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1

The effect of the solar magnetic field on dust-particle orbits in the F corona  

NASA Astrophysics Data System (ADS)

In order to determine whether the solar magnetic field can align circumsolar dust into rings such as those described by Mizutani et al. (1984), the solar magnetic field is divided into its various multipole components and theoretical expressions are derived to determine the effect of each of these components on the orbital elements of circumsolar dust. Simulations are then carried out to determine the effect of a dynamic solar magnetic field on such particles using actual values of the solar magnetic field supplied by Hoeksema (1984). These results are compared to observations of the F corona.

Rusk, Edwin T.

1988-10-01

2

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

3

The New Solar Corona  

NASA Technical Reports Server (NTRS)

We focus on new observational capabilities (Yohkoh, SoHO, TRACE) observations, modeling, approaches, and insights into physical processes of the solar corona. The most impressive new results and problems discussed in this article can be appreciated from the movies and available on the Annual Reviews web site.

Aschwanden, Markus J.; Poland, Arthur I.; Rabin, Douglas M.; Fisher, Richard R. (Technical Monitor)

2001-01-01

4

The New Solar Corona  

NASA Astrophysics Data System (ADS)

We focus on new observational capabilities (Yohkoh, SoHO, TRACE), observations, modeling approaches, and insights into physical processes of the solar corona. The most impressive new results and problems discussed in this article can be appreciated from the movies available on the Annual Reviews website and at http://www.lmsal.com/pub/araa/araa.html. "The Sun is new each day." Heraclites (ca 530-475 BC) "Everything flows." Heraclites (ca 530-475 BC)

Aschwanden, Markus J.; Poland, Arthur I.; Rabin, Douglas M.

5

Topological Dissipation & The Solar Corona  

NASA Astrophysics Data System (ADS)

Reconnection in the solar corona has to take place, as was convincingly shown by tet{Parker72}, the question remains if it is sufficient to heat the corona. One of the major problems in coronal physics, is modeling reconnection. Reconnection is the basis of most heating models, in spite the fact that we really don't know how reconnection works. Simulating reconnection with realistic parameters is highly problematic and the solar corona has a parameter space not well explored. Here I try to give a hint of what conclusions one can reach about reconnection from large scale simulations of the solar corona. A model of the solar corona with a numerical diffusion reproduces a number of observables, and seem to reproduce the corona well, only using minimal assumptions. The overall well reproduced corona, means that it is highly likely that reconnection does not differ much from the diffusion scheme of the numerical code. That means that reconnection in the solar corona transfers most of the liberated magnetic energy into heat locally and mechanisms such as waves and high energy particles can not carry the a significant part of the energy released in reconnection.

Gudiksen, B. V.

2007-10-01

6

The Viking solar corona experiment  

NASA Technical Reports Server (NTRS)

The 1976 Mars solar conjunction resulted in complete occultations 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 R sub s of the photosphere at the 3.5- and 13-cm wavelengths, respectively. The data can be used to determine the plasma density integrated along the radio path, the velocity of density irregularities in the coronal plasma, and the spectrum of the density fluctuations in the plasma. Observations of integrated plasma density near the south pole of the sun generally agree with a model of the corona which has an 8:1 decrease in plasma density from the equator to the pole. Power spectra of the 3.5- and 13-cm signals at a heliocentric radial distance of about 2 R sub s have a 1/2 power width of several hundred hertz and vary sharply with proximate geometric miss distance. Spectral broadening indicates a marked progressive increase in plasma irregularities with decreasing ray altitude at scales between about 1 and 100 km.

Tyler, G. L.; Brenkle, J. P.; Komarek, T. A.; Zygielbaum, A. I.

1977-01-01

7

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

8

Global Magnetohydrodynamic Modeling of the Solar Corona  

NASA Technical Reports Server (NTRS)

The solar corona, the hot, tenuous outer atmosphere of the Sun, exhibits many fascinating phenomena on a wide range of scales. One of the ways that the Sun can affect us here at Earth is through the large-scale structure of the corona and the dynamical phenomena associated with it, as it is the corona that extends outward as the solar wind and encounters the Earth's magnetosphere. The goal of our research sponsored by NASA's Supporting Research and Technology Program in Solar Physics is to develop increasingly realistic models of the large-scale solar corona, so that we can understand the underlying properties of the coronal magnetic field that lead to the observed structure and evolution of the corona. We describe the work performed under this contract.

Linker, Jon A.; Wagner, William (Technical Monitor)

2001-01-01

9

Solar wind acceleration in the solar corona  

NASA Technical Reports Server (NTRS)

The intensity ratio of the O VI doublet in the extended area is analyzed. The O VI intensity data were obtained with the ultraviolet coronagraph spectrometer (UVCS) during the SOHO campaign 'whole sun month'. The long term observations above the north pole of the sun were used for the polar coronal data. Using these measurements, the solar wind outflow velocity in the extended corona was determined. The 100 km/s level is running along the streamer borders. The acceleration of the solar wind is found to be high in regions between streamers. In the central part of streamers, the outflow velocity of the coronal plasma remains below 100 km/s at least within 3.8 solar radii. The regions at the north and south poles, characterized by a more rapid acceleration of the solar wind, correspond to regions where the UVCS observes enhanced O VI line broadenings.

Giordano, S.; Antonucci, E.; Benna, C.; Kohl, J. L.; Noci, G.; Michels, J.; Fineschi, S.

1997-01-01

10

Extraatmospheric observations of the outer solar corona  

Microsoft Academic Search

The paper describes a small, externally occulted Lyot coronagraph intended for the spaceborne photography of the solar corona; the instrument can be modified to perform observations of the corona from stratospheric balloons. The basic characteristics of the coronagraph are considered, and results obtained with the instrument on a rocket flight on December 19, 1976 are briefly discussed.

O. I. Babich; Y. B. Kolesnik; Y. A. Krayev; A. V. Lensky; A. T. Nesmyanovich; V. V. Polezhayev; B. B. Ponomaryov; O. S. Popov

1981-01-01

11

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

12

Dynamics of the quiescent solar corona  

Microsoft Academic Search

A model for the quiescent, inhomogeneous solar corona is developed, based upon the concept of loop structures as the basic structural element of the corona. The results, which are compared with observations obtained by the S-054 Skylab X-ray telescope, show that (a) hydrostatic solutions are stable only if the temperature maximum is located at the top of loop structures, and

R. Rosner; W. H. Tucker; G. S. Vaiana

1978-01-01

13

Global Magnetohydrodynamic Modeling of the Solar Corona  

NASA Technical Reports Server (NTRS)

The coronal magnetic field defines the structure of the solar corona, the position of the heliospheric current sheet, the regions of fast and slow solar wind, and the most likely sites of coronal mass ejections. There are few measurements of the magnetic fields in the corona, but the line-of-sight component of the global magnetic fields in the photosphere have been routinely measured for many years (for example, at Stanford's Wilcox Solar Observatory, and at the National Solar Observatory at Kitt Peak). The SOI/MDI instrument is now providing high-resolution full-disk magnetograms several times a day. Understanding the large-scale structure of the solar corona and inner heliosphere requires accurately mapping the measured photospheric magnetic field into the corona and outward. Ideally, a model should not only extrapolate the magnetic field, but should self-consistently reconstruct both the plasma and magnetic fields in the corona and solar wind. Support from our NASA SR&T contract has allowed us to develop three-dimensional magnetohydrodynamic (MHD) computations of the solar corona that incorporate observed photospheric magnetic fields into the boundary conditions. These calculations not only describe the magnetic field in the corona and interplanetary spice, but also predict the plasma properties as well. Our computations thus far have been successful in reproducing many aspects of both coronal and interplanetary data, including the structure of the streamer belt, the location of coronal hole boundaries, and the position and shape of the heliospheric current sheet. The most widely used technique for extrapolating the photospheric magnetic field into the corona and heliosphere are potential field models, such as the potential field source-surface model (PFSS),and the potential field current-sheet (PFCS) model

Linker, Jon A.

1998-01-01

14

Alfven waves in the solar corona.  

PubMed

Alfvén waves, transverse incompressible magnetic oscillations, have been proposed as a possible mechanism to heat the Sun's corona to millions of degrees by transporting convective energy from the photosphere into the diffuse corona. We report the detection of Alfvén waves in intensity, line-of-sight velocity, and linear polarization images of the solar corona taken using the FeXIII 1074.7-nanometer coronal emission line with the Coronal Multi-Channel Polarimeter (CoMP) instrument at the National Solar Observatory, New Mexico. Ubiquitous upward propagating waves were seen, with phase speeds of 1 to 4 megameters per second and trajectories consistent with the direction of the magnetic field inferred from the linear polarization measurements. An estimate of the energy carried by the waves that we spatially resolved indicates that they are too weak to heat the solar corona; however, unresolved Alfvén waves may carry sufficient energy. PMID:17761876

Tomczyk, S; McIntosh, S W; Keil, S L; Judge, P G; Schad, T; Seeley, D H; Edmondson, J

2007-08-31

15

Global MHD Models of the Solar Corona  

NASA Technical Reports Server (NTRS)

Global magnetohydrodynamic (MHD) models of the solar corona are computationally intensive, numerically complex simulations that have produced important new results over the past few years. After a brief overview of how these models usually work, I will address three topics: (1) How these models are now routinely used to predict the morphology of the corona and analyze Earth and space-based remote observations of the Sun; (2) The direct application of these models to the analysis of physical processes in the corona and chromosphere and to the interpretation of in situ solar wind observations; and (3) The use of results from global models to validate the approximations used to make detailed studies of physical processes in the corona that are not otherwise possible using the global models themselves.

Suess, S. T.; Rose, Franklin (Technical Monitor)

2001-01-01

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

Global Magnetohydrodynamic Modeling of the Solar Corona.  

National Technical Information Service (NTIS)

The coronal magnetic field defines the structure of the solar corona, the position of the heliospheric current sheet, the regions of fast and slow solar wind, and the most likely sites of coronal mass ejections. There are few measurements of the magnetic ...

J. A. Linker

1998-01-01

18

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

19

Topological Structure of the Magnetic Solar Corona  

Microsoft Academic Search

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

R. C. Maclean

2007-01-01

20

Hot Plasma Flows in the Solar Corona  

NASA Astrophysics Data System (ADS)

The Solar Corona is a non-equilibrium open system. Energy and mass are supplied from the lower atmosphere and flow upwards through the corona into the interplanetary space. Steady state could be possible but not equilibrium state. Temperature of the corona varies depending on solar activities. However, even under very quite state, coronal temperature is still kept around million degrees. Coronal heating mechanisms have to work under such condition. Temperature of plasma is an averaged kinetic energy of random motion of particles. Motion of charged particles in magnetic field generates Lorenz force and particles gyrate around magnetic field lines. Gyration of charged particles generates magnetic moment which is directed anti-parallel to the surrounding magnetic field. This is the origin of diamagnetism of plasma. Each particle can be considered as a small magnet directed opposite to the surrounding magnetic field. When these magnets are put in inhomogeneous magnetic field, they are pushed toward weak field region. In case of open magnetic field region in the solar corona, plasma particles are pushed upwards. If this force (diamagnetic or mirror force) exceeds the gravity force, plasma flows upwards. Magnetic moment of each charged particle in thermal plasma is proportional to temperature and inversely proportional to magnetic field strength. The condition for plasma to flow upwards in an open magnetic field is that the scale length of the change of magnetic field strength is shorter than the hydrostatic scale length, which is determined by temperature and the gravity acceleration. This can be a mechanism to regulate the coronal temperature around million degree. The solar corona is filled with magnetic field, which is rooted at the photosphere in the form of flux tubes. Flux tubes connect directly the corona and the sub-photospheric layer where temperature is higher than the photosphere. Hot plasma, trapped in the flux tubes when they are generated around the bottom of the convection zone, will be pushed upwards through the flux tubes due to weakening of magnetic field strength upwards and are fed into the corona. This scenario can explain why the solar corona is kept around million degree independent of solar activity. This mechanism can be applied to explain 1) temperature dependent plasma upflows found in the solar atmosphere, 2) solar wind acceleration, 3) loop-top plasma concentration in post flare loops, and 4) various eruptive phenomena, including some of solar flares, caused by flows along curved magnetic field. The MHD equation does not include this force along the field.

Shibasaki, K.

2012-12-01

21

The quiescent corona and slow solar wind  

NASA Technical Reports Server (NTRS)

The observations of the ultraviolet coronagraph spectrometer (UVCS), operating onboard the Solar and Heliospheric Observatory (SOHO) spacecraft, are discussed. The purpose of the UVCS is the study of the quiescent coronal streamer and the slow solar wind. The observations started in January 1996. Polarized radiance data in the visible continuum were obtained. Some characteristics of the coronal streamer from the UVCS recorded data are discussed. A model for the source of the slow solar wind in the inner corona is proposed.

Noci, G.; Kohl, J. L.; Antonucci, E.; Tondello, G.; Huber, M. C. E.; Fineschi, S.; Gardner, L. D.; Korendyke, C. M.; Nicolosi, P.; Romoli, M.; Spadaro, D.; Maccari, L.; Raymond, J. C.; Siegmund, O. H. W.; Benna, C.; Ciaravella, A.; Giordano, S.; Michels, J.; Modigliani, A.; Naletto, G.

1997-01-01

22

Global Magnetohydrodynamic Modeling of the Solar Corona  

NASA Technical Reports Server (NTRS)

Under this contract, we have continued our investigations of the large scale structure of the solar corona and inner heliosphere using global magnetohydrodynamic (MHD) simulations. These computations have also formed the basis for studies of coronal mass ejections (CMES) using realistic coronal configurations. We have developed a technique for computing realistic magnetohydrodynamic (MHD) computations of the solar corona and inner heliosphere. To perform computations that can be compared with specific observations, it is necessary to incorporate solar observations into the boundary conditions. We have used the Wilcox Solar Observatory synoptic maps (collected during a solar rotation by daily measurements of the line-of-sight magnetic field at central meridian) to specify the radial magnetic field (B,) at the photosphere. For the initial condition, we use a potential magnetic field consistent with the specified distribution of B, at the lower boundary, and a wind solution consistent with the specified plasma density and temperature at the solar surface. Together this initial condition forms a (non-equilibrium) approximation of the state of the solar corona for the time-dependent MHD computation. The MHD equations are then integrated in time to steady state. Here we describe solutions relevant to a recent solar eclipse, as well as Ulysses observations. We have also developed a model configuration of solar minimum, useful for studying CME initiation and propagation.

Linker, Jon A.

1997-01-01

23

Patchy reconnection in the solar corona  

Microsoft Academic Search

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

Silvina Esther Guidoni

2011-01-01

24

The Magnetic Field of the Solar Corona  

Microsoft Academic Search

We propose a novel experiment to examine both the magnetic field and electron content of the solar corona. We intend to measure the Faraday rotation and dispersion evident in observations of background pulsar sources as they are occulted by the Sun. As we will be utilising a number of simultaneous lines of sight, that will cut different paths through the

Stephen Ord; Simon Johnston

2006-01-01

25

EUV Corona in Solar Cycle 23  

Microsoft Academic Search

Extreme-Ultraviolet Telescope (EIT) on board SOHO provides us with unique data since 1996 up to the present time. The solar corona in Extreme-Ultraviolet emissions is visible on the solar disk and demonstrates a good relationship with the magnetic activity (SOHO\\/MDI and NSO\\/Kitt Peak data). We have analysed the EUV data from SOHO\\/EIT in four wavelengths (171A, 195A, 284A, and 304A),

Elena Benevolenskaya

2007-01-01

26

Dynamic Tomographic Imaging of the Solar Corona  

Microsoft Academic Search

Three-dimensional (3-D) maps of the electron density and temperature in the solar atmosphere can be tomographically reconstructed from two-dimensional images that are measured by a variety of ground-based and space-based instruments. The electron density and temperature of the solar corona are fundamental parameters for understanding the physical mechanisms that contribute to space weather, or physical phenomena that can, in extreme

Mark D. Butala; Farzad Kamalabadi; Richard A. Frazin; Yuguo Chen

2008-01-01

27

The three-dimensional structure of the solar corona  

Microsoft Academic Search

Due to the rotation of the sun the solar corona can be observed under different directions at different times. Using methods of computer tomography the three-dimensional structure of the emissivity of the solar corona can be reconstructed. We discuss the feasibility of this method for stationary and for non-stationary corona and also for incomplete and finite resolution data. As example

S. Zidowitz; B. Inhester; A. Epple

1995-01-01

28

STOCHASTIC COUPLING OF SOLAR PHOTOSPHERE AND CORONA  

SciTech Connect

The observed solar activity is believed to be driven by the dissipation of nonpotential magnetic energy injected into the corona by dynamic processes in the photosphere. The enormous range of scales involved in the interaction makes it difficult to track down the photospheric origin of each coronal dissipation event, especially in the presence of complex magnetic topologies. In this paper, we propose an ensemble-based approach for testing the photosphere-corona coupling in a quiet solar region as represented by intermittent activity in Solar and Heliospheric Observatory Michelson Doppler Imager and Solar TErrestrial RElations Observatory Extreme Ultraviolet Imager image sets. For properly adjusted detection thresholds corresponding to the same degree of intermittency in the photosphere and corona, the dynamics of the two solar regions is described by the same occurrence probability distributions of energy release events but significantly different geometric properties. We derive a set of scaling relations reconciling the two groups of results and enabling statistical description of coronal dynamics based on photospheric observations. Our analysis suggests that multiscale intermittent dissipation in the corona at spatial scales >3 Mm is controlled by turbulent photospheric convection. Complex topology of the photospheric network makes this coupling essentially nonlocal and non-deterministic. Our results are in an agreement with the Parker's coupling scenario in which random photospheric shuffling generates marginally stable magnetic discontinuities at the coronal level, but they are also consistent with an impulsive wave heating involving multiscale Alfvenic wave packets and/or magnetohydrodynamic turbulent cascade. A back-reaction on the photosphere due to coronal magnetic reconfiguration can be a contributing factor.

Uritsky, Vadim M.; Ofman, Leon [Catholic University of America at NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Davila, Joseph M. [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Coyner, Aaron J., E-mail: vadim.uritsky@nasa.gov [University of Tulsa, Tulsa, OK 74104 (United States)

2013-05-20

29

Solar Corona Explorer: A mission for the physical diagnosis of the solar corona  

NASA Technical Reports Server (NTRS)

Mission objectives and spacecraft requirements for the Solar Corona Explorer (SCE), a proposed free flying, unmanned solar research craft to be tenatively launched in 1987, were defined. The SCE's purpose is to investigate structure, dynamics and evolution of the corona, globally and in the required physical detail, to study the close coupling between the inner corona and the heliosphere. Investigative objectives are: (1) to understand the corona as the source of varying interplanetary plasma and of varying solar X-ray and extreme ultraviolet fluxes; (2) to develop the capabilities to model the corona with sufficient precision to forecast the Earth's variable environment in space, on the scales from weeks to years; (3) to develop an understanding of the physical processes that determine the dynamics and physical state of the coronal plasma, particularly acceleration processes; and (4) to develop insight and test theory on the Sun applicable to stellar coronae and winds, and in particular, to understand why cool stars put such a large fraction of their energy into X-rays. Considered related factors are: (1) duration of the mission; (2) onboard measuring instrumentation; (3) ground support equipment and procedures; and (4) programs of interpretation and modeling.

1981-01-01

30

Structure and dynamics of the solar corona  

NASA Technical Reports Server (NTRS)

Advanced computational techniques were used to study solar coronal heating and coronal mass ejections. A three dimensional, time dependent resistive magnetohydrodynamic code was used to study the dynamic response of a model corona to continuous, slow, random magnetic footpoint displacements in the photosphere. Three dimensional numerical simulations of the response of the corona to simple smooth braiding flows in the photosphere were calculated to illustrate and understand the spontaneous formation of current filaments. Two dimensional steady state helmet streamer configurations were obtained by determining the time asymptotic state of the interaction of an initially one dimensinal transponic solar wind with a spherical potential dipole field. The disruption of the steady state helmet streamer configuration was studied as a response to shearing of the magnetic footpoints of the closed field lines under the helmet.

Schnack, D. D.

1994-01-01

31

Nanoflare Heating of Solar and Stellar Coronae  

NASA Technical Reports Server (NTRS)

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. Kanoflares 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 A.

2010-01-01

32

Variable Winds and Dust Formation in R Coronae Borealis Stars  

NASA Astrophysics Data System (ADS)

We have observed P-Cygni and asymmetric, blue-shifted absorption profiles in the He I ?10830 lines of 12 R Coronae Borealis stars over short (1 month) and long (3 yr) timescales to look for variations linked to their dust-formation episodes. In almost all cases, the strengths and terminal velocities of the line vary significantly and are correlated with dust formation events. Strong absorption features with blue-shifted velocities ~400 km s-1 appear during declines in visible brightness and persist for about 100 days after recovery to maximum brightness. Small residual winds of somewhat lower velocity are present outside of the decline and recovery periods. The correlations support models in which recently formed dust near the star is propelled outward at high speed by radiation pressure and drags the gas along with it.

Clayton, Geoffrey C.; Geballe, T. R.; Zhang, Wanshu

2013-08-01

33

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

34

Radio seismology of the outer solar corona  

NASA Astrophysics Data System (ADS)

Observed oscillations of coronal loops in extreme ultraviolet (EUV) lines have been successfully used to estimate plasma parameters in the inner corona (< 0.2R0, where R0 is the solar radius). However, coronal seismology in EUV lines fails for higher altitudes because of rapid decrease in line intensity. We aim to use radio observations to estimate the plasma parameters of the outer solar corona (> 0.2R0). 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. 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 (MHD) 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 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. 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. The research leading to these results has received funding from the Austrian 'Fonds zur Förderung der wissenschaftlichen Forschung' under project P24740-N27.

Zaqarashvili, Teimuraz; Melnik, Valentin; Brazhenko, Anatoliy; Panchenko, Mykhaylo; Konovalenko, Alexander; Dorovskyy, Vladimir; Rucker, Helmut

2014-05-01

35

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

36

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

37

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

38

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

39

The three-dimensional structure of the solar corona  

NASA Technical Reports Server (NTRS)

Due to the rotation of the sun the solar corona can be observed under different directions at different times. Using methods of computer tomography the three-dimensional structure of the emissivity of the solar corona can be reconstructed. We discuss the feasibility of this method for stationary and for non-stationary corona and also for incomplete and finite resolution data. As example we present reconstructions based on YOHKOH-images, and we compare the results with ground-based optical corona observations. Structures are interpreted in terms of the solar magnetic field topology.

Zidowitz, S.; Inhester, B.; Epple, A.

1995-01-01

40

Common Periodicities of Gle's and Solar Corona  

NASA Astrophysics Data System (ADS)

Using different techniques of Wavelet Analysis, particularly, cross-wavelet coherence and the Global Wavelet Spectrum, we analyze data of intensity of 70 GLE's of the solar cycles 17 -23 vs data of the solar corona. We have found common periodicities of short period (2.8, 5.2 and 27 days), medium period (0.5, 1.2, 1.8, 3.2) as well as a the 4.6 and 11 yrs. periodicities. The two later are continuous over all the time interval, with a high synchronization and linear phase. In contrast, the short and medium periodicities are rather concentrated around the maximums of solar cycles, with some few cases in the minimums of solar activity, and present in general a complex phase. Results are discussed in terms of the works of others authors related to periodicities of the solar dynamo, solar atmosphere, interplanetary space and cosmic rays. We also evaluated the power anomalies of solar activity by means of sunspots, and have found that anomalies are positives when the GLE 's are of high intensity (higher than 100

Perez-Peraza, Jorge Alberto; Velasco Herrera, Victor Manuel; Miroshnichenko, Leonty I.; Vashenyuk, Eduard V.

41

Aspects of nonlinear magnetohydrodynamics in the solar corona  

Microsoft Academic Search

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

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

2004-01-01

42

The J- and K-Band Brightness of the Solar F-Corona Observed During the Solar Eclipse on February 26, 1998  

NASA Astrophysics Data System (ADS)

The solar eclipse on February 26 1998 was observed from an open flying aircraft at an altitude of almost 6 km above the Pacific about 800 km southwest from Panama City. The solar F-corona, produced by light scattering and thermal emission from dust around the Sun, was observed with a low atmospheric straylight level in the J and K-band over a field of view of 7 degrees. The data show no indication for the existence of pronounced brightness features in the solar F-corona, such as often discussed as evidence for the existence of dust rings. The shape of the corona is slightly elliptic but symmetric in the north-south direction. The data show a reddening of the coronal brightness compared to the solar spectrum. The color of the F-corona is influenced by the temperature of dust particles, by their spatial distribution, as well as by their size distribution that influences especially the forward scattering that is seen in the corona from dust particles close to the observer. We will discuss the color variation from the solar equator to the solar pole and with distances from the Sun and compare it to models of dust light scattering and thermal emission.

Ohgaito, R.; Mann, I.; Kuhn, J. R.; MacQueen, R. M.; Lin, H.; Edmunds, D.

1999-09-01

43

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

44

Magnetohydrodynamic vortices in the solar corona  

NASA Astrophysics Data System (ADS)

Interaction of coronal mass ejections with the plasma of the solar corona is accompanied with the generation of sharp shear flows that cause the induction of Alfvenic vortices. Numerical simulations revealed that for a broad range of parameters, the vortices are essentially compressible, with the perturbations of the density and the absolute value of the magnetic field in the vortex arms reaching 50% of the background density. The typical size of the vortex is about the size of the obstacle. The frequency of the vortex shedding is controlled by a dimensionless parameter known as the Strouhal number. We found that in collisionless low-beta plasma this number is about 0.2. Recent imaging observations with SDO/AIA revealed the generation of Alfvenic vortices at the flanks of emerging plasmoids. The vortices introduce a frictionless aerodynamic drag force, applied to the interacting plasmas. Implication of these findings for the excitation of kink oscillations of coronal loops and CME kinematics is discussed.

Nakariakov, Valery

2012-07-01

45

Untwisting magnetic fields in the solar corona  

NASA Astrophysics Data System (ADS)

The solar corona is the tenuous atmosphere of the Sun characterized by a temperature of the order of million degrees Kelvin, an ambient magnetic field of 10 to 15 Gauss and a very high magnetic Reynolds number because of which it qualifies as a near-ideal magnetofluid system. It is well known that for such a system, the magnetic flux across every fluid surface remains effectively constant to a good approximation. Under this so called ``frozen-in'' condition then, it is possible to partition this magnetofluid into contiguous magnetic subvolumes each entrapping its own subsystem of magnetic flux. Thin magnetic flux tubes are an elementary example of such magnetic subvolumes evolving in time with no exchange of fluid among them. The internal twists and interweaving of these flux tubes, collectively referred as the magnetic topology, remains conserved under the frozen-in condition. Because of the dynamical evolution of the magnetofluid, two such subvolumes can come into direct contact with each other by expelling a third interstitial subvolume. In this process, the magnetic field may become discontinuous across the surface of contact by forming a current sheet there. Because of the small spatial scales generated by steepening of magnetic field gradient, the otherwise negligible resistivity becomes dominant and allows for reconnection of field lines which converts magnetic energy into heat. This phenomenon of spontaneous current sheet formation and its subsequent resistive decay is believed to be a possible mechanism for heating the solar corona to its million degree Kelvin temperature. In this work the dynamics of spontaneous current sheet formation is explored through numerical simulations and the results are presented.

Bhattacharyya, Ramit; Smolarkiewicz, Piotr; Chye Low, Boon

2012-07-01

46

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

47

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

48

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

49

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

50

RADIO OBSERVATIONS OF THE SOLAR CORONA DURING AN ECLIPSE  

SciTech Connect

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 ({approx}15'') in the corona from where the observed radiation originated.

Kathiravan, C.; Ramesh, R.; Barve, Indrajit V.; Rajalingam, M., E-mail: kathir@iiap.res.in, E-mail: ramesh@iiap.res.in, E-mail: indrajit@iiap.res.in, E-mail: rajalingam@iiap.res.in [Indian Institute of Astrophysics, Bangalore 560 034 (India)

2011-04-01

51

Subtelescopic Inhomogeneities of Electron Density in the Solar Corona  

Microsoft Academic Search

The brightness of the solar corona due to Thomson scattering depends linearly on the electron density, while the brightness due to the Balmer continuum is proportional to its square. As a consequence, information on the distribution of the electron density in the corona can be obtained by comparing the radial profiles of the surface brightness in both continua. This idea

L. N. Kurochka; O. T. Matsuura; E. Picazzio

1997-01-01

52

Investigating The Solar Corona With Radio Observations Of Pulsars  

Microsoft Academic Search

We propose to examine both the magnetic field and electron content of the solar corona via measurement of the Faraday rotation and dispersion evident in observations of background pulsar sources as they are occulted by the Sun. As we will be utilise a number of simultaneous lines of sight, that will cut different paths through the corona as the Sun

S. Ord

2006-01-01

53

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

54

Ion cyclotron damping in the solar corona and solar wind  

NASA Astrophysics Data System (ADS)

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 the solar wind have been probed directly by spacecraft (outside the orbit of Mercury), and indirectly by ultraviolet spectroscopy (close to the Sun). Fluctuations in the plasma properties and in electromagnetic fields have been measured on time scales ranging from seconds to years. Despite more than a half-century of study, though, the basic physical processes responsible for heating the million-degree corona and accelerating the solar wind past the Sun's escape velocity are still not known with certainty. Understanding the basic physics of the solar wind is necessary to predict the Sun's impact on the Earth's climate and local space environment. This presentation will review the kinetic origins of several physical processes that are currently believed to be important in depositing energy and momentum in coronal particle velocity distributions. Because ions in the solar wind are heated and accelerated more than would be expected in either thermodynamic equilibrium or via a mass-proportional process, an ion cyclotron resonance has been suggested as a likely mechanism. Other evidence for gyroresonant wave dissipation in the corona will be presented, and possible generation mechanisms for the (as yet unobserved) high-frequency cyclotron waves will be reviewed. The mean state of the coronal and heliospheric plasma is intimately coupled with kinetic fluctuations about that mean, and theories of turbulence, wave dissipation, and instabilities must continue to be developed along with steady state descriptions of the solar wind. .

Cranmer, Steven R.

2001-10-01

55

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 Ĺ 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

56

Solar corona during the 1994 and 1999 eclipses  

Microsoft Academic Search

The lower and middle layers of the corona are studied analyzing the ground-based observations carried out during the November 3, 1994 and August 11, 1999 total solar eclipses. While the 1994 eclipse took place nearby the solar activity minimum, the 1999 eclipse occurred closer to the solar cycle maximum. Structures, isolines of brightness and polarization, and topology of the magnetic

O. G. Badalyan; J. Sýkora

2008-01-01

57

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

58

The origins of hot plasma in the solar corona.  

PubMed

The Sun's outer atmosphere, or corona, is heated to millions of degrees, considerably hotter than its surface or photosphere. Explanations for this enigma typically invoke the deposition in the corona of nonthermal energy generated by magnetoconvection. However, the coronal heating mechanism remains unknown. We used observations from the Solar Dynamics Observatory and the Hinode solar physics mission to reveal a ubiquitous coronal mass supply in which chromospheric plasma in fountainlike jets or spicules is accelerated upward into the corona, with much of the plasma heated to temperatures between ~0.02 and 0.1 million kelvin (MK) and a small but sufficient fraction to temperatures above 1 MK. These observations provide constraints on the coronal heating mechanism(s) and highlight the importance of the interface region between photosphere and corona. PMID:21212351

De Pontieu, B; McIntosh, S W; Carlsson, M; Hansteen, V H; Tarbell, T D; Boerner, P; Martinez-Sykora, J; Schrijver, C J; Title, A M

2011-01-01

59

Current Sheet Formation and Reconnection Dynamics in the Solar Corona  

Microsoft Academic Search

Current sheet formation is a necessary consequence of the evolution of the multi-polar magnetic field topologies that are ubiquitous throughout the solar corona. We present a very high-resolution study of 3D MHD current sheet formation and the resulting reconnection dynamics in an environment appropriate for the corona. The initial field consists of a translationally invariant, potential field with a null-point

Justin K. Edmondson; S. K. Antiochos; C. DeVore; T. H. Zurbuchen

2009-01-01

60

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

61

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

62

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

63

Evolution of twisted magnetic fields. [Of solar corona  

Microsoft Academic Search

The magnetic field of the solar corona evolves quasi-statically in response to slowly changing photospheric boundary conditions. The magnetic topology is preserved by the low resistivity of the solar atmosphere. It is shown that a magnetic flux coordinate system simplifies the problem of calculating field evolution with invariant topology. As an example, the equilibrium of a thin magnetic flux tube

E. G. Zweibel; A. H. Boozer

1985-01-01

64

Dust near the Sun: interaction with the solar wind  

NASA Astrophysics Data System (ADS)

The structure of the circumsolar dust cloud in the vicinity of the Sun is still not well known In this contribution we concentrate on two topics the role of the dust as the inner source of the pick-up ions discovered by SWICS Ulysses and the dynamics of very small few 0 001 micron dust grains the motion of which is strongly affected by electromagnetic forces We have recently shown that mutual collisions of dust vaporize parts of the dust material The dust material contributes to the inner source pick-up ion population in the solar wind that was discovered during the Ulysses space mission Measurements of cometary dust composition show enhanced abundances of light elements C H O N compared to typical meteoritical material generated from asteroids This points to the existence of organic compounds in cometary dust If our model for the generation of pick-up ions is correct then the measurements imply that cometary dust contains organic refractory compounds that can survive high temperatures in the vicinity of the Sun Aside from gravity the small particles in the solar corona are influenced by radiation pressure and Lorentz force We study the motion of particles and show that sub-micrometer particles that are predominantly influenced by Lorentz force attain significantly higher velocities than particles that are influenced by gravity and radiation pressure

Mann, I.; Czechowski, A.

65

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

66

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

67

Probing the solar corona with very long baseline interferometry  

NASA Astrophysics Data System (ADS)

Understanding and monitoring the solar corona and solar wind is important for many applications like telecommunications or geomagnetic studies. Coronal electron density models have been derived by various techniques over the last 45 years, principally by analysing the effect of the corona on spacecraft tracking. Here we show that recent observational data from very long baseline interferometry (VLBI), a radio technique crucial for astrophysics and geodesy, could be used to develop electron density models of the Sun’s corona. The VLBI results agree well with previous models from spacecraft measurements. They also show that the simple spherical electron density model is violated by regional density variations and that on average the electron density in active regions is about three times that of low-density regions. Unlike spacecraft tracking, a VLBI campaign would be possible on a regular basis and would provide highly resolved spatial–temporal samplings over a complete solar cycle.

Soja, B.; Heinkelmann, R.; Schuh, H.

2014-06-01

68

Probing the solar corona with very long baseline interferometry.  

PubMed

Understanding and monitoring the solar corona and solar wind is important for many applications like telecommunications or geomagnetic studies. Coronal electron density models have been derived by various techniques over the last 45 years, principally by analysing the effect of the corona on spacecraft tracking. Here we show that recent observational data from very long baseline interferometry (VLBI), a radio technique crucial for astrophysics and geodesy, could be used to develop electron density models of the Sun's corona. The VLBI results agree well with previous models from spacecraft measurements. They also show that the simple spherical electron density model is violated by regional density variations and that on average the electron density in active regions is about three times that of low-density regions. Unlike spacecraft tracking, a VLBI campaign would be possible on a regular basis and would provide highly resolved spatial-temporal samplings over a complete solar cycle. PMID:24946791

Soja, B; Heinkelmann, R; Schuh, H

2014-01-01

69

HIGH SPATIAL RESOLUTION OBSERVATIONS OF LOOPS IN THE SOLAR CORONA  

SciTech Connect

Understanding how the solar corona is structured is of fundamental importance to determine how the Sun's upper atmosphere is heated to high temperatures. Recent spectroscopic studies have suggested that an instrument with a spatial resolution of 200 km or better is necessary to resolve coronal loops. The High Resolution Coronal Imager (Hi-C) achieved this performance on a rocket flight in 2012 July. We use Hi-C data to measure the Gaussian widths of 91 loops observed in the solar corona and find a distribution that peaks at about 270 km. We also use Atmospheric Imaging Assembly data for a subset of these loops and find temperature distributions that are generally very narrow. These observations provide further evidence that loops in the solar corona are often structured at a scale of several hundred kilometers, well above the spatial scale of many proposed physical mechanisms.

Brooks, David H.; Ugarte-Urra, Ignacio [College of Science, George Mason University, 4400 University Drive, Fairfax, VA 22030 (United States); Warren, Harry P. [Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States); Winebarger, Amy R. [NASA Marshall Space Flight Center, ZP 13, Huntsville, AL 35812 (United States)

2013-08-01

70

Effects of heavy ions on electron temperatures in the solar corona and solar wind  

NASA Technical Reports Server (NTRS)

The effects of the reduction in the thermal conductivity due to heavy ions on electron temperatures in the solar corona and solar wind are examined. Large enhancements of heavy ions in the corona appear to be necessary to give appreciable changes in the thermal gradient of the electrons.

Nakada, M. P.

1972-01-01

71

Magnetohydrodynamic modeling of the solar corona during Whole Sun Month  

Microsoft Academic Search

The Whole Sun Month campaign (August 10 to September 8, 1996) brought together a wide range of space-based and ground-based observations of the Sun and the interplanetary medium during solar minimum. The wealth of data collected provides a unique opportunity for testing coronal models. We develop a three-dimensional magnetohydrodynamic (MHD) model of the solar corona (from 1 to 30 solar

J. A. Linker; Z. Mikic; D. A. Biesecker; R. J. Forsyth; S. E. Gibson; A. J. Lazarus; A. Lecinski; P. Riley; A. Szabo; B. J. Thompson

1999-01-01

72

Wind in the Solar Corona: Dynamics and Composition  

Microsoft Academic Search

The dynamics of the solar corona as observed during solar minimum with the Ultraviolet Coronagraph Spectrometer, UVCS, on\\u000a SOHO is discussed. The large quiescent coronal streamers existing during this phase of the solar cycle are very likely composed\\u000a by sub-streamers, formed by closed loops and separated by open field lines that are channelling a slow plasma that flows close\\u000a to

Ester Antonucci

73

Wind in the Solar Corona: Dynamics and Composition  

Microsoft Academic Search

The dynamics of the solar corona as observed during solar minimum with the Ultraviolet Coronagraph Spectrometer, UVCS, on\\u000a SOHO is discussed. The large quiescent coronal streamers existing during this phase of the solar cycle are very likely composed\\u000a by sub-streamers, formed by closed loops and separated by open field lines that are channelling a slow plasma that flows close\\u000a to

Ester Antonucci

2006-01-01

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

The solar extreme ultra-violet corona: Resolved loops and the unresolved active region corona  

NASA Astrophysics Data System (ADS)

In this work, physical characteristics of the solar corona as observed in the Extreme Ultra-Violet (EUV) regime are investigated. The focus will be the regions of intense EUV radiation generally found near the locations of sunspots. These regions are commonly called active regions. Multiple space- based observing platforms have been deployed in the last decade; it is possible to use several of these observatories in combination to develop a more complete picture of the solar corona. Joint Observing Program 146 was created to collect spectroscopic intensities using the Coronal Diagnostic Spectrometer on Solar and Heliospheric Observatory and EUV images using NASA's Transition Region and Coronal Explorer. The emission line intensities are analyzed to develop an understanding of the temperature and density of the active region coronal plasma. However, the performance of the CDS instrument in the spatial and temporal domains is limited and to compensate for these limitations, data collected by the TRACE instrument provide a high spatial and temporal resolution set of observations. One of the most exciting unsolved problems in solar astrophysics is to understand why the corona maintains a temperature roughly two orders of magnitude higher than the underlying material. A detailed investigation of the coronal emission has provided constraints on models of the heating mechanism, since the temperature, density and evolution of emission rates for multiple ionic species are indicative of the mechanism(s) working to heat the corona. The corona appears to consist of multiple unresolved structures as well as resolved active region structures, called coronal loops. The purpose of the present work is to determine the characteristics of the unresolved background corona. Using the characterizations of the coronal unresolved background, results for loops after background subtraction are also presented. This work demonstrates the magnitude of the unresolved coronal emission with respect to the total emission along the line of sight, and the relationship of the coronal background emission to the resolved loop emission. It is apparent from this analysis that the unresolved corona is the dominant source of radiation in active regions. Additionally, the unresolved active region coronal emission can be characterized by hydrostatic scaling laws.

Cirtain, Jonathan Wesley

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

Imaging and Processing Images of the Solar Corona  

NASA Astrophysics Data System (ADS)

Of all astronomical phenomena visible to the naked eye, none is as spectacular, or as fleeting, as a total eclipse of the Sun. For a few brief minutes, the Moon blocks the Sun's blindingly bright photosphere to reveal the ethereal solar corona. This gossamer halo, forming the outer atmosphere of the Sun, can only be seen in the eerie twilight brought on by totality.

Espenak, Fred

78

Observation of Alfven Waves in the Solar Corona (Invited)  

NASA Astrophysics Data System (ADS)

I will review the extensive progress made in recent years on the observation of Alfven waves in the solar corona, with an emphasis on the measurements made with the Coronal Multi-channel Polarimeter. Application of the wave measurements to coronal seismology will be presented. Future prospects in the field will be discussed.

Tomczyk, S.

2013-12-01

79

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

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

Force-Free Magnetic Flux Ropes in the Solar Corona  

Microsoft Academic Search

In the course of an ongoing investigation of force-free magnetic fields in the spherical geometry appropriate to the solar corona, we have found solutions that represent magnetic flux ropes. The magnetic energy stored in these ropes and the surrounding field is larger than that which can be stored in simple magnetic arcades with the same boundary conditions, and in some

R. Wolfson

2003-01-01

83

Reconnection in multiple current sheet configurations in the solar corona  

Microsoft Academic Search

We investigate magnetic reconnection in a multiple current sheet configuration by means of three-dimensional resistive MHD simulations. This configuration might be of interest in the solar corona context, e.g. for coronal helmet streamers. We present results of our simulations of the linear and nonlinear development of the tearing mode instability. In particular, we highlight the changes in magnetic topology and

G. T Birk; A. Otto

1997-01-01

84

Density Structure of the Solar Corona From Radio Occultation Measurements  

Microsoft Academic Search

Starting with angular broadening measurements five decades ago, a wide variety of radio propagation and scattering phenomena have been observed when natural radio sources or spacecraft radio signals happened to pass behind or were occulted by the solar corona. While yielding information on density, velocity and magnetic fields, these unique measurements probe density most directly, and with unprecedented sensitivity, spatial

R. Woo

2003-01-01

85

Investigating The Magnetic Field of The Solar Corona With Pulsars  

Microsoft Academic Search

We propose a novel experiment to examine both the magnetic field and electron content of the solar corona. We intend to measure the Faraday rotation and dispersion evident in observations of background pulsar sources as they are occulted by the Sun. As we will be utilising a number of simultaneous lines of sight, that will cut different paths through the

S. Ord

2006-01-01

86

Force-Free Magnetic Flux Ropes in the Solar Corona  

Microsoft Academic Search

Magnetic flux ropes offer a venue for storage of magnetic energy in the solar corona, energy that can contribute to eruptive events such as coronal mass ejections (CMEs). When a flux rope encircles the Sun, the associated magnetic field can store more energy than is needed to open the field fully---one of three energy-demanding tasks required for a CME. This

R. Wolfson

2004-01-01

87

Heating the Solar Corona by Magnetic Reconnection  

NASA Astrophysics Data System (ADS)

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 x-ray bright points. Furthermore, it has been shown that the large-scale diffuse corona is heated rather uniformly, so that turbulent reconnection by braiding or ion-cyclotron waves driven by network micro-flares are prime candidates. Finally, reconnection is the natural explanation for a wide variety of phenomena discovered by SOHO including explosive events, blinkers, the magnetic carpet and even possibly tornadoes.

Priest, E. R.

1998-07-01

88

A study of the background corona near solar minimum  

Microsoft Academic Search

The white light coronagraph data from Skylab is used to investigate the equatorial and polarK andF coronal components during the declining phase of the solar cycle near solar minimum. Measurements of coronal brightness and polarization brightness product between 2.5 and 5.5R? during the period of observation (May 1973 to February 1974) lead to the conclusions that: (1) the equatorial corona

Kuniji Saito; Arthur I. Poland; Richard H. Munro

1977-01-01

89

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

90

Evolution of twisted magnetic fields. [Of solar corona  

SciTech Connect

The magnetic field of the solar corona evolves quasi-statically in response to slowly changing photospheric boundary conditions. The magnetic topology is preserved by the low resistivity of the solar atmosphere. It is shown that a magnetic flux coordinate system simplifies the problem of calculating field evolution with invariant topology. As an example, the equilibrium of a thin magnetic flux tube with small twist per unit length was calculated. 22 references.

Zweibel, E.G.; Boozer, A.H.

1985-08-01

91

Effects of heavy ions on electron temperatures in the solar corona and solar wind  

NASA Technical Reports Server (NTRS)

The effects of the reduction in the thermal conductivity due to heavy ions on electron temperatures in the solar corona and solar wind are examined. Large enhancements of heavy ions in the corona appear to be necessary to give appreciable changes in the thermal gradient of the electrons. These enhancements, if they should occur, may contribute to the understanding of some low values of solar wind temperature measurements at 1 AU.

Nakada, M. P.

1974-01-01

92

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

93

Remote Sensing Measurements of the Corona with the Solar Probe  

NASA Technical Reports Server (NTRS)

Remote sensing measurements of the solar corona are indespensible for the exploration of the source and acceleration regions of the solar wind which are inaccessible to in situ plasma, paritcles and field experiments.Furthermore, imaging the solar disk and coronal 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.

Habbal, Shadia Rifai; Woo, Richard

1996-01-01

94

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

95

Heating of the Solar Corona and its Loops  

NASA Technical Reports Server (NTRS)

At several million degrees, the solar corona is more than two orders of magnitude hotter than the underlying solar surface. The reason for these extreme conditions has been a puzzle for decades and is considered one of the fundamental problems in astrophysics. Much of the coronal plasma is organized by the magnetic field into arch-like structures called loops. Recent observational and theoretical advances have led to great progress in understanding the nature of these loops. In particular, we now believe they are bundles of unresolved magnetic strands that are heated by storms of impulsive energy bursts called nanoflares. Turbulent convection at the solar surface shuffles the footpoints of the strands and causes them to become tangled. A nanoflare occurs when the magnetic stresses reach a critical threshold, probably by way of a mechanism called the secondary instability. I will describe our current state of knowledge concerning the corona, its loops, and how they are heated.

Klimchuk, James A.

2009-01-01

96

The solar corona as a quadric surface in three-dimensional space  

Microsoft Academic Search

The topology of the outer solar corona has been analyzed. In so doing the outer corona was treated as a visible manifestation of the heliospheric current sheet base. A generalization of the recent conception of the flat (galaxy-like) solar corona has been suggested. It is shown that the three-dimensional shape of the outer corona is well fitted by the second-degree

R. A. Gulyaev

1994-01-01

97

OBSERVATION OF ULTRAFINE CHANNELS OF SOLAR CORONA HEATING  

SciTech Connect

We report the first direct observations of dynamical events originating in the Sun's photosphere and subsequently lighting up the corona. Continuous small-scale, impulsive events have been tracked from their origin in the photosphere on through to their brightening of the local corona. We achieve this by combining high-resolution ground-based data from the 1.6 m aperture New Solar Telescope (NST) at Big Bear Solar Observatory (BBSO), and satellite data from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). The NST imaging observations in helium I 10830 A reveal unexpected complexes of ultrafine, hot magnetic loops seen to be reaching from the photosphere to the base of the corona. Most of these ultrafine loops are characterized by an apparently constant, but surprisingly narrow diameter of about 100 km all along each loop, and the loops originate on the solar surface from intense, compact magnetic field elements. The NST observations detect the signature of upward injections of hot plasma that excite the ultrafine loops from the photosphere to the base of the corona. The ejecta have their individual footpoints in the intergranular lanes between the Sun's ubiquitous, convectively driven granules. In many cases, AIA/SDO detects cospatial and cotemporal brightenings in the overlying, million degree coronal loops in conjunction with the upward injections along the ultrafine loops. Segments of some of the more intense upward injections are seen as rapid blueshifted events in simultaneous H{alpha} blue wing images observed at BBSO. In sum, the observations unambiguously show impulsive coronal heating events from upward energy flows originating from intergranular lanes on the solar surface accompanied by cospatial mass flows.

Ji, Haisheng [Key Laboratory for Dark Matter and Space Science, Purple Mountain Observatory, CAS, Nanjing 210008 (China); Cao, Wenda; Goode, Philip R. [Big Bear Solar Observatory, 40386 North Shore Lane, Big Bear City, CA 92314 (United States)

2012-05-01

98

Observation of Ultrafine Channels of Solar Corona Heating  

NASA Astrophysics Data System (ADS)

We report the first direct observations of dynamical events originating in the Sun's photosphere and subsequently lighting up the corona. Continuous small-scale, impulsive events have been tracked from their origin in the photosphere on through to their brightening of the local corona. We achieve this by combining high-resolution ground-based data from the 1.6 m aperture New Solar Telescope (NST) at Big Bear Solar Observatory (BBSO), and satellite data from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). The NST imaging observations in helium I 10830 Ĺ reveal unexpected complexes of ultrafine, hot magnetic loops seen to be reaching from the photosphere to the base of the corona. Most of these ultrafine loops are characterized by an apparently constant, but surprisingly narrow diameter of about 100 km all along each loop, and the loops originate on the solar surface from intense, compact magnetic field elements. The NST observations detect the signature of upward injections of hot plasma that excite the ultrafine loops from the photosphere to the base of the corona. The ejecta have their individual footpoints in the intergranular lanes between the Sun's ubiquitous, convectively driven granules. In many cases, AIA/SDO detects cospatial and cotemporal brightenings in the overlying, million degree coronal loops in conjunction with the upward injections along the ultrafine loops. Segments of some of the more intense upward injections are seen as rapid blueshifted events in simultaneous H? blue wing images observed at BBSO. In sum, the observations unambiguously show impulsive coronal heating events from upward energy flows originating from intergranular lanes on the solar surface accompanied by cospatial mass flows.

Ji, Haisheng; Cao, Wenda; Goode, Philip R.

2012-05-01

99

Observation of Hyperfine Channels of Solar Corona Heating  

NASA Astrophysics Data System (ADS)

We report here the first direct observations of dynamical events originating in the sun’s cool photosphere and subsequently lighting up the corona. Continuous impulsive events have been tracked from their origin in the photosphere on through to their brightening of the local corona. We achieve this by combining high resolution ground-based data from the 1.6 meter aperture New Solar Telescope (NST) at Big Bear Solar Observatory (BBSO),and satellite data from the Atmospheric Imaging Assembly (AIA) on-board the Solar Dynamics Observatory (SDO). The NST observations in a narrow band absorption line, Helium I 10830 Ĺ, reveal unexpected complexes of hyperfine, hot magnetic loops seen to be reaching from the photosphere to the base of the corona. Most of these hyperfine loops are characterized by an apparently constant, but surprisingly narrow diameter of about 100 km all along each loop, and the loops originate on the solar surface from intense, small-scale magnetic field elements. The NST observations detect upward injections of hot plasma that excite the hyperfine loops from the photosphere to the base of the corona. The ejecta have their individual footpoints in the intergranular lanes between the sun’s ubiquitous, convectively driven granules. In many cases, AIA/SDO detects co-spatial and co-temporal brightenings in the overlying, million-degree coronal loops in conjunction with the upward injections along the hyperfine loops. Segments of some of the more intense upward injections are seen as rapid blue-shifted events in simultaneous H? blue wing images observed at BBSO. In sum, the observations unambiguously show impulsive coronal heating events from upward energy flows originating from intergranular lanes on the solar surface accompanied by co-spatial mass flows.

Cao, Wenda; Ji, H.; Goode, P. R.

2012-05-01

100

Empirically constrained MHD model of the solar corona and solar wind  

Microsoft Academic Search

We are developing a time stationary self-consistent 2D MHD model of the solar corona and solar wind that explicitly solves the energy equation. For the energy equation we use a semi-empirical 2D MHD model of the corona to provide an empirically determined effective heat flux qeff (i.e., the term effective means the possible presence of wave contributions) for the energy

E. Sittler; L. Ofman; S. Gibson; M. Guhathakurta; J. Davila; R. Skoug; A. Fludra; T. Holzer

2003-01-01

101

Solar Physics and the Coronas Project.  

National Technical Information Service (NTIS)

The three basic problems facing solar physics are addressed. These concern the internal structure of the Sun and the process of transfer of energy from the deeper layers towards the surface; the investigation of solar activity, its mechanism and its influ...

V. Oraevsky

1993-01-01

102

The Structure and Dynamics of the Solar Corona  

NASA Technical Reports Server (NTRS)

This report covers technical progress during the third year of the NASA Space Physics Theory contract "The Structure and Dynamics of the Solar Corona," between NASA and Science Applications International Corporation, and covers the period June 16, 1998 to August 15, 1999. This is also the final report for this contract. Under this contract SAIC, the University of California, Irvine (UCI), and the Jet Propulsion Laboratory (JPL), have conducted research into theoretical modeling of active regions, the solar corona, and the inner heliosphere, using the MHD model. During the three-year duration of this contract we have published 49 articles in the scientific literature. These publications are listed in Section 3 of this report. In the Appendix we have attached reprints of selected articles. We summarize our progress during the third year of the contract. Full descriptions of our work can be found in the cited publications, a few of which are attached to this report.

Mikic, Zoran

2000-01-01

103

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

104

Acceleration in solar corona by electromagnetic ion cyclotron (EMIC) waves  

NASA Astrophysics Data System (ADS)

We investigate the process of acceleration of electrons in the solar corona by the propagation of EMIC waves along a density cavity with density gradients perpendicular to the background magnetic field. We use 2.5-D electromagnetic particle-in-cell simulation code. Simulations show that EMIC waves in interaction with a cavity give rise to a strong local electric field accelerating electrons in the direction of the magnetic field. Non-linear small-scale electrostatic structures are observed inside the deepest cavities, that present similarities with coherent structures observed in other regions of acceleration, as, for example, the Earth auroral zone acceleration regions. As the Earth auroral zone acceleration regions are strong sources of electromagnetic waves, it is possible that the acceleration regions are the sources of radio emissions in the Solar corona.

Daiffallah, K.; Mottez, F.

2012-09-01

105

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

106

The Structure and Dynamics of the Solar Corona  

NASA Technical Reports Server (NTRS)

Under this contract SAIC, the University of California, Irvine (UCI), and the Jet Propulsion Laboratory (JPL), have conducted research into theoretical modeling of active regions, the solar corona, and the inner heliosphere, using the MHD model. During the period covered by this report we have published 17 articles in the scientific literature. These publications are listed in Section 4 of this report. In the Appendix we have attached reprints of selected articles.

Mikic, Zoran

1998-01-01

107

The Structure and Dynamics of the Solar Corona  

NASA Technical Reports Server (NTRS)

This report details progress during the third year of our Space Physics Theory Contract. This is the Final Report for this contract. Under this contract SAIC, the University of California, Irvine (UCI), and the Jet Propulsion Laboratory (JPL), have conducted research into theoretical modeling of active regions, the solar corona. and the inner heliosphere, using the MHD model. During the three-year duration of this contract we have published 49 articles in the scientific literature.

Mikic, Zoran; Grebowsky, J. (Technical Monitor)

2000-01-01

108

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 Ĺ) 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 ą57°.5. It is proposed that at least part of the variability

Ester Antonucci; Leif Svalgaard

1974-01-01

109

Weak compressible magnetohydrodynamic turbulence in the solar corona.  

PubMed

This Letter presents a calculation of the power spectra of weakly turbulent Alfvén waves and fast magnetosonic waves ("fast waves") in low- plasmas. It is shown that three-wave interactions transfer energy to high-frequency fast waves and, to a lesser extent, high-frequency Alfvén waves. High-frequency waves produced by MHD turbulence are a promising explanation for the anisotropic heating of minor ions in the solar corona. PMID:16486367

Chandran, Benjamin D G

2005-12-31

110

Reconnection Between Open and Closed Fields in the Solar Corona  

Microsoft Academic Search

The effects of shear-driven magnetic reconnection in a 2.5D quadrupolar magnetic topology have been calculated previously (Karpen, Antiochos & DeVore 1995, ApJL, 460, L73). A quadrupolar topology in the solar corona corresponds to the interaction of two sheared closed magnetic arcades of opposite polarity. The key result of the previous work is that the reconnection proceeds by the creation of

S. K. Antiochos; J. T. Karpen; C. R. Devore

1996-01-01

111

Three-dimensional magnetic reconnection in the solar corona  

Microsoft Academic Search

In two dimensions the notions of magnetic topology and null-point bifurcations are straightforward. In addition, the nature of magnetic reconnection is fairly well understood and can be described by a new generation of fast reconnection mechanisms known as almost-uniform reconnection and nonuniform reconnection. However, in complex three-dimensional (3-D) magnetic fields, such as exist in the solar corona, these phenomena are

E. R. Priest

1997-01-01

112

Collisional damping of surface waves in the solar corona  

NASA Technical Reports Server (NTRS)

The damping of surface waves by viscosity and heat conduction is evaluated. For the solar corona, it is found that surface waves dissipate efficiently only if their periods are shorter than a few tens of seconds and only if the background magnetic field is less than about 10 Gauss. Heating of quiet coronal regions is possible if the coronal waves have short periods, but they cannot heat regions of strong magnetic field, such as coronal active region loops.

Gordon, B. E.; Hollweg, J. V.

1982-01-01

113

Observational capabilities of solar satellite "Coronas-Photon"  

NASA Astrophysics Data System (ADS)

Coronas-Photon mission is the third satellite of the Russian Coronas program on solar activity observation The main goal of the Coronas-Photon is the study of solar hard electromagnetic radiation in the wide energy range from UV up to high energy gamma-radiation sim 2000MeV Scientific payload for solar radiation observation consists of three type of instruments 1 monitors Natalya-2M Konus-RF RT-2 Penguin-M BRM Phoka Sphin-X Sokol for spectral and timing measurements of full solar disk radiation with timing in flare burst mode up to one msec Instruments Natalya-2M Konus-RF RT-2 will cover the wide energy range of hard X-rays and soft Gamma rays 15keV to 2000MeV and will together constitute the largest area detectors ever used for solar observations Detectors of gamma-ray monitors are based on structured inorganic scintillators with energy resolution sim 5 for nuclear gamma-line band to 35 for GeV-band PSD analysis is used for gamma neutron separation for solar neutron registration T 30MeV Penguin-M has capability to measure linear polarization of hard X-rays using azimuth are measured by Compton scattering asymmetry in case of polarization of an incident flux For X-ray and EUV monitors the scintillation phoswich detectors gas proportional counter CZT assembly and Filter-covered Si-diodes are used 2 Telescope-spectrometer TESIS for imaging solar spectroscopy in X-rays with angular resolution up to 1 in three spectral lines and RT-2 CZT assembly of CZT

Kotov, Yu.

114

Meteoroid ablation during entry into the solar corona  

Microsoft Academic Search

The deposition of dust material in the close vicinity of the sun has been discussed before in the context of pick up ion production near the sun and in the context of the FIP (First Ionization Potential) effect. Pick-up ions are ions that are carried with the solar wind but have distinctly different charge states and velocities than the solar

Hervé Lamy; Ingrid Mann; Joseph Lemaire

2010-01-01

115

Magnetic Nulls and Current Sheet Formation in the Solar Corona  

NASA Astrophysics Data System (ADS)

An outstanding problem in solar physics has been to understand how the solar corona can be so much hotter than the underlying photosphere. Most contemporary coronal heating models require that magnetic energy be transformed into heat through the generation of small scale current structures in the corona. This work is no exception; a simple model is proposed for the heating of low-?, low resistivity plasmas, such as the solar corona, which possess highly tangled magnetic fields, and which respond to external stresses very slowly compared to a typical Alfven crossing time. In the model, the plasma is considered to evolve ``quasi-statically,'' i.e. arbitrarily close to equilibrium at all stages in its evolution. The heating is assumed to follow from the formation of current sheets, which are sheet-like regions of very high current density. These current sheets must satisfy stringent topological requirements, however. Special attention is given to the role of magnetic nulls, or points where the magnetic field vanishes, in determining where current sheets can form in the coronal plasma and where enhanced heating can occur.

Albright, Brian; Cowley, Steven

1997-11-01

116

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

2012-06-28

117

Energy distribution of nanoflares in the quiet solar corona  

NASA Astrophysics Data System (ADS)

We present a detailed statistical analysis of flare-like events in low layer of solar corona detected with TESIS instrument onboard CORONAS-PHOTON satellite in 171 {Ĺ} during high-cadence (5 sec) time-series. The estimated thermal energies of these small events amount to 10^{23} - 10^{26} erg. According to modern classification flare-like events with such energies are usually referred to as nanoflares. The big number of registered events (above 2000) allowed us to obtain precise distributions of geometric and physical parameters of nanoflares, the most intriguing being energy distribution. Following Aschwanden et al. (2000) and other authors we approximated the calculated energy distribution with a single power law slope: N(E)dE ˜ N^{-?}dE. The power law index was derived to be ? = 2.4 ą 0.2, which is very close to the value reported by Krucker & Benz (1998): ? ? 2.3 - 2.4. The total energy input from registered events constitute about 10^4 erg \\cdot cm^{-2} \\cdot s^{-1}, which is well beyond net losses in quiet corona (3 \\cdot 10^5 erg \\cdot cm^{-2} \\cdot s^{-1}). However, the value of ? > 2 indicates that nanoflares with lower energies dominate over nanoflares with bigger energies and could contribute considerably to quiet corona heating.

Ulyanov, Artyom

2012-07-01

118

Inner Source Pickup Ions: Sputtering Of Small Dust Particles And Charge Exchange Of Solar Wind Ions  

NASA Astrophysics Data System (ADS)

The origin of inner-source pickup ions is generally attributed to the interaction of solar wind ions with dust particles in the inner heliosphere. We show that charge states and elemental abundances of weakly ionized species in the solar wind can provide valuable information on the properties of dust in the innermost solar system. Sputtering of sub-micron sized grains by solar wind and suprathermal solar ions plays an important role in shaping the grain sized distribution in the corona. The velocity distribution of inner-source ions reveals details on their production mechanisms. We investigate reasons for the apparent overabundance of neon compared to solar wind abundances in inner-source pickup ions. A plasma instrument capable of measuring charge state distributions and elemental abundances, as well as velocity distributions of weakly ionized species, combined with a dust experiment, promises exciting new results from Solar Orbiter.

Bochsler, P.; Möbius, E.; Wimmer-Schweingruber, R. F.

2007-01-01

119

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

2011-07-28

120

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

121

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

122

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

123

Measurements of Faraday Rotation through the Solar Corona at 4.6 Solar Radii  

NASA Astrophysics Data System (ADS)

Identifying and understanding (1) the coronal heating mechanism and (2) the acceleration mechanism for the high-speed solar wind are two of the most important modern problems in solar physics. Many competing models of the high-speed solar wind depend on the solar magnetic field inside heliocentric distances of 5 solar radii. We report on sensitive VLA full-polarization observations made in August, 2011, at 5.0 and 6.1 GHz (each with a bandwidth of 128 MHz) of the radio galaxy 3C228 through the solar corona at heliocentric distances of 4.6 - 5.0 solar radii. Observations at 5.0 GHz (C-band frequencies) permit measurements deeper in the corona than previous VLA observations at 1.4 and 1.7 GHz. These Faraday rotation observations provide unique information on the plasma density and magnetic field strength in this region of the corona. The measured Faraday rotation on this day was lower than our a priori expectations, but we have successfully modeled the measurement in terms of observed properties of the corona on the day of observation. Further, 3C228 provides two lines of sight (separated by 46”) that allow measurement of differential Faraday rotation. These data may provide constraints on the magnitude of coronal currents and, thus, on the role Joule heating plays in the corona. Fluctuations in the observed rotation measure may also place constraints on wave-turbulence models by constraining the magnitude of coronal Alfvén waves.

Kooi, Jason E.; Fischer, P. D.; Buffo, J. J.; Spangler, S. R.

2013-07-01

124

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

125

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

126

Quantifying Magnetic Reconnection in the Solar Corona  

Microsoft Academic Search

Magnetic reconnection is believed to play a role in many aspects of solar activity including flares, CMEs and quiet sun brightenings. The process itself is fundamentally a change field line topology resulting from some non-ideal term in the generalized Ohm's law such as collisional resistivity or electron inertia. Such non-ideal effects may or may not dissipate energy directly but do

D. W. Longcope

2005-01-01

127

Energy Requirements for Opening the Solar Corona  

Microsoft Academic Search

Eruptive solar events like flares and coronal mass ejections are thought to involve the release of energy stored in nonpotential magnetic fields. If this is the case, then the magnetic field configuration must change as the eruptive event occurs. One possible change is the opening of field lines that were originally closed a change that is observed in many coronagraph

Richard Wolfson

1993-01-01

128

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

129

Diagnosing the Prominence-Cavity Connection in the Solar Corona  

NASA Astrophysics Data System (ADS)

The energetic equilibrium of the corona is described by a balance of heating, thermal conduction, and radiative cooling. Prominences can be described by the thermal instability of coronal energy balance which leads to the formation of cool condensations. Observationally, the prominence is surrounded by a density depleted elliptical structure known as a cavity. In this dissertation, we use extreme ultraviolet remote sensing observations of the prominence-cavity system to diagnose the static and dynamic properties of these structures. The observations are compared with numerical models for the time-dependent coronal condensation process and the time-independent corona-prominence magnetic field. To diagnose the density of the cavity, we construct a three-dimensional structural model of the corona. This structural model allows us to synthesize extreme ultraviolet emission in the corona in a way that incorporates the projection effects which arise from the optically thin plasma. This forward model technique is used to constrain a radial density profile simultaneously in the cavity and the streamer. We use a ?2 minimization to find the density model which best matches a density sensitive line ratio (observed with Hinode/Extreme ultraviolet Imaging Spectrometer) and the white light scattered intensity (observed with Mauna Loa Solar Observatory MK4 coronagraph). We use extreme ultraviolet spectra and spectral images to diagnose the dynamics of the prominence and the surrounding corona. Based on the doppler shift of extreme ultraviolet coronal emission lines, we find that there are large regions of flowing plasma which appear to occur within cavities. These line of sight flows have speeds of 10 km/s-1 and projected spatial scales of 100 Mm. Using the Solar Dynamics Observatory Atmospheric Imaging Assembly (SDO/AIA) dataset, we observe dynamic emission from the prominence-cavity system. The SDO/AIA dataset observes multiple spectral bandpasses with different temperature sensitivities. Time-dependent changes in the observed emission in these bandpass images represent changes in the thermodynamic properties of the emitting plasma. We find that the coronal region surrounding the prominence exhibits larger intensity variations (over tens of hours of observations) as compared to the streamer region. This variability is particularly strong in the cool coronal emission of the 171Ĺ bandpass. We identify the source of this variability as strong brightening events that resemble concave-up loop segments and extend from the cool prominence plasma. Magnetic field lines are the basic structural building block of the corona. Energy and pressure balance in the corona occur along magnetic field lines. The large-scale extreme ultraviolet emission we observe in the corona is a conglomerate of many coronal loops projected along a line of sight. In order to calculate the plasma properties at a particular point in the corona, we use one-dimensional models for energy and pressure balance along field lines. In order to predict the extreme ultraviolet emission along a particular line of sight, we project these one-dimensional models onto the three-dimensional magnetic configuration provided by a MHD model for the coronal magnetic field. These results have allowed us to the establish the first comprehensive picture on the magnetic and energetic interaction of the prominence and the cavity. While the originally hypothesis that the cavity supplies mass to the prominence proved inaccurate, we cannot simply say that these structures are not related. Rather our findings suggest that the prominence and the cavity are distinct magnetic substructures that are complementary regions of a larger whole, specifically a magnetic flux rope. (Abstract shortened by UMI.).

Schmit, D. J.

130

The EUV Emission in Comet-Solar Corona Interactions  

NASA Technical Reports Server (NTRS)

The Atmospheric Imaging Assembly (AlA) 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 AlA 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-alpha, by the solar radiation field to create atomic Hand 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 AlA bandpasses. We will report here on their relative contribution to the emission seen in the AlA telescopes.

Bryans, Paul; Pesnell, William Dean; Schrijver, Carolus J.; Brown, John C.; Battams, Karl; Saint-Hilaire, Pasal; Liu, Wei; Hudson, Hugh S.

2011-01-01

131

Radar studies of the non-spherically symmetric solar corona  

NASA Astrophysics Data System (ADS)

Radar scans of the solar corona at 38 MHz carried out at El Campo, TX from 1961-1969 are reviewed in order to form a numerical model for the average observed cross sections with various geometries and density fluctuations. The range centroid and width of the radar beam encountering the sun are formulated, along with the projected cross section of the solar photosphere in terms of the received power. The numerical model comprises simulation of the propagation of radar signals through coronal models with differing density structures. Results are discussed for cases of scattering and no scattering. A power spectrum analysis of the signal received from the sun after transmission showed that the radar had struck the sun, although influenced by harmonics of the solar rotation frequency. The radar is concluded to have detected large scale coronal features in the centroid region only, but no definite identification of the observed coronal structures has yet been done.

Owocki, S. P.; Newkirk, G. A.; Sime, D. G.

1982-06-01

132

Current Sheet Formation in the Solar Corona---Topological Considerations  

NASA Astrophysics Data System (ADS)

An outstanding problem in solar physics has been to understand how the solar corona, with its temperature of millions of degrees, can be so much hotter than the underlying photosphere, which is typically of only a few thousand degrees. A simple model has been proposed for the heating of low-?, low resistivity plasmas, such as the solar corona, which possess highly tangled magnetic fields, and which evolve very slowly from external stresses compared to a typical Alfven crossing time. These plasmas are considered to evolve ``quasi-statically,'' i.e. arbitrarily close to equilibrium at all stages in their evolution. In the model, the heating has been assumed to result from the formation of regions of intense electrical current, or current sheets. A key ingredient in this model has been the topological restrictions imposed on current sheets, owing to the fact that the low-? property constrains current to flow only along the magnetic field lines. Assuming that the most probable sites for the formation of current sheets are closed loops of magnetic field, an estimate has been made of the statistical properties of current sheets. The special role of magnetic neutral points has been considered, and the implications for coronal heating have been discussed.

Albright, B. J.; Cowley, S. C.

1996-11-01

133

The Structure and Dynamics of the Solar Corona  

NASA Technical Reports Server (NTRS)

This report covers technical progress during the first year of the NASA Space Physics Theory contract between NASA and Science Applications International Corporation. Under this contract SAIC, the University of California, Irvine (UCI), and the Jet Propulsion Laboratory (JPL), have conducted research into theoretical modeling of active regions, the solar corona, and the inner heliosphere, using the MHD model. During the period covered by this report we have published 26 articles in the scientific literature. These publications are listed in Section 4 of this report. In the Appendix we have attached reprints of selected articles.

Mikic, Zoran

1998-01-01

134

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

2006-05-01

135

Predicting the Structure of the Solar Corona During the December 4, 2002 Total Solar Eclipse  

NASA Astrophysics Data System (ADS)

We describe the application of a three-dimensional magnetohydrodynamic (MHD) model to the prediction of the structure of the corona during the total solar eclipse that is expected to occur on 4 December 2002. The calculation uses the observed photospheric radial magnetic field as a boundary condition. This model makes it possible to determine the large-scale structure of the magnetic field in the corona, as well as the distribution of the solar wind velocity, plasma density, and temperature. We will use magnetic fields observed on the solar disk prior to eclipse day to predict what the corona will look like during the eclipse. The estimated coronal density and temperature will be used to predict the plane-of-sky polarization brightness and emission of UV radiation prior to the eclipse. The prediction will be posted on our web site (http://haven.saic.com) prior to the eclipse.

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

2002-12-01

136

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

NASA Technical Reports Server (NTRS)

An improved method for calculating the resonance absorption heating rate is discussed and the results are compared with observations in the solar corona. The primary conclusion to be drawn from these calculations is that to the level of the approximation adopted, the observations of the heating rate and nonthermal line broadening in the solar corona are consistent with heating by the resonance absorption mechanism.

Davila, Joseph M.

1986-01-01

137

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

138

Radio sounding of the solar corona during 1995 solar conjunction of the Ulysses spacecraft  

NASA Technical Reports Server (NTRS)

The Ulysses spacecraft will pass through superior solar conjunction on March 5 1995, a few days before its perihelion and passage through the ecliptic plane. Dual-frequency S/X-band ranging and Doppler observations will be conducted in support of the Ulysses Solar Corona Experiment (SCE) during a three-week interval centered on the conjunction. The occultation geometry is unique in the annals of interplanetary exploration. As viewed from Earth, the spacecraft will appear to cut diagonally through the southwest quadrant of the solar corona from the South Pole to the equator. The minimum proximate distance to the Sun of the radio ray path will be 21.6 solar radius. The entire latitude scan from pole to equator occurs for a limited range of solar offset distances (is less than 30 solar radius thus facilitating the separation of latitudinal from radial variations in the coronal density and associated parameters of interest.

Bird, M. K.; Paetzold, M.; Karl, J.; Edenhofer, P.; Asmar, S. W.

1995-01-01

139

Prediction of Dn-Resonances in the Solar Corona  

NASA Astrophysics Data System (ADS)

A new plasma wave mode has been proposed with quantized frequencies fDn = 3/?(fpefce)˝ n˝ , n = 1,2,... where fpe is the electron plasma frequency and fce is the electron gyrofrequency. These frequencies have been associated with a spectrum of emissions known as the Dn resonance stimulated by ionospheric topside sounders [Osherovich, 1987]. The foundations and observational support for this new electromagnetic mode have been summarized in the recent review by Osherovich et al. [2005] for three plasmas: the Earth's ionosphere (topside radio sounding from Alouette 2, ISIS 1 and ISIS 2 satellites), the Earth's magnetosphere (radio sounding from the IMAGE spacecraft) and in Jupiter's Io plasma torus (radio sounding from the Ulysses space probe). For these plasmas, the electron densities, magnetic fields and electron temperatures are quite different but in each of these plasmas there exists extended regions where the range of fpe/fce is roughly the same, namely 1? fpe/fce ? 8. From available observations of the solar corona and coronal loops, we conclude that the two-million degree corona is the fourth example of a magnetized plasma containing extended regions with fpe/fce in the same range. Therefore we predict the presence of Dn resonances with their distinctive ? n frequency spectrum, in the solar corona. References: Osherovich, V.A.,"Physical nature of diffuse plasma resonances in the ionosphere", J. Geophys. Res, 92, 316-320, 1987. Osherovich, V.A., R.F. Benson and J. Fainberg, "Electromagnetic bounded states and challenges of plasma spectroscopy", IEEE Transactions of Plasma Science, 33(2), 2005.

Osherovich, V. A.; Fainberg, J.; Benson, R. F.; MacDowall, R.; Reinisch, B. W.

2006-05-01

140

Self Organization in the Solar Corona and Interstellar Medium  

NASA Astrophysics Data System (ADS)

Self-organization can be defined as the process by which a physical system, in the course of its evolution, changes its spatial structure, the form of its equations of motions, or key coefficients in those equations. Paradigmatic examples are chemical reactions of the reaction-diffusion type, and biological systems. I discuss astrophysical processes where similar sorts of dynamics may be occurring. The first example is Joule heating of the solar corona. A major problem in astrophysics is the physical mechanism or mechanisms responsible for heating the solar corona to 1-2 million K. Coronal heating by turbulent current sheets is negligible if a standard expression for the resistivity of a plasma is used, but as the current sheets evolve, they develop progressively higher current densities. These high current densities can enhance the resistivity via plasma instabilities, and make Joule heating a more effective process. The second example is from the interstellar medium. The formation of massive stars leads to processes which compress the nearby interstellar medium, making star formation a more efficient process. Similarities and differences with better studied systems exhibiting self organization will be discussed.

Spangler, Steven

2009-11-01

141

3-Dimensional Density Model of the Solar Corona  

NASA Astrophysics Data System (ADS)

We present a 3-D density model of the solar corona, determined from synoptic maps of Carrington Rotations 1942-3 (22 Oct. 1998 - 18 Nov. - 15 Dec. 1998). The rotations we have chosen include the time period of the SPARTAN 201-05 flight (Nov. 1-3, 1998), which had unprecedented spatial and temporal coverage of the white light corona. These rotations are also useful because they occur at a point in the solar cycle (ascending phase) that is complex enough to exhibit interesting 3-D structure, yet not so dynamic that a meaningful density model cannot be constructed using the rotation of the sun to provide the 3-D information. Along with SPARTAN data, we consider observations made by the Mark IV instrument in the Mauna Loa Observatory, and also SOHO/LASCO and EIT observations. Our analytic model, an extension of the axisymmetric model of Guhathakurta et al (1996), allows for multiple streamers varying in both latitude and longitude, and explicitly treats nonradial streamers. Our 3-D model will be useful for testing analysis techniques for the upcoming STEREO mission. We will also compare its structure to magnetic field extrapolation models, coronal hole boundaries, and magnetic neutral lines.

Foster, D.; Gibson, S. E.; Holzer, T.; Guhathakurta, M.

2002-12-01

142

Coronagraphic observations and analyses of the ultraviolet solar corona  

NASA Technical Reports Server (NTRS)

This status report for the period 1 October 1992 to 30 September 1994 covers the final preparation and first observations with the Spartan Ultraviolet Coronal Spectrometer on Spartan 201-1, and the preparation and second flight for Spartan 201-2. Both flights were fully successful and resulted in high quality spectroscopic observations of the extended solar corona out to 3.5 solar radii from Sun-center. The primary focus of this report is the results from Spartan 201-1. There is also a brief description of the evaluation of the quick look data from the second flight. Highlights from the first flight include a discovery that the proton velocity distribution in coronal holes is complex and consists of a central core with elevated high velocity wings compared to a Gaussian shape.

Kohl, John L.

1994-01-01

143

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

144

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 Ĺ, 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

145

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

146

Radio sounding of the solar corona during 1995 solar conjunction of the ULYSSES spacecraft  

Microsoft Academic Search

The Ulysses spacecraft will pass through superior solar conjunction on March 5 1995, a few days before its perihelion and passage through the ecliptic plane. Dual-frequency S\\/X-band ranging and Doppler observations will be conducted in support of the Ulysses Solar Corona Experiment (SCE) during a three-week interval centered on the conjunction. The occultation geometry is unique in the annals of

M. K. Bird; M. Paetzold; J. Karl; P. Edenhofer; S. W. Asmar

1995-01-01

147

A New Diagnostic Technique for the Solar Corona  

NASA Technical Reports Server (NTRS)

Over the last 30-40 years spectroscopic observation of the EUV (extreme ultraviolet) line emission has proved invaluable as a diagnostic of the solar coronal plasma state. Line ratios have been used to determine electron density, electron temperature and ion flow velocity. In this paper, we present results obtained with a new measurement technique that uses spectroscopic observations of the white light corona to obtain the electron density, temperature, and flow velocity. A prototype instrument has been designed and built to obtain visible light spectra (3800-4300 A) with modest resolution. This instrument was used to obtain coronal observations during the June 2001 eclipse in Zambia. The data were corrected for sky and instrument transmission to derive the electron temperature and flow speed. Results from these measurements will be discussed.

Nelson, R.; Davila, Joseph M.; St.Cyr, O. C.; Oegerle, William (Technical Monitor)

2002-01-01

148

Turbulence Transport and Dissipation in the Lower Solar Corona  

NASA Astrophysics Data System (ADS)

We present new improvements to our three-dimensional global two-temperature model of the solar corona that includes the transition region and upper chromosphere. In our previous study, we focused on the wave-energy injection, transmission and dissipation [I.V. Sokolov et al., submitted to Ap.J. (2012)]. We have now also included the wave reflection due to large-scale plasma inhomogeneities. This reflection leads to low-frequency cascade of Alfvén waves due to small-scale nonlinearities. In closed field line regions, the dissipation is enhanced since different wave polarities (Elsässer energy densities) can meet with equal amplitude, resulting in elevated temperatures. The electron heat conduction can subsequently transport this excess of energy deposition down to the chromosphere. We discuss the theoretical framework and contrast the resulting simulated multi-wavelength EUV images with the SDO/AIA observations for Carrington rotation 2107.

van der Holst, B.; Sokolov, I.; Gombosi, T. I.

2012-12-01

149

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.

150

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

151

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

152

Slow wind and magnetic topology in the solar minimum corona in 1996-1997  

Microsoft Academic Search

This study examines the physical conditions of the outer solar corona in order to identify the regions where the slow solar wind is accelerated and to investigate the latitudinal transition from slow to fast wind during the minimum of the solar cycle. The analysis is based on observations of six streamers obtained during the years of solar minimum, 1996 and

E. Antonucci; L. Abbo; M. A. Dodero

2005-01-01

153

The Magnetic Connection between the Solar Photosphere and the Corona  

NASA Astrophysics Data System (ADS)

The solar magnetic field that extends through the chromosphere into the corona is envisioned to fan out from strong flux concentrations located within the supergranular downflow lanes. That so-called network field appears to be surrounded by a mixed-polarity magnetic field with a scale comparable to that of the granulation. We argue that for an internetwork field with a magnitude of a few tens of Mx cm-2, as suggested by both observations and models, the commonly held notion of a wineglass-shaped magnetic canopy of network flux that fully encloses weakly magnetic regions below it is fundamentally wrong. We estimate that in the presence of such a relatively strong internetwork field, as much as half of the coronal field over very quiet Sun may be rooted in that mixed-polarity internetwork field throughout the supergranules rather than in the network flux concentrations, as assumed until now. A corresponding amount of flux forms collars of closed loops around the network concentrations, connecting network flux back down onto the internetwork field over distances of several thousand kilometers. Within such a geometry, the rapid evolution of the internetwork field may substantially affect coronal heating and the acceleration of the solar wind. We discuss the potential consequences of these interacting network and internetwork fields for atmospheric heating, for wave propagation and the formation of acoustic shadows, and for the appearance of the near-surface solar outer atmosphere.

Schrijver, Carolus J.; Title, Alan M.

2003-11-01

154

A New Approach to Modeling the Solar Corona and the Solar Wind  

NASA Astrophysics Data System (ADS)

In spite of many recent developments in observations and models of the solar corona, a good description of the global coronal and solar wind temperatures and heating still eludes us. Here we attempt to make some progress on that problem by applying a previously developed simplified 2D coronal magnetohydrodynamic model to a unique synthesis of remote sensing coronal observations from SOHO and Spartan 201 and in-situ data from Ulysses during the quiscient phase of solar cycle 23 (1995-1997) which also included the Whole Sun Month (August/September, 1996) study period. This to our knowledge is the first model that provides an empirical heating profile of the corona and interplanetary medium, as a function of latitude and radial distance.

Guhathakurta, M.; Sittler, E.

2003-04-01

155

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

156

High frequency Faraday rotation observations of the solar corona  

NASA Astrophysics Data System (ADS)

The million degree solar corona generates the solar wind that in turn controls the Earth's "space weather". The solar coronal magnetic field within 0.25AU (60 solar radii) plays a critical role in the acceleration but is largely "invisible", and can presently only be measured by the Faraday rotation of high frequency electromagnetic radiation. Faraday rotation is the observed rotation in the plane of polarization of an EM wave as it traverses a magnetized medium. The amount of observed Faraday rotation is the integration along the propagation direction of the product of the component of the magnetic field parallel to the propagation vector and the electron density. Faraday rotation is clearly useful for measuring the solar coronal magnetic field. As a remote observation, Faraday rotation measurements require careful consideration of the medium in the analysis. This thesis details the theory of Faraday rotation, previous experiments observing Faraday rotation using the carrier signal from a spacecraft in superior conjunction, the equipment used for the Cassini Faraday rotation observations, the signal analysis and steps taken to acquire a Faraday rotation observation from radio frequency data, the model used to fit the observations, all ancillary data required for these steps, and all the code created for this purpose. The data and code are provided in the attached DVD media. All previous Faraday rotation experiments observed coronal mass ejections (CMEs) producing either 'W' or sigmoid features. These observations are reproduced herein using a Taylor-state flux-rope model crossing the line of sight at different sizes, twist, and orientations, showing that Faraday rotation can be used to measure the magnetic field of CMEs. Using a forward model to fit Faraday rotation and columnar electron density observations, a first order investigation into force balance in the solar corona was conducted. From these fits, the gradients in the magnetic and thermal pressure and the gravitational force per volume were calculated. For the solar wind to escape the gravitational force of the Sun, the magnetic and thermal pressure gradients must dominate. We show from the fits on 2002 June 20 that small adjustments to the PFSS model can provide the necessary magnetic field strengths to supply the needed pressure for solar wind flow; however, the fits from June 21st cannot. The closest approach of the June 21st measurements were all below the source surface of 2.5 solar radii indicating a problem in the use of the PFSS model to determine the structure of the coronal magnetic field below the source surface. Large amplitude 4 minute period Alfven waves have been observed in Helios and Cassini Faraday rotation observations. Using a simple open-ended box model through which magnetohydrodynamic waves can propagate, it is demonstrated that the combination of Faraday rotation and columnar electron density observations can distinguish Alfven waves due to their lack of fluid perturbation. It is also shown that the 2nd harmonic in the Faraday rotation observations is the result of the electron density fluctuation in the magnetosonic (fast and slow) modes. This demonstrates that previous Helios observations producing the 2nd harmonic were MHD magnetosonic waves. Cassini's observation of an Alfven wave is modeled to determine the amplitude of the magnetic perturbation. If we assume that these waves are continuously generated in all directions then the wave energy flux is 1.6 × 10 19 W; for comparison, the kinetic energy flux of the solar wind at 1AU is 1.7 × 10 20 W. With better technology and the maturity of 3D tomography, the solar radioscience community is experiencing a resurgence of interest in the phenomenon of Faraday rotation. This thesis demonstrates that Faraday rotation can be used to determine the magnetic structure of CMEs, the solar wind, and MHD waves propagating from the solar corona. These observations enable us to predict the geoeffectiveness of a CME, study force balance in the solar wind, and measure magnetic ener

Jensen, Elizabeth Annah

157

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

158

Diagnostics of the Solar Corona from Comparison between Faraday Rotation Measurements and Magnetohydrodynamic Simulations  

NASA Astrophysics Data System (ADS)

Polarized natural radio sources passing behind the Sun experience Faraday rotation as a consequence of the electron density and magnetic field strength in coronal plasma. Since Faraday rotation is proportional to the product of the density and the component of the magnetic field along the line of sight of the observer, a model is required to interpret the observations and infer coronal structures. Faraday rotation observations have been compared with relatively ad hoc models of the corona. Here for the first time we compare these observations with magnetohydrodynamic (MHD) models of the solar corona driven by measurements of the photospheric magnetic field. We use observations made with the NRAO Very Large Array of 34 polarized radio sources occulted by the solar corona between 5 and 14 solar radii. The measurements were made during 1997 May, and 2005 March and April. We compare the observed Faraday rotation values with values extracted from MHD steady-state simulations of the solar corona. We find that (1) using a synoptic map of the solar magnetic field just one Carrington rotation off produces poorer agreements, meaning that the outer corona changes in the course of one month, even in solar minimum; (2) global MHD models of the solar corona driven by photospheric magnetic field measurements are generally able to reproduce Faraday rotation observations; and (3) some sources show significant disagreement between the model and the observations, which appears to be a function of the proximity of the line of sight to the large-scale heliospheric current sheet.

Le Chat, G.; Kasper, J. C.; Cohen, O.; Spangler, S. R.

2014-07-01

159

Diagnostics of the Solar corona from Comparison Between Faraday Rotation Measurements and MHD Simulations  

NASA Astrophysics Data System (ADS)

Faraday rotation observations of natural radio sources allow remote diagnostics of the density and magnetic field of the solar corona. We use linear polarization observations made with the NRAO Very Large Array at frequencies of 1465 and 1665 MHz of 33 polarized radio sources occulted by the solar corona within 5 to 14 solar radii. The measurements were made during May 1997 (Mancuso and Spangler, 2000), March 2005 and april 2005 (Ingleby et al., 2005), corresponding to Carrington rotation number 1922, 1923, 2027 and 2028. We compare the observed Faraday rotation values with values extracted from MHD steady-state simulations of the solar corona using the BATS-R-US model. The simulations are driven by magnetogram data taken at the same time as the observed data. We present the agreement between the model and the Faraday rotation measurements, and we discuss the contraints imposed on models of the quiet corona and CMEs by these observations.

LE CHAT, G.; Kasper, J. C.; Cohen, O.; Spangler, S.

2013-05-01

160

Three-Dimensional Magnetohydrodynamic Simulation of a Global Solar Corona Using a Temperature Distribution Map Obtained from SOHO EIT Measurements  

Microsoft Academic Search

The temperature at the base of the solar corona is one of the important factors in determining the solar coronal structure. In this Letter, we performed the time-dependent magnetohydrodynamic (MHD) simulation for the solar corona utilizing the temperature map derived from the multiwavelength observation by the EUV Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO) and the magnetic

Keiji Hayashi; Elena Benevolenskaya; Todd Hoeksema; Yang Liu; Xue Pu Zhao

2006-01-01

161

Three-Dimensional Magnetohydrodynamic Simulation of a Global Solar Corona Using a Temperature Distribution Map Obtained from SOHO EIT Measurements  

Microsoft Academic Search

The temperature at the base of the solar corona is one of the important factors in determining the solar coronal structure. In this Letter, we performed the time-dependent magnetohydrodynamic (MHD) simulation for the solar corona utilizing the temperature map derived from the multiwavelength observation by the EUV Imaging Telescope (EIT) on the Solar and Heliospheric Observatory(SOHO) and the magnetic field

Keiji Hayashi; Elena Benevolenskaya; Todd Hoeksema; Yang Liu; Xue Pu Zhao

2006-01-01

162

Signature of open magnetic field lines in the extended solar corona and of solar wind acceleration  

NASA Technical Reports Server (NTRS)

The observations carried out with the ultraviolet coronagraph spectrometer onboard the Solar and Heliospheric Observatory (SOHO) are discussed. The purpose of the observations was to determine the line of sight and radial velocity fields in coronal regions with different magnetic topology. The results showed that the regions where the high speed solar wind flows along open field lines are characterized by O VI 1032 and HI Lyman alpha 1216 lines. The global coronal maps of the line of sight velocity were reconstructed. The corona height, where the solar wind reaches 100 km/s, was determined.

Antonucci, E.; Giordano, S.; Benna, C.; Kohl, J. L.; Noci, G.; Michels, J.; Fineschi, S.

1997-01-01

163

Solar Corona and plasma effects on Radio Frequency waves  

NASA Astrophysics Data System (ADS)

Solar corona (plasma) effects on radio signal waves for three different frequency bands S (2.3 GHz), X (8.4 GHz), and Ka (32 GHz), currently used to track probes in the solar system, have been computed using different models of the total electron content (TEC) along the propagation path between the Earth and Mars. The Earth-Mars-Sun configuration has been obtained from the planetary ephemerides DE421 (using SPICE kernels) for the period from September 2004 to September 2006. This configuration is expressed as a function of the Sun-Earth-Probe (SEP) angles (the probe being in close orbit to Mars). We used the TEC values provided by the different models proposed in the literature in order to estimate the TEC along the propagation path (STEC, for Slant TEC). From these model-dependent STEC estimates, the time delay on the wave propagation as well as the associated frequency shift with a 10 seconds sampling time have been obtained for each of the three frequency bands. For the X-band mostly used in radio science, we have obtained estimates differing by up to several orders of magnitude due to the different STEC values derived from different models of TEC. For example, if the propagation path passes near the Sun such that SEP angle is 1.55° the STEC is ranging from 4.6x1020 electron/m2 to 6.07x1016 electron/m2, which corresponds to a time delay range between 0.87 ?s and 1.15x10-4 ?s, respectively. For SEP angles between 2° and 8°, the range of the different time delay values reduces to 2.8x10-1 ?s and becomes as small as 1.6x10-2 ?s for SEP angles larger than 8° (1x10-2 ?s is about the order of magnitude of the radioscience instrument precision). These results show that the correction of the solar corona effect on radio frequency waves can be reliably done on usual X-band tracking data of spacecraft for SEP angles >12°, but should be use with caution for lower SEP angles, especially lower than 2°.

Nkono, C.; Rosenblatt, P.; Dehant, V. M.

2009-12-01

164

Destruction of Sun-Grazing Comet C-2011 N3 (SOHO) Within the Low Solar Corona  

NASA Technical Reports Server (NTRS)

Observations of comets in Sun-grazing orbits that survive solar insolation long enough to penetrate into the Suns inner corona provide information on the solar atmosphere and magnetic field as well as on the makeup of the comet. On 6 July 2011, the Solar Dynamics Observatory (SDO) observed the demise of comet C2011 N3 (SOHO) within the low solar corona in five wavelength bands in the extreme ultraviolet (EUV). The comet penetrated to within 0.146 solarradius (100,000 kilometers) of the solar surface before its EUV signal disappeared.

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

2012-01-01

165

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

166

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

1978-01-01

167

Ultra-fine-Scale Filamentary Structures in the Outer Corona and the Solar Magnetic Field  

Microsoft Academic Search

Filamentary structures following magnetic field lines pervade the Sun's atmosphere and offer us insight into the solar magnetic field. Radio propagation measurements have shown that the smallest filamentary structures in the solar corona are more than 2 orders of magnitude finer than those seen in solar imaging. Here we use radio Doppler measurements to characterize their transverse density gradient and

Richard Woo

2006-01-01

168

Spectral Line Non-thermal Broadening and MHD Waves in the Solar Corona  

NASA Astrophysics Data System (ADS)

The rapid temperature rise from the solar surface (6000 K) up to the corona (1 MK) and acceleration of solar wind particles still are unresolved problems in solar physics. The energy source for the coronal heating and the wind acceleration probably lies in the solar photosphere. MHD waves are believed to carry the photospheric energy into the corona. Recent observations from space based telescopes made significant progress in understanding the process of MHD wave propagation from the solar surface towards the corona. Some of MHD wave modes have been observed through intensity variations and Doppler shift oscillations in spectral lines. Another powerful mechanism is to detect the waves through the non-thermal broadening of spectral lines. The lecture gives the basic points of wave induced effects in solar coronal spectral lines and recent progress in wave observations through spectral line non-thermal broadening.

Zaqarashvili, T. V.

2009-04-01

169

The Corona of the Young Solar Analog EK Draconis  

NASA Technical Reports Server (NTRS)

First coronal microwave and new soft X-ray observations of the very active, near-Zero-Age Main-Sequence (ZAMS) dGOe star EK Dra = HD 129333 show that this analog of the young Sun is more luminous in both emissions than most single M-dwarf flare stars. Variations in the 8.4 GHz flux include modulation with the optically determined rotation period of 2.7 days. This result points to a non-uniform filling of the corona with energetic electrons due to an incomplete coverage of the surface with active regions and a source volume that is not concentric with the star. The radio luminosity varying between log L(sub R) = 13.6 and 14.6 (L(sub R) in erg/s/Hz) shows evidence for unpolarized gyrosynchrotron flares, while strongly polarized flares were absent during the observations. This star is the first young, truly solar-like main sequence G star discovered in microwaves. Having just arrived on the main sequence, it conclusively proves that young, solar-like G stars can maintain very high levels of radio emission after their T Tau phase. The X-ray observations were obtained from the ROSAT All-Sky Survey (RASS). The average X-ray luminosity amounts to log L(sub x) = 29.9 (L(sub x) in erg/s). A Raymond-Smith type plasma model fit yields two plasma components at temperatures of 1.9 and 10 MK, with volume emission measures of 1.2 and 2.5 x 10 (exp 52)/cu cm, respectively. The X-ray light curve is significantly variable, with the photon count rate from the cooler plasma being strongly modulated by the rotation period; the emission from the hotter plasma is only weakly variable. Modeling of the source distribution in the stellar corona yields electron densities of the order of 4 x 10(exp 10)/cu cm or higher for the cool plasma component. It indicates that a considerable portion of EK Dra's high X-ray luminosity is due to high-density plasma rather than large emission volume. Parameters for an X-ray flare indicate an electron density of 1.75 x 10(exp 11)/cu cm and a source height of (1-2) x 10(exp 10) cm, compatible with a few times the scale height of the cooler plasma component.

Gudel, M.; Schmitt, J. H. M. M.; Benz, A. O.; Elias, N. M., II

1995-01-01

170

Inbound Waves in the Solar Corona: A Direct Indicator of Alfvén Surface Location  

NASA Astrophysics Data System (ADS)

The tenuous supersonic solar wind that streams from the top of the corona passes through a natural boundary—the Alfvén surface—that marks the causal disconnection of individual packets of plasma and magnetic flux from the Sun itself. The Alfvén surface is the locus where the radial motion of the accelerating solar wind passes the radial Alfvén speed, and therefore any displacement of material cannot carry information back down into the corona. It is thus the natural outer boundary of the solar corona and the inner boundary of interplanetary space. Using a new and unique motion analysis to separate inbound and outbound motions in synoptic visible-light image sequences from the COR2 coronagraph on board the STEREO-A spacecraft, we have identified inbound wave motion in the outer corona beyond 6 solar radii for the first time and used it to determine that the Alfvén surface is at least 12 solar radii from the Sun over the polar coronal holes and 15 solar radii in the streamer belt, well beyond the distance planned for NASA's upcoming Solar Probe Plus mission. To our knowledge, this is the first measurement of inbound waves in the outer solar corona and the first direct measurement of lower bounds for the Alfvén surface.

DeForest, C. E.; Howard, T. A.; McComas, D. J.

2014-06-01

171

Dust removal from solar cells  

NASA Technical Reports Server (NTRS)

A solar panel cleaning device includes a solar panel having a plurality of photovoltaic cells arranged in rows and embedded in the solar panel with space between the rows. A transparent dielectric overlay is affixed to the solar panel. A plurality of electrode pairs each of which includes an upper and a lower electrode are arranged on opposite sides of the transparent dielectric and are affixed thereto. The electrodes may be transparent electrodes which may be arranged without concern for blocking sunlight to the solar panel. The solar panel may be a dielectric and its dielectric properties may be continuously and spatially variable. Alternatively the dielectric used may have dielectric segments which produce different electrical field and which affects the wind "generated."

Ashpis, David E. (Inventor)

2011-01-01

172

Empirically Constrained Multidimensional MHD Model for the Solar Corona and Solar Wind  

NASA Astrophysics Data System (ADS)

We are developing a time stationary self-consistent 2D MHD model of the solar corona and solar wind that explicitly solves the energy equation, using a semi-empirical 2D MHD model of the corona to provide an empirically determined effective heat flux qeff (i.e., the term effective means the possible presence of wave contributions) for the energy equation and effective pressure Peff for the momentum equation. Preliminary results indicated that in order to achieve high speed winds over the poles we not only needed to use qeff in the energy equation, but also needed to include the empirically determined effective pressure Peff as a constraint in the momentum equation, which means that momentum addition by waves above 2 RS are required to produce high speed winds. A solution which only included qeff showed high acceleration over the poles below 2 RS, but then drooped above that radial distance indicating we needed momentum addition above that height to get high speed flows over the poles. We will show new results which include the added constraint of Peff in the momentum equation. This method will allows us to estimate the momentum addition term due to waves as a function of height and latitude within the corona. The estimates of Peff and qeff come from the semi-empirical 2D MHD model of the solar corona by Sittler and Guhathakurta (1999, 2002) which is based on Mk-III, Skylab and Ulysses observations. For future model development we plan to use SOHO LASCO, CDS, EIT, UVCS, Spartan 201-05 and Ulysses data as constraints for our model calculations. The model by Sittler and Guhathakurta (1999, 2002) is not a self-consistent calculation. The calculations presented here are a continuing effort to provide a self-consistent calculation based on empirical constraints.

Sittler, E. C.; Ofman, L.; Gibson, S.; Guthathakurta, M.; Skoug, R.; Fludra, A.; Davila, J.; Holzer, T.

2002-12-01

173

Predicting the Structure of the Solar Corona During the December 4, 2002 Total Solar Eclipse  

NASA Technical Reports Server (NTRS)

The solar magnetic field plays a key role in determining coronal. The principal input to MHD models is the observed solar magnetic field. 3D MHD models can be used to compare with eclipse and coronograph images, SOHO images (LOSCO, EIT), Ulysses and WIND spacecraft data, and interplanetary scintillation (IPS) measurements. MHD computations can tell us about the structure of the corona. Eclipses can help us to verify the accuracy of the models. 4 December, 2002 total eclipce: visible in the southern hemisphere (South Atlantic, southern Africa, Indian Ocean, and Australia). Total in center Angola is at 06:00 UT.

Mikic, Zoran; Linker, Jon A.; Riley, Pete; Lionello, Roberto

2003-01-01

174

CORHEL: A Modeling Suite for Describing the Solar Corona and Inner Heliosphere  

NASA Astrophysics Data System (ADS)

The Sun and its activity is the ultimate driver of space weather at Earth. The ambient solar corona and solar wind plays a key role in transmitting solar activity to the Earth's space environment. Coronal mass ejections (CMEs) propagate and interact with the ambient solar wind; their geoeffectiveness is affected by this interaction. The connection of the ambient interplanetary magnetic field to CME-related shocks and impulsive solar flares determines where solar energetic particles propagate. The partitioning of the ambient solar wind into fast and slow streams is responsible for recurrent geomagnetic activity. CORHEL - for Corona-Heliosphere - is a coupled set of models and tools for quantitatively modeling the ambient solar corona and solar wind in various approximations. It includes two coronal models (the MHD model MAS, and a new implementation of the empirical WSA model) and two heliospheric models (the MHD model Enlil and a heliospheric version of MAS). The primary data input to CORHEL consists of maps of the Sun's photospheric magnetic field derived from magnetograms; data from 6 different observatories can be downloaded and processed. CORHEL solutions are available to the community at the CCMC (http://ccmc.gsfc.nasa.gov) and the Predictive Science web sites (http://www.predsci.com). In this talk we describe progress in CORHEL development and the challenges that remain for transitioning modeling of the ambient corona and solar wind to an operational environment. CORHEL is supported by CISM and the LWS Strategic Capabilities Program (NASA, NSF, and AFOSR).

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

2009-12-01

175

VLBI Observations of Turbulence in the Solar Corona  

NASA Astrophysics Data System (ADS)

We report on very long baseline interferometer (VLBI) observations of 15 extra-galactic radio sources viewed through the inner solar wind at heliocentric distances from 6 to 38 solar radii. The observations were carried out on September 10, 2002 with the Very Long Baseline Array (VLBA) of the National Radio Astronomy Observatory at frequencies of 2.3, 5.0, and 8.4 GHz. The analysis technique utilizes interferometer phase fluctuations caused by turbulent density irregularities along the line of sight. The power spectrum of the phase fluctuations contains information on the level of the density fluctuations and the speed at which the irregularities move relative to the antennas. The technique is most sensitive to irregularities with sizes of order the interferometer baseline length. The current observations differ from previous ones in three ways. (1) The observed "constellation" of radio sources provides nearly simultaneous measurements over a much larger range of both heliographic latitude and heliocentric distance than previous VLBI observations. (2) LASCO images of the Sun's corona are available from the period of observation. These white-light images document the coronal density structure and dynamics at the time of the observations and aid in understanding the results of the power spectra analysis. Specific information of interest includes the position of streamers with respect to observed sources and the documentation of flares or coronal mass ejections which may have occurred during the observing session. (3) Contemporaneous coronal models have been created (through collaboration with Pizzo & Odstrcil) which provide three dimensional bulk density and velocity characteristics of the environment traversed by the lines of sight. Such knowledge allows for improvements to the simple, though appropriate, approximations used in previous analyses. This research was supported by grants ATM99-86887 and ATM03-11825 from the National Science Foundation.

Kortenkamp, P. S.; Spangler, S. R.; Mutel, R. L.

2004-05-01

176

Comparing Eclipse Observations of the August 1, 2008 Solar Corona with an MHD Model Prediction  

NASA Astrophysics Data System (ADS)

Total solar eclipses offer a unique opportunity to study the white light and emission coronae at high resolution. Newly developed image-processing techniques allow us to combine many individual coronal images with different exposures to produce coronal images during an eclipse that resemble those taken with radially graded filters, but with a higher quality. In a separate effort, 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 August 1, 2008 total solar eclipse. The eclipse was observed from Altaj village, Mongolia, under perfect seeing conditions. The white-light corona was observed with 6 telescopes, with a focal lenses ranging from 200 mm to 1250 mm. The emission corona at 530.3 nm (Fe XIV) was imaged thorough a narrow passband filter with a transmission width of 0.03 nm. To separate out the 530.3 nm corona, the scattered background was substracted from a white-light coronal image taken at 529.1 nm, taken simultaneously with another narrow passband filter with a transmission width of 0.03 nm. This was the first time that the green emission corona was observed during an eclipse. We will compare the observed images with features from the predicted MHD model, including magnetic field line traces and simulated polarization brightness images. Research partially supported by NASA and NSF.

Rusin, V.; Mikic, Z.; Aniol, P.; Druckmuller, M.; Saniga, M.; Linker, J. A.; Lionello, R.; Riley, P.; Titov, V.

2008-12-01

177

Solar Wind Magnetic Field Bending of Jovian Dust Trajectories  

Microsoft Academic Search

From September 1991 to October 1992, the cosmic dust detector on the Ulysses spacecraft recorded 11 short bursts, or streams, of dust. These dust grains emanated from the jovian system, and their trajectories were strongly affected by solar wind magnetic field forces. Analyses of the on-board measurements of these fields, and of stream approach directions, show that stream-associated dust grain

H. A. Zook; E. Grun; M. Baguhl; D. P. Hamilton; G. Linkert; J.-C. Liou; R. Forsyth; J. L. Phillips

1996-01-01

178

Shock Formation Height in the Solar Corona Estimated from SDO and Radio Observations  

NASA Technical Reports Server (NTRS)

Wave transients at EUV wavelengths and type II radio bursts are good indicators of shock formation in the solar corona. We use recent EUV wave observations from SDO and combine them with metric type II radio data to estimate the height in the corona where the shocks form. We compare the results with those obtained from other methods. We also estimate the shock formation heights independently using white-light observations of coronal mass ejections that ultimately drive the shocks.

Gopalswamy, N.; Nitta, N.

2011-01-01

179

3D MHD Simulation of CME Propagation from Solar Corona to 1 AU  

Microsoft Academic Search

We present a three-dimensional (3D) numerical ideal magnetohydrodynamics (MHD) model describing the time-dependent expulsion of a CME from the solar corona propagating all the way to 1 A.U.. The simulations are performed using the BATS-R-US (Block Adaptive Tree Solarwind Roe Upwind Scheme) code. We begin by developing a global steady-state model of the corona that possesses high-latitude coronal holes and

W. B. Manchester; I. Roussev; M. Opher; T. Gombosi; D. Dezeeuw; G. Toth; I. Sokolov; K. Powell

2002-01-01

180

CORONAS-F Project: The Study of Solar Activity and Its Effects on the Earth  

NASA Astrophysics Data System (ADS)

The CORONAS-F space mission is characterized in general terms as part of the Russian CORONAS space project aimed at the study of solar activity and solar-terrestrial coupling. The composition of the scientific payload and the basic characteristic of the instruments are described. Some observations carried out on board the CORONAS-F satellite are discussed, including global oscillations of the Sun, active regions, flares and mass ejections, high-energy particles in near-Earth space, etc. The results of investigation of the Earth's upper atmosphere are provided as obtained from the analysis of the absorption of solar hard X-rays at shadow entry and shadow exit of the satellite, as well as the night glow events caused by solar radiation fluxes, galactic cosmic rays, and precipitations of charged particles from the magnetosphere.

Kuznetsov, V. D.

181

Testing a Two-temperature Model of the Solar Corona with Empirically-derived Plasma parameters  

NASA Astrophysics Data System (ADS)

We compare the plasma parameters predicted from the Michigan two-temperature chromosphere-corona model to those parameters obtained from the analyses of UVCS and LASCO data. The empirical data are organized as Carrington rotation maps for the electron densities, proton kinetic temperatures, and outflow velocities. This data format makes it convenient for understanding the differences between the modeled and observed latitudinal variations in the plasma parameters. In addition, we discuss the model performance for characterizing streamers and coronal holes at different phases in the solar activity cycle. These tests are useful for investigating how well coronal and solar wind models simulate the underlying physical processes that operate in the solar corona.

Strachan, L.; Panasyuk, A.; Lamy, P. L.; van der Holst, B.; Oran, R.; Frazin, R. A.; Manchester, W. B.

2012-12-01

182

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

183

Radar Studies of the Solar Corona: A Review of Experiments Using HF wavelengths.  

National Technical Information Service (NTIS)

The use of high frequency (9 to 40 MHz), high power radars to study the solar corona has a remarkable history. Solar radar experiments were proposed and started at the beginning of the modern era of space physics research. Early in the 1960's the El Campo...

P. Rodriguez

1999-01-01

184

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

185

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

186

Study of the solar corona using radio and space observations  

NASA Technical Reports Server (NTRS)

The physics of coronal transients, the characteristics of radiation and accelerated particles at the time of flares, and the density/temperature structure of the transition region and corona and the coronal magnetic field are investigated.

Dulk, G. A.

1984-01-01

187

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

188

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

189

Field Line Random Walk in Reduced MHD models of the Solar Corona  

NASA Astrophysics Data System (ADS)

The dynamics of low ? regions of the Solar Corona threaded by a strong magnetic field is well described by Reduced MHD, a quasi two-dimensional limit of MHD. We perform Reduced MHD simulations of both open and closed regions of the solar corona in Cartesian approximation where photospheric motions are imposed at the boundaries. Generally speaking MHD turbulence develops in both cases contributing to the heating of the Corona and the acceleration of the solar wind. We use these simulations to investigate the dynamics of magnetic field-lines, the influence of field-aligned current sheets where magnetic reconnection occurs on field-line connectivity and the stochastic transition between closed and open field-lines. In particular the Reduced MHD theoretical model for Field Line Random Walk (Ruffolo & Matthaeus, in preparation) will be tested.

Rappazzo, A. F.; Matthaeus, W. H.; Ruffolo, D. J.; Oughton, S.

2011-12-01

190

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

2013-07-01

191

Ultra-fine-scale filamentary structures in the Outer Corona and the Solar Magnetic Field  

NASA Technical Reports Server (NTRS)

Filamentary structures following magnetic field lines pervade the Sun's atmosphere and offer us insight into the solar magnetic field. Radio propagation measurements have shown that the smallest filamentary structures in the solar corona are more than 2 orders of magnitude finer than those seen in solar imaging. Here we use radio Doppler measurements to characterize their transverse density gradient and determine their finest scale in the outer corona at 20-30 R(circled dot operator), where open magnetic fields prevail. Filamentary structures overly active regions have the steepest gradient and finest scale, while those overlying coronal holes have the shallowest gradient and least finest scale. Their organization by the underlying corona implies that these subresolution structures extend radially from the entire Sun, confirming that they trace the coronal magnetic field responsible for the radial expansion of the solar wind. That they are rooted all over the Sun elucidates the association between the magnetic field of the photosphere and that of the corona, as revealed by the similarity between the power spectra of the photospheric field and the coronal density fluctuations. This association along with the persistence of filamentary structures far from the Sun demonstrate that subresolution magnetic fields must play an important role not only in magnetic coupling of the photosphere and corona, but also in coronal heating and solar wind acceleration through the process of small-scale magnetic reconnection. They also explain why current widely used theoretical models that extrapolate photospheric magnetic fields into the corona do not predict the correct source of the solar wind.

Woo, Richard

2006-01-01

192

The Structure and Dynamics of the Solar Corona and Inner Heliosphere  

NASA Technical Reports Server (NTRS)

This report covers technical progress during the fourth quarter of the second year of NASA Sun-Earth Connections Theory Program (SECTP) contract "The Structure and Dynamics of the Solar Corona and Inner Heliosphere," NAS5-99188, between NASA and Science Applications International Corporation (SAIC), and covers the period May 16, 2001 to August 15, 2001. Under this contract SAIC and the University of California, Irvine (UCI) have conducted research into theoretical modeling of active regions, the solar corona, and the inner heliosphere, using the MHD (magnetohydrodynamic) model.

Mikic, Zoran; Grebowsky, J. (Technical Monitor)

2002-01-01

193

Gyroscopic waves in the base of the solar corona: A model and possible observational manifestations  

NASA Technical Reports Server (NTRS)

A linear model for gyroscopic waves in the base of the solar corona is proposed. The purpose was to point out possible observational manifestations of the phenomenon. According to the model, these waves move slowly around the sun along heliolatitude circles. The fact that the red line corona is fainter on the solar side facing the apex and north-south and east-west asymmetries of the red coronal emission line could be interpreted as a possible observational manifestation of the gyroscopic wave phenomenon in the coronal base.

Pisanko, Y. V.; Tritakis, V. P.; Paliatsos, A. G.

1997-01-01

194

Theoretical model of the solar corona during sunspot minimum. I - Quasi-static approximation  

NASA Technical Reports Server (NTRS)

The model of the solar corona (1.5 to 5 solar radius) during sunspot minimum is constructed. It is suggested that pole-equator asymmetry is caused by the interaction between global azimuthal electric currents in the corona and potential magnetic fields originated below. The asymmetry between the two hemispheres, which can be due to the magnetic quadrupole, is considered in detail. It is shown that an additional quadrupole term in the magnetic field representation affects the position of polar coronal hole boundaries differently in the two hemispheres. As a result, the outflow from the two polar regions is found to be different.

Osherovich, V. A.; Tzur, I.; Gliner, E. B.

1984-01-01

195

Statistical seismology of transverse waves in the solar corona  

NASA Astrophysics Data System (ADS)

Context. Observations show that transverse oscillations commonly occur in solar coronal loops. The rapid damping of these waves has been attributed to resonant absorption. The oscillation characteristics carries information of the structuring of the corona. However, self-consistent seismological methods that extract information from individual oscillations are limited because there are fewer observables than unknown parameters in the model, and the problem is underdetermined. Furthermore, it has been shown that one-to-one comparisons of the observed scaling of period and damping times with wave damping theories are misleading. Aims: We aim to investigate whether seismological information can be gained from the observed scaling laws in a statistical sense. Methods: A statistical approach is used whereby scaling laws are produced by forward modelling using distributions of values for key loop cross-sectional structuring parameters. We study two types of observations: 1) transverse loops oscillations as seen mainly with TRACE and SDO and 2) running transverse waves seen with the Coronal Multichannel Polarimeter (CoMP). Results: We demonstrate that the observed period-damping time scaling law does provide information about the physical damping mechanism, if observations are collected from as wide range of periods as possible and a comparison with theory is performed in a statistical sense. The distribution of the ratio of damping time over period, i.e. the quality factor, has been derived analytically and fitted to the observations. A minimum value for the quality factor of 0.65 has been found. From this, a constraint linking the ranges of possible values for the density contrast and inhomogeneity layer thickness is obtained for transverse loop oscillations. If the layer thickness is not constrained, then the density contrast is at most equal to 3. For transverse waves seen by CoMP, it is found that the ratio of maximum to minimum values for these two parameters has to be less than 2.06; i.e., the sampled values for the layer thickness and Alfvén travel time come from a relatively narrow distribution. Conclusions: Now that more and more transverse loop oscillations have been analysed, a statistical approach to coronal seismology becomes possible. Using the observed data cloud, we have found restrictions to the loop's density contrast and inhomogeneity layer thickness. Surprisingly, for running waves, narrow distributions for loop parameters have been found.

Verwichte, E.; Van Doorsselaere, T.; White, R. S.; Antolin, P.

2013-04-01

196

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

2010-07-01

197

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

198

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

199

Energy-Dependent Ionization States of Shock-Accelerated Particles in the Solar Corona  

NASA Technical Reports Server (NTRS)

We examine the range of possible energy dependence of the ionization states of ions that are shock-accelerated from the ambient plasma of the solar corona. If acceleration begins in a region of moderate density, sufficiently low in the corona, ions above about 0.1 MeV/amu approach an equilibrium charge state that depends primarily upon their speed and only weakly on the plasma temperature. We suggest that the large variations of the charge states with energy for ions such as Si and Fe observed in the 1997 November 6 event are consistent with stripping in moderately dense coronal. plasma during shock acceleration. In the large solar-particle events studied previously, acceleration occurs sufficiently high in the corona that even Fe ions up to 600 MeV/amu are not stripped of electrons.

Reames, Donald V.; Ng, C. K.; Tylka, A. J.

2000-01-01

200

Predicting the Structure of the Solar Corona for the Total Solar Eclipse of March 29,2006  

NASA Technical Reports Server (NTRS)

We describe the use of a three-dimensional MHD model to predict the s tructure of the corona prior to the total solar eclipse of March 29, 2006. The calculation uses the observed photospheric radial magnetic f ield as a boundary condition. We use a new version of our model that has an improved description of energy transport in the corona. The mo del allows us to predict the emission of X-ray and EUV radiation in t he corona. We compare the predicted polarization brightness in the co rona with four observations of the eclipse from Greece, Egypt, and Li bya, and we demonstrate that the model accurately predicts the largescale structure of the corona. We also compare X-ray emission from the model with GOES/SXI images.

Mikic, Z.; Linker, J. a.; Lionello, R.; Riley, P.; TItov, V.

2007-01-01

201

Recent Origin of the Solar System Dust Bands  

Microsoft Academic Search

Infrared Astronomical Satellite (IRAS) observations in 1983 revealed the existence of several solar system dust bands. These dust bands are believed to be debris produced by recent disruption events among main-belt asteroids, particularly because dust particles have short dynamical and collisional lifetimes. Using young asteroid families as tracers of recent disruptions in the main belt, we linked the most prominent

David Nesvorný; William F. Bottke; Harold F. Levison; Luke Dones

2003-01-01

202

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

203

Mineralogical similarities between interstellar dust and primitive solar system material  

Microsoft Academic Search

The mineralogy of the interstellar dust is compared with that of primitive material in the solar system. The available data indicate that the silicates in the dust resemble the silicate composition of carbonaceous chondrites, comets, and interplanetary dust. There is also some evidence that interstellar grains contain magnetite and carbonaceous compounds similar to the circumsolar material. Thus, the mineralogy appears

R. F. Knacke

1978-01-01

204

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

Microsoft Academic Search

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

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

2004-01-01

205

A Dust Characterization Experiment for Solar Cells Operating on Mars  

NASA Technical Reports Server (NTRS)

During the Viking and Pathfinder missions to Mars, significant amounts of dust accumulated on the spacecrafts. In Pathfinder's case, the dust obscured the solar panels on the lander and the rover degrading their output current. The material adherence experiment aboard the Pathfinder rover quantified the rate of decrease in short circuit current at 0.28% per day. This rate is unacceptably high for long duration missions. In response, NASA has developed the Dust Accumulation and Removal Technology (DART) experiment. DART has three instruments for characterizing dust settling out of the atmosphere and tests two methods to keep dust from settling on solar cells.

Jenkins, Phillip; Landis, Geoffrey A.; Krasowski, Michael; Greer, Lawrence; Wilt, David; Baraona, Cosmo; Scheiman, David; Lekki, John

2001-01-01

206

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

207

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

208

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

209

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

210

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

211

Magnetic topologies in the solar corona due to four discrete photospheric flux regions  

Microsoft Academic Search

Many dynamic phenomena in the solar corona are driven by the complex and ever-changing magnetic field. It is helpful, in trying to model these phenomena, to understand the structure of the magnetic field, i.e. the magnetic topology. We study here the topological structure of the coronal magnetic field arising from four discrete photospheric flux patches, for which we find that

C. Beveridge; E. R. Priest; D. S. Brown

2004-01-01

212

On the Relation Between Reconnected Flux and Parallel Electric Fields in the Solar Corona  

Microsoft Academic Search

The complicated magnetic topology in the solar corona often does not lend itself to the ready differentiation of topologically different regions. Instead, magnetic reconnection often happens in coronal fields that do not vanish, and for which no separator or separatrix is readily identifiable. For this, rather generic, situation, the question of how to relate observed magnetic flux changes to parallel

J. Johnson; M. Hesse; T. Forbes; J. Birn

2004-01-01

213

Signatures of Slow Solar Wind Streams from Active Regions in the Inner Corona  

NASA Astrophysics Data System (ADS)

The identification of solar-wind sources is an important question in solar physics. The existing solar-wind models ( e.g., the Wang-Sheeley-Arge model) provide the approximate locations of the solar wind sources based on magnetic field extrapolations. It has been suggested recently that plasma outflows observed at the edges of active regions may be a source of the slow solar wind. To explore this we analyze an isolated active region (AR) adjacent to small coronal hole (CH) in July/August 2009. On 1 August, Hinode/EUV Imaging Spectrometer observations showed two compact outflow regions in the corona. Coronal rays were observed above the active-region coronal hole (ARCH) region on the eastern limb on 31 July by STEREO-A/EUVI and at the western limb on 7 August by CORONAS- Photon/TESIS telescopes. In both cases the coronal rays were co-aligned with open magnetic-field lines given by the potential field source surface model, which expanded into the streamer. The solar-wind parameters measured by STEREO-B, ACE, Wind, and STEREO-A confirmed the identification of the ARCH as a source region of the slow solar wind. The results of the study support the suggestion that coronal rays can represent signatures of outflows from ARs propagating in the inner corona along open field lines into the heliosphere.

Slemzin, V.; Harra, L.; Urnov, A.; Kuzin, S.; Goryaev, F.; Berghmans, D.

2013-08-01

214

Reflection of Alfven waves and plasma turbulization in solar corona  

NASA Astrophysics Data System (ADS)

The continuous reflection of Alfven waves in the coronae of the Sun and stars is considered. Based on the WKB approximation, the solution to the linear wave equation in the case of a stratified isothermal atmosphere has been obtained. A critical analysis of results obtained by Ferraro and Plumpton (1958) and Hollweg (1972), as well as the relations in the Elsasser variables has been carried out. It has been shown that Alfven disturbances do not undergo a continuous reflection within the accepted model and are transformed into intermediate-type modes that possess the properties of vibrations and travelling waves. The problem of the turbulization of corona plasma is discussed. The origin of the Alfven waves that propagate toward the Sun is related to the development of parametric instability.

Tsap, Yu. T.

2012-06-01

215

Electron acceleration to high energies at quasi-parallel shock waves in the solar corona  

NASA Technical Reports Server (NTRS)

In the solar corona shock waves are generated by flares and/or coronal mass ejections. They manifest themselves in solar type 2 radio bursts appearing as emission stripes with a slow drift from high to low frequencies in dynamic radio spectra. Their nonthermal radio emission indicates that electrons are accelerated to suprathermal and/or relativistic velocities at these shocks. As well known by extraterrestrial in-situ measurements supercritical, quasi-parallel, collisionless shocks are accompanied by so-called SLAMS (short large amplitude magnetic field structures). These SLAMS can act as strong magnetic mirrors, at which charged particles can be reflected and accelerated. Thus, thermal electrons gain energy due to multiple reflections between two SLAMS and reach suprathermal and relativistic velocities. This mechanism of accelerating electrons is discussed for circumstances in the solar corona and may be responsible for the so-called 'herringbones' observed in solar type 2 radio bursts.

Mann, G.; Classen, H.-T.

1995-01-01

216

Synoptic Solar Cycle 24 in Corona, Chromosphere, and Photosphere Seen by the Solar Dynamics Observatory  

NASA Astrophysics Data System (ADS)

The Solar Dynamics Observatory provides multiwavelength imagery from extreme ultraviolet (EUV) to visible light as well as magnetic-field measurements. These data enable us to study the nature of solar activity in different regions of the Sun, from the interior to the corona. For solar-cycle studies, synoptic maps provide a useful way to represent global activity and evolution by extracting a central meridian band from sequences of full-disk images over a full solar Carrington rotation (? 27.3 days). We present the global evolution during Solar Cycle 24 from 20 May 2010 to 31 August 2013 (CR 2097 - CR 2140), using synoptic maps constructed from full-disk, line-of-sight magnetic-field imagery and EUV imagery (171 Ĺ, 193 Ĺ, 211 Ĺ, 304 Ĺ, and 335 Ĺ). The synoptic maps have a resolution of 0.1 degree in longitude and steps of 0.001 in sine of latitude. We studied the axisymmetric and non-axisymmetric structures of solar activity using these synoptic maps. To visualize the axisymmetric development of Cycle 24, we generated time-latitude (also called butterfly) images of the solar cycle in all of the wavelengths, by averaging each synoptic map over all longitudes, thus compressing it to a single vertical strip, and then assembling these strips in time order. From these time-latitude images we observe that during the ascending phase of Cycle 24 there is a very good relationship between the integrated magnetic flux and the EUV intensity inside the zone of sunspot activities. We observe a North-South asymmetry of the EUV intensity in high-latitudes. The North-South asymmetry of the emerging magnetic flux developed and resulted in a consequential asymmetry in the timing of the polar magnetic-field reversals.

Benevolenskaya, E.; Slater, G.; Lemen, J.

2014-04-01

217

A review of the solar results from CORONAS-F satellite  

Microsoft Academic Search

The solar results from CORONAS-F satellite have been reviewed. The observations with the DIFOS multi-channel photometer in a broad spectral range from 350 to 1500 nm have allowed to determine the dependence of the relative amplitudes of p-modes of the global solar oscillations on the wavelength. The EUV observations in SPIRIT experiment have enabled the study of various manifestations of

V. D. Kuznetsov; Yu. E. Charikov; Yu. D. Kotov; S. N. Kuznetsov; E. P. Mazets; A. A. Nusinov; V. M. Pankov; I. I. Sobelman; J. Sylwester

2004-01-01

218

The structure of the white-light corona and the large-scale solar magnetic field  

Microsoft Academic Search

The large-scale density structure of the white-light solar corona has been compared to the organization of the solar magnetic field as identified by the appearance of neutral lines in the photosphere in order to examine whether any consistent relationship exists between the two. Data from the High Altitude Observatory's Mk-III K-coronameter have been used to describe the coronal density structure,

D. G. Sime; M. K. McCabe

1990-01-01

219

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

220

The nonuniform magnetohydrodynamic nature of the solar corona. IV - Effect of magnetogravity interactions  

NASA Astrophysics Data System (ADS)

Magnetogravity interactions in the solar corona are considered by extending the method proposed by Priest for modeling standing magnetohydrodynamic disturbances. The effects of gravity on the basic solutions are to increase the maxima of the plasma and magnetic pressures and to decrease the curvature of the field lines. Also, the classification of the solutions is altered. When the transverse component of the magnetic field has a zero, more complex magnetic field structures are produced, reminiscent of coronal streamers, in which the type of interaction occurring in the plasma alters with height in the corona.

de Ville, A.; Priest, E. R.

1990-08-01

221

Solar Wind Mass-Loading Due to Dust in the Vicinity of the Sun  

NASA Astrophysics Data System (ADS)

Collisionless shocks due to mass-loading were first discussed to describe the solar wind flow around a cometary atmosphere, showing its choking effects on the flow. Recent observations have led to an increased interest in mass-loading occurring in the solar corona, due to sun-grazing comets and also due to collisional debris production by sunward migrating interplanetary dust particles. Using one-dimensional simulations with a hydrodynamic model we have shown the impact on the solar wind from abrupt mass-loading in the coronal region. Full three-dimensional MHD simulations using the Block-Adaptive-Tree-Solarwind-Roe-Upwind-Scheme (BATS-R-US) accomplish more to mimic specific events applicable to modeling the mass-loaded coronal wind caused by the presence of a sun-grazing comet, for example.

Rasca, A.; Horanyi, M.

2012-12-01

222

Comparison of Hinode\\/XRT and RHESSI Detection of Hot Plasma in the Non-Flaring Solar Corona  

Microsoft Academic Search

We compare observations of the non-flaring solar corona made simultaneously with Hinode\\/XRT and RHESSI. The analyzed corona is dominated by a single active region on 2006 November 12. The comparison is made on emission measures. We derive emission measure distributions versus temperature of the entire active region from multifilter XRT data. We check the compatibility with the total emission measure

Fabio Reale; James M. McTiernan; Paola Testa

2009-01-01

223

An MHD simulation model of time-dependent global solar corona with temporally varying solar-surface magnetic field maps  

NASA Astrophysics Data System (ADS)

We present a model of a time-dependent three-dimensional magnetohydrodynamics simulation of the sub-Alfvenic solar corona and super-Alfvenic solar wind with temporally varying solar-surface boundary magnetic field data. To (i) accommodate observational data with a somewhat arbitrarily evolving solar photospheric magnetic field as the boundary value and (ii) keep the divergence-free condition, we developed a boundary model, here named Confined Differential Potential Field model, that calculates the horizontal components of the magnetic field, from changes in the vertical component, as a potential field confined in a thin shell. The projected normal characteristic method robustly simulates the solar corona and solar wind, in response to the temporal variation of the boundary Br. We conduct test MHD simulations for two periods, from Carrington Rotation number 2009 to 2010 and from Carrington Rotation 2074 to 2075 at solar maximum and minimum of Cycle 23, respectively. We obtained several coronal features that a fixed boundary condition cannot yield, such as twisted magnetic field lines at the lower corona and the transition from an open-field coronal hole to a closed-field streamer. We also obtained slight improvements of the interplanetary magnetic field, including the latitudinal component, at Earth.

Hayashi, K.

2013-11-01

224

Physics of the Corona and Present and Future Major Solar and Heliospheric Space Missions  

NASA Astrophysics Data System (ADS)

Several ground facilities and space missions are currently dedicated to the study of the Sun at high resolution and of the solar corona in particular. However, and despite significant progress with the advent of space missions and UV, EUV and XUV direct observations of the hot chromosphere and million degrees coronal plasma, much is yet to be achieved in the understanding of these high temperatures, fine dissipative structures and of the coronal heating in general. Recent missions, in particular Hinode, have shown the definite role of waves and of the magnetic field deep in the inner corona, at the chromosphere-corona interface, where dramatic changes occur. Observations of multithermal loops and modelling will be presented...

Damé, Luc

2013-03-01

225

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

NASA Technical Reports Server (NTRS)

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. Effects of the magnetic field configuration are illustrated for initially open (radial) and closed (azimuthal) magnetic fields by comparison with the nonmagnetic response. The channeling or blocking effects by the magnetic fields on the mass motion of solar plasma as the consequence of the evolution of fast and slow mode MHD shock waves are demonstrated. Some physically significant applications of the results, useful for the interpretation of observations, are discussed. It is noted, for example, that coronal transients observed in white light probably occur within essentially radial field topologies.

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

1978-01-01

226

Theoretical model of the solar corona during sunspot minimum. II - Dynamic approximation  

NASA Technical Reports Server (NTRS)

The theoretical quasi-static model of the solar corona during sunspot minimum developed in an earlier paper (Osherovich et al., 1984) is extended to include a quasi-radial outflow. The requirement imposed in the above paper on a plasma flow is relaxed. The dynamic equation derived for the combination of a dipole-like and a radial field is used to calculate the electric current density around the sun in the region 1.5-5 solar radii. Comparison with the current density given by the quasi-static model shows that the outflow decreases the current density only slightly in the dynamic case. The dynamic coronal model with a magnetic quadrupole field is also considered, in relation to the north-south asymmetry in the solar corona.

Osherovich, V. A.; Gliner, E. B.; Tzur, I.

1985-01-01

227

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

228

The Substructure of the Solar Corona Observed in the Hi-C Telescope  

NASA Astrophysics Data System (ADS)

In the summer of 2012, the High-resolution Coronal Imager (Hi-C) flew aboard a NASA sounding rocket and collected the highest spatial resolution images ever obtained of the solar corona. One of the goals of the Hi-C flight was to characterize the substructure of the solar corona. We therefore calculate how the intensity scales from a low-resolution (AIA) pixels to high-resolution (Hi-C) pixels for both the dynamic events and “background” emission (meaning, the steady emission over the 5 minutes of data acquisition time). We find there is no evidence of substructure in the background corona; the intensity scales smoothly from low-resolution to high-resolution Hi-C pixels. In transient events, however, the intensity observed with Hi-C is, on average, 2.6 times larger than observed with AIA. This increase in intensity suggests that AIA is not resolving these events. This result suggests a finely structured dynamic corona embedded in a smoothly varying background.

Winebarger, Amy R.; Cirtain, Jonathan W.; Golub, Leon; DeLuca, Ed; Savage, Sabrina; Alexander, Caroline; Schuler, Timothy

2014-06-01

229

Discovery of Finely Structured Dynamic Solar Corona Observed in the Hi-C Telescope  

NASA Astrophysics Data System (ADS)

In the Summer of 2012, the High-resolution Coronal Imager (Hi-C) flew on board a NASA sounding rocket and collected the highest spatial resolution images ever obtained of the solar corona. One of the goals of the Hi-C flight was to characterize the substructure of the solar corona. We therefore examine how the intensity scales from AIA resolution to Hi-C resolution. For each low-resolution pixel, we calculate the standard deviation in the contributing high-resolution pixel intensities and compare that to the expected standard deviation calculated from the noise. If these numbers are approximately equal, the corona can be assumed to be smoothly varying, i.e., have no evidence of substructure in the Hi-C image to within Hi-C's ability to measure it given its throughput and readout noise. A standard deviation much larger than the noise value indicates the presence of substructure. We calculate these values for each low-resolution pixel for each frame of the Hi-C data. On average, 70% of the pixels in each Hi-C image show no evidence of substructure. The locations where substructure is prevalent is in the moss regions and in regions of sheared magnetic field. We also find that the level of substructure varies significantly over the roughly 160 s of the Hi-C data analyzed here. This result indicates that the finely structured corona is concentrated in regions of heating and is highly time dependent.

Winebarger, Amy R.; Cirtain, Jonathan; Golub, Leon; DeLuca, Edward; Savage, Sabrina; Alexander, Caroline; Schuler, Timothy

2014-05-01

230

Solar wind driven dust acoustic instability with Lorentzian kappa distribution  

NASA Astrophysics Data System (ADS)

In a three species electron-ion-dust plasma following a generalized non-Maxwellian distribution function (Lorentzian or kappa), it is shown that a kinetic instability of dust-acoustic mode exists. The instability threshold is affected when such (quasineutral) plasma permeates through another static plasma. Such case is of interest when the solar wind is streaming through the cometary plasma in the presence of interstellar dust. In the limits of phase velocity of the waves larger and smaller than the thermal velocity of dust particles, the dispersion properties and growth rate of dust-acoustic mode are investigated analytically with validation via numerical analysis.

Arshad, Kashif; Ehsan, Zahida; Khan, S. A.; Mahmood, S.

2014-02-01

231

Solar wind magnetic field bending of Jovian dust trajectories.  

PubMed

From September 1991 to October 1992, the cosmic dust detector on the Ulysses spacecraft recorded 11 short bursts, or streams, of dust. These dust grains emanated from the jovian system, and their trajectories were strongly affected by solar wind magnetic field forces. Analyses of the on-board measurements of these fields, and of stream approach directions, show that stream-associated dust grain masses are of the order of 10(-18) gram and dust grain velocities exceed 200 kilometers per second. These masses and velocities are, respectively, about 10(3) times less massive and 5 to 10 times faster than earlier reported. PMID:8929405

Zook, H A; Grün, E; Baguhl, M; Hamilton, D P; Linkert, G; Liou, J; Forsyth, R; Phillips, J L

1996-11-29

232

Energetic protons accelerated by a model Coronal Mass Ejection and associated shock in the solar corona  

NASA Astrophysics Data System (ADS)

Modeling and observational studies of coronal and interplanetary shocks suggest that they are most effective in accelerating Solar Energetic Particles (SEP) relatively close to the Sun. Interplanetary shocks have been quite well studied, thanks to in situ measurements of energetic articles near Earth and throughout the solar system. Many bursts of energetic charged particles observed close to Earth are not directly associated with shocks that pass by Earth. This suggests that energetic particles could be accelerated much lower, in the solar corona, possibly by shocks that form near the Sun or through magnetic reconnection. For the first time, we have used results from a three-dimensional time-dependent magnetohydrodynamic (MHD) simulation of a coronal mass ejection (CME) in the solar corona, coupled with a three-dimensional energetic particle propagation and acceleration model, in order to investigate how suprathermal protons respond to an enhanced traveling plasma structure and shock in the corona. The detailed MHD simulation reveals multiple density and magnetic field enhancements behind the traveling shock, which cause rapid acceleration of suprathermal protons via diffusive shock acceleration in the kinetic simulation. The resulting spectra and time profiles of energetic protons at different radial distances from the Sun are presented. This work will help address the question of whether and how efficient CMEs and shocks close to the Sun are in accelerating suprathermal particle populations to high energies.

Kozarev, K. A.; Evans, R. M.; Dayeh, M. A.; Schwadron, N. A.; Opher, M.; Korreck, K. E.; Gombosi, T. I.

2010-12-01

233

Observations of mode coupling in the solar corona and bipolar noise storms  

NASA Technical Reports Server (NTRS)

High-spatial-resolution observations of the sun which reflect on the role of mode coupling in the solar corona, and a number of new observations are presented. It is shown that typically, polarization inversion is seen at 5 GHz in active region sources near the solar limb, but not at 1.5 GHz. Although this is apparently in contradiction to the simplest form of mode coupling theory, it remains consistent with current models for the active region emission. Microwave bursts show no strong evidence for polarization inversion. Bipolar noise storm continuum emission is discussed in some detail, utilizing recent VLA observations at 327 MHz. It is shown that bipolar sources are common at 327 MHz. Further, the trailing component of the bipole is frequently stronger than the leading component, in apparent conflict with the 'leading-spot' hypothesis. The observations indicate that, at 327 MHz, mode coupling is apparently strong at all mode-coupling layers in the solar corona. The 327 MHz observations require a much weaker magnetic field strength in the solar corona to explain this result than did earlier lower-frequency observations: maximum fields are 0.2 G. This is a much weaker field than is consistent with current coronal models.

White, S. M.; Thejappa, G.; Kundu, M. R.

1992-01-01

234

Unified Models of Turbulence and Nonlinear Wave Evolution in the Extended Solar Corona and Solar Wind  

NASA Technical Reports Server (NTRS)

The PI (Cranmer) and Co-I (A. van Ballegooijen) made significant progress toward the goal of building a "unified model" of the dominant physical processes responsible for the acceleration of the solar wind. The approach outlined in the original proposal comprised two complementary pieces: (1) to further investigate individual physical processes under realistic coronal and solar wind conditions, and (2) to extract the dominant physical effects from simulations and apply them to a one-dimensional and time-independent model of plasma heating and acceleration. The accomplishments in the report period are thus divided into these two categories: 1a. Focused Study of Kinetic MHD Turbulence. We have developed a model of magnetohydrodynamic (MHD) turbulence in the extended solar corona that contains the effects of collisionless dissipation and anisotropic particle heating. A turbulent cascade is one possible way of generating small-scale fluctuations (easy to dissipate/heat) from a pre-existing population of low-frequency Alfven waves (difficult to dissipate/heat). We modeled the cascade as a combination of advection and diffusion in wavenumber space. The dominant spectral transfer occurs in the direction perpendicular to the background magnetic field. As expected from earlier models, this leads to a highly anisotropic fluctuation spectrum with a rapidly decaying tail in the parallel wavenumber direction. The wave power that decays to high enough frequencies to become ion cyclotron resonant depends on the relative strengths of advection and diffusion in the cascade. For the most realistic values of these parameters, though, there is insufficient power to heat protons and heavy ions. The dominant oblique waves undergo Landau damping, which implies strong parallel electron heating. We thus investigated the nonlinear evolution of the electron velocity distributions (VDFs) into parallel beams and discrete phase-space holes (similar to those seen in the terrestrial magnetosphere) which are an alternate means of heating protons via stochastic interactions similar to particle-particle collisions. 1b. Focused Study of the Multi-Mode Detailed Balance Formalism. The PI began to explore the feasibility of using the "weak turbulence," or detailed-balance theory of Tsytovich, Melrose, and others to encompass the relevant physics of the solar wind. This study did not go far, however, because if the "strong" MHD turbulence discussed above is a dominant player in the wind's acceleration region, this formalism is inherently not applicable to the corona. We will continue to study the various published approaches to the weak turbulence formalism, especially with an eye on ways to parameterize nonlinear wave reflection rates. 2. Building the Unified Model Code Architecture. We have begun developing the computational model of a time-steady open flux tube in the extended corona. The model will be "unified" in the sense that it will include (simultaneously for the first time) as many of the various proposed physical processes as possible, all on equal footing. To retain this generality, we have formulated the problem in two interconnected parts: a completely kinetic model for the particles, using the Monte Carlo approach, and a finite-difference approach for the self-consistent fluctuation spectra. The two codes are run sequentially and iteratively until complete consistency is achieved. The current version of the Monte Carlo code incorporates gravity, the zero-current electric field, magnetic mirroring, and collisions. The fluctuation code incorporates WKJ3 wave action conservation and the cascade/dissipation processes discussed above. The codes are being run for various test problems with known solutions. Planned additions to the codes include prescriptions for nonlinear wave steepening, kinetic velocity-space diffusion, and multi-mode coupling (including reflection and refraction).

Cranmer, Steven R.; Wagner, William (Technical Monitor)

2003-01-01

235

2D MHD model of the solar corona and solar wind: Recent results  

NASA Astrophysics Data System (ADS)

We have been developing a self-consistent 2D MHD steady-state model of the solar corona and solar wind. This model is empirically constrained by 2D maps of the effective temperature, Teff , and heat flux, qeff , as originally derived by Sittler and Guhathakurta or SG model. The SG model has been applied to Mark II K-coronameter data, Skylab, Spartan and SOHO/LASCO white light coronagraph data, plus plasma and magnetic field Ulysses data. Our model uses the MHD conservation equations of mass, momentum and energy with a multipole expansion of the coronal magnetic field up to octupole term as the initial state for the MHD solutions. At present our MHD solutions are confined between the coronal base at 1.03 RS and 5 RS and will be expanded to larger heliocentric distances in the future. In order to make our MHD solutions more tractable, we have fit smooth analytical functions to Teff and qeff derived from the data-driven SG model. We will present solutions under these conditions, some of the difficulties we have had to deal with and show the future direction of our research.

Sittler, E. C., Jr.; Ofman, L.

236

Mapping the Solar Wind from its Source Region into the Outer Corona  

NASA Technical Reports Server (NTRS)

The solar wind not only forms the space environment of Earth and other planets, but is also the cause of many phenomena observed in the Earth's atmosphere, such as aurorae. The expansion of the coronal plasma of the Sun is characteristic to many main sequence stars, and thus provides an example for understanding stellar winds as well. In spite of its importance for both space science and stellar physics, basic solar wind properties remain essentially unresolved. Since its discovery about 50 years ago, the complexity of the Sun corona - solar wind system has complicated the interpretation of observations. Recent progress in remote sensing observations as provided for example by YOHKOH, SOHO, SPARTAN and ULYSSES as well as some ground based techniques such as Interplanetary Scintillation observations, offer a compelling opportunity to unravel the 50 year old puzzle regarding the heat source or sources that cause the expansion of the solar corona. The new era of solar wind observations initiated by SOHO and ULYSSES, have also led to a wealth of new theoretical approaches. The goal of the proposed research was to carry out an integrated study of the coronal and solar wind plasma making use of the opportunities provided by the above spacecraft, as well as plasma emission calculations and new ideas on solar wind expansion theory.

Esser, Ruth; Wagner, William J. (Technical Monitor)

2000-01-01

237

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

238

What EUV Observations of Comet ISON Reveal About the Solar Corona  

NASA Astrophysics Data System (ADS)

Recent advances in space-based solar observations have greatly progressed the study of sungrazing comets. They can now be imaged along the entirety of their perihelion passage, revealing details of their composition, structure, and size. Such comets are also unique probes of the solar corona. The debris deposited by sungrazers is rapidly ionized and subsequently forced to follow the ambient magnetic field. In this paper we present preliminary results from EUV observations of Comet ISON. We estimate the size of the comet nucleus based on the EUV radiance and compare with independent estimates. The variation of the EUV emission with wavelength provides limits on the density of the ambient corona, and the motion of ionized debris will be used to infer the coronal magnetic field structure.

Bryans, P.; Pesnell, W. D.

2013-12-01

239

The nonuniform magnetohydrodynamic nature of the solar corona. III - Cylindrical geometry  

NASA Astrophysics Data System (ADS)

The method developed by Priest in 1988 for modeling steady MHD disturbances in the solar corona is extended to a cylindrical geometry, which is more realistic for three-dimensional structures, such as plumes and coronal holes, which are observed in the corona. Both axial symmetric and nonaxial magnetic fields are treated. The basic characteristics of the axisymmetric solutions are found to be similar to the previous Cartesian case. Quantitatively, the interactions are stronger in the central region and weaker at the outer boundary. Pressure gradients are also found to be smaller. Solutions dependent on all three spatial variables exhibit an asymmetry because of the angular dependence. They depend upon the azimuthal magnetic field imposed at the coronal base. The solutions found in this paper may be useful in interpreting the physics of MHD interactions observed in numerical experiments and also in the solar atmosphere.

de Ville, A.; Priest, E. R.

1989-12-01

240

CCD camera for ground- and space-based solar corona observations  

NASA Astrophysics Data System (ADS)

A new concept CCD camera is currently under development at the XUVLab of the Department of Astronomy and Space Science of the University of Florence. This CCD camera is the proposed detector for the space- and ground-based solar corona observations. This camera will be the detector for the polarimetric channels of the UVC coronagraph of the HERSCHEL rocket mission to observe the solar corona in an optical broadband. The ground-based application consists in a UVC prototype for coronagraphic measurements from Earth in the visible range. Within this project, a CCD camera with innovative features has been produced: the camera controller allows the fine tuning of all the parameters related to charge transfer and CCD readout, i.e., the use of virtually any CCD sensor, and it implements the new concept of high level of versatility, easy management, TCP/IP remote control and display.

Gherardi, Alessandro; Gori, Luca; Focardi, Mauro; Pace, Emanuele; Romoli, Marco; Fineschi, Silvano; Zangrilli, Luca; Gardiol, Daniele; Antonucci, Ester

2004-02-01

241

The Structure and Dynamics of the Solar Corona and Inner Heliosphere  

NASA Technical Reports Server (NTRS)

This report covers technical progress during the third quarter of the second year of NASA Sun-Earth Connections Theory Program (SECTP) contract 'The Structure and Dynamics of the Solar Corona and Inner Heliosphere,' NAS5-99188, between NASA and Science Applications International Corporation, and covers the period February 16, 2001 to May 15, 2001. Under this contract SAIC and the University of California, Irvine (UCI) have conducted research into theoretical modeling of active regions, the solar corona, and the inner heliosphere, using the MHD model.In this report we summarize the accomplishments made by our group during the first seven quarters of our Sun-Earth Connection Theory Program contract. The descriptions are intended to illustrate our principal results. A full account can be found in the referenced publications.

Mikic, Zoran; Grebowsky, J. (Technical Monitor)

2001-01-01

242

Skylab and solar exploration. [chromosphere-corona structure, energy production and heat transport processes  

NASA Technical Reports Server (NTRS)

Review of some of the findings concerning solar structure, energy production, and heat transport obtained with the aid of the manned Skylab space station observatory launched on May 14, 1973. Among the topics discussed are the observation of thermonuclear fusion processes which cannot be simulated on earth, the observation of short-wave solar radiation not visible to observers on earth, and the investigation of energy-transport processes occurring in the photosphere, chromosphere, and corona. An apparent paradox is noted in that the cooler chromosphere is heating the hotter corona, seemingly in defiance of the second law of thermodynamics, thus suggesting that a nonthermal mechanism underlies the energy transport. Understanding of this nonthermal mechanism is regarded as an indispensable prerequisite for future development of plasma systems for terrestrial applications.

Von Puttkamer, J.

1973-01-01

243

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

244

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; Ĺke Nordlund

1996-01-01

245

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

246

Magnetic structure and reconnection of x-ray bright points in the solar corona  

Microsoft Academic Search

The three-dimensional magnetic topology of the solar corona is incredibly complex and its effect on the nature of 3D reconnection is profound. We study the supposedly simple topology of a small scale X-ray bright point observed by TRACE and SOHO\\/MDI, and how it is driven by reconnection when it forms and during the early stages of its lifetime.

D. S. Brown; C. E. Parnell; E. E. Deluca; R. A. McMullen; L. Golub; E. R. Priest

2002-01-01

247

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

248

Ka-band and X-band observations of the solar corona aquired during the Cassini 2002 superior conjunction  

NASA Technical Reports Server (NTRS)

A superior solar conjunction occurs when the sun lies near the signal path of a source as observed from the Earth. Interplanetary spacecraft sent to the planets typically encounter one or more solar conjunctions during their mission lifetimes. During these periods, the signals sent to and from the spacecraft encounter degradation due to the intervening charged particles of the solar corona.

Morabito, D. D.

2002-01-01

249

How Structures of the Solar Corona and Eruptions Interact to Create Extreme Energetic Particle Events  

NASA Astrophysics Data System (ADS)

As the Sun approaches maximum activity, the number of solar energetic particle (SEP) events is rapidly increasing. These strong events have the potential to damage technical systems, so it is essential to understand what causes them. Although relationships exist between the characteristics of SEP events and the associated flares and coronal mass ejections (CMEs), the strongest solar events may not lead to the most intense particle events. For example, the first Ground Level Enhancement event of Solar Cycle 24 was associated with only a moderately strong flare and CME. Presumably, there must be other factors that determine the acceleration of the highest energy particles. To address this question, we combine observations and innovative theoretical modeling of recent SEP events. We use a three-dimensional magnetohydrodynamics (MHD) model of the solar corona (within the Space Weather Modeling Framework) to simulate eruptions in the low to middle corona. The MHD output is coupled to a global kinetic simulation of particle acceleration and transport (within the Energetic Particle Radiation Environment Module). The output of the simulation is a synthetic spectral profile response to realistic solar corona conditions during the propagation of a CME. We study the evolution of the CME structures (shock and compression regions within the sheath) and the relation of these features to the preexisting coronal magnetic field geometry and solar wind distribution. Then we determine which factors affect the efficiency of particle acceleration and transport. For the first time, we can probe how particle acceleration varies in different regions of the CME as it interacts with the solar wind. R. M. E. is supported through an appointment to the NASA Postdoctoral Program at GSFC, administered by Oak Ridge Associated Universities through a contract with NASA.

Evans, R. M.; Kozarev, K. A.; Zheng, Y.; Pulkkinen, A.; Taktakishvili, A.; Kuznetsova, M. M.; Opher, M.; Dayeh, M. A.; Schwadron, N. A.; van der Holst, B.

2012-12-01

250

"Kicking Up Some Dust": An Experimental Investigation Relating Lunar Dust Erosive Wear to Solar Power Loss  

NASA Technical Reports Server (NTRS)

The exhaust from retrograde rockets fired by spacecraft landing on the Moon can accelerate lunar dust particles to high velocities. Information obtained from NASA's Apollo 12 mission confirmed that these high-speed dust particles can erode nearby structures. This erosive wear damage can affect the performance of optical components such as solar concentrators. Solar concentrators are objects which collect sunlight over large areas and focus the light into smaller areas for purposes such as heating and energy production. In this work, laboratory-scale solar concentrators were constructed and subjected to erosive wear by the JSC-1AF lunar dust simulant. The concentrators were focused on a photovoltaic cell and the degradation in electrical power due to the erosive wear was measured. It was observed that even moderate exposure to erosive wear from lunar dust simulant resulted in a 40 percent reduction in power production from the solar concentrators.

Mpagazehe, Jeremiah N.; Street, Kenneth W., Jr.; Delgado, Irebert R.; Higgs, C. Fred, III

2013-01-01

251

Magnetic Untwisting in Jets that Go into the Outer Solar Corona in Polar Coronal Holes  

NASA Astrophysics Data System (ADS)

We present results from a study of 14 jets that were observed in SDO/AIA EUV movies to erupt in the Sun’s polar coronal holes. These jets were similar to the many other jets that erupt in coronal holes, but reached higher than the vast majority, high enough to be observed in the outer corona beyond 2 solar radii from Sun center by the SOHO/LASCO/C2 coronagraph. We illustrate the characteristic structure and motion of these high-reaching jets by showing observations of two representative jets. We find that (1) the speed of the jet front from the base of the corona out to 2-3 solar radii is typically several times the sound speed in jets in coronal holes, (2) each high-reaching jet displays unusually large rotation about its axis (spin) as it erupts, and (3) in the outer corona, many jets display lateral swaying and bending of the jet axis with an amplitude of a few degrees and a period of order 1 hour. From these observations we infer that these jets are magnetically driven, propose that the driver is a magnetic-untwisting wave that is basically a large-amplitude (non-linear) torsional Alfven wave that is put into the open magnetic field in the jet by interchange reconnection as the jet erupts, and estimate that the magnetic-untwisting wave loses most of its energy before reaching the outer corona. These observations of high-reaching coronal jets suggest that the torsional magnetic waves observed in Type-II spicules can similarly dissipate in the corona and thereby power much of the coronal heating in coronal holes and quiet regions. This work is funded by the NASA/SMD Heliophysics Division’s Living With a Star Targeted Research & Technology Program.

Moore, Ronald L.; Sterling, Alphonse C.; Falconer, David

2014-06-01

252

Dust Destruction and Ion Formation in the Inner Solar System  

Microsoft Academic Search

We suggest that dust-dust collisions feed ions into the interplanetary medium and produce a significant amount of the heavy inner-source pickup ions detected by the Solar Wind Ion Composition Spectrometer aboard the Ulysses spacecraft. Organic refractory material contained in the cometary dust could explain the existence of carbon among the measured pickup ions. Impact-produced ions may locally influence the plasma

Ingrid Mann; Andrzej Czechowski

2005-01-01

253

Reduction in the intensity of solar X-ray emission in the 2- to 15-keV photon energy range and heating of the solar corona  

SciTech Connect

The time profiles of the energy spectra of low-intensity flares and the structure of the thermal background of the soft X-ray component of solar corona emission over the period of January-February, 2003, are investigated using the data of the RHESSI project. A reduction in the intensity of X-ray emission of the solar flares and the corona thermal background in the 2- to 15-keV photon energy range is revealed. The RHESSI data are compared with the data from the Interball-Geotail project. A new mechanism of solar corona heating is proposed on the basis of the results obtained.

Mirzoeva, I. K., E-mail: colombo2006@mail.ru [Russian Academy of Sciences, Space Research Institute (Russian Federation)

2013-04-15

254

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

255

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

NASA Technical Reports Server (NTRS)

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.

Davila, Joseph M.

1987-01-01

256

Dust to planetesimals - Settling and coagulation in the solar nebula  

Microsoft Academic Search

The behavior of solid particles in a low-mass solar nebula during settling to the central plane and the formation of planetesimals is discussed. The gravitational instability in a dust layer and collisional accretion are examined as possible mechanisms of planetesimal formation. The shear between the gas and a dust layer is considered along with the differences in the planetesimal formation

S. J. Weidenschilling

1980-01-01

257

Evaporation of the Solar Corona into Interplanetary Space.  

National Technical Information Service (NTIS)

A simple kinetic theory model of the interplanetary gaseous medium based on the evaporation of particles from the solar coronal exosphere is considered, using Jeans' equation for the escape of gases from planetary atmospheres. The exosphere is fixed in th...

H. K. Sen

1965-01-01

258

Characterization of the Large-Scale Solar Corona.  

National Technical Information Service (NTIS)

Coronal mass ejections (CMEs) from the Sun constitute one of the primary causes of geomagnetic storms. CMEs also drive shocks, which in turn accelerate solar energetic particles (SEPs) that pose radiation hazards for technological systems in space. With s...

J. Brosius

2003-01-01

259

Destruction of Sun-grazing comet C/2011 N3 (SOHO) within the low solar corona.  

PubMed

Observations of comets in Sun-grazing orbits that survive solar insolation long enough to penetrate into the Sun's inner corona provide information on the solar atmosphere and magnetic field as well as on the makeup of the comet. On 6 July 2011, the Solar Dynamics Observatory (SDO) observed the demise of comet C/2011 N3 (SOHO) within the low solar corona in five wavelength bands in the extreme ultraviolet (EUV). The comet penetrated to within 0.146 solar radius (~100,000 kilometers) of the solar surface before its EUV signal disappeared. Before that, material released into the coma--at first seen in absorption--formed a variable EUV-bright tail. During the final 10 minutes of observation by SDO's Atmospheric Imaging Assembly, ~6 × 10(8) to 6 × 10(10) grams of total mass was lost (corresponding to an effective nucleus diameter of ~10 to 50 meters), as estimated from the tail's deceleration due to interaction with the surrounding coronal material; the EUV absorption by the comet and the brightness of the tail suggest that the mass was at the high end of this range. These observations provide evidence that the nucleus had broken up into a family of fragments, resulting in accelerated sublimation in the Sun's intense radiation field. PMID:22267810

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

2012-01-20

260

Magnetic Reconnection and Particle Acceleration in the Solar Corona  

NASA Astrophysics Data System (ADS)

Reconnection plays a major role for the magnetic activity of the solar atmosphere, for example solar flares. An interesting open problem is how magnetic reconnection acts to redistribute the stored magnetic energy released during an eruption into other energy forms, e.g. gener-ating bulk flows, plasma heating and non-thermal energetic particles. In particular, finding a theoretical explanation for the observed acceleration of a large number of charged particles to high energies during solar flares is presently one of the most challenging problems in solar physics. One difficulty is the vast difference between the microscopic (kinetic) and the macro-scopic (MHD) scales involved. Whereas the phenomena observed to occur on large scales are reasonably well explained by the so-called standard model, this does not seem to be the case for the small-scale (kinetic) aspects of flares. Over the past years, observations, in particular by RHESSI, have provided evidence that a naive interpretation of the data in terms of the standard solar flare/thick target model is problematic. As a consequence, the role played by magnetic reconnection in the particle acceleration process during solar flares may have to be reconsidered.

Neukirch, Thomas

261

Energy release in the solar corona from spatially resolved magnetic braids  

NASA Astrophysics Data System (ADS)

It is now apparent that there are at least two heating mechanisms in the Sun's outer atmosphere, or corona. Wave heating may be the prevalent mechanism in quiet solar periods and may contribute to heating the corona to 1,500,000K (refs 1, 2, 3). The active corona needs additional heating to reach 2,000,000-4,000,000K this heat has been theoretically proposed to come from the reconnection and unravelling of magnetic `braids'. Evidence favouring that process has been inferred, but has not been generally accepted because observations are sparse and, in general, the braided magnetic strands that are thought to have an angular width of about 0.2arc seconds have not been resolved. Fine-scale braiding has been seen in the chromosphere but not, until now, in the corona. Here we report observations, at a resolution of 0.2arc seconds, of magnetic braids in a coronal active region that are reconnecting, relaxing and dissipating sufficient energy to heat the structures to about 4,000,000K. Although our 5-minute observations cannot unambiguously identify the field reconnection and subsequent relaxation as the dominant heating mechanism throughout active regions, the energy available from the observed field relaxation in our example is ample for the observed heating.

Cirtain, J. W.; Golub, L.; Winebarger, A. R.; de Pontieu, B.; Kobayashi, K.; Moore, R. L.; Walsh, R. W.; Korreck, K. E.; Weber, M.; McCauley, P.; Title, A.; Kuzin, S.; Deforest, C. E.

2013-01-01

262

Solar corona photographed from Apollo 15 one minute prior to sunrise  

NASA Technical Reports Server (NTRS)

The solar corona, as photographed from Apollo 15 about one minute prior to sunrise on July 31, 1971, is seen just beyond the lunar horizon. The bright object on the opposite side of the frame is the planet Mercury. The bright star near the frame center is Regulus, and the lesser stars form the head of the constellation Leo. Mercury is approximately 28 degrees from the center of the sun. The solar coronal streamers, therefore, appear to extend about eight degrees from the sun's center.

1971-01-01

263

New Insights into the Physics of the Solar Corona from SOHO/LASCO  

NASA Astrophysics Data System (ADS)

The LASCO coronagraph, on the NASA/ESA SOHO spacecraft, was launched in December 1995 to image the solar corona. The major scientific objectives were to understand where and how the solar wind is accelerated and what causes coronal mass ejections and what role they play in the evolutionary development of the large scale magnetic field of the Sun. The wide field of view (1.1 to 32 solar radii) and the high signal to noise (700:1) has enabled unprecedented observations of the dynamics of the solar corona. One new observation is that the Sun is continually ejecting material in discrete bursts (not the traditional CME) along pre-existing streamers. These ejecta have a speed profile that mimics the theoretical predictions of the slow solar wind. LASCO has also been revealing coronal mass ejections (CMEs) as they are launched from the sun and following them out to distances that were not accessible to previous researchers enabling the discovery of several important, new results. Calculations of the total energy (kinetic, potential and magnetic) show that in some events, magnetic energy is being converted to kinetic energy. Another new observation has been the discovery of inflowing material. These observations are contributing to new insights and to new puzzles in our understanding of the dynamics of the Sun and its impact on Earth.

Howard, Russell

2001-04-01

264

Spectroscopic diagnostics of extended corona and solar wind with UVCS/Spartan  

NASA Technical Reports Server (NTRS)

The primary goal of the Ultraviolet Coronal Spectrometer on Spartan 201 (UVCS/Spartan) is to make spectroscopic diagnostic measurements that can be used to derive plasma parameters in the extended solar corona where it is believed that significant heating of the corona and acceleration of the solar wind take place. Direct and indirect measurements of particle velocity distribution, thermal and non-thermal temperatures, and bulk outflow velocities are crucial to aid in the identification of physical processes that may be responsible for coronal heating and solar wind acceleration. UVCS/Spartan has made two flights in April 1993 and September 1994, the latter coinciding with the South Polar Passage of the Ulysses spacecraft. Observations were made of the large-scale structures and sub-structures of coronal holes and streamers at heliocentric heights between 1.5 solar radii and 3.5 solar radii. Measurements were made of H I Lyman-alpha intensities and profiles, and line intensities of minor ions like O(5+) and Fe(11+). We will present results from the flights and discuss how these measurements are used to constrain values for the proton thermal and non-thermal kinetic temperatures, proton bulk outflow velocities, and minor ion temperatures and bulk outflow velocities. Plans for the upcoming flight in July 1995 will also be discussed.

Strachan, L.; Gardner, L. D.; Kohl, J. L.

1995-01-01

265

Plasmoids in planetary magnetic fields and the solar corona  

Microsoft Academic Search

The formation and acceleration of plasmoids, observed in the laboratory, in the magnetosphere, and in the solar atmosphere are discussed. Results suggest that the formation and ejection of plasmoids is a dominant loss process for mass and energy accumulated in closed flux regions in the magnetic field of planets and stars, under nearly ideal MHD conditions. Formation occurs via an

K. Schindler

1985-01-01

266

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

267

Fast Magnetosonic Waves and Global Coronal Seismology in the Extended Solar Corona  

NASA Astrophysics Data System (ADS)

We present global coronal seismology, for the first time, that allows us to determine inhomogeneous magnetic field strengths in a wide range of the extended solar corona. We use observations of propagating disturbance associated with a coronal mass ejection observed on 2011 August 4 by the COR1 inner coronagraphs on board the STEREO spacecraft. We establish that the disturbance is in fact a fast magnetosonic wave as the upper coronal counterpart of the EIT wave observed by STEREO EUVI and travels across magnetic field lines with inhomogeneous speeds, passing through various coronal regions such as quiet/active corona, coronal holes, and streamers. We derive magnetic field strengths along the azimuthal trajectories of the fronts at heliocentric distances 2.0, 2.5, and 3.0 Rs, using the varying speeds and electron densities. The derived magnetic field strengths are consistent with values determined with a potential field source surface model and reported in previous works. The ranges of the magnetic field strengths at these heliocentric distances are 0.44 ą 0.29, 0.23 ą 0.15, and 0.26 ą 0.14 G, respectively. The uncertainty in determining magnetic field strengths is about 40 %. This work demonstrates that observations of fast magnetosonic waves by white-light coronagraphs can provide us with a unique way to diagnose magnetic field strength of an inhomogeneous medium in a wide spatial range of the extended solar corona.

Kwon, Ryun Young; Zhang, J.; Kramar, M.; Wang, T.; Ofman, L.; Davila, J. M.

2013-07-01

268

Interaction of Cometary Material With the Solar Corona: EUV Observations and MHD Simulations  

NASA Astrophysics Data System (ADS)

Extreme ultraviolet (EUV) emission from two recent sun-grazing comets, C/2011 N3 and C/2011 W3 (Lovejoy), has been observed in the solar corona for the first time by the SDO/AIA and STEREO/EUVI instruments (Schrijver et al. 2011). These observations provided a unique opportunity to investigate the interaction of the cometary material with the solar corona and probe their physical conditions. We present here EUV observations and MHD simulations on this subject, focusing on the deceleration of the cometary tail material within the corona. We found that despite their different local coronal environments, the two comets exhibited quite similar characteristics. The initial EUV emitting tail had a projected velocity of 100-200 km/s, which was much lower than the orbital velocity of 500-600 km/s in the plane-of-sky. This indicates that significant deceleration had taken place while the tail material was heated to coronal temperatures on the order of 1 MK before it started to emit in EUV (Bryans & Pesnell 2012). After its initial appearance, the tail further experienced a projected deceleration of ~1 km/s^2 (or 4 g_Sun). In particular, in the Lovejoy case, the tail appeared as clusters of bright parallel striations roughly at right angles to the orbit direction, suggestive of magnetic field lines illuminated by the plasma frozen onto them. These striations came to a stop and then accelerated in an opposite direction (seen in projection), approaching a constant velocity of ~50 km/s. These observations suggest that a Lorentz force from the coronal magnetic field was operating on the newly ionized cometary plasma. To test this hypothesis and understand tail deceleration mechanisms, we adopted a multi-fluid MHD model (Jia et al. 2012) to simulate the interaction between charged particles and the magnetized coronal plasma. We used potential extrapolation (Schrijver & DeRosa 2003) and a more sophisticated global MHD model (Lionello et al. 2009) to infer the magnetic field and plasma conditions of the corona along the comet's orbit as inputs to the simulations. We will compare the observations and simulation results, and discuss the implications for using sun-grazing comets as probes to the solar corona in the context of NASA's future Solar Probe Plus mission.

Liu, W.; Jia, Y.; Downs, C.; Schrijver, C.; Saint-Hilaire, P.; Battams, K.; Tarbell, T. D.; Shine, R. A.

2012-12-01

269

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

NASA Astrophysics Data System (ADS)

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 comes from that developed by Guhathakurta and coworkers. The electron density model is extended into interplanetary space by using electron densities derived from the Ulysses plasma instrument. The model also requires an estimate of the solar wind velocity as a function of heliographic latitude and radial component of the magnetic field at 1 AU, both of which can be provided by the Ulysses spacecraft. The model makes estimates as a function of radial distance and latitude of various fluid parameters of the plasma such as flow velocity V, effective temperature Teff, and effective heat flux qeff, which are derived from the equations of conservation of mass, momentum, and energy, respectively. The term ``effective'' indicates that wave contributions could be present. The model naturally provides the spiral pattern of the magnetic field far from the Sun and an estimate of the large-scale surface magnetic field at the Sun, which we estimate to be ~12-15 G. The magnetic field model shows that the large-scale surface magnetic field is dominated by an octupole term. The model is a steady state calculation which makes the assumption of azimuthal symmetry and solves the various conservation equations in the rotating frame of the Sun. The conservation equations are integrated along the magnetic field direction in the rotating frame of the Sun, thus providing a nearly self-consistent calculation of the fluid parameters. The model makes a minimum number of assumptions about the physics of the solar corona and solar wind and should provide a very accurate empirical description of the solar corona and solar wind. Once estimates of mass density ?, flow velocity V, effective temperature Teff, effective heat flux qeff, and magnetic field B are computed from the model and waves are assumed unimportant, all other plasma parameters such as Mach number, Alfvén speed, gyrofrequency, etc. can be derived as a function of radial distance and latitude from the Sun. The model can be used as a planning tool for such missions as Solar Probe and provide an empirical framework for theoretical models of the solar corona and solar wind. The model will be used to construct a semiempirical MHD description of the steady state solar corona and solar wind using the SOHO Large Angle Spectrometric Coronagraph (LASCO) polarized brightness white-light coronagraph data, SOHO Extreme Ultraviolet Imaging Telescope data, and Ulysses plasma data.

Sittler, Edward C., Jr.; Guhathakurta, Madhulika

1999-10-01

270

High-frequency Faraday rotation observations of the solar corona  

NASA Astrophysics Data System (ADS)

This thesis, presented on January 31, 2007 under the supervision of Professor Christopher T. Russell, discusses the solar coronal magnetic field observations that can be obtained using the phenomenon of Faraday rotation. It was defended in the Department of Earth and Space Sciences at the University of California, Los Angeles (595 Charles E. Young, Dr. East, Los Angeles, CA 90095). A resume can be found at http://acs-consulting.com/.

Jensen, Elizabeth A.; Russell, Christopher T.

2008-10-01

271

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

272

The writhe of helical structures in the solar corona  

Microsoft Academic Search

Helicity is a fundamental property of magnetic fields, conserved in ideal\\u000aMHD. In flux rope topology, it consists of twist and writhe helicity. Despite\\u000athe common occurrence of helical structures in the solar atmosphere, little is\\u000aknown about how their shape relates to the writhe, which fraction of helicity\\u000ais contained in writhe, and how much helicity is exchanged between

Tibor Toeroek; Mitchell A. Berger; Bernhard Kliem

2010-01-01

273

UNDERSTANDING MAGNETIC STRUCTURE IN THE SOLAR CORONA THROUGH TOPOLOGICAL ANALYSIS  

Microsoft Academic Search

The next generation of solar telescopes will quickly pro- duce a huge quantity of high-quality vector magnetogram data requiring analysis. Realistic magnetic fieldline ex- trapolations (e.g. nonlinear force-free) are useful but can be overcrowded and difficult to interpret, as well as time consuming. Focussing on the magnetic topology is an el- egant way to pick out the key features of

R. C. Maclean; C. E. Parnell; I. De Moortel; E. R. Priest

274

Saddle Structures and Magnetic Nulls in the Solar Corona  

Microsoft Academic Search

Coronal plasma fills the magnetic flux tubes and thus visualises the topology of the magnetic field. Specific saddle structures correspond to magnetic singularities of X-type. Two-dimensional chromospheric saddles are close to the possible intersections of the separators with the chromosphere. The saddle-like structures visible in some soft X-ray solar images obtained by Yohkoh SXTarise in a quadrupolar magnetic configuration which

Boris Filippov

1999-01-01

275

Semiempirical Two-Dimensional Magnetohydrodynamic Model of the Solar Corona and Interplanetary Medium  

NASA Technical Reports Server (NTRS)

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 Skylub 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 comes from that developed by Guhathakurta and coworkers. The electron density model is extended into interplanetary space by using electron densities derived from the Ulysses plasma instrument. The model also requires an estimate of the solar wind velocity as a function of heliographic latitude and radial component of the magnetic field at 1 AU, both of which can be provided by the Ulysses spacecraft. The model makes estimates as a function of radial distance and latitude of various fluid parameters of the plasma such as flow velocity V, effective temperature T(sub eff), and effective heat flux q(sub eff), which are derived from the equations of conservation of mass, momentum, and energy, respectively. The term effective indicates that wave contributions could be present. The model naturally provides the spiral pattern of the magnetic field far from the Sun and an estimate of the large-scale surface magnetic field at the Sun, which we estimate to be approx. 12 - 15 G. The magnetic field model shows that the large-scale surface magnetic field is dominated by an octupole term. The model is a steady state calculation which makes the assumption of azimuthal symmetry and solves the various conservation equations in the rotating frame of the Sun. The conservation equations are integrated along the magnetic field direction in the rotating frame of the Sun, thus providing a nearly self-consistent calculation of the fluid parameters. The model makes a minimum number of assumptions about the physics of the solar corona and solar wind and should provide a very accurate empirical description of the solar corona and solar wind Once estimates of mass density rho, flow velocity V, effective temperature T(sub eff), effective heat flux q(sub eff), and magnetic field B are computed from the model and waves are assumed unimportant, all other plasma parameters such as Mach number, Alfven speed, gyrofrequency, etc. can be derived as a function of radial distance and latitude from the Sun. The model can be used as a planning tool for such missions as Slar Probe and provide an empirical framework for theoretical models of the solar corona and solar wind The model will be used to construct a semiempirical MHD description of the steady state solar corona and solar wind using the SOHO Large Angle Spectrometric Coronagraph (LASCO) polarized brightness white-light coronagraph data, SOHO Extreme Ultraviolet Imaging Telescope data, and Ulysses plasma data.

Sittler, Edward C., Jr.; Guhathakurta, Madhulika

1999-01-01

276

Induced emission of Alfvén waves in inhomogeneous streaming plasma: implications for solar corona heating and solar wind acceleration.  

PubMed

The results of a self-consistent kinetic model of heating the solar corona and accelerating the fast solar wind are presented for plasma flowing in a nonuniform magnetic field configuration of near-Sun conditions. The model is based on a scale separation between the large transit or inhomogeneity scales and the small dissipation scales. The macroscale instability of the marginally stable particle distribution function compliments the resonant frequency sweeping dissipation of transient Alfvén waves by their induced emission in inhomogeneous streaming plasma that provides enough energy for keeping the plasma temperature decaying not faster than r(-1) in close agreement with in situ heliospheric observations. PMID:23863008

Galinsky, V L; Shevchenko, V I

2013-07-01

277

The Funnel Geometry of Open Flux Tubes in the Low Solar Corona Constrained by O VI and Ne VIII Outflow  

NASA Technical Reports Server (NTRS)

Model calculations show that observed outflow velocities of order 7-10 km/s of C IV and O VI ions, and 15-20 km/s of Ne VIII ions, are not only consistent with models of the solar wind from coronas holes, but also place unique constraints on the degree of flow tube expansion as well as the location of the expansion in the transition region/lower corona.

Byhring, Hanne S.; Esser, Ruth; Lie-Svendsen, Oystein

2008-01-01

278

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

279

Acceleration of suprathermal electrons by resonant interaction with whistler waves in the solar corona and wind  

NASA Astrophysics Data System (ADS)

Observations of solar wind electron velocity distribution functions (VDFs) show destinctive deviations from Maxwellian distributions. The number of suprathermal electrons is strongly enhanced. These electron VDFs can be fitted by kappa distributions, or are described as core and halo population. A model for the acceleration of suprathermal electrons is presented. It is based on resonant interaction between electrons and whistler waves. The wave-electron interaction is described within the framework of quasilinear theory and leads to pitch-angle diffusion of the electrons in the reference frame of the waves. Thus, it is possible to accelerate electrons from relatively small negative v\\| to high v_{perp. The higher the wave phase speed, estimated by the electron Alfvén speed, the more energy the electrons can gain. To study this mechanism in detail and to investigate the overall evolution of an electron VDF from the corona into the solar wind, a kinetic model for the electrons is developed. The geometry and plasma conditions of a coronal funnel and fast solar wind are used as a background for the kinetic calculations. Beside the wave-electron interaction, the model includes the effects of the inhomogenous background conditions, the gravitational and electric fields, and Coulomb collisions. From the variation of the Alfvén speed with height it follows that the electron acceleration mechanism should be most effective in the corona, while solar wind electrons hardly gain energy. A study of the relaxation process of an electron VDF with suprathermal tails under typical coronal conditions shows that a coronal origin of the suprathermal tails indeed is possible. Simulation results from the corona up into the interplanetary space and in the energy range of several keV are presented. At the lower bound of the simulation box, a power law spectrum of whistler waves enters the box and propagates anti-sunwards. The electron VDF shows deviations from a Maxwellian that are in coincidence with the pitch-angle diffusion in the wave frame as it is expected from theory. Towards interplanetary space, the mirror force in the opening magnetic field geometry focuses the electrons towards a narrow ``strahl''. The resonant absorption of the whistler waves in the corona results in a considerable enhancement of solar wind suprathermal electron fluxes, as they are observed. Simulations with an electron energy range expanded up to 100 keV are also discussed.

Vocks, C.; Mann, G.

2003-04-01

280

The thermal and spatial structure of the solar corona over the cycle and its implication for the coronae of inactive stars  

NASA Astrophysics Data System (ADS)

We use spectral (SOHO/SUMER and Hinode/EIS) and imaging (Hinode/XRT and SDO/AIA) solar coronal data to systematically measure the thermal structure of different types of solar features (coronal hole, quiet Sun, X-ray bright points, active regions...), and how they vary over the solar cycle. We use a combination of these structures to construct a model for the quiet corona of the inactive G8V star tau Ceti, which is a candidate stellar analog of a solar magnetic minimum. Since tau Ceti is significantly metal-poor relative to the Sun, we reconstruct the solar results with corresponding lower metallicities to generate more appropriate coronal structures.

Testa, P.; Landi, E.; Saar, S.

2012-12-01

281

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

282

Oscillation analysis using optical flow: Application to an EUV movie of the solar corona  

NASA Astrophysics Data System (ADS)

Movies of the solar corona in Extreme UltraViolet (EUV) bandpasses exhibit complex patterns of magnetically structured plasma features surrounding the solar photosphere. Among the various phenomena to be observed in the EUV movies, coronal oscillations are an essential process for determining physical parameters of the plasma. In this paper we demonstrate the ability of our motion estimation algorithm to explore and analyse the oscillating motions of coronal loops present in EUV image sequences. The motion fields of each image pair in the sequence are estimated; selected features are tracked using the motion estimation to form trajectories. The oscillating features are then selected from the Morlet wavelet analysis of the trajectories that provides parameters such as local oscillation period. The proposed method will be particularly useful to process datasets expected from new solar missions.

Gissot, Samuel; Hochedez, J.-F.

2008-07-01

283

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.

284

Generalized Squashing Factors for Covariant Description of Magnetic Connectivity in the Solar Corona  

NASA Technical Reports Server (NTRS)

The study of magnetic connectivity in the solar corona reveals a need to generalize the field line mapping technique to arbitrary geometry of the boundaries and systems of coordinates. Indeed, the global description of the connectivity in the corona requires the use of the photospheric and solar wind boundaries. Both are closed surfaces and therefore do not admit a global regular system of coordinates. At least two overlapping regular systems of coordinates for each of the boundaries are necessary in this case to avoid spherical-pole-like singularities in the coordinates of the footpoints. This implies that the basic characteristic of magnetic connectivity-the squashing degree or factor Q of elemental flux tubes, according to Titov and coworkers-must be rewritten in covariant form. Such a covariant expression of Q is derived in this work. The derived expression is very flexible and highly efficient for describing the global magnetic connectivity in the solar corona. In addition, a general expression for a new characteristic Q1, which defines a squashing of the flux tubes in the directions perpendicular to the field lines, is determined. This new quantity makes it possible to filter out the quasi-separatrix layers whose large values of Q are caused by a projection effect at the field lines nearly touching the photosphere. Thus, the value Q1 provides a much more precise description of the volumetric properties of the magnetic field structure. The difference between Q and Q1 is illustrated by comparing their distributions for two configurations, one of which is the Titov-Demoulin model of a twisted magnetic field.

Titov, V. S.

2007-01-01

285

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

286

Electrodynamic Dust Shield for Solar Panels on Mars  

NASA Technical Reports Server (NTRS)

The Materials Adherence Experiment on the Mars Pathfinder mission measured an obscuration of the solar arrays due to dust deposition at a rate of about 0.2 8% per day. It was estimated that settling dust may cause degradation in performance of a solar panel of between 22% and 89% over the course of two years [1, 2]. These results were obtained without the presence of a global dust storm. Several types of adherence forces keep dust particles attached to surfaces. The most widely discussed adherence force is the electrostatic force. Laboratory experiments [3] as well as indirect evidence from the Wheel Abrasion Experiment on Pathfinder [4] indicate that it is very likely that the particles suspended in the Martian atmosphere are electrostatically charged.

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

2004-01-01

287

Helium and minor ions in the corona and solar wind - Dynamics and charge states  

NASA Technical Reports Server (NTRS)

A theoretical model of the acceleration region of the solar wind with major species (p, alpha, e) and minor ions (e.g., He-3, C, O, Mg, Si) is presented. Observed n(e)-profiles and the equations of continuity and momentum are used to calculate profiles of T, n, and u for all species, as well as charge states of minor ions. The disagreement of the results of a pure p-e model with observations is discussed in some detail, and it is shown that a model consistent with observations both in the corona and at 1 AU requires a finite abundance of He(2+). This model predicts a strong enhancement of He/H in the lower corona. The results for the frozen-in charge states in the p-alpha-e model are in agreement with measurements in the low speed solar wind, especially for the well determined pair O(6+)/O(7+). Finally, a model for a coronal hole is investigated and it is found that wave pressure is necessary to model successfully the observed solar wind speeds and abundances. Although various simplifying assumptions had to be introduced, care was taken to ensure that the model remains physically consistent, i.e., that the same physics is used for the major species as well as the minor ions.

Buergi, A.; Geiss, J.

1986-01-01

288

Spatio - Temporal Organization of the Intermittent Irradiance in the Quiet Solar Corona  

NASA Astrophysics Data System (ADS)

Using data from the EUVI instrument on board the STEREO spacecraft, we show, for the first time, that energy release events in the quiet solar corona exhibit random occurrence times described by an exponential probability distribution of interevent intervals exceding the charateristic Alfven transit time, and the temporal correlation dimension equal to one. This random temporal behavior is accompanied by a pronounced spatial clustering of event locations which mimics the supergranulation pattern of the underling photospheric network. Random temporal organization of the quiet Sun revealed by two independent statistical techniques is in a sharp contrast with power-law interevent time distributions of flaring events in solar active regions reported in previous studies. We propose that quiet solar corona, which is believed to be responsible to the bulk coronal heating, operates as a critical avalanching system driven by spatially nonuniform injection of the photospheric magnetic flux. Graph analysis of nearly-simultaneous dissipation events suggests that quiet-Sun avalanches may involve spatially disconnected sympathetic brightenings interacting across vast coronal distances.

Uritsky, Vadim; Davila, Joseph

2014-05-01

289

Heating of the solar and stellar coronae: a review  

NASA Astrophysics Data System (ADS)

Despite great advances in observations and modelling, the problem of solar and stellar heating still remains one of the most challenging problems of space physics. To find a definite answer to what sort of mechanisms act to heat the plasma to a few million degrees requires a collaborative effort of small scales observations, large capacity numerical modelling and complicated theoretical approaches. A unique theory should incorporate aspects such as the generation of energy, its transport and dissipation. Up to now, the first two problems are rather clarified. However, the modality of transfer of magnetic or kinetic energy into heat is a question still awaiting for an answer. In the present paper we review the various popular heating mechanisms put forward in the existing extensive literature. The heating processes are, somewhat arbitrarily, classified as hydrodynamic, magnetohydrodynamic or kinetic based on the characteristics of the model medium. These mechanisms are further divided based on the time scales of the ultimate dissipation involved (i.e. AC and DC heating, turbulent heating). In particular, special attention is paid to discuss shock dissipation, mode coupling, resonant absorption, phase mixing, and, reconnection. Finally, we briefly review the various heating mechanisms proposed to heat other stars.

Erdélyi, R.; Ballai, I.

2007-10-01

290

Surface and body waves in magnetic flux tubes. [in solar convection zone, photosphere, and corona  

NASA Technical Reports Server (NTRS)

The dispersion relation of surface and body waves in a magnetic flux tube is studied in detail. The properties of the fast and slow bodywaves are described in terms of the filtering characteristics of the flux tube. In addition to the axisymmetric and nonaxisymmetric distinction between the modes, an additional distinction is made between the fundamental mode and the rest of the modes. New results concerning the thin and large flux tube approximation are derived. The behavior of surface and body waves in the solar convection zone, photosphere, and corona is discussed.

Abdelatif, T. E.

1988-01-01

291

High resolution mapping of the magnetic field of the solar corona  

NASA Technical Reports Server (NTRS)

The mapping of the current-free magnetic field of the solar corona and the reliability of the spherical harmonic analysis of the photospheric magnetic field pattern are improved by data with much greater dynamic range and spatial resolution than previously available and a new algorithm which permits spherical harmonic expansion to a much higher value of the principal index. Coronal field maps can be drawn for local regions, for just the open field lines, and for various spatial resolutions on a global scale.

Altschuler, M. D.; Levine, R. H.; Stix, M.; Harvey, J.

1977-01-01

292

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

2007-07-13

293

Sub-arcsecond observations of the solar X-ray corona  

NASA Technical Reports Server (NTRS)

Results from a high-resolution multi-layer-coated X-ray imaging telescope, part of the Normal Incidence X-ray Telescope sounding rocket payload are presented. Images of the peak of a two-ribbon flare showed detailed structure within each ribbon, as well as the expected bright arches of emission connecting the ribbons. The number of X-ray bright points is small, consistent with predictions based on the previous solar cycle. Topology of the magnetic structure is complex and highly tangled, implying that the magnetic complexity of the photosphere is paralleled in the corona.

Golub, L.; Nystrom, G.; Herant, M.; Kalata, K.; Lovas, I.

1990-01-01

294

Basic Physics of Collisionless Three-Dimensional Reconnection in the Solar Corona Related to Yohkoh Observations  

NASA Astrophysics Data System (ADS)

New results concerning magnetic reconnection in the solar corona are reviewed. We apply the collisionless 3D reconnection theory - more exactly, the model of a high-temperature turbulent-current non-neutral current sheet - to the coronal conditions derived from the observations with the HXT and SXT onboard Yohkoh. New interpretations are discussed of the Yohkoh data on the site and mechanism of magnetic energy transformation into kinetic and thermal energies of superhot plasmas and accelerated high-energy particles. Open issues are the focus of our attention

Somov, B. V.; Kosugi, T.; Masuda, S.; Sakao, T.

295

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

296

Formation and Reconnection of Three-Dimensional Current Sheets in the Solar Corona  

NASA Technical Reports Server (NTRS)

Current-sheet formation and magnetic reconnection are believed to be the basic physical processes responsible for much of the activity observed in astrophysical plasmas, such as the Sun s corona. We investigate these processes for a magnetic configuration consisting of a uniform background field and an embedded line dipole, a topology that is expected to be ubiquitous in the corona. This magnetic system is driven by a uniform horizontal flow applied at the line-tied photosphere. Although both the initial field and the driver are translationally symmetric, the resulting evolution is calculated using a fully three-dimensional magnetohydrodynamic (3D MHD) simulation with adaptive mesh refinement that resolves the current sheet and reconnection dynamics in detail. The advantage of our approach is that it allows us to apply directly the vast body of knowledge gained from the many studies of 2D reconnection to the fully 3D case. We find that a current sheet forms in close analogy to the classic Syrovatskii 2D mechanism, but the resulting evolution is different than expected. The current sheet is globally stable, showing no evidence for a disruption or a secondary instability even for aspect ratios as high as 80:1. The global evolution generally follows the standard Sweet- Parker 2D reconnection model except for an accelerated reconnection rate at a very thin current sheet, due to the tearing instability and the formation of magnetic islands. An interesting conclusion is that despite the formation of fully 3D structures at small scales, the system remains close to 2D at global scales. We discuss the implications of our results for observations of the solar corona. Subject Headings: Sun: corona Sun: magnetic fields Sun: reconnection

Edmondson, J. K.; Antiochos, S. K.; DeVore, C. R.; Zurbuchen, T. H.

2010-01-01

297

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

298

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

299

NASA Sun-Earth Connections Theory Program: The Structure and Dynamics of the Solar Corona and Inner Heliosphere  

NASA Technical Reports Server (NTRS)

This report covers technical progress during the fourth quarter of the second year of NASA Sun-Earth Connections Theory Program (SECTP) contract 'The Structure and Dynamics of the Solar Corona and Inner Heliosphere,' NAS5-99188, between NASA and Science Applications International Corporation, and covers the period May 16,2001 to August 15, 2001. Under this contract SAIC and the University of California, Irvine (UCI) have conducted research into theoretical modeling of active regions, the solar corona, and the inner heliosphere, using the MHD model.

Mikic, Zoran; Grebowsky, Joseph M. (Technical Monitor)

2001-01-01

300

Exploring wave propagation in the outer solar corona using the Accelerating Expanding Box  

NASA Astrophysics Data System (ADS)

Magnetic field depressions are ubiquitous in the solar wind: in situ observations provide evidence of such drops in the magnetic field magnitude at different latitudes (from the ecliptic plane up to near-polar latitudes) over a wide range of heliocentric distances (0.3 - 17 AU). Such structures are almost pressure balanced and quasi perpendicular to the average magnetic field. In spite of such well-documented observations, the question remains as to where an how these magnetic field depressions are generated, and weather they are stable or not. Two major paradigms are usually invoked to interpret these magnetic structures, the mirror instability on the one hand, and solitary waves on the other hand. In addition, a realistic description of solar wind dynamics requires that the basic effects of its inhomogeneity are taken into account. We introduce here the "Accelerating Expanding Box" model for the purpose of studying wave propagation from the accelerating region of the solar wind, where the solar wind is most inhomogeneous, out to large heliocentric distances. We propose a self-consistent study of the evolution of magneto-hydrodynamic waves by showing first results on wave mode coupling and subsequent formation of structures due to the expansion. The aim is to highlight the role of the solar wind expansion in both the temporal and spatial evolution of MHD waves propagating out from the lower corona, and how the inhomogeneity, which sets in because of the radial expansion of the solar wind, act to modify the properties of the waves themselves.

Tenerani, Anna; Velli, Marco

2014-05-01

301

Observing the solar corona with a tunable Fabry-Perot filter.  

PubMed

A solid Fabry-Perot etalon with a 0.16 A passband was used during the 180 s solar eclipse of 2006 for rapid scans of an emission line of the solar corona. The etalon was a Y-cut lithium niobate wafer coated with reflective and conductive (ITO) layers. Voltage applied perpendicular to the etalon face produced a passband shift of 0.0011 A V(-1). During the eclipse, 18 filtergrams were obtained at six 0.22 A steps across the profile of the forbidden [Fe X] spectral emission line at 6374.4 A, which results from the 10(6) K coronal plasma. The 9.3 x 9.3 arcmin field of view showed the structure of the corona above a newly emerged sunspot region. We discuss tests performed on the etalon before and after the eclipse. We also discuss the coronal observations, which show some features with 10 km s(-1) velocities in the line of sight. PMID:19122714

Noble, Matthew W; Rust, David M; Bernasconi, Pietro N; Pasachoff, Jay M; Babcock, Bryce A; Bruck, Megan A

2008-11-01

302

The Convex-Hull Method for Solving Differential Emission Measures in the Solar Corona  

NASA Astrophysics Data System (ADS)

The Differential Emission Measure (DEM) describes the temperature distribution of the solar corona, but the inversion of the observations through the instrument's temperature response functions is mathematically ill-posed and typically under-constrained. The most commonly used techniques (e.g., the EM Loci Method, forward-fitting iterators, etc.) each have their drawbacks, but most importantly, they do not guarantee the solution is the globally minimum chi-square solution nor provide a way to quantitatively explore the range of solutions in the neighborhood of the globally minimum solution, which is necessary for properly evaluating levels of confidence. The Convex-Hull Method surmounts the mathematical difficulties of the DEM inversion, providing a more accurate characterization of the solution space with which to evaluate physical models against observations. I demonstrate how this method can be used to constrain the set of temperature distributions observed in the solar corona. This work was supported under contract SP02H1701R from Lockheed-Martin to SAO, and under contract NNM07AB07C from NASA to SAO.

Weber, Mark A.

2011-05-01

303

Fast magnetoacoustic wave trains in magnetic funnels of the solar corona  

NASA Astrophysics Data System (ADS)

Context. Fast magneto-acoustic waves are highly dispersive in waveguides, so they can generate quasi-periodic wave trains if a localised, impulsive driver is applied. Such wave trains have been observed in the solar corona and may be of use as a seismological tool since they depend upon the plasma structuring perpendicular to the direction of propagation. Aims: We extend existing models of magnetoacoustic waveguides to consider the effects of an expanding magnetic field. The funnel geometry employed includes a field-aligned density structure. Methods: We performed 2D numerical simulations of impulsively generated fast magneto-acoustic perturbations. The effects of the density contrast ratio, density stratification, and spectral profile of the driver upon the excited wave trains were investigated. Results: The density structure acts as a dispersive waveguide for fast magneto-acoustic waves and generates a quasi-periodic wave train similar to previous models. The funnel geometry leads to generating additional wave trains that propagate outside the density structure. These newly discovered wave trains are formed by the leakage of transverse perturbations, but they propagate upwards owing to the refraction caused by the magnetic funnel. Conclusions: The results of our funnel model may be applicable to wave trains observed propagating in the solar corona. They demonstrate similar properties to those found in our simulations.

Pascoe, D. J.; Nakariakov, V. M.; Kupriyanova, E. G.

2013-12-01

304

Global MHD Modeling of the Solar Corona and Inner Heliosphere for the Whole Heliosphere Interval  

NASA Astrophysics Data System (ADS)

Whole Heliosphere Interval (WHI), which runs from March 20 through April 16, 2008, and coincides with Carrington Rotation (CR) 2068 is providing a unique opportunity for both observers and modelers to collaborate in an effort to understand the three-dimensional structure and evolution of the solar corona and inner heliosphere. It builds on several previous "Whole Sun Month" intervals, which proved to be exceptionally successful. In support of WHI, we have developed a global MHD model solution for CR 2068. Our model, which includes energy transport processes, such as coronal heating, conduction of heat parallel to the magnetic field, radiative losses, and the effects of Alfven waves, is capable of producing significantly better estimates of the plasma temperature and density in the corona than have been possible in the past. With such a model, we can compute emission in extreme ultraviolet (EUV) and X-ray wavelengths, as well as scattering in polarized white light. Additionally, from our heliospheric solutions, we can deduce magnetic field and plasma parameters along specific spacecraft trajectories. In this presentation, we make detailed comparisons of both remote solar and in situ observations with the model results. Such comparisons allow us and (3) Provide support for (or against) assumptions in the MHD model, such as which physical processes are (or are not) important. The results of these simulations (including post-processing analysis and visualization tools) will be made available to the scientific community at http://predsci.com/WHI.

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

2008-12-01

305

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

306

Kinematics of Waves in the Solar Corona: Analyzing Potential Shock Waves to Predict Solar Energetic Particle Fluxes in Space Weather  

NASA Astrophysics Data System (ADS)

Shock waves associated with coronal mass ejections (CMEs) are known to be one of two major sources of large solar energetic particle (SEP) events responsible for instigating dangerous space weather that can damage satellites and put the health of astronauts in space at risk. In particular, shocks in the solar corona have been shown to produce large fluxes of SEPs, each of which has energy above 10 MeV, in just minutes. We conducted a thorough search for off-limb shock wave candidate events in the solar corona from January 2011 to June 2013 as well as a kinematic analysis of these events. We are interested in studying these shock waves so that we can better predict when large SEP events will occur. To identify shock wave candidates, we used the data catalogs from the Atmosphere Imaging Assembly (AIA), which provided a 12-second high cadence necessary to produce more data on each individual wave and also make it possible to distinguish waves from other events. We searched only for off-limb events, as their profiles and radial propagation are easier to analyze. In 30 months of data, we identified 15 candidate events, 7 of which were associated with Type II radio bursts - one of the better indicators that a candidate event is a shock wave. We present the wave morphology and kinematics for these events.

Hammer, Michael; Kozarev, K. A.; Korreck, K. E.

2014-01-01

307

Predicting minima and maxima of solar cycles based on prominences and emission corona  

NASA Astrophysics Data System (ADS)

Predicting maxima and minima of solar activity cycles, including their magnitude, is important not only for a better understanding of the underlying physical processes on the Sun, but also from the point of view of solar-terrestrial relations. Such predictions employ a variety of well-know relations like those between even and odd cycles, or between the AA index and the Wolf number. Our prediction is based on the properties of large-scale meridional motions of prominences and the areas of enhanced intensities of the green line corona. We predict two maxima of cycle 24; first at the end of 2011, the other at the end of 2012. Although our method is unable to predict the magnitude of cycles, a relatively stable structural pattern of the above-mentioned meridional motions makes this method suitable for long-term predictions of the maxima/minima timings up to 2025.

Minarovjech, M.; Rušin, V.; Saniga, M.

2011-10-01

308

The connection between pressure waves in the corona and solar energetic particle events  

NASA Astrophysics Data System (ADS)

We combine ultraviolet and white-light images obtained by the Solar Dynamics Observatory (SDO) and the Solar-Terrestrial Relations Observatory (STEREO) to track, in the lower corona, the spatial and temporal evolution of pressure waves associated with the onset of Coronal Mass Ejections (CMEs). We use ideal geometrical 3-D surfaces (spheroids, ellipsoids) to follow with time the spatial location of pressure variations observed in EUV and white-light images. This fitting technique provides a tracking of the evolution of coronal shocks from the Sun to 20 solar radii. We use a simple model of the distribution of interplanetary magnetic field lines to determine the footpoint locations of field lines connecting the lower corona to the points of in-situ measurements. We extract the velocity 3-D vector along the shock normal for different intersecting magnetic field lines connected to in-situ spacecraft. We use in-situ measurements of the onset of solar energetic particle events (SEPs) to determine their release time near the Sun. We concentrate on the proton-rich events detected by the near-Earth spacecraft as well as the STEREO spacecraft from 2011 to 2013. We (1) determine the height and spatial extent of the pressure waves at the SEP release times, (2) compare the longitudinal extent of SEP events with the extent of the pressure waves, (3) compare the kinematic properties of pressure waves launched over widely separated longitudes with the intensity of proton-rich events. We discuss the successes and challenges faced when interpreting SEP events in terms of the speed and geometry of coronal shocks.

Rouillard, A. P.; Vourlidas, A.; Tylka, A. J.; Thernisien, A. F.; Cohen, C. M.; Ng, C. K.; Mewaldt, R. A.; Mason, G. M.

2013-12-01

309

The MHD simulation of the solar corona using the synoptic frame map of the solar photospheric magnetic field and the SOHO\\/EIT coronal temperature map  

Microsoft Academic Search

In simulation studies of the solar corona the synoptic map format data of the solar photospheric magnetic field have been used as the boundary value to specify the period of interest This approach successfully works however there remain two problems The first one is that the synoptic maps are constructed by collecting the data made at different date for example

K. Hayashi; X. P. Zhao; B. Benevolenskaya

2006-01-01

310

A new method to study the large-scale structure of the solar corona on the basis of solar wind measurements.  

NASA Astrophysics Data System (ADS)

On the basis of selective measurements of proton and ?-particle hydrodynamical parameters and of the magnetic field on board the Prognoz 7 satellite the structure of the solar wind is studied and is compared with the possible structure of the solar corona.

Ermolaev, Yu. I.

1990-12-01

311

A new approach to the study of the large-scale structure of the solar corona on the basis of measurements of solar wind parameters.  

NASA Astrophysics Data System (ADS)

The structure of the solar wind is studied from selective measurements of the hydrodynamic parameters of protons and ? particles, as well as the magnetic field parameters, and it is suggested that it is related to the structure of the solar corona.

Ermolaev, Yu. I.

1991-05-01

312

The Impact of Solar Activity on the Earth Upper Atmosphere as Inferred from the CORONAS-F Scientific Experiments  

NASA Astrophysics Data System (ADS)

The chapter is devoted to the first results of processing and analysis of data on the absorption of solar XUV radiation in the Earth upper atmosphere measured onboard the CORONAS-F space mission. The variability of the Earth's upper atmosphere associated with solar activity has been studied by analyzing the orbital evolution of the CORONAS-F satellite. Experimental data have been compared with model calculations of the parameters of the upper atmosphere. The mathematical model of the Earth upper atmosphere (WMA01) developed at IZMIRAN is described in general terms. A list of active events on the Sun and associated processes in the Earth magnetosphere recorded during the CORONAS-F flight time (2001-2005) is presented. The comparison of model calculations with the experimental satellite data shows that the Earth atmosphere models available need updating. The possible ways to attack this problem are discussed.

Boldyrev, S. I.; Egorov, I. A.; Zhitnik, I. A.; Ivanov-Kholodny, G. S.; Ignat'yev, S. P.; Ishkov, V. N.; Kolomiitsev, O. P.; Kuzin, S. V.; Kuznetsov, V. D.; Osin, A. I.

313

Charged Dust Dynamics in the Solar System  

Microsoft Academic Search

In most space environments, dust particles are exposed to plasmas and UV radiation and, consequently, carry electrostatic charges. Their motion is influenced by electric and magnetic fields in addition to gravity, drag, and radiation pressure. On the surface of the Moon, in planetary rings, or at comets, for example, electromagnetic forces can shape the spatial and size distribution of micron-sized

Mihaly Horanyi

1996-01-01

314

Solar Wind Mass-Loading Due to Dust  

NASA Astrophysics Data System (ADS)

Collisionless mass-loading by interplanetary dust particles is expected to cause a significant disruption in the flow of the solar wind. Dust particles near the Sun can become a source of ions and neutrals due to evaporation and sputtering. This mass-loading effect can lead to the formation of collisionless shocks, as it was first discussed in the case of solar wind interaction with comets. This effect can also be compared with a de Laval nozzle, which behaves differently between subsonic and supersonic flows. We investigate the effects of mass-loading resulting from sun-grazing comets or collisions in the vicinity of the Sun, where the solar wind transitions from subsonic to supersonic speeds. We implement a hydrodynamic numerical model to generate a steady wind extending out to the inner heliosphere. Dust is introduced through a set of mass-loading source terms, and the model is evolved using a shock-capturing scheme. These results are relevant for understanding the acceleration of the solar wind and possible changes in its composition due to dust.

Rasca, A.; Horanyi, M.

2011-12-01

315

Solar wind mass-loading due to dust  

NASA Astrophysics Data System (ADS)

Collisionless mass-loading by interplanetary dust particles is expected to cause a significant disruption in the flow of the solar wind. Dust particles near the Sun can become a source of ions and neutrals due to evaporation and sputtering. This mass-loading effect can lead to the formation of collisionless shocks, as it was first discussed in the case of solar wind interaction with comets. This effect can also be compared with a de Laval nozzle, which behaves differently between subsonic and supersonic flows. We investigate the effects of mass-loading resulting from sun-grazing comets or collisions by larger bodies in the vicinity of the Sun, where the solar wind transitions from subsonic to supersonic speeds. We look at results obtained using a simple 1D hydrodynamic model to mass-load ionized dust into the the wind near the sonic point, which are relevant for understanding the acceleration of the solar wind and possible changes in its composition due to dust.

Rasca, A. P.; Horányi, M.

2013-06-01

316

New View of Gas and Dust in the Solar Nebula  

Microsoft Academic Search

The recognizable components in meteorites differ in their relative abundances of the three oxygen isotopes (16O, 17O, and 18O). In particular, the amount of 16O varies from being like that of the Earth to substantially enriched compared to the other two isotopes. The current explanation for this interesting range in isotopic composition is that dust and gas in the solar

G. J. Taylor

2010-01-01

317

Solar wind pressure on interplanetary dust  

Microsoft Academic Search

The pseudo-Poynting-Robertson effect on an interplanetary grain due to solar wind bombardments is examined with careful consideration for sputtering of a grain and for the velocity dispersion of the solar wind particles. It is found that for water-ice and obsidian grains with radii in the range 0.01-100 micrometers, the retarding force due to solar wind is stronger than, and of

T. Mukai; T. Yamamoto

1982-01-01

318

FORMATION AND RECONNECTION OF THREE-DIMENSIONAL CURRENT SHEETS IN THE SOLAR CORONA  

SciTech Connect

Current-sheet formation and magnetic reconnection are believed to be the basic physical processes responsible for much of the activity observed in astrophysical plasmas, such as the Sun's corona. We investigate these processes for a magnetic configuration consisting of a uniform background field and an embedded line dipole, a topology that is expected to be ubiquitous in the corona. This magnetic system is driven by a uniform horizontal flow applied at the line-tied photosphere. Although both the initial field and the driver are translationally symmetric, the resulting evolution is calculated using a fully three-dimensional (3D) magnetohydrodynamic simulation with adaptive mesh refinement that resolves the current sheet and reconnection dynamics in detail. The advantage of our approach is that it allows us to directly apply the vast body of knowledge gained from the many studies of two-dimensional (2D) reconnection to the fully 3D case. We find that a current sheet forms in close analogy to the classic Syrovatskii 2D mechanism, but the resulting evolution is different than expected. The current sheet is globally stable, showing no evidence for a disruption or a secondary instability even for aspect ratios as high as 80:1. The global evolution generally follows the standard Sweet-Parker 2D reconnection model except for an accelerated reconnection rate at a very thin current sheet, due to the tearing instability and the formation of magnetic islands. An interesting conclusion is that despite the formation of fully 3D structures at small scales, the system remains close to 2D at global scales. We discuss the implications of our results for observations of the solar corona.

Edmondson, J. K. [NASA Jet Propulsion Laboratory, Pasadena, CA 91109 (United States); Antiochos, S. K. [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); DeVore, C. R. [Naval Research Laboratory, Washington, DC 20375 (United States); Zurbuchen, T. H., E-mail: jkedmond@umich.ed [Department of Atmospheric, Oceanic, and Space Science, University of Michigan, Ann Arbor, MI 48105 (United States)

2010-07-20

319

Formation and Reconnection of Three-dimensional Current Sheets in the Solar Corona  

NASA Astrophysics Data System (ADS)

Current-sheet formation and magnetic reconnection are believed to be the basic physical processes responsible for much of the activity observed in astrophysical plasmas, such as the Sun's corona. We investigate these processes for a magnetic configuration consisting of a uniform background field and an embedded line dipole, a topology that is expected to be ubiquitous in the corona. This magnetic system is driven by a uniform horizontal flow applied at the line-tied photosphere. Although both the initial field and the driver are translationally symmetric, the resulting evolution is calculated using a fully three-dimensional (3D) magnetohydrodynamic simulation with adaptive mesh refinement that resolves the current sheet and reconnection dynamics in detail. The advantage of our approach is that it allows us to directly apply the vast body of knowledge gained from the many studies of two-dimensional (2D) reconnection to the fully 3D case. We find that a current sheet forms in close analogy to the classic Syrovatskii 2D mechanism, but the resulting evolution is different than expected. The current sheet is globally stable, showing no evidence for a disruption or a secondary instability even for aspect ratios as high as 80:1. The global evolution generally follows the standard Sweet-Parker 2D reconnection model except for an accelerated reconnection rate at a very thin current sheet, due to the tearing instability and the formation of magnetic islands. An interesting conclusion is that despite the formation of fully 3D structures at small scales, the system remains close to 2D at global scales. We discuss the implications of our results for observations of the solar corona.

Edmondson, J. K.; Antiochos, S. K.; DeVore, C. R.; Zurbuchen, T. H.

2010-07-01

320

Formation and Reconnection of Three-Dimensional Current Sheets in the Solar Corona  

NASA Astrophysics Data System (ADS)

Current-sheet formation and magnetic reconnection are believed to be the basic physical processes responsible for much of the activity observed in astrophysical plasmas, such as interchange reconnection at the boundaries between coronal holes and helmet streamers in the Sun's corona. We investigate these processes for a magnetic configuration consisting of a uniform background field and an embedded line dipole, a topology that is expected to be ubiquitous in the corona. This magnetic system is driven by a uniform horizontal flow applied at the line-tied photosphere. Although both the initial field and the driver are translationally symmetric, the resulting evolution is calculated using a fully three-dimensional magnetohydrodynamic (3D MHD) simulation with adaptive mesh refinement that resolves the current sheet and reconnection dynamics in detail. The advantage of our approach is that it allows us to apply directly the vast body of knowledge gained from the many studies of 2D reconnection to the fully 3D case. We find that a current sheet forms in close analogy to the classic Syrovatskii 2D mechanism, but the resulting evolution is different than expected. The current sheet is globally stable, showing no evidence for a disruption or a secondary instability even for aspect ratios as high as 80:1. The global evolution generally follows the standard Sweet-Parker 2D reconnection model except for an accelerated reconnection rate at a very thin current sheet, due to the tearing instability and the formation of magnetic islands. An interesting conclusion is that despite the formation of fully 3D structures at small scales, the system remains close to 2D at global scales. We discuss the implications of our results for observations of the solar corona.

Edmondson, Justin K.; Antiochos, S. K.; DeVore, C.; Velli, M.; Zurbuchen, T. H.

2010-05-01

321

Inner Heliospheric Gas and Dust from Solar Wind Charge Exchange  

NASA Astrophysics Data System (ADS)

The Low Energy Neutral Atom (LENA) imager, launched on the IMAGE spacecraft in March of 2000, detects neutral atoms with energies from 10 eV up to >1 keV. Because LENA has low sensitivity to light and looks directly at the Sun every spin during six months of the year, it has observed a neutral component of the solar wind (NSW) that results when solar wind ions charge exchange with interstellar neutrals, with dust and with the Earth's geocorona [Collier et al., JGR, 106, 24,893, 2001]. We examine long-term variations in the intensity of the counting rate from the solar direction (NSW). Results from year 2001, during which the instrument state remained constant, show a maximum in the count rate between June and July with a long, low count-rate period stretching from mid-November through early March. This annual modulation of solar wind energetic neutral atom flux at the Earth is interpreted as a pronounced variation of the neutral gas column density between the Sun and the Earth with season. This modulation is evidently dominated by interstellar neutral gas and the solar erosion of that gas in the galactic downstream region. It also contains a relatively constant contribution from inner solar system dust and relatively smaller variations produced by solar wind fluctuations and possibly structure in the dust population. The LENA observations place an upper limit on the column density of dust at 1 AU of less than 6x10-19 cm-1. Implications of the LENA data on the interpretation of observations of low frequency electromagnetic waves by Tsurutani et al. [GRL, 21, 633, 1994] will also be considered.

Collier, M. R.; Moore, T. E.; Ogilvie, K. W.; Simpson, D.; Fok, M.; Chornay, D.; Keller, J.; Fuselier, S.; Quinn, J.; Wurz, P.; Wuest, M.; Hsieh, J.; Tsurutani, B.

2002-05-01

322

NASA Sun-Earth Connections Theory Program: The Structure and Dynamics of the Solar Corona and Inner Heliosphere  

NASA Technical Reports Server (NTRS)

This report covers technical progress during the first quarter of the second year of NASA Sun-Earth Connections Theory Program (SECTP). SAIC and the University of California, Irvine (UCI) have conducted research into theoretical modeling of active regions, the solar corona, and the inner heliosphere, using the MHD model.

Mikic, Zoran; Grebowsky, Joseph (Technical Monitor)

2001-01-01

323

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 Đrst 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

324

The Structure and Dynamics of the Solar Corona and Inner Heliosphere-First Quarter First Year Progress Report  

NASA Technical Reports Server (NTRS)

This report details progress during the first quarter of the first year of our Sun-Earth Connections Theory Program (SECTP) contract. Science Applications International Corporation (SAIC) and the University of California, Irvine (UCI) have conducted research into theoretical modeling of active regions, the solar corona, and the inner heliosphere, using the MHD model.

Mikic, Zoran; Grebowsky, J. (Technical Monitor)

2000-01-01

325

EVOLUTION OF THE GLOBAL TEMPERATURE STRUCTURE OF THE SOLAR CORONA DURING THE MINIMUM BETWEEN SOLAR CYCLES 23 AND 24  

SciTech Connect

The combination of differential emission measure tomography with extrapolation of the photospheric magnetic field allows determination of the electron density and electron temperature along individual magnetic field lines. This is especially useful in quiet-Sun (QS) plasmas where individual loops cannot otherwise be identified. In Paper I, this approach was applied to study QS plasmas during Carrington rotation (CR) 2077 at the minimum between solar cycles (SCs) 23 and 24. In that work, two types of QS coronal loops were identified: ''up'' loops in which the temperature increases with height, and ''down'' loops in which the temperature decreases with height. While the first ones were expected, the latter ones were a surprise and, furthermore, were found to be ubiquitous in the low-latitude corona. In the present work, we extend the analysis to 11 CRs around the last solar minimum. We found that the ''down'' population, always located at low latitudes, was maximum at the time when the sunspot number was minimum, and the number of down loops systematically increased during the declining phase of SC-23 and diminished during the rising phase of SC-24. ''Down'' loops are found to have systematically larger values of {beta} than do ''up'' loops. These discoveries are interpreted in terms of excitation of Alfven waves in the photosphere, and mode conversion and damping in the low corona.

Nuevo, Federico A.; Vasquez, Alberto M. [Instituto de Astronomia y Fisica del Espacio (CONICET-UBA) and FCEN (UBA), CC 67-Suc 28, Ciudad de Buenos Aires (Argentina); Huang Zhenguang; Frazin, Richard; Manchester, Ward B. IV; Jin Meng [Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI 48109 (United States)

2013-08-10

326

Solar wind pressure on interplanetary dust  

NASA Astrophysics Data System (ADS)

The pseudo-Poynting-Robertson effect on an interplanetary grain due to solar wind bombardments is examined with careful consideration for sputtering of a grain and for the velocity dispersion of the solar wind particles. It is found that for water-ice and obsidian grains with radii in the range 0.01-100 micrometers, the retarding force due to solar wind is stronger than, and of the same order as, respectively, that due to solar radiation. On the other hand, for magnetite this drag force is always less than that due to solar radiation. In addition, since the wind flow generally comes from the east of the sun, a grain in a prograde orbit suffers a larger retarding force compared with a grain in a retrograde orbit.

Mukai, T.; Yamamoto, T.

1982-03-01

327

Origin of the 10deg 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 communution of material associated with the major Hirayama asteroid families (Dermott et al, Nature, 312, 505-509, 1984), the equilibrium model, or random disruptions in the asteroid belt of small, single asteroids (Sykes and Greenberg, Icarus, 65, 51-69, 1986). The IRAS observations of the zodiacal cloud from which we isolate the dust band profiles have excellent resolution, and the manner in which these profiles change around the sky should allow us to determine the origin of the bands, their radial extent, the size-frequency distribution of the material and the optical properites of the dust itself. The equilibrium model of the dust bands suggests Eos as the parent of the 10deg band pair. In this paper we present results from detailed numerical modeling of the 10deg band pair. We demonstrate that a model composed of dust particles having mean semi-major axis, proper eccentricity and proper inclination equal to those of the Eos family member asteroids, but with a dispersion in proper inclination of 2.5deg , produces a convincing match with observations. Indeed, it is impossible to reproduce the observed profiles of the 10deg band pair without imposing such a dispersion on the dust band material. This result is strong evidence in favor of the equilibrium model.

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

1996-09-01

328

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

329

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

330

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

331

Evidence for mass outflow in the low solar corona over a large sunspot  

NASA Technical Reports Server (NTRS)

Spatially resolved EUV coronal emission-line profiles have been obtained in a solar active region, including a large sunspot, using an EUV imaging spectrograph. Relative Doppler velocities were measured in the lines of Mg IX, Fe XV, and Fe XVI with a sensitivity of 2-3 km/s at 350 A. The only significant Doppler shift occurred over the umbra of the large sunspot, in the emission line of Mg IX (at Te of about 1.1 x 10 exp 6 K). The maximum shift corresponded to a peak velocity toward the observer of 14 +/- 3 km/s relative to the mean of measurements in this emission line made elsewhere over the active region. The magnetic field in the low corona was aligned to within 10 deg of the line of sight at the location of maximum Doppler shift. Depending on the closure of the field, such a mass flow could either contribute to the solar wind or reappear as a downflow of material in distant regions on the solar surface. The site of the source, near a major photospheric field boundary, was consistent with origins of low-speed solar wind typically inferred from interplanetary plasma observations.

Neupert, Werner M.; Brosius, Jeffrey W.; Thomas, Roger J.; Thompson, William T.

1992-01-01

332

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

333

Interaction of relativistic dust grains with the solar radiation field  

NASA Astrophysics Data System (ADS)

The effects of the solar radiation field on the propagation of relativistic dust grains are evaluated. It is concluded that relativistic iron grains with energies about 10 exp 19 eV will melt in the solar radiation field before they reach the Earth's orbit around the sun. However iron grains with lower energies will reach the Earth's orbit but grains travelling from the direction of the sun will melt. This directional anisotropy or fingerprint may be used to search for relativistic dust grains in the primary cosmic rays. The fact that no significant solar system anisotropy has been detected places constraints on the hypothesis that the initiating particles of the extensive air showers are relativistic iron grains.

McBreen, B.; Plunkett, S.; Lambert, C. J.

1993-07-01

334

Solar Array Panels With Dust-Removal Capability  

NASA Technical Reports Server (NTRS)

It has been proposed to incorporate piezoelectric vibrational actuators into the structural supports of solar photovoltaic panels, for the purpose of occasionally inducing vibrations in the panels in order to loosen accumulated dust. Provided that the panels were tilted, the loosened dust would slide off under its own weight. Originally aimed at preventing obscuration of photovoltaic cells by dust accumulating in the Martian environment, the proposal may also offer an option for the design of solar photovoltaic panels for unattended operation at remote locations on Earth. The figure depicts a typical lightweight solar photovoltaic panel comprising a backside grid of structural spars that support a thin face sheet that, in turn, supports an array of photovoltaic cells on the front side. The backside structure includes node points where several spars intersect. According to the proposal, piezoelectric buzzers would be attached to the node points. The process of designing the panel would be an iterative one that would include computational simulation of the vibrations by use of finite- element analysis to guide the selection of the vibrational frequency of the actuators and the cross sections of the spars to maximize the agitation of dust.

Dawson, Stephen; Mardesich, Nick; Spence, Brian; White, Steve

2004-01-01

335

Solar Wind-driven Dust Transport in the Lunar Exosphere  

NASA Astrophysics Data System (ADS)

From the Apollo era there is much evidence to show that lunar horizon glow observed at the terminator is caused by sunlight scattered by dust grains originating from the surface. The dust grains and lunar surface are electrically charged by the Moon's interaction with the local plasma environment and the photoemission of electrons due to solar UV and X-rays. This causes the like-charged surface and dust particles to repel each other, and creates a near-surface electric field. We have previously proposed a simple dynamic dust "fountain" model to explain observations of submicron-sized grains "lofted" to altitudes of up to 100km. In this model charged dust grains follow ballistic trajectories, subsequent to being accelerated upwards through a narrow sheath region by the surface electric field. Discussed here are improvements to the simple fountain model in order to make it more realistic; in particular, we investigate the effects of different surface electric field profiles and the cohesion of the grains on the lunar surface. These dust grains in the exosphere will affect the optical quality of the lunar environment for astronomical observations and interfere with exploration activities.

Vondrak, R. R.; Stubbs, T. J.; Farrell, W. M.

2005-12-01

336

Radio Tracking of a White-Light CME from Solar Corona to Interplanetary Medium  

NASA Technical Reports Server (NTRS)

We analyze the radio emissions associated with a flare/CME event on the sun. For this solar event there were type II radio emissions observed in both the metric and decametric to kilometric wavelength regimes. By comparing the dynamics of the CME with that implied by the frequencies and frequency-drift rates of the type II radio emissions, it is concluded that only the decametric/kilometric type II radio emissions are associated with the CME. We provide the first direct one-to-one comparison between a CME and the associated type II radio emissions. The dynamics implied by the metric type II radio emissions suggest a distinct coronal shock, associated with the flare, which only produces radio emissions in the low corona.

Reiner, M. J.; Kaiser, Michael L.; Plunkett, S. P.; Prestage, N. P.

1999-01-01

337

The nonuniform magnetohydrodynamic nature of the solar corona. II - Generalization of basic solutions  

NASA Astrophysics Data System (ADS)

The method developed recently by Priest (1988) for modeling standing MHD disturbances in the solar corona is extended in several ways. Including inertial effects of the uniform plasma flow distorts the isobars and makes the flow and magnetic field vary with altitude in a manner that depends on the value of the flow speed relative to the cusp speed, the sound speed, and the Alfven speed. More general classes of solutions to the governing equation may be determined by seeking nonseparable solutions with a Green's function technique. Allowing magnetic flux to escape across the side boundaries leads to models which are relevant for coronal holes. The relation of this governing equation to the nonlinear MHD equations is indicated.

de Ville, A.; Priest, E. R.

1989-05-01

338

Detection of a corona of fast oxygen atoms during solar maximum  

NASA Technical Reports Server (NTRS)

A series of twilight interferometric observations of the near infrared O(+)(2P) doublets at 7320 and 7330 A between April 1979 and October 1979 detected excessive amounts of emission at shadow heights above 550 km. The scale height deduced from the vertical brightness profile determined from data taken on September 26, 1979, when the 10.7-cm flux was 231, showed a marked increase above 550 km. The equivalent temperature was estimated to be 4000 K or higher. Observations of the emission line shape with the high-resolution capability of the interferometer substantiated these results by a very apparent progressive broadening of the emission profile between times of low and high shadow height. It is concluded from these results that there exists an atomic oxygen corona overlying the thermosphere during the solar maximum period.

Yee, J. H.; Meriwether, J. W., Jr.; Hays, P. B.

1980-01-01

339

Stereoscopic investigation on plasma density fluctuations in the outer solar corona  

NASA Astrophysics Data System (ADS)

This research note extends a previous work focused on the 2D reconstruction of the spatial distribution and temporal evolution of the plasma density fluctuations in the outer solar corona and based on STEREO COR1-A white-light observations. By using the corresponding total brightness images obtained in the same observational period with the coronagraph COR1-B onboard the "Behind" twin STEREO-B spacecraft, and adopting the same methodological approach as for COR1-A data, it was possible to confirm the results of the previous work and argue for the 3D configuration of the fluctuations of the coronal plasma. This provides further evidence in support of a scenario in which the fluctuating features, which are recurrent and spatially coherent, are localized along the magnetic field lines and points out the crucial role played by the 3D magnetic field topology in the confinement and evolution of the plasma density fluctuations.

Telloni, D.; Antonucci, E.; Dolei, S.; Romano, P.; Spadaro, D.; Ventura, R.

2014-05-01

340

Heating and Turbulence from Magnetic Reconnection, Kinetic Alfven Waves and Whistler Waves in the Solar Corona  

NASA Astrophysics Data System (ADS)

Theory and simulations are used to investigate the expected heating and reconnection rates due to tearing modes and kinetic Alfvén waves (KAW) in configurations with magnetic islands and flux tube loops of various heights/diameters and collisionality regimes. A simple nonlinear electron scale magnetic reconnection model for the magnetic flux and electrostatic potential dynamics is used, as detailed in W. Horton, J.-H. Kim, and F. Militello, Physics of Plasmas 14, 012902 (2007). Collisional terms, electron inertia dispersion and ion polarization currents are included in the dynamical equations. Whistler waves are excited by the small scale dynamics around the X-points, which are investigated with nonlinear wave equations for heating, acceleration and energy transport. Energy densities and Alfvénic Poynting fluxes are evaluated. The fractions of the released magnetic energy that goes into plasma flows, plasma heating and radiation are estimated. This analysis informs solar corona heating theories.

Correa, Cynthia; Horton, Wendel

2010-11-01

341

White light solar corona: an atlas of 1985 K- coronameter synoptic charts, December 1984-December 1985. Technical note  

SciTech Connect

The synoptic observing program of the Mauna Loa Solar Observatory (MLSO) has as its goal the specification of the time-dependent structure of the solar corona. The growth of the low intensity polar regions and ordering of the brighter corona into a band near the equator seen in the second, third, and fourth years of observations (1981-1983) continued through 1984. In 1985, the corona remains in the same general form, with the brightest regions concentrated in a band around the equator, similar to the situation noted near the last solar minimum. The apparent excursions of the darkest regions (polar holes) towards the equator seen at the start of the year become less pronounced with time. However, the area embraced by the highest brightness contours tends to increase throughout the year, perhaps indicating that the corona has gone through its minimum configuration. The material presented here is in a format providing a convenient access to investigators intending to make correlation studies or an intercomparison of standard synoptic data sets.

Sime, D.G.; Garcia, C.; Yasukawa, E.; Lundin, E.; Rock, K.

1986-10-01

342

Hot carbon corona in Mars' upper thermosphere and exosphere: 1. Mechanisms and structure of the hot corona for low solar activity at equinox  

NASA Astrophysics Data System (ADS)

important source reactions for hot atomic carbon on Mars are photodissociation of CO and dissociative recombination of CO+; both reactions are highly sensitive to solar activity and occur mostly deep in the dayside thermosphere. The production of energetic particles results in the formation of hot coronae that are made up of neutral atoms including hot carbon. Some of these atoms are on ballistic trajectories and return to the thermosphere, and others escape. Understanding the physics in this region requires modeling that captures the complicated dynamics of hot atoms in 3-D. This study evaluates the carbon atom inventory by investigating the production and distribution of energetic carbon atoms using the full 3-D atmospheric input. The methodology and details of the hot atomic carbon model calculation are given, and the calculated total global escape of hot carbon from the assumed dominant photochemical processes at a fixed condition, equinox (Ls = 180°), and low solar activity (F10.7 = 70 at Earth) are presented. To investigate the dynamics of these energetic neutral atoms, we have coupled a self-consistent 3-D global kinetic model, the Adaptive Mesh Particle Simulator, with a 3-D thermosphere/ionosphere model, the Mars Thermosphere General Circulation Model to provide a self-consistent global description of the hot carbon corona in the upper thermosphere and exosphere. The spatial distributions of density and temperature and atmospheric loss are simulated for the case considered.

Lee, Yuni; Combi, Michael R.; Tenishev, Valeriy; Bougher, Stephen W.

2014-05-01

343

High-spectral-resolution Observations of the Solar Chromosphere and Corona  

NASA Astrophysics Data System (ADS)

We continue to reduce high-spectral-resolution observations of the solar chromosphere from the Swedish 1-m Solar Telescope (SST) and TRACE; and, at the 29 March 2006 total solar eclipse, of the solar corona in the [Fe XIV] green line and the [Fe X] red line. (a) The SST observations in 2006 used the SOUP Lyot filter to observe H-alpha limb spicules in five positions with 128 milliangstrom resolution for velocity imaging with several cameras to allow restoration of even noisy images. One camera is near H-alpha, providing high S/N images for extracting wavefront information. The other is deliberately defocused for Phase Diversity information. We use Multi-Object Multi-Frame Blind Deconvolution (MOMFBD; momfbd.org), assisted by Michiel Van Noort and Mats Löfdahl (Royal Swedish Academy of Sciences) and the CfA Hinode center. Simultaneous TRACE observations show spicules in emission and, silhouetted against the EUV corona, in absorption. (b) Our Fabry-Perot 2006-eclipse coronal spectra were taken with David Rust's (JHUAPL) 0.16 angstrom Y-cut lithium-niobate filter. With Rust and Matthew Noble, the etalon was stepped across the red coronal line every 0.22 angstrom. We present the profile and Doppler shifts of the [Fe X] line. (c) We collected simultaneous 10 Hz observations in the red and green coronal lines at the 2006 eclipse, with the goal of detecting high-frequency intensity oscillations ( 1 Hz), which can be relevant to coronal heating, and to confirm previous results. We present FFT and wavelet analysis of the aligned data. We thank Bryce Babcock and Steven Souza (Williams) for their eclipse collaboration. We acknowledge grants NNG04GK44G, NNG04GE48G, and NN05GG75G from NASA Planetary Astronomy. The eclipse observations were supported by NSF grant ATM-0552116 from the Solar Terrrestrial Program of the Atmospheres Sciences Division. Additional eclipse support was received from National Geographic's Committee on Research and Exploration and Williams's Rob Spring Fund.

Pasachoff, Jay M.; Bruck, M. A.

2007-05-01

344

Double Power-law Distribution of Magnetic Energy in the Solar Corona over an Active Region  

NASA Astrophysics Data System (ADS)

In this paper, we study the magnetic energy (ME) structure contained in the solar corona over the active region NOAA 11158. The time period is chosen as from 0:00 to 06:00 UT on 2011 February 15, during which an X-class flare occurred. The nonlinear force-free field (NLFFF) and the potential field extrapolation are carried out to model the coronal magnetic field over this active region, using high-quality photospheric vector magnetograms observed by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory as boundary conditions. We find that the volume distribution for the density of the ME (B 2/8?) and the ohmic dissipation power (ODP, j 2/?), in which j is the electric current density (c/4?? × B) and ? is the conductivity in the corona, can be readily fitted by a broken-down double-power law. The turn-over density for the spectrum of the ME and ODP is found to be fixed at ~1.0 × 104 erg cm-3 and ~2.0 × 10-15 W cm-3 (assuming ? = 105 ?-1 m-1), respectively. Compared with their first power-law spectra (fitted below the corresponding turn-over value) which remain unchanged, the second power-law spectra (fitted above the corresponding turn-over value) for the NLFFF's ME and ODP show flare-associated changes. The potential field remains steady. These results indicate that a magnetic field with energy density larger than the turn-over energy density plays a dominant role in powering the flare.

Shen, Jinhua; Ji, Haisheng; Wiegelmann, Thomas; Inhester, Bernd

2013-02-01

345

DOUBLE POWER-LAW DISTRIBUTION OF MAGNETIC ENERGY IN THE SOLAR CORONA OVER AN ACTIVE REGION  

SciTech Connect

In this paper, we study the magnetic energy (ME) structure contained in the solar corona over the active region NOAA 11158. The time period is chosen as from 0:00 to 06:00 UT on 2011 February 15, during which an X-class flare occurred. The nonlinear force-free field (NLFFF) and the potential field extrapolation are carried out to model the coronal magnetic field over this active region, using high-quality photospheric vector magnetograms observed by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory as boundary conditions. We find that the volume distribution for the density of the ME (B {sup 2}/8{pi}) and the ohmic dissipation power (ODP, j {sup 2}/{sigma}), in which j is the electric current density (c/4{pi}{nabla} Multiplication-Sign B) and {sigma} is the conductivity in the corona, can be readily fitted by a broken-down double-power law. The turn-over density for the spectrum of the ME and ODP is found to be fixed at {approx}1.0 Multiplication-Sign 10{sup 4} erg cm{sup -3} and {approx}2.0 Multiplication-Sign 10{sup -15} W cm{sup -3} (assuming {sigma} = 10{sup 5} {Omega}{sup -1} m{sup -1}), respectively. Compared with their first power-law spectra (fitted below the corresponding turn-over value) which remain unchanged, the second power-law spectra (fitted above the corresponding turn-over value) for the NLFFF's ME and ODP show flare-associated changes. The potential field remains steady. These results indicate that a magnetic field with energy density larger than the turn-over energy density plays a dominant role in powering the flare.

Shen, Jinhua; Ji, Haisheng [Purple Mountain Observatory, 2 West Beijing Road, Nanjing 210008 (China)] [Purple Mountain Observatory, 2 West Beijing Road, Nanjing 210008 (China); Wiegelmann, Thomas; Inhester, Bernd [Max-Planck-Institut fuer sonnensystemforschung, Max-Planck-Str. 2, D-37191 Katlenburg-Lindau (Germany)] [Max-Planck-Institut fuer sonnensystemforschung, Max-Planck-Str. 2, D-37191 Katlenburg-Lindau (Germany)

2013-02-10

346

MHD Simulation of the Global Solar Corona Using the Synoptic Frame of the Photospheric Magnetic Field and Coronal-Base Temperature  

Microsoft Academic Search

The solar surface boundary map plays an essential role in determining the results of the MHD simulation of the global solar corona and solar wind. In this work, we will present the MHD simulation using the synoptic frame format of the solar photospheric magnetic field and coronal-base temperature. The concept of synoptic frame is developed for the global map to

K. Hayashi; X. Zhao; E. Benevolenskaya

2006-01-01

347

Physics of Stellar Coronae  

Microsoft Academic Search

For the plasma physicist, the solar corona offers an outstanding example of a space plasma, and surely one that deserves a lifetime of study. Not only can we observe the solar corona on scales of a few hundred kilometers and monitor its changes in the course of seconds to minutes, we also have a wide range of detailed diagnostics at

Manuel Gudel

348

Shock Acceleration and Transport of Solar Energetic Particles in the Corona  

NASA Astrophysics Data System (ADS)

In gradual solar energetic particle (SEP) events, the phase-space density of suprathermal seed particles plays an important role in the bootstrap acceleration of SEPs at a coronal-mass-ejection driven shock in the corona. Higher seed proton density causes more rapid resonant amplification of ambient Alfvén waves and hence faster shock acceleration of SEPs. On the other hand, SEP-driven Alfvén wave growth is slowed by higher plasma density and by the thermal damping of left-hand polarized waves at frequencies exceeding a fraction of the proton cyclotron frequency. Damping also influences the background wave distribution. Coronal magnetic field strongly influences the wave-particle interaction since its magnitude scales the resonant wavenumber and its negative parallel gradient focuses the charged particles. The solar-wind velocity and Alfvén speed, relevant to the height of shock formation, are related to the plasma density and magnetic field. Consequently, the spatial dependences of all these environmental parameters influence the coupled evolution of SEP and Alfvén wave distributions. We will present results from our models of SEP acceleration and transport combining the effects of the above physical considerations. The model results will be compared to directly observed and inferred features of SEP events (e.g. streaming-limited intensity, maximum energy, height of first solar particle release) to address the roles and relative importance of the above physical factors.

Ng, C. K.; Ko, Y.; Tylka, A. J.; von Rosenvinge, T. T.

2013-12-01

349

Thermal Structure of Current Sheets and Supra-arcade Downflows in the Solar Corona  

NASA Astrophysics Data System (ADS)

After the peak intensity of many large solar flares, magnetic and thermodynamic processes give rise to a phenomenon known as supra-arcade downflows (SADs). SADs are sunward flowing density depletions, often observed in post-flare plasma sheets. Some models have suggested that the plasma in the dark lanes is heated to temperatures of 20-80 MK, which is much hotter than temperatures of the surrounding plasma. In this work, we use data from the Atmospheric Imaging Assembly on the Solar Dynamics Observatory and the X-Ray Telescope on the Hinode satellite to determine the thermal structure of SADs in the solar corona. We examine four flares that took place on 2011 October 22, 2012 January 14, 2012 January 16, and 2012 January 27. Differential emission measures are calculated for each flare and we compare the temperatures in the SADs to those of the surrounding plasma. We find that the SADs are hotter than the background, but cooler than the surrounding plasma in most cases, with only 1 out of the 11 SADs examined here having a slightly higher temperature than its surroundings.

Hanneman, Will J.; Reeves, Katharine K.

2014-05-01

350

What can the Kelvin-Helmholtz Instability in the Solar Corona Tell us about Local Plasma Properties?  

NASA Astrophysics Data System (ADS)

We discuss observations of the Kelvin-Helmholtz instability (KHI) at boundary layers in the solar corona by the Solar Dynamics Observatory. We present a case study of the 2011 February 24 event, where quasi-periodic vortex-like structures are visible at the northern side of a filament boundary embedded in a coronal mass ejection. We compare results of 2.5D MHD simulations with the observations and obtain quantitative as well as qualitative agreements. By deriving an analytical expression for the instability growth rate and by performing numerical parameter studies, we try to constrain the local plasma parameters. Finally, we present observations of other possible KHI appearances in the solar corona.

Amerstorfer, U.; Temmer, M.; Veronig, A. M.; Scheucher, M.

2013-12-01

351

Dust Hazard Management in the Outer Solar System  

NASA Technical Reports Server (NTRS)

Most robotic missions to the outer solar system must grapple with the hazards posed by the dusty rings of the gas giants. Early assessments of these hazards led simply to ring avoidance due to insufficient data and high uncertainties on the dust population present in such rings. Recent approaches, principal among them the Cassini dust hazard management strategy, provide useful results from detailed modeling of spacecraft vulnerabilities and dust hazard regions, which along with the range of mission trajectories are used to to assess the risks posed by each passage through a zone of potential hazard. This paper shows the general approach used to implement the analysis for Cassini, with recommendations for future outer planet missions.

Seal, David A.

2012-01-01

352

MACS, An Instrument, and a Methodology for Simulations and Global Measurements of the Coronal Electron Temperature and the Solar Wind Velocity on the Solar Corona  

NASA Technical Reports Server (NTRS)

The determination of the radial and latitudinal temperature and wind profiles of the solar corona is of great importance in understanding the coronal heating mechanism and the dynamics of coronal expansion. Cram presented the theory for the formation of the K-coronal spectrum and identified two important observations. He observed the existence of temperature sensitive anti-nodes at certain wavelengths in the theoretical K-coronal spectra. The anti-nodes are separated by temperature-insensitive nodes. Remarkably, Cram showed that the wavelengths of the nodes and anti-nodes are almost independent of altitude above the solar limb. Because of these features, Cram suggested that the intensity ratios at two anti-nodes could be used as a diagnostic of the electron temperature in the K-corona. Based on this temperature diagnostic technique prescribed by Cram a slit-based spectroscopic study was performed by Ichimoto et al. on the solar corona in conjunction with the total solar eclipse of 3 Nov 1994 in Putre, Chile to determine the temperature profile of the solar corona. In this thesis Cram's theory has been extended to incorporate the role of the solar wind in the formation of the K-corona, and we have identified both temperature and wind sensitive intensity ratios. The instrument, MACS, for Multi Aperture Coronal Spectrometer, a fiber optic based spectrograph, was designed for global and simultaneous measurement of the thermal electron temperature and the solar wind velocity in the solar corona. The first ever experiment of this nature was conducted in conjunction with the total solar eclipse of 11 Aug 1999 in Elazig, Turkey. In this instrument one end of each of twenty fiber optic tips were positioned in the focal plane of the telescope in such a way that we could observe conditions simultaneously at many different latitudes and two different radial distances in the solar corona. The other ends of the fibers were vertically aligned and placed at the primary focus of the collimating lens of the spectrograph to obtain simultaneous and global spectra on the solar corona. By isolating the K-coronal spectrum from the spectrum recorded by each fiber the temperature and the wind sensitive intensity ratios were calculated to obtain simultaneous and global measurements of the thermal electron temperature and the solar wind velocity. We were successful in obtaining reliable estimates of the coronal temperature at many positions in the corona. This is the first time that simultaneous measurements of coronal temperatures have been obtained at so many points. However due to instrumental scattering encountered during observations, reliable estimates of the wind velocity turned out to be impossible to obtain. Although remedial measures were taken prior to observation, this task proved to be difficult owing to the inability to replicate the conditions expected during an eclipse in the laboratory. The full extent of the instrumental scattering was apparent only when we analyzed the observational sequence. Nevertheless the experience obtained from this very first attempt to simultaneously and globally measure both the wind velocity and the temperature on the solar corona have provided valuable information to conduct any future observations successfully.

Reginald, Nelson L.; Fisher, Richard R. (Technical Monitor)

2000-01-01

353

Dust in the Solar System - Properties and Origins  

NASA Technical Reports Server (NTRS)

Interplanetary dust pervades the inner Solar System, giving rise to a prominent glow above the horizon at sunrise and sunset known as the zodiacal light. This dust derives from the disintegration of comets as they approach the Sun and from collisions among main-belt asteroids. The Earth accretes roughly 4x10(exp 6) kg/year of 1 - 1,000 micron dust particles as they spiral into the Sun under the influence of Poynting-Robertson drag and solar wind drag. Samples of these grains have been collected from deep sea sediments, Antarctic ice and by high-altitude aircraft and balloon flights. Interplanetary dust particles (IDPs) collected in the stratosphere have been classified by their IR spectra into olivine, pyroxene, and hydrated silicate-dominated classes. Most IDPs have bulk major and minor element abundances that are similar to carbonaceous chondrite meteorites. Hydrated silicate-rich IDPs are thought to derive from asteroids based on their mineralogy and low atmospheric entry velocities estimated from peak temperatures reached during atmospheric entry. Anhydrous IDPs are typically aggregates of 0.1 - approx. 1 micron Mg-rich olivine and pyroxene, amorphous silicates (GEMS), Fe, Nisulfides and rare spinel and oxides bound together by carbonaceous material. These IDPs are often argued to derive from comets based on compositional similarities and high atmospheric entry velocities that imply high eccentricity orbits. Infrared spectra obtained from anhydrous IDPs closely match remote IR spectra obtained from comets. The most primitive (anhydrous) IDPs appear to have escaped the parent-body thermal and aqueous alteration that has affected meteorites. These samples thus consist entirely of grains that formed in the ancient solar nebula and pre-solar interstellar and circumstellar environments. Isotopic studies of IDPs have identified silicate stardust grains that formed in the outflows of red giant and asymptotic giant branch stars and supernovae]. These stardust grains include both amorphous and crystalline silicates. The organic matter in these samples also exhibits highly anomalous H, C, and N isotopic compositions that are consistent with formation in low temperature environments at the outermost regions of the solar nebula or presolar cold molecular cloud. The scientific frontiers for these samples include working toward a better understanding of the origins of the solar system amorphous and crystalline grains in IDPs and the very challenging task of determining the chemical composition of sub-micron organic grains. Laboratory studies of ancient and present-day dust in the Solar System thus reveal in exquisite detail the chemistry, mineralogy and isotopic properties of materials that derive from a range of astrophysical environments. These studies are an important complement to astronomical observations that help to place the laboratory observations into broader context.

Messenger, Scott; Keller, Lindsay; Nakamura-Messenger, Keiko

2013-01-01

354

Small bodies and dust in the outer solar system  

Microsoft Academic Search

We present our current understandings of small bodies and dust grains located in the outer Solar System. Small icy bodies – Edgeworth-Kuiper Belt objects (EKBOs) and Oort Cloud objects orbit the Sun at distances from Neptune's orbit outward to 104–105 AU. Both EKBOs and Oort Cloud objects are believed to be remnants of planetesimals formed in the proto-planetary disk. They

T. Mukai; A. Higuchi; P. S Lykawka; H. Kimura; I. Mann; S. Yamamoto

2004-01-01

355

Tracing the magnetic connectivity between the solar surface, corona and inner heliosphere using combined X-ray and radio observations  

NASA Astrophysics Data System (ADS)

On a few examples of flares observed with RHESSI at X-ray wavelengths and with the Nançay Radioheliograph (NRH) and WIND/WAVES at radio wavelengths, we shall illustrate how these combined observations allow to understand the link between energetic electrons interacting in the flare site and the escaping electrons which produce radio emissions at low frequencies in the high corona and in the interplanetary medium. While in some events, a close correspondence is observed between the timing and the fast variations of the HXR emissions and the radio emissions from electron beams in the high corona observed by Wind/Waves in the 1 to 14 MHz range suggesting a common acceleration/injection site for HXR and radio emitting electrons, in other cases there is a delay of the radio emissions in the high corona with respect to the onset of the HXR emission. We shall discuss in this contribution the input for a few events of the spatially resolved radio observations of the metric/decimetric emissions provided by the Nançay Radioheliograph to better understand the link between the X-ray emissions at the solar c surface and the radio bursts in the high corona. We shall also discuss the percentage of cases for which a close correspondance is observed. We shall also illustrate how these results may help the preparation of the observing modes of X-ray and radio bursts with STIX and RPW on Solar Orbiter.

Vilmer, Nicole; Maksimovic, Milan; Rackovic, Kristina

356

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

357

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

358

The Solar Corona and a CME at the 2010 Total Eclipse  

NASA Astrophysics Data System (ADS)

The 11 July 2010 total solar eclipse was observed on the ground from French Polynesia and, 83 minutes later, from Easter Island, and near-simultaneous images were made with spacecraft instruments including AIA/SDO, HMI/SDO, EUVI/STEREO, SWAP/PROBA2, EIT/SOHO, and LASCO/SOHO. We report on changes in the corona detectable with high-resolution image processing of the ground-based eclipse coronal imaging, including two CME's that were seen to evolve. We compare with the spacecraft images to give a complete depiction of coronal structure at the time of the eclipse, which corresponded to a low but rising phase of the solar-activity cycle. We acknowledge the support of NASA's MSFC NNX10AK47A, NSF REU AST-1005024 with DoD ASSURE, VEGA 2/0098/10 of the Slovak Acad. Sci, 205/09/1469 of the Czech Science Foundation, PRODEX C90345 of ESA/BELSPO, FP7/2007-2013/218816 SOTERIA, Lockheed Martin; for equipment: Nikon Professional Services, ASTELCO Systems GmbH (Germany), and National Geographic Society's Photographic Division; and colleagues Y.-M. Wang (NRL), S. Habbal (U. Hawaii), H. Lanteires (Tatakoto), and J. Kern (Carnegie Obs.).

Pasachoff, Jay M.; Rusin, V.; Druckmüllerová, H.; Saniga, M.; Lu, M.; Malamut, C.; Seaton, D. B.; Golub, L.; Engell, A. J.; Hill, S. W.; Lucas, R.

2011-05-01

359

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

Microsoft Academic Search

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

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

2010-01-01

360

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

361

The Advanced Technology Solar Spectroscopic Imager—a novel experiment employing a transition-edge sensor to probe the soft X-ray solar corona  

Microsoft Academic Search

The Advanced Technology Solar Spectroscopic Imager (ATSSI) is a sounding rocket-borne experiment that will employ a Transition-Edge Sensor (TES) placed at the focus of a Wolter-I mirror to study large active region loops in the solar corona. The TES instrument will operate in the ?500–1500eV EUV\\/soft X-ray bandpass, obtaining ?3eV energy-resolved spectra at ?6.25arcsec image resolution with a count rate

Paul Boerner; Dennis S. Mart??nez-Galarce; Kolo Wamba; Blas Cabrera; Steve Deiker; Kent Irwin; Troy W. Barbee; Phil C. Baker

2004-01-01

362

Microphysics of Waves and Instabilities in the Solar Wind and their Macro Manifestations in the Corona and Interplanetary Space  

NASA Technical Reports Server (NTRS)

Investigations of the physical processes responsible for the acceleration of the solar wind were pursued with the development of two new solar wind codes: a hybrid code and a 2-D MHD code. Hybrid simulations were performed to investigate the interaction between ions and parallel propagating low frequency ion cyclotron waves in a homogeneous plasma. In a low-beta plasma such as the solar wind plasma in the inner corona, the proton thermal speed is much smaller than the Alfven speed. Vlasov linear theory predicts that protons are not in resonance with low frequency ion cyclotron waves. However, non-linear effect makes it possible that these waves can strongly heat and accelerate protons. This study has important implications for study of the corona and the solar wind. Low frequency ion cyclotron waves or Alfven waves are commonly observed in the solar wind. Until now, it is believed that these waves are not able to heat the solar wind plasma unless some cascading processes transfer the energy of these waves to high frequency part. However, this study shows that these waves may directly heat and accelerate protons non-linearly. This process may play an important role in the coronal heating and the solar wind acceleration, at least in some parameter space.

Habbal, Shadia R.; Gurman, Joseph (Technical Monitor)

2003-01-01

363

Three-dimensional models of the global zodiacal dust cloud - A bimodal model of the solar dust heliosphere  

Microsoft Academic Search

Several three-dimensional models of the interplanetary dust cloud or the dust heliosphere describing the number density of particles have been proposed according to infrared and optical measurements. Number densities close to the earth predicted by the different models converge sufficiently. But, for regions close to the solar poles, discrepancies between different models grow dramatically. Infrared observations demand lower particle densities,

B. Kneissel; I. Mann

1990-01-01

364

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

365

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; Ĺke Nordlund

1997-01-01

366

Fine Structure in the Corona and Solar Wind at High Heliographic Latitudes at Solar Maximum  

NASA Technical Reports Server (NTRS)

Microstreams and pressure balance structures in fast solar wind were more easily detected at Ulysses at 2.2 AU over the poles than at Helios at 0.3 AU. This is because solar rotation brings sources of fast solar wind beneath sources of slow solar wind at a rate that depends on latitude, for the same size features. Dynamic interaction between the fast and slow wind tends to mix the flows and make features more difficult to detect with increasing distance from the Sun. A given sized feature takes proportionally longer to pass a longitude when it is at 80 degrees latitude than when it is at the equator. At solar maximum, Ulysses will mainly be sampling solar wind coming from above streamers and from near streamers. The data will provide information on fine structure at the tops of streamers - the stalks - and on the source of slow solar wind, The visibility of the boundaries between fast and slow wind and of the stalk will increase with increasing latitude. We will present quantitative calculations of the visibility of various sized features, with various differences in flow speed, at the location of Ulysses when it is over the south (in 2000) and north (in 2001) polar regions of the Sun.

Suess. S. T.; Poletto, G.

2000-01-01

367

Fine Structure in the Corona and Solar Wind at High Heliographic Latitudes at Solar Maximum  

NASA Technical Reports Server (NTRS)

Microstreams and pressure balance structures in fast solar wind were more easily detected at Ulysses at 2.2 AU over the poles than at Helios at 0.3 AU. This is because solar rotation brings sources of fast solar wind beneath sources of slow solar wind at a rate that depends on latitude, for the same size features. Dynamic interaction between the fast and slow wind tends to mix the flows and make features more difficult to detect with increasing distance from the Sun. A given sized feature takes proportionally longer to pass a longitude when it is at 80 degrees latitude than when it is at the equator. At solar maximum, Ulysses will mainly be sampling solar wind coming from above streamers and from near streamers. The data will provide information on fine structure at the tops of streamers - the stalks - and on the source of slow solar wind. The visibility of the boundaries between fast and slow wind and of the stalk will increase with increasing latitude. I will present quantitative calculations of the visibility of various sized features, with various differences in flow speed, at the location of Ulysses when it is over the south (in 2000) and north (in 2001) polar regions of the Sun.

Suess, S. T.; Rose, M. Franklin (Technical Monitor)

2001-01-01

368

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

369

The solar cycle variation of topological structures in the global solar corona  

NASA Astrophysics Data System (ADS)

Context. The complicated distribution of magnetic flux across the solar photosphere results in a complex web of coronal magnetic field structures. To understand this complexity, the magnetic skeleton of the coronal field can be calculated. The skeleton highlights the (separatrix) surfaces that divide the field into topologically distinct regions, allowing open-field regions on the solar surface to be located. Furthermore, separatrix surfaces and their intersections with other separatrix surfaces (i.e., separators) are important likely energy release sites. Aims: The aim of this paper is to investigate, throughout the solar cycle, the nature of coronal magnetic-field topologies that arise under the potential-field source-surface approximation. In particular, we characterise the typical global fields at solar maximum and minimum. Methods: Global magnetic fields are extrapolated from observed Kitt Peak and SOLIS synoptic magnetograms, from Carrington rotations 1645 to 2144, using the potential-field source-surface model. This allows the variations in the coronal skeleton to be studied over three solar cycles. Results: The main building blocks which make up magnetic fields are identified and classified according to the nature of their separatrix surfaces. The magnetic skeleton reveals that, at solar maximum, the global coronal field involves a multitude of topological structures at all latitudes criss-crossing throughout the atmosphere. Many open-field regions exist originating anywhere on the photosphere. At solar minimum, the coronal topology is heavily influenced by the solar magnetic dipole. A strong dipole results in a simple large-scale structure involving just two large polar open-field regions, but, at short radial distances between ą 60° latitude, the small-scale topology is complex. If the solar magnetic dipole if weak, as in the recent minimum, then the low-latitude quiet-sun magnetic fields may be globally significant enough to create many disconnected open-field regions between ą 60° latitude, in addition to the two polar open-field regions.

Platten, S. J.; Parnell, C. E.; Haynes, A. L.; Priest, E. R.; Mackay, D. H.

2014-05-01

370

Modeling the corona and solar wind using ADAPT maps with data assimilated helioseismic detected active regions (Invited)  

NASA Astrophysics Data System (ADS)

As the primary input to nearly all coronal and solar wind models, global estimates of the solar photospheric magnetic field distribution are critical for reliable modeling of the corona and heliosphere. Over the last several years the Air Force Research Laboratory (AFRL), in collaboration with Los Alamos National Laboratory (LANL) and the National Solar Observatory (NSO), has developed a model that produces more realistic estimates of the instantaneous global photospheric magnetic field distribution than those provided by traditional photospheric field synoptic maps. The Air Force Data Assimilative Photospheric flux Transport (ADAPT) model is a photospheric flux transport model, originally developed at NSO, that makes use of data assimilation methodologies developed at LANL. The flux transport model evolves the observed solar magnetic flux using relatively well understood transport processes when measurements are not available and then updates the modeled flux with new observations using data assimilation methods that rigorously take into account model and observational uncertainties. ADAPT originally only made use of Earth-side magnetograms, but the code has now been modified to assimilate helioseismic active region data such as those available from the Global Oscillation Network Group. In this presentation, we use the Wang-Sheeley-Arge (WSA) model driven by ADAPT maps with and without helioseismic detected active regions data assimilated into them to simulate the corona and solar wind. The WSA model results are then compared with coronal EUV and in situ solar wind observations available from STEREO & ACE.

Arge, C. N.; Henney, C. J.; Gonzalez-Hernandez, I. E.; Toussaint, W.; Koller, J.; Godinez, H. C.

2013-12-01

371

Set of instruments for solar EUV and soft X-ray monitoring onboard satellite Coronas-Photon  

NASA Astrophysics Data System (ADS)

Coronas-Photon mission is the third satellite of the Russian Coronas program on solar activity observation. The main goal of the "Coronas-Photon" is the study of solar hard electromagnetic radiation in the wide energy range from UV up to high energy gamma-radiation (2000MeV). Scientific payload for solar radiation observation consists of three types of instruments: Monitors (Natalya-2M, Konus-RF, RT-2, Penguin-M, BRM, PHOKA, Sphin-X, SOKOL spectral and timing measurements of full solar disk radiation have timing in flare/burst mode up to one msec. Instruments Natalya-2M, Konus-RF, RT-2 will cover the wide energy range of hard X-rays and soft gamma-rays (15keV to 2000MeV) and will together constitute the largest area detectors ever used for solar observations. Detectors of gamma-ray monitors are based on structured inorganic scintillators. For X-ray and EUV monitors the scintillation phoswich detectors, gas proportional counter, CdZnTe assembly and filter-covered Si-diodes are used. Telescope-spectrometer TESIS for imaging solar spectroscopy in X-rays has angular resolution up to 1arcsec in three spectral lines. Satellite platform and scientific payload is under construction to be launched in autumn 2008. Satellite orbit is circular with initial height 550km and inclination 82.5degrees. Accuracy of the spacecraft orientation to the Sun is better 3arcmin. In the report the capability of PHOKA, SphinX, SOKOL and TESIS as well as the observation program are described and discussed.

Kotov, Yury; Kochemasov, Alexey; Kuzin, Sergey; Kuznetsov, Vladimir; Sylwester, Janusz; Yurov, Vitaly

372

Using Solar and In Situ Observations to Improve and Constrain Corona & Solar Wind Models  

NASA Astrophysics Data System (ADS)

Photospheric magnetic field synoptic maps serve as a key driver to all coronal and solar wind models. It is important therefore that these fields are determined as accurately as possible. Measurements of the line-of- sight (LOS) photospheric field near the Sun's poles are often highly unreliable because of their close proximity to the limb (i.e., only a small component of the field vector is directed toward the observer) and because the Sun's rotation axis is inclined 7.25 degrees to the ecliptic plane. The least reliable measurements in photospheric field synoptic maps thus tend to be those located near the poles (i.e., in constructing such maps, individual field measurements far from central meridian have the lowest weighting, while those near central meridian have the highest). Coronal and solar wind models (both simple and advanced) are very sensitive to the Sun's polar fields thus making it especially important that they are known as well as possible. In this study, we apply a polar field correction technique that we have developed [Arge and Pizzo, 2000] to LOS photospheric magnetic field Carrington maps from Mount Wilson and National (at Kitt Peak) Solar Observatories. We then use both the polar corrected as well as the uncorrected maps in the Wang-Sheeley- Arge (WSA) model to determine the improvement in the model's predictions of coronal and solar wind parameters. This is done by comparing the WSA solar wind predictions (i.e., solar wind speed, IMF polarity, and the inclination of the current sheet at sector crossings) at L1 with the observations from the WIND and ACE spacecraft and by comparing observed and predicted coronal holes for a selected set of Carrington maps over the solar cycle.

Arge, C. N.; Owens, M. J.

2006-12-01

373

Toward a Realistic Thermodynamic Magnetohydrodynamic Model of the Global Solar Corona  

Microsoft Academic Search

In this work, we describe our implementation of a thermodynamic energy equation into the global corona model of the Space Weather Modeling Framework and its development into the new lower corona (LC) model. This work includes the integration of the additional energy transport terms of coronal heating, electron heat conduction, and optically thin radiative cooling into the governing magnetohydrodynamic (MHD)

Cooper Downs; Ilia I. Roussev; Bart van der Holst; Noé Lugaz; Igor V. Sokolov; Tamas I. Gombosi

2010-01-01

374

FORMATION AND RECONNECTION OF THREE-DIMENSIONAL CURRENT SHEETS IN THE SOLAR CORONA  

Microsoft Academic Search

Current-sheet formation and magnetic reconnection are believed to be the basic physical processes responsible for much of the activity observed in astrophysical plasmas, such as the Sun's corona. We investigate these processes for a magnetic configuration consisting of a uniform background field and an embedded line dipole, a topology that is expected to be ubiquitous in the corona. This magnetic

J. K. Edmondson; S. K. Antiochos; C. R. DeVore; T. H. Zurbuchen

2010-01-01

375

Formation and Reconnection of Three-dimensional Current Sheets in the Solar Corona  

Microsoft Academic Search

Current-sheet formation and magnetic reconnection are believed to be the basic physical processes responsible for much of the activity observed in astrophysical plasmas, such as the Sun's corona. We investigate these processes for a magnetic configuration consisting of a uniform background field and an embedded line dipole, a topology that is expected to be ubiquitous in the corona. This magnetic

J. K. Edmondson; S. K. Antiochos; C. R. DeVore; T. H. Zurbuchen

2010-01-01

376

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

377

Type II fixed on boards flare continuum in the corona and solar wind  

NASA Astrophysics Data System (ADS)

A solar radio type II/type IV event with exceptionally low frequency flare continuum radiation was observed on May 2, 1998 with the Wind spacecraft. This flare continuum, associated with the type II burst (FCII), descended to 7.5 MHz (2.5-3 solar radii), the lowest frequency ever observed for this type of emission. It lasted for >2 hours at 13.8 MHz. Simultaneous observations were made with ground-based radiospectrographs, and with the Extreme Ultraviolet Imaging Telescope (EIT) and Large Angle and Spectrometric Coronagraph (LASCO) telescopes. The radio event consists of a group of intense type III bursts observed from 1000 MHz down to 0.03 MHz, the plasma frequency at 1 AU. The type II burst was recorded from 45 MHz down to 0.4 MHz, and an interplanetary shock was observed at 1 AU on May 4 at 0500 UT. The type II shock commenced within a few minutes of the flash phase of the flare and of the liftoff time of a coronal mass ejection (CME) observed by EIT and LASCO. The derived speeds of the type II shock, the CME in the plane of the sky, and the shock from the Sun to 1 AU are all ~1000 km s-1. After estimating the liftoff time and radial speed of the CME front, we find that the type II shock and flare continuum were in the wake of the CME. This event shows evidence of acceleration of electrons in the corona out to 3RS for >~2 hours. Theoretical implications on the generation of the flare continuum radiation and its relation to the observed brightness temperature are considered. The source model of type II-flare continuum of Robinson [1985], in which electrons are accelerated by the shock wave traversing CME expanding loops, is discussed in view of these observations.

Leblanc, Y.; Dulk, G. A.; Cairns, I. H.; Bougeret, J.-L.

2000-08-01

378

Collisionless transport of energetic electrons in the solar corona at current-free double layers  

NASA Astrophysics Data System (ADS)

Context: Impinging electron beams in the solar chromosphere generate hard X-ray radiation (HXR) through the collisional Bremstrahlung thick target model. The deduced electron distributions usually exhibit a broken-power-law. Assuming that the initial distribution function was a drift-Maxwellian, this indicates that the distribution of energetic electrons changes in the course of their propagation, from the looptop acceleration site to the high density chromosphere, via a collisionless scattering mechanism. Aims: The formation of a broken-power-law spectrum via the particle interaction with the current-free weak double layers (DLs) in a reverse current beam plasma system. Methods: The unstable waves generated in current-free coronal plasmas are first studied by means of a linear instability analysis. For most probable coronal plasma parameters, a one-dimensional electrostatic Vlasov-code simulation is performed to understand the nonlinear evolution of the instabilities and their influences on the electron distribution. Results: DL structures cause a dissipation of low energy beam electrons and a stagnation of return-current electrons. Fast electron holes are formed, a secondary two-stream instability, caused by the DL-accelerated electrons. Electron and ion heating by DLs also takes place. Conclusions: The plasma distributions of energetic electrons in the solar corona evolve via their interactions with nonlinear large-amplitude phase-space structures. At the late stage of evolution, the low-energy electrons are slowed down while the high energy part stays uninfluenced after the appearance of DLs. A major part of the return-current electrons change their direction to that of the injected beam. As a result the distribution becomes a broken-power-law as observed by chromospheric HXR radiation.

Lee, K. W.; Büchner, J.; Elkina, N.

2008-02-01

379

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

NASA Technical Reports Server (NTRS)

On July 6,2011, the Atmospheric Imaging Assembly (AlA) on the Solar Dynamics Observatory (SDO) observed a comet in most of its EUY passbands. The comet disappeared while moving through the solar corona. The comet penetrated to 0.146 solar radii ($\\simapprox.100,000 km) above the photosphere before its EUY 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 EUY brightness, all yield $\\sim 50$ 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; AlA EUY channels will be described

Pesnell, William Dean; Schrijiver, Carolus J.; Brown, John C.; Battams, Karl; Saint-Hilaire, Pascal; Hudson Hugh S.; Lui, Wei

2012-01-01

380

The Early Stages of Formation of a Solar System Dust Band  

Microsoft Academic Search

A solar system dust band is formed as the dust released in the catastrophic disruption of an asteroid in the main belt decays under the effects of radiation forces and is sculpted by gravitational perturbations. There are currently known to be at least three full dust band pairs (Low et al., 1984) and these have been associated with several-million-year-old asteroidal

Ashley J. Espy; S. F. Dermott; T. J. J. Kehoe

2009-01-01

381

Effects of heavy ions on electron temperatures in the solar corona and solar wind  

Microsoft Academic Search

At 1 AU, observations indicate that solar wind ions have nearly the same mean flow velocities and that their elemental abundances are very approximately the same as th, ose of the photosphere [Formisano and Moreno, 1971]. The abundances are such that the consideration of heavy ions may be expected to give thermal conductivities that are almost the same as those

M. P. Nakada

1974-01-01

382

COMPARISON OF HINODE/XRT AND RHESSI DETECTION OF HOT PLASMA IN THE NON-FLARING SOLAR CORONA  

SciTech Connect

We compare observations of the non-flaring solar corona made simultaneously with Hinode/XRT and RHESSI. The analyzed corona is dominated by a single active region on 2006 November 12. The comparison is made on emission measures. We derive emission measure distributions versus temperature of the entire active region from multifilter XRT data. We check the compatibility with the total emission measure values estimated from the flux measured with RHESSI if the emission comes from isothermal plasma. We find that RHESSI and XRT data analyses consistently point to the presence of a minor emission measure component peaking at log T approx 6.8-6.9. The discrepancy between XRT and RHESSI results is within a factor of a few and indicates an acceptable level of cross-consistency.

Reale, Fabio [Dipartimento di Scienze Fisiche and Astronomiche, Universita di Palermo, Sezione di Astronomia, Piazza del Parlamento 1, 90134 Palermo (Italy); McTiernan, James M. [Space Sciences Laboratory, University of California, Berkeley, CA 94720-7450 (United States); Testa, Paola [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)

2009-10-10

383

On the Fabry-Perot investigations of the solar corona: Eclipse observations of the green line intensities and half widths  

NASA Astrophysics Data System (ADS)

Eclipse data on intensity and half width of the green coronal line obtained using a Fabry-Perot Interferometer (FPI) combined with a blocking Interference Filter (IF) are presented. Demerits of an FPI (necessity of preliminary monochromatization, ghost images, white corona contribution) are discussed. To get reliable data, blocking filters with FWHM of 2 A and 8 A should be used for the red and green lines, respectively. Requirements for transmission at far wings are extremely strict. According to the eclipse interferograms of the solar corona of 1972 and 1981, the green line intensity varies versus distance as 10-5 to 15. On the average, different coronal structures can be characterized by different values of half width: streamers 0.82 A, helmets 0.88 A, and holes 1.00 A.

Kim, Iraida S.

1992-11-01

384

Catalysis by Dust Grains in the Solar Nebula  

NASA Technical Reports Server (NTRS)

In order to determine whether grain-catalyzed reactions played an important role in the chemistry of the solar nebula, we have applied our time-dependent model of methane formation via Fischer-Tropsch catalysis to pressures from 10(exp -5) to 1 bar and temperatures from 450 to 650 K. Under these physical conditions, the reaction 3H2 + CO yields CH4 + H2O is readily catalyzed by an iron or nickel surface, whereas the same reaction is kinetically inhibited in the gas phase. Our model results indicate that under certain nebular conditions, conversion of CO to methane could be extremely efficient in the presence of iron-nickel dust grains over timescales very short compared to the lifetime of the solar nebula.

Kress, Monika E.; Tielens, Alexander G. G. M.

1996-01-01

385

Preliminary analysis of the IRAS solar system dust data  

NASA Technical Reports Server (NTRS)

The structure of the solar system dust cloud as revealed by IRAS all-sky survey data is discussed. Fourier analysis was used to separate the smooth, large-scale zodiacal background from the narrower dust lanes. The geometry of the background zodiacal cloud appears to show features associated with both the forced inclinations and the forced eccentricities of the dust particle orbits. The ecliptic latitude of the peak of the background zodiacal emission varies nearly sinusoidally with ecliptic longitude with an amplitude of 2.1 + or -0.2 degrees. However, there are marked displacements, both in latitude and longitude, between the leading or ascending curve and the trailing or descending curve, implying that the curves exhibit significant deviations from a simple sinusoidal variation. It is suggested that the plane of symmetry of the background cloud is inclined to the ecliptic by 1.47 + or -0.10 degrees with a descending node of 230 + or -4 degrees, and that the sun is not at the center of symmetry of the cloud.

Dermott, S. F.; Nicholson, P. D.; Wolven, B.

1986-01-01

386

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

387

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

NASA Technical Reports Server (NTRS)

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

2000-01-01

388

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

389

Field-Lines-Threaded Model for: (1) the Low Solar Corona; (2) Electrons in the Transition Region; and (3) Solar Energetic Particle Acceleration and Transport  

NASA Astrophysics Data System (ADS)

In numerical simulations of the solar corona, both for the ambient state and especially for dynamical processes the most computational resources are spent for maintaining the numerical solution in the Low Solar Corona and in the transition region, where the temperature gradients are very sharp and the magnetic field has a complicated topology. The degraded computational efficiency is caused by the need in a highest resolution as well as the use of the fully three-dimensional implicit solver for electron heat conduction. On the other hand, the physical nature of the processes involved is rather simple (which still does not facilitate the numerical methods) as long as the heat fluxes as well as slow plasma motional velocities are aligned with the magnetic field. The Alfven wave turbulence, which is often believed to be the main driver of the solar wind and the main source of the coronal heating, is characterized by the Poynting flux of the waves, which is also aligned with the magnetic field. Therefore, the plasma state in any point of the three-dimensional grid in the Low Solar Corona can be found by solving a set of one-dimensional equations for the magnetic field line ('thread'), which passes through this point and connects it to the chromosphere and to the global Solar Corona. In the present paper we describe an innovative computational technology based upon the use of the magnetic-field-line-threads to find the local solution. We present the development of the AWSoM code of the University of Michigan with the field-lines-threaded Low Solar Corona. In the transition region, where the essentially kinetic description of the electron energy fluxes is required, we solve the Fokker-Plank equation on the system of threads, to achieve the physically consistent description of chromosphere evaporation. The third application for the field-lines-treaded model is the Solar Energetic Particle (SEP) acceleration and transport. Being the natural extension of the Field-Line-Advection Model for Particle Acceleration (FLAMPA), earlier suggested for a single magnetic field line advected with the plasma motion, the multiple-field-lines model allows us to simulate the SEP fluxes at multiple points of possible observation (at the Earth location, at STEREOs, at Mercury).

Sokolov, I.; van der Holst, B.; Jin, M.; Gombosi, T. I.; Taktakishvili, A.; Khazanov, G. V.

2013-12-01

390

MAGNETIC FIELD STRENGTH IN THE UPPER SOLAR CORONA USING WHITE-LIGHT SHOCK STRUCTURES SURROUNDING CORONAL MASS EJECTIONS  

SciTech Connect

To measure the magnetic field strength in the solar corona, we examined 10 fast ({>=}1000 km s{sup -1}) limb coronal mass ejections(CMEs) that show clear shock structures in Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph images. By applying the piston-shock relationship to the observed CME's standoff distance and electron density compression ratio, we estimated the Mach number, Alfven speed, and magnetic field strength in the height range 3-15 solar radii (R{sub s} ). The main results from this study are as follows: (1) the standoff distance observed in the solar corona is consistent with those from a magnetohydrodynamic model and near-Earth observations; (2) the Mach number as a shock strength is in the range 1.49-3.43 from the standoff distance ratio, but when we use the density compression ratio, the Mach number is in the range 1.47-1.90, implying that the measured density compression ratio is likely to be underestimated owing to observational limits; (3) the Alfven speed ranges from 259 to 982 km s{sup -1} and the magnetic field strength is in the range 6-105 mG when the standoff distance is used; (4) if we multiply the density compression ratio by a factor of two, the Alfven speeds and the magnetic field strengths are consistent in both methods; and (5) the magnetic field strengths derived from the shock parameters are similar to those of empirical models and previous estimates.

Kim, R.-S.; Gopalswamy, N.; Cho, K.-S.; Yashiro, S. [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Moon, Y.-J., E-mail: rok-soon.kim@nasa.gov [School of Space Research, Kyung Hee University, Yongin-shi 446-701 (Korea, Republic of)

2012-02-20

391

Transport inhibition of coronal energetic electrons by multiple double layers: application to solar flares and expansion of the corona  

NASA Astrophysics Data System (ADS)

The transport of electrons from a coronal acceleration site to the chromosphere and out to the solar wind is a key issue in understanding the dynamics of solar flares and the expansion of the hot corona. The physics of how these energetic electrons transport from the corona remains poorly understood. Using a particle-in-cell code, we recently simulated an initial system of very hot electrons in contact with cold electrons along the local magnetic field, and found that transport inhibition begins when the hot electrons start to propagate from the source region [1]. This is due to the formation of a large-amplitude, localized electrostatic electric field, in the form of a double layer (DL), which is driven by an ion/return-current-electron streaming instability. The DL provides a potential barrier that suppresses the hot electron transport into the cold electron region, and significantly reduces electron heat flux. The result can help explain the observed prolonged duration of looptop hard X-ray emission. As a continued effort, simulations of increasing sizes are performed. Larger simulations allow the system to evolve for longer time and give rise to more complex dynamics. Instead of a single DL observed in smaller simulations [1], multiple DLs are generated. A succession of many weak DLs, occurring from the corona to the Earth, was considered to make up the interplanetary potential difference in exospheric solar wind models [2]. The observation of multiple DLs in the larger simulations favors this scenario. The dynamics of multiple DLs and the associated transport regulation are being investigated, and the application to solar flares and coronal expansion will be discussed. [1] T.C. Li, J.F. Drake and M. Swisdak, ApJ, in press, 2012 [2] C. Lacombe, et. al., Ann. Geophysicae, 20, 609, 2002

Li, T.; Drake, J. F.; Swisdak, M. M.

2012-12-01

392

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

NASA Technical Reports Server (NTRS)

We report on multi-wavelength observations of the corona taken simultaneously in broadband white light, and in seven spectral lines, H-alpha 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. The observations were made during the total solar eclipse of 11 July 2010 from the atoll of Tatakoto in French Polynesia. Simultaneous imaging with narrow bandpass filters in each of these spectral lines and in their corresponding underlying continua maximized the observing time during less than ideal observing conditions and yielded outstanding quality data. The application of two complementary image processing techniques revealed the finest details of coronal structures at 1" resolution in white light, and 6.5" in each of the spectral lines. This comprehensive wavelength coverage confirmed earlier eclipse findings that the solar corona has a clear two-temperature structure: The open field lines, expanding outwards from the solar surface, are characterized by electron temperatures near 1 X 10(exp 6) K, while the hottest plasma around 2X 10(exp 6) K resides in loop-like structures forming the bulges of streamers. The first images of the corona in the forbidden lines of Fe IX and Ni XV, showed that there was very little coronal plasma at temperatures below 5 X 10(exp 5) K and above 2.5X 10(exp 6) K. The data also enabled temperature differentiations as low as 0:2 X 10(exp 6) K in different density structures. These observations showed how the passage of CMEs through the corona, prior to totality, produced large scale ripples and very sharp streaks, which could be identified with distinct temperatures for the first time. The ripples were most prominent in emission from spectral lines associated with temperatures around 10(exp 6) K. The most prominent streak was associated with a conical-shaped void in the emission from the coolest line of Fe IX and from the hottest line of Ni XV. A prominence, which erupted prior to totality, appeared in the shape of a hook in the cooler lines of Fe X and Fe XI, spanning 0.5 R(solar) in extent starting at a heliocentric distance of 1.3 R(solar), with a complex trail of hot and cool twisted structures connecting it to the solar surface. Simultaneous Fe X 17.4 nm observations from space by Proba2/SWAP provided an ideal opportunity for comparing emission from a coronal forbidden line, namely Fe X 637.4 nm, with a space-based EUV allowed line. Comparison of the Fe X 17.4 nm and 637.4 nm emission provided the first textbook example of the role of radiative excitation in extending the detectability of coronal emission to much larger heliocentric distances than its collisionally excited component. These eclipse observations demonstrate the unique capabilities of coronal forbidden lines for exploring the evolution of the coronal magnetic field in the heliocentric distance range of 1 - 3 R(solar), which is currently inaccessible to any space-borne or ground-based observatory.

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

2011-01-01

393

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

394

Possible dust contamination of the early solar system  

NASA Technical Reports Server (NTRS)

Measurements carried out over more than twenty years indicate a deficiency of neutrinos emitted from the deep interior of the Sun in conjunction with the neutrino flux expected from canonical solar models. The early measurements were sensitive only to high-energy neutrinos emitted from B-8 on a minor branch of the energy-producing nuclear reactions in the solar interior. Thus these measurements were not widely considered to be a definitive test of solar physics. However the more recent measurements, which are sensitive to lower energy neutrinos, produced primarily by the p-p reaction on the main energy-producing branch of the solar nuclear reactions, pose a far more significant mystery in physics. One possibility is that the Sun's interior opacity is lower than expected due to a paucity of elements. This paper discusses that the Sun formed from material less abundant in heavy elements than usually believed, and the subsequent contamination due to the settling of surrounding dust brought the abundance of heavy elements - in the protoplanetary nebula, and in the Sun's convective envelope - up to the currently observed value.

Levy, E. H.; Ruzmaikina, T. V.

1993-01-01

395

Possible dust contamination of the early solar system  

NASA Astrophysics Data System (ADS)

Measurements carried out over more than twenty years indicate a deficiency of neutrinos emitted from the deep interior of the Sun in conjunction with the neutrino flux expected from canonical solar models. The early measurements were sensitive only to high-energy neutrinos emitted from B-8 on a minor branch of the energy-producing nuclear reactions in the solar interior. Thus these measurements were not widely considered to be a definitive test of solar physics. However the more recent measurements, which are sensitive to lower energy neutrinos, produced primarily by the p-p reaction on the main energy-producing branch of the solar nuclear reactions, pose a far more significant mystery in physics. One possibility is that the Sun's interior opacity is lower than expected due to a paucity of elements. This paper discusses that the Sun formed from material less abundant in heavy elements than usually believed, and the subsequent contamination due to the settling of surrounding dust brought the abundance of heavy elements - in the protoplanetary nebula, and in the Sun's convective envelope - up to the currently observed value.

Levy, E. H.; Ruzmaikina, T. V.

1993-03-01

396

Towards a Realistic, Data-Driven Thermodynamic MHD Model of the Global Solar Corona  

Microsoft Academic Search

In this work we describe our implementation of a thermodynamic energy\\u000aequation into the global corona model of the Space Weather Modeling Framework\\u000a(SWMF), and its development into the new Lower Corona (LC) model. This work\\u000aincludes the integration of the additional energy transport terms of coronal\\u000aheating, electron heat conduction, and optically thin radiative cooling into\\u000athe governing magnetohydrodynamic

Cooper Downs; Ilia I. Roussev; Bart van der Holst; Noé Lugaz; Igor V. Sokolov; Tamas I. Gombosi

2009-01-01

397

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

398

Generation of ion cyclotron waves in the corona and solar wind  

NASA Astrophysics Data System (ADS)

examine the generation and nonlinear evolution of ion cyclotron waves in the corona and solar wind, we perform electromagnetic simulations using a wide range of plasma conditions and ion velocity distribution functions. The source of the instability is temperature anisotropy of ions with temperature perpendicular to the magnetic field larger than parallel. For velocity distribution we use Maxwellian, bi-Maxwellian, and Fermi-accelerated functions with perpendicular temperature larger than parallel with the aim to understand the extent to which the details of the distribution function impact the general properties and the nonlinear evolution of the instability. The results show that in a proton-electron plasma, ion cyclotron waves are generated over a wide range of temperature anisotropies and plasma beta. Also, the general properties of the instability and the nonlinear evolution of the waves are not sensitive to the details of the velocity distribution functions. Allowing for the presence of minor ion species we show that these ions by themselves can drive the instability and generate waves with frequencies below the gyrofrequency of the minor ions. In the event that protons also have temperature anisotropy, waves on the proton branch are also generated. Results using bi-Maxwellian or Fermi-accelerated velocity distribution functions show similar properties for the instability and the nonlinear evolution of the waves. However, differences are found when allowing for relative drifts between the protons and minor ions in that when using Fermi-accelerated distribution functions oblique ion cyclotron waves are generated that are not observed in simulations using bi-Maxwellian distribution function.

Omidi, N.; Isenberg, P.; Russell, C. T.; Jian, L. K.; Wei, H. Y.

2014-03-01

399

TOWARD A REALISTIC THERMODYNAMIC MAGNETOHYDRODYNAMIC MODEL OF THE GLOBAL SOLAR CORONA  

SciTech Connect

In this work, we describe our implementation of a thermodynamic energy equation into the global corona model of the Space Weather Modeling Framework and its development into the new lower corona (LC) model. This work includes the integration of the additional energy transport terms of coronal heating, electron heat conduction, and optically thin radiative cooling into the governing magnetohydrodynamic (MHD) energy equation. We examine 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 condition where the transition region can be modeled in its entirety. Via observation synthesis from model results and the subsequent comparison to full Sun extreme ultraviolet and soft X-ray observations of Carrington rotation 1913 centered on 1996 August 27, we demonstrate the need for these additional considerations when using global MHD models to describe the unique conditions in the low corona. Through multiple simulations, we examine the ability of the LC model to assess and discriminate between coronal heating models, and find that a relative simple empirical heating model is adequate in reproducing structures observed in the low corona. We show that the interplay between coronal heating and electron heat conduction provides significant feedback onto the three-dimensional magnetic topology in the low corona as compared to a potential field extrapolation, and that this feedback is largely dependent on the amount of mechanical energy introduced into the corona.

Downs, Cooper; Roussev, Ilia I.; Lugaz, Noe [Institute for Astronomy, University of Hawaii at Manoa, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Van der Holst, Bart; Sokolov, Igor V.; Gombosi, Tamas I., E-mail: cdowns@ifa.hawaii.ed [Center for Space Environment Modeling, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109 (United States)

2010-04-01

400

FIELD LINES TWISTING IN A NOISY CORONA: IMPLICATIONS FOR ENERGY STORAGE AND RELEASE, AND INITIATION OF SOLAR ERUPTIONS  

SciTech Connect

We present simulations modeling closed regions of the solar corona threaded by a strong magnetic field where localized photospheric vortical motions twist the coronal field lines. The linear and nonlinear dynamics are investigated in the reduced magnetohydrodynamic regime in Cartesian geometry. Initially the magnetic field lines get twisted and the system becomes unstable to the internal kink mode, confirming and extending previous results. As typical in this kind of investigations, where initial conditions implement smooth fields and flux-tubes, we have neglected fluctuations and the fields are laminar until the instability sets in. However, previous investigations indicate that fluctuations, excited by photospheric motions and coronal dynamics, are naturally present at all scales in the coronal fields. Thus, in order to understand the effect of a photospheric vortex on a more realistic corona, we continue the simulations after kink instability sets in, when turbulent fluctuations have already developed in the corona. In the nonlinear stage the system never returns to the simple initial state with ordered twisted field lines, and kink instability does not occur again. Nevertheless, field lines get twisted, although in a disordered way, and energy accumulates at large scales through an inverse cascade. This energy can subsequently be released in micro-flares or larger flares, when interaction with neighboring structures occurs or via other mechanisms. The impact on coronal dynamics and coronal mass ejections initiation is discussed.

Rappazzo, A. F. [Bartol Research Institute, Department of Physics and Astronomy, University of Delaware, DE 19716 (United States); Velli, M. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Einaudi, G., E-mail: rappazzo@udel.edu [Berkeley Research Associates, Inc., 6537 Mid Cities Avenue, Beltsville, MD 20705 (United States)

2013-07-10

401

Field Lines Twisting in a Noisy Corona: Implications for Energy Storage and Release, and Initiation of Solar Eruptions  

NASA Astrophysics Data System (ADS)

We present simulations modeling closed regions of the solar corona threaded by a strong magnetic field where localized photospheric vortical motions twist the coronal field lines. The linear and nonlinear dynamics are investigated in the reduced magnetohydrodynamic regime in Cartesian geometry. Initially the magnetic field lines get twisted and the system becomes unstable to the internal kink mode, confirming and extending previous results. As typical in this kind of investigations, where initial conditions implement smooth fields and flux-tubes, we have neglected fluctuations and the fields are laminar until the instability sets in. However, previous investigations indicate that fluctuations, excited by photospheric motions and coronal dynamics, are naturally present at all scales in the coronal fields. Thus, in order to understand the effect of a photospheric vortex on a more realistic corona, we continue the simulations after kink instability sets in, when turbulent fluctuations have already developed in the corona. In the nonlinear stage the system never returns to the simple initial state with ordered twisted field lines, and kink instability does not occur again. Nevertheless, field lines get twisted, although in a disordered way, and energy accumulates at large scales through an inverse cascade. This energy can subsequently be released in micro-flares or larger flares, when interaction with neighboring structures occurs or via other mechanisms. The impact on coronal dynamics and coronal mass ejections initiation is discussed.

Rappazzo, A. F.; Velli, M.; Einaudi, G.

2013-07-01

402

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

403

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

404

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

405

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  

NASA Astrophysics Data System (ADS)

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° 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° 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° 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 ?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° 8032 shows emission features that may be associated with C60. The other two stars do not show evidence of C60. 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° 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° 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° 8032 may consist of interstellar medium swept up during mass-loss episodes.

Clayton, Geoffrey C.; De Marco, O.; Whitney, B. A.; Babler, B.; Gallagher, J. S.; Nordhaus, J.; Speck, A. K.; Wolff, M. J.; Freeman, W. R.; Camp, K. A.; Lawson, W. A.; Roman-Duval, J.; Misselt, K. A.; Meade, M.; Sonneborn, G.; Matsuura, M.; Meixner, M.

2011-08-01

406

Solar Heating of Suspended Particles and the Dynamics of Martian Dust Devils  

NASA Technical Reports Server (NTRS)

The heat input to Martian dust devils due to solar warming of suspended particles is assessed based on a prior estimate of dust loading and from an analysis of shadows cast by dust devils in images taken from orbit. Estimated values for solar heating range from 0.12 to 0.57 W/m3 with associated temperature increases of 0.011 to 0.051(deg)C per second. These warming rates are comparable to the adiabatic cooling rate expected for a gas parcel rising on Mars with a vertical velocity of 10 m/s. Solar warming of suspended dust serves to maintain buoyancy in a rising dust plume and may be one cause for the large scale of dust devils observed on Mars.

Fuerstenau, Stephen D.

2006-01-01

407

A Low-Frequency (30 - 110 MHz) Antenna System for Observations of Polarized Radio Emission from the Solar Corona  

NASA Astrophysics Data System (ADS)

An interferometer antenna system to observe polarized radio emission from the solar corona at different frequencies in the range 30 - 110 MHz has been commissioned recently by the Indian Institute of Astrophysics at the Gauribidanur Radio Observatory (latitude 13°36'12''N and longitude 77°27'07''E), about 100 km north of Bangalore ( http://www.iiap.res.in/centres_radio.htm ). This paper describes the antenna system, associated analog/digital receiver setup, calibration scheme, and preliminary results.

Ramesh, R.; Kathiravan, C.; Sundararajan, M. S.; Barve, Indrajit V.; Sastry, C. V.

2008-12-01

408

Physical conditions in the low corona and chromosphere of solar active regions according to spectral radar measurements  

NASA Astrophysics Data System (ADS)

The physical conditions in the low corona and chromosphere of solar active regions are studied. A diagnostics technique based on multiwave observations in the centimeter range, photospheric magnetic field extrapolation, and radioemission calculations has been applied. The calculated spatial and spectral structure of the radioemission has been compared with RATAN-600 spectral-polarization observations with a high spatial resolution. The effect of the plasma physical parameters on the emission structure character in a complex magnetic field topology in active regions is analyzed. Modeling of the spectral singularities at a quasi-periodic propagation of the radioemission is presented.

Kaltman, T. I.; Bogod, V. M.; Stupishin, A. G.; Yasnov, L. V.

2013-12-01

409

Electrostatic Charging of Lunar Dust by UV Photoelectric Emissions and Solar Wind Electrons  

NASA Technical Reports Server (NTRS)

The ubiquitous presence of dust in the lunar environment with its high adhesive characteristics has been recognized to be a major safety issue that must be addressed in view of its hazardous effects on robotic and human exploration of the Moon. The reported observations of a horizon glow and streamers at the lunar terminator during the Apollo missions are attributed to the sunlight scattered by the levitated lunar dust. The lunar surface and the dust grains are predominantly charged positively by the incident UV solar radiation on the dayside and negatively by the solar wind electrons on the night-side. The charged dust grains are levitated and transported over long distances by the established electric fields. A quantitative understanding of the lunar dust phenomena requires development of global dust distribution models, based on an accurate knowledge of lunar dust charging properties. Currently available data of lunar dust charging is based on bulk materials, although it is well recognized that measurements on individual dust grains are expected to be substantially different from the bulk measurements. In this paper we present laboratory measurements of charging properties of Apollo 11 & 17 dust grains by UV photoelectric emissions and by electron impact. These measurements indicate substantial differences of both qualitative and quantitative nature between dust charging properties of individual micron/submicron sized dust grains and of bulk materials. In addition, there are no viable theoretical models available as yet for calculation of dust charging properties of individual dust grains for both photoelectric emissions and electron impact. It is thus of paramount importance to conduct comprehensive measurements for charging properties of individual dust grains in order to develop realistic models of dust processes in the lunar atmosphere, and address the hazardous issues of dust on lunar robotic and human missions.

Abbas, Mian M.; Tankosic, Dragana; Spann, James f.; LeClair, Andre C.; Dube, Michael J.

2008-01-01

410

Dust Accumulation and Solar Panel Array Performance on the Mars Exploration Rover (MER) Project  

NASA Technical Reports Server (NTRS)

One of the most fundamental design considerations for any space vehicle is its power supply system. Many options exist, including batteries, fuel cells, nuclear reactors, radioisotopic thermal generators (RTGs), and solar panel arrays. Solar arrays have many advantages over other types of power generation. They are lightweight and relatively inexpensive, allowing more mass and funding to be allocated for other important devices, such as scientific instruments. For Mars applications, solar power is an excellent option, especially for long missions. One might think that dust storms would be a problem; however, while dust blocks some solar energy, it also scatters it, making it diffuse rather than beamed. Solar cells are still able to capture this diffuse energy and convert it into substantial electrical power. For these reasons, solar power was chosen to be used on the 1997 Mars Pathfinder mission. The success of this mission set a precedent, as NASA engineers have selected solar power as the energy system of choice for all future Mars missions, including the Mars Exploration Rover (MER) Project. Solar sells have their drawbacks, however. They are difficult to manufacture and are relatively fragile. In addition, solar cells are highly sensitive to different parts of the solar spectrum, and finding the correct balance is crucial to the success of space missions. Another drawback is that the power generated is not a constant with respect to time, but rather changes with the relative angle to the sun. On Mars, dust accumulation also becomes a factor. Over time, dust settles out of the atmosphere and onto solar panels. This dust blocks and shifts the frequency of the incoming light, degrading solar cell performance. My goal is to analyze solar panel telemetry data from the two MERs (Spirit and Opportunity) in an effort to accurately model the effect of dust accumulation on solar panels. This is no easy process due to the large number of factors involved. Changing solar flux (the amount of solar energy reaching the planet), solar spectrum, solar angle, rover tilt, and optical depth (the opacity of the atmosphere due to dust) were the most significant. Microsoft Excel and Visual Basic are used for data analysis. The results of this work will be used to improve the dust accumulation and atmosphere effects model that was first created after the Mars Pathfinder mission. This model will be utilized and applied when considering the design of solar panel array systems on future Mars projects. Based on this data, and depending upon the tenure and application of the mission, designers may also elect to employ special tools to abate dust accumulation, or decide that the expected level of accumulation is acceptable.

Turgay, Eren H.

2004-01-01

411

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

412

Observations of R Coronae Borealis stars in decline - Empirical arguments for dust formation near the stellar surface  

NASA Technical Reports Server (NTRS)

We present new IUE observations which monitor the spectroscopic evolution of RY Sgr through a deep decline. These data, along with other IUE, visible, and infrared observations of declines in RY Sgr, R CrB, and V854 Cen, are considered in an attempt to understand the dust formation process and the source of the narrow- and broad-line emission seen during declines. Spectroscopic, photometric, and polarimetric data covering 10 declines of these stars have been analyzed. The evolution of the UV emission spectrum is similar to that found in the visible. Previous models of dust formation assume that dust forms around 20 stellar radii, where gas ejected from the star is cool enough to condense. However, the spectral evolution, and the dispersal times of dust implied by the light curve are consistent with dust forming within a few stellar radii and moving outward due to radiation pressure. The expanding dust cloud eclipses the photosphere and parts of the emission line region, causing the observed spectral evolution.

Clayton, Geoffrey C.; Whitney, Barbara A.; Stanford, S. A.; Drilling, John S.

1992-01-01

413

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

NASA Technical Reports Server (NTRS)

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 Solar Radius from Sun center in the solar north, east and west, respectively, and (0.93 +/- 0.12) MK, at 1.2 Solar Radius from Sun center in the solar west. The corresponding outflow speeds obtained from the spectral fit are (103 +/- 92) km/s, (0 + 10) km/s, (0+10) km/s, and (0+10) km/s. Since the observations were taken only at 1.1 Solar Radius and 1.2 Solar Radius 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 Solar Radius from Sun center is larger at the north (polar region) than the east and west (equatorial region).

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

2011-01-01

414

The white light solar corona--an atlas of k-coronameter synoptic charts August 1980 - September 1981. Technical note  

SciTech Connect

A synoptic observing program was undertaken at the Mauna Loa Solar Observatory, a site operated by the High Altitude Observatory to study the solar corona using the Mark III K-Coronameter. Daily pB images were used to extract three pB ( ) azimuthal scans located at heights of 1.3, 1.7, and 2.1 Rq. Four final data products are given in this atlas: (1) interpolated pB contour plots for h = 1.3 and 1.7 Rq for each Carrington rotation; (2) shaded pB charts for each Carrington rotation; (3) standard zonal pB average values for each day; and (4) autocorrelation estimates of pB variation for equatorial and high latitude structure and an autocorrelation coefficient for an amplitude-independent, first moment of the pB distribution.

Fisher, R.; Garcia, C.; Rock, K.; Seagraves, P.; Yasukawa, E.

1982-01-01

415

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

416

Formation and Reconnection of Three-Dimensional Current Sheets in the Solar Corona  

Microsoft Academic Search

Current-sheet formation and magnetic reconnection are believed to be the basic physical processes responsible for much of the activity observed in astrophysical plasmas, such as interchange reconnection at the boundaries between coronal holes and helmet streamers in the Sun's corona. We investigate these processes for a magnetic configuration consisting of a uniform background field and an embedded line dipole, a

Justin K. Edmondson; S. K. Antiochos; C. DeVore; M. Velli; T. H. Zurbuchen

2010-01-01

417

Dynamical and Collisional Evolution of Asteroidal Dust Particles and the Structure of the Solar System Dust Bands  

NASA Astrophysics Data System (ADS)

Recent modeling of the solar system dust bands has shown a significant discrepancy between the mean proper inclinations of the "ten-degree" band and the Eos asteroid family, its putative source. This has led to the suggestion that the dust bands did not result from the gradual comminution of large, ancient asteroid families but were instead produced by recent catastrophic disruptions of asteroids, such as those that generated the Karin cluster and the Veritas family. The small particles produced in such collisional events spiral rapidly into the Sun under the effect of Poynting-Robertson (P-R) drag. Larger particles have correspondingly longer P-R drag lifetimes but are more likely to be fragmented by inter-particle collisions. It is these large particles and their collisional fragments that we observe today as the dust bands, the decaying remnant of a much larger influx of material. The structure of the dust bands is therefore determined by the combined dynamical and collisional behavior of a realistic size distribution of particles. We present the results of numerical simulations showing the evolution of asteroidal dust particles under the effects of radiation pressure, P-R drag, solar wind drag, planetary perturbations, and stochastic size changes due to particle fragmentation. These results reveal that: (i) the orientation of the mean plane of symmetry of the dust bands outside 2AU is dominated by the effect of Jupiter as it evolves through its secular cycle and it is for this reason that we are able to observe the bands; (ii) the effect of inter-particle collisions introduces dispersion in the distribution of the particle orbits; and (iii) the inner edge to the dust bands at 2AU is a consequence of the effect of secular resonances dispersing particle orbits to the extent that the dust band signal merges into the flux from the background zodiacal cloud.

Dermott, S. F.; Kehoe, T. J. J.; Mahoney-Hopping, L.

2005-12-01

418

The Dust Properties of Hot R Coronae Borealis Stars and a Wolf-Rayet Central Star of a Planetary Nebula: In Search of the Missing Link  

NASA Technical Reports Server (NTRS)

We present new Spitzer IIRS 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. T