaging Assembly on the Solar Dynamics Observatory (AIA/SDO). Results: We find that the synthesized observation of a coronal loop seen in the 3D data cube does match actually observed loops in count rate and that the cross section is roughly constant, as observed. The magnetic field in the loop is expanding and the plasma density is concentrated in this expanding loop; however, the temperature is not constant perpendicular to the plasma loop. The higher temperature in the upper outer parts of the loop is so high that this part of the loop is outside the contribution function of the respective emission line(s). In effect, the upper part of the plasma loop is not bright and thus the loop actually seen in coronal emission appears to have a constant width. Conclusions: From this we can conclude that the underlying field-line-braiding heating mechanism provides the proper spatial and temporal distribution of the energy input into the corona - at least on the observable scales. Movies associated to Figs. 1 and 2 are available in electronic form at http://www.aanda.org

Peter, H.; Bingert, S.

2012-12-01

135

RADIO OBSERVATIONS OF WEAK ENERGY RELEASES IN THE SOLAR CORONA  

SciTech Connect

We report observations of weak, circularly polarized, structureless type III bursts from the solar corona in the absence of H{alpha}/X-ray flares and other related activity, during the minimum between the sunspot cycles 23 and 24. The spectral information about the event obtained with the CALLISTO spectrograph at Mauritius revealed that the drift rate of the burst is {approx}-30 MHz s{sup -1} is in the range 50-120 MHz. Two-dimensional imaging observations of the burst at 77 MHz obtained with the Gauribidanur radioheliograph indicate that the emission region was located at a radial distance of {approx}1.5 R{sub sun} in the solar atmosphere. The estimated peak brightness temperature of the burst at 77 MHz is {approx}10{sup 8} K. We derived the average magnetic field at the aforementioned location of the burst using the one-dimensional (east-west) Gauribidanur radio polarimeter at 77 MHz, and the value is {approx}2.5 {+-} 0.2 G. We also estimated the total energy of the non-thermal electrons responsible for the observed burst as {approx}1.1 x 10{sup 24} erg. This is low compared to the energy of the weakest hard X-ray microflares reported in the literature, which is about {approx}10{sup 26} erg. The present result shows that non-thermal energy releases that correspond to the nanoflare category (energy {approx}10{sup 24} erg) are taking place in the solar corona, and the nature of such small-scale energy releases has not yet been explored.

Ramesh, R.; Kathiravan, C.; Barve, Indrajit V. [Indian Institute of Astrophysics, Bangalore 560 034 (India); Beeharry, G. K.; Rajasekara, G. N., E-mail: ramesh@iiap.res.i [University of Mauritius, Reduit (Mauritius)

2010-08-10

136

An empirically-driven global MHD model of the solar corona and inner heliosphere  

Microsoft Academic Search

In this study we describe a three-dimensional MHD model of the solar corona and heliosphere. We split the modeling region into two distinct parts: the solar corona (1 solar radius, RS, to 30RS) and the inner heliosphere (30RS to 5 AU). This combined model is driven solely by the observed line-of-sight photospheric magnetic field and can thus provide a realistic

Pete Riley; J. A. Linker; Z. Mikic

2001-01-01

137

The green corona, the solar wind and geoactivity  

NASA Astrophysics Data System (ADS)

The paper investigates the long-term distribution of the green corona low brightness regions (GCLBRs) on the solar surface. The frequency curves of the GCLBRs follow the solar cycle, but are displaced considerably relative to the curve of the sunspot number cycle. The observed displacement increases with the size of the GCLBRs and reaches up to 4-5 yr for the largest regions. The displacement in the equatorial zone is opposite that in the higher-latitude zones. The frequency of GCLBRs and the properties of high-speed plasma streams (HSPS) in the solar wind are studied. It is argued that maximum velocity and duration of the coronal-hole-related HSPS are well correlated with the number and size of GCLBRs located in the N 60 - N 20 and S 20 - S 60 latitudinal zones. This is particularly evident at the end of the solar cycle. Geophysical Kp and aa indices are used to demonstrate a possible genetic dependence of geoactivity on the size, position on the sun's surface, and frequency of the GCLBRs. In this sense, the most pronounced period is 1973-1976.

Sykora, J.

1992-08-01

138

The Large-Scale Structure of the Solar Minimum Corona  

NASA Astrophysics Data System (ADS)

I will present the results of my Ph.D. thesis, the goal of which was to find a quantitative description of the large-scale structure of magnetic field and density in the solar minimum corona that was consistent with observations of both white light intensity and the magnetic field at the photosphere. We used white light images from NASA's Solar Maximum Mission (SMM) Coronagraph/Polarimeter and the High Altitude Observatory Mark III (MkIII) K-coronameter, along with photospheric field measurements from Stanford's Wilcox Solar Observatory (WSO), as constraints on the magnetostatic model of Bogdan and Low (B&L) [\\markcite{1986}]. We found a solution to the B&L model that reproduced observations of white light and photospheric flux to within quantifiable model and observational limits, and calculated the physical plasma properties of density, pressure, magnetic field, and temperature that corresponded to these parameters. Further, we extended the model to include current sheets at the equator and around the coronal helmet streamer, and showed that by doing so we improved the fit to white light data and to a lesser extent to the photospheric flux. Moreover, by including current sheets in the model, we produced a magnetic field line structure which better matched the underlying coronal white light structure, and which was more consistent with a solar wind accelerating along the open field lines. This work was partially funded by NASA GSRP grant number 50916.

Gibson, Sarah

1995-12-01

139

Simultaneous Observation of High Temperature Plasma of Solar Corona By TESIS CORONAS-PHOTON and XRT Hinode.  

NASA Astrophysics Data System (ADS)

The Mg XII spectroheliograph is a part of instrumentation complex TESIS (satellite CORONAS-PHOTON). This instrument builds monochromatic images of hot plasma of the solar corona (? = 8.42 Å, T>5 MK). The Mg XII spectroheliograph observed hot plasma in the non-flaring active-region NOAA 11019 during nine days. We reconstructed DEM of this active region with the help of genetic algorithm (we used data of the Mg XII spectroheliograph, XRT and EIT). Emission measure of the hot component amounts 1 % of the emission measure of the cool component.

Reva, A.; Kuzin, S.; Bogachev, S.; Shestov, S.

2012-05-01

140

The Expansion of Active Regions into the Extended Solar Corona  

NASA Astrophysics Data System (ADS)

Advanced image processing of Large Angle and Spectrometric Coronagraph Experiment (LASCO) C2 observations reveals the expansion of the active region closed field into the extended corona. The nested closed-loop systems are large, with an apparent latitudinal extent of 50°, and expanding to heights of at least 12 R ?. The expansion speeds are ~10 km s-1 in the AIA/SDO field of view, below ~20 km s-1 at 2.3 R ?, and accelerate linearly to ~60 km s-1 at 5 R ?. They appear with a frequency of one every ~3 hr over a time period of around three days. They are not coronal mass ejections (CMEs) since their gradual expansion is continuous and steady. They are also faint, with an upper limit of 3% of the brightness of background streamers. Extreme ultraviolet images reveal continuous birth and expansion of hot, bright loops from a new active region at the base of the system. The LASCO images show that the loops span a radial fan-like system of streamers, suggesting that they are not propagating within the main coronal streamer structure. The expanding loops brighten at low heights a few hours prior to a CME eruption, and the expansion process is temporarily halted as the closed field system is swept away. Closed magnetic structures from some active regions are not isolated from the extended corona and solar wind, but can expand to large heights in the form of quiescent expanding loops.

Morgan, Huw; Jeska, Lauren; Leonard, Drew

2013-06-01

141

A nanoflare heating model for the quiet solar corona  

NASA Astrophysics Data System (ADS)

The energy input into the lower solar corona by flare evaporation events has been modeled according to the available observations for quiet regions. The question is addressed whether such heating events can provide the observed average level of the coronal emission measure and thus of the observed flux of extreme ultraviolet (EUV) and X-ray emission without contradicting the observed average power spectrum of the emission measure, the typical emission measure variations observed for individual pixels and the observed flare energy distribution. As the assumed flare height influences the derived flare energy, the mathematical foundations of nanoflare distributions and their conversion to different height assumptions are studied first. This also allows a comparison with various published energy distributions differing in height assumptions and to relate the observations to the input parameters of the heating model. An analytic evaluation of the power spectrum yields the relationship between the average time profile of nanoflares (or microflares), assumed to be self-similar in energy, and the power spectrum. We find that the power spectrum is very sensitive to the chosen time profile of the flares. Models are found by numerical simulation that fit all available observations. They are not unique but severely constrained. We concentrate on a model with a flare height proportional to the square root of the flare area. The existence of a fitting model demonstrates that nanoflare heating of the corona is a viable and attractive mechanism.

Mitra-Kraev, U.; Benz, A. O.

2001-07-01

142

A Nanoflare Heating Model for the Quiet Solar Corona  

NASA Astrophysics Data System (ADS)

The energy input into the lower solar corona by flare evaporation events has been modeled according to the available observations for quiet regions. The question is addressed whether such heating events can provide the observed average level of the coronal emission measure and thus of the observed flux of extreme ultraviolet (EUV) and X-ray emission without contradicting the observed average power spectrum of the emission measure, the typical emission measure variations observed for individual pixels and the observed flare energy distribution. As the assumed flare height influences the derived flare energy, the mathematical foundations of nanoflare distributions and their conversion to different height assumptions are studied first. This also allows a comparison with various published energy distributions differing in height assumptions and to relate the observations to the input parameters of the heating model. An analytic evaluation of the power spectrum yields the relationship between the average time profile of nanoflares (or microflares), assumed to be self-similar in energy, and the power spectrum. We find that the power spectrum is very sensitive to the chosen time profile of the flares. Models are found by numerical simulation that fit all available observations. They are not unique but severely constrained. We concentrate on a model with a flare height proportional to the square root of the flare area. The existence of a fitting model demonstrates that nanoflare heating of the corona is a viable and attractive mechanism.

Mitra Kraev, U.; Benz, A. O.

2001-05-01

143

The Solar Corona above Polar Coronal Holes as Seen by SUMER on SOHO  

Microsoft Academic Search

In order to address two of the principal scientific objectives of the Solar and Heliospheric Observatory (SOHO), studies of the heating mechanisms of the solar corona and the acceleration processes of the solar wind, we deduce electron temperatures, densities, and ion velocities in plumes and interplume regions of polar coronal holes using ultraviolet observations from SUMER (Solar Ultraviolet Measurements of

Klaus Wilhelm; Eckart Marsch; Bhola N. Dwivedi; Donald M. Hassler; Philippe Lemaire; Alan H. Gabriel; Martin C. E. Huber

1998-01-01

144

Observaciones de la corona solar interior con un coronógrafo de espejo  

NASA Astrophysics Data System (ADS)

El plasma de la corona solar es un buen indicador de las líneas de fuerza del campo magnético. Por lo tanto, el análisis de estructuras coronales cuasiestacionarias en la corona da importante información sobre el campo magnético y la actividad asociada. Se trata de poner límites a los modelos teóricos existentes mediante el estudio de distintas estructuras en la corona interior. En agosto de 1997 comenzó a operar el coronógrafo solar (MICA) en El Leoncito como parte del Observatorio Solar Alemán-Argentino. Desde su instalación obtiene imágenes de la corona solar (1.05 a 2.0 radios solares) en 2 líneas espectrales correspondientes a la emisión de Fe XIV y Fe X. El instrumento puede obtener imágenes cada minuto por lo que es ideal para estudiar procesos rápidos. Presentamos observaciones recientes que muestran la capacidad del coronógrafo así como la evolución de algunos eventos dinámicos observados por MICA.

Stenborg, G.; Schwenn, R.; Francile, C.; Rovira, M.

145

Probing the Fundamental Physics of the Solar Corona with Lunar Solar Occultation Observations  

NASA Astrophysics Data System (ADS)

Imaging and spectroscopy of the solar corona, coupled with polarimetry, are the only tools available at present to capture signatures of physical processes responsible for coronal heating and solar wind acceleration within the first few solar radii above the solar limb. With the recent advent of improved detector technology and image processing techniques, broad-band white light and narrow-band multi-wavelength observations of coronal forbidden lines, made during total solar eclipses, have started to yield new views about the thermodynamic and magnetic properties of coronal structures. This paper outlines these unique capabilities, which until present, have been feasible primarily with observations during natural total solar eclipses. This work also draws attention to the exciting possibility of greatly increasing the frequency and duration of solar eclipse observations with Moon orbiting observatories utilizing lunar limb occultation of the solar disk for coronal measurements.

Habbal, S. Rifai; Morgan, H.; Druckmüller, M.; Ding, A.; Cooper, J. F.; Daw, A.; Sittler, E. C.

2013-07-01

146

Magneto-gravity waves and the heating of the solar corona  

Microsoft Academic Search

It is generally believed that the heating of the solar corona is caused by waves originating in the photosphere and propagating into the corona where their energy is dissipated. The medium through which these waves propagate is in general permeated by magnetic fields complicating the behaviour of this propagation considerably. We have therefore analysed the wave motions in a plasma

Alden McLellan IV; F. Winterberg

1968-01-01

147

Comparing MHD Simulations of the Solar Corona and the Solar Wind with Data  

NASA Astrophysics Data System (ADS)

Our global three-dimensional magnetohydrodynamic (MHD) model of the solar corona and the solar wind has been extensively used to model the properties of the magnetic field and of the plasma, from Sun to Earth and beyond. The key observational input to the model is the incorporation of observed photospheric magnetic fields into the boundary conditions. We have studied the geometrical and topological properties of the magnetic field (e.g., the location and evolution of corona holes, the reproduction of streamer structure, the location of the heliospheric current sheet, etc.) and its dynamical reconfiguration (e.g., eruptions and CMEs propagation). Direct comparison with observations have been made in the corona by calculation of emission in several EUV and X-ray bands, both for loops and the global corona. We have also compared the simulated speed, density, temperature, and magnetic field in the solar wind with in situ observations. We will discuss the insights obtained on the strengths and limitations of the models from these comparisons.

Lionello, R.; Linker, J. A.; Mikic, Z.; Riley, P.; Titov, V. S.; Torok, T.

2011-12-01

148

Convective Instability Of The Solar Corona: Why The Solar Wind Blows  

NASA Astrophysics Data System (ADS)

Chapman's conductive model of the solar corona is characterized by a temperature varying as r-2/7 with heliocentric distance r. The density distribution in this non-isothermal hydrostatic model has a minimum value at 123 RS, and increases with r above that altitude. It is shown that this hydrostatic model becomes convectively unstable above r = 35 RS, where the temperature lapse rate becomes superadiabatic. Beyond this radial distance heat conduction fails to be efficient enough to keep the temperature gradient smaller than the adiabatic lapse rate. We report the results obtained by Lemaire who showed that an additional mechanism is then required to transport the energy flux away from the Sun into interplanetary space. He pointed out that this additional mechanism is advection: i.e. the stationary hydrodynamic expansion of the corona. In other words the corona is unable to stay in hydrostatic equilibrium. The hydrodynamic solar wind expansion is thus a physical consequence of the too steep (superadiabatic) temperature gradient beyond the peak of coronal temperature that can be determined from white light brightness distributions observed during solar eclipses. The thermodynamic argument for the existence of a continuous solar wind expansion which is presented here, complements Parker's classical argument based on boundary conditions imposed to the solutions of the hydrodynamic equations for the coronal expansion: i.e. the inability of the mechanical forces to hold the corona in hydrostatic equilibrium. The thermodynamic argument presented here is based on the energy transport equation. It relies on the temperature distribution which becomes super-adiabatic above a certain altitude in the inner corona.

Lemaire, Joseph

2010-03-01

149

Dynamics of Solar System Dust.  

National Technical Information Service (NTIS)

The ongoing aim of the research is to investigate the dynamical and physical evolution of interplanetary dust particles in order to produce a detailed global model of the zodiacal cloud and its constituent components that is capable of predicting thermal ...

S. F. Dermott

2002-01-01

150

THE SOLAR MINIMUM CORONA FROM DIFFERENTIAL EMISSION MEASURE TOMOGRAPHY  

SciTech Connect

We present results derived from a dual-spacecraft tomographic reconstruction of the solar corona's three-dimensional (3D) extreme ultraviolet (EUV) emissivity. We use simultaneously taken STEREO A and B spacecraft EUVI images from Carrington rotation 2077 (UT 2008 November 20 06:56 through UT December 17 14:34). During this period, the spacecraft view angles were separated by an average 85.{sup 0}4 which allowed for the reconstruction to be performed with data gathered in about 3/4 of a full solar rotational time. The EUV reconstructions provide the 3D emissivity in each of the three EUVI Fe bands, in the range of heights 1.00-1.25 R {sub s}. We use this information to perform local differential emission measure (LDEM) analysis. Taking moments of the so-derived LDEM distributions gives the 3D values of the electron density, temperature, and temperature spread. We determine relationships between the moments of the LDEM and the coronal magnetic field by making longitudinal averages of the moments, and relating them to the global-scale structures of a potential field source surface magnetic field model. In this way, we determine how the electron density, mean temperature, and temperature spread vary for different coronal structures. We draw conclusions about the relationship between the LDEM moments and the sources of the fast and slow solar winds, and the transition between the two regimes.

Vasquez, Alberto M. [Instituto de AstronomIa y Fisica del Espacio, CONICET-University of Buenos Aires, Ciudad de Buenos Aires, CC 67-Suc 28 (Argentina); Frazin, Richard A.; Manchester, Ward B., E-mail: albert@iafe.uba.a, E-mail: rfrazin@umich.ed [Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, MI 48109 (United States)

2010-06-01

151

Solar corona caused by juniper pollen in Texas.  

PubMed

Coronas are colorful, concentric rings centered on a bright light such as the Sun, the Moon, or even a streetlamp. Coronas are most commonly caused by water droplets or ice particles of relatively uniform size. Observers in Finland have reported spectacular clear-sky coronas caused by pollen grains. A clear-sky corona in central Texas occurred during the peak of the juniper pollinating season. The aerosol optical thickness at each of three wavelengths was highest when the corona was most prominent. Photographic measurements of the corona infer a particle diameter of ~32.4 mum. Because juniper pollen grains have a diameter of from 22 to 30 mum, they are the aerosol most likely to have caused the corona. PMID:18268739

Mims, F M

1998-03-20

152

DUST AROUND R CORONAE BOREALIS STARS. I. SPITZER/INFRARED SPECTROGRAPH OBSERVATIONS  

SciTech Connect

Spitzer/infrared spectrograph (IRS) spectra from 5 to 37 {mu}m for a complete sample of 31 R Coronae Borealis stars (RCBs) are presented. These spectra are combined with optical and near-infrared photometry of each RCB at maximum light to compile a spectral energy distribution (SED). The SEDs are fitted with blackbody flux distributions and estimates are made of the ratio of the infrared flux from circumstellar dust to the flux emitted by the star. Comparisons for 29 of the 31 stars are made with the Infrared Astronomical Satellite (IRAS) fluxes from three decades earlier: Spitzer and IRAS fluxes at 12 {mu}m and 25 {mu}m are essentially equal for all but a minority of the sample. For this minority, the IRAS to Spitzer flux ratio exceeds a factor of three. The outliers are suggested to be stars where formation of a dust cloud or dust puff is a rare event. A single puff ejected prior to the IRAS observations may have been reobserved by Spitzer as a cooler puff at a greater distance from the RCB. RCBs which experience more frequent optical declines have, in general, a circumstellar environment containing puffs subtending a larger solid angle at the star and a quasi-constant infrared flux. Yet, the estimated subtended solid angles and the blackbody temperatures of the dust show a systematic evolution to lower solid angles and cooler temperatures in the interval between IRAS and Spitzer. Dust emission by these RCBs and those in the LMC is similar in terms of total 24 {mu}m luminosity and [8.0]-[24.0] color index.

Anibal Garcia-Hernandez, D. [Instituto de Astrofisica de Canarias, C/Via Lactea s/n, E-38200 La Laguna (Spain); Kameswara Rao, N. [Indian Institute of Astrophysics, Bangalore 560 034 (India); Lambert, David L., E-mail: agarcia@iac.es, E-mail: nkrao@iiap.res.in, E-mail: dll@astro.as.utexas.edu [W. J. McDonald Observatory, University of Texas at Austin, 1 University Station, C1400, Austin, TX 78712-0259 (United States)

2011-09-20

153

Optical polarization observations of the solar corona during the total solar eclipse of 1991 July 11  

NASA Astrophysics Data System (ADS)

We report on the results of optical polarization observations of the outer solar corona during the total solar eclipse of July 11, 1991, with specially designed telescopes. The observations were carried out near the summit of Mt. Popocatepetl in Mexico at an altitude of 5250 m. Polarization vector maps around the Sun were obtained at wavelengths of 532.5, 596.5, 720.0, and 801.5 nm. Strong polarization was observed in the regions where coronal streamers dominate and is thought to be due to Thomson scattering by free electrons. No excess polarization was observed at around 4-5 solar radii from the Sun on the ecliptic plane.

Tanabe, Toshihiko; Tsumuraya, Fumiaki; Baba, Naoshi; Alvarez, Manuel; Noguchi, Motokazu; Isobe, Syuzo

1992-10-01

154

Magnetohydrodynamics of atmospheric transients. II. Two-dimensional numerical results for a model solar corona  

Microsoft Academic Search

A systematic study of dynamic response of the inner solar corona is made within the context of two-dimensional, time-dependent plane hydromagnetics. The governing equations are written in r-phi coordinates (i.e., in the solar equatorial plane), and numerical solutions are obtained by introducing an impulsive temperature enhancement within a rectangular region (i.e., ''box'') in an initially isothermal corona in magnetohydrostatic equilibrium.

S. T. Wu; M. Dryer; Y. Nakagawa; S. M. Han

1978-01-01

155

Staubbildung in den Huellen von Kohlenstoffsternen: R Coronae Borealis (Dust Production in the Envelopes of Carbon Stars: R Coronae Borealis).  

National Technical Information Service (NTIS)

A quantitative, analytic model of darkening events of R Coronae Borealis, based on phenomenological models of light decline by soot formation, with focus on causal relation between the pulsating atmosphere and episodic condensation processes, is presented...

A. Goeres

1992-01-01

156

The Trieste Solar Radio System: A Surveillance Facility for the Solar Corona  

Microsoft Academic Search

We describe the present status of the Trieste Solar Radio System (TSRS), a dedicated facility for the continuous surveillance of the radio corona in the m-dm band at fixed frequencies, which is operated by the Trieste Astronomical Observatory at the Basovizza Observing Station. Its operational features, such as the ultra-high time resolution and accurate circular polarization measurements, allow the real-time

M. Messerotti; P. Zlobec; M. Comari; G. Dainese; L. Demicheli; L. Fornasari; S. Padovan; L. Perla

2001-01-01

157

Comparing eclipse observations of the 2008 August 1 solar corona with an MHD model prediction  

NASA Astrophysics Data System (ADS)

Context. The structure of the white-light and emission solar coronas and their MHD modelling are the context of our work. Aims: A comparison is made between the structure of the solar corona as observed during the 2008 August 1 total eclipse from Mongolia and that predicted by an MHD model. Methods: The model has an improved energy formulation, including the effect of coronal heating, conduction of heat parallel to the magnetic field, radiative losses, and acceleration by Alfvén waves. Results: The white-light corona, which was visible up to 20 solar radii, was of an intermediate type with well-pronounced helmet streamers situated above a chain of prominences at position angles of 48, 130, 241, and 322 degrees. Two polar coronal holes, filled with a plethora of thin polar plumes, were observed. High-quality pictures of the green (530.3 nm, Fe XIV) corona were obtained with the help of two narrow-passband filters (centered at the line itself and the vicinity of 529.1 nm background), with a FWHM of 0.15 nm. Conclusions: The large-scale shape of both the white-light and green corona was found to agree well with that predicted by the model. In this paper we describe the morphological properties of the observed corona, and how it compares with that predicted by the model. A more detailed analysis of the quantitative properties of the corona will be addressed in a future publication.

Rušin, V.; Druckmüller, M.; Aniol, P.; Minarovjech, M.; Saniga, M.; Miki?, Z.; Linker, J. A.; Lionello, R.; Riley, P.; Titov, V. S.

2010-04-01

158

Comparing an MHD Model of the Corona During the July 11, 2010 Total Solar Eclipse with Observations (Invited)  

Microsoft Academic Search

Total solar eclipses offer a unique opportunity to study the white light and emission coronae at high resolution. Magnetohydrodynamic (MHD) models have been used to predict the structure of the corona prior to eclipses, using measurements of photospheric magnetic fields on the Sun. In particular, such an MHD model was used to predict the structure of the corona for the

Z. Mikic; J. A. Linker; R. Lionello; P. Riley; V. S. Titov

2010-01-01

159

The Large-Scale Structure of the Solar Minimum Corona  

NASA Astrophysics Data System (ADS)

The goal of this thesis is to find a quantitative description of the large-scale structure of magnetic field and density in the solar minimum corona that is consistent with observations of both white light intensity and the magnetic field at the photosphere. We use white light images from NASA's Solar Maximum Mission (SMM) Coronagraph/Polarimeter and the High Altitude Observatory Mark III (MkIII) K-coronameter, along with photospheric field measurements from Stanford's Wilcox Solar Observatory (WSO), as constraints on the magnetostatic model of Bogdan and Low (B&L) (1986). We find a family of solutions to the B&L model that reproduce observations of white light quite well, each with a different magnetic field structure. We show that the observed photospheric field cannot be used as an exact boundary condition on the B&L model, but we can limit the white light solutions by matching the total observed photospheric magnetic flux. We find a set of seven model parameters that reproduces white light and photospheric field to within quantifiable model and observational limits, and calculate the physical plasma properties of density, pressure, magnetic field, and temperature that correspond to these parameters. We extend the model to include current sheets at the equator and around the coronal helmet streamer, and show that by doing so we improve the fit to white light data and to a lesser extent to the photospheric flux. Moreover, by including current sheets in the model, we produce a magnetic field line structure which better matches the underlying coronal white light structure, and which is more consistent with a solar wind accelerating along the open field lines. We use the magnetic field structure determined from our bulk current/current sheet model to calculate expansion factors, which can be used as essential inputs to solar wind models. Finally, we determine that the temperature structure predicted by our model is not in thermal equilibrium. We present a preliminary comparison of this temperature structure to independent emission line temperature diagnostics, and discuss how we hope in future to use such analyses to produce a more energetically consistent temperature distribution.

Gibson, Sarah Elizabeth

1995-01-01

160

Solitary Wave Propagation from the Photosphere into the Solar Corona  

NASA Astrophysics Data System (ADS)

In the present paper we study the excitation and time dependent dynamic evolution of vertically propagating weakly nonlinear (i.e. solitary) waves on vertically open cylindrical magnetic flux tubes in a stratified plasma. The axisymmetric flux tubes have a typical field strength of 1500 G at their photospheric roots, reducing to 20-30 G in the corona. Solitons are excited by a footpoint driver. The propagation of the solitary signal is investigated by solving numerically a set of fully nonlinear 2.5D MHD equations. We compare our results with the analytical solutions of Molotovshchikov &Ruderman (1987) obtained by using the method of multi-scale expansion. The model could be applied to spicule formation in the chromosphere, as suggested by Roberts &Mangeney (1982), where it was demonstrated theoretically, that a solar photospheric magnetic flux tube can support the propagation of two types of soliton, governed either by the Benjamin-Ono (slow mode) or by the Korteweg-de Vries (fast mode) equations. Future possible improvements in modelling and the relevance of the photospheric chromospheric transition region coupling by spicules is suggested.

Erdélyi, R.; Fedun, V.

2004-01-01

161

Kuiper Belt dust in the inner and outer Solar System  

Microsoft Academic Search

The dust produced in the Kuiper Belt (KB) spreads throughout the Solar System forming a dust disk. We have numerically modelled the dynamical evolution of KB dust grains using a modified symplectic integrator which resolves close planetary encounters and includes solar wind and radiation forces. We report here a selection of results from our modeling efforts. (1) We find that

A. Moro-Martin; R. Malhotra

2002-01-01

162

Singular magnetic equilibria in the solar x-ray corona  

NASA Astrophysics Data System (ADS)

Interlaced magnetic field line topologies are expected in the active x-ray solar coronal arches. In the presence of uniform fluid pressure the equilibrium involves magnetic stresses in equilibrium among themselves, i.e. the divergence of the magnetic stress tensor Mij is zero, ?Mij/?xj = 0. In the presence of an ideal infinitely conducting fluid the requirement reduces to the familiar force-free field equilibrium equation, ? × B = ?B. This paper reviews and comments on the formal analytical demonstration that the equilibrium of almost all interlaced field line topologies involves surfaces of tangential discontinuity (TD). Consider, then, the static equilibrium of a randomly interlaced field extending in the z-direction through an infinitely conducting fluid throughout the space 0 < z < L between the end plates z = 0 and z = L. With the field anchored at both ends it is obvious that a stable equilibrium exists for all interlacing topologies. The equilibrium equation can be reduced to the form of the familiar 2D time-dependent vorticity equation. The solutions to the vorticity equation represent a topological set of measure zero compared with the set of all interlacing field line topologies. Lacking the special topology of the vorticity solutions, it follows that the equilibria of almost all interlaced topologies are described by the so-called weak solutions, containing TDs (current sheets). The spaces between the TDs are filled with a continuous field satisfying the vorticity equation. A brief discussion of the mathematical difficulties in constructing illustrative examples of weak solutions is assisted by recent effort at numerical simulation. In the real world resistive dissipation at incipient TDs appears to be the principal heat source for the solar x-ray corona.

Parker, E. N.

2012-12-01

163

Emission lines of inner corona observed during the total solar eclipse of 1980 February 16  

NASA Astrophysics Data System (ADS)

Spectrograms of the inner solar corona were obtained during the 1980 total solar eclipse. Two Ebert-Fastie type spectrographs with circular slits were used to obtain spectra on the east and the west at 1.06 solar radii. These spectrographs were operated at a dispersion of 28.3 A/mm and covered the whole of the visible spectrum. The relative intensities of the emission lines of the inner corona, chromosphere and prominences are reported here. There is an indication of the existence of a highly active isolated pocket in the solar corona with a temperature greater than 4 x 10 to the 6th K. It is found that the ratio of the intensities of Ca(+)K to Ca(+)H is about 1.5 in the prominences whereas it is only 1.0 in the chromosphere.

Singh, J.; Rajamohan, R.; Raheem, K. C. A.

1983-12-01

164

Recent observations of the solar corona with a new ground-based Coronagraph in Argentina (MICA)  

NASA Astrophysics Data System (ADS)

As part of the new German-Argentinian Solar-Observatory in El Leoncito, San Juan, Argentina, a new ground-based solar telescope (MICA: Mirror Coronagraph for Argentina) began to operate in August 1997. MICA is an advanced mirror coronagraph, its design being an almost exact copy of the LASCO-C1 instrument. Since its installation, it has been imaging the inner solar corona (1.05 to 2.0 solar radii) in two spectral ranges, corresponding to the emission lines of the Fe XIV and Fe X ions. The instrument can image the corona as fast as every minute. Thus, it is ideally suited to study fast processes in the inner corona. In this way it is a good complement for the LASCO-C1 instrument. We present a brief review of the characteristics of the instrument, and some recent observations.

Stenborg, G.; Schwenn, R.; Srivastava, N.; Inhester, B.; Podlipnik, B.; Rovira, M.; Francile, C.

1999-06-01

165

Origin and Role of Dust in the Early Solar System.  

National Technical Information Service (NTIS)

Dust was the primary building material of the solar nebula planetesimals that accumulated to form minor planets, solid planets, and the cores of giant planets. Collected interplanetary dust particle (IDP) samples probably contain preserved samples of nebu...

D. E. Brownlee

1994-01-01

166

Migration of dust in the solar system  

Microsoft Academic Search

The migration of dust particles under the gravitational influence of all planets, radiation pressure, Poynting--Robertson drag and solar wind drag was investigated for the ratio between the radiation pressure force and the gravitational force beta = 0.01, 0.05, 0.1, 0.25, and 0.4 with a Bulirsh-Stoer integrator. For silicate particles such values of beta correspond to diameters of about 40, 9,

S. I. Ipatov; J. C. Mather; P. A. Taylor

2003-01-01

167

Aspects of the Global MHD Equilibria and Filament Eruptions in the Solar Corona  

Microsoft Academic Search

This is a review of several promising approaches for analyzing the accumulation and release of magnetic energy in filament eruptions and coronal mass ejections in the solar corona. The importance of the magnetic virial theorem for understanding the role of slowly changing boundary conditions in the photosphere is stressed. A possible role of the magnetic expulsion force in the solar

Yuri E. Litvinenko; Boris V. Somov

2001-01-01

168

Measurement of Magnetic Helicity Injection and Free Energy Loading into the Solar Corona  

Microsoft Academic Search

We develop a new methodology that can determine magnetic helicity flux as well as Poynting flux across the photosphere based on magnetograph observation. By applying this method, we study the injection mechanism of magnetic helicity and magnetic free energy into the solar corona. In order to derive the helicity and energy fluxes, first the velocity tangential to the solar surface

K. Kusano; T. Maeshiro; T. Yokoyama; T. Sakurai

2002-01-01

169

Propagation of hydromagnetic disturbances in the solar corona and Moreton's wave phenomenon  

Microsoft Academic Search

Moreton's wave phenomenon, observed to propagate across the solar disk during certain solar flares, may be explained as the intersection line between an expanding coronal wavefront surface and the chromosphere: The propagation of a hydromagnetic disturbance in a spherically symmetric model corona with a radial magnetic field is studied in the WKB-approximation, and the propagation paths of wavepackets, the shape

Yutaka Uchida

1968-01-01

170

PERPENDICULAR PROTON HEATING DUE TO ENERGY CASCADE OF FAST MAGNETOSONIC WAVES IN THE SOLAR CORONA  

SciTech Connect

Observational data and theoretical models suggest that the wave spectrum in the solar wind and corona may contain a fast magnetosonic mode component. This paper presents two-dimensional hybrid simulations of the energy cascade among the fast waves in the vicinity of the proton inertial scale. The initial spectrum consists of modes propagating in the positive direction, defined by the mean magnetic field, and is allowed to evolve freely in time. The plasma beta is set to low values typical of the solar corona. The cascade proceeds from lower to higher wavenumbers and mostly in the direction across the magnetic field. The highly oblique fast waves are strongly dissipated on the protons. The resulting proton heating is preferentially perpendicular to the magnetic field. If the wave intensity is constrained by the observed density spectra in the corona, the heating is fast enough to generate the solar wind.

Markovskii, S. A.; Vasquez, Bernard J.; Chandran, Benjamin D. G., E-mail: sergei.markovskii@unh.ed, E-mail: bernie.vasquez@unh.ed, E-mail: benjamin.chandran@unh.ed [Space Science Center, University of New Hampshire, Durham, NH 03824 (United States)

2010-02-01

171

Solar corona-induced fluctuations on spacecraft signal amplitude observed during solar superior conjunctions of the Cassini spacecraft  

Microsoft Academic Search

During the superior solar conjunctions of interplanetary spacecraft, the emitted radio signals undergo increased amplitude scintillation, phase scintillation, and spectral broadening due to the intervening charged particles of the solar corona. The magnitude of these parameters generally increases as the angle between the spacecraft and the center of the Sun (Sun-Earth probe (SEP) angle) decreases as observed by the tracking

David D. Morabito

2007-01-01

172

Solar corona–induced fluctuations on spacecraft signal amplitude observed during solar superior conjunctions of the Cassini spacecraft  

Microsoft Academic Search

During the superior solar conjunctions of interplanetary spacecraft, the emitted radio signals undergo increased amplitude scintillation, phase scintillation, and spectral broadening due to the intervening charged particles of the solar corona. The magnitude of these parameters generally increases as the angle between the spacecraft and the center of the Sun (Sun-Earth probe (SEP) angle) decreases as observed by the tracking

David D. Morabito

2007-01-01

173

Optical polarization observations of circumsolar dust during the 1983 solar eclipse  

NASA Astrophysics Data System (ADS)

It is very difficult to make optical observations from the earth where the angular distance from the sun is greater than three angular solar radii, because of the large and uncertain correction for sky radiation. To overcome these difficulties, optical polarization observations have been made at four wavelengths (5330 A, 5970 A, 7200 A, and 8015 A) for the outer solar corona at an altitude of 30 km, using a balloon-borne silicon-intensified TV camera during the total solar eclipse on June 11, 1983 in Indonesia. A polarization excess at an elongation between four and five angular solar radii from the sun in the ecliptic plane was observed at a wavelength of 8015 A on the two-dimensional frame. This is interpreted as an enhancement of dust grains distributed in a ring around the sun approximately in the ecliptic plane.

Isobe, S.; Hirayama, T.; Baba, N.; Miura, N.

1985-12-01

174

Emission lines of inner corona observed during the total solar eclipse of 1980 February 16  

Microsoft Academic Search

Spectrograms of the inner solar corona were obtained during the 1980 total solar eclipse. Two Ebert-Fastie type spectrographs with circular slits were used to obtain spectra on the east and the west at 1.06 solar radii. These spectrographs were operated at a dispersion of 28.3 A\\/mm and covered the whole of the visible spectrum. The relative intensities of the emission

J. Singh; R. Rajamohan; K. C. A. Raheem

1983-01-01

175

Evidence for wave heating in the solar corona.  

PubMed

The temperature of the Sun increases over a short distance from a few thousand degrees in the photosphere to over a million degrees in the corona. To understand coronal heating is one of the major problems in astrophysics. There is general agreement that the energy source is convective motion in and below the photosphere. It remains to determine how this mechanical energy is transported outward into the corona and then deposited as heat. Two classes of models have been proposed, namely those that rely on magnetic reconnection and those that rely on waves, particularly Alfvén waves. There is increasing evidence that waves are ubiquitous in the corona. However, a difficulty for wave-driven models has been that most theories predict Alfvén waves to be undamped in the corona, and therefore they cannot dissipate their energy into heat. Our research has shown unambiguous observational evidence that the waves do damp at sufficiently low heights in the corona to be important for coronal heating. PMID:23676178

Hahn, Michael

2013-05-15

176

Origin of the ten degree Solar System dust bands  

Microsoft Academic Search

The Solar System dust bands discovered by IRAS are toroidal distributions of dust particles with common proper inclinations. It is impossible for particles with high eccentricity (approximately 0.2 or greater) to maintain a near constant proper inclination as they precess, and therefore the dust bands must be composed of material having a low eccentricity, pointing to an asteroidal origin. The

K. Grogan; S. F. Dermott; S. Jayaraman; Y. L. Xu

1997-01-01

177

HERSCHEL/SCORE, imaging the solar corona in visible and EUV light: CCD camera characterization.  

PubMed

The HERSCHEL (helium resonant scattering in the corona and heliosphere) experiment is a rocket mission that was successfully launched last September from White Sands Missile Range, New Mexico, USA. HERSCHEL was conceived to investigate the solar corona in the extreme UV (EUV) and in the visible broadband polarized brightness and provided, for the first time, a global map of helium in the solar environment. The HERSCHEL payload consisted of a telescope, HERSCHEL EUV Imaging Telescope (HEIT), and two coronagraphs, HECOR (helium coronagraph) and SCORE (sounding coronagraph experiment). The SCORE instrument was designed and developed mainly by Italian research institutes and it is an imaging coronagraph to observe the solar corona from 1.4 to 4 solar radii. SCORE has two detectors for the EUV lines at 121.6 nm (HI) and 30.4 nm (HeII) and the visible broadband polarized brightness. The SCORE UV detector is an intensified CCD with a microchannel plate coupled to a CCD through a fiber-optic bundle. The SCORE visible light detector is a frame-transfer CCD coupled to a polarimeter based on a liquid crystal variable retarder plate. The SCORE coronagraph is described together with the performances of the cameras for imaging the solar corona. PMID:20428852

Pancrazzi, M; Focardi, M; Landini, F; Romoli, M; Fineschi, S; Gherardi, A; Pace, E; Massone, G; Antonucci, E; Moses, D; Newmark, J; Wang, D; Rossi, G

2010-04-29

178

Photometric and Spectrometric Investigations of the Solar Corona and Atmospheric Effects during the forthcoming March 29, 2006 Total Solar Eclipse  

NASA Astrophysics Data System (ADS)

A great part of the information about large-scale structure of the solar corona comes from solar observations during total solar eclipses. Space coronagraphs over-occult the Sun, omitting from view exactly the inner and coronal reasons well imaged at total solar eclipses. The total eclipse of the Sun on 2006 March 29, will be visible from within a narrow corridor, which transverse half the Earth. We foresee observations from the territory of Turkey. The aims of observations are: Photometric investigation of the White corona structure and polarization; Investigation of the structure of monochromatic emission corona in green (Fe XIV, ?=5303Å) and red (Fe X, ?=6374Å) line, H ?, and the thermal corona in the 2 -5 ?m region of the Infrared spectrum; Tropospheric and stratospheric O3 and NO2 photochemistry study; Determining of the dynamics of basic microclimatic parameters of the 10 m ground atmospheric layer. The following methods will be used: Taking of photograph of the corona (telescope-refractor 100/1000mm, spectrozonal photoemulsions, polarization and infrared barrier filters), registration of the investigated emissions (telescope-refractor 150/1600mm, high sensitive photo-emulsions, narrow band filters), Differential Optical Absorption Spectroscopy method, measuring of the microclimatic parameters with automatic meteorological station; processing and analysis of the photographs and data, seeking for wave structures in the O3 and NO2 concentration, comparison with other measurements during an eclipse. The results we expect are: Determining of the Solar corona characteristics, finding of regularities in the O3 and NO2 behavior in conditions of reduced solar radiation, and clarifying the dynamical and photochemical processes in the stratosphere and climate of the ground atmosphere.

Stoeva, P. V.; Stoev, A. D.; Kostadinov, I. N.

2006-03-01

179

Global Thermodynamic MHD Modeling of the Solar Corona in the Context of SDO/AIA Observations.  

NASA Astrophysics Data System (ADS)

Realistic magnetohydrodynamic (MHD) models can serve as powerful testbeds for exploring our understanding of magnetic and thermodynamic processes in the solar corona. An important aspect in their development is the use of observations to characterize model results. In this context we investigate the comparison of observations from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) to a thermodynamic MHD model of the global corona (Lionello et al. 2009), with emphasis on exploiting the unique multi-spectral information available from the AIA observing program. We discuss the implications towards modeling multi-temperature magnetic structures observed in the low corona, and focus on the sensitivity of the AIA observables with respect to the choice of coronal heating parameterizations and magnetic boundary data. Research Supported by NASA and NSF.

Downs, Cooper; Linker, J. A.; Mikic, Z.; Lionello, R.; Riley, P.

2012-05-01

180

Radio evidence on shock wave formation in the solar corona  

Microsoft Academic Search

In order to investigate the formation of radio emitting shock waves above flaring active regions, we combine spectral and imaging observations of type II radio events with X-ray imaging and full-Sun observations and, in one case, with the extrapolated magnetic field configuration in the corona. We confirm and extend earlier findings that type II bursts are emitted above active region

A. Klassen; H. Aurass; K.-L. Klein; A. Hofmann; G. Mann

1999-01-01

181

THE LOWER SOLAR CORONA: INTERPRETATION OF THE ULTRAVIOLET SPECTRUM  

Microsoft Academic Search

An analysis of the resonance lines of nine elements (27 ions) formed in ; the chromosphere and corona of the sun yields the following results: the chemical ; composition of this region of the sun can be determined, without any knowledge of ; the detailed temperature-density structure in this region; a further clue ; concerning the detailed structure of this

Stuart R. Pottasch

1963-01-01

182

Joint Soviet--French investigations of the solar corona. 2. Photometry of solar corona of June 30, 1973  

SciTech Connect

The results are presented on a study of eclipse negative obtained on June 30, 1973, in Africa in the program of the Soviet--French experiment ''Dynamics of the White Corona'' by expeditions of Kiev University (Atar, Mauritania) and the Paris Astropysical Institute (Moussoro, Chad). The distributions of the total brightness of the corona out to rapprox. =4.5 R/sub sun/ and of its K and F components for the E and N directions are found with high accuracy on the basis of a new method of photometry and colorimetry using the images of stars down to 8.5/sup m/ as photometric standards. Neither reddening nor flattening of the dusty F component were detected at r<2.5 R/sub sun/. The integral brightness of the corona in the standard zone (1.03--6.0 R/sub sun/) is 0.64 x 10/sup -6/ E/sub sun/.

Vsekhsvyatskii, S.; Dzyubenko, N.; Ivanchuk, V.; Popov, O.; Rubo, G.; Koutchmy, S.; Koutchmy, O.; Stellmacher, G.

1981-03-01

183

New Limits on Small-Scale Turbulence in the Solar Corona  

NASA Astrophysics Data System (ADS)

Many observed characteristics of the solar corona are interpreted as heating by ion cyclotron waves. Intense electromagnetic plasma waves, with wavelengths of the order of the ion inertial length or smaller, can be detected via a phenomenon called Faraday screen depolarization (Spangler and Mancuso, ApJ 530,491,2000). The fine scale turbulent magnetic field randomizes the Faraday rotation within the beam of a radio telescope, causing a decrease in the degree of linear polarization. We present new observations specifically intended to measure this effect. Observations were made with the Very Large Array radiotelescope on August 16 and 18, 2003, of the extended radio source 3C228 when it was occulted by the corona. The line of sight to the source passed at a heliocentric distance of 6.2 R on August 16, and 4.7 R on August 18. No indication is seen of depolarization by the corona. On August 16, the most conservative limit is that the degree of polarization is >=0.75 of its intrinsic value. A more likely limit is that the degree of polarization with the corona interposed is >=0.85 that in the absence of the corona. Even stronger limits are obtained on August 18. We discuss the implications of these measurements for the amplitude and outer scale of Alfv'en-Ion Cyclotron turbulence in the corona.

Spangler, Steven

2005-10-01

184

Dust Models Paint Alien's View of Solar System  

NASA Video Gallery

Dust in the Kuiper Belt, the cold-storage zone that includes Pluto, creates a faint infrared disk potentially visible to alien astronomers looking for planets around the sun. Neptune's gravitational imprint on the dust is detectable in new simulations of how this dust moves through the solar system. The simulations show how the distant view of the solar system might have changed over its history.

gsfcvideo

2010-09-16

185

Solar Magnetic Fields as a Clue for the Mystery of the Permanent Solar Wind and the Solar Corona  

NASA Astrophysics Data System (ADS)

We analyze, generalize, and interpret the data for the permanent solar wind (PSW) velocities measured on board of Ulysses (SWOOPS). A finding of a principal importance extracted from Ulysses' observations is a discovery of the clear-cut inverse coupling between the SW velocities and the solar magnetic fields (SMF) (the stronger close MF, the slower SW, and vice versa), which points to the solar wind plasma deceleration by the SMFs below the source surface. Taking SMF into consideration leads to the alternative paradigm of the SW: flow deceleration instead of the acceleration. In such a case, both the SW and solar corona are converted into products of the interaction of an initial high-velocity plasma outflow ejected from the photosphere by solar magnetic fields. The latter not only divide initial fluxes into fast and slow parts, but also create and heat the corona through capture and stoppage of plasma in magnetic traps and the subsequent plasma heating. Observational arguments are presented in favor of the suggested idea.

Mogilevsky, M. A.; Nikolskaya, K. I.

186

Generalized similarity in magnetohydrodynamic turbulence as seen in the solar corona and solar wind  

NASA Astrophysics Data System (ADS)

A key property of turbulence is that it can be characterized and quantified in a robust and reproducible way in terms of the ensemble averaged statistical properties of fluctuations. Importantly, fluctuations associated with a turbulent field show similarity or scaling in their statistics and we test for this in observations of magnetohydrodynamic turbulence in the solar corona and solar wind with both power spectra and Generalized Structure Functions. Realizations of turbulence that are finite sized are known to exhibit a generalized or extended self-similarity (ESS). ESS was recently demonstrated in magnetic field timeseries of Ulysses single point in-situ observations of fluctuations of quiet solar wind for which a single robust scaling function was found [1-2]. Flows in solar coronal prominences can be highly variable, with dynamics suggestive of turbulence. The Hinode SOT instrument provides observations (images) at simultaneous high spatial and temporal resolution which span several decades in both spatial and temporal scales. We focus on specific Calcium II H-line observations of solar quiescent prominences with dynamic, highly variable small-scale flows. We analyze these images from the perspective of a finite sized turbulent flow. We discuss this evidence of ESS in the SOT images and in Ulysses solar wind observations- is there a single universal scaling of the largest eddies in the finite range magnetohydrodynamic turbulent flow? [1] S. C. Chapman, R. M. Nicol, Generalized Similarity in Finite Range Solar Wind Magnetohydrodynamic Turbulence, Phys. Rev. Lett., 103, 241101 (2009) [2] S. C. Chapman, R. M. Nicol, E. Leonardis, K. Kiyani, V. Carbone, Observation of universality in the generalized similarity of evolving solar wind turbulence as seen by ULYSSES, Ap. J. Letters, 695, L185, (2009)

Chapman, S. C.; Leonardis, E.; Nicol, R. M.; Foullon, C.

2010-12-01

187

Synthetic Images of the Solar Corona from Octree Representation of 3-D Electron Distributions  

Microsoft Academic Search

Empirical and theoretical modeling of 3-D structures in the solar corona is confronted by the tremendous amount of data needed to represent phenomena with a large dynamic range both in size and magnitude, and with a rapid temporal evolution. Octree representation of the 3-D coronal electron distribution offers the right compromise between resolution and size, allowing computation of synthetic images

D. Vibert; A. Llebaria; T. Netter; L. Balard; P. Lamy

1997-01-01

188

Electron velocity distribution functions from the solar wind to the corona  

Microsoft Academic Search

Typical electron velocity distribution functions observed at 1 AU from the Sun by the instrument 3DP aboard of WIND are used as boundary conditions to determine the electron velocity distribution function at 4 solar radii in the corona. The velocity distribution functions (VDF) at low altitude are obtained by solving the Fokker-Planck equation, using two different sets of boundary conditions.

M. Maksimovic; V. Pierrard; J. Lemaire; D. Larson

1999-01-01

189

A kinetic model of the solar wind with Kappa distribution functions in the corona  

Microsoft Academic Search

A kinetic model of the solar wind based on Kappa velocity distribution functions for the electrons and protons escaping out of the corona is presented. The high velocity particles forming the tail of these distribution functions have an enhanced phase space density compared to a Maxwellian. The existence of such velocity distribution functions have been introduced in the pioneering work

M. Maksimovic; V. Pierrard; J. F. Lemaire

1997-01-01

190

Comments on `Possible Role of MHD Waves in Heating the Solar Corona' by Dwivedi and Pandey  

NASA Astrophysics Data System (ADS)

We comment on the recent paper by Dwivedi and Pandey (Solar Physics 216, 59, 2003). Parts of that paper closely reproduce, without reference, material that we had published previously, while other parts that deviate from our earlier analysis contain several critical flaws. We show that magnetoacoustic waves are capable of heating the corona with a modest enhancement in the coefficient of compressive viscosity.

Klimchuk, J. A.; Porter, L. J.; Sturrock, P. A.

2004-05-01

191

Comparative study of the loss cone-driven instabilities in the low solar corona  

Microsoft Academic Search

A comparative study of the loss cone-driven instabilities in the low solar corona is undertaken. The instabilities considered are the electron cyclotron maser, the whistler, and the electrostatic upper hybrid. It is shown that the first-harmonic extraordinary mode of the electron cyclotron maser instability is the fastest growing mode for strong magnetized plasma (the ratio of plasma frequency to cyclotron

R. R. Sharma; L. Vlahos

1984-01-01

192

Deriving the Electron Density of the Solar Corona from the Inversion of Total Brightness Measurements  

Microsoft Academic Search

Usually, the electron density structure of the white-light solar corona is estimated from the inversion of polarized brightness measurements. The inversion technique was developed in the 1950s and has remained largely unchanged since. Here, for the first time, we expand this technique to total brightness observations to take advantage of the extensive Large Angle and Spectrometric Coronagraphs (LASCO) archive. We

A. P. Hayes; A. Vourlidas; R. A. Howard

2001-01-01

193

The Irregular Structure of the Outer Regions of the Solar Corona  

Microsoft Academic Search

The radiation from the radio star in Taurus was recorded on a radio interferometer on occasions when the radiation passed through the outer regions of the solar corona. The recorded intensity was found to decrease rapidly as the radial distance decreased. A series of observations carried out during June 1953 with interferometers of different wave-length and spacing have indicated that

A. Hewish

1955-01-01

194

On the reality of potential magnetic fields in the solar corona  

Microsoft Academic Search

Global magnetic field calculations, using potential field theory, are performed for Carrington rotations 1601–1610 during the Skylab period. The purpose of these computations is to quantitatively test the spatial correspondence between calculated open and closed field distributions in the solar corona with observed brightness structures. The two types of observed structures chosen for this study are coronal holes representing open

G. W. Pneuman; S. F. Hansen; R. T. Hansen

1978-01-01

195

Spectroscopic Constraints on Models of Ion-cyclotron Resonance Heating in the Polar Solar Corona  

Microsoft Academic Search

Using empirical velocity distributions derived from UVCS and SUMER ultraviolet spectroscopy, we construct theoretical models of anisotropic ion temperatures in the polar solar corona. The primary energy deposition mechanism we investigate is the dissipation of high frequency (10-10000 Hz) ion-cyclotron resonant Alfvén waves which can heat and accelerate ions differently depending on their charge and mass. We find that it

S. R. Cranmer; G. B. Field; J. L. Kohl

1999-01-01

196

The possible role of MHD waves in heating the solar corona  

Microsoft Academic Search

The possible role of waves in the heating of the solar corona has been investigated. A general dispersion relation has been derived for waves propagating in a homogeneous plasma subject to dissipation by viscosity and thermal conduction. The dissipation mechanisms have been incorporated self-consistently into the equations, and no assumptions about the strength of the damping have been made. Solutions

Lisa J. Porter; James A. Klimchuk; Peter A. Sturrock

1994-01-01

197

Damping of MHD Waves as a Heating Mechanism of Solar Corona  

Microsoft Academic Search

Damping of MHD waves seems to play an important role in heating the solar corona. In this respect a magnetized flux tube with a specified density profile is considered and the singularity of ideal equation of motion in coronal approximation is removed by introducing the viscous and resistive damping in the tube. The resultant equations are solved by applying the

S. Nasiri; H. Safari; Y. Sobouti

2007-01-01

198

Comments on `Possible Role of MHD Waves in Heating the Solar Corona' by Dwivedi and Pandey  

Microsoft Academic Search

We comment on the recent paper by Dwivedi and Pandey (Solar Physics 216, 59, 2003). Parts of that paper closely reproduce, without reference, material that we had published previously, while other parts that deviate from our earlier analysis contain several critical flaws. We show that magnetoacoustic waves are capable of heating the corona with a modest enhancement in the coefficient

J. A. Klimchuk; L. J. Porter; P. A. Sturrock

2004-01-01

199

Wave heating in astrophysical plasma - examples in the solar corona and in galaxy clusters  

Microsoft Academic Search

It is widely known that hot plasma is ubiquitous in various astrophysical objects from stars to galaxy clusters. I have worked on the wave dissipation which play a role in the momentum and energy transfer in the plasma. In this article, I firstly introduce our results on the wave heating and acceleration in the solar corona. I show that two

Takeru K. Suzuki

2004-01-01

200

High energy particle transport in stochastic magnetic fields in the solar corona  

Microsoft Academic Search

Aims:We study energetic particle transport in the solar corona in the presence of magnetic fluctuations by analyzing the motion of protons injected at the center of a model coronal loop. Methods: We set up a numerical realization of magnetic turbulence, in which the magnetic fluctuations are represented by a Fourier expansion with random phases. We perform test particle simulations by

M. Gkioulidou; G. Zimbardo; P. Pommois; P. Veltri; L. Vlahos

2007-01-01

201

On the temperature profile and heat flux in the solar corona: Kinetic simulations  

Microsoft Academic Search

In the solar corona the collisional mean free path lambda for a thermal particle (electrons or protons) is of the order of 10-2 to 10-4 times the typical scale of variation H of macroscopic quantities like the density or the temperature. Despite the relative smallness of the ratio lambda \\/H, an increasingly large number of authors have become convinced that

S. Landi; F. G. E. Pantellini

2001-01-01

202

Applications of the Principle of Minimum Dissipation Rate to Solar Corona  

Microsoft Academic Search

In analogy to the Principle of Minimum Energy, the Principle of Minimum Dissipation Rate (MDR), originating from irreversible thermodynamics, follows a variational approach, but is more suitable for a complex and externally driven system like the solar corona. And in contrast, while the former yields a linear (constant alpha) force-free magnetic field, the MDR gives a more general non-force free

Q. Hu; B. Dasgupta; D. P. Choudhary

2007-01-01

203

The flow of interstellar dust through the solar system: the role of dust charging  

SciTech Connect

Interstellar dust can enter the solar system through the relative motion of the Sun with respect to the Local Interstellar Cloud. The trajectories of the dust through the solar system are not only influenced by gravitation and solar radiation pressure forces, but also by the Lorentz forces due to the interaction of the interplanetary magnetic field with the charged dust particles. The interplanetary magnetic field changes on two major time scales: 25 days (solar rotation frequency) and 22 years (solar cycle). The short-term variability averages out for regions that are not too close (>{approx}2 AU) to the Sun. This interplanetary magnetic field variability causes a time-variability in the interstellar dust densities, that is correlated to the solar cycle.In this work we characterize the flow of interstellar dust through the solar system using simulations of the dust trajectories. We start from the simple case without Lorentz forces, and expand to the full simulation. We pay attention to the different ways of modeling the interplanetary magnetic field, and discuss the influence of the dust parameters on the resulting flow patterns. We also discuss the possibilities of using this modeling for prediction of dust fluxes for different space missions or planets, and we pay attention to where simplified models are justified, and where or when a full simulation, including all forces is necessary. One of the aims of this work is to understand measurements of spacecraft like Ulysses, Cassini and Stardust.

Sterken, V. J. [MPIK, Saupfercheckweg 1, D-69117 Heidelberg (Germany); TU Braunschweig, IGEP, Mendelssohnstr. 3, D-38106 Braunschweig (Germany); Altobelli, N.; Schwehm, G. [ESA-ESAC - P.O. Box 78, E-28691 Villanueva de la Canada, Madrid (Spain); Kempf, S. [LASP, University of Colorado, 1234 Innovation Dr, Boulder, CO, 80303-7814 (United States); TU Braunschweig, IGEP, Mendelssohnstr. 3, D-38106 Braunschweig (Germany); Srama, R. [MPIK, Saupfercheckweg 1, D-69117 Heidelberg (Germany); Universitaet Stuttgart, IRS, Pfaffenwaldring 31, D-70569 Stuttgart (Germany); Strub, P. [MPS, Max-Planck-Strasse 2, D-37191 Katlenburg-Lindau (Germany); Gruen, E. [MPIK, Saupfercheckweg 1, D-69117 Heidelberg (Germany); LASP, University of Colorado, 1234 Innovation Dr, Boulder, CO, 80303-7814 (United States)

2011-11-29

204

Two colour photometry and polarimetry of the solar corona of 16 February 1980  

NASA Astrophysics Data System (ADS)

Eclipse photographs obtained with a new type of eclipse camera during the solar eclipse of February t6, t980 at Yellapur (India) are analysed, applying special care to relative and absolute calibration and to the coronal aureole. Due to good and stable atmospheric conditions at the observing site, reliable values of coronal intensities, up to r=10 rsun are obtained. Polarization is measured up to r = 3.3 rsun and used to separate K and F corona. The F corona is found to be spherical for r < 2 rsun and to show increasing flattening with distance. No reddening of the F corona is measured for r < 5 rsun. Polarization is in the range explainable by Thomson scattering. Polarization rates of the K corona reveal deviations from a spherical electron density distribution. For regions with spherical density distribution, electron densities are calculated and compared with published models. The integrated flux of the corona (K+F, r=1.03rsun-6 rsun) is 1.29 10-6 solar flux.

Duerst, J.

1982-08-01

205

Three-dimensional MHD modeling of the global corona throughout solar cycle 23  

Microsoft Academic Search

Based on the space-time conservation element and solution element (CESE) method, we have recently developed a novel 3D magnetohydrodynamic (MHD) model for the solar corona and interplanetary study. Our aim here is to describe the application of this new MHD model to study the global coronal magnetic structures by using the observed line-of-sight photospheric magnetic field from the Wilcox Solar

Y. Q. Hu; X. S. Feng; S. T. Wu; W. B. Song

2008-01-01

206

Semiempirical Two-dimensional MagnetoHydrodynamic Model of the Solar Corona and Interplanetary Medium  

Microsoft Academic Search

We have developed a two-dimensional semiempirical MHD model of the solar corona and solar wind. The model uses empirically derived electron density profiles from white-light coronagraph data measured during the Skylab period and an empirically derived model of the magnetic field which is fitted to observed streamer topologies, which also come from the white-light coronagraph data. The electron density model

Edward C. Sittler Jr.; Madhulika Guhathakurta

1999-01-01

207

Alfvén waves in the solar corona, the solar wind, and the magnetosphere  

NASA Astrophysics Data System (ADS)

Observations and theoretical models show that Alfvén waves play an important role in many physical processes taking place in the plasma of the "local cosmos." For example, Alfvén waves are still the major candidates for the acceleration and heating of the fast solar wind, since they were proposed nearly 4 decades ago. Recently, MHD waves were observed in coronal loops in the EUV with the TRACE satellite. The SOHO, and TRACE instrument provide evidence for slow magnetosonic waves in coronal plumes. In-situ Helios and Ulysses spacecraft find ample evidence for the presence of propagating Alfvén waves in the solar wind. The CLUSTER mission provides for the first time multi-point view of the magnetospheric and solar wind plasma environment, and in particular high cadence magnetic field measurements with the Fluxgate Magnetometer (FGM), that enables to study the properties of Alfvén waves in various parts of the magnetosphere simultaneously. I will discuss the observations and modeling of Alfvén waves starting from the low corona (loops), continuing into the solar wind, the magnetosphere, and to the auroral ionosphere. I will present the results of MHD, multifluid, and hybrid models of low-frequency (MHD), as well as kinetic Alfvén waves in the plasma in various parts of the "local cosmos", and I will discuss the role Alfvén waves play in the energization of the plasma, and as a diagnostic tool of the plasma physical processes.

Ofman, L.

2004-12-01

208

Nanoflares and the solar X-ray corona  

SciTech Connect

Observations of the sun with high time and spatial resolution in UV and X-rays show that the emission from small isolated magnetic bipoles is intermittent and impulsive, while the steadier emission from larger bipoles appears as the sum of many individual impulses. We refer to the basic unit of impulsive energy release as a nanoflare. The observations suggest, then, that the active X-ray corona of the sun is to be understood as a swarm of nanoflares. This interpretation suggests that the X-ray corona is created by the dissipation at the many tangential discontinuities arising spontaneously in the bipolar fields of the active regions of the sun as a consequence of random continuous motion of the footpoints of the field in the photospheric convection. The quantitative characteristics of the process are inferred from the observed coronal heat input. 105 references.

Parker, E.N.

1988-07-01

209

Long-Term Variation of the Rotation of the Solar Corona  

NASA Astrophysics Data System (ADS)

Synoptic photoelectric observations of the coronal Fe XIV and Fe X emission lines at 530.3 nm and 637.4 nm, respectively, are analyzed to study the rotational behavior of the solar corona as a function of latitude, height and time. The data used are measurements made with the Sacramento Peak 40-cm coronagraph and Emission-Line Coronal Photometer of the intensity of these lines observed at 1.15 to 1.45 solar radii (Ro) between 1973 (1984 for Fe X) and 2000. An earlier similar temporal-correlation analysis of the Fe XIV data at 1.15 Ro over only one 11-year solar activity cycle (Sime, Fisher and Altrock 1989, Astrophys. J. 336, 454) found suggestions of solar-cycle variations in the differential-rotation and latitude-averaged-rotation patterns that combined the effects of large-scale patterns seen in the white-light corona and smaller-scale patterns seen in chromospheric and photospheric rotation. These results will be tested over the longer epoch now available. In addition, the new 1.15 Ro Fe XIV results will be compared with those at greater heights and with results from the Fe X line and radio frequencies (Vats et al. 2001, Astrophys. J., 548, L87) to form a global picture of solar rotation throughout the corona and over more than two solar cycles.

Altrock, R. C.

2001-05-01

210

Long-Term Variation of the Rotation of the Solar Corona  

NASA Astrophysics Data System (ADS)

Synoptic photoelectric observations of the coronal Fe XIV and Fe X emission lines at 530.3 nm and 637.4 nm, respectively, are analyzed to study the rotational behavior of the solar corona as a function of latitude, height and time. The data used are measurements made with the Sacramento Peak 40-cm coronagraph and Emission-Line Coronal Photometer of the intensity of these lines observed at 1.15 to 1.45 solar radii (Ro) between 1973 (1984 for Fe X) and 2000. An earlier similar temporal-correlation analysis of the Fe XIV data at 1.15 Ro over only one 11-year solar activity cycle (Sime, Fisher and Altrock 1989, Astrophys. J. 336, 454) found suggestions of solar-cycle variations in the differential-rotation and latitude-averaged-rotation patterns that combined the effects of large-scale patterns seen in the white-light corona and smaller-scale patterns seen in chromospheric and photospheric rotation. These results will be tested over the longer epoch now available. In addition, the new 1.15 Ro Fe XIV results will be compared with those at greater heights and with results from the Fe X line and radio frequencies (Vats et al. 2001, Astrophys. J., 548, L87) to form a global picture of solar rotation throughout the corona and over more than two solar cycles.

Altrock, R. C.

2002-01-01

211

STATISTICS OF DENSITY FLUCTUATIONS DURING THE TRANSITION FROM THE OUTER SOLAR CORONA TO THE INTERPLANETARY SPACE  

SciTech Connect

This paper investigates the evolution of the plasma density fluctuations of the fast and slow solar wind from the solar corona into the interplanetary space. The study is performed by comparing the low-frequency spectra and the phase correlation of the proton density oscillations, measured in the inner heliosphere with the Helios 2 in situ instrumentation, with those due to the large-scale density perturbations observed with UVCS/SOHO in the outer corona. We find that the characteristics of density fluctuations of the fast solar wind are maintained in the transition from the outer corona to the inner heliosphere, thus suggesting a coronal imprint for the heliospheric large-scale 1/f {sup 2} noise spectrum. In contrast, a quick dynamical evolution is observed in the slow wind, which, starting from large-scale fluctuations with strong phase correlations in the outer corona, gives rise to a Kolmogorov-like spectrum and an accumulation of density structures at small scales at 0.3 AU. This can be explained in the framework of nearly incompressible turbulence.

Telloni, D.; Antonucci, E. [Istituto Nazionale di Astrofisica (INAF), Osservatorio Astronomico di Torino, Via Osservatorio 20, 10025 Pino Torinese (Italy); Bruno, R.; D'Amicis, R. [Istituto Nazionale di Astrofisica (INAF), Istituto di fisica dello Spazio Interplanetario, Via del Fosso del Cavaliere 100, 00133 Rome (Italy); Carbone, V. [Universita della Calabria, Dipartimento di fisica, Ponte P. Bucci, Cubo 31C, 87036 Rende (Italy)

2009-11-20

212

Heavy ion reflection and heating by collisionless shocks in polar solar corona  

NASA Astrophysics Data System (ADS)

We propose a new model for explaining the observations of preferential heating of heavy ions in the polar solar corona. We consider that a large number of small scale shock waves can be present in the solar corona, as suggested by recent observations of polar coronal jets by the Hinode and STEREO spacecraft. The heavy ion energization mechanism is, essentially, the ion reflection off supercritical quasi-perpendicular collisionless shocks in the corona and the subsequent acceleration by the motional electric field E=-(1/c)V ×B. The acceleration due to E is perpendicular to the magnetic field, giving rise to large temperature anisotropy with T??T?, which can excite ion cyclotron waves. Also, heating is more than mass proportional with respect to protons, because the heavy ion orbit is mostly upstream of the quasi-perpendicular shock foot. The observed temperature ratios between O5+ ions and protons in the polar corona, and between ? particles and protons in the solar wind are easily recovered. We also discuss the mechanism of heavy ion reflection, which is based on ion gyration in the magnetic overshoot of the shock.

Zimbardo, Gaetano

2011-05-01

213

Primitive galactic dust in the solar system  

SciTech Connect

The results of experiments with ion-induced evolution of C-rich frozen gas and organic refractory material typical of astrophysical materials present in interstellar space since the collapse and formation of the Galaxy and solar system are described. The trials featured ion beam energies in the keV-MeV range. New materials emerged when the irradiation reached 10 to the 16th/sq cm. Yellowish, fluffy material appearing at proton energies of 1.5 MeV had a density of 0.5 g/cu cm and IR signatures similar to polymers. At fluences of about 10 to the 17th protons/sq cm, an amorphous, carbon-like material evolved with a higher density. The data, considered in conjunction with estimates of the ion fluxes to which comets are exposed, indicate that galactic and solar fast protons penetrate comets to a depth of 100 m. Significant amounts of carbon-like material is built up and remains on grains which have been captured and interpreted as cometary debris. Therefore, it is unlikely that cometary dust retains any physical characteristics of the primal Galaxy and solar system. 22 references.

Strazzulla, G.

1986-07-01

214

Nonlinear excitation of short scale turbulence in solar corona by kinetic Alfven waves  

SciTech Connect

The model equations for the nonlinear interaction between kinetic Alfven waves and ion acoustic waves in the intermediate-{beta} (thermal to background magnetic pressure ratio) plasmas are presented. The nonlinear dynamical equations satisfy the modified Zakharov system of equations by taking the nonadiabatic response of the background density. Numerical solution has been obtained to study this nonlinear process. The localized magnetic filamentary structures are found in solar corona along with the density dips and humps associated with the kinetic Alfven waves. The power spectra of magnetic field fluctuations indicate that the nonlinear interactions may be redistributing energy among higher wave numbers. The heating of the solar corona observed by Yohkoh and Solar and Heliospheric Observatory may be produced by the coupling of kinetic Alfven waves and ion acoustic waves via filamentation process.

Kumar, Sachin; Sharma, R. P.; Singh, H. D. [Plasma Simulation Laboratory, Centre for Energy Studies, Indian Institute of Technology Delhi, New Delhi 110016 (India)

2009-07-15

215

Spectroscopic Constraints on Models of Ion Cyclotron Resonance Heating in the Polar Solar Corona and High-Speed Solar Wind  

Microsoft Academic Search

Using empirical ion velocity distributions derived from Ultraviolet Coronagraph Spectrometer (UVCS) and Solar Ultraviolet Measurements of Emitted Radiation (SUMER) ultraviolet spectroscopy, we construct theoretical models of the nonequilibrium plasma state of the polar solar corona. The primary energy deposition mechanism we investigate is the dissipation of high-frequency (10-10,000 Hz) ion cyclotron resonant Alfvén waves which can heat and accelerate ions

Steven R. Cranmer; George B. Field; John L. Kohl

1999-01-01

216

Spectroscopic Constraints on Models of Ion Cyclotron Resonance Heating in the Polar Solar Corona and High?Speed Solar Wind  

Microsoft Academic Search

Using empirical ion velocity distributions derived from Ultraviolet Coronagraph Spectrometer (UVCS) and Solar Ultraviolet Measurements of Emitted Radiation (SUMER) ultraviolet spectroscopy, we con- struct theoretical models of the nonequilibrium plasma state of the polar solar corona. The primary energy deposition mechanism we investigate is the dissipation of high-frequency (10¨10,000 Hz) ion cyclotron resonant waves which can heat and accelerate ions

Steven R. Cranmer; George B. Field; John L. Kohl

1999-01-01

217

New Constraints on Plasma Turbulence in the Solar Corona  

NASA Astrophysics Data System (ADS)

One suggestion for coronal heating invokes the dissipation of high frequency, Alfvén-ion cyclotron waves which are generated in the photosphere and chromosphere and propagate into the corona. As we have previously noted (Spangler and Mancuso 2000, ApJ 530, 491) the properties of such waves can be constrained by radioastronomical observations. The observational effect is Faraday screen depolarization, in which stochastic Faraday rotation randomizes the polarization position angle on scales smaller than the telescope beam. We present observations made with the NRAO Very Large Array on August 16 and 18, 2003, when the radio galaxy 3C228 was viewed through the corona at heliocentric distances of 6.7 and 5.2 R?, respectively. The depolarization parameter D ? (m)/(m0) was measured, where m is the fractional linear polarization measured through the corona, and m0 is the intrinsic degree of polarization. Measurements were available for both hot spots of 3C228, and on both days of observation. The measurements are consistent with D=1 for both components on both days. These results are in agreement with, but superior to, previous reports of no coronal screen depolarization. Equations from Spangler and Mancuso (2000) are used to constrain the dimensionless amplitude and outer scale of the coronal turbulence. Turbulence with a dimensionless amplitude of 50 % or greater, and outer scale larger than 1000-2000 km, would have produced depolarization close to, or in excess of our limits. Turbulence with smaller dimensionless amplitude and outer scale would not have been detected with these measurements. This research was supported by grant ATM-0354782 from the National Science Foundation.

Spangler, S. R.; Spitler, L. G.

2005-12-01

218

Interstellar Dust in the Solar System  

Microsoft Academic Search

A fraction of the dust in the interstellar medium (ISM) enters the heliosphere and is measured in situ from spacecraft. This review surveys the in situ measurements and discusses a hence derived model of dust in the local interstellar cloud (LIC). The LIC dust model bears similarities to pristine cometary dust and is characteristic of the warm ISM clouds that

Ingrid Mann

2010-01-01

219

The Role of Transient Brightenings in Heating the Solar Corona  

NASA Astrophysics Data System (ADS)

Nanoflare reconnection events have been proposed as a mechanism for heating the corona. Parker's original suggestion was that frequent reconnection events occur in coronal loops due to the braiding of the magnetic field. Many observational studies, however, have focused on the properties of isolated transient brightenings unassociated with loops, but their cause, role, and relevance for coronal heating have not yet been established. Using Hinode SOT magnetograms and high-cadence EIS spectral data we study the relationship between chromospheric, transition region, and coronal emission and the evolution of the magnetic field. We find that hot, relatively steadily emitting coronal loops and isolated transient brightenings are both associated with magnetic flux regions that are highly dynamic. An essential difference, however, is that brightenings are typically found in regions of flux collision and cancellation whereas coronal loops are generally rooted in magnetic field regions that are locally unipolar with unmixed flux. This suggests that the type of heating (transient vs. steady) is related to the structure of the magnetic field, and that the heating in transient events may be fundamentally different than in coronal loops. This implies that they do not play an important role in heating the ``quiescent'' corona.

Brooks, David H.; Ugarte-Urra, Ignacio; Warren, Harry P.

2008-12-01

220

Solar wind collimation of the Jupiter high velocity dust streams  

NASA Astrophysics Data System (ADS)

The dust bursts discovered by the Ulysses dust sensor when approaching Jupiter in 1992 were later confirmed as collimated streams of high velocity (~200 km/s) charged (~5V) dust grains escaping from Jupiter and dominated by the interplanetary Magnetic field (IMF). With Cassini, a similar phenomenon was observed in Saturn. It was demonstrated that the Jovian dust streams are closely related to the solar wind compressed regions, either Corotating interaction regions (CIRs) or Coronal mass ejections (CMEs) ¨Cto a minor extent-. Actually the dust streams seem ultimately to be generated by such events. This can be explained considering that dust grains are accelerated as they gain substantial energy while compressed at the forward and reverse shocks that bound or precede these solar wind regions.

Flandes, A.; Krueger, H.

2006-12-01

221

Electrodynamic Shield to Remove Dust from Solar Panels on Mars  

Microsoft Academic Search

The Mars Opportunity rover in the current Mars mission has measured an obscuration of the solar arrays due to dust deposition at a rate of 0.15% per day. Dust deposition is the prime mission constraint of the duration for the two rovers operating now on Mars. At the Kennedy Space Center, we have developed a prototype Electrodynamic Shield to be

C. I. Calle; C. R. Buhler; J. G. Mantovani; S. Clements; A. Chen; M. K. Mazumder; A. S. Biris; A. W. Nowicki

222

Evolution of interstellar dust and stardust in the solar neighbourhood  

Microsoft Academic Search

Aims:We studied the evolution of the abundance in interstellar dust species that originate in stellar sources and from condensation in molecular clouds in the local interstellar medium of the Milky Way. We determined from this the input of dust material to the Solar System. Methods: A one-zone chemical evolution model of the Milky Way for the elemental composition of the

Svitlana Zhukovska; H.-P. Gail; Mario Trieloff

2008-01-01

223

Numerical modeling of type III solar radio bursts in the inhomogeneous solar corona and interplanetary medium  

SciTech Connect

The first numerical calculations are presented for type III solar radio bursts in the inhomogeneous solar corona and interplanetary medium that include microscale quasilinear and nonlinear processes, intermediate-scale driven ambient density fluctuations, and large-scale evolution of electron beams, Langmuir and ion-sound waves, and fundamental and harmonic electromagnetic emission. Bidirectional coronal radiation driven by oppositely directed beams is asymmetric between the upward and downward directions due to downward beam narrowing in velocity space, and harmonic emission dominates fundamental emission, consistent with observations and theoretical analysis. In the interplanetary medium, fundamental and/or harmonic emission can be important depending on beam parameters and plasma conditions. Furthermore, Langmuir waves are bursty, ion-sound waves also show some degree of irregularity, while electromagnetic radiations are relatively smooth, all qualitatively consistent with observations. Moreover, the statistics of Langmuir wave energy agree well with the predictions of stochastic growth theory, indicating that the beam-Langmuir wave system evolves to a stochastic growth state.

Li Bo; Robinson, Peter A.; Cairns, Iver H. [School of Physics, University of Sydney, New South Wales 2006 (Australia)

2006-09-15

224

Magnetic activity and the solar corona: first results from the Hinode satellite .  

NASA Astrophysics Data System (ADS)

The structure, dynamics and evolution of the solar corona are governed by the magnetic field. In spite of significant progresses in our insight of the physics of the solar corona, several problems are still under debate, e.g. the role of impulsive events and waves in coronal heating, and the origin of eruptions, flares and CMEs. The Hinode mission has started on 22 september 2006 and aims at giving new answers to these questions. The satellite contains three main instruments, two high resolution telescopes, one in the optical and one in the X-ray band, and an EUV imaging spectrometer. On the Italian side, INAF/Osservatorio Astronomico di Palermo has contributed with the ground-calibration of the filters of the X-ray telescope. We present some preliminary mission results, with particular attention to the X-ray telescope data.

Reale, Fabio; Parenti, Susanna; Reeves, Kathy K.; Weber, Mark; Bobra, Monica G.; Barbera, Marco; Kano, Ryohei; Narukage, Noriyuki; Shimojo, Masumi; Sakao, Taro; Peres, Giovanni; Golub, Leon

225

Simulation of electron acceleration by Alfvén waves in the lower solar corona  

NASA Astrophysics Data System (ADS)

Inertial Alfvén waves have been proposed to accelerate electrons in the low solar corona where they might cause hard X ray radiation during solar flare [Fletcher & Hudson 2008, ApJ, 675, 1645]. Due to their short transverse wave length inertial Alfvén waves carry a longitudinal electric field parallel to the background magnetic field. This longitudinal field can, in principle, reflect and accelerate electrons to velocities in excess of Alfvén wave velocity, i.e. to energies of the order of tens of keV. For this study an electromagnetic two-dimensional particle-in-cell simulation (2D EM PIC) code is used to verify the proposed electron acceleration mechanism in the plasma of the lower corona. To generate an incoming Alfvén wave, an antenna is placed at one boundary that generates sinusoidal oscillating perpendicular electric fields. The dispersion relations of the excited plasma waves and the response of the electrons in their velocities are discussed in this work.

Chai, LiHui; Lee, KuangWu; Büchner, Jörg

2013-04-01

226

Modeling the Solar Terrestrial Environment from the Corona to the Atmosphere  

NASA Astrophysics Data System (ADS)

Traditionally, numerical modeling has focused on distinct regions of the Solar Terrestrial Environment such as the corona, magnetosphere, or ionosphere/thermosphere (ITM). More recently several efforts have begun to model this closely coupled system through linking the regional codes together. We discuss here from the perspective of our project the characteristics of the individual codes, which are well known and respected in the SPA community: the SAIC corona code, the NCAR solar wind code, the LFM magnetosphere code, the Rice RCM, and NCAR ITM code (TING). We further discuss the issues important for coupling of these codes, and explore briefly the methods from the computational and computer sciences that may help address them.

Goodrich, C.; Drake, J.; Sussman, A.; Linker, J.; Lyon, J.; Odstrcil, D.; Toffoletto, F.; Wang, W.

2002-05-01

227

Combined Radio and X-ray Diagnostics of Electron Acceleration Region in the Solar Corona  

NASA Astrophysics Data System (ADS)

Solar flares are believed to accelerate both upward and downward propagating electron beams which can radiate emission at radio and X-ray wavelengths correspondingly. The correlation between X-ray and radio emissions in a well observed solar flare allowed us detailed study of the electron acceleration region properties. We used the Nancey Radioheliograph, Phoenix-2 and RHESSI to infer the type III position, type III starting frequency and spectral index of the HXR emission respectively. Using these datasets, we were able to infer not only the location (the height in the corona), but to estimate the spatial size of the electron acceleration site. Using numerical simulations of the electron transport of the electron beam in the corona plasma to relate X-ray and radio data, we find that the spatial size of 10 Mm at an altitude of 50 Mm above the photosphere are consistent with the observations.

Reid, H.; Vilmer, N.; Kontar, E. P.

2010-12-01

228

Dust acoustic instability driven by solar and stellar winds  

SciTech Connect

A quantitative analysis is presented of the dust acoustic wave instability driven by the solar or stelar wind. This is a current-less kinetic instability which develops in permeating plasmas, i.e.., when one quasi-neutral electron-ion plasma propagates through another quasi-neutral plasma which contains dust, electrons and ions. The cometary dusty plasma in the solar wind appears to be practically always unstable.

Vranjes, J. [Belgian Institute for Space Aeronomy, Ringlaan 3, 1180 Brussels (Belgium)

2011-11-29

229

Variations of radio-wave propagation conditions in the corona during a solar activity cycle  

Microsoft Academic Search

Variations of the propagation conditions of monochromatic radio waves through the solar corona during an 11-year cycle are analyzed on the basis of space-probe (Pioneer, Mariner, Mars, Venera, Helios, Viking, and Voyager) data. It is shown that, besides short-term variations of radio-signal parameters with a characteristic time of 5-20 days, there occur long-term variations of propagation conditions with periods of

A. I. Efimov; O. I. Iakovlev; V. K. Shtrykov; V. I. Rogalskii

1984-01-01

230

MAGNETIC FIELD TOPOLOGY AND THE THERMAL STRUCTURE OF THE CORONA OVER SOLAR ACTIVE REGIONS  

Microsoft Academic Search

Solar extreme ultraviolet (EUV) images of quiescent active-region coronae are characterized by ensembles of bright 1-2 MK loops that fan out from select locations. We investigate the conditions associated with the formation of these persistent, relatively cool, loop fans within and surrounding the otherwise 3-5 MK coronal environment by combining EUV observations of active regions made with TRACE with global

Carolus J. Schrijver; Marc L. DeRosa

2010-01-01

231

Magnetic Field Topology and the Thermal Structure of the Corona over Solar Active Regions  

Microsoft Academic Search

Solar extreme ultraviolet (EUV) images of quiescent active-region coronae are characterized by ensembles of bright 1-2 MK loops that fan out from select locations. We investigate the conditions associated with the formation of these persistent, relatively cool, loop fans within and surrounding the otherwise 3-5 MK coronal environment by combining EUV observations of active regions made with TRACE with global

Carolus J. Schrijver; Marc L. DeRosa

2010-01-01

232

Polarization observation of white light corona during the total solar eclipse on 2006 march 29  

NASA Astrophysics Data System (ADS)

The digital photographic records of the white light corona polarization were made during the total solar eclipse on March 29, 2006 in El-Saloum (Egypt). By means of a reflector telescope, f=640mm (f/D=8), 20 pictures were obtained with different exposure time and successive rotation of a polaroid by 45°. The main results about the degree and direction of polarization in the range of 1.3Rsolar < r < 3.0Rsolar are discussed and graphically presented.

Xu, Zhi; Zhang, Shu-Xin; Sin, Sun Ae; Pak, Hye Yong

2006-12-01

233

Heating and activity of the solar corona 1. Boundary shearing of an initially homogeneous magnetic field  

Microsoft Academic Search

To contribute to the understanding of heating and dynamic activity in boundary-driven, low-beta plasmas such as the solar corona, we investigate how an initially homogeneous magnetic field responds to random large-scale shearing motions on two boundaries, by numerically solving the dissipative MHD equations, with resolutions ranging from 243 to 1363. We find that even a single application of large-scale shear,

Klaus Galsgaard; Åke Nordlund

1996-01-01

234

On determining the electron density distribution of the solar corona from K-coronameter data  

Microsoft Academic Search

The electron density distribution of the inner solar corona (r ? 2 R?) as a function of latitude, longitude, and radial distance is determined from K-coronameter polarization-brightness (pB) data. A Legendre polynomial is assumed for the electron density distribution, and the coefficients of the polynomial are determined by a least-mean-square regression analysis of several days of pB-data. The calculated electron

Martin D. Altschuler; R. Michael Perry

1972-01-01

235

Observational Evidence of Resonantly Damped Propagating Kink Waves in the Solar Corona  

Microsoft Academic Search

In this Letter, we establish clear evidence for the resonant absorption damping mechanism by analyzing observational data from the novel Coronal Multi-Channel Polarimeter. This instrument has established that in the solar corona there are ubiquitous propagating low-amplitude (≈1 km s-1) Alfvénic waves with a wide range of frequencies. Realistically interpreting these waves as the kink mode from magnetohydrodynamic wave theory,

G. Verth; J. Terradas; M. Goossens

2010-01-01

236

Spectroscopic Constraints on Models of Ion-cyclotron Resonance Heating in the Polar Solar Corona  

Microsoft Academic Search

Using empirical velocity distributions derived from UVCS and SUMER ultraviolet spectroscopy, we construct theoretical models\\u000a of anisotropic ion temperatures in the polar solar corona. The primary energy deposition mechanism we investigate is the dissipation\\u000a of high frequency (10-10000 Hz) ion-cyclotron resonant Alfvén waves which can heat and accelerate ions differently depending\\u000a on their charge and mass. We find that it

S. R. Cranmer; G. B. Field; J. L. Kohl

1999-01-01

237

Heating of the solar corona by the resonant absorption of Alfven waves  

SciTech Connect

An improved method for calculating the resonance absorption heating rate is discussed and the results are compared with observations in the solar corona. To accomplish this, the wave equation for a dissipative, compressible plasma is derived from the linearized magnetohydrodynamic equations for a plasma with transverse Alfven speed gradients. For parameters representative of the solar corona, it is found that a two-scale description of the wave motion is appropriate. The large-scale motion, which can be approximated as nearly ideal, has a scale which is on the order of the width of the loop. The small-scale wave, however, has a transverse scale much smaller than the width of the loop, with a width of about 0.3-250 km, and is highly dissipative. These two wave motions are coupled in a narrow resonance region in the loop where the global wave frequency equals the local Alfven wave frequency. Formally, this coupling comes about from using the method of matched asymptotic expansions to match the inner and outer (small and large scale) solutions. The resultant heating rate can be calculated from either of these solutions. A formula derived using the outer (ideal) solution is presented, and shown to be consistent with observations of heating and line broadening in the solar corona. 34 references.

Davila, J.M.

1987-06-01

238

Moon Dust Telescopes, Solar Concentrators, and Structures  

NASA Astrophysics Data System (ADS)

We report development of an ISRU (in situ resource utilization) process to fabricate large telescope mirrors, solar concentrators, and structures on the Moon. The Moon is an excellent site for a future space base and space astrophysics research. However transporting extremely large (10-50m) telescopes to the Moon, building up an observatory structure, and providing power for operation face the obstacles of high cost and logistical difficulties. We suggest a simple and novel approach to the problem. Large mirrors can be made by spincasting a liquid over or mixed with lunar surface soil (regolith). The liquid, which is a special vacuum stable cryogenic polymer, gradually solidifies while spun into a hard parabolic surface. Additives including carbon nanotubes and fibers can be used to increase tensile strength, reduce cure shrinkage, and enhance thermal conductivity. The process uses a single apparatus to make multiple mirrors. Large arrays of solar concentrators can be fabricated to provide power to a lunar base. For astronomy, the mirror surface can be polished or modified in situ with an ion beam like process taking advantage of the high vacuum of the lunar environment. Moreover, we have found that the simple process of mixing a small amount of polymer with lunar regolith yields after curing a material similar to cement in terms of strength, density, and consistency. This `lunar cement’ may be useful as building blocks for human habitats and telescope structures. We report on experiments carried out at GSFC to demonstrate feasibility of the concept. Mirrors and bricks have been made by curing a cryogenic polymer with added JSC-1A Fine lunar soil simulant and carbon nanotubes. Preliminary observations have been carried out using such `Moon dust’ mirrors.

Chen, Peter C.; Van Steenberg, M. E.; Oliversen, R. J.

2008-05-01

239

Dust Measurements in the Outer Solar System by the Student Dust Counter  

NASA Astrophysics Data System (ADS)

The Student Dust Counter (SDC) is an impact dust detector on board the New Horizons Mission to Pluto. SDC was designed to resolve the mass of dust grains in the range of 10^-12 < m < 10^-9 g, covering an approximate size range of 0.5-10 um in particle radius. The measurements can be directly compared to the prediction of a grain tracing trajectory model of dust originating from the Edgeworth-Kuiper Belt. SDC's results are compared to our model to derive estimates for the mass production rate and the ejecta mass distribution power law exponent. Through October 2013, the New Horizons spacecraft reached approximately 27.5 AU, enabling SDC to map the dust density distribution of the solar system farther than any previous dust detector.

Szalay, Jamey; Horanyi, M.

2013-10-01

240

On a source of Alfven waves heating the solar corona  

Microsoft Academic Search

Studies of the origin of coronal heating and acceleration of the solar wind invoke high-frequency Alfv{e}n waves. Here we suggest a source for such waves associated with twisted magnetic loops emerging on the solar surface and reconnecting with the open field. We identify the loops with the ephemeral regions (small-scale bipoles) observed by ground-based instruments and by SOHO. To characterize

Alexander Ruzmaikin; Mitchell A. Berger

1998-01-01

241

Migration of dust in the solar system  

NASA Astrophysics Data System (ADS)

The migration of dust particles under the gravitational influence of all planets, radiation pressure, Poynting--Robertson drag and solar wind drag was investigated for the ratio between the radiation pressure force and the gravitational force ? = 0.01, 0.05, 0.1, 0.25, and 0.4 with a Bulirsh-Stoer integrator. For silicate particles such values of ? correspond to diameters of about 40, 9, 4, 2, and 1 micron, respectively. Initial orbits of the particles were close to the orbits of the first numbered main-belt asteroids or trans-Neptunian objects. Below we present the results for asteroidal dust. The smaller are the particles, the lower is the probability of their collisions with the terrestrial planets. 32%, 62%, and ?99% of particles collided with the Sun during their lifetimes (<0.8 Myr) at ? = 0.4, ? = 0.2, and ? ? 0.1, respectively. The number na of migrating particles with semi-major axis a in intervals with a fixed width is greater for smaller ? (for the same initial number of particles) at a<3 AU. For ? ? 0.1 the values of na are much smaller at a>3.5 AU than at 110 AU perihelia were usually near Jupiter's orbit (for ? = 0.05 and ? = 0.25 also near Saturn's orbit). In almost all cases, inclinations i < 50o; at a>10 AU maximum i was smaller for smaller ?. Usually there are no particles with h/R>0.7 at R<10 AU, with h/R>0.25 at R>20 AU for ? ? 0.1, and with h/R>0.5 at R>50 AU for ? ?0.25, where R is the distance from the Sun and h is the height above the initial plane of the Earth's orbit. The total time spent by 250 particles in inner-Earth, Aten, Apollo and Amor orbits was 5.6, 1.4, 4.5, and 7.5 Myr at ? = 0.01, and 0.09, 0.08, 0.48, and 0.76 Myr at ? = 0.4, respectively. The spatial density of a dust cloud and its luminosity (as seen from outside) were greater for smaller R. For example, depending on ? they were greater at 1 AU than at 3 AU by a factor of 2.5-8 and 7-25, respectively. For migrating dust particles with initial orbits close to those of trans-Neptunian objects, we usually obtained h/R<0.5, and the ratio of the number of particles at h = kR was about 10% of the number at h = 0 usually at k = 0.1, but sometimes at k = 1/4. At ? = 0.4 most particles were outside 50 AU after only 0.02 Myr. This work was supported by NASA (NAG5-10776), INTAS (00-240), and RFBR (01-02-17540).

Ipatov, S. I.; Mather, J. C.; Taylor, P. A.

242

Structure and photometry of the solar corona at the total eclipse of 1997 March 9  

NASA Astrophysics Data System (ADS)

At the solar total eclipse of 1997 March 9, we made a series of photographic observations of the solar corona in Mohe City (Xilinji), Heilongjiang Province. On images taken with different exposures, there are many characteristic coronal structures including long and broad coronal streamers in both east and west equatorial regions, plumes containing over 20 polar rays as well as coronal holes in both south and north polar regions. Comprehensive results of measurements of the structures and brightness in the coronal images, and of the morphology and structures, and isophotometric contours and brightness profiles in both east and west equatorial regions and both south and north polar regions are presented.

Hu, Zhong-wei; Fang, Cheng; Xu, Shi-zhong; Yan, Jia-rong; Wang, Yong; Chen, Dong-hua; Hollstein, S.

243

MHD Wave Turbulence as the Energy and Momentum Source for Heating the Solar Corona and Driving the Solar Wind in Global Space Weather Models  

NASA Astrophysics Data System (ADS)

Recent Hinode observations upped the estimates for the energy associated with Alfven waves generated in the solar chromosphere. This energy has been found to be sufficient to heat the solar corona and to explain the solar wind acceleration and heating. At present time, many physical models for the coronal heating, the solar wind, as well as the energetic particle acceleration and transport, incorporate the MHD wave turbulence. This paper presents a new model for coronal heating which adopts MHD wave turbulence as the dominant energy for heating the solar corona and driving the solar wind. We re-formulate an empirical model for the coronal heating in terms of the dissipation length controlling the wave damping. The model for the solar corona is validated against EUV observations from the EIT instrument on-board SOHO.

Sokolov, I.; Roussev, I. I.; Gombosi, T. I.; Downs, C.

2011-12-01

244

MESSENGER Observations of Magnetohydrodynamic Waves in the Solar Corona from Faraday Rotation  

NASA Astrophysics Data System (ADS)

During the declining phase of the longest solar minimum in a century, the arrival of the MESSENGER spacecraft at superior conjunction allowed the measurement of magnetohydrodynamic (MHD) waves in the solar corona with its 8 GHz radio frequency signal. MHD waves crossing the line of sight were measured via Faraday rotation fluctuations (FRFs) in the plane of polarization (PP) of MESSENGER's signal. FRFs in previous observations of the solar corona (at greater offset distances) consisted of a turbulent spectrum that decreased in power with increasing frequency and distance from the Sun. Occasionally a spectral line, a distinct peak in the power spectral density spectrum around 4 to 8 mHz, was also observed in these early data sets at offset distances of about 5 to 10 solar radii. The MESSENGER FRF data set shows a spectral line at an offset distance between 1.55 to 1.85 solar radii with a frequency of 0.6±0.2 mHz. Other possible spectral lines may be at 1.2, 1.7, and 4.5 mHz; MHD waves with these same frequencies have been observed in X-ray data traveling along closed coronal loops at lower offset distances. An initial analysis of the MESSENGER spectral line(s) shows behavior similar to turbulent spectra: decreasing power with increasing frequency and distance from the Sun. Here we detail the steps taken to process the MESSENGER change in PP data set for the MHD wave investigation.

Jensen, E. A.; Nolan, M.; Bisi, M. M.; Chashei, I.; Vilas, F.

2013-07-01

245

Solar activity and its evolution across the corona: recent advances  

NASA Astrophysics Data System (ADS)

Solar magnetism is responsible for the several active phenomena that occur in the solar atmosphere. The consequences of these phenomena on the solar-terrestrial environment and on Space Weather are nowadays clearly recognized, even if not yet fully understood. In order to shed light on the mechanisms that are at the basis of the Space Weather, it is necessary to investigate the sequence of phenomena starting in the solar atmosphere and developing across the outer layers of the Sun and along the path from the Sun to the Earth. This goal can be reached by a combined multi-disciplinary, multi-instrument, multi-wavelength study of these phenomena, starting with the very first manifestation of solar active region formation and evolution, followed by explosive phenomena (i.e., flares, erupting prominences, coronal mass ejections), and ending with the interaction of plasma magnetized clouds expelled from the Sun with the interplanetary magnetic field and medium. This wide field of research constitutes one of the main aims of COST Action ES0803: Developing Space Weather products and services in Europe. In particular, one of the tasks of this COST Action was to investigate the Progress in Scientific Understanding of Space Weather. In this paper we review the state of the art of our comprehension of some phenomena that, in the scenario outlined above, might have a role on Space Weather, focusing on the researches, thematic reviews, and main results obtained during the COST Action ES0803.

Zuccarello, Francesca; Balmaceda, Laura; Cessateur, Gael; Cremades, Hebe; Guglielmino, Salvatore L.; Lilensten, Jean; Dudok de Wit, Thierry; Kretzschmar, Matthieu; Lopez, Fernando M.; Mierla, Marilena; Parenti, Susanna; Pomoell, Jens; Romano, Paolo; Rodriguez, Luciano; Srivastava, Nandita; Vainio, Rami; West, Matt; Zuccarello, Francesco P.

2013-04-01

246

Reconciling Spectroscopic Electron Temperature Measurements in the Solar Corona with In Situ Charge State Observations.  

PubMed

It has been a puzzle for quite some time that spectroscopic measurements in the inner corona indicate electron temperatures far too low to produce the ion fractions observed in situ in the solar wind. In the present Letter, we show that in order to reconcile the two sets of measurements, a number of conditions have to exist in the inner corona: (1) The electron distribution function has to be Maxwellian or close to Maxwellian at the coronal base, (2) the non-Maxwellian character of the distribution has to develop rapidly as a function of height and has to reach close to interplanetary properties inside of a few solar radii, and (3) ions of different elements have to flow with significantly different speeds to separate their "freezing-in" distances sufficiently so that they can encounter different distribution functions. We choose two examples to demonstrate that these conditions are general requirements if both coronal electron temperatures and in situ ion fractions are correct. However, these two examples also show that the details of the required distribution functions are very sensitive to the exact electron temperature, density, and ion flow speed profiles in the region of the corona where the ions predominantly form. PMID:10702135

Esser; Edgar

2000-03-20

247

Developing a Thermodynamic MHD Model of the Global Solar Corona with the SWMF  

NASA Astrophysics Data System (ADS)

Here we present ongoing work focused on improving the physical description of the low corona and transition region within a global 3D MHD model of the solar corona based on the Space Weather Modeling Framework. This work includes the integration of the non-ideal effects of coronal heating, electron heat conduction, and radiative cooling into MHD equations and solar wind model. Via observation synthesis and the subsequent comparison to full sun EUV observations, we demonstrate the need for these additional considerations when using MHD models to describe the unique conditions in the low corona. Additionally we present the results of two different boundary conditions using this model; one set in the upper transition region (the Radiative Energy Balance model), as well as a uniform chromospheric boundary condition where the transition region can be modeled in its entirety. We also explore bias and limitations inherent in line-of-sight (LOS) image synthesis and explore this in terms of comparison to EUV data.

Downs, C.; Roussev, I. I.; Lugaz, N.; Sokolov, I.

2009-12-01

248

Kuiper Belt dust in the inner and outer Solar System  

NASA Astrophysics Data System (ADS)

The dust produced in the Kuiper Belt (KB) spreads throughout the Solar System forming a dust disk. We have numerically modelled the dynamical evolution of KB dust grains using a modified symplectic integrator which resolves close planetary encounters and includes solar wind and radiation forces. We report here a selection of results from our modeling efforts. (1) We find that the particle size frequency distribution of KB dust is greatly changed from its distribution at production, due to the combined effects of radiation forces and the perturbations of the planets. In particular, the gravitational scattering of dust by the giant planets is able to extend the dust disk beyond the boundaries set by radiation effects alone, and consequently, the size distribution is greatly different at large distances. We plan to investigate the potential of this effect for the detection of planets in debris disks. We also point out that the detection of circumstellar dust disks of wide radial extent, 100 to 1000's of AU, does not necessarily imply the presence of dust-producing planetesimals at such large distances, because the presence of giant planets at much smaller semimajor axes can lead to the spreading of the dust to distances much larger than the aphelion of the parent bodies. (2) We have estimated the contribution of KB dust to the population of IDPs collected at Earth, by calculating geocentric encountering velocities and capture rates. Our models show, in contrast with previous studies, that KB dust grains on Earth-crossing orbits have high eccentricities and inclinations, and therefore their encountering velocities are similar to cometary grains and not to asteroidal grains. We estimate that at most 25% of captured IDPs have cometary or KB origin. Using the Kuiper Belt dust production rates derived from detectors on board Pioneer 10 and 11 spacecraft (Landgraf et al. 2002), we find that presently the KB contribution may be as low as 1-2%. (3) We have calculated the velocity field of KB dust throughout the Solar System; this, together with the number density radial profile, is potentially useful for designing dust detection instruments for future spacecraft missions, as well as for estimating the hazard to space probes in the outer Solar System.

Moro-Martin, A.; Malhotra, R.

2002-09-01

249

Theory of magnetic connectivity in the solar corona  

Microsoft Academic Search

Although the analysis of observational data indicates that quasi-separatrix layers (QSLs) of magnetic configurations have to play an important role in solar flares, the corresponding theory is only at an initial stage so far. In particular, there is still a need of a proper definition of QSLs based on a comprehensive mathematical description of magnetic connectivity. Such a definition is

Vyacheslav S. Titov; Gunnar Hornig; Pascal Démoulin

2002-01-01

250

Observational Evidence for Nanoflares Heating the Solar Corona  

Microsoft Academic Search

We investigated intensity and small fluctuations of the X-ray and EUV coronal emission by using simultaneous Solar Active region observations with the Soft X-ray Telescope (SXT) of the Yohkoh mission, and with the Transition Region and Coronal Explorer (TRACE). It is found that the TRACE light curves exhibit fluctuations which are significantly larger than the estimated photon noise and other

G. Vekstein; Y. Sakamoto; S. Tsuneta

2008-01-01

251

MHD waves and heating of the solar corona  

Microsoft Academic Search

Magnetohydrodynamic (MHD) waves play an important role in the solar atmosphere both directly (or intrinsically), e.g. as the main drivers or causes of atmospheric phenomena, and indirectly, e.g. as diagnostic tools for investigating the inner structure and physical properties of the magnetic configurations observed on the Sun. As a matter of fact, this research domain is actually a 'hot topic'

Stefan Poedts

2002-01-01

252

Modelling the Large Scale Structure of the Solar Corona.  

National Technical Information Service (NTIS)

A quantitative description of the large scale structure of magnetic field and density distribution in the coronal plasma is found. The magnetostatic model of Bogdan and Low and white light images from both NASA's Solar Maximum Mission (SMM) Coronagraph/Po...

S. Gibson F. Bagenal

1992-01-01

253

MHD simulations of the global solar corona around the Halloween event in 2003 using the synchronic frame format of the solar photospheric magnetic field  

Microsoft Academic Search

We performed two time-relaxation magnetohydrodynamics (MHD) simulations of the solar corona: one uses the boundary map representing the solar surface magnetic field distribution before the Halloween event in 2003, and the other uses map representing the postevent distribution. The aims of this study are to test a new concept of a solar surface magnetic field map capable of representing a

Keiji Hayashi; Xue Pu Zhao; Yang Liu

2008-01-01

254

Propagation of Alfvénic Waves from Corona to Chromosphere and Consequences for Solar Flares  

NASA Astrophysics Data System (ADS)

How do magnetohydrodynamic waves travel from the fully ionized corona, into and through the underlying partially ionized chromosphere, and what are the consequences for solar flares? To address these questions, we have developed a two-fluid model (of plasma and neutrals) and used it to perform one-dimensional simulations of Alfvén waves in a solar atmosphere with realistic density and temperature structure. Studies of a range of solar features (faculae, plage, penumbra, and umbra) show that energy transmission from corona to chromosphere can exceed 20% of incident energy for wave periods of 1 s or less. Damping of waves in the chromosphere depends strongly on wave frequency: waves with periods 10 s or longer pass through the chromosphere with relatively little damping, however, for periods of 1 s or less, a substantial fraction (37%-100%) of wave energy entering the chromosphere is damped by ion-neutral friction in the mid- and upper chromosphere, with electron resistivity playing some role in the lower chromosphere and in umbras. We therefore conclude that Alfvénic waves with periods of a few seconds or less are capable of heating the chromosphere during solar flares, and speculate that they could also contribute to electron acceleration or exciting sunquakes.

Russell, A. J. B.; Fletcher, L.

2013-03-01

255

Rocket studies of solar corona and transition region  

Microsoft Academic Search

The XSST (X-Ray Spectrometer\\/Spectrograph Telescope) rocket payload launched by a Nike Boosted Black Brant was designed to provide high spectral resolution coronal soft X-ray line information on a spectrographic plate, as well as time resolved photo-electric records of pre-selected lines and spectral regions. This spectral data is obtained from a 1 x 10 arc second solar region defined by the

L. W. Acton; E. C. Bruner Jr.; W. A. Brown; R. A. Nobles

1979-01-01

256

Magnetic loops, downflows, and convection in the solar corona  

Microsoft Academic Search

Optical and extreme-ultraviolet observations of solar loop structures show that flows of cool plasma from condensations near the loop apex are a common property of loops associated with radiations whose maximum temperature is greater than approximately 7000 K and less than approximately 3,000,000 K. It is suggested that the mass balance of these structures indicates reconnection by means of plasma

P. Foukal

1978-01-01

257

The filtering of interstellar dust in the solar system  

NASA Astrophysics Data System (ADS)

Context. Theoretical predictions demonstrate that small (<0.1 ?m) interstellar grains are mostly excluded from reaching the planetary system by electromagnetic interactions in the heliopause region and in the inner heliosphere. Bigger interstellar grains have been recorded in the planetary system by dust measurements on board Ulysses and other spacecraft. It was found that the interstellar dust flux is modulated by the interplanetary magnetic field. Aims: The objective of this study is to analyze the heliospheric filtering of the interstellar dust flow through the solar system and throughout the solar cycle. In the heliosphere the dynamics of interstellar dust is governed by the gravitational pull of the Sun, by the repulsion of solar radiation, and by the deflection caused by the interaction of the charged interstellar dust (ISD) grains with the interplanetary magnetic field. These interactions are described by the parameters of the radiation pressure constant ? and the charge-to-mass ratio Q/m, which depend on the particle's size, physical properties, and composition. A previous paper studied the flow characteristics of ISD moving through the solar system were studied. In this follow-up paper, we focus on how the ISD size distribution varies during its passage through the solar system. Methods: In a parametric study of 70 different ? and Q/m values, we calculated interstellar dust trajectories starting at the boundary of the heliosphere with starting times spread over a complete solar cycle of 22 years. Results: As a result we obtained the interstellar dust flux and dust speed for these times and positions and demonstrate the effects of the filtering on the dust size distributions. The size distribution of ISD observed at any time and at any position in the planetary system is strongly modified from when it entered the heliosphere. Peaks in relative flux of 10 times the original flux possibly depend on the grain size and place and time in the solar system. We did a detailed study of three cases of the flux and size distribution of interstellar grains reaching the planets Saturn, Jupiter, and the main-belt asteroid Ceres. These cases are used to get a first idea of what a dust detector or collector on a mission to these bodies might see of ISD. Appendices are available in electronic form at http://www.aanda.org

Sterken, V. J.; Altobelli, N.; Kempf, S.; Krüger, H.; Srama, R.; Strub, P.; Grün, E.

2013-04-01

258

Turbulent Alfven Waves as a Solar Wind Driver: Results from a new 4D model for the Solar Corona and Solar Wind  

NASA Astrophysics Data System (ADS)

The mechanisms responsible for plasma heating in the solar corona and solar wind acceleration are still not well understood. Turbulent MHD waves have been suggested as a possible mechanism, which both heats the plasma via wave energy dissipation and accelerates it due to the wave pressure gradient force. In order to account for these processes, a self-consistent model of the solar corona and solar wind must include the wave transport equation. Coupling this equation to the 3D MHD equations allows the exchange of momentum and energy between the wave field and the background plasma. This coupled system of equations is solved in a recently developed computational model of MHD wave turbulence, implemented within the SWMF/BATSRUS. The model is based on a wave transport equation for low frequency Alfven waves derived in Sokolov et. al. (2009). In every spatial cell a frequency grid is constructed, allowing the detailed description of the wave energy spectral evolution, making the model effectively 4D. Recent Hinode observations of chromospheric Alfven waves have shown that their energy flux could constitute a sufficient energy source to drive the solar wind. In this work we examined the possible effects of Alfven wave turbulence by imposing a Kolmogorov - type spectrum as the inner boundary condition for the 4D solar corona model. We found that the solar wind can indeed be totally driven by the Alfven wave pressure. The 4D solar corona model is coupled to an MHD model of the inner heliosphere, which extends the simulation results to larger heliocentric distances. This allows us to compare our results to solar wind in situ data at 1AU.

Oran, R.; Sokolov, I.; Roussev, I. I.; Frazin, R. A.; Gombosi, T. I.

2009-12-01

259

SWAP Observations of the Long-term, Large-scale Evolution of the Extreme-ultraviolet Solar Corona  

NASA Astrophysics Data System (ADS)

The Sun Watcher with Active Pixels and Image Processing (SWAP) EUV solar telescope on board the Project for On-Board Autonomy 2 spacecraft has been regularly observing the solar corona in a bandpass near 17.4 nm since 2010 February. With a field of view of 54 × 54 arcmin, SWAP provides the widest-field images of the EUV corona available from the perspective of the Earth. By carefully processing and combining multiple SWAP images, it is possible to produce low-noise composites that reveal the structure of the EUV corona to relatively large heights. A particularly important step in this processing was to remove instrumental stray light from the images by determining and deconvolving SWAP's point-spread function from the observations. In this paper, we use the resulting images to conduct the first-ever study of the evolution of the large-scale structure of the corona observed in the EUV over a three year period that includes the complete rise phase of solar cycle 24. Of particular note is the persistence over many solar rotations of bright, diffuse features composed of open magnetic fields that overlie polar crown filaments and extend to large heights above the solar surface. These features appear to be related to coronal fans, which have previously been observed in white-light coronagraph images and, at low heights, in the EUV. We also discuss the evolution of the corona at different heights above the solar surface and the evolution of the corona over the course of the solar cycle by hemisphere.

Seaton, Daniel B.; De Groof, Anik; Shearer, Paul; Berghmans, David; Nicula, Bogdan

2013-11-01

260

Evolución de la Estructura Térmica Global de la Corona alrededor del Último Mínimo de Actividad Solar  

NASA Astrophysics Data System (ADS)

We study the solar corona temperature structure during several Carrington rotations (CR) around the last minimum of solar activity (CR 2077). The combination of Differential Emission Measure Tomography (DEMT) with magnetic models allows determination of the electron density and electron temperature along individual magnetic field lines. Two types of quiet Sun (QS) coronal loops were identified: "up" loops in which the temperature increases with height, and "down" loops in which the temperature decreases with height. We find that the population of up loops dominates the intermediate latitudes, while down loops are always located in the low-latitude region. We also find that the population of down loops was maximum at solar minimum. FULL TEXT IN SPANISH

Nuevo, F. A.; Vásquez, A. M.; Huang, Z.; Frazin, R. A.

261

SIMULATIONS OF PROMINENCE FORMATION IN THE MAGNETIZED SOLAR CORONA BY CHROMOSPHERIC HEATING  

SciTech Connect

Starting from a realistically sheared magnetic arcade connecting the chromospheric, transition region to coronal plasma, we simulate the in situ formation and sustained growth of a quiescent prominence in the solar corona. Contrary to previous works, our model captures all phases of the prominence formation, including the loss of thermal equilibrium, its successive growth in height and width to macroscopic dimensions, and the gradual bending of the arched loops into dipped loops, as a result of the mass accumulation. Our 2.5 dimensional, fully thermodynamically and magnetohydrodynamically consistent model mimics the magnetic topology of normal-polarity prominences above a photospheric neutral line, and results in a curtain-like prominence above the neutral line through which the ultimately dipped magnetic field lines protrude at a finite angle. The formation results from concentrated heating in the chromosphere, followed by plasma evaporation and later rapid condensation in the corona due to thermal instability, as verified by linear instability criteria. Concentrated heating in the lower atmosphere evaporates plasma from below to accumulate at the top of coronal loops and supply mass to the later prominence constantly. This is the first evaporation-condensation model study where we can demonstrate how the formed prominence stays in a force balanced state, which can be compared to the Kippenhahn-Schlueter type magnetohydrostatic model, all in a finite low-beta corona.

Xia, C.; Chen, P. F. [School of Astronomy and Space Science, Nanjing University, Nanjing 210093 (China); Keppens, R., E-mail: chenpf@nju.edu.cn [Centre for Plasma Astrophysics, Department of Mathematics, K.U. Leuven, Celestijnenlaan 200B, 3001 Heverlee (Belgium)

2012-04-01

262

Coupling the solar surface and the corona: Coronal rotation, Alfvén wave-driven polar plumes  

NASA Astrophysics Data System (ADS)

The dynamical response of the solar corona to surface and sub-surface perturbations depends on the chromospheric stratification, and specifically on how efficiently these layers reflect or transmit incoming Alfvén waves. While it would be desirable to include the chromospheric layers in the numerical simulations used to study such phenomena, that is most often not feasible. We defined and tested a simple approximation allowing the study of coronal phenomena while taking into account a parametrised chromospheric reflectivity. We addressed the problems of the transmission of the surface rotation to the corona and that of the generation of polar plumes by Alfvén waves [1, 2]. We found that a high (yet partial) effective chromospheric reflectivity is required to properly describe the angular momentum balance in the corona and the way the surface differential rotation is transmitted upwards. Alfvén wave-driven polar plumes maintain their properties for a wide range of values for the reflectivity, but they become bursty (and eventually disrupt) when the limit of total reflection is attained.

Pinto, R. F.; Grappin, R.; Velli, M.; Verdini, A.

2013-06-01

263

Angular scattering of radio waves: Implications for mode coupling in the solar corona  

NASA Astrophysics Data System (ADS)

The solar corona is highly inhomogeneous. The magnetionic modes may therefore couple under certain circumstances, and the polarization properties of solar radio sources may, as a consequence, be modified. An application of the simple theory of mode coupling to the propagation of radio waves in the solar corona leads to the expectation that mode coupling in quasi-transverse (QT) magnetic field regions should always be weak (coupling ratio Q much less than 1) at meter wavelengths. Observations to date suggest that, on the contrary, mode coupling is moderate (Q approximately 1) to strong (Q much greater than 1) in QT regions at meter wavelengths. I suggest that observations and theory can be reconciled by including the effect of turbulence on mode coupling. Specifically, angular scattering on turbulent inhomogeneities greatly reduces the spatial scale relevant to the theory at low frequencies. As a result, the coupling ratio is increased by a corresponding factor and mode coupling may be moderate to strong in QT regions at meter wavelengths.

Bastian, T. S.

1995-01-01

264

STEREO Observations of Fast Magnetosonic Waves in the Extended Solar Corona Associated with EIT/EUV Waves  

NASA Astrophysics Data System (ADS)

We report white-light observations of a fast magnetosonic wave associated with a coronal mass ejection observed by STEREO/SECCHI/COR1 inner coronagraphs on 2011 August 4. The wave front is observed in the form of density compression passing through various coronal regions such as quiet/active corona, coronal holes, and streamers. Together with measured electron densities determined with STEREO COR1 and Extreme UltraViolet Imager (EUVI) data, we use our kinematic measurements of the wave front to calculate coronal magnetic fields and find that the measured speeds are consistent with characteristic fast magnetosonic speeds in the corona. In addition, the wave front turns out to be the upper coronal counterpart of the EIT wave observed by STEREO EUVI traveling against the solar coronal disk; moreover, stationary fronts of the EIT wave are found to be located at the footpoints of deflected streamers and boundaries of coronal holes, after the wave front in the upper solar corona passes through open magnetic field lines in the streamers. Our findings suggest that the observed EIT wave should be in fact a fast magnetosonic shock/wave traveling in the inhomogeneous solar corona, as part of the fast magnetosonic wave propagating in the extended solar corona.

Kwon, Ryun-Young; Ofman, Leon; Olmedo, Oscar; Kramar, Maxim; Davila, Joseph M.; Thompson, Barbara J.; Cho, Kyung-Suk

2013-03-01

265

Turbulent Alfven Waves in the Solar Corona and Solar Wind: A Self Consistent 4D Global Model  

NASA Astrophysics Data System (ADS)

Turbulent MHD waves have been suggested as a possible mechanism to heat and accelerate the plasma in the solar corona and solar wind. Heating is achieved by wave energy dissipation and acceleration is due to the wave pressure gradient force. Here we present a self-consistent model describing these processes, which is based on a wave transport equation for low frequency Alfven waves coupled to the 3D MHD equations (Sokolov et. al. 2009). This allows the exchange of momentum and energy between the wave field and the background plasma. In a recently developed computational model, the coupled system of wave transport equation and the MHD equations is solved. The coupling is achieved by constructing a frequency grid in each spatial cell, allowing the detailed description of the wave energy spectral evolution, making the model effectively 4D. The model is based on an existing global solar corona model (Cohen et. al. 2005). In this work we examined the possible effects of Alfven wave turbulence by imposing inner boundary conditions for the wave energy spectral density by assuming a Kolmogorov - type frequency dependence, and a surface distribution derived from observable quantities. We found that Alfven wave pressure is sufficient to drive the solar wind. Different assumptions regarding the total wave energy at the surface are discussed and compared.

Oran, Rona; Sokolov, I. V.; Van Der Holst, B.; Roussev, I. I.; Manchester, W. B.; Gombosi, T. I.; for Space Environment Modeling, Center

2010-05-01

266

Radio Tracking of a White-Light Coronal Mass Ejection from Solar Corona to Interplanetary Medium.  

PubMed

For a solar flare/coronal mass ejection (CME) event on 1999 May 3, type II radio emissions were observed from the metric through the hectometric wavelength regimes. By comparing the dynamics of the CME with that implied by the frequency range and frequency drift rates of the type II radio emissions, it is concluded that the decametric-hectometric type II radio emissions were associated with the CME. The dynamics implied by the metric type II radio burst suggest a distinct coronal shock, associated with the flare, which only produced radio emissions in the low corona. PMID:10615035

Reiner; Kaiser; Plunkett; Prestage; Manning

2000-01-20

267

Coexistence of self-organized criticality and intermittent turbulence in the solar corona.  

PubMed

An extended data set of extreme ultraviolet images of the solar corona provided by the SOHO spacecraft is analyzed using statistical methods common to studies of self-organized criticality (SOC) and intermittent turbulence (IT). The data exhibit simultaneous hallmarks of both regimes: namely, power-law avalanche statistics as well as multiscaling of structure functions for spatial activity. This implies that both SOC and IT may be manifestations of a single complex dynamical process entangling avalanches of magnetic energy dissipation with turbulent particle flows. PMID:17678227

Uritsky, Vadim M; Paczuski, Maya; Davila, Joseph M; Jones, Shaela I

2007-07-11

268

Coexistence of Self-Organized Criticality and Intermittent Turbulence in the Solar Corona  

NASA Astrophysics Data System (ADS)

An extended data set of extreme ultraviolet images of the solar corona provided by the SOHO spacecraft is analyzed using statistical methods common to studies of self-organized criticality (SOC) and intermittent turbulence (IT). The data exhibit simultaneous hallmarks of both regimes: namely, power-law avalanche statistics as well as multiscaling of structure functions for spatial activity. This implies that both SOC and IT may be manifestations of a single complex dynamical process entangling avalanches of magnetic energy dissipation with turbulent particle flows.

Uritsky, Vadim M.; Paczuski, Maya; Davila, Joseph M.; Jones, Shaela I.

2007-07-01

269

Coexistence of Self-Organized Criticality and Intermittent Turbulence in the Solar Corona  

SciTech Connect

An extended data set of extreme ultraviolet images of the solar corona provided by the SOHO spacecraft is analyzed using statistical methods common to studies of self-organized criticality (SOC) and intermittent turbulence (IT). The data exhibit simultaneous hallmarks of both regimes: namely, power-law avalanche statistics as well as multiscaling of structure functions for spatial activity. This implies that both SOC and IT may be manifestations of a single complex dynamical process entangling avalanches of magnetic energy dissipation with turbulent particle flows.

Uritsky, Vadim M.; Paczuski, Maya [Complexity Science Group, Department of Physics and Astronomy, University of Calgary, Calgary, Alberta, T2N 1N4 (Canada); Davila, Joseph M. [NASA Goddard Space Flight Center, Greenbelt, Maryland 20771 (United States); Jones, Shaela I. [University of Maryland, College Park, Maryland 20742 (United States)

2007-07-13

270

Multi-Spacecraft 3D differential emission measure tomography of the solar corona: STEREO results.  

NASA Astrophysics Data System (ADS)

We have recently developed a novel technique (called DEMT) for the em- pirical determination of the three-dimensional (3D) distribution of the so- lar corona differential emission measure through multi-spacecraft solar ro- tational tomography of extreme-ultaviolet (EUV) image time series (like those provided by EIT/SOHO and EUVI/STEREO). The technique allows, for the first time, to develop global 3D empirical maps of the coronal elec- tron temperature and density, in the height range 1.0 to 1.25 RS . DEMT constitutes a simple and powerful 3D analysis tool that obviates the need for structure specific modeling.

Vásquez, A. M.; Frazin, R. A.

271

Detection of Extra Solar Zodiacal Dust Emission with the MMA  

NASA Astrophysics Data System (ADS)

The current plans for the Millimeter Array hold the promise that this instrument will be capable of detecting dusty disks around nearby stars with high spatial resolution. While systems with dust levels comparable to that in our own Solar system are to faint to be detected, systems with dust of 100 times solar values will be detectable. For the dustiest systems known, imaging of the inner parts of the dusty disks will be possible. In this paper I present the results of the expected emission from a complete set of nearby stars.

Simon, R. S.

1997-12-01

272

Feasibility of using solar power on Mars - Effects of dust storms on incident solar radiation  

Microsoft Academic Search

If the potential use of solar power is to be evaluated for a manned Mars mission, an effective and accurate model of the effects of latitude, season, and atmospheric turbidity on incident solar radiation is required. This paper presents a preliminary dust storm model based on data taken from cameras located on the Viking Landers. The solar radiation incident at

Scott Geels; John B. Miller; Benton C. Clark

1989-01-01

273

Measurements of Faraday Rotation Through the Solar Corona During the 2009 Solar Minimum with the MESSENGER Spacecraft  

NASA Astrophysics Data System (ADS)

Measurements of Faraday rotation through the solar corona were collected using the radio beacon aboard the MESSENGER spacecraft during the longest solar minimum in a century. As MESSENGER entered superior conjunction, the plane of polarization of its radio signal was observed to rotate as it traversed the circularly birefringent plasma of the Sun's atmosphere. On time scales of less than three hours, these uncalibrated plane of polarization observations of Faraday rotation can be used to investigate the dynamic processes in the solar plasma, such as magnetohydrodynamic (MHD) waves and coronal mass ejections (CMEs). Here we describe the MESSENGER Faraday rotation experiment, the data processing conducted to obtain the plane of polarization, and the estimation of error.

Jensen, Elizabeth A.; Bisi, Mario M.; Breen, Andrew R.; Heiles, Carl; Minter, Toney; Vilas, Faith

2013-07-01

274

Direct imaging of a massive dust cloud around R Coronae Borealis  

NASA Astrophysics Data System (ADS)

We present recent polarimetric images of the highly variable star R CrB using ExPo and archival WFPC2 images from the HST. We observed R CrB during its current dramatic minimum where it decreased more than 9 mag due to the formation of an obscuring dust cloud. Since the dust cloud is only in the line-of-sight, it mimics a coronograph allowing the imaging of the star's circumstellar environment. Our polarimetric observations surprisingly show another scattering dust cloud at approximately 1.3'' or 2000 AU from the star. We find that to obtain a decrease in the stellar light of 9 mag and with 30% of the light being reemitted at infrared wavelengths (from R CrB's SED) the grains in R CrB's circumstellar environment must have a very low albedo of approximately 0.07%. We show that the properties of the dust clouds formed around R CrB are best fitted using a combination of two distinct populations of grains size. The first are the extremely small 5 nm grains, formed in the low density continuous wind, and the second population of large grains (~0.14 ?m) which are found in the ejected dust clouds. The observed scattering cloud, not only contains such large grains, but is exceptionally massive compared to the average cloud. Based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias.

Jeffers, S. V.; Min, M.; Waters, L. B. F. M.; Canovas, H.; Rodenhuis, M.; de Juan Ovelar, M.; Chies-Santos, A. L.; Keller, C. U.

2012-03-01

275

T he Faint Drifting Decameter Radio Bursts From The Solar Corona  

NASA Astrophysics Data System (ADS)

The radio observations of solar corona at decameter wavelengths reveal the presence of numerous faint, frequency drifting structures. We analyse observations performed on July 13th , 2002 with the DSP wideband spectrometer instrument implemented at the UTR-2 radiote- lescope. The main characteristics of these structures are statistically studied. Three populations of bursts are iden- tifies. The largest one presents negative frequency drifts of about -0.89 MHz.s-1 and a lifetime extending up to 11 sec (median value 2.72 sec). A second one shows positive frequency drifts of about +0.95 MHz.s-1 and a life- time extending up to 3 sec. The last population consists in structures with very small frequency drifts of about -0.1 MHz.s-1 and a shorter lifetime (about 1 sec). Assuming that those emissions are the signature of elec- tron beams propagating through the solar corona, we deduce that they have a velocity of about 3-5 times the electron thermal velocity. A new mechanism is proposed to explain the formation of plasma waves with such low beam velocity: spatially localized, temporal fluctuations of the electron distribution function width (heating).

Briand, C.; Zaslavsky, A.; Lecacheux, A.; Zarka, P.; Maksimovic, M.; Mangeney, A.

2007-01-01

276

Rank-Ordered Multifractal Analysis (ROMA) of Intermittent Dissipative Structures in Solar Corona  

NASA Astrophysics Data System (ADS)

Rank-Ordered Multifractal Analysis (ROMA) was introduced by Chang and Wu (2008) to describe the multifractal characteristic of intermittent events. The procedure provides a natural connection between the rank-ordered spectrum and the idea of one-parameter scaling for monofractals. This technique has successfully been applied to fluid turbulence, MHD turbulence simulations and turbulence data obtained in various space plasmas. In this paper, the technique is applied to an extended data set of extreme ultraviolet images of the solar corona provided by the extreme ultraviolet imaging telescope (EIT) on board the SOHO spacecraft. The data set was shown by Uritsky et al. (2007) to exhibit coexistence of self-organized criticality and intermittent turbulence. In this study, the SOHO EIT data set is shown to include two multifractal rank-ordered regimes, dependent on spatial scales, which may indicate different physical mechanisms of energy dissipation in the solar corona corresponding to meso- and supergranulation scales of the underlying photospheric network. This crossover behavior of the ranked-order regimes is similar to the characteristics observed by Tam et al. (2010) of the auroral zone electric-field fluctuations.

Wu, C.; Chang, T.; Uritsky, V. M.

2011-12-01

277

Torsional Alfvén waves in small scale current threads of the solar corona  

NASA Astrophysics Data System (ADS)

Context. The magnetic field structuring in the solar corona occurs on large scales (loops and funnels), but also on small scales. For instance, coronal loops are made up of thin strands with different densities and magnetic fields across the loop. Aims: We consider a thin current thread and model it as a magnetic flux tube with twisted magnetic field inside the tube and straight field outside. We prove the existence of trapped Alfvén modes in twisted magnetic flux tubes (current threads) and we calculate the wave profile in the radial direction for two different magnetic twist models. Methods: We used the Hall MHD equations that we linearized in order to derive and solve the eigenmode equation for the torsional Alfvén waves. Results: We show that the trapped Alfv én eigenmodes do exist and are localized in thin current threads where the magnetic field is twisted. The wave spectrum is discrete in phase velocity, and the number of modes is finite and depends on the amount of the magnetic field twist. The phase speeds of the modes are between the minimum of the Alfvén speed in the interior and the exterior Alfén speed. Conclusions: Torsional Alfvén waves can be guided by thin twisted magnetic flux-tubes (current threads) in the solar corona. We suggest that the current threads guiding torsional Alfvén waves, are subject to enhanced plasma heating due to wave dissipation.

Copil, P.; Voitenko, Y.; Goossens, M.

2010-01-01

278

Electron Temperatures and Flow Speeds of the Low Solar Corona: MACS Results from the Total Solar Eclipse of 29 March 2006 in Libya  

Microsoft Academic Search

An experiment was conducted in conjunction with the total solar eclipse on 29 March 2006 in Libya to measure both the electron temperature and its flow speed simultaneously at multiple locations in the low solar corona by measuring the visible K-coronal spectrum. Coronal model spectra incorporating the effects of electron temperature and its flow speed were matched with the measured

Nelson L. Reginald; Joseph M. Davila; O. C. St. Cyr; Douglas M. Rabin; Madhulika Guhathakurta; Donald M. Hassler; Hadi Gashut

2011-01-01

279

The Fe XII 195.1 A/1242 A emission line ratio in the solar corona  

NASA Astrophysics Data System (ADS)

Recent R-matrix calculations of electron impact excitation rates in Fe XII are used to derive the theoretical emission line ratio R1 = I(195.1 A)/I(1242 A), which is potentially a useful electron density diagnostic for the solar inner corona. These results are found to be significantly different from the earlier estimates of Withbroe and Raymond (184), but are in good agreement with the observed values of R1 for the quiet sun and an active region. Adoption of the R-matrix atomic data for the 1242 A line in the coronal iron abundance determination removes an existing discrepancy between results derived from the EUV transition and other iron lines in the solar XUV spectrum.

Keenan, F. P.; Tayal, S. S.; Henry, R. J. W.

1990-01-01

280

Wave heating in astrophysical plasma - examples in the solar corona and in galaxy clusters  

NASA Astrophysics Data System (ADS)

It is widely known that hot plasma is ubiquitous in various astrophysical objects from stars to galaxy clusters. I have worked on the wave dissipation which play a role in the momentum and energy transfer in the plasma. In this article, I firstly introduce our results on the wave heating and acceleration in the solar corona. I show that two kinds of the solar winds, the high-speed wind and low-speed wind, can be explained by the dissipation of different types of the waves. Then, we apply the wave dissipation to the heating in galaxy clusters in collaboration with Yutaka Fujita and Keiichi Wada (NAOJ). We show that the wave heating could be an effective process in reducing the cooling flow.

Suzuki, Takeru K.

2004-05-01

281

Studies of dust accumulation on solar-mirror materials  

Microsoft Academic Search

During outdoor exposure, solar mirror materials accumulate dust particles that can substantially reduce the intensity of the specularly reflected beam. Studies have shown that there is a complex interaction between significant variables such as the mirror material, local weather conditions, mirror orientation, and cleaning procedures. Investigation of different water spray cleaning techniques has shown that the specular reflectance even after

R. B. Pettit; J. M. Freese; E. P. Roth

1981-01-01

282

Large Area Dust Detector onboard Solar Power Sail Spacecraft  

NASA Astrophysics Data System (ADS)

JAXA is aiming to launch the solar power sail engineering demonstrator to the outer planet region of the solar system like Jupiter and the Jovian Trojan asteroids in 2010's. Its interplanetary cruise is a relevant and rare opportunity to monitor physical properties that may be varied by heliocentric distances continuously such as solar wind, solar magnetosphere and micrometeoroid flux. We have been developing the largest but still light-weight dust detector ever to be onboard deep space probes since 2000. PVDF films of a few to 10's of micron thickness are attached as a small part of the solar sail membrane to count and time hypervelocity impacts by micrometeoroids larger than micron size. The first spaceflight test of this dust detector in the order of 100 cm2 detection area was conducted onboard SSSAT (Solar Sail Satellite) as the M-V sub-payload launched to LEO in September 2006. The second opportunity of this series will be the 4- channel impact sensors onboard Kagayaki nano-satellite as an H-IIA piggyback to be launched in 2008. Actual interplanetary measurements can be achieved by the Small Solar Power Sail Demonstrator that will go inside the orbit of the Earth (1 AU) close to Venus around 2010. On this spacecraft, the 8-channel PVDF sensors of about 1 m2 detection area will be onboard to test this system in the interplanetary operation and to hopefully measure dust flux anisotropy in the trailing edge of the Earth, heliocentric flux variance inside 1 AU, and opportunistic detections of possible cometary dust trails and flux enhancement near Venus. The sensors filter electronic, thermal and vibration noises and record time, peak hold value, and relax duration of signals of micrometeoroid impacts. When the full-size solar power sail mission goes beyond 1 AU passing the main asteroid belt to 5 AU in 2010's, this dust detector system will be onboard in the order of several m2 active area. It will also compare its results with infrared observation of zodiacal light scattering as a function of the heliocentric distance in order to investigate possible co-relations between these two independent but simultaneous measurements of the solar system dust environment at the same heliocentric distance.

Yano, Hajime

283

Self consistent 1D numerical calculation of the temperature profile of solar corona heated by Alfvén waves  

NASA Astrophysics Data System (ADS)

Alfvén mechanism [H. Alfvén, Granulation, magnetohydrodynamic waves, and the heating of the solar corona, Mon. Not. R. Astron. Soc. 107, 211-219 (1947)] for heating the solar corona by magnetosonic waves is numerically examined for completely ionized one-dimensional hydrogen plasma. As a boundary condition we suppose a fixed spectral density of the coming from the chromosphere Alfvén waves. The numerical solution to the derived MHD equations gives the width of the transition layer between the chromosphere and the corona as a self-induced opacity of high-frequency Alfvén waves (AWs). The domain wall is a direct consequence of the self-consistent MHD treatment of AWs' propagation. The low-frequency MHD waves coming from the Sun are strongly reflected by the narrow transition layer, while the high-frequency waves are absorbed-that is why we predict considerable spectral density of the AWs in the photosphere.

Topchiyska, R. V.; Zahariev, N. I.

2013-09-01

284

Sources of the Solar System Dust Bands and Interplanetary Dust Particles  

NASA Astrophysics Data System (ADS)

The near-ecliptic and ten-degree solar system dust bands discovered by IRAS have previously been thought to result from the gradual collisional comminution of the three classical Hirayama asteroid families: Koronis, Themis, and Eos. Here, we present new results demonstrating that only two sources of dust particles are required to account for the shape and amplitude of these dust bands. Modeling shows that dust particles comprising the ten-degree band account for approximately 85% of the total cross-sectional area of material in these bands, with the remaining 15% from the central band. The initial mean proper inclination of dust particle orbits needed to account for the ten-degree band and the central band are 9.3o and 2.1o, respectively. These inclinations coincide with the location of two relatively recent catastrophic disruptions of small parent bodies, possibly "rubble-piles". The collisional event that created the Karin cluster component of the Koronis family has been dated at 5.8Myr ago, while the Veritas family was formed less than 100Myr ago. If the recent rubble-pile origin of these prominent dust bands is correct, then the cross-sectional area of dust particles released following their collisional disruption would likely dominate the entire zodiacal cloud for a timescale of 104 to 107 years, until the dust particles released eventually spiraled in from the asteroid belt to the Sun under the effect of Poynting-Robertson drag. A proportion of these dust particles would ultimately be accreted by the Earth, and it therefore follows that roughly 85% of all the asteroidal IDPs collected in Earth's stratosphere could originate from the Veritas family. Thus, in our IDP collections on Earth, we may already have an abundance of samples, from a known C-type asteroid.

Mahoney-Hopping, L.; Dermott, S.; Kehoe, T.; Kolokolova, L.; Grogan, K.

2003-05-01

285

The nature of the dust around R Coronae Borealis stars - Isolated amorphous carbon or graphite fractals  

SciTech Connect

Wright (1989) has proposed that the R CrB phenomenon is caused by the occurrence of graphite fractal grains, each composed of numerous, less than 15-nm-radius graphite spheres. It is shown that both the observational data and models of dust formation are more in accord with an earlier model by Hecht et al. (1984): that the R CrB type dust is composed of isolated small (less than 100-nm-radius) glassy or amorphous carbon grains. It cannot be ruled out that a significant number of fractal grains exist, provided that they have dielectric properties different from bulk graphite and closer to amorphous carbon, and that the individual grains in the fractals are below 1 nm in size. However, the existence of such fractal grains around R CrB stars might be ruled out by the lack of a 2400-A feature in the interstellar extinction curve. 30 refs.

Hecht, J.H. (Aerospace Corp., Los Angeles, CA (USA))

1991-02-01

286

Origin of the ten degree Solar System dust bands  

NASA Astrophysics Data System (ADS)

The Solar System dust bands discovered by IRAS are toroidal distributions of dust particles with common proper inclinations. It is impossible for particles with high eccentricity (approximately 0.2 or greater) to maintain a near constant proper inclination as they precess, and therefore the dust bands must be composed of material having a low eccentricity, pointing to an asteroidal origin. The mechanism of dust band production could involve either a continual comminution of material associated with the major Hirayama asteroid families, the equilibrium model (Dermott et al. (1984) Nature312, 505-509) or random disruptions in the asteroid belt of small, single asteroids (Sykes and Greenberg (1986) Icarus65, 51-69). The IRAS observations of the zodiacal cloud from which the dust band profiles are isolated have excellent resolution, and the manner in which these profiles change around the sky should allow the origin of the bands, their radial extent, the size-frequency distribution of the material and the optical properties of the dust itself to be determined. The equilibrium model of the dust bands suggests Eos as the parent of the 10° band pair. Results from detailed numerical modeling of the 10° band pair are presented. It is demonstrated that a model composed of dust particles having mean semimajor axis, proper eccentricity and proper inclination equal to those of the Eos family member asteroids, but with a dispersion in proper inclination of 2.5°, produces a convincing match with observations. Indeed, it is impossible to reproduce the observed profiles of the 10° band pair without imposing such a dispersion on the dust band material. Since the dust band profiles are matched very well with Eos, Themis and Koronis type material alone, the result is taken as strong evidence in favor of the equilibrium model. The effects of planetary perturbations are included by imposing the appropriate forced elements on the dust particle orbits (these forced elements vary with heliocentric distance). A subsequent model in which material is allowed to populate the inner solar system by a Poynting-Robertson drag distribution is also constructed. A dispersion in proper inclination of 3.5° provides the best match with observations, but close examination of the model profiles reveals that they are slightly broader than the observed profiles. If the variation of the number density of asteroidal material with heliocentric distance r is given by an expression of the form 1/r ? then these results indicate that ? < 1 compared with ? = 1 expected for a simple Poynting-Robertson drag distribution. This implies that asteroidal material is lost from the system as it spirals in towards the Sun, owing to interparticle collisions.

Grogan, K.; Dermott, S. F.; Jayaraman, S.; Xu, Y. L.

1997-12-01

287

Ion Cyclotron Wave Dissipation in the Solar Corona: The Summed Effect of More than 2000 Ion Species  

Microsoft Academic Search

In this paper the dissipation of ion cyclotron resonant waves in the extended solar corona is Alfve n examined in detail. For the Ðrst time, the wave damping arising from more than 2000 low-abundance ion species is taken into account. Useful approximations for the computation of coronal ionization equi- libria for elements heavier than nickel are presented. Also, the Sobolev

Steven R. Cranmer

2000-01-01

288

A Critical Assessment of Nonlinear Force-Free Field Modeling of the Solar Corona for Active Region 10953  

Microsoft Academic Search

Nonlinear force-free field (NLFFF) models are thought to be viable tools for investigating the structure, dynamics, and evolution of the coronae of solar active regions. In a series of NLFFF modeling studies, we have found that NLFFF models are successful in application to analytic test cases, and relatively successful when applied to numerically constructed Sun-like test cases, but they are

Marc L. De Rosa; Carolus J. Schrijver; Graham Barnes; K. D. Leka; Bruce W. Lites; Markus J. Aschwanden; Tahar Amari; Aurélien Canou; James M. McTiernan; Stéphane Régnier; Julia K. Thalmann; Gherardo Valori; Michael S. Wheatland; Thomas Wiegelmann; Mark C. M. Cheung; Paul A. Conlon; Marcel Fuhrmann; Bernd Inhester; Tilaye Tadesse

2009-01-01

289

EUV Tomography and Global Magnetic Modeling of the Solar Corona during the Solar Cycle 24 Rising Phase  

NASA Astrophysics Data System (ADS)

We apply the Differential Emission Measure Tomography (DEMT) technique to STEREO/EUVI and SDO/AIA data obtained during the rising phase of the solar cycle 24. As a result we obtain the three-dimensional (3D) differential emission measure in the height range 1.00 to 1.25 Rsun. We use that information to construct 3D maps of the coronal electron density and temperature. We discuss the 3D distribution of our results in the context of a global potential magnetic field model of the same period. We also discuss the utilization of DEMT results as constraint for the modeling of the solar corona, and the impact of the new information gained by using the six coronal bands of SDO/AIA respect to previous tomographic results based on the three coronal bands of STEREO/EUVI.

Vasquez, A. M.; Nuevo, F. A.; Frazin, R. A.; Huang, Z.

2011-12-01

290

CAN A NANOFLARE MODEL OF EXTREME-ULTRAVIOLET IRRADIANCES DESCRIBE THE HEATING OF THE SOLAR CORONA?  

SciTech Connect

Nanoflares, the basic units of impulsive energy release, may produce much of the solar background emission. Extrapolation of the energy frequency distribution of observed microflares, which follows a power law to lower energies, can give an estimation of the importance of nanoflares for heating the solar corona. If the power-law index is greater than 2, then the nanoflare contribution is dominant. We model a time series of extreme-ultraviolet emission radiance as random flares with a power-law exponent of the flare event distribution. The model is based on three key parameters: the flare rate, the flare duration, and the power-law exponent of the flare intensity frequency distribution. We use this model to simulate emission line radiance detected in 171 A, observed by Solar Terrestrial Relation Observatory/Extreme-Ultraviolet Imager and Solar Dynamics Observatory/Atmospheric Imaging Assembly. The observed light curves are matched with simulated light curves using an Artificial Neural Network, and the parameter values are determined across the active region, quiet Sun, and coronal hole. The damping rate of nanoflares is compared with the radiative losses cooling time. The effect of background emission, data cadence, and network sensitivity on the key parameters of the model is studied. Most of the observed light curves have a power-law exponent, {alpha}, greater than the critical value 2. At these sites, nanoflare heating could be significant.

Tajfirouze, E.; Safari, H. [Department of Physics, University of Zanjan, P.O. Box 45195-313, Zanjan (Iran, Islamic Republic of)

2012-01-10

291

The temperature and density structure in the closed field regions of the solar corona  

NASA Astrophysics Data System (ADS)

In this paper we study the temperature and density structure in the closed field region of the solar corona using a dipole plus current sheet model to simulate the global solar magnetic field and a heating function of the same type used in models of the fast wind. The heat equation, describing the redistributing effects of heat conduction on the heat input in the presence of radiative losses, is solved simultaneously with hydrostatic pressure balance. At the base we prescribe the temperature and assume that the heat flux is zero there. We also insist that the heat flux is zero at the equator. This ensures that whatever heat has been added is radiated away. From the mathematical viewpoint this additional requirement sets up an eigenvalue problem which implies that the density at the base must be chosen in just the right way to fulfill the condition of zero heat flux at the equator. Thus our model not only provides the temperature and density structure in the closed regions of a global solar magnetic field appropriate to solar minimum but also predicts the latitudinal variation of the base density whose characteristic value is determined by the ratio of the amplitudes of the heating to the cooling. However it should be stressed that this last prediction represents, at best, an approximation to the real stale of affairs which is more complex and involves the connection of the coronal field lines to the magnetic funnels of the chromospheric network.

McKenzie, J. F.; Sukhorukova, G. V.; Axford, W. I.

1999-10-01

292

Large-scale magnetic field and density distribution in the solar minimum corona  

NASA Astrophysics Data System (ADS)

We seek a quantitative description of the large-scale structure of magnetic field and density in the solar minimum corona that is consistent with observations of both white light intensity and the magnetic field at the photosphere. We use white light images from NASA's Solar Maximum Mission (SMM) Coronagraph/Polarimeter and the High-Altitude Observatory Mark III (MkIII) K-coronameter, along with photospheric field measurements from Stanford's Wilcox Solar Observatory (WSO), as constraints on the magnetostatic model of Bogdan and Low [1986] (B&L). We find a family of solutions to the B&L model that reproduce observations of white light quite well, each with a different magnetic field structure. We show that the observed photospheric field cannot be used as an exact boundary condition on the B&L model, but we can limit the white light solutions by matching the total observed photospheric magnetic flux. We find a set of model parameters that reproduces white light and photospheric field to within quantifiable model and observational limits and calculate the physical plasma properties corresponding to these parameters. We conclude that this fit represents a self-consistent description of the solar minimum coronal magnetic field and density.

Gibson, S. E.; Bagenal, F.

1995-10-01

293

SDO/AIA OBSERVATION OF KELVIN-HELMHOLTZ INSTABILITY IN THE SOLAR CORONA  

SciTech Connect

We present observations of the formation, propagation, and decay of vortex-shaped features in coronal images from the Solar Dynamics Observatory associated with an eruption starting at about 2:30 UT on 2010 April 8. The series of vortices were formed along the interface between an erupting (dimming) region and the surrounding corona. They ranged in size from several to 10 arcsec and traveled along the interface at 6-14 km s{sup -1}. The features were clearly visible in six out of the seven different EUV wave bands of the Atmospheric Imaging Assembly. Based on the structure, formation, propagation, and decay of these features, we identified the event as the first observation of the Kelvin-Helmholtz instability (KHI) in the corona in EUV. The interpretation is supported by linear analysis and by a nonlinear 2.5-dimensional magnetohydrodynamic model of KHI. We conclude that the instability is driven by the velocity shear between the erupting and closed magnetic field of the coronal mass ejection. The shear-flow-driven instability can play an important role in energy transfer processes in coronal plasma.

Ofman, L. [Department of Physics, Catholic University of America, Washington, DC 20064 (United States); Thompson, B. J. [NASA Goddard Space Flight Center, Code 671, Greenbelt, MD 20771 (United States)

2011-06-10

294

Magnetic Coupling Between the Solar Surface and Corona: Theory and Observations  

NASA Astrophysics Data System (ADS)

Multi-wavelength observations taken simultaneously by several instruments on the Solar and Heliospheric Observatory (SOHO) and Transition Region and Coronal Explorer (TRACE) revealed a clear connection between the photospheric magnetic fields and the energetic events in the overlying atmosphere. We find that the EUV coronal emission above the photosphere dominated by single polarity magnetic elements is spongy in space and has coherent braid-like structures in time. Contrary to these long living structures, corona above the regions with mixed polarity magnetic elements is highly discrete and consists of sporadic microflares, supersonic jets and their combinations. We believe that in the unipolar magnetic regions the energy flow from the surface to corona is associated with the nonlinear collective phenomena in the ensemble of oscillating magnetic flux tubes. These phenomena lead to formation of hot coronal ``clouds'' that have the properties of energetically open turbulence with tendency to self-organization. Jets and microflares above the mixed polarity regions are associated with shock waves produced by reconnecting magnetic flux tubes in the photosphere and subsequent interaction of shocks which leads to hydrodynamic cumulation of energy, which leads to impulsive phenomena similar to shaped charges.

Ryutova, Margarita; Shine, Richard

2004-04-01

295

Free dispersal of a stream of fast electrons in the solar corona with nonsteady injection  

SciTech Connect

The evolution of a stream of fast electrons injected into the corona from a region of solar flares and exciting Langmuir waves (plasmons) which are transformed into type III radio bursts is analyzed. The ''lagging'' of the plasmons behind the nonsteady stream in the inhomogeneous coronal plasma (S.S. Harvey, Sol. Phys. 40, 193 (1975); Astron. Astrophys. 41, 31 (1976)) allows one to treat the motion of the stable part of the stream as free dispersal. Different models of nonsteady injection are discussed within the framework of quasi-equilibrium (exponential) and nonequilibrium (power-law) energy spectra of electrons in the source. Qualitative agreement is established between the calculated results and the data of satellite experiments.

Vigdorchik, V.I.

1979-03-01

296

Making three-temperature maps of the solar corona from EUV images  

NASA Astrophysics Data System (ADS)

One of the challenges with EUV imagers like SDO/AIA is to rapidly retrieve pertinent physical information from the simultaneous observations of multiple wavelengths. As the number of wavelengths steadily increases, so do the difficulties encountered in visualising multispectral images. The classical approach is to model the differential emission measure and infer from it the temperature distribution for each image pixel. This approach involves numerous strong assumptions and is computationally costly, making it inappropriate for near real-time analysis of solar images. A completely different and empirical approach involves blind source separation, where we as-sume that the for each wavelength, the pixel intensity is a linear combination of contributions (source images) with specific emission spectra. The objective then is to recover both the sources and their mixing coefficients without any a priori information. This is a blind source seprara-tion problem, which has recently received considerable attention in various areas such as the processing of hyperspectral images from planets, in acoustics, in airborne surveying, etc. Here we consider a recent technique called Bayesian Positive Source Separation [Amblard et al., AA 487, L13-L16(2008)] to extract sources from SoHO/CDS and SDO/AIA images in multiple wavelengths. In both cases we find that 3 source images capture the salient features of the data. Interestingly, their associated spectra isolate specfic temperature bands corresponding to the chromosphere, the lower corona and the upper corona. We show how these source images can be used to reconstruct solar temperature maps in near real time.

Dudok de Wit, Thierry; Kretzschmar, Matthieu; Benseghir, Thomas

297

The eclipse corona: reality and possible research during the 1999 eclipse  

NASA Astrophysics Data System (ADS)

Solar eclipses provide a unique opportunity to observe the solar corona and to solve many open questions in solar coronal physics, e.g., heating of the corona, small-scale structures, dust particles, formation and distribution of coronal structures around the solar surface with respect to the photospheric activity centers, polarization, dust vaporization near the Sun, formation and spatial orientation of solar wind streamers, etc. The forthcoming 1999 eclipse will pass across many countries in Europe, the Middle East and Asia. This event will provide a good opportunity to perform observations of the corona with 'bigger' equipment to obtain high-resolution. We propose to focus scientific experiments on the following targets: THE WHITE-LIGHT AND EMISSION CORONA: exact photometry of the corona with telescopes of focal length 1-3 m; in detail, photometry around the poles and/or above active regions with a minimum focal length of 5 m; photoelectric detection of oscillations; co-ordinated observations with `smaller' telescopes, of 1 m focal length, along the umbral path (dynamics and large-scale structure), polarization in emission corona, etc. SPECTRAL OBSERVATIONS: detection of short-term oscillations (less than 0.1 s) in individual spectral emission coronal lines or in the white-light corona; polarization in emission coronal lines (the Hanle effect - direction of coronal magnetic field lines); spectral observations with small-scale resolution: colour of the solar corona, large-scale resolution: profiles of emission lines; depth of absorption lines (F-corona), etc. Moreover, high-precision timing of eclipse contacts can help us to obtain more accurate parameters of the Moon's orbit around the Earth and to measure the diameter of the Sun. Comets, if any, should be studied in the close vicinity of the Sun. We are of the opinion that the most important problems in solar coronal research during the 1999 eclipse will be supported by coordinated ground-based and satellite observations.

Rusin, V.; Rybansky, M.

1999-03-01

298

Reflection of Alfvén waves in the corona and solar wind: An impulse function approach  

NASA Astrophysics Data System (ADS)

We consider the reflection of Alfvén waves in the corona and solar wind, using variables f and g which follow sunward and antisunward characteristics, respectively. We show that the basic equations for f and g have the same structure as the Klein-Gordon equation. Unlike previous studies which used a harmonic analysis, we emphasize the impulse response of the system. This is equivalent to finding the Green's function, but it may have direct application to situations where Alfvén waves are launched impulsively. We provide an approximate analysis which can be used to understand most features that appear in detailed numerical solutions. The analysis reveals the origin of a previous result that f and g each has both sunward and antisunward propagating phase in a harmonic analysis, even though f (g) follows only the sunward (antisunward) characteristic. We numerically study the propagation of an antisunward moving impulse in the corona and solar wind. We find that the sunward moving ``wake'' tends to become more important at greater distances beyond the Alfvén critical point, possibly providing a natural explanation of the observation that outward propagating waves become less dominant at greater distances from the Sun. There is an extended region behind the initial impulse in which magnetic energy dominates kinetic energy; it is not clear, however, whether our result can explain the observed dominance of magnetic energy throughout many decades of frequency in the observed power spectrum. We also find that the outgoing wake has a tendency to ``ring,'' with periods of the order of 15-30 min. The ringing is associated mainly with propagation through a structured Alfvén speed profile rather that with the cutoff in the Klein-Gordon equation. These oscillation periods seem too short to explain why Alfvén waves in the solar wind have most power at periods of hours, but other Alfvén speed profiles could yield longer periods. We also investigate whether the same approach can be used for acoustic-gravity waves propagating along magnetic flux tubes in the solar atmosphere.

Hollweg, Joseph V.; Isenberg, P. A.

2007-08-01

299

Solar wind ion dynamics at a charged dust cloud: a hybrid simulation study  

Microsoft Academic Search

The interaction of a small cloud of dust grains with the solar wind is studied by a three-dimensional hybrid simulation code, which treats the electrons as a fluid and the ions as par-ticles. The dust grains are positively ionised by solar radiation and as a result they become an obstacle for the solar wind. Three simulation series are discussed where

Christoph Koenders; Uwe Motschmann; Sven Simon; Hendrik Kriegel; Joachim Mueller; Stefan Wiehle; Karl-Heinz Glassmeier

2010-01-01

300

Dust Particles In Pluto System: The Solar Radiation Pressure Effects  

NASA Astrophysics Data System (ADS)

Stable regions, favorable regions to find new satellites, were found around the two large bodies Pluto and Charon, coorbital to Nix and Hydra and also in a small region between the orbits of these two small satellites (Giuliatti Winter et al., 2010 and Pires dos Santos et al., 2010). The discovery of the small satellites Nix and Hydra, located in the external region of the Pluto-Charon binary system, increased the possibility of rings in this system. If this ring were composed of dust particles the effects of non-gravitational forces, such as the solar radiation pressure, has also to be taken into account. In this work we analyzed the effects of the solar radiation pressure on a sample of micrometer-sized dust grains in circular orbits around Pluto, assuming spherical dust grains and neglecting the planetary shadow and the light reflected from the planet. As result we verified that the Poynting-Robertson component of the solar radiation force is responsible for the decreasing in the semimajor axis of the particles leading them to a collision with the planet on a timescale between 1.47 x 106 years (particles of 1 micrometer-sized in radius) and 1.47 x 107 years (particles of 10 micrometer-sized in radius), according to the value estimated by Burns et al. (1979); while the radiation pressure component causes an increase in the eccentricity of the particles, leading particles smaller than 10 micrometer-sized in radius to collide with the planet in less than 10 years. For those particles closer to the planet, located at 20 times Pluto's radius, the effect of radiation pressure is weaker. We also analyzed the collisions between these dust particles and the four massive bodies Pluto-Charon-Nix and Hydra.

Pires Dos Santos, Pryscilla Maria; Giuliatti Winter, S.; Sfair, R.

2010-10-01

301

Rocket borne solar eclipse experiment to measure the temperature structure of the solar corona via lyman-. cap alpha. line profile observations  

SciTech Connect

A rocket borne experiment to measure the temperature structure of the inner solar corona via the doppler broadening of the resonance hydrogen Lyman-..cap alpha.. (lambda1216A) radiation scattered by ambient neutral hydrogen atoms was attempted during the 16 Feb 1980 solar eclipse. Two Nike-Black Brant V sounding rockets carrying instrumented payloads were launched into the path of the advancing eclipse umbra from the San Marco satellite launch platform 3 miles off the east coast of Kenya.

Argo, H.V.

1981-01-01

302

Direct Imaging of Quasi-periodic Fast Propagating Waves of ~2000 km s-1 in the Low Solar Corona by the Solar Dynamics Observatory Atmospheric Imaging Assembly  

Microsoft Academic Search

Quasi-periodic propagating fast mode magnetosonic waves in the solar corona were difficult to observe in the past due to relatively low instrument cadences. We report here evidence of such waves directly imaged in EUV by the new Atmospheric Imaging Assembly instrument on board the Solar Dynamics Observatory. In the 2010 August 1 C3.2 flare\\/coronal mass ejection event, we find arc-shaped

Wei Liu; Junwei Zhao; Leon Ofman; Carolus J. Schrijver; Markus J. Aschwanden; Bart De Pontieu; Theodore D. Tarbell

2011-01-01

303

Electron temperatures and its bulk flow speeds in the low solar corona measured during the total solar eclipse on 29 March 2006 in Libya  

Microsoft Academic Search

We conducted an experiment that measured the K-coronal spectra in the visible wavelength region, simultaneously at multiple locations in the low solar corona in conjunction with the total solar eclipse on 29 March 2006 in Libya. The shapes of these measured K-coronal spectra were then matched with K-coronal models with different combinations of electron temperatures and electron bulk flow speeds

N. L. Reginald; J. M. Davila; O. C. St. Cyr; M. Guhathakurta; D. M. Hassler

2008-01-01

304

The Effect of Hydrostatic Weighting on the Vertical Temperature Structure of the Solar Corona.  

PubMed

We investigate the effect of hydrostatic scale heights lambda(T) in coronal loops on the determination of the vertical temperature structure T&parl0;h&parr0; of the solar corona. Every method that determines an average temperature at a particular line of sight from optically thin emission (e.g., in EUV or soft X-ray wavelengths) of a mutlitemperature plasma is subject to the emission measure-weighted contributions dEM&parl0;T&parr0;&solm0;dT from different temperatures. Because most of the coronal structures (along open or closed field lines) are close to hydrostatic equilibrium, the hydrostatic temperature scale height introduces a height-dependent weighting function that causes a systematic bias in the determination of the temperature structure T&parl0;h&parr0; as function of altitude h. The net effect is that the averaged temperature seems to increase with altitude, dT&parl0;h&parr0;&solm0;dh>0, even if every coronal loop (of a multitemperature ensemble) is isothermal in itself. We simulate this effect with differential emission measure distributions observed by SERTS for an instrument with a broadband temperature filter such as Yohkoh/Soft X-Ray Telescope and find that the apparent temperature increase due to hydrostatic weighting is of order DeltaT approximately T0h&solm0;r middle dot in circle. We suggest that this effect largely explains the systematic temperature increase in the upper corona reported in recent studies (e.g., by Sturrock et al., Wheatland et al., or Priest et al.), rather than being an intrinsic signature of a coronal heating mechanism. PMID:10829008

Aschwanden; Nitta

2000-05-20

305

Observation And Simulation Of P-mode Propagation Into The Solar Corona  

NASA Astrophysics Data System (ADS)

Observations have shown the connection between oscillations within the sunspot photosphere and photospheric p-modes. In the strong, vertical, magnetic field regions of sunspot umbrae, it is thought that these acoustic p-modes undergo mode conversion to slow-magnetoacoustic waves, and that these slow-magnetoacoustic p-modes may be waveguided from the photosphere into the solar corona along the magnetic field. Observations are presented of the propagation of these waves and their channelling into the coronal parts of magnetic loops, originally emerging from a sunspot region. These observations are combined with 2-D MHD numerical simulations of wave leakage and direct propagation within the model sunspot atmosphere. The simulations are driven at the photospheric level by the Doppler velocity field of p-modes observed within the sunspot, and the response of forward modelling of the atmosphere is compared to observations. In the future, this combined approach of observation and theoretical modelling may be exploited to allow magneto-seismology of the solar atmosphere above sunspots or active regions. M.S. Marsh supported through the NASA post doctoral program.

Marsh, Michael; Malins, C.; Erdelyi, R.

2007-05-01

306

Beyond the Solar Corona: Mercury's Magnetic Fields seen with Large Solar Telescopes  

NASA Astrophysics Data System (ADS)

Solar telescopes have a potential in non-solar observations thanks to their instrumentation and their ability to observe in daylight, and despite their smaller mirror size compared to night-time telescopes. We review, as an illustration, THEMIS observations of Mercury's exosphere including the polarization of exospheric emission lines, and speculate that through analysis of this polarization made possible by the large photon-collecting capabilities of the upcoming large solar telescope we may expect to map Mercury's magnetosphere.

López Ariste, A.; Leblanc, F.

2012-12-01

307

Modeling Solar Wind Mass-Loading Due to Cometary Dust  

NASA Astrophysics Data System (ADS)

Collisionless mass-loading was first discussed to describe interactions between the solar wind and cometary atmospheres. Recent observations have led to an increased interest in coronal mass-loading due to sun-grazing comets and collisional debris by sunward-migrating interplanetary dust particles. Using three-dimensional MHD simulations with the Block-Adaptive-Tree-Solarwind-Roe-Upwind-Scheme (BATS-R-US) we have shown the impact on the solar wind from abrupt mass-loading in the coronal region. We also use the model as an application for a mass-loaded coronal wind due to a cometary source, which helps predict the impacts on solar wind acceleration and composition from past and upcoming sungrazing comets.

Rasca, Anthony; Horanyi, M.

2013-10-01

308

Heating and activity of the solar corona. 3. Dynamics of a low beta plasma with three-dimensional null points  

Microsoft Academic Search

We investigate the self-consistent nonlinear evolution of an initially force-free three-dimensional magnetic field subjected to stress on two boundaries. The results illustrate how complicated magnetic field structures, such as those found in the solar corona, evolve dynamically when forced by stress from boundaries and how the energy which is temporarily stored in the magnetic field may be converted into other

Klaus Galsgaard; Åke Nordlund

1997-01-01

309

3D Differential Emission Measure of the 2008 Solar Minimum Corona with Dual-Spacecraft EUVI/STEREO Tomography  

NASA Astrophysics Data System (ADS)

We have recently developed solar rotational tomography (SRT) of EUV image time series for the empirical determination of the three-dimensional (3D) distribution of the differential emission measure (DEM) of the global corona. Using this technique, we present a 3D tomographic reconstruction of the local DEM (which also yields the electron density) of the global solar corona between 1.03 and 1.25 Rs for Carrington Rotation 2077 (starting 2008 November 20). The reconstructions were performed using simultaneous STEREO A and B spacecraft EUVI data in the 17.1, 19.5, 28.4 and 30.4 nm bands. At this time, the positions of the two spacecraft were separated by about 90°, which allowed for the EUV reconstruction to be performed in about 3/4 of a solar rotational time instead of a full Carrington rotation, which improved the time resolution of the technique. We complement this reconstruction with a simultaneous potential field source-surface (PFSS) reconstruction of the magnetic field. During this period there were only two important active regions (ARs), and the corona was dominated by a large scale bipolar structure. We show both the full 3D results as well as the azimuthally averaged 2D results, excluding the ARs. The comparison of the 2D results among the tomographic local DEM and the PFSSM results, allows for the construction of a large scale quantitative semiempirical model of the geometry and thermodynamical properties of the equatorial streamer and subpolar regions of the solar minimum corona.

Vasquez, A. M.; Frazin, R. A.

2009-12-01

310

Development of the 3-D MHD model of the solar corona-solar wind combining system  

Microsoft Academic Search

In the framework of integrated numerical space weather prediction, we have developed a 3-D MHD simulation model of the solar surface-solar wind system. We report the construction method of the model and its first results. By implementing a grid system with angularly unstructured and increasing radial spacing, we realized a spherical grid that has no pole singularity and realized a

A. Nakamizo; T. Tanaka; Y. Kubo; S. Kamei; H. Shimazu; H. Shinagawa

2009-01-01

311

Dynamical and Observational Constraints on the Origin and Evolution of the Solar System Dust Bands  

Microsoft Academic Search

The Solar System dust bands discovered by the Infrared Astronomical Satellite (IRAS) are toroidal distributions of dust particles with common proper inclinations. It is impossible for particles with high eccentricity (approximately 0.2 or greater) to maintain a near constant proper inclination as they precess, and therefore the dust bands must be composed of material having a low eccentricity, pointing to

Keith Grogan

1997-01-01

312

A solar system dust ring with earth as its shepherd  

NASA Astrophysics Data System (ADS)

Numerical integrations are used here to show that small dust grains can be temporarily captured into exterior orbit-orbit resonances with the earth, lasting from less than 10,000 years to more than 100,000 years. Grains with radii of 30-100 microns, orbiting in planes less than 10 deg from the plane of the solar system and with orbital eccentricities of less than 0.3, are captured most easily. It is argued that there should be an approximately toroidal cloud of particles, derived mostly from the asteroid belt, trapped into a variety of these exterior resonances. The cloud is mostly beyond the earth's orbit, but includes it.

Jackson, A. A.; Zook, H. A.

1989-02-01

313

Polarization of Hard X-Rays in October-November, 2003 Solar Flares Observed Onboard CORONAS-F Satellite  

NASA Astrophysics Data System (ADS)

Hard X-ray radiation from several powerful solar flares was detected in October-November, 2003 by the SPR-N hard X-ray polarimeter onboard CORONAS-F satellite. In the October, 29 solar flare (20:40 - 21:00 UT) the X-ray radiation was strongly polarized (more than 70% of photons with energies 40-100 keV). In the flares 28.10.03 and 04.11.03 the emission was not polarized. The upper limits for the part of polarized photons at the level of tens percents were obtained in these flares.

Bogomolov, A. V.; Denisov, Yu. I.; Logachev, Yu. I.; Morozov, O. V.; Myagkova, I. N.; Svertilov, S. I.; Zhitnik, I. A.; Ignat'ev, A. P.; Oparin, S. N.; Pertsov, A. A.

314

Mate and Dart: An Instrument Package for Characterizing Solar Energy and Atmospheric Dust on Mars  

NASA Astrophysics Data System (ADS)

The MATE (Mars Array Technology Experiment) and DART (Dust Accumulation and Removal Test) instruments were developed to fly as part of the Mars ISPP Precursor (MIP) experiment on the (now postponed) Mars-2001 Surveyor Lander. MATE characterizes the solar energy reaching the surface of Mars, and measures the performance and degradation of solar cells under Martian conditions. DART characterizes the dust environment of Mars, measures the effect of settled dust on solar arrays, and investigates methods to mitigate power loss due to dust accumulation.

Landis, Geoffrey A.; Jenkins, Phillip; Scheiman, David; Baraona, Cosmo

2000-07-01

315

Generation of radiation in solar corona and interplanetary space by energetic electrons  

NASA Astrophysics Data System (ADS)

Emissions of electromagnetic waves with frequencies close to the plasma frequency and/or its second harmonic have been frequently observed in the solar corona and interplanetary space. In the past, a number of theories have been put forward to esplain the generation mechanism of the observed radiation. In this paper, a new model is proposed. The essential point of the present theory is that the Langmuir waves amplified as a result of the usual beam instability can lead to two important effects: first, electrostatic waves with frequencies close to twice the plasma frequency can be excited; and second, a significant modification of the dispersion relation can occur, so that these electrostatic waves can naturally change into electomagnetic waves as they propagate in a plasma in which the plasma density decreases spatially. The latter effect is attributed to a mode couplng process. In addition to the second harmonic emission, emission at the fundamental is also briefly discussed. In this case, as in many other theories, the presence of a very low frequency electostatic wave such as the ion-acoustic wave is assumed. The emission process discussed in the present theory stresses the importance of mode coupling and conversion rather than kinetic processes such as a nonlinear wave-wave or wave-particle scattering.

Wu, C. S.; Yoon, Peter H.; Zhou, G. C.

1994-07-01

316

On the Anisotropy in Expansion of Magnetic Flux Tubes in the Solar Corona  

NASA Astrophysics Data System (ADS)

Most one-dimensional hydrodynamic models of plasma confined to magnetic flux tubes assume circular tube cross sections. We use potential field models to show that flux tubes in circumstances relevant to the solar corona do not, in general, maintain the same cross-sectional shape through their length and therefore the assumption of a circular cross section is rarely true. We support our hypothesis with mathematical reasoning and numerical experiments. We demonstrate that lifting this assumption in favor of realistic, non-circular loops makes the apparent expansion of magnetic flux tubes consistent with that of observed coronal loops. We propose that in a bundle of ribbon-like loops, those that are viewed along the wide direction would stand out against those that are viewed across the wide direction due to the difference in their column depths. That result would impose a bias toward selecting loops that appear not to be expanding, seen projected in the plane of sky. An implication of this selection bias is that the preferentially selected non-circular loops would appear to have increased pressure scale heights even if they are resolved by current instruments.

Malanushenko, A.; Schrijver, C. J.

2013-10-01

317

Magnetic Field Topology and the Thermal Structure of the Corona over Solar Active Regions  

NASA Astrophysics Data System (ADS)

Solar extreme ultraviolet (EUV) images of quiescent active-region coronae are characterized by ensembles of bright 1-2 MK loops that fan out from select locations. We investigate the conditions associated with the formation of these persistent, relatively cool, loop fans within and surrounding the otherwise 3-5 MK coronal environment by combining EUV observations of active regions made with TRACE with global source-surface potential-field models based on the full-sphere photospheric field from the assimilation of magnetograms that are obtained by the Michelson Doppler Imager (MDI) on SOHO. We find that in the selected active regions with largely potential-field configurations these fans are associated with (quasi-)separatrix layers (QSLs) within the strong-field regions of magnetic plage. Based on the empirical evidence, we argue that persistent active-region cool-loop fans are primarily related to the pronounced change in connectivity across a QSL to widely separated clusters of magnetic flux, and confirm earlier work that suggested that neither a change in loop length nor in base field strengths across such topological features are of prime importance to the formation of the cool-loop fans. We discuss the hypothesis that a change in the distribution of coronal heating with height may be involved in the phenomenon of relatively cool coronal loop fans in quiescent active regions.

Schrijver, Carolus J.; DeRosa, Marc L.; Title, Alan M.

2010-08-01

318

Using the EUV to Weigh a Sun-grazing Comet as it Disappears in the Solar Corona  

NASA Astrophysics Data System (ADS)

On July 6, 2011, the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) observed a comet in most of its EUV passbands. The comet disappeared while moving through the solar corona. The comet penetrated to 0.146 solar radii ( ˜~100,000 km) above the photosphere before its EUV faded. Before then, the comet's coma and a tail were observed in absorption and emission, respectively. The material in the variable tail quickly fell behind the nucleus. An estimate of the comet's mass based on this effect, one derived from insolation, and one using the tail's EUV brightness, all yield ˜ 50 giga-grams some 10 minutes prior to the end of its visibility. These unique first observations herald a new era in the study of Sun-grazing comets close to their perihelia and of the conditions in the solar corona and solar wind. We will discuss the observations and interpretation of the comet by SDO as well as the coronagraph observations from SOHO and STEREO. A search of the SOHO comet archive for other comets that could be observed in the SDO/AIA EUV channels will be described.

Pesnell, W. D.; Schrijver, C. J.; Brown, J. C.; Battams, K.; Saint-Hilaire, P.; Hudson, H. S.; Lui, W.

2011-12-01

319

Grain Sorting in Cometary Dust from the Outer Solar Nebula  

NASA Astrophysics Data System (ADS)

Most young stars are surrounded by a disk of gas and dust. Close to the hot stars, amorphous dust grains from the parent molecular cloud are reprocessed into crystals that are then distributed throughout the accretion disk. In some disks, there is a reduction in crystalline grain size with heliocentric distance from the star. We investigated crystalline grain size distributions in chondritic porous (CP) interplanetary dust particles (IDPs) believed to be from small, icy bodies that accreted in outer regions of the solar nebula. The grains are Mg-rich silicates and Fe-rich sulfides, the two most abundant minerals in CP IDPs. We find that they are predominantly <0.25 ?m in radius with a mean grain size that varies from one CP IDP to another. We report a size-density relationship between the silicates and sulfides. A similar size-density relationship between much larger silicate and sulfide grains in meteorites from the asteroid belt is ascribed to aerodynamic sorting. Since the silicate and sulfide grains in CP IDPs are theoretically too small for aerodynamic sorting, their size-density relationship may be due to another process capable of sorting small grains.

Wozniakiewicz, P. J.; Bradley, J. P.; Ishii, H. A.; Brownlee, D. E.; Kearsley, A. T.; Burchell, M. J.; Price, M. C.

2012-12-01

320

GRAIN SORTING IN COMETARY DUST FROM THE OUTER SOLAR NEBULA  

SciTech Connect

Most young stars are surrounded by a disk of gas and dust. Close to the hot stars, amorphous dust grains from the parent molecular cloud are reprocessed into crystals that are then distributed throughout the accretion disk. In some disks, there is a reduction in crystalline grain size with heliocentric distance from the star. We investigated crystalline grain size distributions in chondritic porous (CP) interplanetary dust particles (IDPs) believed to be from small, icy bodies that accreted in outer regions of the solar nebula. The grains are Mg-rich silicates and Fe-rich sulfides, the two most abundant minerals in CP IDPs. We find that they are predominantly <0.25 {mu}m in radius with a mean grain size that varies from one CP IDP to another. We report a size-density relationship between the silicates and sulfides. A similar size-density relationship between much larger silicate and sulfide grains in meteorites from the asteroid belt is ascribed to aerodynamic sorting. Since the silicate and sulfide grains in CP IDPs are theoretically too small for aerodynamic sorting, their size-density relationship may be due to another process capable of sorting small grains.

Wozniakiewicz, P. J.; Bradley, J. P.; Ishii, H. A. [Institute of Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); Brownlee, D. E. [Department of Astronomy, University of Washington, Seattle, WA (United States); Kearsley, A. T. [Department of Mineralogy, Natural History Museum, London SW7 5BD (United Kingdom); Burchell, M. J.; Price, M. C., E-mail: P.Wozniakiewicz@kent.ac.uk [School of Physical Sciences, University of Kent, Canterbury, Kent CT2 7NH (United Kingdom)

2012-12-01

321

Generalized similarity observed in finite range magnetohydrodynamic turbulence in the corona and solar wind  

NASA Astrophysics Data System (ADS)

Fluctuations associated with fully developed magnetohydrodynamic (MHD) turbulent flows in an infinite medium are characterized by non-Gaussian statistics which are scale invariant; this implies power law power spectra and multiscaling for the Generalized Structure Functions (GSFs). Given an observable f(r,t) and assuming statistical stationary, the p'th order moment of the GSF of the fluctuating differences <|f(r+L)-f(r)|p> scales as Lzeta(p), where L is the observation scale and ? (p) are the scaling exponents. For turbulence in a system that is of finite size, or that is not fully developed, the statistical property of scale invariance is replaced by a generalized scale invariance, or extended self- similarity (ESS), for which the various moments of the GSF have a power-law dependence on an initially unknown functions, G, such that <|f(r+L)-f(r)|p ˜ G(L)? (p). We have demonstrated [1] ESS in Ulysses in-situ observations of magnetic field fluctuations of the fast, quiet solar polar wind, and shoe that there is a single robust scaling function, G, which is anticipated to be a universal property of finite range MHD turbulent flows. However these are purely temporal observations at a single point in space. We therefore for the first time test ESS on direct measurements of the intensity field, I(r,t), associated with an imaged solar Quiescent Prominence (QP). The Solar Optical Telescope (SOT) on board Hinode provides suitable long time intervals of observation of the solar corona via images at a very high spatial and temporal resolution simultaneously. We focus on specific Ca II H-line observations of a QP which exhibits small scale up-flows with a high degree of variability suggestive of turbulence. We test self-similar properties and power-law scaling behaviour of spatio-temporal intensity fluctuations in the prominence plasma by applying GSF and ESS. We first verify that the statistics of the spatial variations of the intensity measurements are non-Gaussian. We then find power-law power spectra and evidence of ESS. By using ESS we calculate ratios of the scaling exponents ? (p), which we find are consistent with a multifractal field. Finally, we recover the dependence of the 3rd moment of the GSF for the spatial fluctuations on a function G(L) as anticipated for finite range turbulence. [1] S. C. Chapman, R. M. Nicol, Generalized Similarity in Finite Range Solar Wind Magnetohydrodynamic Turbulence, Phys. Rev. Lett. 103, 241101 (2009); S. C. Chapman, R. M. Nicol, E. Leonardis, K. Kiyani, V. Carbone, Observation of universality in the generalized similarity of evolving solar wind turbulence as seen by ULYSSES, Ap. J. Letters, 695, L185, (2009)

Nicol, R.; Leonardis, E.; Chapman, S. C.; Foullon, C.

2011-12-01

322

Raytracing Software for the Simulation of the Solar K-Corona  

NASA Astrophysics Data System (ADS)

In this talk we will present RAYTRACE, a raytracing software developed at the U.S. Naval Research Laboratory. The program is an implementation of the Thomson scattering equations applied to the solar corona (Billings 1966). Synthetic coronal images in total or polarized brightness can be calculated using models of various coronal structures. We have implemented many models for quiescent and dynamic coronal stuctures such as streamers, the heliospheric current sheet (HCS), jets and CMEs. The models are generally analytic representations of the volume electron density, but a generic data cube of electron density can also be used. The core of the program has been written in C++ pimarily for computation speed. An earlier version was written in IDL, but was quite slow. Due to the processing speed of common computers, a high resolution image (512 x 512) of the HCS streamer belt for instance can be generated in less than 1 minute (Pentium 4, 2.5 GHz, 512 Mb RAM, Linux OS). A graphical user interface has been developed in IDL and allows the user to easily enter the parameters required for each model, specifying the position and orientation of the observer and structure, the size and resolution of the images, and then to visualize the output and compare the results to actual coronal images obtained by SOHO/LASCO and in the future by the STEREO/SECCHI coronagraphs (COR1 and COR2). Some of the main features of the front-end interface include mesh plot positioning of structures in space, parameter tuning for the structures and movie making. Different studies have already been done using this software, such as the inversion of the electron density of the streamer belt or the modeling of CMEs for the STEREO mission (presented in another paper at this meeting).

Thernisien, A. F.; Patel, N. S.; Howard, R. A.; Marqué, C.; Vourlidas, A.

2004-12-01

323

COUPLING THE SOLAR DYNAMO AND THE CORONA: WIND PROPERTIES, MASS, AND MOMENTUM LOSSES DURING AN ACTIVITY CYCLE  

SciTech Connect

We study the connections between the Sun's convection zone and the evolution of the solar wind and corona. We let the magnetic fields generated by a 2.5-dimensional (2.5D) axisymmetric kinematic dynamo code (STELEM) evolve in a 2.5D axisymmetric coronal isothermal magnetohydrodynamic code (DIP). The computations cover an 11 year activity cycle. The solar wind's asymptotic velocity varies in latitude and in time in good agreement with the available observations. The magnetic polarity reversal happens at different paces at different coronal heights. Overall the Sun's mass-loss rate, momentum flux, and magnetic braking torque vary considerably throughout the cycle. This cyclic modulation is determined by the latitudinal distribution of the sources of open flux and solar wind and the geometry of the Alfven surface. Wind sources and braking torque application zones also vary accordingly.

Pinto, Rui F.; Brun, Allan Sacha [Laboratoire AIM Paris-Saclay, CEA/Irfu Universite Paris-Diderot CNRS/INSU, 91191 Gif-sur-Yvette (France); Jouve, Laurene [Universite de Toulouse, UPS-OMP, CNRS, IRAP, F-31400 Toulouse (France); Grappin, Roland, E-mail: rui.pinto@cea.fr [UMR 8102 CNRS-Observatoire de Paris, Universite Paris-Diderot, Laboratoire Univers et Theories, 5 Place Jules Janssen, Bat 18, 92195 Meudon (France)

2011-08-20

324

On the Origin of Coronal Mass Ejections: How Does the Emergence of a Magnetic Flux Rope Reorganize the Solar Corona?  

NASA Astrophysics Data System (ADS)

The physical causes leading to the occurrence of Coronal Mass Ejections (CMEs) on the Sun have been debated for almost four decades now. One of the leading mechanisms suggests that a CME may occur as the result of the emergence of a twisted magnetic flux rope from the convection zone into the solar corona. This process have been investigated by a number of researchers over the years, and it has been demonstrated that an eruption of the coronal magnetic field can in principle occur. The majority of these studies, however, involve some ad-hoc prescription of the electric field at the photosphere resembling flux emergence, and they neglect the ambient coronal magnetic field. In addition, most of these flux-emergence simulations are performed in a Cartesian domain, which extends only to a few dozen pressure scale-heights into the corona. Thus, it is difficult to assess the role of boundary driving and limited computational domain on the resulting evolution of the erupting coronal magnetic field. In this paper, we present a new model of CMEs that mitigates these two effects. To achieve this, we couple the "local" magnetic-flux-emergence (MFE) model of Archontis et al. (2004) with a global MHD model of the solar corona and solar wind. The model coupling is performed using the Space Weather Modeling Framework. In the coupled model, the MFE simulation provides time-dependent boundary conditions for all MHD quantities into the global model, where the physical coupling is done at the photospheric boundary. The physical evolution of the system is followed using the BATS-R-US "ideal" MHD code well beyond the complete emergence of the magnetic flux from the convection zone. We discuss the dynamics of the flux emergence process and the related response of the pre-existing coronal magnetic field in the context of CME production.

Roussev, I. I.; Galsgaard, K.; Lugaz, N.; Sokolov, I.

2010-12-01

325

On the Origin of Coronal Mass Ejections: How Does the Emergence of a Magnetic Flux Rope Reorganize the Solar Corona?  

NASA Astrophysics Data System (ADS)

The physical effects responsible for the occurrence of Coronal Mass Ejections (CMEs) on the Sun have been debated for almost four decades now. One of the leading mechanisms suggests that a CME may occur as the result of the emergence of a twisted magnetic flux rope from the convection zone into the solar corona. This process has been investigated by a number of researchers over the years, and it has been demonstrated that an eruption of the coronal magnetic field can in principle occur. The majority of these studies, however, involve some ad-hoc prescription of the electric field at the photosphere resembling flux emergence, and they neglect the ambient coronal magnetic field. In addition, most of these flux-emergence simulations are performed in a Cartesian domain, which extends into the corona up to only a few dozen pressure scale-heights. Because of this, it is difficult to assess how strongly the ad-hoc character of the driving motions and the limited computational domain affect the simulation results for the evolution of the erupting coronal magnetic field. In this paper, we present a new model of CMEs that mitigates these two effects. To achieve this, we couple the "local" magnetic-flux-emergence (MFE) model of Archontis et al. (2004) with a global MHD model of the solar corona and solar wind. The model coupling is performed using the Space Weather Modeling Framework. In the coupled model, the MFE simulation provides time-dependent boundary conditions for all MHD quantities into the global model, where the physical coupling is done at the photospheric boundary. The physical evolution of the system is followed using the BATS-R-US "ideal" MHD code well beyond the complete emergence of the magnetic flux from the convection zone. We discuss the dynamics of the flux emergence process and the related response of the pre-existing coronal magnetic field in the context of CME production.

Roussev, Ilia; Galsgaard, Klaus; Lugaz, Noe; Jacobs, Carla; Sokolov, Igor

2010-05-01

326

A Critical Assessment of Nonlinear Force-Free Field Modeling of the Solar Corona for Active Region 10953  

NASA Astrophysics Data System (ADS)

Nonlinear force-free field (NLFFF) models are thought to be viable tools for investigating the structure, dynamics, and evolution of the coronae of solar active regions. In a series of NLFFF modeling studies, we have found that NLFFF models are successful in application to analytic test cases, and relatively successful when applied to numerically constructed Sun-like test cases, but they are less successful in application to real solar data. Different NLFFF models have been found to have markedly different field line configurations and to provide widely varying estimates of the magnetic free energy in the coronal volume, when applied to solar data. NLFFF models require consistent, force-free vector magnetic boundary data. However, vector magnetogram observations sampling the photosphere, which is dynamic and contains significant Lorentz and buoyancy forces, do not satisfy this requirement, thus creating several major problems for force-free coronal modeling efforts. In this paper, we discuss NLFFF modeling of NOAA Active Region 10953 using Hinode/SOT-SP, Hinode/XRT, STEREO/SECCHI-EUVI, and SOHO/MDI observations, and in the process illustrate three such issues we judge to be critical to the success of NLFFF modeling: (1) vector magnetic field data covering larger areas are needed so that more electric currents associated with the full active regions of interest are measured, (2) the modeling algorithms need a way to accommodate the various uncertainties in the boundary data, and (3) a more realistic physical model is needed to approximate the photosphere-to-corona interface in order to better transform the forced photospheric magnetograms into adequate approximations of nearly force-free fields at the base of the corona. We make recommendations for future modeling efforts to overcome these as yet unsolved problems.

De Rosa, Marc L.; Schrijver, Carolus J.; Barnes, Graham; Leka, K. D.; Lites, Bruce W.; Aschwanden, Markus J.; Amari, Tahar; Canou, Aurélien; McTiernan, James M.; Régnier, Stéphane; Thalmann, Julia K.; Valori, Gherardo; Wheatland, Michael S.; Wiegelmann, Thomas; Cheung, Mark C. M.; Conlon, Paul A.; Fuhrmann, Marcel; Inhester, Bernd; Tadesse, Tilaye

2009-05-01

327

MHD Waves and Instabilities of a Temperature-Anisotropic Plasma in the Solar Corona As a Source of Its Heating  

NASA Astrophysics Data System (ADS)

A strong interaction of MHD waves propagating against the direction of the thermal flux is established to exist in the temperature-anisotropic collisionless plasma with thermal fluxes. Such conditions are typical of the lower corona, where the thermal flux is directed downward, and waves propagate upward from the lower atmosphere. We have shown that aperiodic mirror instabilities of slow MHD waves can develop under solar coronal conditions for weak magnetic fields (B< 1 G), and periodic ion-acoustic instabilities can develop for strong magnetic fields (B> 10 G). It is supposed that the instabilities under consideration can play an important role in the energy balance of the corona and may be considered a large-scale energy source of the wave mechanism of coronal heating. In the process, a self-maintained heating mechanism is formed, i.e., the waves dissipate due to the thermal counter flow, and the downward directed thermal flux itself arises, in turn, because of the plasma heating due to wave dissipation. The growth rates and spatial scales of unstable modes are given for the conditions of the lower corona.

Kuznetsov, V. D.; Dzhalilov, N. S.

2012-04-01

328

Effect of measured surface albedo on modeled Saharan dust solar radiative forcing  

NASA Astrophysics Data System (ADS)

The clear-sky solar radiative forcing of Saharan dust is computed for a case study during the SAharan Mineral dUst experiMent (SAMUM) in May 2006. Size-resolved dust concentrations simulated with a regional model and spectrally resolved surface albedo measurements were used as input for a 1-D radiative transfer model to study the dependence of the dust radiative forcing at solar wavelengths on surface albedo and particle optical properties. Within the considered parameter range, the surface albedo can have a larger impact on the solar radiative forcing of dust at the top of atmosphere (TOA) than the variations of optical properties. At the location of Ouarzazate in Morocco, different measured surface albedo values lead to differences in instantaneous solar TOA solar forcing of up to 15 W m-2 for identical dust properties. This highlights the importance of using an accurate characterization of surface albedo values for estimating solar dust forcing over land. In the regional average over the Sahara using either the standard model values or satellite-based surface albedos leads to differences in the order of 9 W m-2 in the instantaneous solar forcing at TOA, and 5 W m-2 for the diurnal mean TOA forcing.

Tegen, Ina; Bierwirth, Eike; Heinold, Bernd; Helmert, Jürgen; Wendisch, Manfred

2010-12-01

329

THE DUST PROPERTIES OF TWO HOT R CORONAE BOREALIS STARS AND A WOLF-RAYET CENTRAL STAR OF A PLANETARY NEBULA: IN SEARCH OF A POSSIBLE LINK  

SciTech Connect

We present new Spitzer/IRS spectra of two hot R Coronae Borealis (RCB) stars, one in the Galaxy, V348 Sgr, and one lying in the Large Magellanic Cloud, HV 2671. These two objects may constitute a link between the RCB stars and the late Wolf-Rayet ([WCL]) class of central stars of planetary nebulae (CSPNe), such as CPD -56{sup 0} 8032, that has little or no hydrogen in their atmospheres. HV 2671 and V348 Sgr are members of a rare subclass that has significantly higher effective temperatures than most RCB stars, but shares the traits of hydrogen deficiency and dust formation that define the cooler RCB stars. The [WC] CSPN star, CPD -56{sup 0} 8032, displays evidence of dual-dust chemistry showing both polycyclic aromatic hydrocarbons (PAHs) and crystalline silicates in its mid-IR spectrum. HV 2671 shows strong PAH emission but no sign of having crystalline silicates. The spectrum of V348 Sgr is very different from that of CPD -56{sup 0} 8032 and HV 2671. The PAH emission seen strongly in the other two stars is not present. Instead, the spectrum is dominated by a broad emission centered at about 8.2 {mu}m. This feature is not identified with either PAHs or silicates. Several other cool RCB stars, novae, and post-asymptotic giant branch stars show similar features in their IR spectra. The mid-IR spectrum of CPD -56{sup 0} 8032 shows emission features that may be associated with C{sub 60}. The other two stars do not show evidence of C{sub 60}. The different nature of the dust around these stars does not help us in establishing further links that may indicate a common origin. HV 2671 has also been detected by Herschel/PACS and SPIRE. V348 Sgr and CPD -56{sup 0} 8032 have been detected by AKARI/Far-Infrared Surveyor. These data were combined with Spitzer, IRAS, Two Micron All Sky Survey, and other photometry to produce their spectral energy distributions (SEDs) from the visible to the far-IR. Monte Carlo radiative transfer modeling was used to study the circumstellar dust around these stars. HV 2671 and CPD -56{sup 0} 8032 require both a flared inner disk with warm dust and an extended diffuse envelope with cold dust to fit their SEDs. The SED of V348 Sgr can be fit with a much smaller disk and envelope. The cold dust in the extended diffuse envelopes inferred around HV 2671 and CPD -56{sup 0} 8032 may consist of interstellar medium swept up during mass-loss episodes.

Clayton, Geoffrey C.; Gallagher, J. S.; Freeman, W. R.; Camp, K. A., E-mail: gclayton@fenway.phys.lsu.edu, E-mail: wfreem2@lsu.edu, E-mail: kcamp5@tigers.lsu.edu [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 (United States)

2011-08-15

330

SIMULTANEOUS OBSERVATIONS OF A LARGE-SCALE WAVE EVENT IN THE SOLAR ATMOSPHERE: FROM PHOTOSPHERE TO CORONA  

SciTech Connect

For the first time, we report a large-scale wave that was observed simultaneously in the photosphere, chromosphere, transition region, and low corona layers of the solar atmosphere. Using the high temporal and high spatial resolution observations taken by the Solar Magnetic Activity Research Telescope at Hida Observatory and the Atmospheric Imaging Assembly (AIA) on board Solar Dynamic Observatory, we find that the wave evolved synchronously at different heights of the solar atmosphere, and it propagated at a speed of 605 km s{sup -1} and showed a significant deceleration (-424 m s{sup -2}) in the extreme-ultraviolet (EUV) observations. During the initial stage, the wave speed in the EUV observations was 1000 km s{sup -1}, similar to those measured from the AIA 1700 A (967 km s{sup -1}) and 1600 A (893 km s{sup -1}) observations. The wave was reflected by a remote region with open fields, and a slower wave-like feature at a speed of 220 km s{sup -1} was also identified following the primary fast wave. In addition, a type-II radio burst was observed to be associated with the wave. We conclude that this wave should be a fast magnetosonic shock wave, which was first driven by the associated coronal mass ejection and then propagated freely in the corona. As the shock wave propagated, its legs swept the solar surface and thereby resulted in the wave signatures observed in the lower layers of the solar atmosphere. The slower wave-like structure following the primary wave was probably caused by the reconfiguration of the low coronal magnetic fields, as predicted in the field-line stretching model.

Shen, Yuandeng; Liu, Yu, E-mail: ydshen@ynao.ac.cn [Yunnan Astronomical Observatory, Chinese Academy of Sciences, Kunming 650011 (China)

2012-06-20

331

THE DYNAMICS OF DUST GRAINS IN THE OUTER SOLAR SYSTEM  

SciTech Connect

We study the dynamics of large dust grains {approx}>1 {mu}m with orbits outside of the heliosphere (beyond 250 AU). Motion of the solar system through the interstellar medium (ISM) at a velocity of 26 km s{sup -1} subjects these particles to gas and Coulomb drag (grains are expected to be photoelectrically charged) as well as the Lorentz force and the electric force caused by the induction electric field. We show that to zeroth order the combined effect of these forces can be well described in the framework of the classical Stark problem: particle motion in a Keplerian potential subject to an additional constant force. Based on this analogy, we elucidate the circumstances in which the motion becomes unbound, and show that under local ISM conditions dust grains smaller than {approx}100 {mu}m originating in the Oort Cloud (e.g., in collisions of comets) beyond 10{sup 4} AU are ejected from the solar system under the action of the electric force. Orbital motion of larger, bound grains is described analytically using the orbit-averaged Hamiltonian approach and consists of orbital plane precession at a fixed semimajor axis, accompanied by the periodic variations of the inclination and eccentricity (the latter may approach unity in some cases). A more detailed analysis of the combined effect of gas and Coulomb drag shows it is possible to reduce particle semimajor axes, but that the degree of orbital decay is limited (a factor of several at best) by passages through atomic and molecular clouds, which easily eject small particles.

Belyaev, Mikhail A.; Rafikov, Roman R., E-mail: mbelyaev@astro.princeton.ed, E-mail: rrr@astro.princeton.ed [Department of Astrophysical Sciences, Princeton University, Ivy Lane, Princeton, NJ 08540 (United States)

2010-11-10

332

A Comparison of Solar Cycle Variations in the Equatorial Rotation Rates of the Sun's Subsurface, Surface, Corona, and Sunspot Groups  

NASA Astrophysics Data System (ADS)

Using the Solar Optical Observing Network (SOON) sunspot-group data for the period 1985 - 2010, the variations in the annual mean equatorial-rotation rates of the sunspot groups are determined and compared with the known variations in the solar equatorial-rotation rates determined from the following data: i) the plasma rotation rates at 0.94R?,0.95R?,…,1.0R? measured by the Global Oscillation Network Group (GONG) during the period 1995 - 2010, ii) the data on the soft-X-ray corona determined from Yohkoh/SXT full-disk images for the years 1992 - 2001, iii) the data on small bright coronal structures (SBCS) that were traced in Solar and Heliospheric Observatory (SOHO)/EIT images during the period 1998 - 2006, and iv) the Mount Wilson Doppler-velocity measurements during the period 1986 - 2007. A large portion (up to ? 30? latitude) of the mean differential-rotation profile of the sunspot groups lies between those of the internal differential-rotation rates at 0.94R? and 0.98R?. The variation in the yearly mean equatorial-rotation rate of the sunspot groups seems to be lagging behind that of the equatorial-rotation rate determined from the GONG measurements by one to two years. The amplitude of the GONG measurements is very small. The solar-cycle variation in the equatorial-rotation rate of the solar corona closely matches that determined from the sunspot-group data. The variation in the equatorial-rotation rate determined from the Mount Wilson Doppler-velocity data closely resembles the corresponding variation in the equatorial-rotation rate determined from the sunspot-group data that included the values of the abnormal angular motions (> |3?| day-1) of the sunspot groups. Implications of these results are pointed out.

Javaraiah, J.

2013-10-01

333

MHD simulations of the solar corona and solar wind with the observation-based time-varying boundary maps of B_r and other variables  

NASA Astrophysics Data System (ADS)

We will show our recent efforts on the MHD simulation of the solar corona nearby the Sun and the solar wind in the heliosphere up to 20--40 AUs. In resent years, most of our efforts had been focused on the boundary treatment to introduce the observation-based map of B_r (the radial component of the magnetic field in the heliocentric frame, normal to the boundary surface) and other plasma parameters such as the coronal temperature derived from SOHO/EIT emission at the coronal base and the solar wind speed in the interplanetary space derived from IPS (interplanetary scintillation) measurements. Because of the large differences in time-scale, the simulation region is separated into two regions; the sub/trans-Alfvenic nearby-Sun region within 50 -- 100 solar radii, and the heliospheric part from 30--50 solar radii up to 10--40 AUs. In the time-varying nonlinear MHD simulation it is a challenge to handle the time-varying normal component of the magnetic field to the computation boundary. We employed a somehow simple model (differential layer model) that allows us to avoid some computational difficulties and obtain mathematical consistency: the characteristics of the hyperbolic MHD system can be fully taken into account to treat the time-variations of the unspecified MHD variables matching those of the specified time-varying variables on the sub-Alfvenic solar surface boundary. The boundary map rotating with the Sun is applied to the heliospheric rest-frame simulations. By introducing the time-varying boundary map and adding computational treatments, we are now able to obtain the theoretically and observationally consistent MHD solutions of the solar corona and solar wind in both time and space, and thus able to examine how the global corona and interplanetary space respond to the gradual but ceaseless solar-origin variations. We have tested this MHD simulation model with various dataset in various situations and found it is very robust and can give good agreements with the other independent measurements. In this presentation, we will focus on two periods; the last solar activity maximum (around 2002) and the minimum (around 2008 and 2009).

Hayashi, K.

2009-12-01

334

Structure of the Solar System's Dust Disk: Influence of Massive Bodies  

NASA Astrophysics Data System (ADS)

Dust in the solar system is derived from two large reservoirs of collisionally evolved bodies: dust in the outer solar system originates from the Kuiper belt, while the solar system dust bands discovered by IRAS show that the asteroid belt is the dominant source of dust in the inner solar system. The rate of accretion of dust by the Earth inferred from the microcratering record on LDEF is shown to be consistent with an asteroidal source and we use this rate to assess the rate of accretion of dust by the other planets, and hence to discuss the probability of transporting dust from the Kuiper belt to the inner solar system. The structure of the zodiacal cloud is determined by an interplay Between the gravitational and drag forces acting on particles in the cloud, which in turn depends upon the size of the particles. Observed asymmetries of the zodiacal cloud include: the warping of the mean plane of symmetry of the cloud due to planets in inclined orbits; an offset of the center of the cloud from the Sun due to planets in eccentric orbits; and clumping due to resonant trapping of particles by planets. The injection of dust into the zodiacal cloud is a stochastic process and large variations in the optical depth of the cloud are produced by the total disruption of both large asteroids and large comets. The catastrophic fragmentation and dispersal of the large asteroids that were the precursors of the Hirayama asteroid families produced numerous smaller asteroids that, with low probability, may have eventually impacted the Earth. However, these colossal, family-producing collisional events would have also given rise to waves of dust that would have swept through the inner solar system on timescales of tens of thousands to millions of years. The Earth could not have avoided these waves of dust and it is of interest to speculate on the possible climatic consequences of this interaction.

Dermott, S. F.; Kehoe, T. J. J.

2004-12-01

335

Global Coronal Seismology in the Extended Solar Corona through Fast Magnetosonic Waves Observed by STEREO SECCHI COR1  

NASA Astrophysics Data System (ADS)

We present global coronal seismology for the first time, which allows us to determine inhomogeneous magnetic field strength in the extended corona. From the measurements of the propagation speed of a fast magnetosonic wave associated with a coronal mass ejection (CME) and the coronal background density distribution derived from the polarized radiances observed by the STEREO SECCHI COR1, we determined the magnetic field strengths along the trajectories of the wave at different heliocentric distances. We found that the results have an uncertainty less than 40%, and are consistent with values determined with a potential field model and reported in previous works. The characteristics of the coronal medium we found are that (1) the density, magnetic field strength, and plasma ? are lower in the coronal hole region than in streamers; (2) the magnetic field strength decreases slowly with height but the electron density decreases rapidly so that the local fast magnetosonic speed increases while plasma ? falls off with height; and (3) the variations of the local fast magnetosonic speed and plasma ? are dominated by variations in the electron density rather than the magnetic field strength. These results imply that Moreton and EIT waves are downward-reflected fast magnetosonic waves from the upper solar corona, rather than freely propagating fast magnetosonic waves in a certain atmospheric layer. In addition, the azimuthal components of CMEs and the driven waves may play an important role in various manifestations of shocks, such as type II radio bursts and solar energetic particle events.

Kwon, Ryun-Young; Kramar, Maxim; Wang, Tongjiang; Ofman, Leon; Davila, Joseph M.; Chae, Jongchul; Zhang, Jie

2013-10-01

336

Self-Cleaning Transparent Dust Shields for Protecting Solar Panels and Other Devices  

Microsoft Academic Search

The development of transparent flexible dust shields using both single- and three-phase electrodynamic shields is reported here for possible application on Mars and Earth to minimize obscuration of solar panels from the deposition of dust. The electrodynamic screens (EDS) are made of transparent plastic sheets, such as polyethylene terephthalate (PET) for its UV radiation resistance, and a set of parallel

M. K. Mazumder; R. Sharma; A. S. Biris; J. Zhang; C. Calle; M. Zahn

2007-01-01

337

Current-less solar wind driven dust acoustic instability in cometary plasma  

SciTech Connect

A quantitative analysis is presented of the dust acoustic wave instability driven by the solar and stellar winds. This is a current-less kinetic instability which develops in permeating plasmas, i.e.., when one quasi-neutral electron-ion wind plasma in its propagation penetrates through another quasi-neutral plasma which contains dust, electrons, and ions.

Vranjes, J. [Belgian Institute for Space Aeronomy, Ringlaan 3, 1180 Brussels (Belgium)

2011-08-15

338

How Much Dust is Processed by a Single Lightning Bolt in the Proto-Solar Nebula?  

NASA Astrophysics Data System (ADS)

We have created a simple model of the oxygen isotopic evolution of dust in the proto-solar nebula due to nebular lightning. The effects of varying lightning temperature and the evaporation coefficient of SiO will be presented.

Paquette, J. A.; Nuth, J. A.

2013-09-01

339

Using the nonlinear geometrical acoustics method in the problem of moreton and EUV wave propagation in the solar corona  

NASA Astrophysics Data System (ADS)

Propagation of shock related Moreton and EUV waves in the solar atmosphere is simulated by the nonlinear geometrical acoustics method. This method is based on the ray approximation and takes account of nonlinear wave features: dependence of the wave velocity on its amplitude, nonlinear dissipation of wave energy in the shock front, and the increase in its duration with time. The paper describes ways of applying this method to solve the propagation problem of a blast magnetohydrodynamic shock wave. Results of analytical modeling of EUV and Moreton waves in the spherically symmetric and isothermal solar corona are also presented. The calculations demonstrate deceleration of these waves and an increase in their duration. The calculation results of the kinematics of the EUV wave observed on the Sun on January 17, 2010 are presented as an example.

Afanasyev, An. N.; Uralov, A. M.; Grechnev, V. V.

2011-12-01

340

The long-term stability of the visible F corona at heights of 3-6 R_?  

NASA Astrophysics Data System (ADS)

Context: CMEs can effect the distribution of dust grains in the corona. The brightness of the visible F corona is expected therefore to change as the frequency of CMEs varies with solar cycle. Aims: We search for a variation in the F corona by comparing LASCO C2 observations from solar minimum and maximum. Methods: An established inversion method is used to calculate the visible F corona brightness from LASCO C2 solar minimum observations made during 1996/10. Good agreement is found with the F corona brightness calculated from Skylab observations during 1973/05-1974/02 for heights of 3-6 R_?. The unpolarized brightness, which is dominated by the unpolarized F corona brightness at these heights, is obtained by subtracting many pairs of polarized brightness images from total brightness images and averaging over a solar rotation. We calculate the unpolarized brightness for both solar activity minimum and maximum. Results: The unpolarized brightness, and therefore the F corona, remain virtually unchanged between solar minimum and maximum at heights above 2.6 R_?, despite the large change in the shape and activity of the corona. Using a simple density model, it is shown that the small variation in unpolarized brightness seen below 2.6 R_? can arise from differences in the distribution of electron density, and therefore cannot be attributed to a variation in the F corona. Conclusions: Despite the large rise in frequency of CMEs from solar minimum to maximum, the F coronal brightness, at heights of 3-6 R_? in the visible, remains very stable.

Morgan, H.; Habbal, S. R.

2007-08-01

341

Selective heating of minority ions in the lower solar corona by electrostatic ion cyclotron waves  

Microsoft Academic Search

Assuming that monochromatic ion cyclotron wave trains are generated in the corona above active regions on the sun, the influence of these waves on the distribution function of minority ion species is studied using a numerical test particle approach. In certain regions of phase space a sensitive dependence on the initial conditions of the nonlinearly coupled system of waves and

A. Luhn

1984-01-01

342

Observation of sectored structure in the outer solar corona: Correlation with interplanetary magnetic field  

Microsoft Academic Search

Daily images of the white light corona between 3 and 10 R? have been recorded by a coronagraph aboard the OSO-7 unmanned satellite since October 3, 1971. Images for the years 1972 and 1973 have been examined for persistent coronal forms. For most of 1972 there passed over the Sun's east limb a regular alternation of northern and southern streamers

R. A. Howard; M. J. Koomen

1974-01-01

343

HIGH DYNAMIC RANGE IMAGES OF THE SOLAR CORONA BETWEEN 150 AND 450 MHz  

SciTech Connect

We present radio images of the quiet Sun obtained with the Nancay Radioheliograph between 150 and 450 MHz, using the latest improvements in the instrument and in the data processing techniques. We emphasize new aspects of the corona observable in this frequency range, particularly the prominence of coronal holes, and discuss implications for future studies.

Mercier, Claude; Chambe, Gilbert [Meudon Observatory, 92190 Meudon (France)], E-mail: claude.mercier@obspm.fr, E-mail: gilbert.chambe@obspm.fr

2009-08-01

344

Nonlinear Damping of Fast Waves and Plasma Heating in the Solar Corona  

Microsoft Academic Search

Fast waves can be excited in the corona by compressional perturbations of magnetic field lines which are anchored into the dense convective zone and displaced by the plasma motions there. The consequent linear dissipation of fast waves in the resonant layers can contribute to coronal heating. A difficulty of this dissipation mechanism is that the setup time of the linear

Y. Voitenko; M. Goossens

2001-01-01

345

Heating of the Solar Corona by Alfvén Waves: Self-Induced Opacity  

Microsoft Academic Search

There have been derived equations describing the static distributions of temperature and wind velocity at the transition region within the framework of the magnetohydrodynamics (MHD) of fully ionized hydrogen plasma. We have also calculated the width of the transition between the chromosphere and corona as a self-induced opacity of the high-frequency Alfvén waves (AWs). The domain wall is a direct

N. I. Zahariev; T. M. Mishonov

2011-01-01

346

Method of and Apparatus for Reducing Back Corona Effects.  

National Technical Information Service (NTIS)

The invention relates to a method of, and apparatus for, reducing back corona effects in the process of charging particulate material in an electrostatic precipitator. An apparatus for reducing back corona effects while charging high resistivity dust or t...

Pontius Smith

1978-01-01

347

The Solar Eclipse of 2006 and the Origin of Raylike Features in the White-Light Corona  

NASA Astrophysics Data System (ADS)

Solar eclipse observations have long suggested that the white-light corona is permeated by long fine rays. By comparing photographs of the 2006 March 29 total eclipse with current-free extrapolations of photospheric field measurements and with images from the Solar and Heliospheric Observatory (SOHO), we deduce that the bulk of these linear features fall into three categories: (1) polar and low-latitude plumes that overlie small magnetic bipoles inside coronal holes, (2) helmet streamer rays that overlie large loop arcades and separate coronal holes of opposite polarity, and (3) ``pseudostreamer'' rays that overlie twin loop arcades and separate coronal holes of the same polarity. The helmet streamer rays extend outward to form the plasma sheet component of the slow solar wind, while the plumes and pseudostreamers contribute to the fast solar wind. In all three cases, the rays are formed by magnetic reconnection between closed coronal loops and adjacent open field lines. Although seemingly ubiquitous when seen projected against the sky plane, the rays are in fact rooted inside or along the boundaries of coronal holes.

Wang, Y.-M.; Biersteker, J. B.; Sheeley, N. R., Jr.; Koutchmy, S.; Mouette, J.; Druckmüller, M.

2007-05-01

348

Height of shock formation in the solar corona inferred from observations of type II radio bursts and coronal mass ejections  

NASA Astrophysics Data System (ADS)

Employing coronagraphic and EUV observations close to the solar surface made by the Solar Terrestrial Relations Observatory (STEREO) mission, we determined the heliocentric distance of coronal mass ejections (CMEs) at the starting time of associated metric type II bursts. We used the wave diameter and leading edge methods and measured the CME heights for a set of 32 metric type II bursts from solar cycle 24. We minimized the projection effects by making the measurements from a view that is roughly orthogonal to the direction of the ejection. We also chose image frames close to the onset times of the type II bursts, so no extrapolation was necessary. We found that the CMEs were located in the heliocentric distance range from 1.20 to 1.93 solar radii (Rs), with mean and median values of 1.43 and 1.38 Rs, respectively. We conclusively find that the shock formation can occur at heights substantially below 1.5 Rs. In a few cases, the CME height at type II onset was close to 2 Rs. In these cases, the starting frequency of the type II bursts was very low, in the range 25-40 MHz, which confirms that the shock can also form at larger heights. The starting frequencies of metric type II bursts have a weak correlation with the measured CME/shock heights and are consistent with the rapid decline of density with height in the inner corona.

Gopalswamy, N.; Xie, H.; Mäkelä, P.; Yashiro, S.; Akiyama, S.; Uddin, W.; Srivastava, A. K.; Joshi, N. C.; Chandra, R.; Manoharan, P. K.; Mahalakshmi, K.; Dwivedi, V. C.; Jain, R.; Awasthi, A. K.; Nitta, N. V.; Aschwanden, M. J.; Choudhary, D. P.

2013-06-01

349

Solar heating of the Uranian mesopause by dust of ring origin  

SciTech Connect

Submicron dust absorption of visible-wavelength solar energy, in conjunction with inhibition of IR radiation, is assumed in the present estimate of the magnitude of an equatorial heat source due to such dust in the upper atmosphere of Uranus. The dust is noted to be capable of generating enough mesopause-level heat to account for heat sources observed only near the equator. Such dust is nevertheless excluded as a heat source for the 500-800 K thermospheric temperatures recorded by the Voyager UV spectrometer. The influx needed for a significant heat source corresponds to decomposition into submicron dust of about 100, 10-km diameter moons with 1.5 g/cu cm density; this is a plausible average dust flux for the rings of Uranus. 32 refs.

Rizk, B.; Hunten, D.M. (Arizona Univ., Tucson (USA))

1990-12-01

350

A Numerical Method for the Visualization of the Fe XIV Emission in the Solar Corona Using Broadband Filters  

NASA Astrophysics Data System (ADS)

The goal of this article is to demonstrate how the emission from the Fe XIV 530.3 nm coronal emission line, also known as the green line, can be extracted from images taken during total solar eclipses with commercially available color cameras. This concept is technically feasible because Fe XIV is the brightest optical emission line in the inner corona, and because the sensors of these cameras are retrofitted with a standard Bayer mask, namely, a square grid of spectrally broad (about 100 nm) green, blue, and red filters in the ratio of 2:1:1. The technique presented here, and developed for this purpose, yields qualitatively accurate Fe XIV images, as tested by comparing with Fe XIV eclipse images taken with a 0.15 nm narrow-bandpass filter. While this approach cannot replace narrow-bandpass Fe XIV images for quantitative studies of the corona, it provides a simple and affordable tool for studying the morphology of coronal structures emitting preferentially at the peak ionization temperature of Fe XIV, namely, 1.8 × 106 K.

Martišek, K.; Druckmüllerová, H.

2011-12-01

351

Coupling of the Photosphere to the Solar Corona: A laboratory and observational study of Alfvén wave interaction with a neutral gas  

SciTech Connect

The grant funded a three year project to investigate the role of Alfvén waves as a possible mechanism heating plasmas, with relevance to solar coronal heating. Evidence suggests that there is strong coupling between the solar photosphere, corona and solar wind through Alfvén wave interaction with the neutral gas particles. A laboratory experimental and solar observational plan was designed to investigate in detail this interaction. Although many of the original research goals were met, difficulties in detecting the Alfvén wave signature meant that much of the research was stymied. This report summaries the work during the grant period, the challenges encountered and overcome, and the future research directions.

watts, Christopher

2010-01-31

352

Stereoscopic observations of a solar flare hard X-ray source in the high corona  

Microsoft Academic Search

The vertical structure of the impulsive and gradual hard X-ray sources in high coronae and the characteristics of the impulsive soft X-ray emission are investigated on the basis of PVE, ICE, and GOES observations of the energetic flare on February 16, 1984. The average photon spectra observed by these instruments during the impulsive and gradual hard X-ray bursts are summarized.

S. R. Kane; J. McTiernan; J. Loran; E. E. Fenimore; R. W. Klebesadel; J. G. Laros

1992-01-01

353

Homologous sudden disappearances of transequatorial interconnecting loops in the solar corona  

Microsoft Academic Search

Wehavefoundaremarkable sequenceof homol- ogousdisappearances of transequatorial X-ray loops linking active regions. Each disappearance was closely associated with a major flare and coronal mass ejection (CME). In each case the flarings precede the disappearances and the CMEs. Mass estimates for the X-ray loops are similar to CME masses. This, the timing of the disappearances, their morphology,andthehomologyoftheeventsinthesequence, providedirectevidenceforanewclassofCMEoriginsinthe low corona. We also

Josef I. Khan; Hugh S. Hudson

1999-01-01

354

The origin and role of dust in the early Solar System  

Microsoft Academic Search

Dust is believed to have been the fundamental building material of the planetesimals that accumulated to form minor planets, solid planets and the cores of giant planets. In this model the first generation particulates were pre-solar interstellar grains. At the end of the 10 K free-fall collapse phase that preceded the solar nebula 1, these grains contained nearly all of

Don Brownlee

1994-01-01

355

CHARGE STATE EVOLUTION IN THE SOLAR WIND. II. PLASMA CHARGE STATE COMPOSITION IN THE INNER CORONA AND ACCELERATING FAST SOLAR WIND  

SciTech Connect

In the present work, we calculate the evolution of the charge state distribution within the fast solar wind. We use the temperature, density, and velocity profiles predicted by Cranmer et al. to calculate the ionization history of the most important heavy elements in the solar corona and solar wind: C, N, O, Ne, Mg, Si, S, and Fe. The evolution of each charge state is calculated from the source region in the lower chromosphere to the final freeze-in point. We show that the solar wind velocity causes the plasma to experience significant departures from equilibrium at very low heights, well inside the field of view (within 0.6 R{sub sun} from the solar limb) of nearly all the available remote-sensing instrumentation, significantly affecting observed spectral line intensities. We also study the evolution of charge state ratios with distance from the source region, and the temperature they indicate if ionization equilibrium is assumed. We find that virtually every charge state from every element freezes in at a different height, so that the definition of freeze-in height is ambiguous. We also find that calculated freeze-in temperatures indicated by charge state ratios from in situ measurements have little relation to the local coronal temperature of the wind source region, and stop evolving much earlier than their correspondent charge state ratio. We discuss the implication of our results on plasma diagnostics of coronal holes from spectroscopic measurements as well as on theoretical solar wind models relying on coronal temperatures.

Landi, E.; Gruesbeck, J. R.; Lepri, S. T.; Zurbuchen, T. H.; Fisk, L. A. [Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI 48109 (United States)

2012-12-10

356

A flux of EUV emission measured on-board the “CORONAS” artificial satellites near minimum and maximum of the 23rd cycle of solar activity  

NASA Astrophysics Data System (ADS)

The paper presents data on ionizing short-wave UV-emission of the Sun in a wave-range ? ? 130 nm measured on-board the CORONAS-I and CORONAS-F satellites. There were obtained absolute values of solar flux emission in the spectrum range ? ? 130 nm and the band near H L? hydrogen line on-board both satellites. Measurements on-board the CORONAS-I satellite coincided with a phase near the minimum of solar activity (F10.7 = 80 100). In the period from March to June of 1994 the solar flux was equal on the average to 7.5 erg cm-2 s-1 for ? ? 130 nm and the intensity of emission in H L? was equal to (5.5 6.1) erg cm-2 s-1. The measurements on-board the CORONAS-F were performed near the maximum of solar activity (F10.7 = 143 279). Emission intensity in H L? line was about 6.8 8.2 erg cm-2 s-1 and in the wave-range ? ? 130 nm it was equal on the average to 11 13 erg cm-2 s-1. EUV measurements are in agreement with the data obtained on-board UARS satellite and with the results of ionospheric measurement of E-layer critical frequencies. These measurements agree with data of contemporary models as well. A lot of flares including bright ones were observed. The measurement data of a bright flare of X-ray class X5.3 on 25.05.2001 are given. The paper presents the results of comparison between the CORONAS-F data and the X-ray fluxes in waveband 0.1 0.8 nm (GOES). This comparison demonstrated that X-ray emission measured on-board the GOES spacecraft and measured due to SUVR instrument (with filters in wave-range <12 nm) changed almost synchronously in the ranges 0.1 0.8 and 0.1 12 nm. The data measured due to VUSS showed that EUV emission appeared a few minutes (1 13) before X-ray emission. Apparently it evidences that at first a flare begins in the chromosphere and then a heating area is spreading higher. Solar emission increases by ˜20 30% in the range ? < 130 nm, and only by 8 10% in EUV range. Changes of extreme ultraviolet (EUV) solar flux were registered during the annular solar eclipse of May 31, 2003, when the CORONAS-F satellite thrice intersected a zone of the solar eclipse.

Nusinov, A. A.; Kazachevskaya, T. V.; Katyushina, V. V.

357

Heating of the quiet solar corona from measurements of the FET/TESIS instrument on-board the KORONAS-FOTON satellite  

NASA Astrophysics Data System (ADS)

The paper presents the first results of the observations of time evolution of the quiet solar corona brightenings obtained due to very rapid photography of the corona with full-disk EUV telescopes of the FET/TESIS instrument onboard the KORONA FOTON satellite. The measurements were performed simultaneously in the emission of the Fe IX / X 17.1 and Fe VIII 13.1 spectral lines with 10 second temporal cadence and spatial scale of 1.7 arc seconds within one hour. This test observation, carried out on 15 July 2009, was analyzed in order to determine whether this type of observation can be used to identify individual microevents in the solar corona heating that are above the tresholds of spatial and temporal resolutions of the observations of non-active regions in the solar atmosphere. For this purpose, a simple method was used involving cross-correlation of the plasma emission time evolution at different temperatures, each time from observations of identical elements. The results obtained are confronted with the expected observable manifestations of the corona heating via nanoflares. TESIS is a set of instruments for the Sun photography developed in the Lebedev Physics Institute of the Russian Academy of Sciences that was launched into orbit in January 2009.

Rybák, J.; Gömöry, P.; Benz, A.; Bogachev, P.; Brajša, R.

2010-12-01

358

The role of presolar dust in the formation of the solar system  

SciTech Connect

This thesis attempts to construct an interpretive framework encompassing all of the apparently contradictory data on meteorites and other solar-system objects. The most important single difference between this new theoretical framework and the one presently popular is the explicit elimination of the assumption that the majority of the solids that make up the meteorites and terrestrial planets formed by condensation from a hot, gaseous, solar nebula. This assumption requires that the pre-existing interstellar dust evaporated during the formation of the solar system, but a growing body of isotopic data on components from primitive meteorites indicates that a considerable fraction of this presolar dust survived. The thrust of this thesis is that the primary building material for meteorites and terrestrial planets was presolar dust which survived evaporation during the formation of the solar system.

Huss, G.R.

1987-01-01

359

Dust exploration in the outer solar system by the power sail mission  

NASA Astrophysics Data System (ADS)

We propose the observations of interplanetary dust at outer region of the solar system by the Power Sail mission which is planned in Japan. In this paper, we report the design and expected performance of this planning. Recent observations from space and ground-based telescopes show the exo-zodiacal disks around pre main-sequence and main-sequence stars. To extend our knowledge into the extra solar systems, it is very important to understand the interplanetary dust of "our" solar system. The origin and evolution of the zodiacal dust are not yet fully understood. Unfortunately, Earth-bound telescopes have a disadvantage in observations because they only observe the scattered light and/or thermal emission integrated along the line of sight. The Power Sail mission, which is a spacecraft cruising around the interplanetary space toward Jupiter, is a unique opportunity to observe the zodiacal light from the various view points and will give us the spatial distribution and spectral behavior of the dust along the heliocentric distance. The mission also plans to employ a dust counter, which will realize "in-situ" number count of the dusts. A large area PVDF-type counter on large area sail part is designed, which will give us the first statistically-meaningful number of data on the interplanetary dust particles.

Usui, F.; Yano, H.; Hasegawa, S.; Matsuura, S.; Ishiguro, M.; Ueno, M.

360

Electron-Temperature Maps of the Low Solar Corona: ISCORE Results from the Total Solar Eclipse of 29 March 2006 in Libya  

NASA Astrophysics Data System (ADS)

We conducted an experiment in conjunction with the total solar eclipse of 29 March 2006 in Libya that measured the coronal intensity through two filters centered at 3850 Å and 4100 Å with bandwidths of ? 40 Å. The purpose of these measurements was to obtain the intensity ratio through these two filters to determine the electron temperature. The instrument, Imaging Spectrograph of Coronal Electrons (ISCORE), consisted of an eight inch, f/10 Schmidt Cassegrain telescope with a thermoelectrically-cooled CCD camera at the focal plane. Results show electron temperatures of 105 K close to the limb to 3×106 K at 1.3 R ?. We describe this novel technique, and we compare our results to other relevant measurements. This technique could be easily implemented on a space-based platform using a coronagraph to produce global maps of the electron temperature of the solar corona.

Reginald, Nelson L.; St. Cyr, O. C.; Davila, Joseph M.; Rabin, Douglas M.; Guhathakurta, Madhulika; Hassler, Donald M.

2009-12-01

361

Recent rubble-pile origin of asteroidal solar system dust bands and asteroidal interplanetary dust particles  

NASA Astrophysics Data System (ADS)

25% of all the dust in the zodiacal cloud may be associated with the "ten-degree" dust band and 5% with the "near-ecliptic" bands. Dynamical modeling of the structure of the ten-degree band shows that the initial mean proper inclination of the dust particle orbits needed to account for this band is 9.3° and equal to the mean proper inclination of the Veritas family asteroids. Dynamical evidence on the ages of asteroid families, and chemical and physical evidence on the nature of interplanetary dust particles (IDPs), makes it likely that the dust bands are the result of the recent catastrophic disruptions of small "rubble piles". If this is the case, we calculate that 85% of all the asteroidal IDPs collected in Earth's stratosphere could originate from the Veritas family. Thus, in our IDP collections on Earth, we may already have an abundance of sample from a known C-type asteroids.

Dermott, Stanley F.; Kehoe, Thomas J. J.; Durda, Daniel D.; Grogan, Keith; Nesvorný, David

2002-11-01

362

Soft X-ray Images of the Solar Corona with a Normal-Incidence Cassegrain Multilayer Telescope.  

PubMed

High-resolution images of the sun in the soft x-ray to extreme ultraviolet(EUV) regime have been obtained with normal-incidence Cassegrain multilayer telescopes operated from a sounding rocket in space. The inherent energy-selective property of multilayer-coated optics allowed distinct groups of emission lines to be isolated in the solar corona and the transition region. The Cassegrain telescopes provided images in bands centered at 173 and 256 angstroms. The bandpass centered at 173 angstroms is dominated by emission from the ions Fe IX Fe X. This emission is from coronal plasma in the temperature range 0.8 x 10(6) to 1.4 x 10(6)K. The images have angular resolution of about 1.0 to 1.5 arc seconds, and show no degradation because of x-ray scattering. Many features of coronal structure, including magnetically confined loops of hot plasma, coronal plumes, polar coronal holes, faint structures on the size scale of supergranulation and smaller, and features due to overlying cool prominences are visible in the images. The density structure of polar plumes, which are thought to contribute to the solar wind, has been derived from the observations out to 1.7 solar radii. PMID:17783129

Walker, A B; Lindblom, J F; Barbee, T W; Hoover, R B

1988-09-30

363

Simulation Experiments on Dust Aggregation in the Early Solar Nebula  

NASA Astrophysics Data System (ADS)

The evolution of dust particles in the early solar nebula is most probably determined by aggregation of micron-sized grains. With respect to different scenarios as Brownian motion, differential sedimentation, orbital decay and turbulence, relative velocities between different particles are generated which lead to subsequent collisions, sticking and growth. The aggregates evolve to certain structures which might be characterized by a fractal dimension d, relating the mass m of the clusters to its size s, m ~ s(d) . Computer simulations show that d is supposed to be close to 2. The value of d is important for the timescales of the formation of planetesimals. Parameters for the model calculations, such as sticking probabilities for different velocities and the ability of the particles for sliding and rolling on the surfaces during impacts are needed. We carried out collision experiments with aggregates consisting of up to a few hundred single micron-sized amorphous SiO_2 particles. The device generating these aggregates, an aggregation experiment of its own, produces clusters of the fractal dimension 1.9. In 'levitation tube' experiments, we observed collisions between single clusters due to differential sedimentation. The collision velocities ranged from 1 mm/s to 1 cm/s. All collisions resulted in sticking as predicted by theory. We found no significant restructuring within the limits of our optical system, a long distance microscope and flash lamp illumination. Images were taken by a digital CCD camera (256 * 256 pixels) with 150 frames per second. In another series of experiments under the microgravity conditions of the drop tower in Bremen as well as in the laboratory, we directed a beam of the above-mentioned clusters to a thin target and observed sticking and restructuring due to the impact and gravitational torques. We will present new results of these investigations.

Wurm, G.; Blum, J.

1996-09-01

364

The EUV Unresolved Corona  

NASA Astrophysics Data System (ADS)

The unresolved corona for three active regions (ARs) above the solar limb is investigated. Intensities measured for ions formed above 1 MK are presented as a function of height above the solar surface. The observed decrease in intensity with altitude is found to be best fit by an exponential. Furthermore, this exponential decrease is approximately the decrease in emission expected for a hydrostatic planar geometry atmosphere, where the scale height temperature is dependent on the dynamics of the AR. For two of the ARs analyzed, we have found that the best-fit temperature derived from the exponential fits is consistent with an isothermal hydrostatic unresolved corona.

Cirtain, Jonathan; Martens, P. C. H.; Acton, L. W.; Weber, Mark

2006-05-01

365

Self-similar signature of the active solar corona within the inertial range of solar-wind turbulence.  

PubMed

We quantify the scaling of magnetic energy density in the inertial range of solar-wind turbulence seen in situ at 1 AU with respect to solar activity. At solar maximum, when the coronal magnetic field is dynamic and topologically complex, we find self-similar scaling in the solar wind, whereas at solar minimum, when the coronal fields are more ordered, we find multifractality. This quantifies the solar-wind signature that is of direct coronal origin and distinguishes it from that of local MHD turbulence, with quantitative implications for coronal heating of the solar wind. PMID:17677760

Kiyani, K; Chapman, S C; Hnat, B; Nicol, R M

2007-05-23

366

Heating of the Solar Chromosphere and Corona by Alfvén Wave Turbulence  

NASA Astrophysics Data System (ADS)

A three-dimensional magnetohydrodynamic (MHD) model for the propagation and dissipation of Alfvén waves in a coronal loop is developed. The model includes the lower atmospheres at the two ends of the loop. The waves originate on small spatial scales (less than 100 km) inside the kilogauss flux elements in the photosphere. The model describes the nonlinear interactions between Alfvén waves using the reduced MHD approximation. The increase of Alfvén speed with height in the chromosphere and transition region (TR) causes strong wave reflection, which leads to counter-propagating waves and turbulence in the photospheric and chromospheric parts of the flux tube. Part of the wave energy is transmitted through the TR and produces turbulence in the corona. We find that the hot coronal loops typically found in active regions can be explained in terms of Alfvén wave turbulence, provided that the small-scale footpoint motions have velocities of 1-2 km s-1 and timescales of 60-200 s. The heating rate per unit volume in the chromosphere is two to three orders of magnitude larger than that in the corona. We construct a series of models with different values of the model parameters, and find that the coronal heating rate increases with coronal field strength and decreases with loop length. We conclude that coronal loops and the underlying chromosphere may both be heated by Alfvénic turbulence.

van Ballegooijen, A. A.; Asgari-Targhi, M.; Cranmer, S. R.; DeLuca, E. E.

2011-07-01

367

Characterization of small dust particles in the Solar System through polarization: Laboratory measurements  

NASA Astrophysics Data System (ADS)

Small dust particles are present in different scenarios in the Solar System like in the atmospheres of planets, satellites an comets, surfaces of different objects, in the space between them, and planetary rings. By analyzing the solar light scattered by those particles we can retrieve valuable information about their physical properties (shape, size, and composition) as well as their location within a certain atmosphere. The main purpose of this talk is to show how experimental data of intensity and polarization of the scattered light of different atmospheric dust analogues can be used to shed some light on the nature of dust particles in the Solar System. The experimental data presented in this talk are available in digital form in the Amsterdam-Granada Light scattering Database at www.iaa.es/scattering (Muñoz, Moreno, Guirado, Dabrowska, Volten, Hovenier; JQSRT 2012; 113(7): 565-574).

Muñoz, Olga

2013-04-01

368

Large Area Dust Detector onboard Solar Power Sail Spacecraft  

Microsoft Academic Search

JAXA is aiming to launch the solar power sail engineering demonstrator to the outer planet region of the solar system like Jupiter and the Jovian Trojan asteroids in 2010's. Its interplanetary cruise is a relevant and rare opportunity to monitor physical properties that may be varied by heliocentric distances continuously such as solar wind, solar magnetosphere and micrometeoroid flux. We

Hajime Yano

2008-01-01

369

Solar Wind Slowdown Due to Dust Pickup during Interplanetary Field Enhancements  

NASA Astrophysics Data System (ADS)

The interplanetary field enhancements (IFEs) are characterized by their cusp-shaped enhancement in the magnetic field magnitude. They are observed throughout the inner solar system from 0.72AU by Pioneer Venus Orbiter to 5AU by Ulysses. The annual IFE rate is ten at 0.72AU and around eight at 1AU, i.e., decreases as the heliocentric distance increases. Multiple-spacecraft observations show that IFEs are moving radially away from the Sun at nearly the ambient solar wind speed. During the IFE events, case studies show that while there are correlated diamagnetic compensations in pressure there are no significant correlated changes in the solar wind speed. An IFE formation mechanism that explains most of the IFE features is that IFEs result from interactions between solar wind and clouds of picked up nanoscale charged dust, which is released in interplanetary collisions between objects of 10 to 1000m in diameter. The enhanced magnetic field behaves as a magnetic barrier that can transfer momentum to the charged dust from the solar wind. Momentum lifts the dust outward in the solar gravitational well. A prediction of this hypothesis is that solar wind will be slowed down even when the IFEs have reached exactly the solar wind speed. To test this hypothesis, we perform a superposed analysis on the radial velocity of IFEs observed at 1AU. In contrast to the case studies, the statistical results have a significant change in speed. The velocity on the solar wind side of the IFEs is smaller than the ambient velocity. This slowdown increases for larger IFEs with larger estimated mass. In addition, the amount of momentum due to the solar wind slowdown is quantitatively consistent with the momentum expected to be needed to lift the dust out of the Sun's gravitational potential well, which is in strong support of our IFE formation mechanism.

Lai, Hairong; Russell, Christopher; Wei, Hanying

2013-04-01

370

Tomography and the distribution of streamers in the extended solar corona: some implications for large-scale MHD models  

NASA Astrophysics Data System (ADS)

cycle. Streamers are most often shaped as extended, often very narrow, plasma sheets. At most times outside the height of solar maximum, there are two separate stable large helmet streamer belts extending from mid-latitudes (in both North and South). At solar minimum, the streamers converge and join near the equator, giving the impression of a single large helmet streamer. Outside of solar minimum, the two streamers do not join, forming separate high-density sheets in the extended corona (one in the North, another in the South). At solar maximum, streamers rise radially from their source regions, whilst during the ascending and descending activity phases, streamers are skewed towards the equator. For most of the activity cycle, streamers share the same latitudinal extent as filaments on the disk, showing that large-scale stable streamers are closely linked to the same large-scale photospheric magnetic configuration which give rise to large filaments. The polewards footpoints of the streamers are often above crown polar filaments and the equatorial footpoints are above filaments or active regions (or above the photospheric neutral lines which underlie these structures). The high-density structures arising from the equatorial active regions either rise and form the equatorial footpoints of mid-latitude quiescent streamers, or form unstable streamers at the equator, not connected to the quiescent streamer structure at higher latitude (so there are often three streamer sheets sharing the same extended longitudinal region). Comparison between the tomography results and a potential field source surface model shows that streamers are not necessarily associated with a magnetic polarity reversal, but rather are regions containing field lines arising from widely-separated sources at the Sun. We call these convergence sheets (sometimes called 'pseudostreamers'). Large-scale coronal MHD models could improve their agreement with observation by incorporating the results of tomography.

Morgan, H.; Habbal, S. R.

2010-12-01

371

Hanle effect from a dipolar magnetic structure: the case of the solar corona and the case of a star  

NASA Astrophysics Data System (ADS)

Context. The context is the magnetic field measurement in external solar or stellar layers by interpreting line polarization measurements and the Hanle effect. Aims: The aim is to model the Hanle effect depolarization by integrating upon a star on the one hand, and by integrating along a line-of-sight through the solar corona on the other hand. Methods: The formalism of the atomic density matrix is recalled. Particular attention was devoted to the four axis rotations necessary to transform the magnetic field reference frame into that of the line-of-sight. Results: In the stellar case, the discrepancy between the results by López Ariste et al. (2011, A&A, 527, A120) and the symmetry considerations by Ignace etal. (2011, A&A, 530, A82) is resolved. In the solar case, the computations of the hydrogen Ly? polarization by Derouich et al. (2010, A&A, 511, A7) are revisited, owing to symmetry considerations. Conclusions: In the stellar case, we confirm that the effect integrated on a star leads to a non-vanishing magnetic depolarization due to the high non-linearity of the Hanle effect. In the solar case, we find that the Hanle sensitivity of hydrogen Ly? and Ly? could be better adapted to the measurement of the coronal background magnetic field. They form a pair of lines of different and complementary sensitivity, which makes it possible to determine the full vector. Ly? would be instead adapted to the coronal loop magnetic field measurement, because this field is stronger and suited to the Ly? Hanle sensitivity.

Bommier, V.

2012-03-01

372

Electron Temperatures and Flow Speeds of the Low Solar Corona: MACS Results from the Total Solar Eclipse of 29 March 2006 in Libya  

NASA Astrophysics Data System (ADS)

An experiment was conducted in conjunction with the total solar eclipse on 29 March 2006 in Libya to measure both the electron temperature and its flow speed simultaneously at multiple locations in the low solar corona by measuring the visible K-coronal spectrum. Coronal model spectra incorporating the effects of electron temperature and its flow speed were matched with the measured K-coronal spectra to interpret the observations. Results show electron temperatures of (1.10±0.05) MK, (0.70±0.08) MK, and (0.98±0.12) MK, at 1.1 R ? from Sun center in the solar north, east and west, respectively, and (0.93±0.12) MK, at 1.2 R ? from Sun center in the solar west. The corresponding outflow speeds obtained from the spectral fit are (103±92) km s-1, (0+10) km s-1, (0+10) km s-1, and (0+10) km s-1. Since the observations were taken only at 1.1 R ? and 1.2 R ? from Sun center, these speeds, consistent with zero outflow, are in agreement with expectations and provide additional confirmation that the spectral fitting method is working. The electron temperature at 1.1 R ? from Sun center is larger at the north (polar region) than the east and west (equatorial region).

Reginald, Nelson L.; Davila, Joseph M.; St. Cyr, O. C.; Rabin, Douglas M.; Guhathakurta, Madhulika; Hassler, Donald M.; Gashut, Hadi

2011-05-01

373

A NEW IMPLEMENTATION OF THE MAGNETOHYDRODYNAMICS-RELAXATION METHOD FOR NONLINEAR FORCE-FREE FIELD EXTRAPOLATION IN THE SOLAR CORONA  

SciTech Connect

The magnetic field in the solar corona is usually extrapolated from a photospheric vector magnetogram using a nonlinear force-free field (NLFFF) model. NLFFF extrapolation needs considerable effort to be devoted to its numerical realization. In this paper, we present a new implementation of the magnetohydrodynamics (MHD) relaxation method for NLFFF extrapolation. The magnetofrictional approach, which is introduced for speeding the relaxation of the MHD system, is realized for the first time by the spacetime conservation-element and solution-element scheme. A magnetic field splitting method is used to further improve the computational accuracy. The bottom boundary condition is prescribed by incrementally changing the transverse field to match the magnetogram, and all other artificial boundaries of the computational box are simply fixed. We examine the code using two types of NLFFF benchmark tests, the Low and Lou semi-analytic force-free solutions and a more realistic solar-like case constructed by van Ballegooijen et al. The results show that our implementation is successful and versatile for extrapolations of either the relatively simple cases or the rather complex cases that need significant rebuilding of the magnetic topology, e.g., a flux rope. We also compute a suite of metrics to quantitatively analyze the results and demonstrate that the performance of our code in extrapolation accuracy basically reaches the same level of the present best-performing code, i.e., that developed by Wiegelmann.

Jiang Chaowei; Feng Xueshang, E-mail: cwjiang@spaceweather.ac.cn, E-mail: fengx@spaceweather.ac.cn [SIGMA Weather Group, State Key Laboratory for Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190 (China)

2012-04-20

374

A New Implementation of the Magnetohydrodynamics-relaxation Method for Nonlinear Force-free Field Extrapolation in the Solar Corona  

NASA Astrophysics Data System (ADS)

The magnetic field in the solar corona is usually extrapolated from a photospheric vector magnetogram using a nonlinear force-free field (NLFFF) model. NLFFF extrapolation needs considerable effort to be devoted to its numerical realization. In this paper, we present a new implementation of the magnetohydrodynamics (MHD) relaxation method for NLFFF extrapolation. The magnetofrictional approach, which is introduced for speeding the relaxation of the MHD system, is realized for the first time by the spacetime conservation-element and solution-element scheme. A magnetic field splitting method is used to further improve the computational accuracy. The bottom boundary condition is prescribed by incrementally changing the transverse field to match the magnetogram, and all other artificial boundaries of the computational box are simply fixed. We examine the code using two types of NLFFF benchmark tests, the Low & Lou semi-analytic force-free solutions and a more realistic solar-like case constructed by van Ballegooijen et al. The results show that our implementation is successful and versatile for extrapolations of either the relatively simple cases or the rather complex cases that need significant rebuilding of the magnetic topology, e.g., a flux rope. We also compute a suite of metrics to quantitatively analyze the results and demonstrate that the performance of our code in extrapolation accuracy basically reaches the same level of the present best-performing code, i.e., that developed by Wiegelmann.

Jiang, Chaowei; Feng, Xueshang

2012-04-01

375

Theory for the radiation of magnetohydrodynamic surface waves and body waves into the solar corona  

SciTech Connect

The Green's function for the slab coronal hole is obtained explicitly. The Fourier integral representation for the radiated field inside and outside the coronal hole waveguide is obtained. The radiated field outside the coronal hole is calculated using the method of steepest descents. It is shown that the radiated field can be written as the sum of two contributions: (1) a contribution from the integral along the steepest descent path and (2) a contribution from all the poles of the integrand between the path of the original integral and the steepest descent path. The free oscillations of the waveguide can be associated with the pole contributions in the steepest descent representation for the Green's function. These pole contributions are essentially generalized surface waves with a maximum amplitude near the interface which separates the plasma inside the coronal hole from the surrounding background corona. The path contribution to the integral is essentially the power radiated in body waves. 21 references.

Davila, J.M.

1988-09-01

376

Interactions of solar wind plasma with dust grains: Effects of strong plasma anisotropy  

NASA Astrophysics Data System (ADS)

In this paper we re-examined the fundamental physics of charging of a dust particle in the moon environment by tenuous anisotropic solar wind plasma. The majority of work on dusty (complex) plasmas is largely concerns with laboratory plasmas, in which charging process of dust grains is very fast, thus making practical the working concept of dynamically equilibrium floating potential and grain charge. However, solar wind plasma parameters are considerably different at the moon orbit, and we found the characteristic charging time of lunar dust grains to be considerably longer, ranging from 3 to 4.6 min for micron size particles, and up to 7.6 h for 10-nm grains, depending on the value of plasma streaming velocity. These findings make it clear that the transient stage of charging process is important in the moon environment, and equilibrium floating potential and grain charge could be considered as long time asymptotic values. For this reason we re-formulated the moon dust charging process as an inherently time-dependent problem and derived the time-dependent charging equation for the grain potential for general case of anisotropic solar wind plasma. Using the results of our kinetics analysis we found that the distribution of charge density over grain surface submerged into solar wind plasma is highly anisotropic, thus making the OML model, which is based on the assumption of isotropic distribution of surface charge density, not applicable to the grain charging problem by the solar wind plasma.

Pines, Vladimir; Zlatkowski, Marianna; Chait, Arnon

2009-01-01

377

Thermodynamics of the Solar Corona and Evolution of the Solar Magnetic Field as Inferred from the Total Solar Eclipse Observations of 2010 July 11  

NASA Astrophysics Data System (ADS)

We report on the first multi-wavelength coronal observations, taken simultaneously in white light, H? 656.3 nm, Fe IX 435.9 nm, Fe X 637.4 nm, Fe XI 789.2 nm, Fe XIII 1074.7 nm, Fe XIV 530.3 nm, and Ni XV 670.2 nm, during the total solar eclipse of 2010 July 11 from the atoll of Tatakoto in French Polynesia. The data enabled temperature differentiations as low as 0.2 × 106 K. The first-ever images of the corona in Fe IX and Ni XV showed that there was very little plasma below 5 × 105 K and above 2.5 × 106 K. The suite of multi-wavelength observations also showed that open field lines have an electron temperature near 1× 106 K, while the hottest, 2× 106 K, plasma resides in intricate loops forming the bulges of streamers, also known as cavities, as discovered in our previous eclipse observations. The eclipse images also revealed unusual coronal structures, in the form of ripples and streaks, produced by the passage of coronal mass ejections and eruptive prominences prior to totality, which could be identified with distinct temperatures for the first time. These trails were most prominent at 106 K. Simultaneous Fe X 17.4 nm observations from Proba2/SWAP provided the first opportunity to compare Fe X emission at 637.4 nm with its extreme-ultraviolet (EUV) counterpart. This comparison demonstrated the unique diagnostic capabilities of the coronal forbidden lines for exploring the evolution of the coronal magnetic field and the thermodynamics of the coronal plasma, in comparison with their EUV counterparts in the distance range of 1-3 R sun. These diagnostics are currently missing from present space-borne and ground-based observatories.

Habbal, Shadia Rifai; Druckmüller, Miloslav; Morgan, Huw; Ding, Adalbert; Johnson, Judd; Druckmüllerová, Hana; Daw, Adrian; Arndt, Martina B.; Dietzel, Martin; Saken, Jon

2011-06-01

378

UVCS\\/[ITAL]SOHO[\\/ITAL] Empirical Determinations of Anisotropic Velocity Distributions in the Solar Corona  

Microsoft Academic Search

We present a self-consistent empirical model for several plasma parameters of a polar coronal hole near solar minimum, derived from observations with the Solar and Heliospheric ObservatoryUltraviolet Coronagraph Spectrometer. The model describes the radial distribution of density for electrons, H , and O and the outflow 05 1

J. L. Kohl; G. Noci; E. Antonucci; G. Tondello; M. C. E. Huber; S. R. Cranmer; L. Strachan; A. V Panasyuk; L. D. Gardner; M. Romoli; S. Fineschi; D. Dobrzycka; J. C. Raymond; P. Nicolosi; O. H. W. Siegmund; D. Spadaro; C. Benna; A. Ciaravella; S. Giordano; S. R. Habbal; M. Karovska; X. Li; R. Martin; J. G. Michels; A. Modigliani; G. Naletto; R. H. O'Neal; C. Pernechele; G. Poletto; P. L. Smith; R. M. Suleiman

1998-01-01

379

Possible evidence for a rigidity-dependent release of relativistic protons from the solar corona  

Microsoft Academic Search

A model of the time evolving relativistic solar proton spectra for the 7 May 1978 ground level solar cosmic ray event is presented. This event, with associated cosmic ray neutron monitor increases of over 100% and containing relativistic particles with energies greater than 10 GeV\\/nucleon was characterized by an extreme anisotropy and a rapidly evolving spectrum, particularly during the initial

M. A. Shea; D. F. Smart

1982-01-01

380

Deflection of the local interstellar dust flow by solar radiation pressure.  

PubMed

Interstellar dust grains intercepted by the dust detectors on the Ulysses and Galileo spacecrafts at heliocentric distances from 2 to 4 astronomical units show a deficit of grains with masses from 1 x 10(-17) to 3 x 10(-16) kilograms relative to grains intercepted outside 4 astronomical units. To divert grains out of the 2- to 4-astronomical unit region, the solar radiation pressure must be 1.4 to 1.8 times the force of solar gravity. These figures are consistent with the optical properties of spherical or elongated grains that consist of astronomical silicates or organic refractory material. Pure graphite grains with diameters of 0.2 to 0.4 micrometer experience a solar radiation pressure force as much as twice the force of solar gravity. PMID:10600737

Landgraf, M; Augustsson, K; Grün, E; Gustafson, B A

1999-12-17

381

Signatures of Exo-Solar Planets in Dust Debris Disks  

NASA Astrophysics Data System (ADS)

We have developed a new numerical approach to the dynamics of minor bodies and dust particles, which enables us to increase, without using a supercomputer, the number of employed particle positions in each model up to 1010 - 1011, a factor of 106 - 107 higher than existing numerical simulations. We apply this powerful approach to the high-resolution modeling of the structure and emission of circumstellar dust disks, incorporating all relevant physical processes. In this Letter, we examine the resonant structure of a dusty disk induced by the presence of one planet of mass in the range of (5 x 10-5 - 5 x 10-3)M. It is shown that the planet, via resonances and gravitational scattering, produces (i) a central cavity void of dust; (ii) a trailing (sometimes leading) off-center cavity; and (iii) an asymmetric resonant dust belt with one, two, or more clumps. These features can serve as indicators of planet(s) embedded in the circumstellar dust disk and, moreover, can be used to determine the mass of the planet and even some of its orbital parameters. The results of our study reveal a remarkable similarity with various types of highly asymmetric circumstellar disks observed with the JCMT around Epsilon Eridani and Vega.

Ozernoy, Leonid M.; Gorkavyi, Nick N.; Mather, John C.; Taidakova, Tanya A.

1999-10-01

382

Variability of Solar Five-Minute Oscillations in the Corona as Observed by the Extreme Ultraviolet Spectrophotometer (ESP) on the Solar Dynamics Observatory/Extreme Ultraviolet Variability Experiment (SDO/EVE)  

NASA Astrophysics Data System (ADS)

Solar five-minute oscillations have been detected in the power spectra of two six-day time intervals from soft X-ray measurements of the Sun observed as a star using the Extreme Ultraviolet Spectrophotometer (ESP) onboard the Solar Dynamics Observatory (SDO)/ Extreme Ultraviolet Variability Experiment (EVE). The frequencies of the largest amplitude peaks were found to match the known low-degree ( ?=0 - 3) modes of global acoustic oscillations within 3.7 ?Hz and can be explained by a leakage of the global modes into the corona. Due to the strong variability of the solar atmosphere between the photosphere and the corona, the frequencies and amplitudes of the coronal oscillations are likely to vary with time. We investigated the variations in the power spectra for individual days and their association with changes of solar activity, e.g. with the mean level of the EUV irradiance, and its short-term variations caused by evolving active regions. Our analysis of samples of one-day oscillation power spectra for a 49-day period of low and intermediate solar activity showed little correlation with the mean EUV irradiance and the short-term variability of the irradiance. We suggest that some other changes in the solar atmosphere, e.g., magnetic fields and/or inter-network configuration may affect the mode leakage to the corona.

Didkovsky, L.; Kosovichev, A.; Judge, D.; Wieman, S.; Woods, T.

2013-10-01

383

On acceleration and motion of ions in corona and solar wind  

Microsoft Academic Search

Assuming a stationary, radial, spherically symmetric solar wind and a radial magnetic field direction in the vicinity of the\\u000a sun, an equation of motion for ions heavier than protons in the solar wind is derived. The general properties of this equation\\u000a are discussed and the results of numerical integrations are given. These results are based on the assumption of maxwellian

Johannes Geiss; Peter Hirt; Heinrich Leutwyler

1970-01-01

384

Large-scale Bright Fronts in the Solar Corona: A Review of “EIT waves”  

Microsoft Academic Search

“EIT waves” are large-scale coronal bright fronts (CBFs) that were first observed in 195 Å images obtained using the Extreme-ultraviolet\\u000a Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO). Commonly called “EIT waves”, CBFs typically appear as diffuse fronts that propagate pseudo-radially across the solar disk\\u000a at velocities of 100–700 km?s?1 with front widths of 50–100 Mm. As their speed is greater

Peter T. Gallagher; David M. Long

385

Are Non-thermal Motions in the Solar Corona Evidence for Coronal Heating by MHD Turbulence?  

Microsoft Academic Search

Recent solar observations suggest that the solar outer atmosphere is turbulent. In the present talk, I focus on the SOHO\\/SUMER observations of non-thermal motions --- unresolved plasma motions that are required to explain the line width excess over thermal broadening --- of UV\\/EUV emitting plasma whose temperature ranges from 10^4 to 10^6 K. It has been found from a thorough

Jongchul Chae

2001-01-01

386

Constraints on the Kuiper belt dust in the outer Solar System  

NASA Astrophysics Data System (ADS)

The Edgeworth-Kuiper belt (EKB) and its presumed dusty debris are a natural reference for extrasolar debris disks. The dust in the EKB cannot be seen directly due to the strong foreground emission of the zodiacal cloud but in-situ measurements show that dust is present in the outer solar system. To model the dust distribution we take advantage of the knowledge of the parent bodies of dust, namely the transneptunian objects (TNOs). On the base of [8] we generate the dust with our collisional code to determine the radial and size distribution of the dust using a 50% ice and 50% astrosilicate composition of the particles. In addition we included a simple estimation of the influence of the three outermost planets and sublimation. To calibrate our model we used the in-situ measurements of the New Horizons dust counter [7]. It is shown that the influence of the planets and sublimation on the spectral energy distribution is very small. Our model can reproduce the in-situ measurements the New Horizons and is roughly consistent with the upper limit on the thermal emission flux from the COBE spacecraft [1].

Vitense, C.; Krivov, A. V.; Kobayashi, H.; Löhne, T.

2011-10-01

387

Hard X-ray Radiation from Solar Flares in the Second Half of 2001: Preliminary Results of the SPR-N Experiment Onboard the Coronas-F Satellite  

NASA Astrophysics Data System (ADS)

The first results of the experiment with the SPR-N hard X-ray (20-100 keV) polarimeter onboard the Coronas-F observatory (the experiment started on August 15, 2001) are presented. Hard X-ray radiation was detected from several solar flares. The spectral and temporal parameters were determined and the polarization was estimated. Comparison with the GOES observations of thermal X-ray radiation shows that hard X-ray bursts occur at the growth phase of the thermal radiation and that they are associated with the bremsstrahlung of energetic electrons precipitating into the solar atmosphere.

Bogomolov, A. V.; Denisov, Yu. I.; Kuznetsov, S. N.; Lisin, D. V.; Logachev, Yu. I.; Morozov, O. V.; Myagkova, I. N.; Svertilov, S. I.; Zhitnik, I. A.; Ignat'ev, A. P.; Oparin, S. N.; Pertsov, A. A.; Stepanov, A. I.; Tindo, I. P.

2003-03-01

388

Comparison of the solar/stellar wind and the Poynting-Robertson effect in secular orbital evolution of dust particles  

NASA Astrophysics Data System (ADS)

Properties of the solar/stellar winds are discussed and applied to the effects of the winds on motion of dust particles in the Solar system and around stars. As for the secular orbital evolution of the spherical interplanetary dust particles, the solar electromagnetic radiation is 1.5-times more important than the solar corpuscular radiation, the solar wind. The relevant contributions of the solar wind action contain also the sputtering and reflection components in addition to direct impact. The importance of the wind can be partially increased by considering the decrease of dust particle mass due to the wind bombardment, and, mainly, due to the non-radial component of the solar wind velocity. Time dependence of the solar wind properties plays a less important role. The presented equation of motion of a dust particle under the action of the solar radiation respects reality in a much better way than the conventionally used equation. The dimensionless cross-section the dust grain presents to wind pressure is about 9/4. This value differs from the conventionally used value 1.0. The mass-loss rate of the zodiacal cloud is (7/3)-times higher than the currently accepted value, as for the micron-sized dust particles.

Kla?ka, J.

2013-10-01

389

Observations of ULF waves in the solar corona and in the solar wind at the Earth's orbit  

NASA Astrophysics Data System (ADS)

Signs were looked for that would indicate a possible connection between plasma velocity oscillations observed in the region of solar coronal holes and magnetic field oscillations as recorded in the interplanetary medium. The problem appears to be quite important since the presence of large-scale ULF waves in the solar wind can increase geoeffectiveness of high speed streams in the interplanetary plasma. Observations of solar oscillations in the FeI 6569 Å spectral line in a coronal hole were taken as a basis. The measurements were carried out at the Horizontal Automated Solar Telescope of the Sayan Solar Observatory. High speed solar wind stream ejected from the coronal hole reached the Earth's orbit after approximately 60 h. The spectra of solar oscillations were compared with those of ultra low frequency (ULF) oscillations of the interplanetary magnetic field (IMF) at libration point L1. The oscillations were recorded with the ACE magnetometer when the leading edge of the high speed stream, bringing increased ULF wave activity, reached the Earth. The spectra of solar oscillations had a sharp peak at about 3.4-3.6 mHz. The spectrum of the solar wind ULF oscillations is much more complex, being formed by different sources. Nevertheless, ULF oscillations of the IMF often had peaks that were close in frequency to those of the solar oscillations. Analysis of the ULF wave spectra observed in the 92 high speed streams confirmed the presence of 3- and 5-min oscillations in the total wave spectrum. It is emphasized that the results cannot be regarded as proving a direct connection between solar oscillations and ULF waves at the Earth's orbit even though they do support such a possibility. Additional research is needed involving IMF wave trajectory calculations.

Potapov, A. S.; Polyushkina, T. N.; Pulyaev, V. A.

2013-09-01

390

Low-frequency Observations of Polarized Emission from Long-lived Non-thermal Radio Sources in the Solar Corona  

NASA Astrophysics Data System (ADS)

We report observations of circularly polarized emission from the solar corona at 77 MHz during the periods 2006 August 11-18, 2006 August 23-29, and 2007 May 16-22 in the minimum phase between the sunspot cycles 23 and 24. The observations were carried out with the east-west one-dimensional radio polarimeter at the Gauribidanur observatory located about 100 km north of Bangalore. Two-dimensional imaging observations at 77 MHz during the same period with the radioheliograph at the same observatory revealed that the emission region co-rotated with the Sun during the three aforementioned periods. Their rotation rates, close to the central meridian on the Sun, are 4farcm6, 5farcm2, and 4farcm9 ± 0farcm5 per day, respectively. We derived the radial distance of the region from the above observed rotation rates and the corresponding values are ?1.24 ± 0.03 R sun (2006 August 11-18), ?1.40 ± 0.03 R sun (2006 August 23-29), and ?1.32 ± 0.03 R sun (2007 May 16-22). The estimated lower limit for the magnetic field strength at the above radial distances and periods are ?1.1, 0.6, and 0.9 G, respectively.

Ramesh, R.; Kathiravan, C.; Narayanan, A. Satya

2011-06-01

391

LOW-FREQUENCY OBSERVATIONS OF POLARIZED EMISSION FROM LONG-LIVED NON-THERMAL RADIO SOURCES IN THE SOLAR CORONA  

SciTech Connect

We report observations of circularly polarized emission from the solar corona at 77 MHz during the periods 2006 August 11-18, 2006 August 23-29, and 2007 May 16-22 in the minimum phase between the sunspot cycles 23 and 24. The observations were carried out with the east-west one-dimensional radio polarimeter at the Gauribidanur observatory located about 100 km north of Bangalore. Two-dimensional imaging observations at 77 MHz during the same period with the radioheliograph at the same observatory revealed that the emission region co-rotated with the Sun during the three aforementioned periods. Their rotation rates, close to the central meridian on the Sun, are 4.'6, 5.'2, and 4.'9 {+-} 0.'5 per day, respectively. We derived the radial distance of the region from the above observed rotation rates and the corresponding values are {approx}1.24 {+-} 0.03 R{sub sun} (2006 August 11-18), {approx}1.40 {+-} 0.03 R{sub sun} (2006 August 23-29), and {approx}1.32 {+-} 0.03 R{sub sun} (2007 May 16-22). The estimated lower limit for the magnetic field strength at the above radial distances and periods are {approx}1.1, 0.6, and 0.9 G, respectively.

Ramesh, R.; Kathiravan, C.; Satya Narayanan, A., E-mail: ramesh@iiap.res.in, E-mail: kathir@iiap.res.in, E-mail: satya@iiap.res.in [Indian Institute of Astrophysics, Bangalore 560 034 (India)

2011-06-10

392

On the Berkowski daguerreotype (Königsberg, 1851 July 28): the first correctly-exposed photograph of the solar corona  

NASA Astrophysics Data System (ADS)

The first correctly-exposed photograph of the solar corona was made during the total phase of the solar eclipse of 28 July 1851 at Königsberg (now Kaliningrad) by a local daguerreotypist named Berkowski. Berkowski observed at the Royal Observatory following a proposal by its director A. Busch. A small refracting telescope (D = 6.1 cm, f = 81.2 cm) was attached to the hour drive of the 15.8-cm Fraunhofer heliometer, and a 84-s exposure was taken shortly after the beginning of totality. After the eclipse, Busch (who did not observe the eclipse at Königsberg but at Rixhöft), published some details about the daguerreotype (without mentioning Berkowski's first name) and ordered a local artist (R. Trossin) to make an enlarged steel engraving from the daguerreotype plate. On the original plate the moon's diameter is 7.85 mm, and at least 5 prominences are well visible on the limb of the sun. Later Berkowski himself made some daguerreotype reproductions from his original plate. One of these is still preserved at Jena University Observatory, it has a moon diameter of 8.69 mm. In 1891 the Königsberg Astronomer C.F.W. Peters ordered photographic reproductions of the original daguerreotype (which then still existed) to be made, some of which have been published in astronomical textbooks. We have calculated the local circumstances, in particular the contact times, of the Königsberg eclipse and compared them with observations. We describe the Berkowski daguerreotype and some of its copies, and we report about the Jena copy of this famous daguerreotype.

Schielicke, Reinhard; Wittmann, Axel D.

393

Weather Modification by Carbon Dust Absorption of Solar Energy  

Microsoft Academic Search

Growing global population pressures and predicted future food and energy shortages dictate that man fully explore his potential use of solar energy. This paper investigates the possibility of beneficial weather modification through artificial solar energy absorption. A variety of physical ideas related to artificial heat sources on different scales of motion are considered. Interest is concentrated on the feasibility of

William M. Gray; William M. Frank; Myron L. Corrin; Charles A. Stokes

1976-01-01

394

Polarization of Hard X-Rays in October-November, 2003 Solar Flares Observed Onboard CORONAS-F Satellite  

NASA Astrophysics Data System (ADS)

In the experiment with X-ray polarimeter SPR-N onboard satellite ``CORONAS-F'' (altitude 500 km, inclination 82.5°, period ˜ 94.5 min.) the hard (20-100 keV) X-ray emission from several Solar flares in October-November, 2003 was detected. This work presents the results of measuring of the X-ray polarization in the powerful Solar flares 28.10.2003, 29.10.2003 and 04.11.2003. Measuring of polarization in SPR-N is based on the Compton scattering of X-ray photons in a hexagonal prism of beryllium. The scattered photons are detecting by six CsI(Na) detectors, positioned in the prism sides. Non-polarized emission scatters omnidirectionally, therefore the count rates of all detectors in this case will be equal. Polarized photons are mainly scattering normally to a polarization plane. Proportions between count rates of detectors give information about à part of polarized photons and à position of polarization plane. Scattered photons are detecting in the energy bands 20-40, 40-60 and 60-100 keV. Experimental data of SPR-N show that X-ray emission in October, 29, 2003 Solar flare (20:40 -- 21:00 UT) was strongly polarized, mainly in the peaks of X-ray intensity (at ˜ 20:44 UT and ˜ 20:51 UT). In the energy band 40-60 keV >85% of photons were polarized in the first peak, and >75% in the second peak. The similar situation is in the band 60-100 keV. In the band 20-40 keV X-ray emission is less polarized. For the Solar flare 28.10.2003 (11:00 -- 11:20 UT) and for the first stage of the flare 4.11.2003 (˜ 19:34 UT) significant values of the polarization were not detected. Only upper limits <25% for the event 28.10.2003 and <40% for 4.11.2003 were obtained.

Bogomolov, A. V.; Denisov, Yu. I.; Logachev, Yu. I.; Morozov, O. V.; Myagkova, I. N.; Svertilov, S. I.; Zhitnik, I. A.; Ignat'ev, A. P.; Oparin, S. N.; Pertsov, A. A.

395

Mode Conversion of Langmuir to Electromagnetic Waves with Parallel Inhomogeneity in the Solar Wind and the Corona  

SciTech Connect

Linear mode conversion of Langmuir waves to radiation near the plasma frequency at density gradients is potentially relevant to multiple solar radio emissions, ionospheric radar experiments, laboratory plasma devices, and pulsars. Here we study mode conversion in warm magnetized plasmas using a numerical electron fluid simulation code with the density gradient parallel to the ambient magnetic field B0 for a range of incident Langmuir wavevectors. Our results include: (1) Both o- and x-mode waves are produced for ? ? (?L)1/3(?c/?) somewhat less than 1, contrary to previous ideas. Only o mode is produced for ? and somewhat greater than 1.5. Here ?c is the (angular) electron cyclotron frequency, ? the angular wave frequency, and L the length scale of the (linear) density gradient. (2) In the unmagnetized limit, equal amounts of o- and x-mode radiation are produced. (3) The mode conversion window narrows as ? increases. (4) As ? increases the total electromagnetic field changes from linear to circular polarization, with the o- and x- mode signals remaining circularly polarized. (5) The conversion efficiency to the x mode decreases monotonically as ? increases while the o-mode conversion efficiency oscillates due to an interference phenomenon between incoming and reflected Langmuir/z modes. (6) The total conversion efficiency for wave energy from the Langmuir/z mode to radiation is typically less than 10%, but the corresponding power efficiencies differ by the ratio of the group speeds for each mode and are of order 50 ? 70%. (7) The interference effect and the disappearance of the x mode at ? somewhat greater than 1 can be accounted for semiquantitatively using a WKB-like analysis. (8) Constraints on density turbulence are developed for the x mode to be generated and be able to propagate from the source. (9) Standard parameters for the corona and the solar wind near 1 AU suggest that linear mode conversion should produce both o- and x- mode radiation for solar and interplanetary radio bursts. It is therefore possible that linear mode conversion under these conditions might explain the weak total circular polarizations of type II and III solar radio bursts.

Eun-Hwa Kim, Iver H. Cairns, and Peter A. Robinson

2008-06-09

396

Solar wind plasma profiles during interplanetary field enhancements (IFEs): Consistent with charged-dust pickup  

NASA Astrophysics Data System (ADS)

The solar wind contains many magnetic structures, and most of them have identifiable correlated changes in the flowing plasma. However, the very characteristic rise and fall of the magnetic field in an interplanetary field enhancement has no clear solar wind counterpart. It appears to be a pure magnetic ``barrier'' that transfers solar wind momentum to charged dust produced in collisions of interplanetary bodies in the size range of tens to hundreds of meters. This transfer lifts the fine scale dust out of the Sun's gravitational well. We demonstrate the lack of field-plasma correlation with several examples from spacecraft records as well as show an ensemble average velocity profile during IFEs which is consistent with our IFE formation hypothesis.

Lai, H. R.; Wei, H. Y.; Russell, C. T.

2013-06-01

397

Radio evidence for shock acceleration of electrons in the solar corona  

Microsoft Academic Search

It is pointed out that the new class of kilometer-wavelength solar radio bursts observed with the ISEE-3 Radio Astronomy Experiment occurs at the reported times of type II events, which are indicative of a shock wave. An examination of records from the Culgoora Radio Observatory reveals that the associated type II bursts have fast drift elements emanating from them; that

H. V. Cane; R. G. Stone; J. Fainberg; J. L. Steinberg; S. Hoang; R. T. Stewart

1981-01-01

398

High resolution mapping of the magnetic field of the solar corona  

Microsoft Academic Search

High resolution KPNO magnetograph measurements of the line-of-sight component of the photospheric magnetic field over the entire dynamic range from 0 to 4000 gauss are used as the basic data for a new analysis of the photospheric and coronal magnetic field distributions. The daily magnetograph measurements collected over a solar rotation are averaged onto a 180 × 360 synoptic grid

Martin D. Altschuler; Randolph H. Levine; Michael Stix; John Harvey

1977-01-01

399

Topological Aspects of Global Magnetic Field Reversal in the Solar Corona  

Microsoft Academic Search

Every eleven years on average, the dipolar component of the Sun's global coronal magnetic field reverses in sign a consequence of the sunspot cycle. In this paper we begin to investigate the complex changes in coronal structure during the reversal. We present a simplified model of the solar cycle containing six time-varying photospheric sources of magnetic field and analyse the

R. C. Maclean; E. R. Priest

2007-01-01

400

Direct Imaging of Quasi-periodic Fast Propagating Waves of ~2000 km s-1 in the Low Solar Corona by the Solar Dynamics Observatory Atmospheric Imaging Assembly  

NASA Astrophysics Data System (ADS)

Quasi-periodic propagating fast mode magnetosonic waves in the solar corona were difficult to observe in the past due to relatively low instrument cadences. We report here evidence of such waves directly imaged in EUV by the new Atmospheric Imaging Assembly instrument on board the Solar Dynamics Observatory. In the 2010 August 1 C3.2 flare/coronal mass ejection event, we find arc-shaped wave trains of 1%-5% intensity variations (lifetime ~200 s) that emanate near the flare kernel and propagate outward up to ~400 Mm along a funnel of coronal loops. Sinusoidal fits to a typical wave train indicate a phase velocity of 2200 ± 130 km s-1. Similar waves propagating in opposite directions are observed in closed loops between two flare ribbons. In the k-? diagram of the Fourier wave power, we find a bright ridge that represents the dispersion relation and can be well fitted with a straight line passing through the origin. This k-? ridge shows a broad frequency distribution with power peaks at 5.5, 14.5, and 25.1 mHz. The strongest signal at 5.5 mHz (period 181 s) temporally coincides with quasi-periodic pulsations of the flare, suggesting a common origin. The instantaneous wave energy flux of (0.1-2.6) × 107 erg cm-2 s-1 estimated at the coronal base is comparable to the steady-state heating requirement of active region loops.

Liu, Wei; Title, Alan M.; Zhao, Junwei; Ofman, Leon; Schrijver, Carolus J.; Aschwanden, Markus J.; De Pontieu, Bart; Tarbell, Theodore D.

2011-07-01

401

THE FIRST MEASUREMENT OF THE ADIABATIC INDEX IN THE SOLAR CORONA USING TIME-DEPENDENT SPECTROSCOPY OF HINODE/EIS OBSERVATIONS  

SciTech Connect

We use observations of a slow magnetohydrodynamic wave in the corona to determine for the first time the value of the effective adiabatic index, using data from the Extreme-ultraviolet Imaging Spectrometer on board Hinode. We detect oscillations in the electron density, using the CHIANTI atomic database to perform spectroscopy. From the time-dependent wave signals from multiple spectral lines the relationship between relative density and temperature perturbations is determined, which allows in turn to measure the effective adiabatic index to be {gamma}{sub eff} = 1.10 {+-} 0.02. This confirms that the thermal conduction along the magnetic field is very efficient in the solar corona. The thermal conduction coefficient is measured from the phase lag between the temperature and density, and is shown to be compatible with Spitzer conductivity.

Van Doorsselaere, Tom; Wardle, Nick; Jansari, Kishan; Verwichte, Erwin; Nakariakov, Valery M. [CFSA, Physics Department, University of Warwick, Coventry CV4 7AL (United Kingdom); Del Zanna, Giulio, E-mail: Tom.VanDoorsselaere@wis.kuleuven.BE [DAMTP, Centre for Mathematical Sciences, Wilberforce Road, Cambridge CB3 0WA (United Kingdom)

2011-02-01

402

Release of solar cosmic rays from the corona: Rayleigh-Taylor instability and reconnection  

SciTech Connect

We point out that the coronal bottle model (including Rayleigh-Taylor instability and reconnection) proposed by Schatten and Mullan for propagation and release of solar cosmic rays (SCR) is useful for interpreting data on the durations t/sub s/ of type II radio bursts compiled recently by Kahler. In particular, a natural release time scale (t/sub r/approx.10/sup 3/) which plays a key role in the bottle model allows a significant ordering of Kahler's data: essentially all flare shocks having t/sub s/>t/sub r/ release solar particles into interplanetary space, while essentially all flare shocks which release no energetic particles into interplanetary space have t/sub s/

Mullan, D.J.

1983-06-15

403

Parameters of the Intense X-ray and Gamma-ray Radiation from the Solar Flare of May 20, 2002, as Observed from the CORONAS-F Spacecraft  

NASA Astrophysics Data System (ADS)

We consider temporal, spectral, and polarization parameters of the hard X-ray and gamma-ray radiation observed during the solar flare of May 20, 2002, in the course of experiments with the SONG and SPR-N instruments onboard the CORONAS-F spacecraft. This flare is one of the most intense gamma-ray events among all of the bursts of solar hard electromagnetic radiation detected since the beginning of the CORONAS-F operation (since July 31, 2001) and one of the few gamma-ray events observed during solar cycle 23. A simultaneous analysis of the CORONAS-F and GOES data on solar thermal X-ray radiation suggests that, apart from heating due to currents of matter in the the flare region, impulsive heating due to the injection of energetic electrons took place during the near-limb flare S21E65 of May 20, 2002. These electrons produced intense hard X-ray and gamma-ray radiation. The spectrum of this radiation extends up to energies > 7 MeV. Intense gamma-ray lines are virtually unobservable against the background of the nonthermal continuum. The polarization of the hard X-ray (20-100 keV) radiation was estimated to be less than 15-20%. No significant increase in the flux of energetic protons from the flare under consideration was found. At the same time, according to ACE data, the fluxes of energetic electrons in interplanetary space increased shortly (~25 min) after the flare.

Bogomolov, A. V.; Ignat'ev, A. P.; Kudela, K.; Kuznetsov, S. N.; Logachev, Yu. I.; Morozov, O. V.; Myagkova, I. N.; Oparin, S. N.; Pertsov, A. A.; Svertilov, S. I.; Yushkov, B. Yu.

2003-03-01

404

Topological Aspects of Global Magnetic Field Reversal in the Solar Corona  

Microsoft Academic Search

Every eleven years on average, the dipolar component of the Sun’s global coronal magnetic field reverses in sign – a consequence\\u000a of the sunspot cycle. In this paper we begin to investigate the complex changes in coronal structure during the reversal.\\u000a We present a simplified model of the solar cycle containing six time-varying photospheric sources of magnetic field and analyse

R. C. Maclean; E. R. Priest

2007-01-01

405

Light Scattering Measurements To Infer Solar System Dust Physical Properties:from Parabolic Flights To The Iss Laboratories  

Microsoft Academic Search

Information about the physical properties of dust clouds and regoliths in the solar sys- tem is mainly provided by remote light scattering observations. Laboratory measure- ments, which avoid multiple scattering on gravity packed layers by elaborate levitation techniques, are required to accurately interpret such observations. The feasibility of light scattering measurements under microgravity conditions, both on dust clouds and on

A. C. Levasseur-Regourd

2002-01-01

406

Martian Ionospheric Variability as Observed by MARSIS: The Effects of Solar Energetic Particles, Ionizing Radition, Meteors, and Dust Activity  

Microsoft Academic Search

We present evidence for time variability in the martian ionosphere due to solar energetic particles. We also discuss possible ionospheric effects from meteoric material, dust storms, the diurnal ionization cycle, and crustal magnetic fields.

J. R. Espley; W. Farrell; D. A. Brain; D. D. Morgan; M. H. Acuña; B. Cantor; J. Plaut; G. Picardi

2007-01-01

407

Electron Temperature Maps of Low Solar Corona: Results from the Total Solar Eclipse of 29 March 2006 in Libya  

Microsoft Academic Search

We conducted an experiment in conjunction with the total solar eclipse of 29 March 2006 in Libya that measured the coronal intensity through two filters centered at 3850 and 4100 Angstroms with bandwidths of 40 Angstroms. The purpose of these measurements was to obtain the intensity ratio through these two filters to determine the electron temperature. The instrument, Imaging Spectrograph

Nelson Leslie Reginald; J. Davila; C. St. Cyr

2009-01-01

408

Modelling the Global Solar Corona II: Coronal Evolution and Filament Chirality Comparison  

NASA Astrophysics Data System (ADS)

This paper considers the hemispheric pattern of solar filaments using newly developed simulations of the real photospheric and 3D coronal magnetic fields over a six-month period, on a global scale. The magnetic field direction in the simulation is compared directly with the chirality of observed filaments, at their observed locations. In our model the coronal field evolves through a continuous sequence of nonlinear force-free equilibria, in response to the changing photospheric boundary conditions and the emergence of new magnetic flux. In total 119 magnetic bipoles with properties matching observed active regions are inserted. These bipoles emerge twisted and inject magnetic helicity into the solar atmosphere. When we choose the sign of this active-region helicity to match that observed in each hemisphere, the model produces the correct chirality for up to 96% of filaments, including exceptions to the hemispheric pattern. If the emerging bipoles have zero helicity, or helicity of the opposite sign, then this percentage is much reduced. In addition, the simulation produces a higher proportion of filaments with the correct chirality after longer times. This indicates that a key element in the evolution of the coronal field is its long-term memory, and the build-up and transport of helicity from low to high latitudes over many months. It highlights the importance of continuous evolution of the coronal field, rather than independent extrapolations at different times. This has significant consequences for future modelling such as that related to the origin and development of coronal mass ejections.

Yeates, A. R.; Mackay, D. H.; van Ballegooijen, A. A.

2008-01-01

409

Large-scale Bright Fronts in the Solar Corona: A Review of "EIT waves"  

NASA Astrophysics Data System (ADS)

"EIT waves" are large-scale coronal bright fronts (CBFs) that were first observed in 195 Å images obtained using the Extreme-ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory ( SOHO). Commonly called "EIT waves", CBFs typically appear as diffuse fronts that propagate pseudo-radially across the solar disk at velocities of 100-700 km s-1 with front widths of 50-100 Mm. As their speed is greater than the quiet coronal sound speed ( c s ?200 km s-1) and comparable to the local Alfvén speed ( v A ?1000 km s-1), they were initially interpreted as fast-mode magnetoacoustic waves (vf=(cs2 + vA2)^{1/2}). Their propagation is now known to be modified by regions where the magnetosonic sound speed varies, such as active regions and coronal holes, but there is also evidence for stationary CBFs at coronal hole boundaries. The latter has led to the suggestion that they may be a manifestation of a processes such as Joule heating or magnetic reconnection, rather than a wave-related phenomena. While the general morphological and kinematic properties of CBFs and their association with coronal mass ejections have now been well described, there are many questions regarding their excitation and propagation. In particular, the theoretical interpretation of these enigmatic events as magnetohydrodynamic waves or due to changes in magnetic topology remains the topic of much debate.

Gallagher, Peter T.; Long, David M.

2011-07-01

410

Microwave study of coronal active regions from the CORONAS-F list of solar flares observed in Gamma- and X- rays  

NASA Astrophysics Data System (ADS)

We analyze some of the tens of active regions (AR) each supposed to produce at least one solar flare detected in Gamma- and hard X-rays by the SONG-M spectrometer on board the CORONAS-F satellite. Of special interest is the AR NOAA 9601, which gave rise to the solar flare at 14:30 UT on September 5, 2001 with up to 4 MeV intensity in Gamma and of M6.0 class only in soft X-rays. We examine 1D radio scans of NOAA 9601, taken with the RATAN-600 in Stokes I and V at a set of wavelengths from 1.92 to 10 cm and radio maps taken with the Solar Siberian Radio Telescope (SSRT) at 5.2 cm. The type of this microwave source is classified among the other sources. The some prediction evidences of such type sources are listed.

Agalakov, B. V.; Borisevich, T. P.; Peterova, N. G.; Ryabov, B. I.; Topchilo, N. A.; Myagkova, I. N.; Kuznetsov, S. N.; Yushkov, B. Yu.; Kudela, K.

411

Fluid motions in the solar chromosphere-corona transition region. IV - Mass motions over sunspot umbrae  

NASA Astrophysics Data System (ADS)

Doppler velocity measurements in the C IV resonance line ?1548.19 have been obtained over the umbrae of eight sunspots with the Ultraviolet Spectrometer and Polarimeter (UVSP) on the Solar Maximum Mission. The velocity bandpass of these observations is approximately ±30 km s-1, and their spatial resolution is 3" × 3". Although a few individual resolution elements display flow velocities ? ±15 km s-1 relative to the quiet network, we measure a mean upflow of (1.2 ± 5.6) km s-1 when averaged over all the resolution elements. Means over individual umbrae frequently show smaller variances, which is evidence for a real distribution of umbral transition region velocity fields. We also examine two possible explanations for the smaller nonthermal broadening of the sunspot C IV line.

Gurman, J. B.; Athay, R. G.

1983-10-01

412

Fragmentation of electric currents in the solar corona by plasma flows  

NASA Astrophysics Data System (ADS)

Aims: We consider a magnetic configuration consisting of an arcade structure and a detached plasmoid, resulting from a magnetic reconnection process, as is typically found in connection with solar flares. We study spontaneous current fragmentation caused by shear and vortex plasma flows. Methods: An exact analytical transformation method was applied to calculate self-consistent solutions of the nonlinear stationary magnetohydrodynamic equations. The assumption of incompressible field-aligned flows implies that both the Alfvén Mach number and the mass density are constant on field lines. We first calculated nonlinear magnetohydrostatic equilibria with the help of the Liouville method, emulating the scenario of a solar eruptive flare configuration with plasmoids (magnetic ropes or current-carrying loops in 3D) and flare arcade. Then a Mach number profile was constructed that describes the upflow along the open magnetic field lines and implements a vortex flow inside the plasmoid. This Mach number profile was used to map the magnetohydrostatic equilibrium to the stationary one. Results: We find that current fragmentation takes place at different locations within our configuration. Steep gradients of the Alfvén Mach number are required, implying the strong influence of shear flows on current amplification and filamentation of the magnetohydrostatic current sheets. Crescent- or ring-like structures appear along the outer separatrix, butterfly structures between the upper and lower plasmoids, and strong current peaks close the lower boundary (photosphere). Furthermore, impressing an intrinsic small-scale structure on the upper plasmoid results in strong fragmentation of the plasmoid. Hence fragmentation of current sheets and plasmoids is an inherent property of magnetohydrodynamic theory. Conclusions: Transformations from magnetohydrostatic into magnetohydrodynamic steady-states deliver fine-structures needed for plasma heating and acceleration of particles and bulk plasma flows in dissipative events that are typically connected to magnetic reconnection processes in flares and coronal mass ejections.

Nickeler, D. H.; Karlický, M.; Wiegelmann, T.; Kraus, M.

2013-08-01

413

The Old Feeble Coronae of Solar-like Dwarf Stars in the Arcturus Moving Group  

NASA Astrophysics Data System (ADS)

The Arcturus Moving Group (AMG) is very likely a remnant of the merger of a dwarf galaxy with the Milky Way Galaxy in the distant past. This kinematically distinct group has members located very close to the Sun, allowing study of coronal activity on very old stars that would typically not be possible. We are investigating a sample of nearby AGM dwarfs to study the properties of stellar magnetic activity on old (7-8 Gyr), low metallicity stars. Our sample has metallicities between 0.4 and 0.04 solar, spectral types F9 K0, and distances less than 35 pc from the Sun. We have detected X-ray emission from two AMG dwarfs with the Chandra ACIS-S S3 BI detector during Cycle 7 and two further stars have been approved for observation in Cycle 8. The detected stars are HD199288 (G0 V, V=6.6, d = 21.6 pc, [Fe/H] = -0.68) and HD65583 (G8 V, V=6.9, d = 16.8 pc, [Fe/H] = -0.68) and their derived X-ray luminosities are 4.4 and 1.9 1026 erg s-1 respectively. These X-ray luminosities are somewhat less than the minimum solar Lx (range 6 -20 1026 erg s-1 ) but are comparable with that of the inactive, more metal rich ([Fe/H] = -0.42] G8 dwarf Tau Cet. All the detected source X-rays are very soft with energies of 0.2-0.3 keV, indicating very cool (˜ 1 MK) coronal temperatures. These results were obtained and funded by CXO project 7200977.

Brown, Alexander; Hodges-Kluck, E.; Ayres, T. R.; Harper, G. M.

2006-12-01

414

The Size-Frequency Distribution of the Zodiacal Cloud: Evidence from the Solar System Dust Bands  

NASA Astrophysics Data System (ADS)

Recent observations of the size-frequency distribution of zodiacal cloud particles obtained from the cratering record on the LDEF satellite are the latest evidence for a significant large particle population (100-?m diameter or greater) near 1 AU. Our previous modeling of the Solar System dust bands, features of the zodiacal cloud associated with the comminution of Hirayama family asteroids, has been limited by the fact that only small particles (25-?m diameter or smaller) have been considered. This was due to the prohibitively large amount of computing power required to numerically analyze the dynamics of larger particles. The recent availability of inexpensive, fast processors has finally made this work possible. Models of the dust bands are created, built from individual dust particle orbits, taking into account a size-frequency distribution of the material and the dynamical history of the constituent particles. These models are able to match both the shapes and amplitudes of the dust band structures observed by IRAS in multiple wavebands. The size-frequency index, q, that best matches the observations is approximately 1.4, a distribution in which the surface area (and hence the infrared emission) is dominated by large particles. However, in order to successfully model the "ten degree" band, which is usually associated with collisional activity within the Eos family, we find that the mean proper inclination of the dust particle orbits has to be approximately 9.35°, significantly different from the mean proper inclination of the Eos family (10.08°).

Grogan, Keith; Dermott, Stanley F.; Durda, Daniel D.

2001-08-01

415

Elemental Abundances in the Solar Corona as Measured by the X-ray Solar Monitor Onboard Chandrayaan-1  

NASA Astrophysics Data System (ADS)

The X-ray Solar Monitor (XSM) on the Indian lunar mission Chandrayaan-1 was flown to complement lunar elemental abundance studies by the X-ray fluorescence experiment C1XS. XSM measured the ? 1.8 - 20 keV solar X-ray spectrum during its nine months of operation in lunar orbit. The soft X-ray spectra can be used to estimate absolute coronal abundances using intensities of emission-line complexes and the plasma temperature derived from the continuum. The best estimates are obtained from the brightest flare observed by XSM: a C2.8-class flare. The well-known first-ionization potential (FIP) effect is observed; abundances are enhanced for the low-FIP elements Fe, Ca, and Si, while the intermediate-FIP element S shows values close to the photospheric abundance. The derived coronal abundances show a quasi-mass-dependent pattern of fractionation.

Narendranath, S.; Sreekumar, P.; Alha, L.; Sankarasubramanian, K.; Huovelin, J.; Athiray, P. S.

2013-10-01

416

Langmuir turbulence and quasilinear interactions of a hot electron beam in the inhomogeneous solar corona plasma with a uniform electric field  

NASA Astrophysics Data System (ADS)

Using numerical simulation of the quasilinear equations, the propagation of an electron beam through inhomogeneous solar corona plasma and generation of Langmuir waves are investigated by taking into account a uniform electric field. The level of the excited Langmuir waves is remarkably enhanced by decreasing density and the applied electric field. The mean velocity of propagation of the beam is not a constant and decreases with distance from the injection point. The effect of the electric field is more pronounced on the slow electrons and accelerates them to high velocity region while the density gradient mainly affects the fast electrons and effectively decelerates them.

Khalilpour, H.; Foroutan, G.

2012-01-01

417

MHD modeling of the solar corona using 4D-VAR data assimilation.  

NASA Astrophysics Data System (ADS)

Solar activity is driven by magnetic energy release processes when perturbed coronal magnetic structures relax magnetohydrodynamically. The long-lived force-free structures become unstable as they absorb flux and magnetic helicity produced in the solar interior. One observable process involves twisted flux ropes emerging from the surface and undergoing kink instability. This has been shown to be favorable to magnetic reconnection where opposing tube polarities intersect and form current sheets. We simulate numerically an anchored flux tube in an overlying magnetic arcade undergoing kink instability. Magnetic diffusivity is not included in our ideal isothermal MHD model meaning that we have not yet included energy release processes and we simulate on smaller scales than the size of a whole active region, both facts justifying the isothermal approximation. Given that there is no direct way to measure the MHD state variables in real cases, reconstruction models should be applied to generate a suitable background three dimensional initial state. Data assimilation is used next to further adjust this background state so that the forecasting is optimal. We have therefore implemented a 4D-VAR data assimilation algorithm that acts as a corrector on the initial state by minimizing the deviation between the observed and MHD-computed time series of observations. This is achieved using a cost function quantifying the discrepancy between observations and simulation over an assimilation window. In sum, the correction of possible errors on the initial state optimizes the trajectory of the model output. Minimization using the conjugate gradient algorithm requires the gradient of the cost function and this is a problem in itself that is solved by integrating along the adjoint equations of the MHD model. Having constructed such a system, we have conducted a series of test cases using artificial observations generated with an error in initial flux rope twist. A substantial error in initial twist leads to very distinct kinked final structures in the magnetic field lines. Using one value of twist, we generate a time series of synthetic observations and with another, an initial background state. By varying the nature of these experiments, we search for the minimum observational information requirement for an adequate correction.

Benslimane, Ali

418

Dynamical and Observational Constraints on the Origin and Evolution of the Solar System Dust Bands  

NASA Astrophysics Data System (ADS)

The Solar System dust bands discovered by the Infrared Astronomical Satellite (IRAS) are toroidal distributions of dust particles with common proper inclinations. It is impossible for particles with high eccentricity (approximately 0.2 or greater) to maintain a near constant proper inclination as they precess, and therefore the dust bands must be composed of material having a low eccentricity, pointing to an asteroidal origin. The IRAS observations of the zodiacal cloud from which we isolate the dust band profiles have excellent resolution (2 arcminutes) and the manner in which these profiles change around the sky helps to determine the origin of the bands, their radial extent, the size-frequency distribution of the material and the optical properties of the dust itself. The 'equilibrium model', which associates the dust bands with a continual comminution of material from the major Hirayama asteroid families, suggests Themis and Koronis as the parents of the central band and Eos as the parent of the ten degree band. This dissertation presents evidence from detailed numerical modeling of the bands which strengthens the genetic link between the bands and these families and argues in favor of the equilibrium model. Evidence is also presented suggesting that there are significant dispersions in the orbital inclinations of the Eos material. Investigation of the effects of a random walk in the dispersion of orbital inclinations (a rudimentary treatment of the effect of electromagnetic scattering) suggests that such a mechanism does not produce the Eos dispersion. Evidence is also presented to suggest that the distribution of asteroidal material in the inner solar system is more heavily weighted towards the asteroid belt than expected from a simple Poynting-Robertson drag distribution, implying that particles break up and are blown out of the system. Results of modeling the dust bands including a size-frequency distribution may suggest that a significant large particle component is required in the inner Solar System, consistent with LDEF cratering records. Future work with the COBE data at low elongation angles will further reveal the extent of the three-dimensional structure of the bands and serve to constrain estimates for the asteroidal component of the zodiacal cloud.

Grogan, Keith

1997-09-01

419

Magnetic field value in the weak energy release region of the solar corona  

SciTech Connect

Spectrographic data from observations of the polarized weak steplike (with relatively sharp growth t {approximately} 3 sec and slow decay t {approximately} 10{sup 2} sec) solar continuum radioemission are analyzed below. The main results are found using a sweeping spectrograph in the 8-12 GHz frequency range (sweep rate 1 sample per second and frequency resolution 120 MHz) and using the RT-22 radio telescope at the Crimean Astrophysical Observatory (angular resolution 4{prime}-6{prime}). In a series of events at the leading edge of the continuum a narrow-band frequency drifting emission termed {open_quotes}blip-type{close_quotes} is found. The degree of continuum circular polarization (p < 10%) is low compared to that of the narrow-band component (p {approx} 20%). Both components of the aforementioned events should be radiating on the second harmonic of the local plasma frequency in the context of a plasma generating mechanism. Based on the model proposed and using the observed degree of circular polarization of each component, we can estimate the strength of the magnetic field within the area of the source and the width of the angular spectrum from the radiating plasma turbulence. The results of analysis of the real microwave events are given below.

Levin, B.N.; Fridman, V.M.; Sheiner, O.A. [Radiophysical Research Institute, Novgorod (Russian Federation)

1995-01-01

420

Potential Magnetic Field around a Helical Flux Rope Current Structure in the Solar Corona  

NASA Astrophysics Data System (ADS)

We consider the potential magnetic field associated with a helical electric line current flow, idealizing the near-potential coronal field within which a highly localized twisted current structure is embedded. It is found that this field has a significant axial component off the helical magnetic axis where there is no current flow, such that the flux winds around the axis. The helical line current field, in including the effects of flux rope writhe, is therefore more topologically complex than the straight line and ring current fields sometimes used in solar flux rope models. The axial flux in magnetic fields around confined current structures may be affected by the writhe of these current structures such that the field twists preferentially with the same handedness as the writhe. This property of fields around confined current structures with writhe may be relevant to classes of coronal magnetic flux ropes, including structures observed to have sigmoidal forms in soft X-rays and prominence magnetic fields. For example, ``bald patches'' and the associated heating by Parker current sheet dissipation seem likely. Thus, some measurements of flux rope magnetic helicities may derive from external, near-potential fields. The predicted hemispheric preference for positive and negative magnetic helicities is consistent with observational results for prominences and sigmoids and past theoretical results for flux rope internal fields.

Petrie, G. J. D.

2007-05-01

421

Solar Corona Loop Studies with the Atmospheric Imaging Assembly. I. Cross-sectional Temperature Structure  

NASA Astrophysics Data System (ADS)

We present a first systematic study on the cross-sectional temperature structure of coronal loops using the six coronal temperature filters of the Atmospheric Imaging Assembly (AIA) instrument on the Solar Dynamics Observatory (SDO). We analyze a sample of 100 loop snapshots measured at 10 different locations and 10 different times in active region NOAA 11089 on 2010 July 24, 21:00-22:00 UT. The cross-sectional flux profiles are measured and a cospatial background is subtracted in six filters in a temperature range of T ? 0.5-16 MK, and four different parameterizations of differential emission measure (DEM) distributions are fitted. We find that the reconstructed DEMs consist predominantly of narrowband peak temperature components with a thermal width of ?log (T) <= 0.11 ± 0.02, close to the temperature resolution limit of the instrument, consistent with earlier triple-filter analysis from the Transition Region and Coronal Explorer by Aschwanden & Nightingale and from EIS/Hinode by Warren et al. or Tripathi et al. We find that 66% of the loops could be fitted with a narrowband single-Gaussian DEM model, and 19% with a DEM consisting of two narrowband Gaussians (which mostly result from pairs of intersecting loops along the same line of sight). The mostly isothermal loop DEMs allow us also to derive an improved empirical response function of the AIA 94 Å filter, which needs to be boosted by a factor of q 94 = 6.7 ± 1.7 for temperatures at log (T) <~ 6.3. The main result of near-isothermal loop cross-sections is not consistent with the predictions of standard nanoflare scenarios, but can be explained by flare-like heating mechanisms that drive chromospheric evaporation and upflows of heated plasma coherently over loop cross-sections of w ? 2-4 Mm.

Aschwanden, Markus J.; Boerner, Paul

2011-05-01

422

KINETIC INSTABILITY OF DRIFT-ALFVEN WAVES IN SOLAR CORONA AND STOCHASTIC HEATING  

SciTech Connect

The solar atmosphere is structured and inhomogeneous, both horizontally and vertically. The omnipresence of coronal magnetic loops implies gradients of the equilibrium plasma quantities such as the density, magnetic field, and temperature. These gradients are responsible for the excitation of drift waves that grow both within the two-component fluid description (both in the presence of collisions and without it) and within the two-component kinetic descriptions (due to purely kinetic effects). In this work, the effects of the density gradient in the direction perpendicular to the magnetic field vector are investigated within the kinetic theory, in both electrostatic (ES) and electromagnetic (EM) regimes. The EM regime implies the coupling of the gradient-driven drift wave with the Alfven wave. The growth rates for the two cases are calculated and compared. It is found that, in general, the ES regime is characterized by stronger growth rates, as compared with the EM perturbations. Also discussed is the stochastic heating associated with the drift wave. The released amount of energy density due to this heating should be more dependent on the magnitude of the background magnetic field than on the coupling of the drift and Alfven waves. The stochastic heating is expected to be much higher in regions with a stronger magnetic field. On the whole, the energy release rate caused by the stochastic heating can be several orders of magnitude above the value presently accepted as necessary for a sustainable coronal heating. The vertical stratification and the very long wavelengths along the magnetic loops imply that a drift-Alfven wave, propagating as a twisted structure along the loop, in fact occupies regions with different plasma-{beta} and, therefore, may have different (EM-ES) properties, resulting in different heating rates within just one or two wavelengths.

Vranjes, J.; Poedts, S., E-mail: Jovo.Vranjes@wis.kuleuven.b, E-mail: Stefaan.Poedts@wis.kuleuven.b [Center for Plasma Astrophysics, K. U. Leuven, Celestijnenlaan 200B, 3001 Leuven (Belgium)

2010-08-20

423

Kinetic Instability of Drift-Alfvén Waves in Solar Corona and Stochastic Heating  

NASA Astrophysics Data System (ADS)

The solar atmosphere is structured and inhomogeneous, both horizontally and vertically. The omnipresence of coronal magnetic loops implies gradients of the equilibrium plasma quantities such as the density, magnetic field, and temperature. These gradients are responsible for the excitation of drift waves that grow both within the two-component fluid description (both in the presence of collisions and without it) and within the two-component kinetic descriptions (due to purely kinetic effects). In this work, the effects of the density gradient in the direction perpendicular to the magnetic field vector are investigated within the kinetic theory, in both electrostatic (ES) and electromagnetic (EM) regimes. The EM regime implies the coupling of the gradient-driven drift wave with the Alfvén wave. The growth rates for the two cases are calculated and compared. It is found that, in general, the ES regime is characterized by stronger growth rates, as compared with the EM perturbations. Also discussed is the stochastic heating associated with the drift wave. The released amount of energy density due to this heating should be more dependent on the magnitude of the background magnetic field than on the coupling of the drift and Alfvén waves. The stochastic heating is expected to be much higher in regions with a stronger magnetic field. On the whole, the energy release rate caused by the stochastic heating can be several orders of magnitude above the value presently accepted as necessary for a sustainable coronal heating. The vertical stratification and the very long wavelengths along the magnetic loops imply that a drift-Alfvén wave, propagating as a twisted structure along the loop, in fact occupies regions with different plasma-? and, therefore, may have different (EM-ES) properties, resulting in different heating rates within just one or two wavelengths.

Vranjes, J.; Poedts, S.

2010-08-01

424

Clarifying the Picture of Fe XVII Opacity in the Solar Corona  

NASA Astrophysics Data System (ADS)

Several recent studies of opacity in the bright resonance line of Fe XVII at 15.01 Angstroms have yielded disparate results. Discrepancies include the magnitude of the inferred resonance scattering effects, the amount of center-to-limb variation, and even the sign of the center-to-limb change. The larger optical depths inferred by Waljeski et al. (1994 ApJ 429, 909) compared to those found by Schmelz, Saba, & Strong (1992 ApJ 398, L115) and by Saba et al. (1997, in prep.) in active region data from the Solar Maximum Mission Flat Crystal Spectrometer (FCS) could be explained by allowing for an estimated 20% relative uncertainty in the calculated emissivities of pairs of Fe XVII lines (A.K. Bhatia, private communication). The lower values of optical depth are supported by a demonstrated lack of measurable opacity in other potentially affected FCS lines (Schmelz et al. 1997 ApJ 477, 509). On the other hand, it is impossible to reconcile the report by Phillips et al. (1997 ApJ 469, L57) of a large decrease in opacity from disk center to the limb, with the more usual behavior found by Schmelz et al. (1997) and Saba et al. (1997), i.e., a slight increase in opacity for regions at or near the limb due to the increased line of sight. A reality check can be made with Yohkoh SXT intensities and with other soft X-ray spectroscopic data sets. We will also discuss the use and abuse of resonance scattering as a coronal plasma diagnostic tool. Resonance scattering is likely to be relevant for SOHO observations, for some bright EUV resonance lines with high elemental abundance, large ionization fraction, and moderate oscillator strength, such as Fe XV at 284 Angstroms. This work was supported by NASA contract NASW-4814 and the Lockheed-Martin Independent Research Program.

Saba, J. L. R.; Strong, K. T.; Schmelz, J. T.

1997-05-01

425

Evolution of dust particle orbits under the influence of solar wind outflow asymmetries and the formation of the zodiacal dust cloud  

NASA Astrophysics Data System (ADS)

The secular orbital evolution of zodiacal dust particles is mainly influenced by the electromagnetic and the plasma Poynting-Robertson effects. Whereas the first effect is radially symmetric, the second one, caused by the dynamical friction of the dust particles in the ambient solar wind flow, depends on heliographic latitude. This is because the solar wind appears to have pronounced mass and momentum flow variations with respect to heliographic latitudes, with mass flows decreasing by about 50% from the ecliptic toward the poles. We take into account related asymmetries in the plasma Poynting-Robertson effect and study orbital evolution of dust particles orbiting with different inclinations. We derive equations describing the secular changes of the orbital elements under these conditions. We show that the radial migration rates are greater by about 5 to 10% for particles close to the ecliptic as compared to those at higher inclinations. This leads to typical changes in the distribution of inclinations with decreasing semimajor axes of the particles and also shows that the dust distribution function cannot be factored into parts solely dependent on radial distance or inclination alone. Furthermore, the kinetic equation for the distribution function of dust particles is solved numerically, yielding the distribution in orbital element space. The spatial density of the particles can then be found as an integral over this distribution function after application of a Jacobian transformation of element space differentials into configuration space differentials and can be compared with earlier results. Some observational consequences are drawn from this comparison and are discussed in some more detail. It is also pointed out that the plasma Poynting-Robertson effect in a two-temperature solar wind produces normal components of perturbation forces and thus tends to change the inclination of the dust particle orbits. This is of special importance in the solar wind regime inside the critical point where low-Mach-number flows prevail.

Banaszkiewicz, M.; Fahr, H. J.; Scherer, K.

1994-02-01

426

Formation of fast shocks by magnetic reconnection in the solar corona  

SciTech Connect

Reconnections of magnetic fields over the solar surface are expected to generate abundant magnetohydrodynamic (MHD) discontinuities and shocks, including slow shocks and rotational discontinuities. However, the generation of fast shocks by magnetic reconnection process is relatively not well studied. In this paper, magnetic reconnection in a current sheet is studied based on two-dimensional resistive MHD numerical simulations. Magnetic reconnections in the current sheet lead to the formation of plasma jets and plasma bulges. It is further found that the plasma bulges, the leading part of plasma jets, in turn lead to the generation of fast shocks on flanks of the bulges. The simulation results show that during the magnetic reconnection process, the plasma forms a series of structures: plasma jets, plasma bulges, and fast shocks. As time increases, the bulges spread out along the current sheet ({+-}z direction) and the fast shocks move just ahead of the bulges. The effects of initial parameters {rho}{sub s}/{rho}{sub m}, {beta}{sub {infinity}}, and t{sub rec} on the fast shock generation are also examined, where {rho}{sub s}/{rho}{sub m} is the ratio of plasma densities on two sides of the initial current sheet, {beta}{sub {infinity}}=P{sub {infinity}}/(B{sub {infinity}}{sup 2}/2{mu}{sub 0}), P{sub {infinity}} is the plasma pressure and B{sub {infinity}} is the magnetic field magnitude far from the current sheet, and t{sub rec} is the reconnection duration. In the asymmetric case with {rho}{sub s}/{rho}{sub m}=2, {beta}{sub {infinity}}=0.01 and t{sub rec}=1000, the maximum Alfven Mach number of fast shocks (M{sub A1max}) is M{sub A1max} congruent with 1.1, where M{sub A1}=V{sub n1}/V{sub A1}, and V{sub n1} and V{sub A1} are, respectively, the normal upstream fluid velocity and the upstream Alfven speed in the fast shocks frame. As the density ratio {rho}{sub s}/{rho}{sub m} (=1-8) and plasma beta {beta}{sub {infinity}} (=0.0001-1) increase, M{sub A1max} varies slightly. For the case with a large plasma beta {beta}{sub {infinity}} (=5), the fast shock is very weak. As the reconnection duration t{sub rec} increases, the bulges lead to generation of fast shocks with a higher M{sub A1max}. The present results can be applied to the mechanism of coronal heating by fast shocks.

Hsieh, M. H. [Department of Physics, National Cheng Kung University, Tainan 701, Taiwan (China); Institute of Space Science, National Central University, Jhongli 320, Taiwan (China); Tsai, C. L. [Department of Physics, National Cheng Kung University, Tainan 701, Taiwan (China); I