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1

The Solar Corona  

NSDL National Science Digital Library

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

David Hathaway

2

Polarization of the solar corona.  

NASA Technical Reports Server (NTRS)

A method of obtaining polarized photographs of the solar corona during total eclipse is described. The required equipment is a reflex viewing type camera with a lens of adequate focal length to give an image of the corona a few millimeters in diameter at the focal plane. A sheet of linear polarizing filter material is placed directly in front of the lens. The filter is mounted in such a way so as to permit a set of four exposures of equal length to be taken after totality begins. Since the light of the corona is highly polarized, the resultant set of photographs will show marked differences in the shape of the corona.

Feibelman, W. A.

1972-01-01

3

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

4

Petrovay: Solar physics Chromosphere and corona THE SOLAR CHROMOSPHERE  

E-print Network

Petrovay: Solar physics Chromosphere and corona THE SOLAR CHROMOSPHERE Visible in eclipses as red.) The quiet chromosphere Lower boundary: T-minimum at z = 500 km (T = 4200K, = 10-13 g/cm3 ) Upper boundary brightness temperature at 10.7 cm: Tb 10 000 K. #12;Petrovay: Solar physics Chromosphere and corona Mean

Petrovay, Kristóf

5

Global Magnetohydrodynamic Modeling of the Solar Corona  

NASA Astrophysics Data System (ADS)

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.

1997-02-01

6

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

7

The solar corona on 31 July, 1981  

NASA Astrophysics Data System (ADS)

Results of observations of the solar corona near or at the time of total eclipse, 31 July 1981, are presented. The High Altitude Observatory coronal eclipse camera and the MK-III K-coronameter were employed to record the lower portions of the corona, while the distribution of white light material above 3 solar radii was observed with the Naval Research Laboratory satellite coronagraph on P78-1. The coronal structure is described and the coronal active regions are identified using these data sets. It is found that the polar coronal holes, as developed at this time in the solar cycle, were offset from the poles of rotation and both were seen displaced eastward on the eclipse day. High altitude streamers are found in all three data sets, extending from the base of the corona outward to at least eight solar radii from the center of the sun. In addition, at least two transients were observed on the eclipse day, but it is likely that no transient was in progress during any observation along the eclipse path. A distribution of the white-light corona, derived from synoptic K-coronameter data, is also presented.

Fisher, R. R.; Lacey, L. R.; Rock, K. A.; Yasukawa, E. A.; Sheeley, N. R., Jr.; Michels, D. J.; Howard, R. A.; Koomen, M. J.; Bagrov, A.

1983-03-01

8

Turbulent photospheric drivers of multiscale solar corona  

NASA Astrophysics Data System (ADS)

We investigate the collective dynamics of transient photospheric and coronal events detected using high-resolution solar magnetograms and coronal emission images. We focus on statistical, ensemble-averaged properties of the interacting solar regions [Uritsky et al., 2011, 2013, 2014; Uritsky and Davila, 2012], as opposed to case-oriented methodologies recruited in some previous studies. The behavior of solar events is studied in the three-dimensional space-time enabling accurate representation of the event evolution. By applying advanced data analysis methods including feature tracking algorithms, multiscale correlation analysis and scaling analysis techniques, we identify leading physical scenarios of the photosphere - corona coupling in quiet and active solar regions, and strive to identify new statistical precursors of coronal eruptions. We also discuss the possibility of modeling multiscale photosphere - corona interactions using idealized three-dimensional MHD models. The obtained results shed a new light on the origin of multiscale dissipation in the solar corona by enabling quantitative validation of several popular statistical physical scenarios, such as e.g. intermittent turbulence, self-organized criticality, and topological complexity.

Uritsky, Vadim M.; Ofman, Leon; Davila, Joseph M.

2015-04-01

9

MASC: Magnetic Activity of the Solar Corona  

NASA Astrophysics Data System (ADS)

We present MASC, an innovative payload designed to explore the magnetic activity of the solar corona. It is composed of three complementary instruments: a Hard-X-ray spectrometer, a UV / EUV imager, and a Visible Light / UV polarimetric coronagraph able to measure the coronal magnetic field. The solar corona is structured in magnetically closed and open structures from which slow and fast solar winds are respectively released. In spite of much progress brought by two decades of almost uninterrupted observations from several space missions, the sources and acceleration mechanisms of both types are still not understood. This continuous expansion of the solar atmosphere is disturbed by sporadic but frequent and violent events. Coronal mass ejections (CMEs) are large-scale massive eruptions of magnetic structures out of the corona, while solar flares trace the sudden heating of coronal plasma and the acceleration of electrons and ions to high, sometimes relativistic, energies. Both phenomena are most probably driven by instabilities of the magnetic field in the corona. The relations between flares and CMEs are still not understood in terms of initiation and energy partition between large-scale motions, small-scale heating and particle acceleration. The initiation is probably related to magnetic reconnection which itself results magnetic topological changes due to e.g. flux emergence, footpoints motions, etc. Acceleration and heating are also strongly coupled since the atmospheric heating is thought to result from the impact of accelerated particles. The measurement of both physical processes and their outputs is consequently of major importance. However, despite its fundamental importance as a driver for the physics of the Sun and of the heliosphere, the magnetic field of our stars outer atmosphere remains poorly understood. This is due in large part to the fact that the magnetic field is a very difficult quantity to measure. Our knowledge of its strength and orientation is primarily based on extrapolations from photospheric observations, not from direct measurements. These extrapolations require strong assumptions on critical but unobserved quantities and thus fail to accurately reproduce the complex topologies inferred from remote-sensing observations of coronal structures in white light, EUV, and X-rays. Direct measurements of the coronal magnetic field are also clearly identified by the international heliophysics community as a key element susceptible to lead to major breakthroughs in the understanding of our star. MASC is thus designed to answer the following top-level scientific questions: 1. What is the global magnetic field configuration in the corona? 2. What is the role of the magnetic field in the triggering of flares and CMEs? 3. What is the role of the magnetic field in the acceleration mechanisms of the solar winds? 4. What is the energy spectrum and in particular what are the highest energies to which charged particles can be accelerated in the solar corona? MASC will address these fundamental questions with a suite of instruments composed of an X-ray spectrometer, a UV / EUV imager, and a coronagraph working in the visible and at Lyman alpha. The spectrometer will provide information on the energetics of solar flares, in particular at very high energies of accelerated particles. The UV / EUV imager will provide constraints on the temperature of the flaring and non-flaring corona. The coronagraph will provide the number density of free electrons in the corona, maps of the outflow velocity of neutral hydrogen, and measurements of the coronal magnetic field, via the Hanle effect. These measurements will be performed at all steps of the flare-CME processes, thus providing a detailed picture of the solar coronal dynamics in the quiet and eruptive periods.

Auchere, Frederic; Fineschi, Silvano; Gan, Weiqun; Peter, Hardi; Vial, Jean-Claude; Zhukov, Andrei; Parenti, Susanna; Li, Hui; Romoli, Marco

10

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

11

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

12

Recycling of the Solar Corona's Magnetic Field  

NASA Astrophysics Data System (ADS)

Magnetic fields play a dominant role in the atmospheres of the Sun and other Sun-like stars. Outside sunspot regions, the photosphere of the so-called quiet Sun contains myriads of small-scale magnetic concentrations, with strengths ranging from the detection limit of ~1016 Mx up to ~31020 Mx. The tireless motion of these magnetic flux concentrations, along with the continual appearance and disappearance of opposite-polarity pairs of fluxes, releases a substantial amount of energy that may be associated with a whole host of physical processes in the solar corona, not least the enigma of coronal heating. We find here that the timescale for magnetic flux to be remapped in the quiet-Sun corona is, surprisingly, only 1.4 hr (around 1/10 of the photospheric flux recycling time), implying that the quiet-Sun corona is far more dynamic than previously thought. Besides leading to a fuller understanding of the origins of magnetically driven phenomena in our Sun's corona, such a process may also be crucial for the understanding of stellar atmospheres in general.

Close, R. M.; Parnell, C. E.; Longcope, D. W.; Priest, E. R.

2004-09-01

13

Turbulent heating of the corona and solar wind: the heliospheric  

E-print Network

Turbulent heating of the corona and solar wind: the heliospheric dark energy problem Stuart D. Bale that the gas is highly ionized, i.e. a magnetized collisionless plasma ( solar wind model A `solar wind' is accelerated from the corona - Hydrostatic solution (similar to Bondi accretion

14

High Energy Particles in the Solar Corona  

E-print Network

Collective Ampere law interactions producing magnetic flux tubes piercing through sunspots into and then out of the solar corona allow for low energy nuclear reactions in a steady state and high energy particle reactions if a magnetic flux tube explodes in a violent event such as a solar flare. Filamentous flux tubes themselves are vortices of Ampere currents circulating around in a tornado fashion in a roughly cylindrical geometry. The magnetic field lines are parallel to and largely confined within the core of the vortex. The vortices may thereby be viewed as long current carrying coils surrounding magnetic flux and subject to inductive Faraday and Ampere laws. These laws set the energy scales of (i) low energy solar nuclear reactions which may regularly occur and (ii) high energy electro-weak interactions which occur when magnetic flux coils explode into violent episodic events such as solar flares or coronal mass ejections.

A. Widom; Y. N. Srivastava; L. Larsen

2008-04-16

15

High Energy Particles in the Solar Corona  

E-print Network

Collective Ampere law interactions producing magnetic flux tubes piercing through sunspots into and then out of the solar corona allow for low energy nuclear reactions in a steady state and high energy particle reactions if a magnetic flux tube explodes in a violent event such as a solar flare. Filamentous flux tubes themselves are vortices of Ampere currents circulating around in a tornado fashion in a roughly cylindrical geometry. The magnetic field lines are parallel to and largely confined within the core of the vortex. The vortices may thereby be viewed as long current carrying coils surrounding magnetic flux and subject to inductive Faraday and Ampere laws. These laws set the energy scales of (i) low energy solar nuclear reactions which may regularly occur and (ii) high energy electro-weak interactions which occur when magnetic flux coils explode into violent episodic events such as solar flares or coronal mass ejections.

Widom, A; Larsen, L

2008-01-01

16

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

17

VARIABLE WINDS AND DUST FORMATION IN R CORONAE BOREALIS STARS  

SciTech Connect

We have observed P-Cygni and asymmetric, blue-shifted absorption profiles in the He I {lambda}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 {approx}400 km s{sup -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.; Zhang Wanshu [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 (United States); Geballe, T. R., E-mail: gclayton@fenway.phys.lsu.edu, E-mail: wzhan21@lsu.edu, E-mail: tgeballe@gemini.edu [Gemini Observatory, 670 N. A'ohoku Place, Hilo, HI 96720 (United States)

2013-08-01

18

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

19

Polarization studies of the solar corona on July 31, 1981.  

NASA Astrophysics Data System (ADS)

The solar corona continuous emission polarization features were studied on the basis of the measurements during the 31 July 1981 eclipse. During the total phase (74 s) the total radiation of the solar corona, the intensity of the linearly polarized component, the orientation of the polarization plane at 1700 points of the corona from 0.1 R_sun; to 6.5 R_sun; were investigated.

Kulidzhanishvili, V. I.; Nikol'Skij, G. M.; Stepanov, A. I.; Suladze, A. S.; Khutsishvili, Eh. V.

20

The Solar Corona at the 2015 Total Solar Eclipse  

NASA Astrophysics Data System (ADS)

We report on our successful observations of the solar corona at the 20 March 2015 total solar eclipse from our site at a latitude of about 78 on the Svalbard archipelago, and related observations by colleagues aloft. Our equipment included cameras for imaging at a variety of scales for use in making high-contrast composites, as reported our Astrophysical Journal article (2015) about our 2012 total solar eclipse observations and similar articles about the corona and changes in it at previous total eclipses. Our Svalbard equipment also included a spectrograph, with which we continued our monitoring of the ratio of the Fe XIV and Fe X coronal lines, which has recently been >1 with the solar maximum, a reversal from <1 at earlier eclipses closer to the last solar minimum. Our 2013 observations from Gabon showed two coronal mass ejections and an erupting prominence; the 2015 eclipse showed an erupting prominence and some unusual coronal structure in an overall coronal shape typical of solar maximum. We use our ground-based eclipse observations to fill the gap in imaging between the SDO and SWAP (17.4 nm) EUV observations on the solar disk and the inner location of the LASCO C2 occultation disk, with STEREO observations providing the possibility of three-dimensional interpretations. Our expedition was supported by a grant (9616-14) from the Committee for Research and Exploration of the National Geographic Society.

Pasachoff, Jay M.; Carter, Allison L.

2015-04-01

21

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

22

A study of the background corona near solar minimum  

NASA Technical Reports Server (NTRS)

Equatorial and polar K and F coronal components during the declining phase of the solar cycle are studied through use of the white light coronagraph data obtained by Skylab. At this phase of the solar cycle, streams and holes dominate the equatorial corona (approximately 50 and 30% of the time, respectively) between 2.5 and 5.5 solar radii; however, two episodes are noted when equatorial background density of the corona could be distinguished. The derived background density is less than 15% below values predicted by the models of Newkirk (1967) and Saito (1970). The brightness of the F-corona is also discussed.

Saito, K.; Poland, A. I.; Munro, R. H.

1977-01-01

23

Solar corona/prominence seen through the White Light Coronograph  

NASA Technical Reports Server (NTRS)

The solar corona and a solar prominence as seen through the White Light Coronograph, Skylab Experiment S052, on January 17, 1974. This view was reproduced from a television transmission made by a TV camera aboard the Skylab space station in Earth orbit. The bright spot is a burn in the vidicon. The solar corona is the halo around the Sun which is normally visible only at the time of solar eclipse by the Moon. The Skylab coronography uses an externally-mounted disk system which occults the brilliant solar surface while allowing the fainter radiation of the corona to enter an annulus and be photographed. A mirror system allows either TV viewing of the corona or photographic recording of the image.

1974-01-01

24

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

25

Photometry and structure of the solar corona during the solar eclipse of July 31, 1981  

NASA Astrophysics Data System (ADS)

The observational material taken by the Abastumani Astrophysical Observatory expedition at the total solar eclipse of July 31, 1981 has been used for the structural and photometric investigation of the corona. The photometry of the corona is made by the equidensity method. The intensities are expressed in absolute units. The structural peculiarities of the corona are described. The geometric shape and photometric data permit to assign the corona to the solar activity maximum type.

Khetsuriani, Ts. S.; Dzhaparidze, D. R.

26

Pulsed corona modelling of a wire-cylinder ESP under dust loading condition  

Microsoft Academic Search

Modelling of the electrical conditions of an electrostatic precipitator (ESP) with dust loading under pulsed corona is difficult, and little progress has been made in this field. A method for the pulsed corona modelling of a wire-cylinder ESP based on the characteristics of Trichel pulses and the applied pulse voltage is developed and a novel way of dealing the particle

X. Liang; S. Jayaram; J. S. Chang; A. Berezein

1999-01-01

27

Color photometry of the solar corona on July 31, 1981  

NASA Astrophysics Data System (ADS)

Photographs of the outer solar corona obtained by the Soviet-French expedition to Kazakhstan during the total eclipse of July 31, 1981, are investigated. An F = 300 mm/5.6 camera and 60-millimeter color reversal Ektachrome-64 film were used. The radial brightness distribution is obtained along radial cross sections passing through the south 'coronal hole' and a bright region of the corona in blue (450 nm) and red (630 nm) light. By comparison with the sun, the corona is redder (by at least 10 percent) at distances of 2-6 solar radii. Allowance is made for the emission of the sky and the aureole. Isophotes are constructed (r less than 10 solar radii) in blue and red light. The brightness of the corona averaged over all directions also points to reddening. The flattening of the outer isophotes increases with distance.

Nikolskij, G. M.

1983-12-01

28

New Images of the Solar Corona  

NASA Astrophysics Data System (ADS)

In 1.5 years of operation, The Extreme Ultraviolet Imaging Telescope (EIT) on SOHO has obtained over 40,000 images of the Sun in four wavebands between 171 Angstroms and 304 Angstroms, with spatial resolution limited only by the pixel scale of 2.59 arcsec. These images, and in particular compilations of time series of images into digital movies, have changed several of our ideas about the corona at temperatures of 0.9 - 2.5 MK. For the first time, we are able to see outflow in polar plumes and microjets inputting momentum into the high-speed, polar wind flow. For the first time, in conjunction with the LASCO coronagraphs and ground-based He I imagers, we have been able to see all the structures involved in coronal mass ejections (CMEs), from the surface of the Sun to 30 solar radii above it. In several cases, we have been able to observe directly the dramatic Moreton waves emanating from the active region where the CMEs originate, and radiating across virtually the entire visible hemisphere of the Sun. We interpret these large-scale coronal disturbances as fast-mode waves. Such events appear in the SOHO-LASCO coronagraphs as earthward-directed, and several have been detected by solar wind monitoring experiments on SOHO and other spacecraft. We have been able to view a variety of small-scale phenomena as well, including motions in prominences and filaments, macrospicular and polar microjet eruptions, and fine structures in the polar crown filament belt. The multi-wavelength capability of EIT makes it possible to determine the temperature of the coronal plasma and, here, too, we have been afforded a novel view: the heating in coronal active regions occurs over a considerably larger area than the high-density loops structures alone (i.e., bright features) would indicate.

Gurman, Joseph B.; Thompson, Barbara J.; Newmark, Jeffrey A.; Deforest, Craig E.

29

MAGNETOHYDRODYNAMIC SIMULATIONS OF THE SOLAR CORONA AND SOLAR WIND USING A BOUNDARY TREATMENT TO LIMIT SOLAR WIND MASS FLUX  

E-print Network

MAGNETOHYDRODYNAMIC SIMULATIONS OF THE SOLAR CORONA AND SOLAR WIND USING A BOUNDARY TREATMENT TO LIMIT SOLAR WIND MASS FLUX Keiji Hayashi W. W. Hansen Experimental Physics Laboratory, Stanford ABSTRACT Magnetohydrodynamic simulations of the solar corona and solar wind are sensitive to conditions

California at Berkeley, University of

30

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

31

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

32

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

33

Probing the solar corona with very long baseline interferometry  

PubMed Central

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 Suns 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 spatialtemporal samplings over a complete solar cycle. PMID:24946791

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

2014-01-01

34

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

35

A theory of heating of quiet solar corona  

NASA Astrophysics Data System (ADS)

A theory is proposed to discuss the creation of hot solar corona. We pay special attention to the transition region and the low corona, and consider that the sun is quiet. The proposed scenario suggests that the protons are heated by intrinsic Alfvnic turbulence, while the ambient electrons are heated by the hot protons via collisions. The theory contains two prime components: the generation of the Alfvnic fluctuations by the heavy minor ions in the transition region and second, the explanation of the temperature profile in the low solar atmosphere. The proposed heating process operates continuously in time and globally in space.

Wu, C. S.; Yoon, P. H.; Wang, C. B.

2015-03-01

36

Radio Remote Sensing of the Corona and the Solar Wind  

E-print Network

Modern radio telescopes are extremely sensitive to plasma on the line of sight from a radio source to the antenna. Plasmas in the corona and solar wind produce measurable changes in the radio wave amplitude and phase, and the phase difference between wave fields of opposite circular polarization. Such measurements can be made of radio waves from spacecraft transmitters and extragalactic radio sources, using radio telescopes and spacecraft tracking antennas. Data have been taken at frequencies from about 80 MHz to 8000 MHz. Lower frequencies probe plasma at greater heliocentric distances. Analysis of these data yields information on the plasma density, density fluctuations, and plasma flow speeds in the corona and solar wind, and on the magnetic field in the solar corona. This paper will concentrate on the information that can be obtained from measurements of Faraday rotation through the corona and inner solar wind. The magnitude of Faraday rotation is proportional to the line of sight integral of the plasma density and the line-of-sight component of the magnetic field. Faraday rotation provides an almost unique means of estimating the magnetic field in this part of space. This technique has contributed to measurement of the large scale coronal magnetic field, the properties of electromagnetic turbulence in the corona, possible detection of electrical currents in the corona, and probing of the internal structure of coronal mass ejections (CMEs). This paper concentrates on the search for small-scale coronal turbulence and remote sensing of the structure of CMEs. Future investigations with the Expanded Very Large Array (EVLA) or Murchison Widefield Array (MWA) could provide unique observational input on the astrophysics of CMEs.

Steven R. Spangler; Catherine A. Whiting

2008-09-26

37

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

38

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

39

Measurement of Electrical Currents in the Solar Corona  

NASA Astrophysics Data System (ADS)

Some theories for heating of the solar corona invoke Joule heating by electrical currents. Observations of spatially-extended radio sources through the corona show times when there is a difference in the Faraday rotation between two lines of sight separated by about 33,000 km in the corona. Ampere's Law is used to relate these observations to the presence of electrical current flowing between the two lines of sight. I infer a current of 2.5 x10^9 Amperes in the case of the strongest signal, and a current of 2.3 x10^8 Amperes in another, marginally significant detection. A model of coronal current sheets is used to interpret the current measurements, and estimate the volumetric heating rate due to Joule dissipation. The model uses the Spitzer resistivity. The model heating rate is approximately 6 orders of magnitude less than independent, observational estimates in the relevant part of the corona. Either the currents detected play a negligible role in coronal heating, or the effective resistivity in the corona is 6 orders of magnitude larger than the Spitzer value.

Spangler, Steven

2007-11-01

40

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 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

41

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

42

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

43

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.

44

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

45

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

46

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

47

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

SciTech Connect

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

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

2012-12-20

48

Radio seismology of the outer solar corona  

E-print Network

Observed oscillations of coronal loops in EUV lines have been successfully used to estimate plasma parameters in the inner corona ( 0.2 R_0). We use the large Ukrainian radio telescope URAN-2 to observe type IV radio burst at the frequency range of 8-32 MHz during the time interval of 09:50-12:30 UT in 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 R_0 altitude. We derive and solve the dispersion relation of trapped MHD oscilla...

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

2013-01-01

49

Magnetic tornadoes as energy channels into the solar corona  

NASA Astrophysics Data System (ADS)

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.

Wedemeyer-Bhm, Sven; Scullion, Eamon; Steiner, Oskar; Rouppe van der Voort, Luc; de La Cruz Rodriguez, Jaime; Fedun, Viktor; Erdlyi, Robert

2012-06-01

50

Alfvnic 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). Alfvn 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 Alfvnic 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 Alfvnic motions permeate the dynamic and finely structured outer solar atmosphere. The ubiquitous outward-propagating Alfvnic 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

51

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 {} 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 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

52

On the Size of Structures in the Solar Corona  

E-print Network

Fine-scale structure in the corona appears not to be well resolved by current imaging instruments. Assuming this to be true offers a simple geometric explanation for several current puzzles in coronal physics, including: the apparent uniform cross-section of bright threadlike structures in the corona; the low EUV contrast (long apparent scale height) between the top and bottom of active region loops; and the inconsistency between loop densities derived by spectral and photometric means. Treating coronal loops as a mixture of diffuse background and very dense, unresolved filamentary structures address these problems with a combination of high plasma density within the structures, which greatly increases the emissivity of the structures, and geometric effects that attenuate the apparent brightness of the feature at low altitudes. It also suggests a possible explanation for both the surprisingly high contrast of EUV coronal loops against the coronal background, and the uniform ``typical'' height of the bright portion of the corona (about 0.3 solar radii) in full-disk EUV images. Some ramifications of this picture are discussed, including an estimate (10-100 km) of the fundamental scale of strong heating events in the corona.

C. E. DeForest

2007-02-22

53

A Technique for Measuring Electrical Currents in the Solar Corona  

E-print Network

A technique is described for measuring electrical currents in the solar corona. It uses radioastronomical polarization measurements of a spatially-extended radio source viewed through the corona. The observations yield the difference in the Faraday rotation measure between two closely-spaced lines of sight through the corona, a measurement referred to as {\\em differential Faraday rotation}. It is shown that the expression for differential Faraday rotation is proportional to the path integral $\\oint n \\vec{B}\\cdot \\vec{ds}$ where $n$ is the plasma density and $\\vec{B}$ is the coronal magnetic field. The integral is around a closed loop (Amperian Loop) in the corona. If the plasma density is assumed roughly constant, the differential Faraday rotation is proportional to the current within the loop, via Ampere's Law. The validity of the constant density approximation is discussed, and two test cases are presented in which the associated error in the inferred current is small, of order tens of percent or less. The method is illustrated with observations of the radio source 3C228 with the Very Large Array (VLA) in August, 2003. A measurement of a differential Faraday rotation ``event'' on August 16, 2003, yields an estimate of $2.5 \\times 10^9$ Amperes in the Amperian Loop. A smaller event on August 18 yields an enclosed current of $2.3 \\times 10^8$ Amperes. The implications of these currents for coronal heating are briefly discussed.

Steven R. Spangler

2007-09-11

54

Release timescales of solar energetic particles in the low corona  

NASA Astrophysics Data System (ADS)

Aims: We present a systematic study of the timing and duration of the release processes of near-relativistic (NR; >50 keV) electrons in the low corona. Methods: We analyze seven well-observed events using in situ measurements by both the ACE and Wind spacecraft and context electromagnetic observations in soft X-rays, radio, hard X-rays and white light. We make use of velocity dispersion analysis to estimate the release time of the first arriving electrons and compare with the results obtained by using a simulation-based approach, taking interplanetary transport effects into account to unfold the NR electron release time history from in situ measurements. Results: The NR electrons observed in interplanetary space appear to be released during either short (<30 min) or long (>2 h) periods. The observation of NR electron events showing beamed pitch-angle distributions (PADs) during several hours is the clearest observational signature of sustained release in the corona. On the other hand, the in situ observation of PADs isotropizing in less than a couple of hours is a clear signature of a prompt release of electrons in the low corona. Short release episodes appear to originate in solar flares, in coincidence with the timing of the observed type III radio bursts. Magnetic connectivity plays an important role. Only type III radio bursts reaching the local plasma line measured at 1 AU are found to be related with an associated release episode in the low corona. Other type III bursts may also have a release of NR electrons associated with them, but these electrons do not reach L1. Long release episodes appear associated with signatures of long acceleration processes in the low corona (long decay of the soft X-ray emission, type IV radio bursts, and time-extended microwave emission). Type II radio bursts are reported for most of the events and do not provide a clear discrimination between short and long release timescales.

Agueda, N.; Klein, K.-L.; Vilmer, N.; Rodrguez-Gasn, R.; Malandraki, O. E.; Papaioannou, A.; Subir, M.; Sanahuja, B.; Valtonen, E.; Drge, W.; Nindos, A.; Heber, B.; Braune, S.; Usoskin, I. G.; Heynderickx, D.; Talew, E.; Vainio, R.

2014-10-01

55

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

56

Dynamics and Thermodynamics of the Solar Corona as Inferred from Total Solar Eclipse Observations  

NASA Astrophysics Data System (ADS)

Imaging the solar corona during total solar eclipses in broadband white light and in a number of forbidden emission lines in the visible continues to yield unique insights into the dynamics and thermodynamics of the coronal plasma. An overview of recent multiwavelength eclipse observations, spanning almost a solar cycle, will be presented. Particular emphasis will be placed on the thermodynamics of dynamic events such prominence eruptions, plasmoids and CMEs, that are captured in the eclipse images either as they occurred, or from the trails they left behind in the corona.

Habbal, Shadia; Druckmuller, Miloslav; Morgan, Huw; Ding, Adalbert

2015-04-01

57

Solar cycle 24 in Photosphere, Chromosphere and Corona.  

NASA Astrophysics Data System (ADS)

The solar cycle 24 shows an interesting behavior and it is a subject of current discussions. Comparison this cycle with previous ones displays relatively small activity which may be a consequence of the interaction of the long-tem variations of the solar activity and sunspot solar cycle. For example, the Solar Dynamics Observatory (SDO) provides us with multi-waves imagery from Extreme Ultraviolet (EUV) to visible light as well as magnetic field measurements. These data give us an opportunity 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). Here, present the global evolution of solar cycle 24 from May 20, 2010 to up the present, using synoptic maps constructed from full disk line-of sight magnetic field imagery (HMI/SDO) and EUV imagery (171, 193, 211, 304 and 335 (AIA/SDO). The synoptic maps have a resolution of 0.1 degree in longitude and steps of 0.001 in sine of latitude. From the 'time-latitude' images we observe that during the ascending phase of cycle 24 a very strong North-South asymmetry of topology of emerging magnetic flux develops, resulting in a consequential asymmetry in the timing of the polar magnetic field reversals.

Benevolenskaya, Elena

58

Solar-Panel Dust Accumulation and Cleanings  

NASA Technical Reports Server (NTRS)

Air-fall dust accumulates on the solar panels of NASA's Mars Exploration Rovers, reducing the amount of sunlight reaching the solar arrays. Pre-launch models predicted steady dust accumulation. However, the rovers have been blessed with occasional wind events that clear significant amounts of dust from the solar panels.

This graph shows the effects of those panel-cleaning events on the amount of electricity generated by Spirit's solar panels. The horizontal scale is the number of Martian days (sols) after Spirit's Jan. 4, 2005, (Universal Time) landing on Mars. The vertical scale indicates output from the rover's solar panels as a fraction of the amount produced when the clean panels first opened. Note that the gradual declines are interrupted by occasional sharp increases, such as a dust-cleaning event on sol 420.

2005-01-01

59

Exploring the Prominence-Corona Connection and its Expansion into the Outer Corona Using Total Solar Eclipse Observations  

NASA Astrophysics Data System (ADS)

Prominences constitute the most complex magnetic structures in the solar corona. The ubiquitous presence of their seemingly confined dense and cool plasma in an otherwise million-degree environment remains a puzzle. Using a decade of white light total solar eclipse observations, we show how these images reveal an intricate relationship between prominences and coronal structures both in their immediate vicinity, known as coronal cavities, and in the extended corona out to several solar radii. Observations of suspended prominences and twisted helical structures spanning several solar radii are central to these findings. The different manifestations of the prominence-corona interface that emerge from this study underscore the fundamental role played by prominences in defining and controlling the complex expansion and dynamic behavior of the solar magnetic field in the neighborhood of magnetic polarity reversal regions. This study suggests that the unraveling of prominences and the outward expansion of the helical twisted field lines linked to them could be the solar origin of twisted magnetic flux ropes detected in interplanetary space, and of the mechanism by which the Sun sheds its magnetic helicity. This work also underscores the likely role of the prominence-corona interface as a source of the slow solar wind.

Habbal, Shadia Rifai; Morgan, Huw; Druckmller, Miloslav

2014-10-01

60

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

61

Heating of the solar corona by dissipative Alfvn solitons.  

PubMed

Solar photospheric convection drives myriads of dissipative Alfvn 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

62

Heating of the Solar Corona by Dissipative Alfven Solitons  

E-print Network

Solar photospheric convection drives myriads of dissipative Alfven solitons (hereinafter called alfvenons) capable of accelerating electrons and ions to energies of hundreds of keV and producing the X-ray corona. Alfvenons are exact solutions of two-fluid equations for a collisionless plasma and represent natural accelerators for conversion of the electromagnetic energy flux driven by convective flows into kinetic energy of charged particles in space and astrophysical plasmas. Their properties have been experimentally verified in the magnetosphere, where they accelerate auroral electrons to tens of keV.

K. Stasiewicz

2006-04-25

63

Results of solar observations by the CORONAS-F payload  

NASA Astrophysics Data System (ADS)

The CORONAS-F mission experiments and results have been reviewed. The observations with the DIFOS multi-channel photometer in a broad spectral range from 350 to 1500 nm have revealed the dependence of the relative amplitudes of p-modes of the global solar oscillations on the wavelength that agrees perfectly well with the earlier data obtained in a narrower spectral ranges. The SPIRIT EUV observations have enabled the study of various manifestations of solar activity and high-temperature events on the Sun. The data from the X-ray spectrometer RESIK, gamma spectrometer HELICON, flare spectrometer IRIS, amplitude-temporal spectrometer AVS-F, and X-ray spectrometer RPS-1 have been used to analyze the X- and gamma-ray emission from solar flares and for diagnostics of the flaring plasma. The absolute and relative content of various elements (such as potassium, argon, and sulfur) of solar plasma in flares has been determined for the first time with the X-ray spectrometer RESIK. The Solar Cosmic Ray Complex monitored the solar flare effects in the Earth's environment. The UV emission variations recorded during solar flares in the vicinity of the 120-nm wavelength have been analyzed and the amplitude of relative variations has been determined.

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

2011-05-01

64

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

65

Remote-sensing Observations of the Corona and Solar Wind  

NASA Astrophysics Data System (ADS)

On June 25, 1908, George Ellery Hale used the 60-foot Tower Telescope on Mount Wilson to make the first measurements of magnetic fields in sunspots. This began a series of studies that led to Hale's Law of sunspot polarities and established the Mount Wilson Observatory as a leading center of solar magnetic field research. The magnetic aura was still present in 1962 when I began solar research there as a Caltech graduate student. Mount Wilson astronomer Horace Babcock and his father had invented the solar magnetograph, discovered the polar fields of the Sun, and observed their reversal near the 1958 sunspot maximum. Caltech physicist Robert Leighton had added new instrumentation to the Mount Wilson spectroheliograph and obtained high-resolution maps of the magnetic field. Babcock had just published his classic paper on the topology of the field and its 22-year cycle. The paper contained a sketch, illustrating the coronal field-line reconnection, which he thought must occur in response to changes of the photospheric field. Some loops flew away in the yet-to-be-discovered solar wind and other loops collapsed back to the Sun. In this talk, I will present new observations from the SOHO and STEREO spacecraft, which show such coronal changes. Loops stretch out in the expanding corona and tear away from the Sun like drops from a leaky faucet. Simultaneous observations with different perspectives show that the detached loops are really helices in 3-D. Off-pointed heliospheric imagers allow us to track these ejections outward past planets (including Earth) and comets, and to observe their compression into a heliospheric spiral, as a consequence of longitudinal speed gradients on the rotating Sun. And XUV observations of the solar disk show brightness changes associated with reconnections high in the corona, like auroral displays in the magnetosphere.

Sheeley, Neil R., Jr.

2009-05-01

66

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

67

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

68

Interferometric observation of the F-corona radial velocities fields between 3 and 7 solar radii  

NASA Astrophysics Data System (ADS)

During the July 31, 1981 solar eclipse, F-corona interferograms near Mg I 5184 A were obtained using a Fabry-Perot etalon with an FWHM of 0.5 A (corresponding to 30 km/sec) and an image tube. Radial velocities V(r) of the interplanetary dust (ID) were measured in different directions. Both prograde and retrograde motions of ID in the ecliptic region is discovered. Most of velocity values do not exceed 50 km/sec. A negative velocity component appears after averaging all V(r) for all directions. Its average increases to -20 km/sec toward the sun. Some ejections are observed. The strongest (+130 km/sec) is located at the north ecliptic pole at a distance of 6 to 7 solar radii. From the lack of unshifted Fraunhofer lines in the scattered sky light, it is concluded that the sky brigntness continuous component is predominant and its source is K-corona scattered light in the earth's atmosphere.

Shcheglov, P. V.; Shestakova, L. I.; Aimanov, A. K.

69

Interstellar Dust in the Solar System  

E-print Network

The Ulysses spacecraft has been orbiting the Sun on a highly inclined ellipse almost perpendicular to the ecliptic plane (inclination 79 deg, perihelion distance 1.3 AU, aphelion distance 5.4 AU) since it encountered Jupiter in 1992. The in-situ dust detector on board continuously measured interstellar dust grains with masses up to 10^-13 kg, penetrating deep into the solar system. The flow direction is close to the mean apex of the Sun's motion through the solar system and the grains act as tracers of the physical conditions in the local interstellar cloud (LIC). While Ulysses monitored the interstellar dust stream at high ecliptic latitudes between 3 and 5 AU, interstellar impactors were also measured with the in-situ dust detectors on board Cassini, Galileo and Helios, covering a heliocentric distance range between 0.3 and 3 AU in the ecliptic plane. The interstellar dust stream in the inner solar system is altered by the solar radiation pressure force, gravitational focussing and interaction of charged grains with the time varying interplanetary magnetic field. We review the results from in-situ interstellar dust measurements in the solar system and present Ulysses' latest interstellar dust data. These data indicate a 30 deg shift in the impact direction of interstellar grains w.r.t. the interstellar helium flow direction, the reason of which is presently unknown.

Harald Krueger; Markus Landgraf; Nicolas Altobelli; Eberhard Gruen

2007-06-21

70

Solar wind Acceleration from the Upper Chromosphere to the Corona in Coronal Hole Regions  

NASA Technical Reports Server (NTRS)

The dynamic behavior of the plasma in the chromosphere/transition region /inner corona is vital for the acceleration of the solar wind. With new theoretical descriptions of the solar atmosphere and corona, and the increased observational possibilities provided by the SOHO spacecraft, it is possible to conduct an integrated study of the solar atmosphere and corona using observational and theoretical approaches. Over the past few years a series of observational techniques have been used to estimate the solar wind densities, temperatures and flow speed in the inner corona. These estimates suggest that the solar wind has higher outflow speeds in the inner corona and lower densities than previously assumed. A comparison with densities derived from atmospheric models support these lower densities.

Esser, Ruth

1998-01-01

71

Radiative transfer of X-rays in the solar corona  

NASA Technical Reports Server (NTRS)

The problem of resonance scattering of X-ray emission lines in the solar corona is investigated. For the resonance lines of some helium-like ions, significant optical depths are reached over distances small compared with the size of typical coronal features. A general integral equation for the transfer of resonance-line radiation under solar coronal conditions is derived. This expression is in a form useful for modeling the complex three-dimensional temperature and density structure of coronal active regions. The transfer equation is then cast in a form illustrating the terms which give rise to the attenuation or enhancement of the resonance-line intensity. The source function for helium-like oxygen (O VII) under coronal conditions is computed and discussed in terms of the relative importance of scattering.

Acton, L. W.

1978-01-01

72

Off-limb EUV observations of the solar corona and transients with the CORONAS-F/SPIRIT telescope-coronagraph  

NASA Astrophysics Data System (ADS)

The SPIRIT telescope aboard the CORONAS-F satellite (in orbit from 26 July 2001 to 5 December 2005), observed the off-limb solar corona in the 175 (Fe IX, X and XI lines) and 304 (He II and Si XI lines) bands. In the coronagraphic mode the mirror was tilted to image the corona at the distance of 1.1...5 Rsun from the solar center, the outer occulter blocked the disk radiation and the detector sensitivity was enhanced. This intermediate region between the fields of view of ordinary extreme-ultraviolet (EUV) telescopes and most of the white-light (WL) coronagraphs is responsible for forming the streamer belt, acceleration of ejected matter and emergence of slow and fast solar wind. We present here the results of continuous coronagraphic EUV observations of the solar corona carried out during two weeks in June and December 2002. The images showed a "diffuse" (unresolved) component of the corona seen in both bands, and non-radial, ray-like structures seen only in the 175 band, which can be associated with a streamer base. The correlations between latitudinal distributions of the EUV brightness in the corona and at the limb were found to be high in 304 at all distances and in 175 only below 1.5 Rsun. The temporal correlation of the coronal brightness along the west radial line, with the brightness at the underlying limb region was significant in both bands, independent of the distance. On 2 February 2003 SPIRIT observed an expansion of a transient associated with a prominence eruption seen only in the 304 band. The SPIRIT data have been compared with the corresponding data of the SOHO LASCO, EIT and UVCS instruments.

Slemzin, V.; Bougaenko, O.; Ignatiev, A.; Kuzin, S.; Mitrofanov, A.; Pertsov, A.; Zhitnik, I.

2008-10-01

73

Constant cross section of loops in the solar corona  

NASA Astrophysics Data System (ADS)

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

Peter, H.; Bingert, S.

2012-12-01

74

Interstellar dust measurements in the solar system  

NASA Astrophysics Data System (ADS)

In the early 1990s, after its Jupiter yby, the Ulysses spacecraft identified interstellar dust in the solar system. Since 1992 until the end of 2007 the in-situ dust detector on board Ulysses continuously monitored interstellar grains with masses up to 10-13 kg, penetrating deep into the solar system. While Ulysses measured the interstellar dust stream at high ecliptic latitudes between 3 and 5 AU, interstellar impactors were also measured with the dust detectors on board Cassini, Galileo and Helios, covering a heliocentric distance range between 0.3 and 3 AU in the ecliptic plane. The interstellar dust stream in the inner solar system is altered by the solar radiation pressure force, gravitational focussing and interaction of charged grains with the time varying interplanetary magnetic field. The grains act as tracers of the physical conditions in the local interstellar cloud (LIC). Our in-situ measurements imply the existence of a population of 'big' interstellar grains (up to 10-13 kg) and a gas-to-dust-mass ratio in the LIC which is a factor of > 2 larger than the one derived from astronomical observations, indicating a concentration of interstellar dust in the very local interstellar medium. Until 2004, the interstellar dust ow direction measured by Ulysses was close to the mean apex of the Sun's motion through the LIC, while in 2005, the data showed a 30 degree shift, the reason of which is presently unknown. We review the in-situ interstellar dust measurements obtained from a fleet of four spacecraft in the solar system and present the latest results from the Ulysses mission.

Krger, H.; Altobelli, Nicolas; Landgraf, Markus; Grn, Eberhard

2008-09-01

75

Burgulence and Alfven waves heating mechanism of solar corona  

E-print Network

Heating of magnetized turbulent plasma is calculated in the framework of Burgers turbulence [A.M. Polyakov, Phys. Rev. E. 52, 6183 (1995)]. Explicit formula for the energy flux of Alfven waves along the magnetic field is presented. The Alfven waves are considered as intermediary between the turbulent energy and the heat. The derived results are related to a wave channel of heating of the solar corona. If we incorporate amplification of Alfven waves by shear flow the suggested model of heating can be applied to analysis of the missing viscosity of accretion discs and to reveal why the quasars are the most powerful sources of light in the universe. We suppose that the Langevin-Burgers approach to turbulence we have applied in the current work can be also helpful for other systems where we have intensive interaction between a stochastic turbulent system and waves and can be used in many multidisciplinary researches in hydrodynamics and MHD.

T. M. Mishonov; Y. G. Maneva

2007-01-16

76

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 , 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

77

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

78

Results of interferometric observations of the F-corona radial velocity field between 3 and 7 solar radii  

NASA Astrophysics Data System (ADS)

During the July 31, 1981 eclipse, F-corona interferograms were obtained near the 5184-A Mg I line covering the 3-7 solar radius region. A Fabry-Perot etalon in the exit pupil and a contact fiber-optic intensifier were used, the instrumental FWHM being 0.5 A = about 30 km/s. Radial velocities of interplanetary dust were obtained measuring Doppler shift of absorption lines. A prograde Keplerian velocity component was found, giving after averaging Vr = (5.4 + or - 0.7)R/solar radius + (5 + or - 4) km/s, as well as a retrograde motion. At 6-7 solar radius near the north coronal hole, a local stream with Vr = +130 km/s was observed. Although at large distances from the sun the sky brightness exceeds that of the F-corona, absorption lines are absent, so the sky brightness continuous component is predominant, and the K-corona scattered light may be its main source.

Shcheglov, P. V.; Shestakova, L. I.; Aimanov, A. K.

1987-02-01

79

Self-consistent model of the quiet solar corona with a wave source of energy  

Microsoft Academic Search

A self-consistent, spherically symmetric model of the solar corona is considered with a heating source connected with linear damping of MHD waves propagating away from the strongly turbulized chromosphere. The regime of the corona is shown to be fully determined by one parameter: the induction B of the coronal magnetic field. If the magnetic field is sufficiently weak, B <

I. V. Chashej; V. I. Shishov

1988-01-01

80

White-light corona and solar polar magnetic field strength over solar cycles  

NASA Astrophysics Data System (ADS)

We discuss the large-scale structure of the solar corona, in particular its helmet streamers, as observed during total solar eclipses around maxima of solar cycles and make its comparison with solar polar magnetic field strength as observed by the Wilcox Solar Observatory (WSO) since 1976. Even though the magnetic field strength at the solar poles around cycle minima decreased minimally twice in the last forty years, distributions of helmet streamers around the Sun in different cycles around cycle maxima remain nearly the same. This indicates that large-scale magnetic structures governing the shape and evolution of helmet streamers must be of a different nature than those related with solar polar fields.

Ruin, V.; Saniga, M.; Komk, R.

2014-10-01

81

Multi-wavelength Analysis to Solar Corona Heating Events  

NASA Astrophysics Data System (ADS)

With the advent and successful running of the 1.6 meter aperture New Solar Telescope at Big Bear Solar Observatory (BBSO/NST), solar observation has entered the era of 0.1 arc second. This permits us to carry out case studies for single coronal heating event, accumulating original high-resolution observational evidences for a final resolving of the coronal heating problem. By combining the high-resolution Helium I 10830 , TiO 7057 , and H_? - 0.7 imaging data from NST, and the satellite data from the Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO), we analyze the evolution of magnetic field in the roots of two tiny dynamical events originating from the Sun's intergranular lanes as seen from Helium I 10830 images. The two events caused subsequent brightening in the corona, but no obvious feature is found at H_? -0.7 images. We find that the two events are rooted at one side of magnetic polarity inversion line. One event is apparently accompanied by the disappearance of a tiny magnetic element, while, in another event, weakening of a magnetic concentration area is found. Changes for granules are also found during the two events. The results suggest that the two heating events are caused by small-scale magnetic activities in intergranular lanes driven by constant granule convection. It appears that ubiquitous small-scale magnetic activities produce outflow of cold matter as seen at 10830 and hot matter as seen at extreme ultraviolet bands.

Yang, X.; Ji, H. S.; Li, H. C.

2014-05-01

82

THE EXPANSION OF ACTIVE REGIONS INTO THE EXTENDED SOLAR CORONA  

SciTech Connect

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

Morgan, Huw; Jeska, Lauren; Leonard, Drew, E-mail: hmorgan@aber.ac.uk [Sefydliad Mathemateg a Ffiseg, Prifysgol Aberystwyth, Ceredigion SY23 3BZ (United Kingdom)

2013-06-01

83

Current Sheet Formation and Reconnection Dynamics in the Solar Corona  

NASA Astrophysics Data System (ADS)

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 topology (i.e., 4-flux systems) and a low-beta plasma. A finite-extent, 3D Syrovatskii-type current sheet forms as a result of stressing of this system by a uniform, incompressible flow applied at the line-tied photospheric boundary. The system is assumed to be ideal, except for the presence of numerical resistivity. The fully 3-D evolution is calculated with very high resolution (9x and 10x refinement across the full extent of the current sheet) using the Adaptively Refined MHD Solver (ARMS). The initial evolution of this computationally-intensive simulation results in a current sheet with a nearly 30-to-1 aspect ratio, a significant fraction of the system characteristic length, that unexpectedly appears to be stable. In addition, up to this point in the evolution any magnetic reconnection that we observe is of the slow Sweet-Parker type. We expect, however, that as we continue stressing the field, the current sheet will become unstable and develop explosive dynamics. We discuss the implications of our results on coronal structure and activity, such as heating and eruptions. This work has been supported, in part, by the NASA HTP and SR&T programs.

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

2009-05-01

84

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

85

Diagnostics of solar wind streams and their sources in the solar corona  

NASA Astrophysics Data System (ADS)

The studies are based on the experimental mass sounding of the interplanetary plasma near the Sun at radial distances of R = 4-70 R S, performed at Pushchino RAO, Russian Academy of Sciences, and on the calculated magnetic fields in the solar corona based on the magnetic field strength and structure measured on the Sun's surface at J. Wilcox Solar Observatory, United States. The experimental data make it possible to localize the position of the boundary closest to the Sun of the transition transonic region of the solar wind in the near-solar space ( R ? 10-20 R S) and to perform an interrelated study of the solar wind structure and its sources, namely, the magnetic field components in the solar corona based on these data. An analysis of the evolution of the flow types in 2000-2007 makes it possible to formulate the physically justified criterion responsible for the time boundaries of different epochs in the solar activity cycle.

Lotova, N. A.; Vladimirskii, K. V.; Obridko, V. N.

2010-12-01

86

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

87

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

88

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

89

Solar corona effects on angle of arrival fluctuations for microwave telecommunication links during superior solar conjunction  

NASA Astrophysics Data System (ADS)

During the superior solar conjunction of spacecraft, the transmitted signals from a spacecraft to the Earth ground station graze the region near the Sun's photospheric surface, passing through dense and turbulent regions of solar-charged particles. Phase changes due to solar coronal irregularities cause raypath wandering, wavefront tilting, and fluctuations in the apparent angle of arrival when observed from the Earth. This study presents a first theoretical investigation of solar wind and solar coronal effects on the angle of arrival fluctuations for RF signals. On the basis of the Chandrasekhar relationship between phase and angular fluctuations, an analytical integrating solution for angle of arrival fluctuations is derived by applying solar corona and plasma irregularity spectrum models. It is found that angular fluctuations rapidly decrease with increasing heliocentric distance at a rate of ~r -5.5 and also decrease with increasing frequency at a rate of ~1/f 2. It is found that when using Ka band at ? = 0.4 (r = 1.6 solar radii), there is a 19 millidegrees (mdeg) angular scattering, corresponding to a 9 dB gain degradation. In comparison, lower-frequency X and S band signals undergo much worse degradation effects. Beyond ? = 2 (r > 8 solar radii), angular fluctuations at microwave frequency bands can almost be neglected ($\\theta$ RMS < 1 mdeg). A solution to minimize this degradation is to use Ka- or higher-frequency bands for the telecommunication link during periods of solar conjunction. This study not only quantifies the angular fluctuations caused by solar corona irregularities but also provides an effective method for diagnosing the plasma density fluctuations in a region very close to the solar photospheric surface.

Ho, C. M.; Morabito, D. D.; Woo, R.

2008-03-01

90

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

NASA Astrophysics Data System (ADS)

The tenuous supersonic solar wind that streams from the top of the corona passes through a natural boundarythe Alfvn surfacethat marks the causal disconnection of individual packets of plasma and magnetic flux from the Sun itself. The Alfvn surface is the locus where the radial motion of the accelerating solar wind passes the radial Alfvn 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 Alfvn 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 Alfvn surface.

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

2014-06-01

91

DUST AROUND R CORONAE BOREALIS STARS. II. INFRARED EMISSION FEATURES IN AN H-POOR ENVIRONMENT  

SciTech Connect

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 {approx}6-10 {mu}m dust emission complex is seen in the RCBs showing an extreme H-deficiency. A secondary and much weaker {approx}11.5-15 {mu}m broad emission feature is detected in a few RCBs with the strongest {approx}6-10 {mu}m dust complex. The Spitzer infrared spectra reveal for the first time the structure within the {approx}6-10 {mu}m dust complex, showing the presence of strong C-C stretching modes at {approx}6.3 and 8.1 {mu}m as well as of other dust features at {approx}5.9, 6.9, and 7.3 {mu}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 {mu}m feature, which is blueshifted in those RCBs showing also the UIRs, i.e., the RCBs with the smallest H deficiency.

Garcia-Hernandez, D. A. [Instituto de Astrofisica de Canarias, C/Via Lactea s/n, E-38200 La Laguna (Spain); Rao, N. Kameswara [543, 17th Main, IV Sector, HSR Layout, Bangalore 560102 and Indian Institute of Astrophysics, Bangalore 560034 (India); Lambert, D. 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)

2013-08-20

92

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

93

Force-Free Magnetic Flux Ropes in the Solar Corona  

NASA Astrophysics Data System (ADS)

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 cases exceeds slightly the Aly-Sturrock limit on the energy of a closed force-free magnetic field with all its magnetic flux connected to the coronal base. Flux-rope solutions with the highest energies tend to arise when a strong potential field overlies a region of sheared field containing field-aligned currents. These flux-rope solutions have an unusual topology; instead of a single twisted, disconnected flux system, there are two distinct rope structures. A two-dimensional slice through each rope contains an O-type magnetic neutral point, and the overall solution therefore correspondingly contains two X-type neutral points. We speculate on the relation of this unusual topology to observations of magnetic clouds as interplanetary signatures of coronal mass ejections. This work was supported by NASA grant NAG5-9733 to Middlebury College.

Wolfson, R.

2003-05-01

94

Coronae of Stars with Super Solar Elemental Abundances  

E-print Network

Coronal elemental abundances are known to deviate from the photospheric values of their parent star, with the degree of deviation depending on the First Ionization Potential (FIP). This study focuses on the coronal composition of stars with super-solar photospheric abundances. We present the coronal abundances of six such stars: 11 LMi, $\\iota$ Hor, HR 7291, $\\tau$ Boo, and $\\alpha$ Cen A and B. These stars all have high-statistics X-ray spectra, three of which are presented for the first time. The abundances measured in this paper are obtained using the line-resolved spectra of the Reflection Grating Spectrometer (RGS) in conjunction with the higher throughput EPIC-pn camera spectra on board the XMM-Newton observatory. A collisionally ionized plasma model with two or three temperature components is found to represent the spectra well. All elements are found to be consistently depleted in the coronae compared to their respective photospheres. For 11 LMi and $\\tau$ Boo no FIP effect is present, while $\\iota$ H...

Peretz, Uria; Drake, Stephen A

2015-01-01

95

Investigation of the orientation of coronal rays and forecasting of solar-corona structure  

NASA Astrophysics Data System (ADS)

The procedures developed by Nikolskii for corona-structure forecasts is described. Synoptic maps and variations in the solar cycle are analyzed in order to forecast the coronal structure. Three types of solar corona structures, minimal, intermediate, and maximal, which are dependent on solar cycle activity are observed; a fan-ray orientation is detected for the magnetic fields and a direct-ray orientation for the active regions. The forecast for the eclipse of July 31, 1981 using Nikolskii's method is examined and compared with solar eclipse observations; good correlation of the data for the coronal ray orientation is noted.

Fatianov, M. P.

96

ApJ, in press On Heating of Solar Corona and Acceleration of Low-Speed Solar Wind by Acoustic Waves Generated in Corona  

E-print Network

We investigate possibilities of solar coronal heating by acoustic waves generated not at the photosphere but in the corona, aiming at heating in the mid- to low-latitude corona where the low-speed wind is expected to come from. Acoustic waves of period ? ? 100s are triggered by chromospheric reconnection, one model of small scale magnetic reconnection events recently proposed by Sturrock. These waves having a finite amplitude eventually form shocks to shape sawtooth waves (N-waves), and directly heat the surrounding corona by dissipation of their wave energy. Outward propagation of the N-waves is treated based on the weak shock theory, so that the heating rate can be evaluated consistently with physical properties of the background coronal plasma without setting a dissipation length in an ad hoc manner. We construct coronal structures from the upper chromosphere to the outside of 1AU for various inputs of the acoustic waves having a range of energy flux of Fw,0 = (1 ? 20) 10 5 erg cm ?2 s ?1 and a period of ? = 60 ? 300s. The heating by the N-wave dissipation effectively works in the inner corona and we find that the waves of Fw,0 ? 210 5 erg cm ?2 s ?1 and ? ? 60s could maintain peak coronal temperature, Tmax> 10 6 K. The model could also reproduce the density profile observed in the streamer region. However, due to its short dissipation length, the location of Tmax is closer to the surface than the observation, and the resultant flow velocity of the solar wind is lower than the observed profile of the low-speed wind. The cooperations with other heating and acceleration sources with the larger dissipation length are inevitable to reproduce the real solar corona. Subject headings: Sun: corona solar wind waves 2 1.

Takeru Ken Suzuki

2002-01-01

97

The Soft X-Ray/Microwave Ratio of Solar and Stellar Flares and Coronae  

NASA Technical Reports Server (NTRS)

We have carried out plasma diagnostics of solar flares using soft X-ray (SXR) and simultaneous microwave observations and have compared the ratio of X-ray to microwave luminosities of solar flares with various active late-type stars available in the published literature. Both the SXR low-level ('quiescent') emission from stellar coronae and the flaring emission from the Sun and stars are generally interpreted as thermal radiations of coronal plasmas. On the other hand, the microwave emission of stars and solar flares is generally attributed to an extremely hot or nonthermal population of electrons. Solar flare SXR are conventionally measured in a narrower and harder passband than the stellar sources. Observations of the GOES-2 satellite in two energy channels have been used to estimate the luminosity of solar flares as it would appear in the ROSAT satellite passband. The solar and stellar flare luminosities fit well at the lower end of the active stellar coronae. The flare SXR/microwave ratio is similar to the ratio for stellar coronae. The average ratio follows a power-law relation L(sub X) varies as L(sub R)(sup 0.73 +/- 0.03) over 10 orders of magnitude from solar microflares to RS CVn and FK Com-type coronae. Dwarf Me and Ke stars, and RS CVn stars are also compatible with a linear SXR/microwave relation, but the ratio is slightly different for each type of star. Considering the differences between solar flares, stellar flares and the various active stellar coronae, the similarity of the SXR/microwave ratios is surprising. It suggests that the energetic electrons in low-level stellar coronae observed in microwaves are related in a similar way to the coronal thermal plasma as flare electrons to the flare thermal plasma, and, consequently, that the heating mechanism of active stellar coronae is a flare-like process.

Benz, A. O.; Guedel, M.

1994-01-01

98

On the nature of the transition region between the solar corona and chromosphere  

NASA Astrophysics Data System (ADS)

We have calculated an equilibrium temperature distribution over the column depth of plasma in the transition region between the solar corona and chromosphere by assuming the plasma in the transition region and the chromosphere to be heated by the heat flux from the corona and the energy fluxes from the convective zone, respectively. The corona-chromosphere transition region is shown to be actually a stable, very thin layer in which, however, the standard collision approximation is well applicable for describing the heat flux. The solution we found explains well the currently available results of satellite observations of extreme ultraviolet (EUV) radiation from the transition region.

Ptitsyna, O. V.; Somov, B. V.

2012-12-01

99

The Writhe of Helical Structures in the Solar Corona  

NASA Technical Reports Server (NTRS)

Context. Helicity is a fundamental property of magnetic fields, conserved in ideal MHD. In flux rope topology, it consists of twist and writhe helicity. Despite the common occurrence of helical structures in the solar atmosphere, little is known about how their shape relates to the writhe, which fraction of helicity is contained in writhe, and how much helicity is exchanged between twist and writhe when they erupt. Aims. Here we perform a quantitative investigation of these questions relevant for coronal flux ropes. Methods. The decomposition of the writhe of a curve into local and nonlocal components greatly facilitates its computation. We use it to study the relation between writhe and projected S shape of helical curves and to measure writhe and twist in numerical simulations of flux rope instabilities. The results are discussed with regard to filament eruptions and coronal mass ejections (CMEs). Results. (1) We demonstrate that the relation between writhe and projected S shape is not unique in principle, but that the ambiguity does not affect low-lying structures, thus supporting the established empirical rule which associates stable forward (reverse) S shaped structures low in the corona with positive (negative) helicity. (2) Kink-unstable erupting flux ropes are found to transform a far smaller fraction of their twist helicity into writhe helicity than often assumed. (3) Confined flux rope eruptions tend to show stronger writhe at low heights than ejective eruptions (CMEs). This argues against suggestions that the writhing facilitates the rise of the rope through the overlying field. (4) Erupting filaments which are S shaped already before the eruption and keep the sign of their axis writhe (which is expected if field of one chirality dominates the source volume of the eruption), must reverse their S shape in the course of the rise. Implications for the occurrence of the helical kink instability in such events are discussed.

Toeroek, T.; Berger, M. A.; Kliem, B.

2010-01-01

100

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

Microsoft Academic Search

The HERSCHEL (helium resonant scattering in the corona and heliosphere) experiment is a rocket mission that was successfully\\u000a launched last September from White Sands Missile Range, New Mexico, USA. HERSCHEL was conceived to investigate the solar corona\\u000a in the extreme UV (EUV) and in the visible broadband polarized brightness and provided, for the first time, a global map of\\u000a helium

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

2010-01-01

101

Assimilative 3D Models of Density and Temperature in the Solar Corona  

Microsoft Academic Search

White-light and extreme ultraviolet images of the solar corona, as measured routinely by a variety of dedicated space- and ground-based instruments, offer an opportunity for empirical determination of the global, 3D distribution of density and temperature in the Sun's corona. In this work, we describe a 3D model for the estimation of coronal density from polarized brightness measurements and a

F. Kamalabadi; M. Butala; R. Frazin; Y. Chen

2007-01-01

102

Turbulent Heating in the Solar Wind and in the Solar Corona  

E-print Network

In this paper we calculate the turbulent heating rates in the solar wind using the Kolmogorov-like MHD turbulence phenomenology with Kolmogorov's constants calculated by {\\it Verma and Bhattacharjee }[1995b,c]. We find that the turbulent heating can not account for the total heating of the nonAlfv\\'enic streams in the solar wind. We show that dissipation due to thermal conduction is also a potential heating source. Regarding the Alfv\\'enic streams, the predicted turbulent heating rates using the constants of {\\it Verma and Bhattacharjee }[1995c] are higher than the observed heating rates; the predicted dissipation rates are probably overestimates because Alfv\\'enic streams have not reached steady-state. We also compare the predicted turbulent heating rates in the solar corona with the observations; the Kolmogorov-like phenomenology predicts dissipation rates comparable to the observed heating rates in the corona [{\\it Hollweg, }% 1984], but Dobrowoly et al.'s generalized Kraichnan model yields heating rates much less than that required.

Mahendra K. Verma

1995-09-05

103

Dust Accumulation and Cleaning of the MER Spirit Solar Array  

NASA Astrophysics Data System (ADS)

The solar array of the NASA Mars Exploration Rover (MER) Spirit was expected to accumulate so much dust after ninety Martian days (sols) that it could no longer provide enough energy to guarantee continued surface operations. Instead, due in part to low dust accumulation rates and numerous dust cleaning events, Spirit carried out surface operations for over 2200 sols (over three Mars years). During this time period, the rover experienced four Martian winters and several dust storms. Because the sources of solar energy loss are known, the solar array energy output offers a tool to quantitatively estimate the loading and aeolian removal of dust from the solar array each sol. We will discuss the accumulation of dust on the solar panels as a proxy for dust movement at Gusev Crater over the course of the entire mission.

Herman, J. A.; Lemmon, M. T.; Johnson, J. R.; Cantor, B. A.; Stella, P. M.; Chin, K. B.; Wood, E. G.

2012-12-01

104

Photometric studies of light scattering above the lunar terminator from Apollo solar corona photography  

NASA Technical Reports Server (NTRS)

Excess brightness is found in 70-mm photographs of the solar corona above the lunar terminator during Apollo 15 and 17. Maximum brightness of this scattered light is determined from calibration of image density. The observed excess brightness displays circular symmetry above the lunar-horizon subsolar point, characteristic of forward diffraction scattering from micron or submicron size (solid) grains, and decays rapidly in intensity with altitude and distance from the lunar terminator. The observed brightness cannot be accounted for by a co-orbiting cloud of spacecraft contaminants, but requires a variable lunar dust 'atmosphere' over the terminator regions extending to altitudes in excess of 100 km. To maintain such large masses of lunar fines above the terminator requires either local mass-churning rates in excess of 2 by 10 to the -11th power g/sq cm sec or the assumption of some degree of high-altitude electrostatic suspension to increase the dwell time of individual grains at the altitudes observed. Such a model would reduce mass-churning rates while causing selective erosion/deposition and potential for escape of significant mass from the moon

Mccoy, J. E.

1976-01-01

105

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 Alfvn 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 Alfvn 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

106

The large-scale structure of the solar corona and inner heliosphere  

NASA Astrophysics Data System (ADS)

The helmet streamers that are observed to dominate the structure of the inner corona are formed by the interaction of the solar wind with coronal magnetic fields. We have simulated this interaction in three dimensions using the magnetohydrodynamic (MHD) equations. In order to create a realistic model, we use the magnetic field that is observed at the Sun's surface (deduced from daily Wilcox Solar Observatory magnetic field synoptic maps) as input, in combination with specified density and temperature profiles at the surface. A self-consistent 3D solar-wind solution is developed by integrating the MHD equations in time to steady state. Such solutions can reproduce the observed structures that are seen in coronagraph images and eclipse photographs of the corona. We compare the results obtained from our model with with an eclipse photograph of the corona on November 3, 1994. We also compare the position of the heliospheric current sheet with Ulysses observations during the period May-June 1993.

Miki?, Zoran; Linker, Jon A.

1996-07-01

107

Konus-Wind and Helicon-Coronas-F Observations of Solar Flares  

E-print Network

Results of solar flare observations obtained in the Konus-Wind experiment from November, 1994 to December, 2013 and in the Helicon Coronas-F experiment during its operation from 2001 to 2005, are presented. For the periods indicated Konus-Wind detected in the trigger mode 834 solar flares, and Helicon-Coronas-F detected more than 300 solar flares. A description of the instruments and data processing techniques are given. As an example, the analysis of the spectral evolution of the flares SOL2012-11-08T02:19 (M 1.7) and SOL2002-03-10T01:34 (C5.1) is made with the Konus-Wind data and the flare SOL2003-10-26T06:11 (X1.2) is analyzed in the 2.223 MeV deuterium line with the Helicon-Coronas-F data.

Pal'shin, V D; Aptekar, R L; Golenetskii, S V; Kokomov, A A; Svinkin, D S; Sokolova, Z Ya; Ulanov, M V; Frederiks, D D; Tsvetkova, A E

2014-01-01

108

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

E-print Network

We investigate possibilities of solar coronal heating by acoustic waves generated not at the photosphere but in the corona, aiming at heating in the mid- to low-latitude corona where the low-speed wind is expected to come from. Acoustic waves of period tau ~ 100s are triggered by chromospheric reconnection, one model of small scale magnetic reconnection events recently proposed by Sturrock. These waves having a finite amplitude eventually form shocks to shape sawtooth waves (N-waves), and directly heat the surrounding corona by dissipation of their wave energy. Outward propagation of the N-waves is treated based on the weak shock theory, so that the heating rate can be evaluated consistently with physical properties of the background coronal plasma without setting a dissipation length in an ad hoc manner. We construct coronal structures from the upper chromosphere to the outside of 1AU for various inputs of the acoustic waves having a range of energy flux of F_{w,0} = (1-20) times 10^5 erg cm^{-2} s^{-1} and a period of tau = 60-300s. The heating by the N-wave dissipation effectively works in the inner corona and we find that the waves of F_{w,0} >= 2 times 10^5 erg cm^{-2} s^{-1} and tau >= 60s could maintain peak coronal temperature, T_{max} > 10^6 K. The model could also reproduce the density profile observed in the streamer region. However, due to its short dissipation length, the location of T_{max} is closer to the surface than the observation, and the resultant flow velocity of the solar wind is lower than the observed profile of the low-speed wind. The cooperations with other heating and acceleration sources with the larger dissipation length are inevitable to reproduce the real solar corona.

Takeru Ken Suzuki

2002-08-06

109

Alfvenically driven slow shocks in the solar chromosphere and corona  

NASA Technical Reports Server (NTRS)

The nonlinear evolution of an Alfvenic impulse launched from the photosphere and its dynamical effects on the chromosphere, transition region (TR), and corona are investigated using a simple 1D model. It is found that the leading edge of the torsional pulse can steepen into a fast shock in the chromosphere if the pulse is of sufficiently large amplitude and short duration. A slow shock which develops behind the Alfvenic pulse can reflect downgoing Alfven waves back up to the corona. The upgoing reflected wave can induce a significant upward ejection of the TR. Nonlinear dynamics are found to lead to very impulsive behavior at later times. It is suggested that impulsive events occurring in the TR or corona need not be interpreted in terms of reconnection-driven microflares. It is also found that B(0) in the chromosphere can be amplified when the TR and chromosphere fall.

Hollweg, Joseph V.

1992-01-01

110

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

111

Observational studies of reconnection in the solar corona  

SciTech Connect

In recent years, observational studies of the corona have shifted focus. Where they were once purely qualitative morphological explorations seeking to support the presence of reconnection, more investigations are providing empirical estimates of the physical conditions in the reconnecting corona. These studies are enabled and enhanced by orbiting telescopes with high angular and temporal resolution. In this article, some recent findings about the empirical quantities are reviewed, including recent estimates of the flux transferred in individual patchy reconnection episodes, the size distribution of post-reconnection flux tubes, and the energy released by the flux tubes as they shrink.

McKenzie, David E. [Department of Physics, Montana State University, P.O. Box 173840, Bozeman, Montana 59717-3840 (United States)

2011-11-15

112

The 1981 total solar eclipse corona. II - Global absolute photometric analysis  

NASA Astrophysics Data System (ADS)

Detailed results of the absolute photometry of the solar corona during the July 31, 1981 total eclipse are presented together with a morphological analysis. The basic calibration method uses the detailed photometry of images of stars present on the same coronal picture. Both sky intensity and coronal aureola variations over the field are carefully evaluated. The recent axi-symmetric non-spherical model of the F-corona is introduced and the relevant K-corona intensity variations are derived. The determinations of the Ludendorf index of flattening and the integrated total brightness of the K-corona alone are made and discussed in relation to the phase of the sunspot cycle of activity.

Lebecq, C.; Koutchmy, S.; Stellmacher, G.

1985-11-01

113

Evolution of interstellar dust and stardust in the solar neighbourhood  

E-print Network

The abundance evolution of interstellar dust species originating from stellar sources and from condensation in molecular clouds in the local interstellar medium of the Milky Way is studied and the input of dust material to the Solar System is determined. A one-zone chemical evolution model of the Milky Way for the elemental composition of the disk combined with an evolution model for its interstellar dust component similar to that of Dwek (1998) is developed. The dust model considers dust-mass return from AGB stars as calculated from synthetic AGB models combined with models for dust condensation in stellar outflows. Supernova dust formation is included in a simple parameterized form which is gauged by observed abundances of presolar dust grains with supernova origin. For dust growth in the ISM a simple method is developed for coupling this with disk and dust evolution models. The time evolution of the abundance of the following dust species is followed in the model: silicate, carbon, silicon carbide, and iron dust from AGB stars and from SNe as well as silicate, carbon, and iron dust grown in molecular clouds. It is shown that the interstellar dust population is dominated by dust accreted in molecular clouds; most of the dust material entering the Solar System at its formation does not show isotopic abundance anomalies of the refractory elements, i.e., inconspicuous isotopic abundances do not point to a Solar System origin of dust grains. The observed abundance ratios of presolar dust grains formed in SN ejecta and in AGB star outflows requires that for the ejecta from SNe the fraction of refractory elements condensed into dust is 0.15 for carbon dust and is quite small ($\\sim10^{-4}$) for other dust species.

Svitlana Zhukovska; Hans-Peter Gail; Mario Trieloff

2007-06-08

114

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

115

The Structure and Dynamics of the Solar Corona and Inner Heliosphere  

NASA Astrophysics Data System (ADS)

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

2002-08-01

116

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

117

Large-scale structure of the solar corona and inner heliosphere  

NASA Astrophysics Data System (ADS)

The large-scale structure of the solar corona influences solar activity particularly coronal mass ejections (CMEs). The helmet streamers that are observed to dominate the structure of the inner corona are formed by the interaction of the solar wind with coronal magnetic fields. We have simulated this interaction in three dimensions using the magnetohydrodynamic (MHD) equations. In order to create a realistic model, we use the magnetic field that is observed at the Sun's surface (deduced from daily Wilcox Solar Observatory magnetograms) as input, in combination with specified density and temperature profiles at the surface. A self-consistent 3D solar-wind solution is developed by integrating the MHD equations in time to steady state. Such solutions can reproduce the observed structures that are seen in coronagraph images and eclipse photographs of the corona. This model allows us to accurately determine the position of the heliospheric current sheet. We will compare the results obtained from our model with Ulysses observations during the period May-June 1993, and with an eclipse photograph of the corona on November 3, 1994.

Mikic, Z.; Linker, J. A.

1995-06-01

118

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

119

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

120

WEATHER MODIFICATION BY CARBON DUST ABSORPTION OF SOLAR ENERGY  

E-print Network

WEATHER MODIFICATION BY CARBON DUST ABSORPTION OF SOLAR ENERGY by WM. M. GRAY, WM. M. FRANK, M COLLINS, COLORADO Atmospheric Science PAPER NO. 225 #12;WEATHER MODIFICATION BY CARBON DUST ABSORPTION meteorologists and other scientists on the possibility of meso-scale weather modification through carbon dust

Gray, William

121

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 , 193 , 211 , 304 , and 335 ). 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.

2014-09-01

122

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

123

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

124

Torsional Alfvn waves in small scale density threads of the solar corona  

Microsoft Academic Search

The density structuring of the solar corona is observed at large scales (loops and funnels), but also at small scales (sub-structures of loops and funnels). Coronal loops consist of thin density threads with sizes down to (and most probably below) the resolution limit. We study properties of torsional Alfvn waves propagating in inhomogeneous cylindrical density threads using the two-fluid magnetohydrodynamic

P. Copil; Y. Voitenko; M. Goossens

2008-01-01

125

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

NASA Astrophysics Data System (ADS)

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

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

2004-05-01

126

MAGNETIC FIELD CONFINEMENT IN THE SOLAR CORONA. I. FORCE-FREE MAGNETIC FIELDS B. Fornberg,2  

E-print Network

MAGNETIC FIELD CONFINEMENT IN THE SOLAR CORONA. I. FORCE-FREE MAGNETIC FIELDS N. Flyer,1 B Axisymmetric force-free magnetic fields external to a unit sphere are studied as solutions to boundary value total azimuthal flux with a power-law distribution over the poloidal field. Particular attention is paid

Fornberg, Bengt

127

MAGNETIC FIELD CONFINEMENT IN THE SOLAR CORONA. II. FIELD-PLASMA INTERACTION B. Fornberg,2  

E-print Network

MAGNETIC FIELD CONFINEMENT IN THE SOLAR CORONA. II. FIELD-PLASMA INTERACTION N. Flyer,1 B. Fornberg study of axisymmetric force-free magnetic fields in the unbounded space outside a unit sphere, presented pressure and weight in a polytropic atmosphere. The study considers dipolar magnetic fields all sharing

Fornberg, Bengt

128

The problem of phase mixed shear Alfvn waves in the solar corona revisited  

Microsoft Academic Search

The problem of phase mixing of shear Alfvn waves is revisited taking into account dissipative phenomena specific for the solar corona. In regions of space plasmas where the dynamics is controlled by the magnetic field, transport coefficients become anisotropic with transport mechanism having different behavior and magnitude depending on the orientation with respect to the ambient magnetic field. Taking into

G. Mocanu; A. Marcu; I. Ballai; B. Orza

2008-01-01

129

THE CYCLING OF MATERIAL BETWEEN THE SOLAR CORONA AND CHROMOSPHERE  

SciTech Connect

Observations of transition region emission lines reveal the presence of redshifts in lines formed from the top of the chromosphere up to temperatures of about 2.5 Multiplication-Sign 10{sup 5} K and blueshifts for temperatures above that. However, it is doubtful that the apparent large downward flows in the lower transition region represents an emptying of the corona, so some mechanism must be responsible for maintaining the mass balance between the corona and the lower atmospheric layers. We use a three-dimensional magnetohydrodynamics code to study the cycling of mass between the corona, transition region, and chromosphere by adding a tracer fluid to the simulation in various temperature intervals in the transition region. We find that most of the material seen in transition region emission lines formed at temperatures below 3 Multiplication-Sign 10{sup 5} K is material that has been rapidly heated from chromospheric temperatures and thereafter is pushed down as it cools. This implies that the bulk of transition region material resides in small loops. In these loops, the density is high and radiative cooling is efficient.

Guerreiro, N.; Hansteen, Viggo [Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, N-0315 Oslo (Norway); De Pontieu, B., E-mail: n.m.r.guerreiro@astro.uio.no [Lockheed Martin Solar and Astrophysics Laboratory, Org. A021S, Building 252, 3251 Hanover Street, Palo Alto, CA 94304 (United States)

2013-05-20

130

The Structure and Dynamics of the Solar Corona and Inner Heliosphere  

NASA Technical Reports Server (NTRS)

This report covers technical progress during the second quarter of the first 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 November 16, 1999 to February 15, 2000. 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. The topics studied include: the effect of emerging flux on the stability of helmet streamers, coronal loops and streamers, the solar magnetic field, the solar wind, and open magnetic field lines.

Mikic, Zoran

2002-01-01

131

CORONAS-F measurements of high-energy solar proton spectra  

Microsoft Academic Search

Fluxes of protons at the energies 0.8 - 4 GeV accelerated during solar flares of October-November 2003 were detected onboard the CORONAS-F satellite (polar circular orbit with an altitude ~450 km). The SONG instrument had sufficient geometric factor (~1500 cm2sr) to detect directly solar protons as a count rate exceeding above a background level when the satellite crossed a wide

S. N. Kuznetsov; B. Yu. Yushkov; K. Kudela

2008-01-01

132

Is it Possible that the Solar Corona Temperature Profile Does Not Require Mechanical Deposition of Energy?  

NASA Astrophysics Data System (ADS)

The solar corona, like other main sequence stars, has a non-monotonic temperature inversion. Prevailing ideas have suggested that the inversion is the result of deposition of mechanical energy near the temperature maximum, possibly afforded by the damping of wave trains. The adequacy of ones quantitative description of heat flow in the corona plays a central role in the association of non-monotonic profile and a heating requirement. Using first principles calculations we demonstrate that neither the size nor the direction of the heat flow in the corona is implied by knowing the temperature profile. The usually used Spitzer-Braginskii transport is not appropriate for the solar corona, but has until now been used to infer the sign of the heat flow divergence at the temperature maximum. By vacating the certainty of heat flow diverging from the coronal temperature maximum there is no immediate connection between the non-monotonic temperature profile and the need for energy or momentum addition to the corona at the temperature maximum. Thus the coronal problem is to explain the temperature profile, not necessarily produce an energy deposition, predicted by a broken transport description. The same argument that shows that Spitzer-Braginskii transport is inadequate also implies that the underlying kinetic state of the plasma is non-local and will be permeated by non-thermal distributions. Such non-thermal distributions are a necessary prerequisite for the alternate velocity filtration model that explains the non-monotonic temperature profile of the solar corona as well as all stars on the zero age main sequence.

Scudder, J. D.; Roytershteyn, V.; Karimabadi, H.; Daughton, W. S.

2012-12-01

133

Observations of Solar EUV Radiation with the CORONAS-F/SPIRIT and SOHO/EIT Instruments  

NASA Astrophysics Data System (ADS)

The SPIRIT complex onboard the CORONAS-F satellite has routinely imaged the Sun in the 171, 175, 195, 284, and 304 spectral bands since August 2001. The complex incorporates two telescopes. The Ritchey-Chretien telescope operates in the 171, 195, 284, and 304 bands and has an objective similar to that of the SOHO/EIT instrument. The Herschel telescope obtains solar images synchronously in the 175 and 304 bands with two multilayer-coated parabolic mirrors. The SPIRIT program includes synoptic observations, studies of the dynamics of various structures on the solar disk and in the corona up to 5 solar radii, and coordinated observations with other spaceborne and ground-based telescopes. In particular, in the period 2002-2003, synoptic observations with the SPIRIT Ritchey-Chretien telescope were coordinated with regular 6-hour SOHO/EIT observations. Since June 2003, when EIT data were temporarily absent ( SOHO keyholes), the SPIRIT telescope has performed synoptic observations at a wavelength of 175 A. These data were used by the Solar Influence Data Analysis Center (SIDC) at the Royal Observatory of Belgium for an early space weather forecast. We analyze the photometric and spectral parameters of the SPIRIT and EIT instruments and compare the integrated (over the solar disk) EUV fluxes using solar images obtained with these instruments during the CORONAS-F flight from August 2001 through December 2003.

Slemzin, V. A.; Kuzin, S. V.; Zhitnik, I. A.; Delaboudiniere, J.-P.; Auchere, F.; Zhukov, A. N.; van der Linden, R.; Bugaenko, O. I.; Ignat'ev, A. P.; Mitrofanov, A. V.; Pertsov, A. A.; Oparin, S. N.; Stepanov, A. I.; Afanas'ev, A. N.

2005-11-01

134

SWAP Observations of the Long-Term, Large-Scale Evolution of the EUV Solar Corona  

E-print Network

The Sun Watcher with Active Pixels and Image Processing (SWAP) EUV solar telescope on board the Project for On-Board Autonomy 2 (PROBA2) spacecraft has been regularly observing the solar corona in a bandpass near 17.4 nm since February 2010. With a field-of-view of 54x54 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 (PSF) 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 persiste...

Seaton, Daniel B; Shearer, Paul; Berghmans, David; Nicula, Bogdan

2013-01-01

135

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

SciTech Connect

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

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

2009-11-20

136

Reoccurring Heavy Ion Dropouts in the Solar Wind: Rates, Locations, and Constraints on Magnetic Reconnection in the Solar Corona  

NASA Astrophysics Data System (ADS)

The abundance and charge state variations of heavy elements within the solar wind yield unique insight into processes occurring in the solar corona. Previously we have reported in-situ observations of heavy ion dropouts in the solar wind with depletion factors ranging from 2 - 25. Many of these dropouts exhibit mass-dependent fractionation in qualitative agreement with remote observations of gravitational settling in large, streamer belt coronal loops. We present here a robust statistical analysis pertaining to the occurrence rate and fractionation patterns of dropouts found in the ACE/SWICS data set between February 1998 and August 2011. In particular, we focus on dropouts which appear to reoccur over the course of multiple Carrington rotations. Such sequences of dropouts indicate source regions which are long lived structures in the solar corona and, as such, may provide important observational constraints on magnetic reconnection and magnetic diffusion processes at the edges of coronal holes.

Weberg, M. J.; Zurbuchen, T.; Lepri, S. T.

2012-12-01

137

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

E-print Network

There have been derived equations describing the static distributions of temperature and wind velocity at the transition region within the framework of the magnetohydrodynamics (MHD) of fully ionized hydrogen plasma . We have also calculated the width of the transition between the chromosphere and corona as a self-induced opacity of the high-frequency Alfven waves (AWs). The domain wall is a direct consequence of the self-consistent MHD treatment of AWs propagation. We predict considerable spectral density of the high-frequency AWs in the photosphere. The idea that Alfven waves might heat the solar corona belong to Alfven - we simply derived the corresponding MHD equations. The comparison of the solutions to those equations with the observational/measured data will be crucial for revealing the heating mechanism. The analysis of those solutions will explain how Alfven waves brick unto the corona and dissipate their energy there.

Zahariev, N I

2011-01-01

138

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 (1010,000 Hz) ion cyclotron resonant waves which can heat and accelerate ions

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

1999-01-01

139

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

140

Theory of heating of hot magnetized plasma by Alfven waves. Application for solar corona  

E-print Network

The heating of magnetized plasma by propagation of Alfven waves is calculated as a function of the magnetic field spectral density. The results can be applied to evaluate the heating power of the solar corona at known data from satellites' magnetometers. This heating rate can be incorporated in global models for heating of the solar corona and creation of the solar wind. The final formula for the heating power is illustrated with a model spectral density of the magnetic field obtained by analysis of the Voyager 1 mission results. The influence of high frequency dissipative modes is also taken into account and it is concluded that for evaluation of the total coronal heating it is necessary to know the spectral density of the fluctuating component of the magnetic field up to the frequency of electron-proton collisions.

T. M. Mishonov; M. V. Stoev; Y. G. Maneva

2007-02-13

141

EIT: Solar corona synoptic observations from SOHO with an Extreme-ultraviolet Imaging Telescope  

NASA Technical Reports Server (NTRS)

The Extreme-ultraviolet Imaging Telescope (EIT) of SOHO (solar and heliospheric observatory) will provide full disk images in emission lines formed at temperatures that map solar structures ranging from the chromospheric network to the hot magnetically confined plasma in the corona. Images in four narrow bandpasses will be obtained using normal incidence multilayered optics deposited on quadrants of a Ritchey-Chretien telescope. The EIT is capable of providing a uniform one arc second resolution over its entire 50 by 50 arc min field of view. Data from the EIT will be extremely valuable for identifying and interpreting the spatial and temperature fine structures of the solar atmosphere. Temporal analysis will provide information on the stability of these structures and identify dynamical processes. EIT images, issued daily, will provide the global corona context for aid in unifying the investigations and in forming the observing plans for SOHO coronal instruments.

Delaboudiniere, J. P.; Gabriel, A. H.; Artzner, G. E.; Michels, D. J.; Dere, K. P.; Howard, R. A.; Catura, R.; Stern, R.; Lemen, J.; Neupert, W.

1988-01-01

142

Polarization of the solar corona and the sky during the total solar eclipse of July 31, 1981  

NASA Astrophysics Data System (ADS)

The coronal and background skylight polarization have been studied on the basis of the measurements with the photo-electric polarimeters at the July 31, 1981 eclipse. During the total phase (74s) the radiation of the solar corona, intensity of linearly polarized component, orientation of the polarization plane at 1700 points of the corona from 0.1 R_sun; to 6.5 R_sun; were investigated. The measurements were carried out at a rate of 24 points per second.

Kulidzhanishvili, V. I.; Stepanov, A. I.; Nikolskii, G. M.

143

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

144

Composition of the Solar Wind  

NASA Technical Reports Server (NTRS)

The solar wind reflects the composition of the Sun and physical processes in the corona. Analysis produces information on how the solar system was formed and on physical processes in the corona. The analysis can also produce information on the local interstellar medium, galactic evolution, comets in the solar wind, dust in the heliosphere, and matter escaping from planets.

Suess, S. T.

2007-01-01

145

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 substantial progress toward the goal of producing a unified model of the basic physical processes responsible for solar wind acceleration. 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 1D model of plasma heating and acceleration. The accomplishments in Year 2 are divided into these two categories: 1a. Focused Study of Kinetic Magnetohydrodynamic (MHD) Turbulence. lb. Focused Study of Non - WKB Alfven Wave Rejection. and 2. The Unified Model Code. We have continued the development of the computational model of a time-study open flux tube in the extended corona. The proton-electron Monte Carlo model is being tested, and collisionless wave-particle interactions are being included. In order to better understand how to easily incorporate various kinds of wave-particle processes into the code, the PI performed a detailed study of the so-called "Ito Calculus", i.e., the mathematical theory of how to update the positions of particles in a probabilistic manner when their motions are governed by diffusion in velocity space.

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

2004-01-01

146

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

147

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

NASA Technical Reports Server (NTRS)

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, A.; Cirtain, J.; Golub, L.; DeLuca, E.; Savage, S.; Alexander, C.; Schuler, T.

2014-01-01

148

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

NASA Technical Reports Server (NTRS)

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 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 percent 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, A.; Cirtain, J.; Golub, L.; DeLuca, E.; Savage, S.; Alexander, C.; Schuler, T.

2014-01-01

149

Spatiotemporal Organization of Energy Release Events in the Quiet Solar Corona  

NASA Astrophysics Data System (ADS)

Using data from the STEREO and SOHO spacecraft, we show that temporal organization of energy release events in the quiet solar corona is close to random, in contrast to the clustered behavior of flaring times in solar active regions. The locations of the quiet-Sun events follow the meso- and supergranulation pattern of the underling photosphere. Together with earlier reports of the scale-free event size statistics, our findings suggest that quiet solar regions responsible for bulk coronal heating operate in a driven self-organized critical state, possibly involving long-range Alfvnic interactions.

Uritsky, Vadim M.; Davila, Joseph M.

2014-11-01

150

Solar wind driven dust acoustic instability with Lorentzian kappa distribution  

SciTech Connect

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 [National Center for Physics (NCP), Quaid-i-Azam University Campus, Shahdra Valley Road, Islamabad 44000 (Pakistan) [National Center for Physics (NCP), Quaid-i-Azam University Campus, Shahdra Valley Road, Islamabad 44000 (Pakistan); Pakistan Institute of Engineering and Applied Sciences, P.O. Nilore, Islamabad and University of Wah, Wah Cantt 47040 (Pakistan); Ehsan, Zahida, E-mail: Ehsan.zahida@gmail.com [National Center for Physics (NCP), Quaid-i-Azam University Campus, Shahdra Valley Road, Islamabad 44000 (Pakistan) [National Center for Physics (NCP), Quaid-i-Azam University Campus, Shahdra Valley Road, Islamabad 44000 (Pakistan); Universita degli Studi del Molise, 86090 Pesche - IS (Italy); INFN Sezione di Napoli, 80126 Napoli (Italy); Department of Physics, COMSATS Institute of Information Technology (CIIT), Defence Road, Off Raiwind Road, Lahore 86090 (Pakistan); Khan, S. A. [National Center for Physics (NCP), Quaid-i-Azam University Campus, Shahdra Valley Road, Islamabad 44000 (Pakistan)] [National Center for Physics (NCP), Quaid-i-Azam University Campus, Shahdra Valley Road, Islamabad 44000 (Pakistan); Mahmood, S. [Theoretical Plasma Physics Division, PINSTEC, PO Box Nilore, Islamabad 44000 (Pakistan)] [Theoretical Plasma Physics Division, PINSTEC, PO Box Nilore, Islamabad 44000 (Pakistan)

2014-02-15

151

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

152

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

153

Spectrophotometry of the solar corona of July 31, 1981.  

NASA Astrophysics Data System (ADS)

Data of photometric measurements of spectrograms obtained during the total solar eclipse of 31 July 1981 are given. The coronal temperature of 2.45106K is derived from measurements of the emission of five coronal ions.

Merzlyakov, V. L.

154

The Source of Alfven Waves That Heat the Solar Corona  

NASA Technical Reports Server (NTRS)

We suggest a source for high-frequency Alfven waves invoked in coronal heating and acceleration of the solar wind. The source is associated with small-scale magnetic loops in the chromospheric network.

Ruzmaikin, A.; Berger, M. A.

1998-01-01

155

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

156

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 Suns 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 Divisions Living With a Star Targeted Research & Technology Program.

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

2014-06-01

157

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

158

Dynamic properties of the solar corona: SOHO/LASCO observations  

NASA Astrophysics Data System (ADS)

With the launch of the SOHO spacecraft in December 1995, the quality of corona observations has improved significantly. The LASCO instruments with their field of view now extending from 1.1 Rs (C1) to 30 Rs (C3) offer sufficient sensitivity to make an almost continuous outflow in the streamer belt visible. We report on two different approaches to study the plasma motion, both in the plane of the sky and along the line of sight. 1. By means of a multi-resolution image processing technique based on wavelet packets the boundaries and the internal details of originally faint and diffuse structures are enhanced. This approach allows unambiguous image interpretation and provides a means for the quantification of stationary and dynamic coronal structures required for conducting morphological studies. 2. The LASCO/C1 telescope was designed to perform spectral analysis on coronal structures. The tunable Fabry-Perot interferometer allows to obtain images at different wavelengths. Results from spectral scans of the coronal green and red emission lines are presented. From the line profiles physical quantities like temperatures (from line widths), and flow velocities (from Doppler shifts) along the line of sight are deduced.

Mierla, M.; Schwenn, R.; Stenborg, G.; Teriaca, L.; Podlipnik, B.

159

"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

160

Suprathermal Electrons in the Solar Corona: Can Nonlocal Transport Explain Heliospheric Charge States?  

NASA Astrophysics Data System (ADS)

There have been several ideas proposed to explain how the Sun's corona is heated and how the solar wind is accelerated. Some models assume that open magnetic field lines are heated by Alfvn waves driven by photospheric motions and dissipated after undergoing a turbulent cascade. Other models posit that much of the solar wind's mass and energy is injected via magnetic reconnection from closed coronal loops. The latter idea is motivated by observations of reconnecting jets and also by similarities of ion composition between closed loops and the slow wind. Wave/turbulence models have also succeeded in reproducing observed trends in ion composition signatures versus wind speed. However, the absolute values of the charge-state ratios predicted by those models tended to be too low in comparison with observations. This Letter refines these predictions by taking better account of weak Coulomb collisions for coronal electrons, whose thermodynamic properties determine the ion charge states in the low corona. A perturbative description of nonlocal electron transport is applied to an existing set of wave/turbulence models. The resulting electron velocity distributions in the low corona exhibit mild suprathermal tails characterized by "kappa" exponents between 10 and 25. These suprathermal electrons are found to be sufficiently energetic to enhance the charge states of oxygen ions, while maintaining the same relative trend with wind speed that was found when the distribution was assumed to be Maxwellian. The updated wave/turbulence models are in excellent agreement with solar wind ion composition measurements.

Cranmer, Steven R.

2014-08-01

161

Faraday Rotation Fluctuations of MESSENGER radio signals through the Corona during the 2009 Solar Minimum.  

NASA Astrophysics Data System (ADS)

Faraday rotation (FR) techniques have been used to probe variations of coronal plasma velocity, density and magnetic field. The plane of polarization for an electromagnetic wave rotates in proportion to the integrated product of parallel magnetic field components and electron density along the radio signal line-of-sight as directed towards the receiving antenna. Fluctuations in FR through the corona thus represent the evolution of these line-integrated plasma parameters, providing a unique measurement of regional corona physics. The MESSENGER spacecraft radio 8 GHz radio beacon, transmitting through the corona at offsets 1.6 to 1.9 solar radii and near-equatorial heliolatitude, was recorded on the Green Bank radio telescope during the solar minimum of 2009. Here we reanalyze at higher temporal resolution the data previously published (Jensen et al 2013, Solar Physics 285:83-95). Combinations of coherent and incoherent integration were used to estimate Stokes parameters, from which the FR phase differences were obtained for serial one-second frames. Results were concatenated and corrected for phase wrap-around to produce a continuous FR phase curve. The general FR phase curve was broad and sweeping, with greatest spectral power observed in periods of hours. Also, finer wave-like fluctuations were noted with periods on the order of 100s of seconds. With the lowest-frequency components removed by detrending techniques, spectral analysis revealed a power spectrum of form P=k

Wexler, David; Vierinen, Juha; Coster, Anthea; Jensen, Elizabeth A.

2015-04-01

162

Electrodynamic Shield to Remove Dust from Solar Panels on Mars  

Microsoft Academic Search

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

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

163

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

164

Penetration of nearby supernova dust in the inner solar system  

NASA Astrophysics Data System (ADS)

We investigate the method by which nearby supernovae - within a few tens of pc of the solar system - can penetrate the solar system and deposit live radioactivities on earth. The radioactive isotopic signatures that could potentially leave an observable geological imprint are in the form of refractory metals; consequently, it is likely they would arrive in the form of supernova-produced dust grains. Such grains can penetrate into the solar system more easily than the bulk supernova plasma, which gets stalled and deflected near the solar system due to the solar wind plasma pressure. We therefore examine the motion of charged grains as they decouple from the supernova plasma and are influenced by the solar magnetic, radiation, and gravitational fields. We characterize the dust trajectories with analytical approximations which display the roles of grain size, initial velocity, and surface voltage. These results are verified with full numerical simulations for wide ranges of dust properties. We find that supernova dust grains traverse the inner solar system nearly undeflected, if the incoming grain velocity - which we take to be that of the incident supernova remnant - is comparable to the solar wind speeds and much larger than the escape velocity at 1 AU. Consequently, the dust penetration to 1 AU has essentially 100% transmission probability and the dust capture onto the earth should have a geometric cross section. Our results cast in a new light the terrestrial deposition of radioisotopes from nearby supernovae in the geological past. For explosions beyond 10 pc from earth, dust grains can still deliver supernova ejecta to earth, and thus the amount of supernova material deposited is set by the efficiency of dust condensation and survival in supernovae. Turning the problem around, we use observations of live 60Fe in both deep-ocean and lunar samples to infer a conservative lower bound iron condensation efficiency of Mdust,Fe/ Mtot,Fe ? 4 10 -4 for the supernova which apparently produced these species 2-3 Myr ago.

Athanassiadou, Themis; Fields, B. D.

2011-07-01

165

Solar Cycle Indices from the Photosphere to the Corona: Measurements and Underlying Physics  

NASA Astrophysics Data System (ADS)

A variety of indices have been proposed in order to represent the many different observables modulated by the solar cycle. Most of these indices are highly correlated with each other owing to their intrinsic link with the solar magnetism and the dominant eleven year cycle, but their variations may differ in fine details, as well as on short- and long-term trends. In this paper we present an overview of the indices that are often employed to describe the many features of the solar cycle, moving from the ones referring to direct observations of the inner solar atmosphere, the photosphere and chromosphere, to those deriving from measurements of the transition region and solar corona. For each index, we summarize existing measurements and typical use, and for those that quantify physical observables, we describe the underlying physics.

Ermolli, Ilaria; Shibasaki, Kiyoto; Tlatov, Andrey; van Driel-Gesztelyi, Lidia

2014-12-01

166

Multi-wavelength Analysis to Solar Corona Heating Events  

NASA Astrophysics Data System (ADS)

With the advent and successful operation of the 1.6 m aperture New Solar Telescope of Big Bear Solar Observatory (BBSO/NST), solar observation has entered the era of high resolution better than 0.1". This permits us to carry out the case studies of single coronal heating events, to provide the original high-resolution observational evidence for finally solving the problem of coronal heating. By combining the high-resolution Helium I 10830 , TiO 7057 , and Ha blue-wing (-0.7 ) imaging data from the NST with the imaging data of extreme ultraviolet and longitudinal magnetic field observed simultaneously by the Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) on board of the Solar Dynamics Observatory (SDO), we have analyzed the evolution of magnetic field in two tiny dynamical events of coronal heating (brightening of magnetic loops) that originate from the solar intergranular lanes. It is found that the footpoints of both brightening magnetic loops were all located in the one side of nearby neutral line of magnetic fields, the footpoints of one magnetic loop were accompanied by the disappearance of a small longitudinal magnetic element and the newly formed connection between two granulations, while the footpoints of another magnetic loop were accompanied by a weak variation of longitudinal magnetic field and the breakdown of a granulation. The observed result tends to suggest that the low-temperature and high-temperature outflows were produced simultaneously by the magnetic reconnection occurred among the solar granulations in the low-layer atmosphere. Meanwhile, it is noted that the high-resolution and high-accuracy polarization measurement of photospheric magnetic field is crucial for finally solving the problem of coronal heating.

Xu, YANG; Hai-sheng, JI; Hao-chuan, LI

2015-01-01

167

Energy release in the solar corona from spatially resolved magnetic braids.  

PubMed

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 1,500,000?K (refs 1-3). The active corona needs additional heating to reach 2,000,000-4,000,000?K; 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 0.2?arc 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 0.2?arc seconds, of magnetic braids in a coronal active region that are reconnecting, relaxing and dissipating sufficient energy to heat the structures to about 4,000,000?K. 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. PMID:23344359

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

2013-01-24

168

Method for Tracking and Mapping a Motion Based on Images of the Solar Corona  

NASA Astrophysics Data System (ADS)

This work continues our investigations on possibilities of presentation the time development of eruptive solar protuberance and related magnetic field. The aim of this work is mapping the direction of movement of different layers of protuberance. The map construction is based on compass directions dividing them to 8 possible North, South, West, East, North-West, North-East, South-West, South-East. The tests in this investigation are carried on sequences of images obtained from 15 cm Lio coronagraph-telescope of NAO Rozhen, used for observation of protuberance of low solar corona.

Pavlova, P.; Duncheva, E., Koleva, K.

2012-01-01

169

Solar origins of intense geomagnetic storms in 2002 as seen by the CORONAS-F satellite  

NASA Astrophysics Data System (ADS)

We analyze solar origins of intense geomagnetic perturbations recorded during 2002. All of them were related to coronal mass ejections (CMEs). The initiation of CMEs was documented using the SPIRIT instrument (SPectrohelIographic Soft X-Ray Imaging Telescope) onboard the CORONAS-F satellite. Monochromatic full Sun images taken in the Mg XII doublet at 8.418 and 8.423 showed the appearance of free energy release sites at altitudes up to 0.4 solar radii. CMEs were initiated at these sites and propagated in interplanetary space under appropriate local conditions including the geometry of the magnetic fields.

Panasenco, O.; Veselovsky, I. S.; Dmitriev, A. V.; Zhukov, A. N.; Yakovchouk, O. S.; Zhitnik, I. A.; Ignat'ev, A. P.; Kuzin, S. V.; Pertsov, A. A.; Slemzin, V. A.; Boldyrev, S. I.; Romashets, E. P.; Stepanov, A.; Bugaenco, O. I.; Bothmer, V.; Koutchmy, S.; Adjabshirizadeh, A.; Fazel, Z.; Sobhanian, S.

170

Assessment and Validation of MHD Models for the Solar Corona and Inner Heliosphere  

NASA Astrophysics Data System (ADS)

We describe the status of a model assessment and validation project for testing MHD codes that simulate the solar corona and inner heliosphere. The goal of the project is to test MHD codes by applying firm empirical constraints to their boundary conditions in the corona and at 1 AU. The project has produced a database of coronal and solar wind observations from SOHO, ACE, Wind, and Ulysses. In addition to the database, software tools for comparing these data sets to the outputs for the MHD model codes under test will be demonstrated. The first step is to take the plasma parameters that are produced from the model codes and apply forward modeling to simulate the coronal observations of emission lines (H I Lyman alpha and O VI 103.2 nm). In situ solar wind data are used not only to provide benchmarks near 1 AU but also to provide coronal constraints for the coronal source regions of the solar wind. Future stages will involve making more direct comparisons of the plasma properties predicted from the model codes through the use of empirical coronal and solar wind models. We also describe a set of metrics that are used for making comparisons between the model code outputs and the empirical data. This work is supported by NASA under Grants NNX07AB98G to the Smithsonian Astrophysical Observatory and NNX07AB99G to the University of Michigan.

Strachan, L.; Zurbuchen, T. H.; Kohl, J. L.; Panasyuk, A. V.; Raymond, J. R.; van Ballegooijen, A.

2007-12-01

171

Turbulence And Wave Dissipation In The Chromosphere, Corona, And Solar Wind  

NASA Astrophysics Data System (ADS)

The continually evolving convection below the solar photospheregives rise to a wide spectrum of acoustic and magneticfluctuations that propagate out into the heliosphere.In this talk I will review the various ways that waves,shocks, and turbulent eddies are expected to interact withthe mean plasma conditions of the outer solar atmosphere.For open magnetic flux tubes, the heating of the chromosphereand corona, as well as the acceleration of the solar wind,can be understood from the standpoint of wave dissipation andturbulent cascade.For example, the importance of magnetohydrodynamic turbulence inthe extended corona has been affirmed by the surprisingmeasurements of the UVCS instrument on SOHO that heavy ions areheated to hundreds of times the temperatures of protons andelectrons, indicating collisionless Alfven wave dissipation.Complete theoretical models are difficult to construct, though,because many of the proposed physical processes act on amultiplicity of spatial scales (from centimeters to solar radii)with feedback effects not yet well understood.Despite these difficulties, progress has been made toward the goalof producing models that predict the plasma properties everywhereabove the solar surface using only lower boundary conditions atthe photosphere.

Cranmer, Steven R.

2006-06-01

172

MAXIMIZING MAGNETIC ENERGY STORAGE IN THE SOLAR CORONA  

SciTech Connect

The energy that drives solar eruptive events such as coronal mass ejections (CMEs) almost certainly originates in coronal magnetic fields. Such energy may build up gradually on timescales of days or longer before its sudden release in an eruptive event, and the presence of free magnetic energy capable of rapid release requires nonpotential magnetic fields and associated electric currents. For magnetic energy to power a CME, that energy must be sufficient to open the magnetic field to interplanetary space, to lift the ejecta against solar gravity, and to accelerate the material to speeds of typically several hundred km s{sup -1}. Although CMEs are large-scale structures, many originate from relatively compact active regions on the solar surface-suggesting that magnetic energy storage may be enhanced when it takes place in smaller magnetic structures. This paper builds on our earlier work exploring energy storage in large-scale dipolar and related bipolar magnetic fields. Here we consider two additional cases: quadrupolar fields and concentrated magnetic bipoles intended to simulate active regions. Our models yield stored energies whose excess over that of the corresponding open field state can be greater than 100% of the associated potential field energy; this contrasts with maximum excess energies of only about 20% for dipolar and symmetric bipolar configurations. As in our previous work, energy storage is enhanced when we surround a nonpotential field with a strong overlying potential field that acts to 'hold down' the nonpotential flux as its magnetic energy increases.

Wolfson, Richard; Drake, Christina; Kennedy, Max, E-mail: wolfson@middlebury.edu [Department of Physics, Middlebury College, Middlebury, VT 05753 (United States)

2012-05-01

173

Interstellar Dust Flow through the Solar System  

NASA Astrophysics Data System (ADS)

The in-situ dust detector on board the Ulysses spacecraft has collected the most comprehensive dataset of interstellar dust (ISD) particles penetrating the heliosphere between 1992 and 2007. In 2005 we identified a shift in dust flow direction by 50, whereas before (from 1992 to 2004) it was aligned within 20 with the direction of the undisturbed dust flow through the interstellar environment. Furthermore, in this time period the dust flux shows a steep rise, which is observed in the small particles 4 months ahead of an increase in the larger particle flux. These variations of the dust flux and angular distribution can only be understood in terms of the grain interaction with the heliospheric plasma environment.

Strub, Peter; Sterken, Veerle J.; Krger, Harald; Grn, Eberhard; Horanyi, Mihaly

2011-11-01

174

Common observations of solar X-rays from SPHINX/CORONAS-PHOTON and XRS/MESSENGER  

NASA Astrophysics Data System (ADS)

SphinX was a soft X-ray spectrophotometer constructed in the Space Research Centre of Polish Academy of Sciences. The instrument was launched on 30 January 2009 aboard CORONAS-PHOTON satellite as a part of TESIS instrument package. SphinX measured total solar X-ray flux in the energy range from 1 to 15 keV during the period of very low solar activity from 20 February to 29 November 2009. For these times the solar detector (X-ray Spectrometer - XRS) onboard MESSENGER also observed the solar X-rays from a different vantage point. XRS measured the radiation in similar energy range. We present results of the comparison of observations from both instruments and show the preliminary results of physical analysis of spectra for selected flares.

Kepa, Anna; Sylwester, Janusz; Sylwester, Barbara; Siarkowski, Marek; Mrozek, Tomasz; Gryciuk, Magdalena; Phillips, Kenneth

175

Investigation of absorption of solar EUV-radiation in the Earth's atmosphere at altitudes of 100-500 km using solar images in the experiments TEREK-C (CORONAS-I) and SPIRIT (CORONAS-F)  

NASA Astrophysics Data System (ADS)

The results of measurements of absorption of solar EUV-radiation in the Earth's high atmosphere (100-500 km) using solar images obtained in occultation mode with the TEREK-C telescope on-board the CORONAS-I satellite (1994) and with the SPIRIT telescope/spectroheliograph on-board the CORONAS-F satellite (launched in 2001) are presented. Use of high resolution attenuated solar EUV images recorded in presence of absorption instead of a total flux from the whole Sun allows to determine attenuation height profiles with an accuracy better than 1 km. Possible effects of geomagnetic activity on EUV-absorption data are discussed.

Slemzin, V.; Bugaenko, O.; Ignatiev, A.; Krutov, V.; Kuzin, S.; Mitrofanov, A.; Oparin, S.; Pertsov, A.; Stepanov, A.; Zhitnik, I.

2003-09-01

176

Self-consistent model of the quiet solar corona with a wave source of energy  

NASA Astrophysics Data System (ADS)

A self-consistent, spherically symmetric model of the solar corona is considered with a heating source connected with linear damping of MHD waves propagating away from the strongly turbulized chromosphere. The regime of the corona is shown to be fully determined by one parameter: the induction B of the coronal magnetic field. If the magnetic field is sufficiently weak, B < B2 ? 2 G, the pressure in the transition layer, the maximum coronal temperature and the altitude of the temperature maximum increase with increasing B, heating is conditioned by the Alfvn and slow magnetosonic waves. If B > B2, the dependences of the coronal parameters on B become weak due to the regulation by the plasma flow. Coronal heating is conditioned by partial damping of Alfvn waves in this regime, the influence of magnetosonic waves is negligible.

Chashej, I. V.; Shishov, V. I.

1988-02-01

177

Induced emission of Alfvn 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 Alfvn 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

178

A Space Weather mission concept: Observatories of the Solar Corona and Active Regions (OSCAR)  

NASA Astrophysics Data System (ADS)

Coronal Mass Ejections (CMEs) and Corotating Interaction Regions (CIRs) are major sources of magnetic storms on Earth and are therefore considered to be the most dangerous space weather events. The Observatories of Solar Corona and Active Regions (OSCAR) mission is designed to identify the 3D structure of coronal loops and to study the trigger mechanisms of CMEs in solar Active Regions (ARs) as well as their evolution and propagation processes in the inner heliosphere. It also aims to provide monitoring and forecasting of geo-effective CMEs and CIRs. OSCAR would contribute to significant advancements in the field of solar physics, improvements of the current CME prediction models, and provide data for reliable space weather forecasting. These objectives are achieved by utilising two spacecraft with identical instrumentation, located at a heliocentric orbital distance of 1 AU from the Sun. The spacecraft will be separated by an angle of 68 to provide optimum stereoscopic view of the solar corona. We study the feasibility of such a mission and propose a preliminary design for OSCAR.

Strugarek, Antoine; Janitzek, Nils; Lee, Arrow; Lschl, Philipp; Seifert, Bernhard; Hoilijoki, Sanni; Kraaikamp, Emil; Isha Mrigakshi, Alankrita; Philippe, Thomas; Spina, Sheila; Brse, Malte; Massahi, Sonny; O'Halloran, Liam; Pereira Blanco, Victor; Stausland, Christoffer; Escoubet, Philippe; Kargl, Gnter

2015-02-01

179

Polarization observations and results of the 1998 February 26th solar corona  

NASA Astrophysics Data System (ADS)

In the frame of the long-term study program of the solar corona, we have organized an expedition in Curacao (Dutch Antillas) to observe the total solar eclipse of February 26th, 1998. As the totality duration was quite short, we had to improve again the CCD experiment layout in order to record a sample of images as wide as possible in both polarization and brightness ranges. This was made possible by the acquisition of a new PC with fast hard disc and data transfer port. We managed then to record 7 series of different exposures, each containing polarization measurements of 24 images (thus 8 times oversampled). The data processing led to accurate brightness and polarization maps as well as electron density models. The shape of the corona is highly flattened with large polar holes filled by numerous wide plumes. Large streamers are also observed and are essentially aligned along the solar equatorial plane. Moreover, the polarization indicates that these structures are located in the vicinity of the plane of the sky. Unfortunately, the unusually high sky brightness hid the faintest coronal structures and limited the visibility up to 3 solar radii implying a similar limitation in our modelling. We present here these results and give a brief comparison with our previous eclipse observation.

Gabryl, J.-R.; Cugnon, P.; Clette, F.

1999-03-01

180

PROPAGATION OF ALFVENIC WAVES FROM CORONA TO CHROMOSPHERE AND CONSEQUENCES FOR SOLAR FLARES  

SciTech Connect

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

Russell, A. J. B.; Fletcher, L. [SUPA School of Physics and Astronomy, University of Glasgow, Glasgow (United Kingdom)

2013-03-10

181

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

182

A review of the solar results from CORONAS-F satellite  

NASA Astrophysics Data System (ADS)

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 solar activity and high-temperature events on the Sun. The data from the flare instruments-gamma spectrometer HELICON, flare spectrometer IRIS, amplitude-time spectrometer AVS-F, and X-ray spectrometer RPS-1 have been used to analyze the hard emission from solar flares and to carry out the diagnostics of the solar flare plasma. The Solar Cosmic Ray Complex has investigated the solar flare effects in the Earth's environment. The UV emission variations during solar flares in the vicinity of the 120-nm wavelengh have been recorded and the relative variation amplitude has been determined.

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

183

Results of solar observations on-board the CORONAS-F satellite  

NASA Astrophysics Data System (ADS)

The CORONAS-F mission experiments and results have been reviewed. The observations with the DIFOS multi-channel photometer in a broad spectral range from 350 to 1500 nm have revealed that the relative amplitudes of p-modes of the global solar oscillations depend on the wavelength (This result agrees perfectly well with the earlier data obtained in a narrower spectral range. The SPIRIT EUV observations have enabled the study of various manifestations of solar activity and high-temperature events on the Sun. The data from the gamma spectrometer HELICON, flare spectrometer IRIS, amplitude-time spectrometer AVS-F, and X-ray spectrometer RPS-1 have been used to analyze the X- and gamma-ray emission from solar flares and to simulate the parameters of solar plasma and supra-thermal electron beams in the generation region. The absolute and relative content of various elements (such as potassium, argon, and sulfur) in the flare-generated solar plasma has been determined for the first time with the X-ray spectrometer RESIK. The Solar Cosmic Ray Complex has been used to study the solar flare effects in the Earth's environment. The UV emission variations recorded during solar flares in the vicinity of the 120-nm wavelengh been analyzed and the relative variation amplitude has been determined.

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

184

Nonequilibrium ionization effects in asymmetrically heated loops. [in solar corona  

NASA Technical Reports Server (NTRS)

The effects of nonequilibrium ionization on magnetic loop models with a steady siphon flow that is driven by a nonuniform heating rate are investigated. The model developed by Mariska (1988) to explain the observed redshifts of transition region emission lines is examined, and the number densities of the ions of carbon and oxygen along the loop are computed, with and without the approximation of ionization equilibrium. Considerable deviations from equilibrium were found. In order to determine the consequences of these nonequilibrium effects on the characteristics of the EUV emission from the loop plasma, the profiles and wavelength positions of all the important emission lines due to carbon and oxygen were calculated. The calculations are in broad agreement with Mariska's conclusions, although they show a significant diminution of the Doppler shifts, as well as modifications to the line widths. It is concluded that the inclusion of nonequilibrium effects make it more difficult to reproduce the observed characteristics of the solar transition region by means of the asymmetric-heating models.

Spadaro, D.; Antiochos, Spiro K.; Mariska, J. T.

1991-01-01

185

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

186

Modelling Magnetic Reconnection and Nano-flare Heating in the Solar Corona  

NASA Astrophysics Data System (ADS)

Current models describing magnetic reconnection in the solar corona assume single reconnection events occurring at random crossings between magnetic flux tubes. However, in the avalanche model of magnetic reconnection, multiple reconnections are expected to occur. The purpose of this research is to first, calculate the point of the greatest stress between magnetic flux tubes and then to allow for dynamic evolution utilising the avalanche model. This represents a significant increase in sophistication over previous models. This undertaking is not purely theoretical since we compare the results of our modelling with HI-C data. Using key inputs from the HIC and AIA observations such as loop length and magnetic field strength, we predict the number of reconnection events likely to take place. As a single reconnection event cannot currently be directly observed, the distribution of flare events are recorded instead. The power law fit yielded as a result of our simulations is within the expected range given the observational evidence of flare distributions and temperature values in the corona. This provides further evidence to support the role of Nano-flares in the heating of the corona.

Biggs, George; Asgari-Targhi, Mahboubeh

2015-01-01

187

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

188

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

E-print Network

We study 14 large solar jets observed in polar coronal holes. In EUV movies from SDO/AIA, each jet appears similar to most X-ray jets and EUV jets that erupt in coronal holes, but each is exceptional in that it goes higher than most, so high that it is observed in the outer corona beyond 2.2 RSun in images from the SOHO/LASCO/C2 coronagraph. From AIA He II 304 {\\AA} movies and LASCO/C2 running-difference images of these high-reaching jets, we find: (1) the front of the jet transits the corona below 2.2 RSun at a speed typically several times the sound speed; (2) each jet displays an exceptionally large amount of spin as it erupts; (3) in the outer corona, most of the jets display measureable swaying and bending of a few degrees in amplitude; in three jets the swaying is discernibly oscillatory with a period of order 1 hour. These characteristics suggest that the driver in these jets is a magnetic-untwisting wave that is basically a large-amplitude (i.e., non-linear) torsional Alfven wave that is put into the ...

Moore, Ronald L; Falconer, David A

2015-01-01

189

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

190

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

191

SWAP OBSERVATIONS OF THE LONG-TERM, LARGE-SCALE EVOLUTION OF THE EXTREME-ULTRAVIOLET SOLAR CORONA  

SciTech Connect

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; Berghmans, David; Nicula, Bogdan [Royal Observatory of Belgium-SIDC, Avenue Circulaire 3, B-1180 Brussels (Belgium); Shearer, Paul [Department of Mathematics, 2074 East Hall, University of Michigan, 530 Church Street, Ann Arbor, MI 48109-1043 (United States)

2013-11-01

192

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

NASA Astrophysics Data System (ADS)

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

Vsquez, A. M.; Frazin, R. A.

193

Solar origins of intense geomagnetic storms in 2002 as seen by the CORONAS-F satellite.  

NASA Astrophysics Data System (ADS)

The initiation of coronal mass ejections responsible for intense heliospheric perturbations and strong geomagnetic storms was observed by the SPIRIT (Spectro-heliographic soft X-ray imaging telescope) onboard CORONAS-F satellite. Monochromatic full Sun images in MgXII doublet 8,418 and 8,423 revealed the appearance of the free energy releases at altitudes up to 0,4 R?. Sometimes complex situations on the Sun and in the heliosphere arise. The continuous monitoring of the solar images with a time resolution of minutes could be a useful tool for "space weather" application.

Panasenco, O.; Panasenco Team

194

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

195

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

196

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

197

Hot carbon corona in Mars' upper thermosphere and exosphere: 2. Solar cycle and seasonal variability  

NASA Astrophysics Data System (ADS)

This work presents the variability over seasons (i.e., orbital position) and solar cycle of the Martian upper atmosphere and hot carbon corona. We investigate the production and distribution of energetic carbon atoms and the impacts on the total global hot carbon loss from dominant photochemical processes at five different cases: AL (aphelion and low solar activity), EL (equinox and low solar activity), EH (equinox and high solar activity), PL (perihelion and low solar activity), and PH (perihelion and high solar activity). We compare our results with previously published results but only on the limited cases due to the dearth of studies on solar EUV flux and seasonal variabilities. Photodissociation of CO and dissociative recombination of CO+ are generally regarded as the two most important source reactions for the production of hot atomic carbon. Of these two, photodissociation of CO is found to be the dominant source in all cases considered. To describe self-consistently the exosphere and the upper thermosphere, a 3-D kinetic particle simulator, the Adaptive Mesh Particle Simulator, and the 3-D Mars Thermosphere General Circulation Model are one-way coupled. The basic description of this hot carbon calculation can be found in the companion paper to this one. The spatial distributions and profiles of density and temperature and atmospheric loss rates are discussed for the cases considered. Finally, our computed global escape rate of hot carbon ranges from 5.28 1023 s-1 (AL) to 55.1 1023 s-1 (PL).

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

2014-12-01

198

Solar Spectral Radiative Forcing Due to Dust Aerosol During the Puerto Rico Dust Experiment  

NASA Technical Reports Server (NTRS)

During the Puerto Rico Dust Experiment (PRIDE) upwelling and downwelling solar spectral irradiance was measured on board the SPAWAR Navajo and downwelling solar spectral flux was measured at a surface site using the NASA Ames Solar Spectral Flux Radiometer. These data will be used to determine the net solar radiative forcing of dust aerosol and to quantify the solar spectral radiative energy budget in the presence of elevated aerosol loading. We will assess the variability in spectral irradiance using formal principal component analysis procedures and relate the radiative variability to aerosol microphysical properties. Finally, we will characterize the sea surface reflectance to improve aerosol optical depth retrievals from the AVHRR satellite and to validate SeaWiFS ocean color products.

Pilewskie, P.; Bergstrom, R.; Rabbette, M.; Livingston, J.; Russell, P.; Gore, Warren J. (Technical Monitor)

2000-01-01

199

ON THE CONSTANCY OF THE ELECTRON TEMPERATURE IN THE EXPANDING CORONA THROUGHOUT SOLAR CYCLE 23  

SciTech Connect

A recent analysis of Fe emission lines observed during the total solar eclipses of 2006 March 29 and 2008 August 1 established the first empirical link between the electron temperature in the expanding corona and Fe charge states measured in interplanetary space. In this Letter, we use this link to infer this temperature throughout solar cycle 23 from in situ charge state measurements from the Solar Wind Ion Composition Spectrometer (SWICS) on the Advanced Composition Explorer (ACE) and on Ulysses. The distribution of the SWICS/ACE Fe charge states, which span cycle 23 from 1998 to 2009, is skewed with a peak centered on Fe{sup 8+}, Fe{sup 9+}, and Fe{sup 10+} and a tail spanning Fe{sup 12+} to Fe{sup 20+}. An iterative process based on this distribution and on the Fe ion fraction as a function of electron temperature yields a narrow peak at 1.1 x 10{sup 6} K. The tail in the measured charge state distribution is attributed to the sporadic release of material hotter than 2 x 10{sup 6} K from closed magnetic structures within the bulges of streamers. The Fe Ulysses charge state measurements between 1992 and 1997 from cycle 22 peaked at Fe{sup 11+}, indicative of a slightly higher temperature of 1.5 x 10{sup 6} K. The relative constancy of the electron temperature in the expanding corona throughout solar cycle 23 points to the presence of an unknown mechanism regulating the energy input to electrons in the acceleration region of the solar wind at all latitudes during this cycle.

Habbal, Shadia Rifai; Morgan, Huw [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Druckmueller, Miloslav [Faculty of Mechanical Engineering, Brno University of Technology, 616 69 Brno (Czech Republic); Ding, Adalbert [Institute of Optics and Atomic Physics, Technische Universitaet Berlin and Institute of Technical Physics, Berlin (Germany)], E-mail: shadia@ifa.hawaii.edu

2010-03-10

200

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

201

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

202

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

203

Observations of high-energy jets in the corona above the quiet sun, the heating of the corona, and the acceleration of the solar wind  

NASA Technical Reports Server (NTRS)

High spatial resolution observations of the ultraviolet solar spectrum which reveal high-energy events in the quiet sun are presented. The tandem Wadsworth spectrograph used to make the observations is described along with the observing techniques, and a brief description of the characteristics of high-resolution transition zone spectra is given. The sizes, velocities, line profiles, time behavior, temperature range, differential emission measures, densities, masses, energies, and birthrates of turbulent events and jets in the quiet sun are derived from the observations and discussed. Possible accelerating mechanisms for these events are discussed, and the consequences of these events for the heating of the solar corona are discussed. A cloud model of the solar wind is proposed and possible correlations between the high-energy events and other solar fine-structure features are discussed.

Brueckner, G. E.; Bartoe, J.-D. F.

1983-01-01

204

Channeled propagation of slow magnetosonic waves in an inhomogeneous solar corona  

SciTech Connect

The propagation of magneto-acoustic waves in the atmosphere of the Sun is commonly associated with possible wave heating of the solar chromosphere and corona. The distributions of the magnetic field, the plasma density and the temperature in these regions do not posses a spherical symmetry and under certain conditions such nonuniformities may provide the localization of travelling magnetosonic waves near the magnetic field lines. In this note we draw attention to the localization of the slow magnetosonic waves (SMW) which can contribute to the creation of streamer-like structures of the solar corona. To illustrate this point of view we consider two-dimensional waves propagating in an axisymmetric cylindrical steady plasma configuration with a given axial magnetic field B = B(r)e{sub z}, and with given radial profiles of the temperature T(r) and the electron density n(r). It is assumed that the characteristic radial wavelength is much less than the characteristic length of plasma nonuniformity, so that the WKB method for calculating the wave solutions can be applied. In the framework of ideal magnetohydrodynamics (MHD), the two-dimensional axisymmetric solutions for small perturbations are sought.

Mond, M.; Rutkevich, I. [Ben-Gurion Univ. of the Negev, Beer Sheva (Israel)

1995-12-31

205

A study of line widths and kinetic parameters of ions in the solar corona  

NASA Astrophysics Data System (ADS)

Solar extreme-ultraviolet (EUV) lines emitted by highly charged ions have been extensively studied to discuss the issue of coronal heating and solar wind acceleration. Based on observations of the polar corona by the SUMER/SOHO spectrometer, this paper investigates the relation between the line widths and kinetic parameters of ions. It is shown that there exists a strongly linear correlation between two variables ( ?/ ?)2 and M -1, where ?, ? and M are the half-width of the observed line profile at , the wavelength and the ion mass, respectively. The Pearson product-moment correlation coefficients exceed 0.9. This finding tends to suggest that the ions from a given height of polar corona have a common temperature and a common non-thermal velocity in terms of existing equation. The temperature and non-thermal velocity are obtained by linear least-square fit. The temperature is around 2.8 MK at heights of 57? and 102?. The non-thermal velocity is typical 21.6 km s-1 at height of 57? and 25.2 km s-1 at height of 102?.

Zhao, G. Q.; Wu, D. J.; Wang, C. B.

2014-10-01

206

Solar wind and the motion of dust grains  

NASA Astrophysics Data System (ADS)

In this paper, we investigate the action of solar wind on an arbitrarily shaped interplanetary dust particle. The final relativistically covariant equation of motion of the particle also contains the change of the particle's mass. The non-radial solar wind velocity vector is also included. The covariant equation of motion reduces to the Poynting-Robertson effect in the limiting case when a spherical particle is treated, when the speed of the incident solar wind corpuscles tends to the speed of light and when the corpuscles spread radially from the Sun. The results of quantum mechanics have to be incorporated into the physical considerations, in order to obtain the limiting case. If the solar wind affects the motion of a spherical interplanetary dust particle, then ?. Here, p'in and p'out are the incoming and outgoing radiation momenta (per unit time), respectively, measured in the proper frame of reference of the particle, and ? and ? are the solar wind pressure and the total scattering cross-sections, respectively. An analytical solution of the derived equation of motion yields a qualitative behaviour consistent with numerical calculations. This also holds if we consider a decrease of the particle's mass. Using numerical integration of the derived equation of motion, we confirm our analytical result that the non-radial solar wind (with a constant value of angle between the radial direction and the direction of the solar wind velocity) causes outspiralling of the dust particle from the Sun for large values of the particle's semimajor axis. The non-radial solar wind also increases the time the particle spirals towards the Sun. If we consider the periodical variability of the solar wind with the solar cycle, then there are resonances between the particle's orbital period and the period of the solar cycle.

Kla?ka, J.; Petrala, J.; Pstor, P.; Kmar, L.

2012-04-01

207

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

208

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

209

Reconstructing the open-field magnetic geometry of solar corona using coronagraph images  

NASA Astrophysics Data System (ADS)

The upcoming Solar Probe Plus and Solar Orbiter missions will provide an new insight into the inner heliosphere magnetically connected with the topologically complex and eruptive solar corona. Physical interpretation of these observations will be dependent on the accurate reconstruction of the large-scale coronal magnetic field. We argue that such reconstruction can be performed using photospheric extrapolation codes constrained by white-light coronagraph images. The field extrapolation component of this project is featured in a related presentation by S. Jones et al. Here, we focus on our image-processing algorithms conducting an automated segmentation of coronal loop structures. In contrast to the previously proposed segmentation codes designed for detecting small-scale closed loops in the vicinity of active regions, our technique focuses on the large-scale geometry of the open-field coronal features observed at significant radial distances from the solar surface. Coronagraph images are transformed into a polar coordinate system and undergo radial detrending and initial noise reduction followed by an adaptive angular differentiation. An adjustable threshold is applied to identify candidate coronagraph features associated with the large-scale coronal field. A blob detection algorithm is used to identify valid features against a noisy background. The extracted coronal features are used to derive empirical directional constraints for magnetic field extrapolation procedures based on photospheric magnetograms. Two versions of the method optimized for processing ground-based (Mauna Loa Solar Observatory) and satellite-based (STEREO Cor1 and Cor2) coronagraph images are being developed.

Uritsky, Vadim M.; Davila, Joseph M.; Jones, Shaela; Burkepile, Joan

2015-04-01

210

The Time-dependent Chemistry of Cometary Debris in the Solar Corona  

NASA Astrophysics Data System (ADS)

Recent improvements in solar observations have greatly progressed the study of sungrazing comets. They can now be imaged along the entirety of their perihelion passage through the solar atmosphere, revealing details of their composition and structure not measurable through previous observations in the less volatile region of the orbit further from the solar surface. Such comets are also unique probes of the solar atmosphere. The debris deposited by sungrazers is rapidly ionized and subsequently influenced by the ambient magnetic field. Measuring the spectral signature of the deposited material highlights the topology of the magnetic field and can reveal plasma parameters such as the electron temperature and density. Recovering these variables from the observable data requires a model of the interaction of the cometary species with the atmosphere through which they pass. The present paper offers such a model by considering the time-dependent chemistry of sublimated cometary species as they interact with the solar radiation field and coronal plasma. We expand on a previous simplified model by considering the fully time-dependent solutions of the emitting species' densities. To compare with observations, we consider a spherically symmetric expansion of the sublimated material into the corona and convert the time-dependent ion densities to radial profiles. Using emissivities from the CHIANTI database and plasma parameters derived from a magnetohydrodynamic simulation leads to a spatially dependent emission spectrum that can be directly compared with observations. We find our simulated spectra to be consistent with observation.

Pesnell, W. D.; Bryans, P.

2014-04-01

211

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

212

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

213

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

214

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

215

Can a Nanoflare Model of Extreme-ultraviolet Irradiances Describe the Heating of the Solar Corona?  

NASA Astrophysics Data System (ADS)

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 , 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, ?, greater than the critical value 2. At these sites, nanoflare heating could be significant.

Tajfirouze, E.; Safari, H.

2012-01-01

216

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

217

The Energetics of a Global Shock Wave in the Low Solar Corona  

NASA Astrophysics Data System (ADS)

As the most energetic eruptions in the solar system, coronal mass ejections (CMEs) can produce shock waves at both their front and flanks as they erupt from the Sun into the heliosphere. However, the amount of energy produced in these eruptions, and the proportion of their energy required to produce the waves, is not well characterized. Here we use observations of a solar eruption from 2014 February 25 to estimate the energy budget of an erupting CME and the globally propagating "EIT wave" produced by the rapid expansion of the CME flanks in the low solar corona. The "EIT wave" is shown using a combination of radio spectra and extreme ultraviolet images to be a shock front with a Mach number greater than one. Its initial energy is then calculated using the Sedov-Taylor blast-wave approximation, which provides an approximation for a shock front propagating through a region of variable density. This approach provides an initial energy estimate of ?2.8 1031 erg to produce the "EIT wave," which is approximately 10% the kinetic energy of the associated CME (shown to be ?2.5 1032 erg). These results indicate that the energy of the "EIT wave" may be significant and must be considered when estimating the total energy budget of solar eruptions.

Long, David M.; Baker, Deborah; Williams, David R.; Carley, Eoin P.; Gallagher, Peter T.; Zucca, Pietro

2015-02-01

218

The energetics of a global shock wave in the low solar corona  

NASA Astrophysics Data System (ADS)

As the most energetic eruptions in the solar system, coronal mass ejections (CMEs) can produce shock waves at both their front and flanks as they erupt from the Sun into the heliosphere. However, the amount of energy produced in these eruptions, and the proportion of their energy required to produce the waves, is not well characterised. Here we use observations of a solar eruption from 2014 February 25 to estimate the energy budget of an erupting CME and the globally-propagating "EIT wave" produced by the rapid expansion of the CME flanks in the low solar corona. The "EIT wave" is shown using a combination of radio spectra and extreme ultraviolet images to be a shock front with a Mach number greater than one. Its initial energy is then calculated using the Sedov-Taylor blast-wave approximation, which provides an approximation for a shock front propagating through a region of variable density. This approach provides an initial energy estimate of ~2.8 x 10^31 ergs to produce the "EIT wave", which is approximately 10% the kinetic energy of the associated CME (shown to be ~2.5 x 10^32 ergs). These results indicate that the energy of the "EIT wave" may be significant and must be considered when estimating the total energy budget of solar eruptions.

Long, David; Baker, Deborah; Williams, David; Carley, Eoin; Gallagher, Peter; Zucca, Pietro

2015-04-01

219

Possible signature of Alfvn wave dissipation in the localized magnetic funnels of the equatorial solar corona  

NASA Astrophysics Data System (ADS)

We analyse the Hinode/EIS 2?-spectroscopic scan data containing the spectral line formed at typical inner coronal temperature. The strong Fe XII 195.120 line shows the existence of funnel-like expanding flux-tubes which exhibit the signature of blue-/red-shifted plasma motions in the off-limb equatorial corona. These coronal funnels expand in the form of open magnetic field channels up to inner coronal heights. They are most likely the parts of large-scale and closed magnetic fields (loops) which exist at higher heights in the diffused equatorial corona. We also find the signature of decreasing line-widths with altitude in observed coronal funnels (e.g., funnel 1), which is the lower part of a curved loop system. This provides the most likely signature of Alfvn wave dissipation in lower part of this loop system. We also examine the blue-shifted and diffused coronal loop boundary and interfaced region (funnel 3) which shows increasing Fe XII 195.120 line-width along it. Therefore, it exhibits the most likely signature of Alfvn wave growth in this region which is slightly curved and rising higher in the corona. Density measurements in these funnels show that it falls off with height, but more rapidly in the second funnel. We conjecture the almost constant line-width trend as a most likely signature of Alfvn wave dissipation in this density-stratified second coronal funnel, which is also the lower part of a large-scale closed loop system. Both dissipative and growing Alfvn waves can change the non-thermal component and thus the full width at half-maximum of the Fe XII 195.120 line. We find the clues of Alfvn wave dissipation along the expanding field lines of the coronal funnel (lower parts of the loop system) imparting its energy to the outflowing plasma and thereby contributing to the formation of the nascent solar wind in the inner corona.

Dwivedi, Bhola N.; Srivastava, Abhishek Kumar; Mohan, Anita

2014-12-01

220

On the processing and analysis of the data of the CORONAS-F/SPIRIT and other solar experiments  

NASA Astrophysics Data System (ADS)

More than 300000 solar images in the extreme ultraviolet and soft X-ray regions were obtained using two telescopes and four spectroheliometers of the CORONAS-F/SPIRIT device from August 2001 to December 2005. Methods for the processing of such data and extracting physical information are presented, taking into account the experience of processing and analysis of other space experiments on solar research. Some results on applications of the considered methods are presented.

Bogachev, S. A.; Grechnev, V. V.; Kuzin, S. V.; Slemzin, V. A.; Bugaenko, O. I.; Chertok, I. M.

2009-04-01

221

Spectrally-resolved Soft X-ray Observations and the Temperature Structure of the Solar Corona  

NASA Astrophysics Data System (ADS)

Solar X-ray observations provide important diagnostics of plasma heating and particle acceleration, during solar flares and quiescent periods. How the corona is heated to its ~1-3 MK nominal temperature remains one of the fundamental unanswered questions of solar physics; heating of plasma to tens of MK during solar flares -- particularly to the hottest observed temperatures of up to ~50 MK -- is also still poorly understood. Soft X-ray emission (~0.1-10 keV; or ~0.1-10 nm) is particularly sensitive to hot coronal plasma and serves as a probe of the thermal processes driving coronal plasma heating. Spectrally- and temporally-resolved measurements are crucial for understanding these energetic processes, but there have historically been very few such observations. We present new solar soft X-ray spectra from the Amptek X123-SDD, measuring quiescent solar X-ray emission from ~0.5 to ~30 keV with ~0.15 keV FWHM resolution from two SDO/EVE calibration sounding rocket underflights in 2012 and 2013. Combined with observations from RHESSI, GOES/XRS, SDO/EVE, and SDO/AIA, the temperature distribution derived from these data suggest significant hot (5-10 MK) emission from active regions, and the 2013 spectra suggest a low-FIP enhancement of only ~1.6 relative to the photosphere, 40% of the usually-observed value from quiescent coronal plasma. We explore the implications of these findings on coronal heating. We discuss future missions for spectrally-resolved soft X-ray observations using the X123-SDD, including the upcoming MinXSS 3U CubeSat using the X123-SDD and scheduled for deployment in mid-2015, and the CubIXSS 6U CubeSat mission concept.

Caspi, Amir; Warren, Harry; McTiernan, James; Woods, Thomas N.

2015-04-01

222

The relative abundance of neon and magnesium in the solar corona  

NASA Technical Reports Server (NTRS)

A technique is proposed for specifically determining the relative solar coronal abundance of neon and magnesium. The relative abundance is calculated directly from the relative intensity of the resonance lines of Ne X (12.134A) and Mg XI (9.169A) without the need for the development of a detailed model of the thermal structure of the corona. Moderate resolution Bragg crystal spectrometer results from the OVI-10 satellite were used to determine a coronal neon to magnesium relative abundance of 1.47 + or - 0.38. The application of this technique to a recent higher resolution rocket observation gave an abundance ratio of approximately 0.93 + or - 0.15.

Rugge, H. R.; Walker, A. B. C., Jr.

1976-01-01

223

Three-Dimensional Numerical Simulations of Interaction Between Flux Ropes in the Solar Corona  

NASA Astrophysics Data System (ADS)

We have recently identified in three-dimensional (3D) reduced magnetohydrodynamics (RMHD) simulations that interaction between magnetic flux ropes is a fundamental process in the solar corona that leads to current-sheet formation, 3D magnetic reconnection, and coronal heating. In the case of long flux ropes, this process essentially reduces to the coalescence of magnetic islands in 2D, which we have also studied extensively using MHD simulations. In the high-Lundquist number (S) limit, which requires high-resolution to simulate, the reconnection rate between the flux ropes becomes small following the Sweet-Parker description, and thus they bounce back and forth while they reconnect. We will present 3D simulations to demonstrate this process, which can potentially have great implications in the generation of Alfven waves and MHD turbulence. This work is supported by a NASA grant NNX08BA71G, and a NSF grant AGS-0962477.

Yasin, E. S.; Ng, C.; Lin, L.

2011-12-01

224

The possible role of MHD waves in heating the solar corona  

NASA Technical Reports Server (NTRS)

The possible role of waves in the heating of the solar corona has been investigated. A general dispersion relation has been derived for waves propagating in a homogeneous plasma subject to dissipation by viscosity and thermal conduction. The dissipation mechanisms have been incorporated self-consistently into the equations, and no assumptions about the strength of the damping have been made. Solutions of the sixth-order dispersion relation provide information on how the damping of both slow and fast mode waves depends upon the plasma density, temperature, field strength, and angle of propagation relative to the background magnetic field. We provide a detailed comparison to the standard approach, which is to solve for the wave quantities in the absence of dissipation and then to use these quantities in expressions for the heating due to viscosity and thermal conduction.

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

1994-01-01

225

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

226

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

227

Analysis of a Solar Eruptive Event on November 4, 2001, Using CORONAS-F/SPIRIT Data  

NASA Astrophysics Data System (ADS)

We analyze large-scale solar activity following the eruption of a very powerful, geoeffective coronal mass ejection in the 23rd solar cycle, observed at 175, 284, and 304 on November 4, 2001, using data from the CORONAS-F/SPIRIT telescope. In particular, we have shown that the restructuring of the magnetic field above the eruption center was accompanied by the formation of a multicomponent post-eruptive arcade, which was observed in all three bands over many hours and had an extent of the order of 0.5R ?. Two kinds of dimmings were observed, i.e., compact dimmings on either side of this arcade and channeled dimmings along some extended features beyond the active region. The intensity in the dimmings decreased by several tens of percent. The enhanced emission observed at the top of the post-eruptive arcade can be due to energy release in the course of magnetic reconnection high in the corona at the relaxation stage of the perturbed magnetic field to a new equilibrium state with a closed configuration. It can also be due to an enhanced emission measure because of the oblique direction of the line of sight crossing both loop tops and footpoint regions. The spatial coincidence of the main dimmings in lines corresponding to different temperatures indicates that a plasma outflow from the transition region and coronal structures with opened field lines are responsible for these dimmings. Variations in the plasma temperature associated with coronal mass ejections probably play an important role for some dimmings, which appear different in different lines.

Chertok, I. M.; Slemzin, V. A.; Kuzin, S. V.; Grechnev, V. V.; Bugaenko, O. I.; Zhitnik, I. A.; Ignat'ev, A. P.; Pertsov, A. A.

2004-05-01

228

Non-equilibrium Ionization Modeling of Simulated Pseudostreamers in a Solar Corona Model  

NASA Astrophysics Data System (ADS)

Time-dependent ionization is important for diagnostics of coronal streamers, where the thermodynamic time scale could be shorter than the ionization or recombination time scales, and ions are therefor in non-equilibrium ionization states. In this work, we perform post-processing time-dependent ionization calculations for a three dimensional solar corona and inner heliosphere model from Predictive Sciences Inc. (Miki? & Linker 1999) to analyze the influence of non-equilibrium ionization on emission from coronal streamers. Using the plasma temperature, density, velocity and magnetic field distributions provided by the 3D MHD simulation covering the Whole Sun Month (Carrington rotation CR1913, 1996 August 22 to September 18), we calculate non-equilibrium ionization states in the region around a pseudostreamer. We then obtain the synthetic emissivities with the non-equilibrium ion populations. Under the assumption that the corona is optically thin, we also obtain intensity profiles of several emission lines. We compare our calculations with intensities of Lyman-alpha lines and OVI lines from SOHO/Ultraviolet Coronagraph Spectrometer (UVCS) observations at 14 different heights. The results show that intensity profiles of both Lyman-alpha and OVI lines match well UVCS observations at low heights. At large heights, OVI intensites are higher for non-equilibrium ionization than equilibrium ionization inside this pseudostreamer. The assumption of ionization equilibrium would lead to a underestimate of the OVI intensity by about ten percent at a height of 2 solar radii, and the difference between these two ionization cases increases with height. The intensity ratio of OVI 1032 line to OVI 1037 lines is also obtained for non-equilibrium ionization modeling.

Shen, Chengcai; Raymond, John C.; Miki?, Zoran; Linker, Jon; Reeves, Katharine K.; Murphy, Nicholas A.

2015-04-01

229

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

NASA Astrophysics Data System (ADS)

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

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

230

Three-Dimensional MHD Modeling of The Solar Corona and Solar Wind: Comparison with The Wang-Sheeley Model  

NASA Technical Reports Server (NTRS)

We present simulation results from a tilted-dipole steady-state MHD model of the solar corona and solar wind and compare the output from our model with the Wang-Sheeley model which relates the divergence rate of magnetic flux tubes near the Sun (inferred from solar magnetograms) to the solar wind speed observed near Earth and at Ulysses. The boundary conditions in our model specified at the coronal base and our simulation region extends out to 10 AU. We assumed that a flux of Alfven waves with amplitude of 35 km per second emanates from the Sun and provides additional heating and acceleration for the coronal outflow in the open field regions. The waves are treated in the WKB approximation. The incorporation of wave acceleration allows us to reproduce the fast wind measurements obtained by Ulysses, while preserving reasonable agreement with plasma densities typically found at the coronal base. We find that our simulation results agree well with Wang and Sheeley's empirical model.

Usmanov, A. V.; Goldstein, M. L.

2003-01-01

231

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 Alfvn waves and hence faster shock acceleration of SEPs. On the other hand, SEP-driven Alfvn 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 Alfvn 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 Alfvn 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

232

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

233

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

234

Are coronae of late type stars made of solar-like structures? The FX-HR diagram and the pressure-temperature correlation.  

E-print Network

Are coronae of late type stars made of solar-like structures? The FX-HR diagram and the pressure) diagram as a fundamental tool for our study. We find that FX is strongly correlated to HR in stellar corona, i.e. the most quiet regions. We use the X-ray surface flux (FX) vs. spectral hardness ratio (HR

235

Validation of the Earth atmosphere models using the EUV solar occultation data from the CORONAS and PROBA 2 instruments  

NASA Astrophysics Data System (ADS)

Absorption in the atmosphere below 500 km results in attenuation of the solar EUV flux, variation of its spectra and distortion of solar images acquired by solar EUV instruments operating on LEO satellites even on solar synchronous orbits. Occultation measurements are important for planning of solar observations from these satellites, and can be used for monitoring the upper atmosphere as well as for studying its response to the solar activity. We present the results of the occultation measurements of the solar EUV radiation obtained by the CORONAS-F/SPIRIT telescope at high solar activity (2002), by the CORONAS-Photon/TESIS telescope at low activity (2009), and by the SWAP telescope and LYRA radiometer onboard the PROBA 2 satellite at moderate activity (2010). The measured attenuation profiles and the retrieved linear extinction coefficients at the heights 200-500 km are compared with simulations by the NRLMSIS-00 and DTM2013 atmospheric models. It was shown that the results of simulations by the DTM2013 model are well agreed with the data of measurements at all stages of solar activity and in presence of the geomagnetic storm, whereas the results of the NRLMSISE-00 model significantly diverge from the measurements, in particular, at high and low activity. The research leading to these results has received funding from the European Unions Seventh Programme for Research, Technological Development and Demonstration under Grant Agreement eHeroes (project ? 284461, www.eheroes.eu).

Slemzin, Vladimir; Kuzin, Sergey; Berghmans, David; Pertsov, Andrey; Dominique, Marie; Ulyanov, Artyom; Gaikovich, Konstantin

236

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

E-print Network

We investigate possibilities of solar coronal heating by acoustic waves generated not at the photosphere but in the corona, aiming at heating in the mid- to low-latitude corona where the low-speed wind is expected to come from. Acoustic waves of period ? ? 100s are triggered by chromospheric reconnection, one model of small scale magnetic reconnection events recently proposed by Sturrock. These waves having a finite amplitude eventually form shocks to shape sawtooth waves (N-waves), and directly heat the surrounding corona by dissipation of their wave energy. Outward propagation of the N-waves is treated based on the weak shock theory, so that the heating rate can be evaluated consistently with physical properties of the background coronal plasma without setting a dissipation length in an ad hoc manner. We construct coronal structures from the upper chromosphere to the outside of 1AU for various inputs of the acoustic waves having a range of energy flux of Fw,0 = (1 ? 20) 10 5 erg cm ?2 s ?1 and a period of ? = 60 ? 300s. The heating by the N-wave dissipation effectively works in the inner corona and we find that the waves of Fw,0 ? 210 5 erg cm ?2 s ?1 and ? ? 60s could maintain peak coronal temperature, Tmax> 10 6 K. The model could also reproduce the density profile observed in the streamer region. However, due to its short dissipation length, the location of Tmax is closer to the surface than the observation, and the resultant flow velocity of the solar wind is lower than the observed profile of the low-speed wind. The cooperations with other heating and acceleration sources with the larger dissipation length are inevitable to reproduce the real solar corona. Subject headings: Sun: corona solar wind waves 2 1.

Takeru Ken Suzuki

2002-01-01

237

A 2D dust chemistry of the inner Solar Nebula  

NASA Astrophysics Data System (ADS)

The chemical composition of the dust in the inner layers of protoplanetary discs is unknown since infrared observation only probe the chemistry of the thin surface layer of discs. Given that planets formation occurs in the midplane, direct important information from the bulk chemistry of the disc is missing, and modelling is required. We compute for the first time the 2D chemical distribution of condensates in the inner Solar Nebula using a thermodynamic equilibrium model, and derive timescales for vertical settling and radial migration of the dust to predict the chemical evolution of the dust. We find two enstatite-rich zones within 1 AU from the protosun: a band 0.1 AU thick in the upper layer of the disc interior to 0.8 AU, and in the disc midplane out to 0.4 AU. Our results are consistent with infrared observation of protoplanetary disc which show emission of enstatite-rich dust arising from the inner warmer surface of the disc. The inner midplane of the disc is a chemically diverse zone in which enstatite-rich dust coexists with sulfides and unprocessed material. Our finding of two enstatite-rich zones in the disc supports recent evidence that Mercury and enstatite chondrites shared a bulk material with similar composition. The derived timescales for vertical settling suggest that dust can be chemically sorted in the hotter, inner surface of the disc leading to fractionated Mg-Fe-poor gas which can produce enstatite-rich dust. We suggest that the migration of enstatite-rich grains toward the midplane and-or condensation after gas fractionation may account for the formation of the bulk material which then formed the EL (low-Fe) chondrites.

Pignatale, F. C.; Liffman, K.; Maddison, S. T.; Brooks, G.

2014-12-01

238

SIMULTANEOUS OBSERVATION OF SOLAR OSCILLATIONS ASSOCIATED WITH CORONAL LOOPS FROM THE PHOTOSPHERE TO THE CORONA  

SciTech Connect

The solar oscillations along one coronal loop in AR 11504 are observed simultaneously in white light emission and Doppler velocity by SDO/HMI, and in UV and EUV emissions by SDO/AIA. The technique of the time-distance diagram is used to detect the propagating oscillations of the emission intensities along the loop. We find that although all the oscillation signals were intercorrelated, the low chromospheric oscillation correlated more closely to the oscillations of the transition region and corona than to those of the photosphere. Situated above the sunspot, the oscillation periods were {approx}3 minutes in the UV/EUV emissions; however, moving away from the sunspot and into the quiet Sun, the periods became longer, e.g., up to {approx}5 minutes or more. In addition, along another loop we observe both the high-speed outflows and oscillations, which roughly had a one-to-one corresponding relationship. This indicates that the solar periodic oscillations may modulate the magnetic reconnections between the loops of the high and low altitudes that drive the high-speed outflows along the loop.

Su, J. T.; Liu, S.; Zhang, Y. Z.; Zhao, H.; Xu, H. Q.; Xie, W. B. [Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Science, Beijing 100012 (China)] [Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Science, Beijing 100012 (China); Liu, Y. [National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011 (China)] [National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011 (China)

2013-01-01

239

Neon and Oxygen Abundances and Abundance Ratio in the Solar Corona  

NASA Astrophysics Data System (ADS)

In this work we determine the Ne/O abundance ratio from Solar and Heliospheric Observatory (SOHO)/Solar Ultraviolet Measurement of Emitted Radiation (SUMER) off-disk observations of quiescent streamers over the 1996-2008 period. We find that the Ne/O ratio is approximately constant over solar cycle 23 from 1996 to 2005, at a value of 0.099 0.017 this value is lower than the transition region determinations from the quiet Sun used to infer the neon photospheric abundance from the oxygen photospheric abundance. Also, the Ne/O ratio we determined from SUMER is in excellent agreement with in situ determinations from ACE/SWICS. In 2005-2008, the Ne/O abundance ratio increased with time and reached 0.25 0.05, following the same trend found in the slowest wind analyzed by ACE/SWICS. Further, we measure the absolute abundance in the corona for both oxygen and neon from the data set of 1996 November 22, obtaining A o = 8.99 0.04 and A Ne = 7.92 0.03, and we find that both elements are affected by the first ionization potential (FIP) effect, with oxygen being enhanced by a factor of 1.4-2.1 over its photospheric abundance, and neon being changed by a factor of 0.75-1.20. We conclude that the Ne/O ratio is not constant in the solar atmosphere, both in time and at different heights, and that it cannot be reliably used to infer the neon abundance in the photosphere. Also, we argue that the FIP effect was less effective during the minimum of solar cycle 24, and that the Ne/O = 0.25 0.05 value measured at that time is closer to the true photospheric value, leading to a neon photospheric abundance larger than assumed by ?40%. We discuss the implications of these results for the solar abundance problem, for the FIP effect, and for the identification of the source regions of the solar wind.

Landi, E.; Testa, P.

2015-02-01

240

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

241

Dynamical behaviour of interstellar dust particles in the solar system  

NASA Astrophysics Data System (ADS)

Motion and possible capture of interstellar dust particles (ISDPs) in the Solar System are investigated. Gravitational force of the Sun, solar electromagnetic and corpuscular radiation and interplanetary magnetic field are considered. The effect of solar electromagnetic radiation plays an important role in the sense that nonspherical ISDPs can be captured (and survive) much more effectively than spherical particles. It turns out that particles of effective radii ?0.4?m, moving initially near the solar equatorial plane and with impact parameter 400 RS?b? 500 RS (solar radii) exhibit a high probability of capture and survival in the Solar System. Only a very small number of spherical particles can be captured. Survived nonspherical ISDPs orbiting around the Sun are characterized by a quantity analogous to the Kepler's third law: /T, where T is orbital period and is time average of cubed solar distance over the period T. The value of the quantity /T is 0.6730.002[AU/year].

Kocifaj, Miroslav; Kla?ka, Jozef

2004-11-01

242

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

NASA Technical Reports Server (NTRS)

In Cram's theory for the formation of the K-coronal spectrum he observed the existence of temperature sensitive anti-nodes, which were separated by temperature insensitive nodes, at certain wave-lengths in the K-coronal spectrum. Cram also showed these properties were remarkably independent of altitude above the solar limb. 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 measurements 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 August 1999 in Elazig, Turkey. Here twenty fiber optic tips were positioned in the focal plane of the telescope to observe simultaneously at many different latitudes and two different radial distances in the solar corona. The other ends were vertically stacked and placed at the primary focus of the spectrograph. By isolating the K-coronal spectrum from each fiber the temperature and the wind sensitive intensity ratios were calculated.

Reginald, Nelson L.

2000-01-01

243

Are coronae of late type stars made of solar-like structures? The Fx-HR diagram and the pressure-temperature correlation  

E-print Network

We show that stellar coronae can be composed of X-ray emitting structures like those in the solar corona, using a large set of ROSAT/PSPC observations of late-type-stars, and a large set of solar X-ray data collected with Yohkoh/SXT. We have considered data on the solar corona at various phases of the cycle and various kinds of X-ray coronal structures, from flares to the background corona. The surface flux (F_x) vs. spectral hardness ratio (HR) diagram is a fundamental tool for our study. We find that $F_X$ is strongly correlated to HR in stellar coronae, in the solar corona at all phases of the cycle, and in the individual solar coronal structures; all follow the same law. We therefore claim that coronae of late type stars are formed with X-ray structures very similar to the solar ones. In this scenario, the fraction of the stellar surface covered with active regions and with their bright cores increases with activity; the most active stars are brighter and hotter than if they were entirely covered with active regions so they can be explained only with the additional presence of several flares (or flare-like structures) at any time. Using the F_x vs. HR correlation (F_X ~ T^6) we derive new laws relating the temperature, pressure, volumetric heating and characteristic loop length of the coronal plasma, on all the late type stars Individual solar coronal structures and the whole solar corona, follow the same laws. We claim that the strong correlation between surface flux and temperature and the laws mentioned above are just the effect of more fundamental physical mechanisms driving the coronal structures of all the late-type stars from the emergence of new magnetic structures to their dissipation.

G. Peres; S. Orlando; F. Reale

2004-05-14

244

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

245

Laboratory simulation of sputtering dust grains in the solar wind  

NASA Astrophysics Data System (ADS)

Dust grains in space are exposed to energetic ions, electrons and UV irradiation. An impact of energetic ions can lead to sputtering of the grain resulting, consequently, in a grain destruction during long-term exposures to space environment. In the solar wind, dust grains are bombarded by ions and electrons simultaneously and it is known that an impact of electrons can influence the sputtering yield of glass material during the ion bombardment. This mechanism preferentially sputters oxygen and we suggest that it could be valid for silicate-type grains as well. For the presented simulation, we have chosen spherical SiO2 grains with diameter in the range of 1 micron. Our experimental set-up enables us to catch and to store a single dust grain which can be simultaneously influenced by argon ions with an energy of 2 keV and by 1 keV electron beam. The mass of the grain is determined after each bombardment session (approx every 3 hours) and we can judge the sputtering efficiency from temporal changes of the mass. Although the 2 keV Ar+ and 1 keV e- beams are only rough representatives of solar wind conditions, the results can give us some conclusions on the electron influence on the sputtering rate in space.

Vysinka, Marek; Vaverka, Jakub; Pavlu, Jiri; Safrankova, Jana; Nemecek, Zdenek

2014-05-01

246

Radio interferometer observations of solar wind turbulence from the orbit of Helios to the solar corona  

NASA Technical Reports Server (NTRS)

We report observations of Very Long Baseline Interferometer (VLBI) phase scintillations due to turbulence in the solar wind. The observations were made at 5.00 and 8.42 GHz with the Very Long Baseline Array (VLBA) on three dates in 1991 July and August. We observed the sources 0851 + 202 and 0735 + 178 at solar elongations ranging from 2.66 deg to 13.29 deg; the closest approach of the line of sight to the Sun ranged from 10 to 49.8 solar radii. We have also included previously unpublished 5 GHz VLBI phase scintillation measurements from 1989. These measurements probe solar wind density fluctuations on spatial scales from about 200 km to 2000 km. Our measurements are in quite good agreement with the Coles & Harmon model for the radio phase structure function, which was largely determined from observations on both shorter and larger spatial scales. Departures from the Coles & Harmon functions are attributable to day-to-day variations in the solar wind conditions. Phase scintillations at the greatest solar elongations are in very good agreement with extrapolated estimates from direct measurements made with the Helios spacecraft at slightly larger heliocentric distances. Thus there is a consistency between the in-situ spacecraft and radio sensing measurements of density turbulence. All of the VLBI data are consistent with a Kolmogorov spectrum for the density fluctuations, although at the closest elongations there may be excess power at small spatial scales. An advantage of interferometric techniques over other radio propagation measurements is that they provide a measure of the anisotropy of the irregularities. Our observations at closest approach (10 solar radii) show weak evidence for anisotropic, field-aligned density irregularities with an axial ratio of order 2. This degree of anisotropy would appear to be less than that measured at similar solar elongations but on smaller spatial scales by Armstrong and colleagues. Finally, a combination of the radio propagation data and in situ Helios measurements is used to determine the heliocentric distance dependence of the normalization coefficient of the density power spectrum, C(sup 2)(sub N). Modeling C(sup2)(sub N) varies as (R/solar radii)(sup -Kappa), we find Kappa = 3.72 +/- 0.30. Subject to a number of assumptions, this result is consistent with the conclusion of D. A. Roberts that turbulence within 0.28 astronomical units adheres to a WKB formula for turbulence amplitude as a function of heliocentric distance.

Spangler, Steven R.; Sakurai, Takayuki

1995-01-01

247

Imaging Observation of Quasi-periodic Disturbances' Amplitudes Increasing with Height in the Polar Region of the Solar Corona  

NASA Astrophysics Data System (ADS)

At present, there have been few extreme ultraviolet (EUV) imaging observations of spatial variations of the density perturbations due to the slow magnetoacoustic waves (SMWs) propagating along the solar coronal magnetic fields. In this paper, we present such observations taken from the polar region of the corona with the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory and investigate the amplitude of quasi-periodic propagating disturbances that increase with height in the lower corona (0-9 Mm over the solar limb). We statistically determined the following parameters associated with the disturbances: pressure scale height, period, and wavelength in AIA 171 , 193 , and 211 channels. The scale height and wavelength are dependent of temperature, while the period is independent of temperature. The acoustic velocities inferred from the scale height highly correlate with the ratios of wavelength to period, i.e., phase speeds. They provide evidence that the propagating disturbances in the lower corona are likely SMWs and the spatial variations in EUV intensity in the polar region likely reflects the density compressional effect by the propagating SMWs.

Su, J. T.; Liu, Y.; Shen, Y. D.; Priya, T. G.

2014-08-01

248

Interpretation of F-corona radial velocity observations  

NASA Astrophysics Data System (ADS)

The observations made during the July 31, 1981 solar eclipse of the F-corona radial velocities between 3 and 7 solar radii are interpreted, assuming direct circular Keplerian motion of dust grains. Diffraction and isotropic scattering are considered. If the grains are assumed to be of silica, a best fit to observations is found for grain radii of about 0.4 micron, a border of dust-free zone from 6 to 14 solar radii, or a high concentration of grains at the same interval of heliocentric distances.

Shestakova, L. I.

1987-03-01

249

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

250

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

251

Probing the Large Scale Plasma Structure of the Solar Corona with Faraday Rotation Measurements  

E-print Network

Faraday rotation measurements of the solar corona made with the Very Large Array (VLA) at frequencies of 1465 and 1665 MHz are reported. The measurements were made along 20 lines of sight to 19 extragalactic radio sources in March and April, 2005. The closest heliocentric distances of the lines of sight ranged from 9.7 to 5.6 $R_{\\odot}$. Measured rotation measures range from -25 to +61 rad/m$^2$. The purpose of these observations is to probe the three dimensional structure of the coronal plasma in the heliocentric distance range $5-10 R_{\\odot}$, and particularly the strength and structure of the coronal magnetic field. The measured rotation measures are compared with models for the coronal plasma structure. For the majority of the lines of sight, the observed rotation measures are reasonably well represented by the predictions from the models. However, 4 of the 20 lines of sight have large observed-model residuals, which do not seem associated with coronal mass ejections. The magnitude of the field necessary to reproduce the majority of the observations is in the range 46-120 milliGauss at $5 R_{\\odot}$, with a smaller, preferred range of 46-52 mG at $5 R_{\\odot}$.

Laura D. Ingleby; Steven R. Spangler; Catherine A. Whiting

2007-01-18

252

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

SciTech Connect

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

Schrijver, Carolus J.; DeRosa, Marc L.; Title, Alan M., E-mail: schryver@lmsal.co [Lockheed Martin Advanced Technology Center, Palo Alto, CA 94304 (United States)

2010-08-20

253

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

254

Gyrokinetic simulation and theory of forced current sheet equilibria in the solar corona  

NASA Astrophysics Data System (ADS)

In the solar corona sharp current sheets may develop as a result of magnetic flux tube motion. The current, which flows parallel to the strong potential field of the flux tubes, creates a perpendicular sheared magnetic field. A class of forced current sheet equilibria, with a nearly singular current profile, has been studied previously and shown to be linearly unstable to resistive tearing instabilities. The linear growth of the resistive tearing modes in this equilibrium was shown to be 4 to 5 orders of magnitude greater than those of standard tearing modes in a diffuse current sheet current equilibrium. In this presentation we examine the kinetic effects on the stability and dissipation of the forced current sheet equilibrium. It is shown that kinetic effects greatly enhance the time scales of magnetic energy dissipation via magnetic reconnection and secondary instabilities play an important role in the dynamical evolution. For this investigation we utilize 2D and 3D finite beta gyrokinetic particle-in-cell simulation models. This model allows us to include finite gyroradius and wave-particle interaction effects accurately, using realistic plasma parameters (compared with conventional full dynamics particle simulations). Electron-ion collisional effects are included using a Monte Carlo implementation of a Lorentz gas collision operator. This allows us to explore the full range of collisionality, including the collisionless or nearly infinite Lundquist number regime. It is demonstrated that nonlinear kinetic tearing modes play an important role in coronal heating when sharp current sheets form as a result of global magnetic stresses.

Sydora, R.

255

Inferring the Structure of the Solar Corona and Inner Heliosphere During the Maunder Minimum Using Global Thermodynamic Magnetohydrodynamic Simulations  

NASA Astrophysics Data System (ADS)

Observations of the Suns corona during the space era have led to a picture of relatively constant, but cyclically varying solar output and structure. Longer-term, more indirect measurements, such as from 10Be, coupled by other albeit less reliable contemporaneous reports, however, suggest periods of significant departure from this standard. The Maunder Minimum was one such epoch where: (1) sunspots effectively disappeared for long intervals during a 70 yr period; (2) eclipse observations suggested the distinct lack of a visible K-corona but possible appearance of the F-corona; (3) reports of aurora were notably reduced; and (4) cosmic ray intensities at Earth were inferred to be substantially higher. Using a global thermodynamic MHD model, we have constructed a range of possible coronal configurations for the Maunder Minimum period and compared their predictions with these limited observational constraints. We conclude that the most likely state of the corona duringat leastthe later portion of the Maunder Minimum was not merely that of the 2008/2009 solar minimum, as has been suggested recently, but rather a state devoid of any large-scale structure, driven by a photospheric field composed of only ephemeral regions, and likely substantially reduced in strength. Moreover, we suggest that the Sun evolved from a 2008/2009-like configuration at the start of the Maunder Minimum toward an ephemeral-only configuration by the end of it, supporting a prediction that we may be on the cusp of a new grand solar minimum.

Riley, Pete; Lionello, Roberto; Linker, Jon A.; Cliver, Ed; Balogh, Andre; Beer, Jrg; Charbonneau, Paul; Crooker, Nancy; DeRosa, Marc; Lockwood, Mike; Owens, Matt; McCracken, Ken; Usoskin, Ilya; Koutchmy, S.

2015-04-01

256

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

257

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

258

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

259

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

260

Development of a solar-cell dust opacity measurement instrument for Mars Pathfinder  

NASA Technical Reports Server (NTRS)

The atmosphere of Mars has a considerable load of suspended dust. Over time, this dust is deposited out of the atmosphere. The mechanism and the temporal and geographical variation of this deposition are not well characterized. Measurements of settling rates and dust properties are of considerable scientific interest. Atmospheric dust affects the atmospheric solar absorption and thus the heat balance of Mars, as well as serving as nucleation sites for water and CO2 frost. Knowledge of dust properties is of critical interest to design and prediction of the lifetime and power output of solar arrays, and also to design of mechanical mechanisms and radiators. An instrument has been designed and fabricated to measure the dust accumulation during the course of the Mars Pathfinder rover mission. The solar-cell coverglass transmission experiment will measure the change in optical opacity of a transparent coverglass as dust settles on the surface, and a quartz crystal monitor will measure the mass deposited.

Landis, Geoffrey; Jenkins, Phillip P.

1996-01-01

261

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

262

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

263

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

264

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

265

Ion Temperatures in the Low Solar Corona: Polar Coronal Holes at Solar Minimum  

E-print Network

In the present work we use a deep-exposure spectrum taken by the SUMER spectrometer in a polar coronal hole in 1996 to measure the ion temperatures of a large number of ions at many different heights above the limb between 0.03 and 0.17 solar radii. We find that the measured ion temperatures are almost always larger than the electron temperatures and exhibit a non-monotonic dependence on the charge-to-mass ratio. We use these measurements to provide empirical constraints to a theoretical model of ion heating and acceleration based on gradually replenished ion-cyclotron waves. We compare the wave power required to heat the ions to the observed levels to a prediction based on a model of anisotropic magnetohydrodynamic turbulence. We find that the empirical heating model and the turbulent cascade model agree with one another, and explain the measured ion temperatures, for charge-to-mass ratios smaller than about 0.25. However, ions with charge-to-mass ratios exceeding 0.25 disagree with the model; the wave power they require to be heated to the measured ion temperatures shows an increase with charge-to-mass ratio (i.e., with increasing frequency) that cannot be explained by a traditional cascade model. We discuss possible additional processes that might be responsible for the inferred surplus of wave power.

Enrico Landi; Steven R. Cranmer

2008-09-30

266

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

E-print Network

Nonlinear force-free field (NLFFF) models are thought to be viable tools for investigating the structure, dynamics and evolution of the coronae of solar active regions. In a series of NLFFF modeling studies, we have found that NLFFF models are successful in application to analytic test cases, and relatively successful when applied to numerically constructed Sun-like test cases, but they are less successful in application to real solar data. Different NLFFF models have been found to have markedly different field line configurations and to provide widely varying estimates of the magnetic free energy in the coronal volume, when applied to solar data. NLFFF models require consistent, force-free vector magnetic boundary data. However, vector magnetogram observations sampling the photosphere, which is dynamic and contains significant Lorentz and buoyancy forces, do not satisfy this requirement, thus creating several major problems for force-free coronal modeling efforts. In this article, we discuss NLFFF modeling o...

DeRosa, Marc L; Barnes, Graham; Leka, K D; Lites, Bruce W; Aschwanden, Markus J; Amari, Tahar; Canou, Aurelien; McTiernan, James M; Regnier, Stephane; Thalmann, Julia K; Valori, Gherardo; Wheatland, Michael S; Wiegelmann, Thomas; Cheung, Mark C M; Conlon, Paul A; Fuhrmann, Marcel; Inhester, Bernd; Tadesse, Tilaye

2009-01-01

267

A CRITICAL ASSESSMENT OF NONLINEAR FORCE-FREE FIELD MODELING OF THE SOLAR CORONA FOR ACTIVE REGION 10953  

SciTech Connect

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

DeRosa, Marc L.; Schrijver, Carolus J.; Aschwanden, Markus J.; Cheung, Mark C. M. [Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover St. B/252, Palo Alto, CA 94304 (United States); Barnes, Graham; Leka, K. D. [North West Research Associates, Colorado Research Associates Division, 3380 Mitchell Ln., Boulder, CO 80301 (United States); Lites, Bruce W. [High Altitude Observatory, National Center for Atmospheric Research , P.O. Box 3000, Boulder, CO 80307 (United States); Amari, Tahar; Canou, Aurelien [CNRS, Centre de Physique Theorique de l'Ecole Polytechnique, 91128 Palaiseau Cedex (France); McTiernan, James M. [Space Sciences Laboratory, University of California at Berkeley, 7 Gauss Way, Berkeley, CA 94720 (United States); Regnier, Stephane [Mathematics Institute, University of St Andrews, St Andrews, Fife KY16 9SS (United Kingdom); Thalmann, Julia K.; Wiegelmann, Thomas; Inhester, Bernd; Tadesse, Tilaye [Max-Planck-Institut fuer Sonnensystemforschung, Max-Planck-Strasse 2, 37191 Katlenburg-Lindau (Germany); Valori, Gherardo [Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam (Germany); Wheatland, Michael S. [School of Physics, University of Sydney, Sydney, NSW 2006 (Australia); Conlon, Paul A. [Astrophysics Research Group, School of Physics, Trinity College Dublin, Dublin 2 (Ireland); Fuhrmann, Marcel [Institut fuer Physik, Universitaet Potsdam, Am Neuen Palais 10, 14469 Potsdam (Germany)

2009-05-10

268

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

269

The relation between the properties of pressure variations in the lower 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 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 and the STEREOs during 2011 and 2012. We use a simple model of the distribution of interplanerary magnetic field lines to determine the foopoint locations of field lines connecting the lower corona to the points of in-situ measurements. 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. We discuss the successes and challenges faced when interpreting these observations in terms of the acceleration of particles at coronal shocks.

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

2012-12-01

270

Time delay occultation data of the Helios spacecraft for probing the electron density distribution in the solar corona  

NASA Technical Reports Server (NTRS)

S-band time delay measurements were collected from the spacecraft Helios A and B during three solar occultations in 1975/76 within heliocentric distances of about 3 and 215 earth radius in terms of range, Doppler frequency shift, and electron content. Characteristic features of measurement and data processing are described. Typical data sets are discussed to probe the electron density distribution near the sun (west and east limb as well) including the outer and extended corona. Steady-state and dynamical aspects of the solar corona are presented and compared with earth-bound-K-coronagraph measurements. Using a weighted least squares estimation, parameters of an average coronal electron density profile are derived in a preliminary analysis to yield electron densities at r = 3, 65, 215 earth radius. Transient phenomena are discussed and a velocity of propagation v is nearly equal to 900 km/s is determined for plasma ejecta from a solar flare observed during an extraordinary set of Helios B electron content measurements.

Edenhofer, P.; Lueneburg, E.; Esposito, P. B.; Martin, W. L.; Zygielbaum, A. I.; Hansen, R. T.; Hansen, S. F.

1978-01-01

271

Impact of Temperature-dependent Resistivity and Thermal Conduction on Plasmoid Instabilities in Current Sheets in the Solar Corona  

NASA Astrophysics Data System (ADS)

In this paper, we investigate, by means of two-dimensional magnetohydrodynamic simulations, the impact of temperature-dependent resistivity and thermal conduction on the development of plasmoid instabilities in reconnecting current sheets in the solar corona. We find that the plasma temperature in the current-sheet region increases with time and it becomes greater than that in the inflow region. As secondary magnetic islands appear, the highest temperature is not always found at the reconnection X-points, but also inside the secondary islands. One of the effects of anisotropic thermal conduction is to decrease the temperature of the reconnecting X-points and transfer the heat into the O-points, the plasmoids, where it gets trapped. In the cases with temperature-dependent magnetic diffusivity, ? ~ T -3/2, the decrease in plasma temperature at the X-points leads to (1) an increase in the magnetic diffusivity until the characteristic time for magnetic diffusion becomes comparable to that of thermal conduction, (2) an increase in the reconnection rate, and (3) more efficient conversion of magnetic energy into thermal energy and kinetic energy of bulk motions. These results provide further explanation of the rapid release of magnetic energy into heat and kinetic energy seen during flares and coronal mass ejections. In this work, we demonstrate that the consideration of anisotropic thermal conduction and Spitzer-type, temperature-dependent magnetic diffusivity, as in the real solar corona, are crucially important for explaining the occurrence of fast reconnection during solar eruptions.

Ni, Lei; Roussev, Ilia I.; Lin, Jun; Ziegler, Udo

2012-10-01

272

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

SciTech Connect

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

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

2012-06-20

273

Complex of instrumentation KORTES for the EUV and x-ray imaging and spectroscopy of the solar corona  

NASA Astrophysics Data System (ADS)

We report on the current status of the KORTES project - the first sun-oriented mission for the International Space Station to be launched in 2016-2017. KORTES will comprise several imaging and spectroscopic instruments that will observe solar corona in a number of wavebands, covering EUV and X-Ray ranges. A brief overview of the instrumentation of KORTES, its' layout, technical parameters and scientific objectives is given. An additional attention is given to the design of multilayer optics and filters to be employed in EUV instruments of KORTES.

Shestov, Sergey V.; Ulyanov, Artem S.; Vishnyakov, Eugene A.; Pertsov, Andrei A.; Kuzin, Sergey V.

2014-07-01

274

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

275

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

276

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

277

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

278

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

NASA Astrophysics Data System (ADS)

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

Javaraiah, J.

2013-10-01

279

On the spatial and temporal characteristics and formation mechanisms of soft X-ray emission in the solar corona  

NASA Astrophysics Data System (ADS)

Our main goal is to show that the spatial and temporal dynamics of the temperature content for plasma structures in the solar corona can be described quantitatively in principle, which is necessary for understanding the formation mechanisms of soft X-ray emission. An approach based on a consistent modeling of complex data from the CORONAS-F, GOES, and RHESSI satellites is suggested. A basically new element of this approach is the use of time series of monochromatic full-Sun images in the X-ray MgXII 8.42 line and EUV lines obtained in the SPIRIT experiment onboard CORONAS-F. Two inversion procedures have been used to determine the volume and column differential emission measures defined by the Stieltjes integral: an optimization one based on a multitemperature parametric model and an iterative one based on the Bayesian theorem, respectively. The calculations with coronal abundances agree with the RHESSI data within the experimental error limits, while those with photospheric abundances give no satisfactory agreement. The relatively cold (with temperature 2 4 MK) and transient (4 10 MK) plasmas are shown to play a significant role in producing soft X-ray emission during flare events and in their energy budget. The spatial electron density and temperature distributions and their time evolution have been obtained for long-duration events that were first observed in the monochromatic MgXII channel and were previously called spiders. The method used has allowed us to verify the absolute intercalibration of the fluxes recorded in all experiments and to reference the SPIRIT MgXII images to the solar disk. We also consider possible flare plasma heating mechanisms for impulsive and long-duration (spider) flare events.

Urnov, A. M.; Shestov, S. V.; Bogachev, S. A.; Goryaev, F. F.; Zhitnik, I. A.; Kuzin, S. V.

2007-06-01

280

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

281

The Corona at Solar Maximum as Imaged during the Total Solar Eclipses of 2012 November 13-14 and 2013 November 3-4  

NASA Astrophysics Data System (ADS)

The total solar eclipses of 2012 November 13-14 and 2013 November 3-4 coincided with peaks of activity in solar cycle 24. Despite challenging observing conditions due to weather patterns in both Australia and central Africa, respectively for these two eclipses, white light images were successfully obtained from groups stationed at different sites along the path of totality on both occasions. We show here how the corona during these two eclipses was remarkable in many ways. In 2012, a prominence eruption reflecting a classic example of a current sheet, with a linear extension of almost 0.25 Rs, ending in a bubble-shaped cavity, was captured in white light. In 2013, two plasmoids were observed at more than a solar radius above the solar limb, both associated with filament eruptions, and one ending in a classic CME bubble. In addition, the intricate complexity of the corona at these two eclipses, revealed by state-of-the art image processing, reflected the ubiquitous presence of large expanding loops, and the fingerprints of plasma instabilities in the form of twisted helical structures and vortex rings.

Habbal, Shadia R.; Druckmuller, Miloslav; Emmanouilides, Constantinos; Morgan, Huw

2015-01-01

282

GLOBAL CORONAL SEISMOLOGY IN THE EXTENDED SOLAR CORONA THROUGH FAST MAGNETOSONIC WAVES OBSERVED BY STEREO SECCHI COR1  

SciTech Connect

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

Kwon, Ryun-Young; Kramar, Maxim; Wang, Tongjiang; Ofman, Leon [Department of Physics, Institute for Astrophysics and Computational Sciences, Catholic University of America, 620 Michigan Avenue, Washington, DC 20064 (United States); Davila, Joseph M. [NASA Goddard Space Flight Center, Solar Physics Laboratory, Code 671, Greenbelt, MD 20771 (United States); Chae, Jongchul [Astronomy Program, Department of Physics and Astronomy, Seoul National University (Korea, Republic of); Zhang, Jie [School of Physics, Astronomy and Computational Sciences, George Mason University, 4400 University Drive, MSN 6A2, Fairfax, VA 22030 (United States)

2013-10-10

283

Catastrophic eruption of magnetic flux rope in the corona and solar wind with and without magnetic reconnection  

E-print Network

It is generally believed that the magnetic free energy accumulated in the corona serves as a main energy source for solar explosions such as coronal mass ejections (CMEs). In the framework of the flux rope catastrophe model for CMEs, the energy may be abruptly released either by an ideal magnetohydrodynamic (MHD) catastrophe, which belongs to a global magnetic topological instability of the system, or by a fast magnetic reconnection across preexisting or rapidly-developing electric current sheets. Both ways of magnetic energy release are thought to be important to CME dynamics. To disentangle their contributions, we construct a flux rope catastrophe model in the corona and solar wind and compare different cases in which we either prohibit or allow magnetic reconnection to take place across rapidly-growing current sheets during the eruption. It is demonstrated that CMEs, even fast ones, can be produced taking the ideal MHD catastrophe as the only process of magnetic energy release. Nevertheless, the eruptive speed can be significantly enhanced after magnetic reconnection sets in. In addition, a smooth transition from slow to fast eruptions is observed when increasing the strength of the background magnetic field, simply because in a stronger field there is more free magnetic energy at the catastrophic point available to be released during an eruption. This suggests that fast and slow CMEs may have an identical driving mechanism.

Y. Chen; Y. Q. Hu; S. J. Sun

2007-05-26

284

Two Dimensional Analysis of Fast Mode Speed in Solar Corona and Interplanetary Medium  

Microsoft Academic Search

In order to investigate the seemingly poor correlation between coronal and inter-planetary (IP) shocks we examined the characteristics of the ambient medium through which the shocks propagate. We looked at a series of metric type II bursts from June 1997 through July 2000 and created a profile of the fast mode speed from the inner corona to IP space. We

H. R. Norton

2001-01-01

285

Ascent motions in the monochromatic corona during total solar eclipseof July 31, 1981.  

NASA Astrophysics Data System (ADS)

Using pictures of the monochromatic corona taken in Fe XIV 5303 and Fe X 6374 , spectral lines at two points of the path of totality, differing by one hour in time of observation, the authors were able to detect motions of some structural details.

Delone, A. B.; Makarova, E. A.; Skora, J.

286

Electron density diagnostics for various plasma structures of the solar corona based on Fe XI-FeXIII lines in the range 176 207 measured in the SPIRIT/CORONAS-F experiment  

NASA Astrophysics Data System (ADS)

The relative intensities of FeXI-Fe XIII lines in the range 176 207 have been measured for various plasma structures of the solar corona using data from the XUV spectroheliograph of the SPIRIT instrumentation onboard the CORONAS-F satellite with an improved spectral sensitivity calibration. Electron density diagnostics of a plasma with temperatures 0.8 2.5 MK has been carried out in active regions, quiet-Sun and off-limb areas, and, for the first time, in extremely intense solar flares. The density range is (1.6 8) 109 cm-3 for flares, (0.6 1.6) 109 cm-3 for active regions, and 5 108 cm-3 for quiet-Sun areas. The calibration accuracy of the spectral sensitivity for the spectroheliograph has been analyzed based on spectral lines with density-independent intensity ratios.

Shestov, S. V.; Urnov, A. M.; Kuzin, S. V.; Zhitnik, I. A.; Bogachev, S. A.

2009-01-01

287

The Multi-Instrument, Comprehensive Differential Emission Measure (DEM) of the Solar Corona During Flares and Quiescent Periods  

NASA Astrophysics Data System (ADS)

Thermal plasma in the solar corona, while often modeled as isothermal for ease of analysis, is in fact decidedly multi-thermal, ranging from ~1-2 MK in the quiescent corona to ~30-50 MK in intensely flaring loops. It has proven difficult to obtain a well-constrained differential emission measure (DEM) from a single instrument, as the wavelength ranges of individual instruments, even those with broadband coverage, provide sensitivity to only a limited range of plasma temperatures. Recently, we developed a new technique using combined extreme ultraviolet (EUV) and soft and hard X-ray (SXR, HXR) data from the EUV Variability Experiment (EVE) onboard the Solar Dynamics Observatory (SDO) and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), respectively, to obtain a self-consistent DEM that is strongly constrained across the full range of coronal plasma temperatures (<2 to >50 MK). An accurate, precise determination of the plasma temperature distribution enables not only studies of plasma heating and thermal plasma evolution, but can also provide strong constraints on the non-thermal accelerated electron population, including the low-energy cutoff which is typically determined only as a loose upper limit.We present EVE+RHESSI DEM results from selected intense (X-class) flares from solar cycle 24, including determining the non-thermal low-energy cutoff and examining how this evolves with the temperature distribution. We also apply this technique to combine EUV data from EVE with SXR data from the GOES X-ray Sensor (XRS) and the X123, a new SXR spectrometer flown on two recent SDO/EVE calibration sounding rockets, to examine the DEM during quiescent (non-flaring) times with varying activity levels; the X-ray data provide crucial constraints on the high-temperate extent of the DEM and any potential non-thermal emission. We compare these results with those from a parallel technique to derive DEMs from imaging data from the Atmospheric Imaging Assembly (AIA) onboard SDO, and we discuss the implications for plasma heating, both during flares and in the quiescent corona. This research is supported by NASA contracts NAS5-98033 and NAS5-02140, and NASA Heliophysics Guest Investigator Grant NNX12AH48G.

Caspi, Amir; McTiernan, James; Warren, Harry; Woods, Thomas N.

2014-06-01

288

Solar Flares, Solar Energetic Particle Events and Their Influence on Near-Earth Environment in May 2005 as Observed by CORONAS-F and Universitetskiy-Tatiana Spacecrafts  

NASA Astrophysics Data System (ADS)

In spite of the fact that the year 2005 is far enough from the maximum of the current solar cycle, some rather powerful flares and solar energetic particle (SEP) events were observed during the first half of May 2005. These solar events were detected by instruments onboard two Russian polar low-altitude satellites: CORONAS-F and Universitetskiy-Tatiana. It was obtained that the location of SEP penetration boundary in the Earth's magnetosphere was similar at 350 km and 1000 km. The real disappearance of the outer Earth Radiation Belt (ERB) during the main phase of a geomagnetic storm and a significant increase of relativistic electron flux at L=4-5.5 during several days after the recovery phase were observed in both experiments.

Myagkova, I. N.; Kuznetsov, S. N.; Panasyuk, M. I.; Muravieva, E. A.; Starostin, L. I.; Ivanova, T. A.; Pavlov, N. N.; Rubinshtein, I. A.; Vedenkin, N. N.; Vlasova, N. A.

2006-12-01

289

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

Microsoft Academic Search

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

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

2007-01-01

290

Dynamics of Interstellar Dust in the Solar System: From In-Situ Measurements to Models  

NASA Astrophysics Data System (ADS)

Interstellar Dust particles (ISD) of submicron to micron sizes have been observed by in-situ dust instruments inside the solar system since the early 1990s [1]. The dust detector on board the Ulysses spacecraft has collected the most comprehensive dataset of ISD particles penetrating the heliosphere between 1992 and 2007. While mostly compatible to be within 20 of the direction of the neutral gas flow through the solar system, the measured dust exhibits peculiarities in several time periods. In 2005 we measured a shift in dust direction by 50, as previously hinted at by [2]. Furthermore, in this time period the dust flux shows a steep rise, which is observed in the small particles 4 months ahead of an increase in the larger particle flux. These variations of the dust flux and angular distribution can only be understood in terms of the grain interaction with the heliospheric plasma environment. We are modeling these processes by numerically integrating the ISD flow through the solar system [3][4]. Here we present new results from our analysis of the Ulysses measurements, and provide an improved interpretation in terms of our modeling of the dust's interaction with the interplanetary plasma environment. We examine the discrepancies between the observed and the modeled masses, the impact on dust dynamics, and discuss a moderate porosity of the ISD grains as a possible explanation.

Strub, P.; Sterken, V.; Krger, H.; Grn, E.

2012-09-01

291

Study of Active Phenomena in the Solar Corona in the 8-350 Range by Imaging Spectroscopy Methods (SPIRIT Experiment)  

NASA Astrophysics Data System (ADS)

This review presents the basic characteristics of the SPIRIT instrument onboard the CORONAS-F satellite, description of observation programmes, summary of observation sessions and scientific data obtained, as well as the main results in the research of hot coronal plasma, solar flares and the eruptive phenomena.

Zhitnik, I. A.; Kuzin, S. V.; Bogachev, S. A.; Bugaenko, O. I.; Ivanov, Yu. S.; Ignatyev, A. P.; Krutov, V. V.; Mitrofanov, A. V.; Oparin, S. N.; Pertsov, A. A.; Slemzin, V. A.; Sukhodrev, N. K.; Sobelman, I. I.; Urnov, A. M.; Shestov, S. V.; Goryaev, F. F.

292

MAPPING THE DISTRIBUTION OF ELECTRON TEMPERATURE AND Fe CHARGE STATES IN THE CORONA WITH TOTAL SOLAR ECLIPSE OBSERVATIONS  

SciTech Connect

The inference of electron temperature from the ratio of the intensities of emission lines in the solar corona is valid only when the plasma is collisional. Once collisionless, thermodynamic ionization equilibrium no longer holds, and the inference of an electron temperature and its gradient from such measurements is no longer valid. At the heliocentric distance where the transition from a collision-dominated to a collisionless plasma occurs, the charge states of different elements are established, or frozen-in. These are the charge states which are subsequently measured in interplanetary space. We show in this study how the 2006 March 29 and 2008 August 1 eclipse observations of a number of Fe emission lines yield an empirical value for a distance, which we call R{sub t} , where the emission changes from being collisionally to radiatively dominated. R{sub t} ranges from 1.1 to 2.0 R{sub sun}, depending on the charge state and the underlying coronal density structures. Beyond that distance, the intensity of the emission reflects the distribution of the corresponding Fe ion charge states. These observations thus yield the two-dimensional distribution of electron temperature and charge state measurements in the corona for the first time. The presence of the Fe X 637.4 nm and Fe XI 789.2 nm emission in open magnetic field regions below R{sub t} , such as in coronal holes and the boundaries of streamers, and the absence of Fe XIII 1074.7 nm and Fe XIV 530.3 nm emission there indicate that the sources of the solar wind lie in regions where the electron temperature is less than 1.2 x 10{sup 6} K. Beyond R{sub t} , the extent of the Fe X [Fe{sup 9+}] and Fe XI emission [Fe{sup 10+}], in comparison with Fe XIII [Fe{sup 12+}] and Fe XIV [Fe{sup 13+}], matches the dominance of the Fe{sup 10+} charge states measured by the Solar Wind Ion Composition Spectrometer, SWICS, on Ulysses, at -43{sup 0} latitude at 4 AU, in March-April 2006, and Fe{sup 9+} and Fe{sup 10+} charge states measured by SWICS on the Advanced Composition Explorer, ACE, in the ecliptic plane at 1 AU, at the time of both eclipses. The remarkable correspondence between these two measurements establishes the first direct link between the distribution of charge states in the corona and in interplanetary space.

Habbal, S. Rifai; Morgan, H.; Scholl, I. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Druckmueller, M. [Faculty of Mechanical Engineering, Brno University of Technology, 616 69 Brno (Czech Republic); Daw, A. [Appalachian State University, Boone, NC 28608 (United States); Johnson, J. [Electricon, Boulder, CO 80204 (United States); Ding, A. [Institute of Optics and Atomic Physics, Technische Universitaet Berlin and Institute of Technical Physics, Berlin (Germany); Arndt, M. [Bridgewater State College, Bridgewater, MA 02325 (United States); Esser, R. [University of Tromsoe (Norway); Rusin, V., E-mail: shadia@ifa.hawaii.ed [Astronomical Institute, Slovak Academy of Sciences, 059 60 Tatranska Lomnica (Slovakia)

2010-01-10

293

THE TEMPERATURE AND DENSITY STRUCTURE OF THE SOLAR CORONA. I. OBSERVATIONS OF THE QUIET SUN WITH THE EUV IMAGING SPECTROMETER ON HINODE  

SciTech Connect

Measurements of the temperature and density structure of the solar corona provide critical constraints on theories of coronal heating. Unfortunately, the complexity of the solar atmosphere, observational uncertainties, and the limitations of current atomic calculations, particularly those for Fe, all conspire to make this task very difficult. A critical assessment of plasma diagnostics in the corona is essential to making progress on the coronal heating problem. In this paper, we present an analysis of temperature and density measurements above the limb in the quiet corona using new observations from the EUV Imaging Spectrometer (EIS) on Hinode. By comparing the Si and Fe emission observed with EIS we are able to identify emission lines that yield consistent emission measure distributions. With these data we find that the distribution of temperatures in the quiet corona above the limb is strongly peaked near 1 MK, consistent with previous studies. We also find, however, that there is a tail in the emission measure distribution that extends to higher temperatures. EIS density measurements from several density sensitive line ratios are found to be generally consistent with each other and with previous measurements in the quiet corona. Our analysis, however, also indicates that a significant fraction of the weaker emission lines observed in the EIS wavelength ranges cannot be understood with current atomic data.

Warren, Harry P. [Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States); Brooks, David H. [College of Science, George Mason University, 4400 University Drive, Fairfax, VA 22030 (United States)

2009-07-20

294

A NUMERICAL METHOD FOR THE VISUALIZATION OF THE Fe XIV EMISSION IN THE SOLAR CORONA USING BROADBAND FILTERS  

SciTech Connect

The goal of this article is to demonstrate how the emission from the Fe XIV 530.3 nm coronal emission line, also known as the green line, can be extracted from images taken during total solar eclipses with commercially available color cameras. This concept is technically feasible because Fe XIV is the brightest optical emission line in the inner corona, and because the sensors of these cameras are retrofitted with a standard Bayer mask, namely, a square grid of spectrally broad (about 100 nm) green, blue, and red filters in the ratio of 2:1:1. The technique presented here, and developed for this purpose, yields qualitatively accurate Fe XIV images, as tested by comparing with Fe XIV eclipse images taken with a 0.15 nm narrow-bandpass filter. While this approach cannot replace narrow-bandpass Fe XIV images for quantitative studies of the corona, it provides a simple and affordable tool for studying the morphology of coronal structures emitting preferentially at the peak ionization temperature of Fe XIV, namely, 1.8 Multiplication-Sign 10{sup 6} K.

Martisek, K.; Druckmuellerova, H., E-mail: kmartisek@email.cz [Institute of Mathematics, Faculty of Mechanical Engineering, Brno University of Technology, Technicka 2, 616 69 Brno (Czech Republic)

2011-12-01

295

Spectra of the hot plasma power of solar flares according to the experimental data of CORONAS-F/SPIRIT  

NASA Astrophysics Data System (ADS)

Results of the search and investigations of the periodic processes in the high-temperature plasma of solar flares are presented. Such plasma with a temperature of more than 5 million K is formed mainly in the corona and is observed on the images of the Sun as sources of soft X rays (SX). In the paper, data from the Russian SPIRIT experiment on the satellite CORONAS-F, that occurred from August 2001 to December 2005, are used. A unique duration and temporal resolution of the observation of the Sun in the SX range were used during the experiment. As a consequence of the processing of these data, especially, several thousand images of the NOAA active regions 9825 and 9830 obtained from February 19 to 22, 2009, stable oscillations with a period of 5-20 min in radiation from flares were successfully discovered and the connection between the type of flare and its power spectrum was established. An interpretation of the obtained results is presented.

Bogachev, S. A.; Kuzin, S. V.; Pertsov, A. A.; Zykov, M. S.

2010-04-01

296

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. These two objects constitute a link between the RCB stars and the [WCL] class of central stars of planetary nebula (CSPNe) that has little or no hydrogen in their atmospheres such as CPD -560 8032. HV 2671 and V348 Sgr are members of a rare subclass that has significantly higher effective temperatures than most RCB stars, but sharing the traits of hydrogen deficiency and dust formation that define the cooler RCB stars. The [WC] CSPNe star, CPD -560 8032, displays evidence for dual-dust chemistry showing both PAHs and crystalline silicates in its mid-IR spectrum. HV 2671 shows strong PAH emission but shows no sign of having crystalline silicates. The spectrum of V348 Sgr is very different from those of CPD -56deg 8032 and HV 2671. The PAH emission seen strongly in the other two stars is only weakly present. Instead, the spectrum is dominated by a broad emission centered at about 8.5 microns. This feature is not identified with either PAHs or silicates. Several other novae and post-asymptotic giant branch stars show similar features in their IR spectra. The mid-IR spectrum of CPD -56deg 8032 shows emission features associated with C60 . The other two stars do not show evidence for C60. The nature of the dust around these stars does not help us in establishing further links that may indicate a common origin.

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.

2012-01-01

297

Solar panel clearing events, dust devil tracks, and in-situ vortex detections on Mars  

NASA Astrophysics Data System (ADS)

Spirit rover solar array data, which if publicly-archived would provide a useful window on Mars meteorology, shows dust-clearing events coinciding with the onset of dust devil season in three Mars years. The recurrence interval of 100-700 days is consistent with the extrapolation of Pathfinder and Phoenix vortex encounters indicated by pressure drops of ?6-40 Pa (similar to laboratory measurements of dust lifting threshold) and with observed areas and rates of generation of dust devil tracks on Mars.

Lorenz, Ralph D.; Reiss, Dennis

2015-03-01

298

Extreme vacuum ultraviolet solar spectra obtained during the SPIRIT experiment aboard CORONAS-F: A catalog of lines in the range 280 330  

NASA Astrophysics Data System (ADS)

We present a catalog of 100 lines in the wavelength range 280 330 detected by the RES-C spectroheliograph in solar active regions and flares during the SPIRIT experiment aboard the CORONAS-F orbital station. We identified 54 lines. The line intensities recorded during the X3.4 (GOES) solar flare of December 28, 2001, are given. The data reduction procedure is discussed.

Zhitnik, I. A.; Kuzin, S. V.; Urnov, A. M.; Beigman, I. L.; Bozhenkov, S. A.; Tolstikhina, I. Yu.

2005-01-01

299

Charge State Evolution in the Solar Wind. II. Plasma Charge State Composition in the Inner Corona and Accelerating Fast Solar Wind  

NASA Astrophysics Data System (ADS)

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

Landi, E.; Gruesbeck, J. R.; Lepri, S. T.; Zurbuchen, T. H.; Fisk, L. A.

2012-12-01

300

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

SciTech Connect

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

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

2012-12-10

301

Dynamics of Interstellar Dust in the Solar System: From In-Situ Measurements to Models  

NASA Astrophysics Data System (ADS)

Interstellar Dust particles (ISD) of submicron to micron sizes have been observed by in-situ dust instruments inside the solar system since the early 1990s [1]. The dust detector on board the Ulysses spacecraft has collected the most comprehensive dataset of ISD particles penetrating the heliosphere between 1992 and 2007. While mostly compatible to be within 20 of the direction of the neutral gas flow through the solar system, the measured dust exhibits peculiarities in several time periods. In 2005 we measured a shift in dust direction by 50, as previously hinted at by [2]. Furthermore, in this time period the dust flux shows a steep rise, which is observed in the small particles 4 months ahead of an increase in the larger particle flux. These variations of the dust flux and angular distribution can only be understood in terms of the grain interaction with the heliospheric plasma environment. We are modeling these processes by numerically integrating the ISD flow through the solar system [3][4]. Here we present a detailed analysis of the Ulysses measurements, and provide an interpretation in terms of our simulations of the dust's interaction with the interplanetary plasma environment.

Strub, P.; Sterken, V. J.; Krger, H.; Grn, E.

2011-10-01

302

Constraints on Nonlinear and Stochastic Growth Theories for Type 3 Solar Radio Bursts from the Corona to 1 AU  

NASA Technical Reports Server (NTRS)

Existing, competing theories for coronal and interplanetary type III solar radio bursts appeal to one or more of modulational instability, electrostatic (ES) decay processes, or stochastic growth physics to preserve the electron beam, limit the levels of Langmuir-like waves driven by the beam, and produce wave spectra capable of coupling nonlinearly to generate the observed radio emission. Theoretical constraints exist on the wavenumbers and relative sizes of the wave bandwidth and nonlinear growth rate for which Langmuir waves are subject to modulational instability and the parametric and random phase versions of ES decay. A constraint also exists on whether stochastic growth theory (SGT) is appropriate. These constraints are evaluated here using the beam, plasma, and wave properties (1) observed in specific interplanetary type III sources, (2) predicted nominally for the corona, and (3) predicted at heliocentric distances greater than a few solar radii by power-law models based on interplanetary observations. It is found that the Langmuir waves driven directly by the beam have wavenumbers that are almost always too large for modulational instability but are appropriate to ES decay. Even for waves scattered to lower wavenumbers (by ES decay, for instance), the wave bandwidths are predicted to be too large and the nonlinear growth rates too small for modulational instability to occur for the specific interplanetary events studied or the great majority of Langmuir wave packets in type III sources at arbitrary heliocentric distances. Possible exceptions are for very rare, unusually intense, narrowband wave packets, predominantly close to the Sun, and for the front portion of very fast beams traveling through unusually dilute, cold solar wind plasmas. Similar arguments demonstrate that the ES decay should proceed almost always as a random phase process rather than a parametric process, with similar exceptions. These results imply that it is extremely rare for modulational instability or parametric decay to proceed in type III sources at any heliocentric distance: theories for type III bursts based on modulational instability or parametric decay are therefore not viable in general. In contrast, the constraint on SGT can be satisfied and random phase ES decay can proceed at all heliocentric distances under almost all circumstances. (The contrary circumstances involve unusually slow, broad beams moving through unusually hot regions of the Corona.) The analyses presented here strongly justify extending the existing SGT-based model for interplanetary type III bursts (which includes SGT physics, random phase ES decay, and specific electromagnetic emission mechanisms) into a general theory for type III bursts from the corona to beyond 1 AU. This extended theory enjoys strong theoretical support, explains the characteristics of specific interplanetary type III bursts very well, and can account for the detailed dynamic spectra of type III bursts from the lower corona and solar wind.

Cairns, Iver H.; Robinson, P. A.

1998-01-01

303

X-ray observations of characteristic structures and time variations from the solar corona - Preliminary results from Skylab.  

NASA Technical Reports Server (NTRS)

Examples taken from the S-054 X-ray telescope observations made during the first Skylab mission show the hot coronal plasma tracing the configuration of the magnetic fields. The high spectral resolution and sensitivity of the instrument has enabled the following two facts to be more firmly established: (1) that the 'quiet homogeneous corona' is in fact highly structured and that the structures observed appear to be the results of dispersed active region magnetic fields; and (2) that numerous bright points are distributed randomly on the disk. Their presence at high latitudes may play a role in solar cycle models. In addition, the capability of Skylab for studying time evolution has enabled the restructuring of coronal features to be seen at times of high activity, indicating a restructuring of the coronal magnetic fields.

Vaiana, G. S.; Davis, J. M.; Giacconi, R.; Krieger, A. S.; Silk, J. K.; Timothy, A. F.; Zombeck, M.

1973-01-01

304

The impact of UVCS/SOHO observations on models of ion-cyclotron resonance heating of the solar corona  

NASA Technical Reports Server (NTRS)

The compatibility between theoretical models and observations of the temperatures and anisotropic distributions of hydrogen and minor ions in the solar corona is examined. The ultraviolet coronagraph spectrometer (UVCS) instrument onboard SOHO measured hydrogen kinetic temperatures along lines of sight in coronal holes in excess of 3 x 10(exp 6) K and O(+5) ion kinetic temperatures of at least 2 x 10(exp 8) K. Various features of plasma heating by the dissipation of high-frequency ion-cyclotron resonance Alfven waves, which may be the most natural physical mechanism to produce certain plasma conditions, are examined. Preliminary quantitative models of the ion motion in polar coronal holes are presented, and it is shown that such models can be used to predict the spectrum of waves required to reproduce the observations. Indeed, the more ionic species that are observed spectroscopically, the greater the extent in frequency space the wave spectrum can be inferred.

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

1997-01-01

305

Dielectronic recombination rates, ionization equilibrium, and radiative energy-loss rates for neon, magnesium, and sulfur ions in low-density plasmas. [in solar corona  

NASA Technical Reports Server (NTRS)

Results of detailed and systematic calculations are presented for the total dielectronic recombination rate coefficients for the ions of Ne, Mg, and S in a low-density predominantly hydrogen plasma. The new recombination rates are used to calculate solar corona ionization-equilibrium distributions of the ions. The most important effect of dielectronic recombination for ions in corona equilibrium is found to be a shift in the maximum-abundance temperatures toward higher temperatures, which are in some cases reduced from those predicted on the basis of the simple Burgess formula.

Jacobs, V. L.; Davis, J.; Rogerson, J. E.; Blaha, M.

1979-01-01

306

Solar heating of the Uranian mesopause by dust of ring origin  

SciTech Connect

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

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

1990-12-01

307

Solar Wind Modulation of Jupiter Dust Stream Detection  

NASA Astrophysics Data System (ADS)

During late 2002 and mid 2005, the Ulysses spacecraft approached Jupiter ( 0.8 AU at its closest distance) and detected 28 new Jovian dust particle streams. The tiny positively charged dust grains ( 10 nm) in the streams are accelerated away from Jupiter by its corotational electric field to very high speeds (greater than 200 km s^{-1}). Data indicate that, once outside the Jovian magnetosphere, dust grains are under the influence of the interplanetary magnetic field (IMF) and some characteristics of this field are observed on the dust streams. On the whole, every detected dust stream is preceded by a high IMF event that in most cases corresponds to corotating interaction regions (CIRs) and in few cases to coronal mass ejections (CMEs). The dust stream duration matches roughly the duration of these previous events indicating a confinement of the dust stream particles in the compressed regions of the interplanetary plasma. Additionally, most dust stream peaks and the precedent high IMF events peaks seem to be separated by an interval roughly similar to the time needed by a dust particle to travel from the source to the spacecraft's detector.

Flandes, A.; Krueger, H.

2007-01-01

308

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

NASA Astrophysics Data System (ADS)

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

Rybk, J.; Gmry, P.; Benz, A.; Bogachev, P.; Braja, R.

2010-12-01

309

The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: Magnetohydrodynamics Simulation Module for the Global Solar Corona  

E-print Network

Time-dependent three-dimensional magnetohydrodynamics (MHD) simulation modules are implemented at the Joint Science Operation Center (JSOC) of Solar Dynamics Observatory (SDO). The modules regularly produce three-dimensional data of the time-relaxed minimum-energy state of the solar corona using global solar-surface magnetic-field maps created from Helioseismic Magnetic Imager (HMI) full-disk magnetogram data. With the assumption of polytropic gas with specific heat ratio of 1.05, three types of simulation products are currently generated: i) simulation data with medium spatial resolution using the definitive calibrated synoptic map of the magnetic field with a cadence of one Carrington rotation, ii) data with low spatial resolution using the definitive version of the synchronic frame format of the magnetic field, with a cadence of one day, and iii) low-resolution data using near-real-time (NRT) synchronic format of the magnetic field on daily basis. The MHD data available in the JSOC database are three-dimen...

Hayashi, Keiji; Liu, Yang; Bobra, Monica G; Sun, Xudong D; Norton, Aimee A

2015-01-01

310

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

E-print Network

Using the Solar Optical Observing Network (SOON) sunspot-group data for the period 1985-2010, the variations in the annual mean equatorial-rotation rates of the sunspot groups are determined and compared with the known variations in the solar equatorial-rotation rates determined from the following data: i) the plasma rotation rates at 0.94Rsun, 0.95Rsun,...,1.0Rsun measured by Global Oscillation Network Group (GONG) during the period 1995-2010, ii) the data on the soft X-ray corona determined from Yohkoh/SXT full disk images for the years 1992-2001, iii) the data on small bright coronal structures (SBCS) which were traced in Solar and Heliospheric Observatory (SOHO)/EIT images during the period 1998-2006, and iv) the Mount Wilson Doppler-velocity measurements during the period 1986-2007. A large portion (up to approximate 30 deg latitude) of the mean differential-rotation profile of the sunspot groups lies between those of the internal differential-rotation rates at 0.94Rsun and 0.98Rsun.The variation in the ...

Javaraiah, J

2013-01-01

311

The Soft XRay/Microwave Ratio of Solar and Stellar Flares and Coronae  

E-print Network

We have carried out plasma diagnostics of solar flares using soft X­ray (SXR) and simultaneous microwave observations and have compared the ratio of X­ray to microwave luminosities of solar flares as thermal radiations of coronal plasmas. On the other hand, the microwave emission of stars and solar flares

Guedel, Manuel

312

Magnetic neutral sheets in evolving fields. I - General theory. II - Formation of the solar corona  

NASA Technical Reports Server (NTRS)

The problem of the hydrostatic equilibrium of a large-scale magnetic field embedded in a fluid with infinite electrical conductivity is considered. It is pointed out that a necessary condition for static equilibrium is the invariance of the small-scale pattern in the field along the large-scale direction. A varying topological pattern implies that no fluid pressure distribution exists for which the field is everywhere static. Magnetic neutral sheets form, and dynamical reconnection of the field takes place. It is shown here that the invariance is also a sufficient condition for the existence of a fluid pressure distribution producing static equilibrium. Even in the simplest cases, however, the requirements on the fluid pressure are extreme and, a priori, are unlikely. It is concluded that almost all twisted flux tubes packed together produce dynamical nonequilibrium and dissipation of their twisting. This is the basic effect underlying the long-standing conjecture that the shuffling of the footpoints of the bipolar magnetic fields in the sun is responsible for heating the active corona. Attention is then given to the consequences of this general dynamical dissipation in the magnetic fields that produce the active corona of the sun. The footpoints of the field are continually manipulated by the subphotospheric convection in such a way that the lines of force are continually wrapped and rotated about one another.

Parker, E. N.

1983-01-01

313

HEATING OF THE SOLAR CHROMOSPHERE AND CORONA BY ALFVEN WAVE TURBULENCE  

SciTech Connect

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

Van Ballegooijen, A. A.; Cranmer, S. R.; DeLuca, E. E. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street MS-15, Cambridge, MA 02138 (United States); Asgari-Targhi, M. [Mathematics Department, University College London, London, WC1E 6BT (United Kingdom)

2011-07-20

314

Observational Study of the Tridimensional Trajectory of Small White-Light Transients in the Inner Solar Corona  

NASA Astrophysics Data System (ADS)

The physical mechanisms responsible for the low corona origin and subsequent interplanetary development of the small scale white-light transients, known as blobs, is relevant to the formation and acceleration mechanisms of the slow solar wind (Sheeley et al., 1997). Since they are considered to be reliable tracers of the slow solar wind, a statistical kinematical characterization of these faint features should provide to the understanding of its origins and acceleration. The vantage observing points provided by the SECCHI and LASCO imagers aboard the STEREO and SOHO missions, respectively, allows us to get a good estimation of their trajectory in the 3D space and hence perform a detailed analysis of their unprojected kinematical parameters. To address this issue, we have surveyed the SOHO/LASCO C2 and C3, and the STEREO/SECCHI COR 1 and COR 2 databases for the year 2007 through 2010 (i.e., a period comprising the declining phase of the extended past solar minimum and the ascending phase of cycle 24) and selected about 100 blob-like features. The selection of events was facilitated by the scarce presence of coronal mass ejection events during this period, and it was limited to 30 from the Sun's equator. The restricted latitudinal range is inspired by the work of Wang et al. (1998), who proposed that blobs are liberated from the cusp of helmet steamers. Two methods have been considered for the determination of the 3D kinematical parameters: (1) the tie-pointing and triangulation technique (Thompson W.T., 2008) and (2) the Height-Time analysis as developed by Mierla et al. (2008). In this work, we report on the set of transients studied by both techniques, discuss the limitations encountered on the determination of the 3D trajectories, and explore their significance on understanding the physical mechanisms behind the generation/propagation of the slow solar wind.

Lopez-Portela, C.; Blanco-Cano, X.; Stenborg, G.; Vourlidas, A.

2013-05-01

315

Observations of the solar corona with a high resolution EUV imaging spectrograph  

NASA Technical Reports Server (NTRS)

An extreme ultraviolet imaging spectrograph was used to obtain coronal observations with high spectral and spatial resolution. The imaging properties of the instrument enable measurements of spectral line shapes and positions in discrete spatial elements of a region, so that the dynamic characteristics of the coronal plasma, as well as the distribution of emission measure with temperature and well known density diagnostics, can be studied for specific features. The instrumentation is described and several results of a sounding rocket flight on 5 May 1989, when the corona over NOAA Region 5464 including emission over the umbra of the region's largest sunspot and the pre-impulsive phase emission of a small flare was recorded, are summarized.

Neupert, Werner M.; Epstein, G. L.; Thomas, R. J.; Thompson, W. T.

1992-01-01

316

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

SciTech Connect

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

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

2012-04-20

317

Generation and propagation of ion cyclotron waves in nonuniform magnetic field: Application to the corona and solar wind  

NASA Astrophysics Data System (ADS)

With the objective to understand the generation, propagation, and nonlinear evolution of ion cyclotron waves (ICWs) in the corona and solar wind, we use electromagnetic hybrid (kinetic ions and fluid electrons) simulations with a nonuniform magnetic field. ICWs are generated by the temperature anisotropy of O5+ ions as minority species in a proton-electron plasma with uniform density. A number of magnetic field models are used including radial and spiral with field strength decreasing linearly or with the square of the radial distance. O5+ ions with perpendicular temperature larger than parallel are initially placed in the high-magnetic field regions. These ions are found to expand outward along the magnetic field. Associated with this expansion, ion cyclotron waves propagating along the magnetic field are also seen to expand outward. These waves are generated at frequencies below the local gyrofrequency of O5+ ions propagating parallel and antiparallel to the magnetic field. Through analysis of the simulation results we demonstrate that wave generation and absorption take place at all radial distances. Comparing the simulation results to observations of ICWs in the solar wind shows some of the observed wave characteristics may be explained by the mechanism discussed in this paper.

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

2014-11-01

318

THERMODYNAMICS OF THE SOLAR CORONA AND EVOLUTION OF THE SOLAR MAGNETIC FIELD AS INFERRED FROM THE TOTAL SOLAR ECLIPSE OBSERVATIONS OF 2010 JULY 11  

SciTech Connect

We report on the first multi-wavelength coronal observations, taken simultaneously in white light, 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, during the total solar eclipse of 2010 July 11 from the atoll of Tatakoto in French Polynesia. The data enabled temperature differentiations as low as 0.2 x 10{sup 6} K. The first-ever images of the corona in Fe IX and Ni XV showed that there was very little plasma below 5 x 10{sup 5} K and above 2.5 x 10{sup 6} K. The suite of multi-wavelength observations also showed that open field lines have an electron temperature near 1x 10{sup 6} K, while the hottest, 2x 10{sup 6} K, plasma resides in intricate loops forming the bulges of streamers, also known as cavities, as discovered in our previous eclipse observations. The eclipse images also revealed unusual coronal structures, in the form of ripples and streaks, produced by the passage of coronal mass ejections and eruptive prominences prior to totality, which could be identified with distinct temperatures for the first time. These trails were most prominent at 10{sup 6} K. Simultaneous Fe X 17.4 nm observations from Proba2/SWAP provided the first opportunity to compare Fe X emission at 637.4 nm with its extreme-ultraviolet (EUV) counterpart. This comparison demonstrated the unique diagnostic capabilities of the coronal forbidden lines for exploring the evolution of the coronal magnetic field and the thermodynamics of the coronal plasma, in comparison with their EUV counterparts in the distance range of 1-3 R{sub sun}. These diagnostics are currently missing from present space-borne and ground-based observatories.

Habbal, Shadia Rifai; Morgan, Huw [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Druckmueller, Miloslav; Druckmuellerova, Hana [Faculty of Mechanical Engineering, Brno University of Technology, Technicka 2, 616 69 Brno (Czech Republic); Ding, Adalbert [Institute of Optics and Atomic Physics, Technische Universitaet Berlin, and Institute of Technical Physics, Berlin (Germany); Johnson, Judd [Electricon, Boulder, CO 80204 (United States); Daw, Adrian [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Arndt, Martina B. [Physics Department, Bridgewater State University, Bridgewater, MA 02325 (United States); Dietzel, Martin [ASTELCO, Munich (Germany); Saken, Jon, E-mail: shadia@ifa.hawaii.edu [Department of Physics and Astronomy, Appalachian State University, Boone, NC 28608 (United States)

2011-06-20

319

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

Microsoft Academic Search

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

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

1998-01-01

320

A Resolved Ring of Debris Dust Around the Solar Analog HD 107146  

E-print Network

We present resolved images of the dust continuum emission from the debris disk around the young (80-200 Myr) solar-type star HD 107146 with CARMA at $\\lambda$1.3 mm and the CSO at $\\lambda$350 $\\mu$m. Both images show that the dust emission extends over an $\\sim$10\\arcsec diameter region. The high resolution (3\\arcsec) CARMA image further reveals that the dust is distributed in a partial ring with significant decrease in flux inward of 97 AU. Two prominent emission peaks appear within the ring separated by $\\sim$140 degrees in position angle. The morphology of the dust emission is suggestive of dust captured into a mean motion resonance, which would imply the presence of a planet at an orbital radius of $\\sim$45-75 AU.

S. A. Corder; J. M. Carpenter; A. I. Sargent; B. A. Zauderer; M. C. H. Wright; S. White; D. P. Woody; P. Teuben; S. L. Scott; M. W. Pound; R. L. Plambeck; J. W. Lamb; J. Koda; M. W. Hodges; D. W. Hawkins; D. C. -J. Bock

2008-12-09

321

Magnetic Energy and Helicity Budgets in the Active-Region Solar Corona. I. Linear Force-Free Approximation  

E-print Network

We self-consistently derive the magnetic energy and relative magnetic helicity budgets of a three-dimensional linear force-free magnetic structure rooted in a lower boundary plane. For the potential magnetic energy we derive a general expression that gives results practically equivalent to those of the magnetic Virial theorem. All magnetic energy and helicity budgets are formulated in terms of surface integrals applied to the lower boundary, thus avoiding computationally intensive three-dimensional magnetic field extrapolations. We analytically and numerically connect our derivations with classical expressions for the magnetic energy and helicity, thus presenting a so-far lacking unified treatment of the energy/helicity budgets in the constant-alpha approximation. Applying our derivations to photospheric vector magnetograms of an eruptive and a noneruptive solar active regions, we find that the most profound quantitative difference between these regions lies in the estimated free magnetic energy and relative magnetic helicity budgets. If this result is verified with a large number of active regions, it will advance our understanding of solar eruptive phenomena. We also find that the constant-alpha approximation gives rise to large uncertainties in the calculation of the free magnetic energy and the relative magnetic helicity. Therefore, care must be exercised when this approximation is applied to photospheric magnetic field observations. Despite its shortcomings, the constant-alpha approximation is adopted here because this study will form the basis of a comprehensive nonlinear force-free description of the energetics and helicity in the active-region solar corona, which is our ultimate objective.

M. K. Georgoulis; Barry J. LaBonte

2007-06-27

322

Simulation of generation and transfer of polarized gyrosynchrotron radiation in the solar corona  

NASA Astrophysics Data System (ADS)

We perform 3D simulations of gyrosynchrotron emission from solar flaring loops. The full polarization transfer equation is solved; the radio brightness maps and spectral dependences of the Stokes parameters of the emission are obtained. We discuss the conditions required to detect the linear polarization of the solar microwave emission by the existing and perspective instruments, as well as the information that could be inferred from such observations. The numerical codes for calculating the radio emission are available online.

Kuznetsov, A. A.

2011-10-01

323

Weather modification by carbon dust absorption of solar energy  

Microsoft Academic Search

The possibility was investigated of beneficial weather modification through artificial solar energy absorption. A variety of physical ideas related to artificial heat sources on different scales of motion are considered. Interest is concentrated on the feasibility of mesoscale weather modification through solar energy absorption by carbon aerosol particles of .1 ..mu..m or less. Particles of this size maximize solar energy

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

1976-01-01

324

On the Remote Detection of Suprathermal Ions in the Solar Corona and their Role as Seeds for Solar Energetic Particle Production  

NASA Astrophysics Data System (ADS)

We calculate the growth rate for field aligned Alfven waves generated by streaming preshock ions. The ions are assumed to be in a "kappa" distribution, and we calculate growth rates as a function of shock obliquity and kappa, for shocks of different Alfven Mach number. As the shock Alfven Mach number increases, the constraints on kappa and the shock obliquity lessen. Less significant departures from a Maxwellian distribution in the upstream medium are required for wave growth, which may also extend out to quasi-perpendicular shocks of higher obliquity. Taking a positive wave growth in such conditions ahead of a shock as a necessary condition for particle acceleration, we use the derived values of kappa to predict the detectability of a seed particle distribution upstream of shocks of various parameters through spectroscopic observations of the Lyman alpha line profile. Within 3-4 solar radii, suprathermal protons can charge exchange with neutral H in the solar corona giving rise to a kappa distribution of neutral H, that scatters disk Lyman alpha radiation into a line profile with extended wings. We define the essential characteristics of a spectrometer designed to detect such a seed particle population, as a means of forecasting the likely solar energetic particle effectiveness of any following coronal mass ejection. Work supported by basic research funds of the Office of Naval Research and by NASA ADAP grant NNH10A009I.

Laming, J. Martin; Moses, Daniel; Ko, Yuan-Kuen; Ng, Chee; Tylka, Allan; Rakowski, Cara

325

LADEE UVS Observations of Solar Occulation by Exospheric Dust above the Lunar Limb  

NASA Technical Reports Server (NTRS)

The Lunar Atmosphere and Dust Environment Explorer (LADEE) is a lunar orbiter launched in September 2012 that investigates the composition and temporal variation of the tenuous lunar exosphere and dust environment. The primary goals of the mission are to characterize the pristine gas and dust exosphere prior to future lunar exploration activities, which may alter the lunar environment. To address this goal, the LADEE instrument suite includes an Ultraviolet/ Visible Spectrometer (UVS), which searches for dust, Na, K, and trace gases such as OH, H2O, Si, Al, Mg, Ca, Ti, Fe, as well as other previously undetected species. UVS has two sets of optics: a limb-viewing telescope, and a solar viewing telescope. The solar viewer is equipped with a diffuser (see Figure 1a) that allows UVS to stare directly at the solar disk as the Sun starts to set (or rise from) behind the lunar limb. Solar viewer measurements generally have very high signal to noise (SNR>500) for 20-30 ms integration times. The 1-degree solar viewer field of view subtends a diameter of 8 km at a distance of 400-450 km

Wooden, Diane; Cook, Amanda Marie; Colaprete, A.; Shirley, M. H.; Vargo, K. E.; Elphic, R. C.; Stubbs, T. J.; Glenar, D. A.

2014-01-01

326

INFLUENCE OF SOLAR WIND HEATING FORMULATIONS ON THE PROPERTIES OF SHOCKS IN THE CORONA  

SciTech Connect

One of the challenges in constructing global magnetohydrodynamic (MHD) models of the inner heliosphere for, e.g., space weather forecasting purposes, is to correctly capture the acceleration and expansion of the solar wind. In current models, various ad hoc heating prescriptions are introduced in order to obtain a realistic steady-state solar wind solution. In this work, we demonstrate, by performing MHD simulations of erupting coronal mass ejections (CMEs) on identical solar wind solutions employing different heating formulations, that the dynamics and properties of the CME-driven shocks are significantly altered depending on the applied heating prescription. Furthermore, we show how two popular heating formulations can be altered so as to yield shock properties consistent with theory and available coronal shock observations.

Pomoell, J.; Vainio, R., E-mail: jens.pomoell@helsinki.fi [Department of Physics, University of Helsinki (Finland)

2012-02-01

327

Deflection of the local interstellar dust flow by solar radiation pressure  

NASA Technical Reports Server (NTRS)

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

Landgraf, M.; Augustsson, K.; Grun, E.; Gustafson, B. A.

1999-01-01

328

ANALYTIC APPROXIMATE SEISMOLOGY OF PROPAGATING MAGNETOHYDRODYNAMIC WAVES IN THE SOLAR CORONA  

SciTech Connect

Observations show that propagating magnetohydrodynamic (MHD) waves are ubiquitous in the solar atmosphere. The technique of MHD seismology uses the wave observations combined with MHD wave theory to indirectly infer physical parameters of the solar atmospheric plasma and magnetic field. Here, we present an analytical seismological inversion scheme for propagating MHD waves. This scheme uses the observational information on wavelengths and damping lengths in a consistent manner, along with observed values of periods or phase velocities, and is based on approximate asymptotic expressions for the theoretical values of wavelengths and damping lengths. The applicability of the inversion scheme is discussed and an example is given.

Goossens, M.; Soler, R. [Centre for Mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Celestijnenlaan 200B, B-3001 Leuven (Belgium); Arregui, I. [Instituto de Astrofisica de Canarias, Via Lactea s/n, E-38205 La Laguna, Tenerife (Spain); Terradas, J., E-mail: marcel.goossens@wis.kuleuven.be [Solar Physics Group, Departament de Fisica, Universitat de les Illes Balears, E-07122 Palma de Mallorca (Spain)

2012-12-01

329

Understanding Coronal Mass Ejections and Associated Shocks in the Solar Corona by Merging Multiwavelength Observations  

NASA Astrophysics Data System (ADS)

Using multiwavelength imaging observations, in EUV, white light and radio, and radio spectral data over a large frequency range, we analyzed the triggering and development of a complex eruptive event. This one includes two components, an eruptive jet and a coronal mass ejection (CME), which interact during more than 30 minutes, and can be considered as physically linked. This was an unusual event. The jet is generated above a typical complex magnetic configuration that has been investigated in many former studies related to the build-up of eruptive jets; this configuration includes fan-field lines originating from a corona null point above a parasitic polarity, which is embedded in one polarity region of a large active region. The initiation and development of the CME, observed first in EUV, does not show usual signatures. In this case, the eruptive jet is the main actor of this event. The CME appears first as a simple loop system that becomes destabilized by magnetic reconnection between the outer part of the jet and the ambient medium. The progression of the CME is closely associated with the occurrence of two successive type II bursts from a distinct origin. An important part of this study is the first radio type II burst for which the joint spectral and imaging observations were allowed: (1) to follow, step by step, the evolution of the spectrum and of the trajectory of the radio burst, in relationship with the CME evolution and (2) to obtain, without introducing an electronic density model, the B field and the Alfvn speed.

Zucca, P.; Pick, M.; Dmoulin, P.; Kerdraon, A.; Lecacheux, A.; Gallagher, P. T.

2014-11-01

330

Extreme Ultraviolet Spectra of Solar Flares from the Extreme Ultraviolet Spectroheliograph SPIRIT Onboard the CORONAS-F Satellite  

NASA Astrophysics Data System (ADS)

We present detailed extreme ultraviolet (EUV) spectra of four large solar flares: M5.6, X1.3, X3.4, and X17 classes in the spectral ranges 176-207 and 280-330 . These spectra were obtained by the slitless spectroheliograph SPIRIT onboard the CORONAS-F satellite. To our knowledge, these are the first detailed EUV spectra of large flares obtained with a spectral resolution of ~0.1 . We performed a comprehensive analysis of the obtained spectra and provide identification of the observed spectral lines. The identification was performed based on the calculation of synthetic spectra (the CHIANTI database was used), with simultaneous calculations of the differential emission measure (DEM) and density of the emitting plasma. More than 50 intense lines are present in the spectra that correspond to a temperature range of T = 0.5-16 MK most of the lines belong to Fe, Ni, Ca, Mg, and Si ions. In all the considered flares, intense hot lines from Ca XVII, Ca XVIII, Fe XX, Fe XXII, and Fe XXIV are observed. The calculated DEMs have a peak at T ~ 10 MK. The densities were determined using Fe XI-Fe XIII lines and averaged 6.5 109 cm-3. We also discuss the identification, accuracy, and major discrepancies of the spectral line intensity prediction.

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

2014-01-01

331

Weak Compressible Magnetohydrodynamic Turbulence in the Solar Corona Benjamin D. G. Chandran  

E-print Network

moment kBT?=B of O5 ions increases rapidly with r and strongly suggest that O5 ions are heated by plasma- frequency waves, including reconnection events in the coronal base [3­5], heat-flux-driven plasma heating, but for particle acceleration in solar flares as well [15,16]. The MHD momentum and induction

Chandran, Ben

332

The Effects of Differential Rotation on the Magnetic Structure of the Solar Corona: MHD Simulations  

NASA Technical Reports Server (NTRS)

Coronal holes are magnetically open regions from which the solar wind streams. Magnetic reconnection has been invoked to reconcile the apparently rigid rotation of coronal holes with the differential rotation of magnetic flux in the photosphere. This mechanism might also be relevant to the formation of the slow solar wind, the properties of which seem to indicate an origin from the opening of closed magnetic field lines. We have developed a global MHD model to study the effect of differential rotation on the coronal magnetic field. Starting from a magnetic flux distribution similar to that of Wang et al., which consists of a bipolar magnetic region added to a background dipole field, we applied differential rotation over a period of 5 solar rotations. The evolution of the magnetic field and of the boundaries of coronal holes are in substantial agreement with the findings of Wang et al.. We identified examples of interchange reconnection and other changes of topology of the magnetic field. Possible consequences for the origin of the slow solar wind are also discussed.

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

2004-01-01

333

STELLAR CORONAE, SOLAR FLARES: A DETAILED COMPARISON OF {sigma} GEM, HR 1099, AND THE SUN IN HIGH-RESOLUTION X-RAYS  

SciTech Connect

The Chandra High Energy Transmission Grating Spectrometer (HETG) spectra of the coronally active binary stars {sigma} Gem and HR 1099 are among the highest fluence observations for such systems taken at high spectral resolution in X-rays with this instrument. This allows us to compare their properties in detail to solar flare spectra obtained with the Russian CORONAS-F spacecraft's RESIK instrument at similar resolution in an overlapping bandpass. Here we emphasize the detailed comparisons of the 3.3-6.1 A region (including emission from highly ionized S, Si, Ar, and K) from solar flare spectra to the corresponding {sigma} Gem and HR 1099 spectra. We also model the larger wavelength range of the HETG, from 1.7 to 25 A - having emission lines from Fe, Ca, Ar, Si, Al, Mg, Ne, O, and N-to determine coronal temperatures and abundances. {sigma} Gem is a single-lined coronally active long-period binary which has a very hot corona. HR 1099 is a similar, but shorter period, double-lined system. With very deep HETG exposures we can even study emission from some of the weaker species, such as K, Na, and Al, which are important since they have the lowest first ionization potentials, a parameter well known to be correlated with elemental fractionation in the solar corona. The solar flare temperatures reach Almost-Equal-To 20 MK, comparable to the {sigma} Gem and HR 1099 coronae. During the Chandra exposures, {sigma} Gem was slowly decaying from a flare and its spectrum is well characterized by a collisional ionization equilibrium plasma with a broad temperature distribution ranging from 2 to 60 MK, peaking near 25 MK, but with substantial emission from 50 MK plasma. We have detected K XVIII and Na XI emission which allow us to set limits on their abundances. HR 1099 was also quite variable in X-rays, also in a flare state, but had no detectable K XVIII. These measurements provide new comparisons of solar and stellar coronal abundances, especially at the lowest first ionization potential (FIP) values. The low FIP elements do not show enhancement in the stellar coronae as they do in the Sun, except perhaps for K in {sigma} Gem. While {sigma} Gem and HR 1099 differ in their emission measure distributions, they have very similar elemental abundances.

Huenemoerder, David P. [Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, 70 Vassar St., Cambridge, MA 02139 (United States); Phillips, Kenneth J. H. [Visiting Scientist, Space Research Center, Polish Academy of Sciences, 51-622, Kopernika 11, Wroclaw (Poland); Sylwester, Janusz; Sylwester, Barbara, E-mail: dph@space.mit.edu, E-mail: kennethjhphillips@yahoo.com, E-mail: js@cbk.pan.wroc.pl, E-mail: bs@cbk.pan.wroc.pl [Space Research Center, Polish Academy of Sciences, 51-622, Kopernika 11, Wroclaw (Poland)

2013-05-10

334

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

SciTech Connect

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

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

2008-06-09

335

The origin of organic matter in the solar system: evidence from the interplanetary dust particles  

Microsoft Academic Search

The detailed examination of meteorites and interplanetary dust particles provides an opportunity to infer the origin of the organic matter found in primitive Solar System materials. If this organic matter were produced by aqueous alteration of elemental (graphitic or amorphous) carbon on an asteroid, then we would expect to see the organic matter occurring preferentially in interplanetary materials that exhibit

G. J. FLYNN; L. P Keller; M. Feser; S. Wirick; C. Jacobsen

2003-01-01

336

Formation and Evolution of the Dust in Galaxies. II. The Solar Neighbourhood  

Microsoft Academic Search

Over the past decade a new generation of chemical models have included the dust in the treatment of the ISM. This major accomplishment has been spurred by the growing amounts of data on the highly obscured high-z Universe and the intriguing local properties of the Solar Neighbourhood (SoNE). We present here a new model able to simulate the formation and

L. Piovan; C. Chiosi; E. Merlin; T. Grassi; R. Tantalo; U. Buonomo; L. P. Cassar

2011-01-01

337

North-South Asymmetric Solar Cycle Evolution: Signatures in the Photosphere and Consequences in the Corona  

NASA Astrophysics Data System (ADS)

The heliospheric current sheet is the continuum of the coronal magnetic equator that divides the heliospheric magnetic field into two sectors (polarities). Several recent studies have shown that the heliospheric current sheet is southward shifted during approximately 3 years in the solar declining phase (the so-called bashful ballerina phenomenon). In this article we study the hemispherical asymmetry in the photospheric and coronal magnetic fields using Wilcox Solar Observatory measurements of the photospheric magnetic field since 1976 as well as the potential field source surface model. Multipole analysis of the photospheric magnetic field shows that during the late declining phase of solar cycles since the 1970s, the "bashful ballerina phenomenon" is a consequence of the g^{0}_{2} quadrupole term, signed oppositely to the dipole moment. Surges of new flux transport magnetic field from low latitudes to the poles, thus leading to a systematically varying contribution to the g^{0}_{2}-term from different latitudes. In the case of a north-south asymmetric flux production, this is seen as a quadrupole contribution traveling toward higher latitudes. When the quadrupole term is largest, the main contribution comes from the polar latitudes. At least during the four recent solar cycles, the g^{0}_{2}-term arises because the magnitude of the southern polar field is larger than the magnitude found in the north in the declining phase of the cycle. In the heliosphere this hemispheric asymmetry of the coronal fields is seen as a southward shift of the heliospheric current sheet by about 2.

Virtanen, I. I.; Mursula, K.

2014-02-01

338

Solar Activity and Motions in the Solar Chromosphere and Corona at the 2012 and 2013 Total and Annular Eclipses in the U.S., Australia, and Africa  

NASA Astrophysics Data System (ADS)

Our studies of the solar chromosphere and corona at the 2012 and 2013 eclipses shortly after cycle maximum 24 (2011/2012) of solar activity (see: http://www.swpc.noaa.gov/SolarCycle/) involved radio observations of the 2012 annular eclipse with the Jansky Very Large Array, optical observations of the 2012 total eclipse from Australia, optical observations of the 2013 annular eclipse from Tennant Creek, Australia, and the 3 November 2013 total solar eclipse from Gabon. Our observations are coordinated with those from solar spacecraft: Solar Dynamics Observatory AIA and HMI, Hinode XRT and SOT, SOHO LASCO and EIT, PROBA2 SWAP, and STEREO SECCHI. Our 2012 totality observations include a CME whose motion was observed with a 37-minute interval. We include first results from the expedition to Gabon for the 3 November 2013 eclipse, a summary of eclipse results from along the path of totality across Africa, and a summary of the concomitant spacecraft observations. The Williams College 2012 expeditions were supported in part by NSF grant AGS-1047726 from Solar Terrestrial Research/NSF AGS, and by the Rob Spring Fund and Science Center funds at Williams. The JVLA is supported by the NSF. The Williams College 2013 total-eclipse expedition was supported in part by grant 9327-13 from the Committee for Research and Exploration of the National Geographic Society. ML was also supported in part by a Grant-In-Aid of Research from the National Academy of Sciences, administered by Sigma Xi, The Scientific Research Society (Grant ID: G20120315159311). VR and MS acknowledge support for 2012 from projects VEGA 2/0003/13 and NGS-3139-12 of the National Geographic Society. We are grateful to K. Shiota (Japan) for kindly providing us with some of his 2012 eclipse coronal images. We thank Alec Engell (Montana State U) for assistance on site, and Terry Cuttle (Queensland Amateur Astronomers) for help with site arrangements. We thank Aram Friedman (Ansible Technologies), Michael Kentrianakis, and Nicholas Weber (Dexter Southfield School) for collaboration on imaging at the Australian total eclipse.

Pasachoff, Jay M.; Babcock, B. A.; Davis, A. B.; Demianski, M.; Lucas, R.; Lu, M.; Dantowitz, R.; Rusin, V.; Saniga, M.; Seaton, D. B.; Gaintatzis, P.; Voulgaris, A.; Seiradakis, J. H.; Gary, D. E.; Shaik, S. B.

2014-01-01

339

MESSENGER soft X-ray observations of the quiet solar corona  

NASA Astrophysics Data System (ADS)

In a remarkable result from their "SphinX" experiment, Sylwester et al. (2012) found a non-varying base level of soft X-ray emission at the quietest times in 2009. We describe comparable data from the soft X-ray monitor on board MESSENGER (en route to Mercury) which had excellent coverage both in 2009 and during the true solar minimum of 2008. These observations overlap SphinX's and also are often exactly at Sun-MESSENGER-Earth conjunctions. During solar minimum the Sun-MESSENGER distance varied substantially, allowing us to use the inverse-square law to help distinguish the aperture flux (ie, solar X-rays) from that due to sources of background in the 2-5 keV range. The MESSENGER data show a non-varying background level for many months in 2008 when no active regions were present. We compare these data in detail with those from SphinX. Both sets of data reveal a different behavior when magnetic active regions are present on the Sun, and when they are not.Reference: Sylwester et al., ApJ 751, 111 (2012)

Schwartz, Richard A.; Hudson, Hugh S.; Tolbert, Anne K; Dennis, Brian R.

2014-06-01

340

Relative elemental abundance and heating constraints determined for the solar corona from SERTS measurements  

NASA Technical Reports Server (NTRS)

Intensities of EUV spectral lines were measured as a function of radius off the solar limb by two flights of Goddard's Solar EUV Rocket Telescope and Spectrograph (SERTS) for three quiet sun regions. The density scale height, line-ratio densities, line-ratio temperatures, and emission measures were determined. The line-ratio temperature determined from the ionization balances of Arnaud and Rothenflug (1985) were more self-consistent than the line-ratio temperatures obtained from the values of Arnaud and Raymond (1992). Limits on the filling factor were determined from the emission measure and the line-ratio densities for all three regions. The relative abundances of silicon, aluminum, and chromium to iron were determined. Results did agree with standard coronal relative elemental abundances for one observation, but did not agree for another. Aluminum was overabundant while silicon was underabundant. Heating was required above 1.15 solar radii for all three regions studied. For two regions, local nonconductive heating is needed for any filling factor, and in all three regions for filling factor of 0.1.

Falconer, David A.

1994-01-01

341

THE FIRST MEASUREMENT OF THE ADIABATIC INDEX IN THE SOLAR CORONA USING TIME-DEPENDENT SPECTROSCOPY OF HINODE/EIS OBSERVATIONS  

SciTech Connect

We use observations of a slow magnetohydrodynamic wave in the corona to determine for the first time the value of the effective adiabatic index, using data from the Extreme-ultraviolet Imaging Spectrometer on board Hinode. We detect oscillations in the electron density, using the CHIANTI atomic database to perform spectroscopy. From the time-dependent wave signals from multiple spectral lines the relationship between relative density and temperature perturbations is determined, which allows in turn to measure the effective adiabatic index to be {gamma}{sub eff} = 1.10 {+-} 0.02. This confirms that the thermal conduction along the magnetic field is very efficient in the solar corona. The thermal conduction coefficient is measured from the phase lag between the temperature and density, and is shown to be compatible with Spitzer conductivity.

Van Doorsselaere, Tom; Wardle, Nick; Jansari, Kishan; Verwichte, Erwin; Nakariakov, Valery M. [CFSA, Physics Department, University of Warwick, Coventry CV4 7AL (United Kingdom); Del Zanna, Giulio, E-mail: Tom.VanDoorsselaere@wis.kuleuven.BE [DAMTP, Centre for Mathematical Sciences, Wilberforce Road, Cambridge CB3 0WA (United Kingdom)

2011-02-01

342

Viscous Energy Dissipation by Flux Pile-Up Merging in the Solar Corona  

NASA Astrophysics Data System (ADS)

Magnetic field annihilation in resistive viscous incompressible plasmas is analyzed. Anisotropic viscous transport is modeled by the dominant terms in the Braginskii viscous stress tensor. An analytical solution for steady-state magnetic merging, driven by vortical plasma flows in two dimensions, is derived. Resistive and viscous energy dissipation rates are calculated. It is shown that, except in the limiting case of zero vorticity, viscous heating can significantly exceed Joule heating at the merging site. The results strongly suggest that viscous dissipation can provide a significant fraction of the total energy release in solar flares, which may have far-reaching implications for flare models.

Litvinenko, Yuri E.

2005-07-01

343

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

Microsoft Academic Search

We conducted an experiment in conjunction with the total solar eclipse of 29 March 2006 in Libya that measured the coronal intensity through two filters centered at 3850 and 4100 Angstroms with bandwidths of 40 Angstroms. The purpose of these measurements was to obtain the intensity ratio through these two filters to determine the electron temperature. The instrument, Imaging Spectrograph

Nelson Leslie Reginald; J. Davila; C. St. Cyr

2009-01-01

344

Long-period intensity pulsations in the solar corona during activity cycle 23  

E-print Network

We report on the detection ($10\\ \\sigma$) of 917 events of long-period (3 to 16 hours) intensity pulsations in the 19.5 nm passband of the SOHO Extreme ultraviolet Imaging Telescope. The data set spans from January 1997 to July 2010, i.e the entire solar cycle 23 and the beginning of cycle 24. The events can last for up to six days and have relative amplitudes up to 100%. About half of the events (54%) are found to happen in active regions, and 50% of these have been visually associated with coronal loops. The remaining 46% are localized in the quiet Sun. We performed a comprehensive analysis of the possible instrumental artifacts and we conclude that the observed signal is of solar origin. We discuss several scenarios which could explain the main characteristics of the active region events. The long periods and the amplitudes observed rule out any explanation in terms of magnetohydrodynamic waves. Thermal nonequilibrium could produce the right periods, but it fails to explain all the observed properties of c...

Auchre, F; Solomon, J; Tison, E

2013-01-01

345

Absorption and scattering properties of the Martian dust in the solar wavelengths  

NASA Technical Reports Server (NTRS)

A new wavelength-dependent model of the single-scattering properties of the Martian dust is presented. The model encompasses the solar wavelengths (0.3 to 4.3 micrometers at 0.02 micrometer resolution) and does not assume a particular mineralogical composition of the particles. We use the particle size distribution, shape, and single-scattering properties at Viking Lander wavelengths presented by Pollack et al. [1995]. We expand the wavelength range of the aerosol model by assuming that the atmospheric dust complex index of refraction is the same as that of dust particles in the bright surface geologic units. The new wavelength-dependent model is compared to observations taken by the Viking Orbiter Infrared Thermal Mapper solar channel instrument during two dust storms. The model accurately matches afternoon observations and some morning observations. Some of the early morning observations are much brighter than the model results. The increased reflectance can be ascribed to the formation of a water ice shell around the dust particles, thus creating the water ice clouds which Colburn et al. [1989], among others, have predicted.

Ockert-Bell, M. E.; Pollack, J. B.; McKay, C. P.; Forget, F.

1997-01-01

346

A dust ring around Epsilon Eridani analogue to the young Solar System  

E-print Network

Dust emission around the nearby star epsilon Eridani has been imaged using a new submillimetre camera (SCUBA at the JCMT). At 850 microns wavelength a ring of dust is seen, peaking at 60 AU from the star and with much lower emission inside 30 AU. The mass of the ring is at least 0.01 Earth masses in dust, while an upper limit of 0.4 Earth masses in molecular gas is imposed by CO observations. The total mass is comparable to the estimated amount of material, 0.04-0.3 Earth masses, in comets orbiting the Solar System. The most probable origin of the the ring structure is that it is a young analogue to the Kuiper Belt in our Solar System, and that the central region has been partially cleared by the formation of grains into planetesimals. Dust clearing around epsilon Eri is seen within the radius of Neptune's orbit, and the peak emission at 35-75 AU lies within the estimated Kuiper Belt zone of 30-100 AU radius. epsilon Eri is a main-sequence star of type K2V (0.8 Solar masses) with an estimated age of 0.5-1.0 G...

Greaves, J S; Moriarty-Schieven, G H; Jenness, T; Dent, W R F; Zuckerman, B; McCarthy, C; Webb, R A; Butner, H M; Gear, W K; Walker, H J

1998-01-01

347

Elemental Abundances in the Solar Corona as Measured by the X-ray Solar Monitor Onboard Chandrayaan-1  

NASA Astrophysics Data System (ADS)

The X-ray Solar Monitor (XSM) on the Indian lunar mission Chandrayaan-1 was flown to complement lunar elemental abundance studies by the X-ray fluorescence experiment C1XS. XSM measured the ? 1.8 - 20 keV solar X-ray spectrum during its nine months of operation in lunar orbit. The soft X-ray spectra can be used to estimate absolute coronal abundances using intensities of emission-line complexes and the plasma temperature derived from the continuum. The best estimates are obtained from the brightest flare observed by XSM: a C2.8-class flare. The well-known first-ionization potential (FIP) effect is observed; abundances are enhanced for the low-FIP elements Fe, Ca, and Si, while the intermediate-FIP element S shows values close to the photospheric abundance. The derived coronal abundances show a quasi-mass-dependent pattern of fractionation.

Narendranath, S.; Sreekumar, P.; Alha, L.; Sankarasubramanian, K.; Huovelin, J.; Athiray, P. S.

2014-05-01

348

Soft X-ray images of the solar corona using normal incidence optics  

NASA Technical Reports Server (NTRS)

A solar coronal loop system has been photographed in soft X-rays using a normal incidence telescope based on multilayer mirror technology. The telescope consisted of a spherical objective mirror of 4 cm aperture and 1 m focal length, a film cassette, and a focal plane shutter. A metallized thin plastic film filter was used to exclude visible light. The objective mirror was covered with a multilayer coating consisting of alternating layers of tungsten and carbon whose combined thicknesses satisfied the Bragg diffraction condition for 44 A radiation. The image was recorded during a rocket flight on October 25, 1985 and was dominated by emission lines arising from the Si XII spectrum. The rocket also carried a high resolution soft X-ray spectrograph that confirmed the presence of Si XII line radiation in the source. This image represents the first successful use of multilayer technology for astrophysical observations.

Bruner, M. E.; Haisch, B. M.; Brown, W. A.; Acton, L. W.; Underwood, J. H.

1988-01-01

349

The magnetic non-equilibrium of buoyant flux tubes in the solar corona  

NASA Technical Reports Server (NTRS)

The magnetic field in the convection zone and photosphere of the sun exists mostly as concentrated tubes of magnetic flux. It is, therefore, necessary to study the basic properties of magnetic flux tubes to obtain a basis for understanding the behavior of the sun's magnetic field. The present investigation is concerned with the global equilibrium shape of a flux tube in the stratified solar atmosphere. A fundamental property of isolated flux tubes is magnetic buoyancy. Attention is given to flux tubes with external field, and twisted flux tubes. It is shown that the analysis of Parker (1975, 1979) and Spruit (1981) for calculating the equilibrium of a slender flux tube in a stratified atmosphere may be extended to more general situations. The slender tube approximation provides a method of solving the problem of modeling the overall curvature of flux tubes. It is found that for a twisted flux tube, there can be two possible equilibrium values of the height.

Browning, P. K.; Priest, E. R.

1984-01-01

350

Rigorous new limits on magnetic helicity dissipation in the solar corona  

NASA Astrophysics Data System (ADS)

The Cauchy-Schwarz inequality is employed to find geometry-independent limits on the magnetic helicity dissipation rate in a resistive plasma. These limits only depend upon the total energy of the plasma, the energy dissipation rate, and a mean diffusion coefficient. For plasmas isolated from external energy sources, limits can also be set on the minimum time necessary to dissipate a net amount of helicity. As evaluated in the context of a solar coronal loop, these limits strongly suggest that helicity decay occurs on a diffusion timescale which is far too great to be relevant to most coronal processes. Furthermore, rapid reconnection is likely to approximately conserve magnetic helicity. The difficulties involved in determining the free energy residing in a magnetic structure (given the constraint of magnetic helicity conservation) are discussed.

Berger, M. A.

1984-09-01

351

Observations of steady anomalous magnetic heating in thin current sheets. [of solar corona  

NASA Technical Reports Server (NTRS)

The Hard X-ray Imaging Spectrometer of the Solar Maximum Mission has yielded observations of a faint, steadily emitting loop-like structure, which have allowed the thermal evolution of this loop over a period of about 15 hr to be followed. Only 0.1 percent of the volume of the loop appears to be steadily heated, at the large rate of 0.6 erg/cu cm sec; this suggests that the heating represents the dissipation of magnetic fields in thin current sheets. Ion-kinetic tearing, as proposed by Galeev et al. (1981), is noted to be especially consonant with these observations. The source of the present X-ray emission is identified with the H-alpha filament in the same region. The present findings are held to constitute the first direct evidence for the steady dissipation of coronal magnetic fields via enhanced thin current sheet resistivity.

Martens, P. C. H.; Van Den Oord, G. H. J.; Hoyng, P.

1985-01-01

352

Formation and Evolution of the Dust in Galaxies. II. The Solar Neighbourhood  

E-print Network

Over the past decade a new generation of chemical models have included the dust in the treatment of the ISM. This major accomplishment has been spurred by the growing amounts of data on the highly obscured high-z Universe and the intriguing local properties of the Solar Neighbourhood (SoNE). We present here a new model able to simulate the formation and evolution of dust in the ISM. The model follows the evolution of 16 elemental species, with particular attention to those that are simultaneously present in form of gas and dust, e.g. C, N, O, Mg, Si, S, Ca and Fe. In this study we focus on the SoNe and the MW Disk as a whole which are considered as laboratories to test the physical ingredients governing the dust evolution. Infall of primordial gas, birth and death of stars, radial flows of matter between contiguous shells, presence of a central bar, star-dust emission by SNae and AGB stars, dust destruction and accretion are taken into account. The model reproduces the local depletion of the elements in the g...

Piovan, L; Merlin, E; Grassi, T; Tantalo, R; Buonomo, U; Cassar, L P

2011-01-01

353

A HR-like Diagram for Solar/Stellar Flares and Corona -- Emission Measure vs Temperature Diagram  

E-print Network

In our previous paper, we have presented a theory to explain the observed universal correlation between the emission measure ($EM=n^2 V$) and temperature (T) for solar/stellar flares on the basis of the magnetic reconnection model with heat conduction and chromospheric evaporation. Here n is the electron density and V is the volume. By extending our theory to general situations, we examined the EM-T diagram in detail, and found the following properties: 1) The universal correlation sequence (``main sequence flares'') with $EM \\propto T^{17/2}$ corresponds to the case of constant heating flux or equivalently the case of constant magnetic field strength in the reconnection model. 2) The EM-T diagram has a forbidden region, where gas pressure of flares exceeds magnetic pressure. 3) There is a coronal branch with $EM \\propto T^{15/2}$ for $T 10^7$ K. This branch is situated left side of the main sequence flares in the EM-T diagram. 4) There is another forbidden region determined by the length of flare loop; a lower limit of flare loop is $10^7$ cm. Small flares near this limit correspond to nanoflares observed by SOHO/EIT. 5) We can plot flare evolution track on the EM-T diagram. A flare evolves from the coronal branch to main sequence flares, then returns to the coronal branch eventually. These properties of the EM-T diagram are similar to those of the HR diagram for stars, and thus we propose that the EM-T diagram is quite useful to estimate the physical quantities (loop length, heating flux, magnetic field strength, total energy and so on) of flares and corona when there is no spatially resolved imaging observations.

Kazunari Shibata; Takaaki Yokoyama

2002-06-03

354

Core and Wing Densities of Asymmetric Coronal Spectral Profiles: Implications for the Mass Supply of the Solar Corona  

NASA Astrophysics Data System (ADS)

Recent solar spectroscopic observations have shown that coronal spectral lines can exhibit asymmetric profiles, with enhanced emissions at their blue wings. These asymmetries correspond to rapidly upflowing plasmas at speeds exceeding ?50 km s-1. Here, we perform a study of the density of the rapidly upflowing material and compare it with that of the line core that corresponds to the bulk of the plasma. For this task, we use spectroscopic observations of several active regions taken by the Extreme Ultraviolet Imaging Spectrometer of the Hinode mission. The density sensitive ratio of the Fe XIV lines at 264.78 and 274.20 is used to determine wing and core densities. We compute the ratio of the blue wing density to the core density and find that most values are of order unity. This is consistent with the predictions for coronal nanoflares if most of the observed coronal mass is supplied by chromospheric evaporation driven by the nanoflares. However, much larger blue wing-to-core density ratios are predicted if most of the coronal mass is supplied by heated material ejected with type II spicules. Our measurements do not rule out a spicule origin for the blue wing emission, but they argue against spicules being a primary source of the hot plasma in the corona. We note that only about 40% of the pixels where line blends could be safely ignored have blue wing asymmetries in both Fe XIV lines. Anticipated sub-arcsecond spatial resolution spectroscopic observations in future missions could shed more light on the origin of blue, red, and mixed asymmetries.

Patsourakos, S.; Klimchuk, J. A.; Young, P. R.

2014-02-01

355

Insensitivity of Line-Ratio Diagnostics to Steady-State Non-Maxwellian Electron Distributions in Solar Corona  

NASA Technical Reports Server (NTRS)

We examine the idea that the corona is heated by a population of nonthermal particles. An upper limit on the size of the nonthermal population is derived by assuming that all of the radiation and conduction losses in the corona are provided by the nonthermal tail of the particle distribution. Only a very small percentage of nonthermal particles are allowed. These particles have a negligable effect on temperature sensitive line ratios typically observed in the EUV (Extreme Ultraviolet Radiation).

Falconer, D. A.; Davila, J. M.

1999-01-01

356

CHINA'S DUST AFFECTS SOLAR RESOURCE IN THE U.S.: A CASE STUDY Christian A. Gueymard Nels S. Laulainen  

E-print Network

a significant im- pact. Concentrating systems such as parabolic troughs and solar tower plants utilize onlyCHINA'S DUST AFFECTS SOLAR RESOURCE IN THE U.S.: A CASE STUDY Christian A. Gueymard Nels S of how long- range aerosol transport may temporarily affect the U.S. solar resource. Broadband

Oregon, University of

357

Dynamics of a multi-thermal loop in the solar corona  

NASA Astrophysics Data System (ADS)

Context. We present an observation of a long-living multi-thermal coronal loop, visible in different extreme ultra-violet wavebands of SDO/AIA in a quiet-Sun region close to the western solar limb. Aims: Analysis of persistent kink displacements of the loop seen in different bandpasses that correspond to different temperatures of the plasma allows sub-resolution structuring of the loop to be revealed. Methods: A vertically oriented slit is taken at the loop top, and time-distance maps are made from it. Loop displacements in time-distance maps are automatically tracked with the Gaussian fitting technique and fitted with a sinusoidal function that is "guessed". Wavelet transforms are further used in order to quantify the periodicity variation in time of the kink oscillations. Results: The loop strands are found to oscillate with the periods ranging between 3 and 15 min. The oscillations are observed in intermittent regime with temporal changes in the period and amplitude. The oscillations are different at three analysed wavelengths. Conclusions: This finding suggests that the loop-like threads seen at different wavelengths are not co-spatial, hence that the loop consists of several multi-thermal strands. The detected irregularity of the oscillations can be associated with a stochastic driver acting at the footpoints of the loop. A movie associated to Fig. 1 is available in electronic form at http://www.aanda.org

Nistic, G.; Anfinogentov, S.; Nakariakov, V. M.

2014-10-01

358

Potential Magnetic Field around a Helical Flux-rope Current Structure in the Solar Corona  

E-print Network

We consider the potential magnetic field associated with a helical electric line current flow, idealizing the near-potential coronal field within which a highly localized twisted current structure is embedded. It is found that this field has a significant axial component off the helical magnetic axis where there is no current flow, such that the flux winds around the axis. The helical line current field, in including the effects of flux rope writhe, is therefore more topologically complex than straight line and ring current fields sometimes used in solar flux rope models. The axial flux in magnetic fields around confined current structures may be affected by the writhe of these current structures such that the field twists preferentially with the same handedness as the writhe. This property of fields around confined current structures with writhe may be relevant to classes of coronal magnetic flux rope, including structures observed to have sigmoidal forms in soft X-rays and prominence magnetic fields. For example, ``bald patches'' and the associated heating by Parker current sheet dissipation seem likely. Thus some measurements of flux rope magnetic helicities may derive from external, near-potential fields. The predicted hemispheric preference for positive and negative magnetic helicities is consistent with observational results for prominences and sigmoids and past theoretical results for flux rope internal fields.

G. J. D. Petrie

2007-02-06

359

Vertical Kink Oscillation of a Magnetic Flux Rope Structure in the Solar Corona  

NASA Astrophysics Data System (ADS)

Vertical transverse oscillations of a coronal magnetic rope, observed simultaneously in the 171 and 304 bandpasses of the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory (SDO), are detected. The oscillation period is about 700 s and the displacement amplitude is about 1 Mm. The oscillation amplitude remains constant during the observation. Simultaneous observation of the rope in the bandpasses corresponding to the coronal and chromospheric temperatures suggests that it has a multi-thermal structure. Oscillatory patterns in 171 and 304 are coherent, which indicates that the observed kink oscillation is collective, in which the rope moves as a single entity. We interpret the oscillation as a fundamental standing vertically polarized kink mode of the rope, while the interpretation in terms of a perpendicular fast wave could not be entirely ruled out. In addition, the arcade situated above the rope and seen in the 171 bandpass shows an oscillatory motion with the period of about 1000 s.

Kim, S.; Nakariakov, V. M.; Cho, K.-S.

2014-12-01

360

The Solar Corona as Probed by Comet Lovejoy (C/2011 W3)  

NASA Astrophysics Data System (ADS)

Extreme-ultraviolet images of Comet Lovejoy (C/2011 W3) from the Atmospheric Imaging Assembly show striations related to the magnetic field structure in both open and closed magnetic regions. The brightness contrast implies coronal density contrasts of at least a factor of six between neighboring flux tubes over scales of a few thousand kilometers. These density structures imply variations in the Alfvn speed on a similar scale. They will drastically affect the propagation and dissipation of Alfvn waves, and that should be taken into account in models of coronal heating and solar wind acceleration. In each striation, the cometary emission moves along the magnetic field and broadens with time. The speed and the rate of broadening are related to the parallel and perpendicular components of the velocities of the cometary neutrals when they become ionized. We use a magnetohydrodynamic model of the coronal magnetic field and the theory of pickup ions to compare the measurements with theoretical predictions, in particular with the energy lost to Alfvn waves as the cometary ions isotropize.

Raymond, J. C.; McCauley, P. I.; Cranmer, S. R.; Downs, C.

2014-06-01

361

Laboratory identification of storage-and-release eruption regimes in the solar corona  

NASA Astrophysics Data System (ADS)

Ideal magnetohydrodynamic (MHD) instabilities such as the kink and torus instabilities are believed to play an important role in driving long-lived solar magnetic flux ropes to erupt. In this paper, we report the findings of a laboratory flux rope experiment that is specifically designed to explore the parameter space for these two eruptive instabilities. In particular, we scan the twist in the flux rope for the kink instability and the decay index of the potential field for the torus instability. Using in situ magnetic probes, we identify four distinct stability regimes in the experiment: (1) stable; (2) eruptive; (3) failed kink; and (4) failed torus. The identification of the failed kink regime validates the importance of the torus instability in driving flux rope eruptions. The identification of the failed torus regime, on the other hand, constitutes an entirely new finding. By directly measuring the forces acting on the flux rope plasma, we show that a strong magnetic tension force that is derived from the toroidal magnetic field in the flux rope suppresses eruptions in the failed torus regime.This research is supported by DoE Contract Number DE-AC02-09CH11466 and by the NSF/DoE Center for Magnetic Self-Organization (CMSO).

Myers, Clayton E.; Yamada, Masaaki; Ji, Hantao; Yoo, Jongsoo; Fox, Will; Jara-Almonte, Jon

2015-04-01

362

SOLAR CORONA LOOP STUDIES WITH THE ATMOSPHERIC IMAGING ASSEMBLY. I. CROSS-SECTIONAL TEMPERATURE STRUCTURE  

SciTech Connect

We present a first systematic study on the cross-sectional temperature structure of coronal loops using the six coronal temperature filters of the Atmospheric Imaging Assembly (AIA) instrument on the Solar Dynamics Observatory (SDO). We analyze a sample of 100 loop snapshots measured at 10 different locations and 10 different times in active region NOAA 11089 on 2010 July 24, 21:00-22:00 UT. The cross-sectional flux profiles are measured and a cospatial background is subtracted in six filters in a temperature range of T {approx} 0.5-16 MK, and four different parameterizations of differential emission measure (DEM) distributions are fitted. We find that the reconstructed DEMs consist predominantly of narrowband peak temperature components with a thermal width of {sigma}{sub log(T)} {<=} 0.11 {+-} 0.02, close to the temperature resolution limit of the instrument, consistent with earlier triple-filter analysis from the Transition Region and Coronal Explorer by Aschwanden and Nightingale and from EIS/Hinode by Warren et al. or Tripathi et al. We find that 66% of the loops could be fitted with a narrowband single-Gaussian DEM model, and 19% with a DEM consisting of two narrowband Gaussians (which mostly result from pairs of intersecting loops along the same line of sight). The mostly isothermal loop DEMs allow us also to derive an improved empirical response function of the AIA 94 A filter, which needs to be boosted by a factor of q{sub 94} = 6.7 {+-} 1.7 for temperatures at log (T) {approx}< 6.3. The main result of near-isothermal loop cross-sections is not consistent with the predictions of standard nanoflare scenarios, but can be explained by flare-like heating mechanisms that drive chromospheric evaporation and upflows of heated plasma coherently over loop cross-sections of w {approx} 2-4 Mm.

Aschwanden, Markus J.; Boerner, Paul, E-mail: aschwanden@lmsal.com [Lockheed Martin Advanced Technology Center, Solar and Astrophysics Laboratory, Org. ADBS, Bldg. 252, 3251 Hanover St., Palo Alto, CA 94304 (United States)

2011-05-10

363

Solar C: Scatter-Free Observatory for Limb Active Regions and Coronae  

NASA Technical Reports Server (NTRS)

The SOLARC observatory is a 0.5m off-axis reflecting coronagraph. NASA SRT funding has allowed the completion of this telescope facility, which we believe is now the world's largest operational coronagraph. We have achieved our proposal goals both in the development of the new technology for this facility and in the demonstration of its scientific and educational potential: 1) The SOLARC engineering development was successful and has spawned other similar instruments. The off-axis design of ATST (a new 4m telescope) has benefited from the SOLARC development. The off-axis 1.6m NST facility at BBSO is also now under construction and will be the world's largest solar disk observing telescope until ATST is completed. Both of these telescope designs are derivatives of the SOLARC 0.5m off-axis. Some of this technical development is described in the publications. 2) The most important scientific goal of SOLARC has been to demonstrate that coronal magnetic fields can be measured using infrared spectropolarimetry techniques. With the completion of the optical fiber-bundle imaging spectropolarimeter we have measured the coronal field strength with a sensitivity to the line-of-sight field component of 2G at 150,OOOkm above the limb. We believe this capability opens new opportunities for space weather, and coronal physics research. In particular we have demonstrated a new tool for understanding the effect of the Sun on the terrestrial space environment. A paper reporting these results has recently been submitted to the Astrophysical Journal Letters.

2004-01-01

364

OBSERVATIONAL EVIDENCE OF SAUSAGE-PINCH INSTABILITY IN SOLAR CORONA BY SDO/AIA  

SciTech Connect

We present the first observational evidence of the evolution of sausage-pinch instability in active region 11295 during a prominence eruption using data recorded on 2011 September 12 by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). We have identified a magnetic flux tube visible in AIA 304 A that shows curvatures on its surface with variable cross-sections as well as enhanced brightness. These curvatures evolved and thereafter smoothed out within a timescale of a minute. The curved locations on the flux tube exhibit a radial outward enhancement of the surface of about 1-2 Mm (a factor of two larger than the original thickness of the flux tube) from the equilibrium position. AIA 193 A snapshots also show the formation of bright knots and narrow regions in-between at the four locations as that of 304 A along the flux tube where plasma emission is larger compared to the background. The formation of bright knots over an entire flux tube as well as the narrow regions in <60 s may be the morphological signature of the sausage instability. We also find the flows of confined plasma (propagation of brightness) in these bright knots along the field lines, which indicates the dynamicity of the flux tube that probably causes the dominance of the longitudinal field component over short temporal scales. The observed longitudinal motion of the plasma frozen in the magnetic field lines further vanishes the formed curvatures and plasma confinements as well as growth of instability to stabilize the flux tube.

Srivastava, A. K.; Joshi, N. C.; Kayshap, P. [Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital 263 129 (India); Erdelyi, R.; Fedun, V. [Solar Physics and Space Plasma Research Centre (SP2RC), School of Mathematics and Statistics, The University of Sheffield, Sheffield S3 7RH (United Kingdom); Tripathi, Durgesh [Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune 411007 (India)

2013-03-10

365

Clementine Observations of the Zodiacal Light and the Dust Content of the Inner Solar System  

NASA Technical Reports Server (NTRS)

Using the Moon to occult the Sun, the Clementine spacecraft used its navigation cameras to map the inner zodiacal light at optical wavelengths over elongations of 3 approx. less than epsilon approx. less than 30 deg from the Sun. This surface brightness map is then used to infer the spatial distribution of interplanetary dust over heliocentric distances of about 10 solar radii to the orbit of Venus. The averaged ecliptic surface brightness of the zodiacal light falls off as Z(epsilon) is a member of epsilon(sup -2.45 +/- 0.05), which suggests that the dust cross-sectional density nominally falls off as sigma(r) is a member of r(sup - 1.45 +/- 0.05). The interplanetary dust also has an albedo of alpha approx. = 0.1 that is uncertain by a factor of approx. 2. Asymmetries of approx. 10% are seen in directions east-west and north-south of the Sun, and these may be due the giant planets' secular gravitational perturbations. We apply a simple model that attributes the zodiacal light as due to three dust populations having distinct inclination distributions, namely, dust from asteroids and Jupiter-family comets (JFCs) having characteristic inclinations of i approx. 7 deg, dust from Halley-type comets having i approx. 33 deg, and an isotropic cloud of dust from Oort Cloud comets. The best-fitting scenario indicates that asteroids + JFCs are the source of about 45% of the optical dust cross section seen in the ecliptic at 1 AU but that at least 89% of the dust cross section enclosed by a 1-AU-radius sphere is of a cometary origin. Each population's radial density variations can also deviate somewhat from the nominal sigma(r) is a member of r(sup -1.45). When these results are extrapolated out to the asteroid belt, we find an upper limit on the mass of the light-reflecting asteroidal dust that is equivalent to a 12-km asteroid, and a similar extrapolation of the isotropic dust cloud out to Oort Cloud distances yields a mass equivalent to a 30-km comet, although the latter mass is uncertain by orders of magnitude.

Hahn, Joseph M.; Zook, Herbert A.; Cooper, Bonnie; Sunkara, Bhaskar

2002-01-01

366

Fluxes of MeV particles at Earth's orbit and their relationship with the global structure of the solar corona: Observations from SOHO  

NASA Technical Reports Server (NTRS)

The SOHO satellite, launched on 2 December 1995, combines a unique set of instruments which allow comparative studies of the interior of the sun, the outer corona and solar to be carried out. In its halo orbit around the L1 Lagrangian point of the sun-earth system, SOHO's comprehensive suprathermal and energetic particle analyzer (COSTEP) measures in situ energetic particles in the energy range of 44 keV/particle to greater than 53 MeV/n. The MeV proton, electron and helium nuclei measurements from the COSTEP electron proton helium instrument (EPHIN) were used to investigate the relationships of intensity increases of these particle species with the large-scale structures of the solar corona and heliosphere, including temporal variations. Coronal observatons are provided by the large angle spectroscopic coronagraph (LASCO) and the extreme ultraviolet imaging telescope (EIT). It was found that during times of minimum solar activity, intensity increases of the particles have two well defined sources: corotating interaction regions (CIRs) in the heliosphere related to coronal holes at the sun and coronal mass ejections.

Posner, A.; Bothmer, V.; Kunow, H.; Heber, B.; Mueller-Mellin, R.; Delaboudiniere, J.-P.; Thompson, B. J.; Brueckner, G. E.; Howard, R. A.; Michels, D. J.

1997-01-01

367

Dust indicator maps for improving solar radiation estimation from satellite data  

NASA Astrophysics Data System (ADS)

Measurement of solar radiation from ground-based sensors is an expensive process as it requires large number of ground measurement stations to account for the spatial variability. Moreover, the instruments require regular maintenance. Satellite data can be used to model solar radiation and produce maps in regular intervals, which can be used for solar resource assessment. The models can either be empirical, physics-based or statistical models. However, in environments such as the United Arab Emirates (UAE) which are characterized by heavy dust, the results obtained by the models will lead to lower accuracies. In this study, we build on the model developed in [1], where ensembles of ANNs are used separately for cloudy and cloud-free pixels to derive solar radiation maps using the data acquired in the thermal channels of the Meteosat SEVIRI instrument. The model showed good accuracies for the estimation of direct normal irradiance (DNI), diffuse horizontal irradiance (DHI) and global horizontal irradiance (GHI); where the relative root mean square error (rRMSE) values for the DNI, DHI and GHI were 15.7, 23.6 and 7.2%, respectively, while the relative mean bias error (rMBE) values were +0.8, +8.3 and +1.9%, respectively. However, an analysis of the results on different dusty days showed varying accuracy. To further improve the model, we propose to use the dust indicator maps as inputs to the model. An interception index was proposed in [2] to detect dust over desert regions using visible channels of the SEVIRI instrument. The index has a range of 0 to 1 where the value of 1 corresponds to heavy dust and 0 corresponds to clear conditions. There is ongoing work to use the measurements from AERONET stations to derive dust indicator maps based on canonical correlation analysis, which relates the thermal channels to the aerosol optical depth (AOD) derived at different wavelengths from the AERONET measurements. There is also an ongoing work to analyze the time series of the SEVIRI data to derive dust maps. In this work, the dust indicator maps are used as extra inputs to the ANN to model the dusty conditions in a better way.

Marpu, P. R.; Eissa, Y.; Al Meqbali, N.; Ghedira, H.

2012-12-01

368

Evolution and Activity in the Solar Corona: A Comparison of Coronal and Chromospheric Structures Seen in Soft X-Rays, White Light and H-Alpha Emission  

NASA Technical Reports Server (NTRS)

The work completed under this project, 'Evolution and Activity in the Solar Corona: A Comparison of Coronal and Chromospheric Structures Seen in Soft X-Rays, White Light and H-Alpha Emission', includes the following presentations: (1) Analysis of H-alpha Observations of High-altitude Coronal Condensations; (2) Multi-spectral Imaging of Coronal Activity; (3) Measurement and Modeling of Soft X-ray Loop Arcades; (4) A Study of the Origin and Dynamics of CMEs; and various poster presentations and thesis dissertations.

Bagenal, Fran

2001-01-01

369

Formation of fast shocks by magnetic reconnection in the solar corona  

SciTech Connect

Reconnections of magnetic fields over the solar surface are expected to generate abundant magnetohydrodynamic (MHD) discontinuities and shocks, including slow shocks and rotational discontinuities. However, the generation of fast shocks by magnetic reconnection process is relatively not well studied. In this paper, magnetic reconnection in a current sheet is studied based on two-dimensional resistive MHD numerical simulations. Magnetic reconnections in the current sheet lead to the formation of plasma jets and plasma bulges. It is further found that the plasma bulges, the leading part of plasma jets, in turn lead to the generation of fast shocks on flanks of the bulges. The simulation results show that during the magnetic reconnection process, the plasma forms a series of structures: plasma jets, plasma bulges, and fast shocks. As time increases, the bulges spread out along the current sheet ({+-}z direction) and the fast shocks move just ahead of the bulges. The effects of initial parameters {rho}{sub s}/{rho}{sub m}, {beta}{sub {infinity}}, and t{sub rec} on the fast shock generation are also examined, where {rho}{sub s}/{rho}{sub m} is the ratio of plasma densities on two sides of the initial current sheet, {beta}{sub {infinity}}=P{sub {infinity}}/(B{sub {infinity}}{sup 2}/2{mu}{sub 0}), P{sub {infinity}} is the plasma pressure and B{sub {infinity}} is the magnetic field magnitude far from the current sheet, and t{sub rec} is the reconnection duration. In the asymmetric case with {rho}{sub s}/{rho}{sub m}=2, {beta}{sub {infinity}}=0.01 and t{sub rec}=1000, the maximum Alfven Mach number of fast shocks (M{sub A1max}) is M{sub A1max} congruent with 1.1, where M{sub A1}=V{sub n1}/V{sub A1}, and V{sub n1} and V{sub A1} are, respectively, the normal upstream fluid velocity and the upstream Alfven speed in the fast shocks frame. As the density ratio {rho}{sub s}/{rho}{sub m} (=1-8) and plasma beta {beta}{sub {infinity}} (=0.0001-1) increase, M{sub A1max} varies slightly. For the case with a large plasma beta {beta}{sub {infinity}} (=5), the fast shock is very weak. As the reconnection duration t{sub rec} increases, the bulges lead to generation of fast shocks with a higher M{sub A1max}. The present results can be applied to the mechanism of coronal heating by fast shocks.

Hsieh, M. H. [Department of Physics, National Cheng Kung University, Tainan 701, Taiwan (China); Institute of Space Science, National Central University, Jhongli 320, Taiwan (China); Tsai, C. L. [Department of Physics, National Cheng Kung University, Tainan 701, Taiwan (China); Institute of Space Science, National Central University, Jhongli 320, Taiwan (China); Earth Dynamic System Research Center, National Cheng Kung University, Tainan 701, Taiwan (China); Ma, Z. W. [Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027 (China); Lee, L. C. [Institute of Space Science, National Central University, Jhongli 320, Taiwan (China)

2009-09-15

370

Hydrocarbons on Saturns Satellites: Relationship to Interstellar Dust and the Solar Nebula  

NASA Technical Reports Server (NTRS)

To understand the origin and evolution of our Solar System, and the basic components that led to life on Earth, we study interstellar and planetary spectroscopic signatures. The possible relationship of organic material detected in carbonaceous meteorites, interplanetary dust particles (IDPs), comets and the interstellar medium have been the source of speculation over the years as the composition and processes that governed the early solar nebula have been explored to understand the extent to which primitive material survived or became processed. The Cassini VIMS has provided new data relevant to this problem. Three of Saturn's satellites, Phoebe, Iapetus, and Hyperion, are found to have aromatic and aliphatic hydrocarbons on their surfaces. The aromatic hydrocarbon signature (C-H stretching mode at 3.28 micrometers) is proportionally significantly stronger (relative to the aliphatic bands) than that seen in other Solar System bodies (e.g., comets) and materials (Stardust samples, IDPs, meteorites) and the distinctive sub-features of the 3.4 micrometer aliphatic band (CH2 and CH3 groups) are reminiscent of those widely detected throughout the diffuse ISM. Phoebe may be a captured object that originated in the region beyond the present orbit of Neptune, where the solar nebula contained a large fraction of original interstellar ice and dust that was less processed than material closer to the Sun. Debris from Phoebe now resident on Iapetus and Hyperion, as well as o Phoebe itself, thus presents a unique blend of hydrocarbons, amenable to comparisons with interstellar hydrocarbons and other Solar System materials. The dust ring surrounding Saturn, in which Phoebe is embedded, probably originated from a collision with Phoebe. Dust ring particles are the likely source of the organic-bearing materials, and perhaps the recently identified small particles of Fe detected on Saturn's satellites. Lab measurements of the absolute band strengths of representative aliphatic and aromatic molecules, together with measurements from the VIMS data, allow us to calculate the number of C atoms to find the relative abundances of C atoms in the two kinds of organic molecules. The strength of the prominent aromatic C-H stretch band relative to the aliphatic band complex in Phoebe and Iapetus indicates that the relative abundance of aromatic to aliphatic carbon is very large (greater than 200). In contract, the aromatic band is nearly imperceptible in spectra of interplanetary dust particles (IDP), returned samples from comet 91P/Wild 2, insoluable carbonaceous material in most meteorites, and the diffuse interstellar dust (DISM) (although aromatics are known in all these materials-here we consider only the spectroscopic signature)

Cruikshank, D. P.

2012-01-01

371

More than Mass Proportional Heating of Heavy Ions by Collisionless Quasi-Perpendicular Shocks in the Solar Corona  

NASA Astrophysics Data System (ADS)

In addition to the high temperatures, SOHO/UVCS observations have shown that heavy ions in the polar corona are heated more than protons, and that heavy ion heating is more than mass proportional; further, the perpendicular temperatures are much larger than parallel temperatures. Here, we propose that the more than mass proportional heating of heavy ions in coronal holes is due to the ion reflection at supercritical quasi-perpendicular shocks and to the ion acceleration by the motional electric field in the shock frame. We also discuss the formation of collisionless shock in the polar corona.

Zimbardo, Gaetano

2010-03-01

372

Solar wind dominance over the Poynting-Robertson effect in secular orbital evolution of dust particles  

NASA Astrophysics Data System (ADS)

Properties of the solar wind are discussed and applied to the effect of the wind on motion of bodies in the Solar system. The velocity density function for the solar wind constituents is given by the ?-distribution. The relevant contributions to the solar wind action contain also the sputtering and reflection components in addition to direct impact. The solar wind effect is more important than the action of the solar electromagnetic radiation, as for the secular orbital evolution. The acceleration of a body under the action of the solar radiation, electromagnetic and corpuscular, is proportional to [1 - (1 + ? 1 / overline{Q} ^' }_{pr})v \\cdot hat{r}/c] hat{r}- (1 + ? 2 / overline{Q} ^' }_{pr}) v /c, approximately. Here, overline{Q} ^' }_{pr} is the dimensionless efficiency factor of the radiation pressure, v is the body's velocity at the position vector r with respect to the Sun, c is the speed of light and ?1 ? 1.1, ?2 ? 1.4. The dimensionless cross-section the dust grain presents to wind pressure is about 4.7, while the conventional value is 1.0.

Kla?ka, J.

2014-09-01

373

On the Coexistence of a Radial Magnetic Field with the Large Scale Field in the Solar Corona  

Microsoft Academic Search

Polarimetric measurements of the corona out to 2 Rs in the Fe XIII 10747 A line, the strongest of the iron forbidden lines, are placed for the first time in the context of spatially resolved images of coronal density structures. These measurements, which are the only tool currently available to yield the direction of the magnetic field, date to 1980,

S. R. Habbal; R. Woo; J. Arnaud

2001-01-01

374

A Sungrazing Comet Application of Modeling Solar Wind Mass-Loading Due to 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 sungrazing 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 such as C/2012 S1 (ISON).

Rasca, A.; Horanyi, M.

2013-12-01

375

Aeolian dust deposition on photovoltaic solar cells: the effects of wind velocity and airborne dust concentration on cell performance  

Microsoft Academic Search

Wind tunnel experiments were conducted to investigate the effect of wind velocity and airborne dust concentration on the drop of photovoltaic (PV) cell performance caused by dust accumulation on such cells. Performance drop was investigated at four wind velocities and four dust concentrations. IV characteristics were determined for various intensities of cell pollution. The evolutions of the short circuit current,

Dirk Goossens; Emmanuel Van Kerschaever

1999-01-01

376

Comprehensive Analyses of Data Collected from TEREK (Solar EUV Telescope) RES-C (Solar X-Ray Spectrometer) and SORS (Solar Radio Spectrometer) on board CORONAS-1 Using Magnetohydrodynamic Models  

NASA Technical Reports Server (NTRS)

By using the observed magnetic field data obtained from the Wilcox Solar Observatory at Stanford University as the inputs to a two-dimensional plane-of-sky magnetohydrodynamic model, via numerical relaxation method, we have deduced the plasma and magnetic field parameters for the observed coronal hole by CORONAS-1. The method for this self-consistent MHD analysis will be discussed in detail. Numerical results for the magnetic field configuration, velocity distribution, density and temperature distributions will be presented. We have converted the computed density to polarization brightness in order to directly compare the MHD outputs with observations. Also included is a summary of achievements made during the grant period. This section is summarized into three categories: 1) Visit of Co-Investigators; 2) Presentations; and 3) Papers published, accepted and submitted for publication in journals.

Wu, S. T.

1997-01-01

377

PROBA2/SWAP EUV images of the large-scale EUV corona up to 3 solar radii: Can we close the gap in coronal magnetic field structure between 1.3 and 2.5 solar radii?  

NASA Astrophysics Data System (ADS)

The EUV telescope PROBA2/SWAP has been observing the solar corona in a bandpass near 17.4 nm since February 2010. SWAP's wide field-of-view provides a unique and continuous view of the extended EUV corona up to 2-3 solar radii. By carefully processing and combining multiple SWAP images, low-noise composites were produced that reveal large-scale, EUV-emitting, coronal structures. These extended structures appear mainly above or at the edges of active regions and typically curve towards the poles. As they persist for multiple Carrington rotations and cannot easily be related to white-light features, they give an interesting view on how the coronal magnetic field is structured between 1.3 and 2-3 solar radii, in the gap between SDO/AIAs FOV and typical lower boundaries of coronagraph FOVs. With the help of magnetic field models, we analyse the geometry of the extended EUV structures in more detail and compare with sporadic EUV coronagraph measurements up to as close as 1.5Rs. The opportunities that Solar Orbiters future observations will bring are explored.

De Groof, Anik; Seaton, Daniel B.; Rachmeler, Laurel; Berghmans, David

2015-04-01

378

Structure of Cometary and Interplanetary Dust, a Clue to the Formation and Early Evolution of Dust Particles in the Solar System  

NASA Astrophysics Data System (ADS)

Cometary dust particles have been suspected to be fragile since the Giotto and Vega missions to comet Halley. More recently, numerous observations of the solar light scattered by dust particles in comet Hale-Bopp coma, together with versatile numerical simulations, have allowed us to suggest that these particles are likely to be built of both very fluffy aggregates and of more compact grains, with (to the first order) equivalent proportions in mass of absorbing material and transparent silicates [1,2]. The same approach, used to fit zodiacal light observations, indicates that a significant proportion of fluffy absorbing particles is found in the interplanetary dust cloud [3]. Laboratory simulations also lead to similar results, with e.g. polarimetric phase curves obtained for agglomerates of magnesio-ferrosilica comparable to those observed for cometary dust [4]. These estimations are now confirmed by the analysis of Stardust samples, with, e.g. evidence for both dense grains and aggregates with low bulk density within the coma of comet Wild 2 [5]. The relevance of such a structure for the formation and early evolution of dust particles in the solar system will be discussed. [1] Lasue & Levasseur-Regourd, JQSRT 100, 220-236, 2006. [2] Levasseur-Regourd, Mukai, Lasue, Okada, PSS, 55, 1010-1020, 2007. [3] Lasue, Levasseur-Regourd, Fray, Cottin, A&A, in press, 2007 [4] Hadamcik, Renard, Rietmeijer, Levasseur-Regourd et al., Icarus, in press, 2007 [5] Hoerz, Bastien, Borg, Bradley et al., Science 314, 1716 - 1719, 2006

Levasseur-Regourd, A. C.; Lasue, J.; Hadamcik, E.; Botet, R.

2007-10-01

379

Quasi-synchronism of bursts in solar coronal structures in the Mg XII 0.84-nm line from CORONAS-F/SPIRIT experimental data  

NASA Astrophysics Data System (ADS)

Based on CORONAS-F/SPIRIT images of the Sun in the MgXII 0.84-nm line, we have performed photometric measurements and investigated the time dependence of the surface brightness for fragments of ten active regions. Continuous observations were carried out on March 3 4, 2002, for about 19 h when the satellite moved in shadowless orbits. The interval between the images was, on average, about 1 min. A time correlation has been found between the brightness variations in some pairs of high-temperature regions spaced from 10 to 106 apart. We have analyzed the statistical characteristics of the temporal distribution of bursts: the observed nonuniformity of the distribution was found to be impossible for a random Poisson process. To identify sympathetic (induced) bursts, we have studied the connections in the form of magnetic loops between active regions using CORONAS-F/SPIRIT and SOHO/EIT solar images. The most probable delays between events (X-ray bursts) in various active regions have been estimated. By assuming that the disturbance propagates along the coronal loops connecting active regions, we have estimated the propagation velocity of the disturbance, 1700 km s-1. In the period under study, the active regions in which a large number of bursts were observed lay along the periphery of a developing equatorial coronal hole. We have concluded that the simultaneous emergence of new magnetic fluxes in the photosphere was responsible for most of the quasi-synchronous events on March 3 4, 2002. We have calculated the physical conditions in coronal loops by assuming that the propagation of magnetohydrodynamic waves in the corona could be responsible for the appearance of connected events.

Akimov, L. A.; Belkina, I. L.; Kuzin, S. V.; Pertsov, A. A.; Zhitnik, I. A.

2008-12-01

380

Relaxation of the loss-cone by quasi-linear diffusion of the electron-cyclotron maser instability in the solar corona  

NASA Technical Reports Server (NTRS)

A self-consistent numeric two-dimensional code using kinetic-wave particle equations has been developed and applied to the maser dynamics of the solar corona. Time histories generated by the code reveal details of the evolution of the linear phase, the saturation and subsequent relaxation of the loss cone. Quantitative values are obtained for the saturation time, the amount of the converted free energy, the critical wave energy level for onset of maser diffusion, the velocity and pitch angle range of the resonant particles, and the relative importance of the different magnetoionic modes and harmonics. A wide range of initial conditions is covered by varying the loss-cone distribution and the ambient cold plasma parameters.

Aschwanden, Markus J.

1990-01-01

381

Solar radiative transfer simulations in Saharan dust plumes: particle shapes and 3-D effect  

NASA Astrophysics Data System (ADS)

Radiative fields of three-dimensional inhomogeneous Saharan dust clouds have been calculated at solar wavelength (0.6 ?m) by means of a Monte Carlo radiative transfer model. Scattering properties are taken from measurements in the SAMUM campaigns, from light scattering calculations for spheroids based on the MIESCHKA code, from Mie theory for spheres and from the geometric optics method assuming irregular shaped particles. Optical properties of different projected area equivalent shapes are compared. Large differences in optical properties are found especially in the phase functions. Results of radiative transfer calculations based on the Monte Carlo method are shown exemplarily for one dust cloud simulated by the cloud resolving atmospheric circulation model LM-MUSCAT-DES. Shape-induced differences in the radiation fluxes are pronounced, for example, the domain averaged normalized radiance is about 30% lower in the case of a dust plume consisting of spheroids or irregular particles compared to spheres. The effect of net horizontal photon transport (3-D effect) on the reflected radiance fields is only notable at the largest gradients in optical thickness. For example, the reflectance at low sun position differs locally about 15% when horizontal photon transport is accounted for. 'Sharp edges' due to 1-D calculations are smoothed out in the 3-D case.

Torge, Antje; Macke, Andreas; Heinold, Bernd; Wauer, Jochen

2011-09-01

382

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 coronal heating and the acceleration of the solar wind were pursued with the use of our recently developed 2D MHD solar wind code and our 1D multifluid code. In particular, we explored: (1) the role of proton temperature anisotropy in the expansion of the solar (2) the role of plasma parameters at the coronal base in the formation of high (3) a three-fluid model of the slow solar wind (4) the heating of coronal loops (5) a newly developed hybrid code for the study of ion cyclotron resonance in wind, speed solar wind streams at mid-latitudes, the solar wind.

Habbal, Shadia Rifai

2005-01-01

383

Alteration of Organic Compounds in Small Bodies and Cosmic Dusts by Cosmic Rays and Solar Radiation  

NASA Astrophysics Data System (ADS)

A wide variety of complex organic compounds have been detected in extraterrestrial bodies like carbonaceous chondrites and comets, and their roles in the generation of terrestrial life are discussed. It was suggested that organics in small bodies were originally formed in ice mantles of interstellar dusts in dense cloud. Irradiation of frozen mixture of possible interstellar molecules including CO (or CH _{3}OH), NH _{3} and H _{2}O with high-energy particles gave complex amino acid precursors with high molecular weights [1]. Such complex organic molecules were taken in planetesimals or comets in the early solar system. In prior to the generation of the terrestrial life, extraterrestrial organics were delivered to the primitive Earth by such small bodies as meteorites, comets and space dusts. These organics would have been altered by cosmic rays and solar radiation (UV, X-rays) before the delivery to the Earth. We examined possible alteration of amino acids, their precursors and nucleic acid bases in interplanetary space by irradiation with high energy photons and heavy ions. A mixture of CO, NH _{3} and H _{2}O was irradiated with high-energy protons from a van de Graaff accelerator (TIT, Japan). The resulting products (hereafter referred to as CAW) are complex precursors of amino acids. CAW, amino acids (dl-Isovaline, glycine), hydantoins (amino acid precursors) and nucleic acid bases were irradiated with continuous emission (soft X-rays to IR; hereafter referred to as soft X-rays irradiation) from BL-6 of NewSUBARU synchrotron radiation facility (Univ. Hyogo). They were also irradiated with heavy ions (eg., 290 MeV/u C ^{6+}) from HIMAC accelerator (NIRS, Japan). After soft X-rays irradiation, water insoluble materials were formed. After irradiation with soft X-rays or heavy ions, amino acid precursors (CAW and hydantoins) gave higher ratio of amino acids were recovered after hydrolysis than free amino acids. Nucleic acid bases showed higher stability than free amino acids. Complex amino acid precursors with high molecular weights could be formed in simulated dense cloud environments. They would have been altered in the early solar system by irradiation with soft X-rays from the young Sun, which caused increase of hydrophobicity of the organics of interstellar origin. They were taken up by parent bodies of meteorites or comets, and could have been delivered to the Earth by meteorites, comets and cosmic dusts. Cosmic dusts were so small that they were directly exposed to the solar radiation, which might be critical for the survivability of organics in them. In order to evaluate the roles of space dusts as carriers of bioorganic compounds to the primitive Earth, we are planning the Tanpopo Mission, where collection of cosmic dusts by using ultra low-density aerogel, and exposure of amino acids and their precursors for years are planned by utilizing the Japan Experimental Module / Exposed Facility of the ISS [2]. The mission is now scheduled to start in 2013. We thank Dr. Katsunori Kawasaki of Tokyo Institute of Technology, and Dr. Satoshi Yoshida of National Institute of Radiological Sciences for their help in particles irradiation. We also thank to the members of JAXA Tanpopo Working Group (PI: Prof. Akihiko Yamagishi) for their helpful discussion. [1] K. Kobayashi, et al., in ``Astrobiology: from Simple Molecules to Primitive Life,'' ed. by V. Basiuk, American Scientific Publishers, Valencia, CA, (2010), pp. 175-186. [2] K. Kobayashi, et al., Trans. Jpn. Soc. Aero. Space Sci., in press (2012).

Kobayashi, Kensei; Kaneko, Takeo; Mita, Hajime; Obayashi, Yumiko; Takahashi, Jun-ichi; Sarker, Palash K.; Kawamoto, Yukinori; Okabe, Takuto; Eto, Midori; Kanda, Kazuhiro

2012-07-01

384

Penetration of solar radiation into pure and Mars-dust contaminated snow  

NASA Astrophysics Data System (ADS)

Rock and soil surface layers absorb and reflect incoming solar radiation immediately at the surface. Ices on the other hand, whilst opaque in the infrared, are partially transparent in the visible spectral range. These properties are responsible for the "solid-state greenhouse effect" (SSGE), which may play an important role in the energy balance of icy surfaces in the Solar System. To model the SSGE, we need to know not only thermal properties but also optical properties such as the albedo and the absorption scale length of the ice. We have investigated the absorption scale length, also known as e-folding scale, of snow/dust mixtures within the scope of a project directed at investigating the behaviour of the martian polar caps. After measuring the e-folding scale of recrystallized snow we can now also relate the dust content of contaminated snow to the penetration depth of sunlight into the mixture. Equally important, however, is our observation that light penetration through the mixture is dramatically affected by small-scale inhomogeneities.

Kaufmann, E.; Hagermann, A.

2015-05-01

385

Spectral line width decrease in the solar corona: resonant energy conversion from Alfv{}n to acoustic waves  

E-print Network

Observations reveal an increase with height of the line width of several coronal spectral lines probably caused by outwardly propagating Alfv{\\'e}n waves. However, the spectral line width sometimes shows a sudden decrease at a height 0.1-0.2 R, where the ratio of sound to Alfven speeds may approach unity. Qualitative analysis shows that the resonant energy conversion from Alfven to acoustic waves near the region of the corona where the plasma $\\beta$ approaches unity may explain the observed spectral line width reduction.

T. V. Zaqarashvili; R. Oliver; J. L. Ballester

2007-03-13

386

Experiment with the SPR-N Instrument Onboard the CORONAS-F Satellite: Polarization, Temporal, and Spectral Characteristics of the Hard X-Ray of the Solar Flares  

NASA Astrophysics Data System (ADS)

During the experiment with a polarimeter SPR-N onboard the CORONAS-F satellite, polarization of the X-ray of solar flares within the energy ranges of 20-40, 40-60, and 60-100 keV was measured according to Thomson scattering of X-ray photons in Beryllium plates with the following registration of the scattered photons by means of a system of six scintillation detectors based on Cs I(Na). As a result of observations for the period from August 2001 till December 2005, hard X-ray radiation was registered for 128 solar flares. During the event of 29 October 2003 degree of polarization of the radiation within the channels 40-60 and 60-100 keV exceeded 70 %, and within the channel 20-40 keV50 %. Time profiles of the part of polarized radiation, orientation of the maximum polarization on the solar disc were obtained. The upper limit of the polarized radiation part for 25 events was estimated at the level of 8-40 %. For all registered flares time profiles (with resolution of up to 4 s) were registered, hard X-ray fluxes were determined, and spectrum factor was estimated. For the most powerful events which were observed during October-November 2003 and on January 20, 2005, the data on the dynamics of the characteristics of thermal and non-thermal components of X-radiation were obtained.

Zhitnik, I. A.; Logachev, Yu. I.; Bogomolov, A. V.; Bogomolov, V. V.; Denisov, Yu. I.; Kavanosyan, S. S.; Kuznetsov, S. N.; Morozov, O. V.; Myagkova, I. N.; Svertilov, S. I.; Ignatiev, A. P.; Oparin, S. N.; Pertsov, A. A.

387

Interferometry of the e corona.  

PubMed

Descriptions are given of Fabry-Perot spectrometer systems used in the total eclipses of 1965, 1966, and 1970 to observe the emission lines 5303 A, Fe XIV and 6374 A, Fe x at different points in the solar corona. Some results of coronal temperature measurements for the 12 November 1966 eclipse are presented. PMID:20094331

Henderson, G

1970-12-01

388

Remote sensing of dust in the Solar system and beyond using wavelength dependence of polarization  

NASA Astrophysics Data System (ADS)

For a long time, the main polarimetric tool to study dust in the Solar system has been the dependence of polarization on phase (scattering) angle. Surprisingly, a variety of cosmic dusts (interplanetary and cometary dust, dust on the surfaces of asteroids and in debris disks) possesses a very similar phase dependence of polarization with a negative bowl-shaped part at small phase angles and a positive bell-shaped region with maximum polarization around 95-105 deg. Numerous laboratory and theoretical simulations showed that a polarimetric phase curve of this shape is typical for fluffy materials, e.g., porous, aggregated particles. By contrast, the wavelength dependence of polarization is different for different types of dust. In the visual, polarization decreases with wavelength (negative gradient) for asteroids and interplanetary dust, but usually increases with wavelength (positive gradient) for cometary dust. In debris disks both signs of the spectral gradient of polarization have been found. Moreover, it was found that a cometary positive spectral gradient can change to a negative one as observations move to longer (near-infrared) wavelengths (Kelley et al. AJ, 127, 2398, 2004) and some comets(Kiselev et al. JQSRT, 109, 1384, 2008) have negative gradient even in the visible. The diversity of the spectral dependence of polarization therefore gives us hope that it can be used for characterization of the aggregates that represent different types of cosmic dust. To accomplish this, the physics behind the spectral dependence of polarization need to be revealed. Our recent study shows that the spectral dependence of polarization depends on the strength of electromagnetic interaction between the monomers in aggregates. The strength of the interaction mainly depends on how many monomers the electromagnetic wave covers on the light path equal to one wavelength. Since the electromagnetic interaction depolarizes the light, the more particles a single wavelength covers the smaller is the polarization of the scattered light. Thus, at a given monomer size the polarization decreases as wavelength increases resulting in the negative spectral gradient of polarization. However, this tendency occurs only for rather compact aggregates. For porous particles, an increase of wavelength may not increase the number of the covered monomers. In this case, polarization increases with wavelength as a result of decreasing monomer's size parameter. We performed computer modeling of light scattering by aggregates of different porosity using MSTM (multisphere T-matrix) code by D. Mackowski (see http://eng.auburn.edu/users/dmckwski/scatcodes/). The results show that for each porosity a critical wavelength exists at which the spectral gradient of polarization changes from positive to negative. The electromagnetic interaction is also stronger for more transparent materials which in turn affects the value of the critical wavelength. Thus, measurements of polarization over a broad range of wavelength can be a powerful tool to study the porosity and composition of dust in a variety of cosmic environments, especially when detailed phase dependence of polarization cannot be established (e.g. for TNO and other distant objects).

Kolokolova, L.

2011-12-01

389

Laboratory Drop Towers for the Experimental Simulation of Dust-aggregate Collisions in the Early Solar System  

NASA Astrophysics Data System (ADS)

For the purpose of investigating the evolution of dust aggregates in the early Solar System, we developed two vacuum drop towers in which fragile dust aggregates with sizes up to ~10 cm and porosities up to 70% can be collided. One of the drop towers is primarily used for very low impact speeds down to below 0.01 m/sec and makes use of a double release mechanism. Collisions are recorded in stereo-view by two high-speed cameras, which fall along the glass vacuum tube in the center-of-mass frame of the two dust aggregates. The other free-fall tower makes use of an electromagnetic accelerator that is capable of gently accelerating dust aggregates to up to 5 m/sec. In combination with the release of another dust aggregate to free fall, collision speeds up to ~10 m/sec can be achieved. Here, two fixed high-speed cameras record the collision events. In both drop towers, the dust aggregates are in free fall during the collision so that they are weightless and match the conditions in the early Solar System.

Blum, Jrgen; Beitz, Eike; Bukhari, Mohtashim; Gundlach, Bastian; Hagemann, Jan-Hendrik; Heielmann, Daniel; Kothe, Stefan; Schrpler, Rainer; von Borstel, Ingo; Weidling, Ren

2014-06-01

390

Laboratory drop towers for the experimental simulation of dust-aggregate collisions in the early solar system.  

PubMed

For the purpose of investigating the evolution of dust aggregates in the early Solar System, we developed two vacuum drop towers in which fragile dust aggregates with sizes up to ~10 cm and porosities up to 70% can be collided. One of the drop towers is primarily used for very low impact speeds down to below 0.01 m/sec and makes use of a double release mechanism. Collisions are recorded in stereo-view by two high-speed cameras, which fall along the glass vacuum tube in the center-of-mass frame of the two dust aggregates. The other free-fall tower makes use of an electromagnetic accelerator that is capable of gently accelerating dust aggregates to up to 5 m/sec. In combination with the release of another dust aggregate to free fall, collision speeds up to ~10 m/sec can be achieved. Here, two fixed high-speed cameras record the collision events. In both drop towers, the dust aggregates are in free fall during the collision so that they are weightless and match the conditions in the early Solar System. PMID:24962693

Blum, Jrgen; Beitz, Eike; Bukhari, Mohtashim; Gundlach, Bastian; Hagemann, Jan-Hendrik; Heielmann, Daniel; Kothe, Stefan; Schrpler, Rainer; von Borstel, Ingo; Weidling, Ren

2014-01-01

391

Laboratory Drop Towers for the Experimental Simulation of Dust-aggregate Collisions in the Early Solar System  

PubMed Central

For the purpose of investigating the evolution of dust aggregates in the early Solar System, we developed two vacuum drop towers in which fragile dust aggregates with sizes up to ~10 cm and porosities up to 70% can be collided. One of the drop towers is primarily used for very low impact speeds down to below 0.01 m/sec and makes use of a double release mechanism. Collisions are recorded in stereo-view by two high-speed cameras, which fall along the glass vacuum tube in the center-of-mass frame of the two dust aggregates. The other free-fall tower makes use of an electromagnetic accelerator that is capable of gently accelerating dust aggregates to up to 5 m/sec. In combination with the release of another dust aggregate to free fall, collision speeds up to ~10 m/sec can be achieved. Here, two fixed high-speed cameras record the collision events. In both drop towers, the dust aggregates are in free fall during the collision so that they are weightless and match the conditions in the early Solar System. PMID:24962693

Blum, Jrgen; Beitz, Eike; Bukhari, Mohtashim; Gundlach, Bastian; Hagemann, Jan-Hendrik; Heielmann, Daniel; Kothe, Stefan; Schrpler, Rainer; von Borstel, Ingo; Weidling, Ren

2014-01-01

392

On realistic size equivalence and shape of spheroidal Saharan mineral dust particles applied in solar and thermal radiative transfer calculations  

NASA Astrophysics Data System (ADS)

Realistic size equivalence and shape of Saharan mineral dust particles are derived from on in-situ particle, lidar and sun photometer measurements during SAMUM-1 in Morocc