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1

The colour of the solar corona and dust grains in it  

NASA Astrophysics Data System (ADS)

The paper examines the photometry of coronal color negatives and determines the distribution of the coronal brightness in the red, green, and blue wavelength intervals up to distances of 6-7 solar radii. A correlation between the color indexes and diffuse external reinforcement brightness (RED) is indicated, and the results show that RED consists of dust grains with radii of at least 1 micron. It is concluded that the whole dust mass of RED is at least 1% of the coronal mass within the RED region, and the dust grain number density is about 10 to the -11th power/cu cm.

Aimanov, A. K.; Nikolskii, G. M.

1980-02-01

2

Solar corona heating  

Microsoft Academic Search

Despite of the large number of models and mechanisms proposed in the literature, the problem of the heating of the solar corona is still unsolved and represents one of the challenge of solar physics. In this context, a basic question to be addressed by any viable theoretical model concerns understanding the mechanism capable of transferring ``efficiently'' the energy from the

Francesco Califano

2000-01-01

3

Heating of the solar corona  

Microsoft Academic Search

The suggestion is advanced that heating of the solar corona results from Landau damping of ion-acoustic waves generated in the motion of photospheric granules. Laboratory experiments relevant to the question of corona heating are discussed, together with the available observational information on the extent of energy deposition in the corona.

N. D'Angelo

1969-01-01

4

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

5

A physical mechanism of solar corona heating  

Microsoft Academic Search

Time profiles of solar soft X-ray microflares and structure soft X-ray solar corona thermal background are studied on RHESSI data. The observations of 2003 year are analyzed. Decrease fluxe of solar soft X-ray microflares and thermal background of solar corona in the X-ray range 2-15 kev are revealed. The new model of solar corona heating in based on this new

I. K. Mirzoeva

2011-01-01

6

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 brightness temperature at 10.7 cm: Tb 10 000 K. #12;Petrovay: Solar physics Chromosphere and corona Mean temperature profile: VAL model atmosphere, based on lines #12;Petrovay: Solar physics Chromosphere and corona

Petrovay, Kristóf

7

Solar corona electron density distribution  

NASA Technical Reports Server (NTRS)

The paper discusses the three and one-half months of single-frequency time delay data which were acquired from the Helios 2 spacecraft around the time of its solar occultation. The excess time delay due to integrated effect of free electrons along the signal's ray path could be separated and modeled following the determination of the spacecraft trajectory. An average solar corona and equatorial electron density profile during solar minimum were deduced from the time delay measurements acquired within 5-60 solar radii of the sun. As a point of reference at 10 solar radii from the sun, an average electron density was 4500 el/cu cm. However, an asymmetry was found in the electron density as the ray path moved from the west to east solar limb. This may be related to the fact that during entry into occultation the heliographic latitude of the ray path was about 6 deg, while during exit it was 7 deg. The Helios density model is compared with similar models deduced from different experimental techniques.

Esposito, P. B.; Edenhofer, P.; Lueneburg, E.

1980-01-01

8

Global Magnetohydrodynamic Modeling of the Solar Corona.  

National Technical Information Service (NTIS)

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 ...

J. A. Linker

1997-01-01

9

Global Magnetohydrodynamic Modeling of the Solar Corona.  

National Technical Information Service (NTIS)

This report describes the progress made in the investigation of the solar corona using magnetohydrodynamic (MHD) simulations. Coronal mass ejections (CME) are believed to be the primary cause of nonrecurrent geomagnetic storms and these have been investig...

J. A. Linker

2001-01-01

10

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, hot magnetized plasma (Cranmer et al., 2008) An important measurement: perpendicular heating F corona solar corona 1919 eclipse photo, Sobral 1571, Caron #12;The solar corona Coronal structure often

11

Global Magnetohydrodynamic Modeling of the Solar Corona  

NASA Technical Reports Server (NTRS)

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

Linker, Jon A.

1998-01-01

12

Hot Plasma Flows in the Solar Corona  

NASA Astrophysics Data System (ADS)

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

Shibasaki, K.

2012-12-01

13

The quiescent corona and slow solar wind  

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

14

Plasma Diagnostics of the Solar Corona Using Decimetric Radio Waves  

E-print Network

process may have different forms. Are they enough to heat the solar corona? The answer seems to become electric currents, must also be con­ sidered. The heating problem of the solar corona can only be solved. Plasma Diagnostics of the Solar Corona Using Decimetric Radio Waves (Review) Arnold O. Benz

15

Solar corona heating by kinetic Alfven waves  

Microsoft Academic Search

The nonlinear mechanism of the kinetic Alfven waves (KAW) generation in the solar corona with small plasma parameter beta <<1 is investigated. The parametric instability, where the magnetosound wave (MSW) is the pump wave, is considered as the generation mechanism,. Using a two-fluid magnetohydrodynamics and Maxwell's equation, we derive a nonlinear dispersion relation governing this three-wave interaction process and the

A. D. Voitsekhovskaia; V. N. Fedun; A. K. Yukhimuk

2004-01-01

16

Global Magnetohydrodynamic Modeling of the Solar Corona  

NASA Technical Reports Server (NTRS)

This report describes the progress made in the investigation of the solar corona using magnetohydrodynamic (MHD) simulations. Coronal mass ejections (CME) are believed to be the primary cause of nonrecurrent geomagnetic storms and these have been investigated through the use of three-dimensional computer simulation.

Linker, Jon A.

2001-01-01

17

The Heating of the Solar Corona by Kink Instabilities.  

E-print Network

??The million-degree temperature of the solar corona might be due to the combined effectof barely distinguishable energy releases, called nanoflares, that occur throughoutthe solar atmosphere. (more)

Bareford, Michael

2012-01-01

18

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

19

Nanoflare Heating of Solar and Stellar Coronae  

NASA Technical Reports Server (NTRS)

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

Klimchuk, James A.

2010-01-01

20

Meteoroids in solar corona and planetary atmospheres  

Microsoft Academic Search

We simulate the meteoroid entry into the solar corona with a model similar to the one-dimensional ablation model developed by Campbell-Brown and Koschny (2004) for the Earth's atmosphere and by McAuliffe and Christou (2005) for the case of the atmosphere of Venus. We present the results of mass deposition profiles for a wide range of masses for objects falling into

Herve Lamy; Ingrid Mann; Emeritus Joseph Lemaire

2010-01-01

21

Radio seismology of the outer solar corona  

NASA Astrophysics Data System (ADS)

Observed oscillations of coronal loops in extreme ultraviolet (EUV) lines have been successfully used to estimate plasma parameters in the inner corona (< 0.2R0, where R0 is the solar radius). However, coronal seismology in EUV lines fails for higher altitudes because of rapid decrease in line intensity. We aim to use radio observations to estimate the plasma parameters of the outer solar corona (> 0.2R0). We used the large Ukrainian radio telescope URAN-2 to observe type IV radio bursts at the frequency range of 8-32 MHz during the time interval of 09:50-12:30 UT on April 14, 2011. The burst was connected to C2.3 flare, which occurred in AR 11190 during 09:38-09:49 UT. The dynamic spectrum of radio emission shows clear quasi-periodic variations in the emission intensity at almost all frequencies. Wavelet analysis at four different frequencies (29 MHz, 25 MHz, 22 MHz, and 14 MHz) shows the quasi-periodic variation of emission intensity with periods of ~ 34 min and ~ 23 min. The periodic variations can be explained by the first and second harmonics of vertical kink oscillation of transequatorial coronal loops, which were excited by the same flare. The apex of transequatorial loops may reach up to 1.2 R0 altitude. We derive and solve the dispersion relation of trapped magnetohydrodynamic (MHD) oscillations in a longitudinally inhomogeneous magnetic slab. The analysis shows that a thin (with width to length ratio of 0.1), dense (with the ratio of internal and external densities of ? 20) magnetic slab with weak longitudinal inhomogeneity may trap the observed oscillations. Seismologically estimated Alfvn speed inside the loop at the height of ~ 1 R0 is ~ 1000 km s-1. The magnetic field strength at this height is estimated as ~ 0.9 G. Extrapolation of magnetic field strength to the inner corona gives ~ 10 G at the height of 0.1 R0. Radio observations can be successfully used for the sounding of the outer solar corona, where EUV observations of coronal loops fail. Therefore, radio seismology of the outer solar corona is complementary to EUV seismology of the inner corona. The research leading to these results has received funding from the Austrian 'Fonds zur Frderung der wissenschaftlichen Forschung' under project P24740-N27.

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

2014-05-01

22

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

23

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

24

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

25

RADIATIVE HEATING OF THE SOLAR CORONA  

SciTech Connect

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

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

2011-10-20

26

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

27

Probing the Solar Corona with Radio Ranging Measurements  

NASA Technical Reports Server (NTRS)

An asymmetry in the radial variation of electron density above the east and west limbs of the Sun was inferred from centimeter wavelength ranging measurements conducted by Voyager 2 during its 1985 solar conjunction. The Voyager 2 ranging measurements are compared with the Mauna Loa Solar Observatory white-light coronagraph measurements of the underlying corona. Corona probing abilities are summarized.

Woo, R.

1995-01-01

28

Shock Acceleration in the Solar Corona  

NASA Astrophysics Data System (ADS)

In this thesis acceleration of energetic particles at collisionless shock waves in space plasmas is studied using numerical simulations, with an emphasis on physical conditions applicable to the solar corona. The thesis consists of four research articles and an introductory part that summarises the main findings reached in the articles and discusses them with respect to theory of diffusive shock acceleration and observations. This thesis gives a brief review of observational properties of solar energetic particles and discusses a few open questions that are currently under active research. For example, in a few large gradual solar energetic particle events the heavy ion abundance ratios and average charge states show characteristics at high energies that are typically associated with flare-accelerated particles, i.e. impulsive events. The role of flare-accelerated particles in these and other gradual events has been discussed a lot in the scientific community, and it has been questioned if and how the observed features can be explained in terms of diffusive shock acceleration at shock waves driven by coronal mass ejections. The most extreme solar energetic particle events are the so-called ground level enhancements where particle receive so high energies that they can penetrate all the way through Earth's atmosphere and increase radiation levels at the surface. It is not known what conditions are required for acceleration into GeV/nuc energies, and the presence of both very fast coronal mass ejections and X-class solar flares makes it difficult to determine what is the role of these two accelerators in ground level enhancements. The theory of diffusive shock acceleration is reviewed and its predictions discussed with respect to the observed particle characteristics. We discuss how shock waves can be modeled and describe in detail the numerical model developed by the author. The main part of this thesis consists of the four scientific articles that are based on results of the numerical shock acceleration model developed by the author. The novel feature of this model is that it can handle complex magnetic geometries which are found, for example, near active regions in the solar corona. We show that, according to our simulations, diffusive shock acceleration can explain the observed variations in abundance ratios and average charge states, provided that suitable seed particles and magnetic geometry are available for the acceleration process in the solar corona. We also derive an injection threshold for diffusive shock acceleration that agrees with our simulation results very well, and which is valid under weakly turbulent conditions. Finally, we show that diffusive shock acceleration can produce GeV/nuc energies under suitable coronal conditions, which include the presence of energetic seed particles, a favourable magnetic geometry, and an enhanced level of ambient turbulence.

Sandroos, Arto

2010-03-01

29

Exploring dynamic events in the solar corona  

NASA Astrophysics Data System (ADS)

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

Downs, Cooper James

30

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

31

Indian Solar mission to study inner solar corona: Aditya 1  

NASA Astrophysics Data System (ADS)

Aditya-I is India's first dedicated scientific mission to study the sun. This is a low-earth orbit (LEO) mission at an altitude of 800 km. A visible emission line space solar coronagraph (VELC) has been selected as a payload under the small-satellite program of ISRO. It will provide high time cadence sharp images of the solar corona in the Green and Red Emission lines. These images will be used to study the highly dynamic nature of the solar corona including the small-scale coronal loops and large-scale Coronal Mass Ejections (CMEs). The uniqueness of this payload compared to previously flown space instruments are: (a) Observations in the visible wavelength closer to the disk (down to 1.05 solar radii), (b) high time cadence capability (better than 2-images per second), and (c) Simultaneous observations of at least two spectral windows all the time and three spectral windows for short durations. I will update the current status of the project and will point out the complimentary role Aditya can play in conjunction with other solar big missions like SDO.

Singh, Jagdev; Banerjee, Dipankar; Venkatakrishnan, Parameswaran; Kasiviswanathan, Sankarasubramanian; Prasad B, Raghavendra

2012-07-01

32

ENERGY DISTRIBUTION OF MICROEVENTS IN THE QUIET SOLAR CORONA Arnold O. Benz  

E-print Network

of information on the heating process of the corona. Subject headings: Sun: activity -- Sun: corona -- Sun: flares -- Sun: X-rays, gamma rays 1. INTRODUCTION The heating of the solar corona has been a riddle sinceENERGY DISTRIBUTION OF MICROEVENTS IN THE QUIET SOLAR CORONA Arnold O. Benz Institute of Astronomy

33

Nonlinear Plasma Physics of the Solar Corona Eric R Priest  

E-print Network

Nonlinear Plasma Physics of the Solar Corona Eric R Priest Mathematics Institute, St Andrews of some recent ideas in solar coronal plasma physics. In particular we discuss some models of coronal plasma physics seemed so complex, I decided to focus on the simpler area of MHD. Dennis on the other hand

Priest, Eric

34

Synoptic, Global Mhd Model For The Solar Corona  

Microsoft Academic Search

The common techniques for mimic the solar corona heating and the solar wind acceleration in global MHD models are as follow. 1) Additional terms in the momentum and energy equations derived from the WKB approximation for the Alfv'en wave turbulence; 2) some empirical heat source in the energy equation; 3) a non-uniform distribution of the polytropic index, gamma, used in

Ofer Cohen; I. V. Sokolov; I. I. Roussev; T. I. Gombosi

2007-01-01

35

Energy Distribution of Heating Processes in the Quiet Solar Corona  

Microsoft Academic Search

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

Saem Krucker; Arnold O. Benz

1998-01-01

36

Probing the Solar Corona with Radio Ranging Measurements  

NASA Technical Reports Server (NTRS)

An asymmetry in the radial variation of electron density above the east and west limbs of the Sun was inferred from centimeter wavelength ranging measurements conducted by Voyager 2 during its 1985 solar conjunction. These older data are compared with white- light coronagraph measurements of the underlying corona collected by the Mark III K-coronameter at the Mauna Loa Solar Observatory.

Woo, R.

1995-01-01

37

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

38

How is the Solar Corona Heated ?  

Microsoft Academic Search

Trying to determine which mechanisms are heating the corona is one of the main aims of the SOHO mission. A summary is given of the mechanisms that have been proposed together with the observational properties that have so far been determined. A new technique for determining the heating mechanisms is presented together with the results from applying it to Yohkoh

Eric R. Priest

1997-01-01

39

Heating of the Solar Corona by Dissipative Alfven Solitons K. Stasiewicz*  

E-print Network

Heating of the Solar Corona by Dissipative Alfve´n Solitons K. Stasiewicz* Swedish Institute locally to heat particles in the solar corona [5]. During the past 50 years there have been many attempts aspects of electromagnetic energy dissipa- tion and heating in the solar corona and in planetary

Stasiewicz, Krzysztof

40

How Accurately Can We Determine the Coronal Heating Mechanism in the Large-Scale Solar Corona ?  

E-print Network

How Accurately Can We Determine the Coronal Heating Mechanism in the Large-Scale Solar Corona ? D of the coronal heating mechanism in the large-scale solar corona was considered. The authors compared that turbulent reconnection is a likely method to heat the large-scale solar corona. Here we reconsider

Mackay, Duncan

41

Total light flux and colour of solar corona  

NASA Astrophysics Data System (ADS)

Measurements were made of the light flux and color of the corona in 1.03-6.0 solar radii with a multiple-band electrophotometer. The effective wavelengths of the instrument are 450, 555, 650 and 940. In one of them, the 555 band, the spectral rresponse defines a system that is in close agreement with the spectral response of the human eye. The results of the measurements are as follows: (1) the total light flux of the corona Lc is equal to 1.23 times 10 to the minus 7th power L(Solar); (2) in 555, 650 and 940 bands, there is no color difference between the corona and the photosphere.

Hao, Y.

42

ENERGY DISTRIBUTION OF MICROEVENTS IN THE QUIET SOLAR CORONA Arnold O. Benz  

E-print Network

of information on the heating process of the corona. Subject headings: Sun: activity --- Sun: corona --- Sun: flares --- Sun: X­rays, gamma rays 1. INTRODUCTION The heating of the solar corona has been a riddle nonstationary heating process. In the quiet corona on which we concentrate here, small brightenings above

43

Solar Wind Speed Charged Dust  

NASA Astrophysics Data System (ADS)

The correlation of the occurrence of magnetic disturbances, known as interplanetary field enhancements (IFEs), with the asteroid 2201 Oljato can only be explained as the interaction with charged dust in the asteroid's orbit, because the events occurred both before and after alignment with the asteroid. These single spacecraft observations did not determine how fast the dust was accelerated, or if they were affected at all by the solar wind. Shortly after STEREO A and B were launched, an IFE crossed the two spacecraft as well as ACE and Wind. This four-spacecraft configuration allowed us to determine that the disturbance was moving radially outward at 700 km/s, the solar wind speed. The conventional wisdom is that only the smallest dust particles can be affected by the solar wind, but examination of periods on STEREO when the spacecraft is being sprayed with multiple beta-meteoroid strikes shows no obvious correlation. Further, the IFEs are much less frequent than the "beta-meteoroid" impacts. Hence, it is possible that IFEs are associated with much larger dust particles, perhaps 1 micron-sized dust. If true, then those particles may be very dangerous albeit rare, possessing about 104 ergs.

Russell, C. T.; Weimer, D.; Jian, L. K.; Luhmann, J. G.; Omidi, N.

2009-04-01

44

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

45

Gas-magnetic field interactions in the solar corona  

Microsoft Academic Search

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

G. W. Pneuman; Roger A. Kopp

1971-01-01

46

Observation of Alfven Waves in the Solar Corona (Invited)  

NASA Astrophysics Data System (ADS)

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

Tomczyk, S.

2013-12-01

47

Electron heat flow in the solar corona: Implications of non-Maxwellian velocity distributions, the solar gravitational  

E-print Network

Electron heat flow in the solar corona: Implications of non-Maxwellian velocity distributions of such nonlocal heat flow for electrons in the solar corona, comparing a new analytical theory to numerical of coronal heating mechanisms. INDEX TERMS: 7509 Solar Physics, Astrophysics, and Astronomy: Corona; 7859

Scudder, Jack

48

BINARY RECONNECTION AND THE HEATING OF THE SOLAR CORONA E. R. Priest  

E-print Network

BINARY RECONNECTION AND THE HEATING OF THE SOLAR CORONA E. R. Priest School of Mathematics heating among the magnetic field lines that spread from these fragments into the solar corona. We suggest in driving reconnection (e.g., Priest & Forbes 2000), and therefore heating, in the overlying corona

Priest, Eric

49

Heating Events in the Quiet Solar Corona Arnold O. Benz and Sam Krucker  

E-print Network

Heating Events in the Quiet Solar Corona Arnold O. Benz and S¨am Krucker Institute of Astronomy for heating (Shimizu et al. 1994). In the quiet corona (excluding active regions and coronal holes per second over the whole Sun. Their estimated energy #12; Heating Events in the Quiet Solar Corona 3

50

ON PLASMA KINETIC MODEL OF A 3D SOLAR CORONA AND SOLAR WIND AT HELIOSPHERIC SHEET  

Microsoft Academic Search

The dynamical solar corona in 3D consists of transient type magnetic island elements and radial type magnetic flux rope structures in a heliospheric sheet. During the formation and relaxation these elements produce inductive elec- tromagnetic fields where energetic particles are produced. We study the 3D corona formation in the kinetic approach and parameterize it like a hot current-carrying collisionless plasma

V. M. GUBCHENKO; M. L. KHODACHENKO; H. K. BIERNAT

51

A study of inner solar corona during total solar eclipse of October 24, 1995.  

NASA Astrophysics Data System (ADS)

An experiment to study the intensity variations in the inner corona was setup at Kalpi, in Uttar Pradesh, during the total solar eclipse of October 24, 1995. The details of the experiment and the preliminary results are presented.

Saxena, A. K.; Cowsik, R.; Lancelot, J. P.; Samson, J. P. A.; Bagare, S. P.; Ismail, R.

52

Weak Compressible Magnetohydrodynamic Turbulence in the Solar Corona  

SciTech Connect

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

Chandran, Benjamin D.G. [Space Science Center and Department of Physics, University of New Hampshire, Durham, New Hampshire 03824 (United States)

2005-12-31

53

The transformation of MHD Alfvn waves and solar corona heating  

Microsoft Academic Search

One of the most interesting phenomena appearances on the Sun is the high temperature of the solar corona, which reaches 10^6 K (compared with 510^3 K at the level of the photosphere). To maintain such a high temperature and compensate for radiative cooling, the constant inflow of energy is needed. The necessary energy is considered to be carried by Alfvn

A. D. Voitsekhovska; A. K. Yukhimuk

2006-01-01

54

Weak compressible magnetohydrodynamic turbulence in the solar corona  

E-print Network

This Letter presents a calculation of the power spectra of weakly turbulent Alfven waves and fast magnetosonic waves ("fast waves") in low-beta plasmas. It is shown that three-wave interactions transfer energy to high-frequency fast waves and, to a lesser extent, high-frequency Alfven waves. MHD turbulence is thus a promising mechanism for producing the high-frequency waves needed to explain the anisotropic heating of minor ions in the solar corona.

Benjamin D. G. Chandran

2005-11-21

55

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

56

The Structure and Dynamics of the Solar Corona  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

57

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

58

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

59

Differential Rotation of the Ultraviolet Corona at Solar Maximum  

NASA Astrophysics Data System (ADS)

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

Mancuso, Salvatore; Giordano, Silvio

2011-03-01

60

Magnetic tornadoes as energy channels into the solar corona.  

PubMed

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

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

2012-06-28

61

Atomic Data for Solar Corona Studies  

SciTech Connect

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

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

2011-05-11

62

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

SciTech Connect

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

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

2012-08-10

63

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

64

HEATING EVENTS IN THE QUIET SOLAR CORONA ARNOLD O. BENZ and SM KRUCKER  

E-print Network

HEATING EVENTS IN THE QUIET SOLAR CORONA ARNOLD O. BENZ and S?M KRUCKER Institute of Astronomy, ETH originating in the corona are presented. The thermal radiation of the quiet corona is found to fluctutate that the brightenings are caused by additional plasma injected from below and heated to slightly higher temperature than

65

Joule Heating and Anomalous Resistivity in the Solar Corona  

E-print Network

Recent radioastronomical observations of Faraday rotation in the solar corona can be interpreted as evidence for coronal currents, with values as large as $2.5 \\times 10^9$ Amperes (Spangler 2007). These estimates of currents are used to develop a model for Joule heating in the corona. It is assumed that the currents are concentrated in thin current sheets, as suggested by theories of two dimensional magnetohydrodynamic turbulence. The Spitzer result for the resistivity is adopted as a lower limit to the true resistivity. The calculated volumetric heating rate is compared with an independent theoretical estimate by Cranmer et al (2007). This latter estimate accounts for the dynamic and thermodynamic properties of the corona at a heliocentric distance of several solar radii. Our calculated Joule heating rate is less than the Cranmer et al estimate by at least a factor of $3 \\times 10^5$. The currents inferred from the observations of Spangler (2007) are not relevant to coronal heating unless the true resistivity is enormously increased relative to the Spitzer value. However, the same model for turbulent current sheets used to calculate the heating rate also gives an electron drift speed which can be comparable to the electron thermal speed, and larger than the ion acoustic speed. It is therefore possible that the coronal current sheets are unstable to current-driven instabilities which produce high levels of waves, enhance the resistivity and thus the heating rate.

Steven R. Spangler

2008-12-22

66

Joule Heating and Anomalous Resistivity in the Solar Corona  

E-print Network

Recent radioastronomical observations of Faraday rotation in the solar corona can be interpreted as evidence for coronal currents, with values as large as $2.5 \\times 10^9$ Amperes (Spangler 2007). These estimates of currents are used to develop a model for Joule heating in the corona. It is assumed that the currents are concentrated in thin current sheets, as suggested by theories of two dimensional magnetohydrodynamic turbulence. The Spitzer result for the resistivity is adopted as a lower limit to the true resistivity. The calculated volumetric heating rate is compared with an independent theoretical estimate by Cranmer et al (2007). This latter estimate accounts for the dynamic and thermodynamic properties of the corona at a heliocentric distance of several solar radii. Our calculated Joule heating rate is less than the Cranmer et al estimate by at least a factor of $3 \\times 10^5$. The currents inferred from the observations of Spangler (2007) are not relevant to coronal heating unless the true resistivi...

Spangler, Steven R

2008-01-01

67

MAGNETIC RECONNECTION AND ENERGY RELEASE IN THE SOLAR CORONA BY TAYLOR RELAXATION  

E-print Network

) Abstract.The heating ofthe solar corona by resistiveturbulenceofcoronal magneticfieldsis consideredMAGNETIC RECONNECTION AND ENERGY RELEASE IN THE SOLAR CORONA BY TAYLOR RELAXATION G. E. VEKSTEIN plays a dominant role in heating the solar coronal plasma to high temperatures. Energy from convective

Priest, Eric

68

Diagnosing the Prominence-Cavity Connection in the Solar Corona  

NASA Astrophysics Data System (ADS)

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

Schmit, D. J.

69

The EUV Emission in Comet-Solar Corona Interactions  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

70

Dust mitigation for Mars solar arrays  

Microsoft Academic Search

Settling of atmospheric dust onto the surface of the solar array is potentially a lifetime-limiting factor for a power system on any Mars mission. For long-term operation of arrays on Mars, it will be necessary to develop techniques to remove deposited dust. Dust is expected to adhere to the array by Van der Waals adhesive forces. These forces are quite

G. A. Landis; P. P. Jenkins

2002-01-01

71

Dust obscuration of Mars solar arrays  

Microsoft Academic Search

The atmosphere of Mars contains a considerable amount of suspended dust. Over a period of time, this dust will settle out of the atmosphere and deposit onto the surfaces of solar arrays, resulting in degradation of performance. This paper attempts to quantify the amount of dust coverage expected and the amount of performance lost, using available data on Martian conditions.

Geoffrey A. Landis

1996-01-01

72

Dust Mitigation for Mars Solar Arrays  

NASA Technical Reports Server (NTRS)

Settling of atmospheric dust onto the surface of the solar array is potentially a lifetime-limiting factor for a power system on any Mars mission. For long-term operation of arrays on Mars, it will be necessary to develop techniques to remove deposited dust. Dust is expected to adhere to the array by Van der Waals adhesive forces. These forces are quite strong at the dust particle sizes expected. Dust removal methods must overcome this force. Removal methods can be categorized briefly into four categories: natural, mechanical, electromechanical, and electrostatic. The environment of Mars is expected to be an ideal one for use of electrostatic dust-removal techniques.

Landis, Geoffrey A.; Jenkins, Phillip P.

2002-01-01

73

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

74

Solar Explosive Events: Nanoflares and Their Potential to Heat the Solar Corona  

Microsoft Academic Search

The question of how the solar corona is heated is one of the more interesting aspects of solar physics. One theory is that small reconnective events (nanoflares) are responsible for coronal heating, but it has not yet been demonstrated that such small events heat plasma to cornal temperatures. To address this issue, we used active region observations from SUMER to

A. Updike; A. Winebarger; K. Reeves

2001-01-01

75

Evidence for Flux Ropes in the Solar Corona  

NASA Astrophysics Data System (ADS)

Although twisted magnetic flux ropes are clearly ejected from the Sun, as demonstrated by LASCO and EIT movies of erupting prominences, there has been some controversy about whether flux ropes exist in the corona before ejection. It has been argued that they are formed only upon ejection. The issue is important because of the need to understand how eruptions are initiated. Now a clearer picture of solar flux ropes is emerging with recent high-resolution observations of solar filaments. Filament's twist and writhe are frequently detectable even when they do not escape the Sun. The observations of November 1, 2001 and May 27, 2002 made by the TRACE solar telescope both appear to show the sudden eruption without ejection of a filament, with transformation of some internal twist into a writhe of approx. + 1. Since magnetic helicity is approximately conserved, even in these rapid events, it follows that these kink events are strong evidence that flux ropes are present in the corona. We suggest that a flux rope may undergo several kink instabilities before it is ejected from the Sun. We identify coronal X-ray sigmoids as the aftermath of these sudden kink events. NASA supported this work under grant NAG5-11584.

Rust, D. M.

2003-05-01

76

David Elijah Packer: cluster variables, meteors and the solar corona  

E-print Network

David Elijah Packer (1862-1936), a librarian by profession, was an enthusiastic amateur astronomer who observed from London and Birmingham. He first came to the attention of the astronomical community in 1890 when he discovered a variable star in the globular cluster M5, only the second periodic variable to be discovered in a globular cluster. He also observed meteors and nebulae, on one occasion reporting a brightening in the nucleus of the galaxy M77. However, his remarkable claims in 1896 that he had photographed the solar corona in daylight were soon shown to be flawed.

Shears, Jeremy

2014-01-01

77

Binary Reconnection and the Heating of the Solar Corona E.R. PRIEST  

E-print Network

Binary Reconnection and the Heating of the Solar Corona E.R. PRIEST School of Mathematics surface are likely to drive magnetic reconnection and therefore heating amongst the magnetic #12;eld lines that spread from these fragments into the solar corona. We suggest that the fundamental mechanism is one

Priest, Eric

78

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

79

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

80

A study of the expansin of the solar corona with radiation heat flux  

Microsoft Academic Search

The expansion of the solar corona, with the aid of hydrodynamic blast wave theory using the concept of the Roche model, is studied here when both the solar gravity and radiation heat flux are taken into consideration.

J. B. Bhowmick

1980-01-01

81

Coronagraphic observations and analyses of the ultraviolet solar corona  

NASA Technical Reports Server (NTRS)

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

Kohl, John L.

1994-01-01

82

3D Simulations of the Solar Corona using Octree Compression  

NASA Astrophysics Data System (ADS)

We present a new powerful tool to simulate the streamer belt of the solar corona based on forward modeling. It takes into account the temporal evolution of the corona and provides both qualitative and quantitative results. Starting from the National Solar Observatory photospheric magnetograms, the position of the neutral line at the source surface (2.5 Rsun) is caculated using the potential field source surface model. The plasma sheet of the streamer belt is centered around the current sheet represented as the radial extension of the neutral line. The 3D electron density is represented with octree compression and the radiance images are computed by a ray-tracing algorithm implementing the Thomson scattering. A multi-octree method allows to simulate the temporal evolution of the streamer belt and to compute the synoptic maps from time-series of generated images. The comparison between the synoptic maps of the streamer belt obtained with the SOHO/LASCO-C2 coronagraph and the simulated synoptic maps constructed from our model shows a global agreement for both radiance profiles and global behaviour of the streamer and confirms earlier findings by Wang et al. (1997) that the streamers are associated with folds in the plasma sheet. However, some features cannot be explained using this method and are interpreted by introducing two types of large-scale structures. Our results suggest that the potential field source surface model is not fully adequate for the description of the fine structure of the streamer belt, even during the time of low solar activity. We present new applications of our method to future coronographic observations with SECCHI/COR-2 on STEREO and SILC on Solar Orbiter.

Saez, F.; Lamy, P.; Llebaria, A.

83

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

84

DRIVEN WAVES AS A DIAGNOSTICS TOOL IN THE SOLAR CORONA  

SciTech Connect

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

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

2009-10-01

85

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

86

A nanoflare heating model for the quiet solar corona  

E-print Network

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

U. Mitra-Kraev; A. O. Benz

2001-04-12

87

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

2006-09-21

88

Turbulence Transport and Dissipation in the Lower Solar Corona  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

89

Latitudinal and Radial Variation of Solar Corona Rotation at Solar Minimum  

Microsoft Academic Search

The rotation of the solar corona at different heliolatitudes from 1.5 to 3.0 Rsolar from Sun center has been studied at solar minimum from the reconstructed intensity time series of the O VI 1032 and H I Lyalpha l216 spectral lines and visible light polarized brightness obtained by the observations of UVCS\\/SOHO instrument. The time period analyzed range

S. Giordano; S. Mancuso; M. Romoli

2007-01-01

90

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

Microsoft Academic Search

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

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

2001-01-01

91

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

E-print Network

heating, but for particle acceleration in solar flares as well [15,16]. The MHD momentum and induction explanation for the anisotropic heating of minor ions in the solar corona. DOI: 10.1103/PhysRevLett.95.265004 PACS numbers: 52.35.Bj, 52.35.Ra, 96.60.Pb, 96.60.Rd The heating of the solar corona is a long

Chandran, Ben

92

3d solar corona at heliospheric sheet and structures in current carrying plasma with flows  

Microsoft Academic Search

Magnetic island and magnetic rope elements are basic topological structures of space plasma for construction of its 3D state. As for islands in the solar corona they observed near Sun like coronal mass ejections (CME), blobs, transients, as for ropes they observed like streamer belt and rays located above and submerged into forming heliospheric current sheet. Corona here is hot

V. Gubchenko; V. Zaitsev; H. Biernat; M. Khodachenko; H. Rucker

2004-01-01

93

Observaciones de la corona solar interior con un corongrafo de espejo  

NASA Astrophysics Data System (ADS)

El plasma de la corona solar es un buen indicador de las lneas de fuerza del campo magntico. Por lo tanto, el anlisis de estructuras coronales cuasiestacionarias en la corona da importante informacin sobre el campo magntico y la actividad asociada. Se trata de poner lmites a los modelos tericos existentes mediante el estudio de distintas estructuras en la corona interior. En agosto de 1997 comenz a operar el corongrafo solar (MICA) en El Leoncito como parte del Observatorio Solar Alemn-Argentino. Desde su instalacin obtiene imgenes de la corona solar (1.05 a 2.0 radios solares) en 2 lneas espectrales correspondientes a la emisin de Fe XIV y Fe X. El instrumento puede obtener imgenes cada minuto por lo que es ideal para estudiar procesos rpidos. Presentamos observaciones recientes que muestran la capacidad del corongrafo as como la evolucin de algunos eventos dinmicos observados por MICA.

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

94

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

95

ON THE DYNAMICS OF THE SOLAR CORONA: FIRST RESULTS OBTAINED WITH A NEW 3D MHD MODEL  

E-print Network

- ner heliosphere, and they could well be partly responsible for heating the corona to its tem- perature1 ON THE DYNAMICS OF THE SOLAR CORONA: FIRST RESULTS OBTAINED WITH A NEW 3D MHD MODEL J. Kleimann 1) is applied to the problem of the dynamics of the solar corona. First, we present the basic system

Grauer, Rainer

96

Radiophysics and Quantum. Electronics, VoI. 2Z No. 7, 1994 PLASMA DIAGNOSTICS OF THE SOLAR CORONA USING  

E-print Network

to account for the heating of the entire corona. Noise storm sources or other microflares having energiesRadiophysics and Quantum. Electronics, VoI. 2Z No. 7, 1994 PLASMA DIAGNOSTICS OF THE SOLAR CORONA USING DECIMETRIC RADIO WAVES (Review) A. O. Benz The solar corona is a very dynamic plasma on time

97

Prediction of the Solar Corona for the 2012 November 13 Total Solar Eclipse  

NASA Astrophysics Data System (ADS)

It has become our tradition to predict the structure of the corona prior to eclipses, using a magnetohydrodynamic (MHD) model based on measurements of photospheric magnetic fields on the Sun. We plan to continue this tradition by predicting the structure of the corona for the November 13, 2012 total solar eclipse, using SDO/HMI photospheric magnetic field data. We will predict the structure of the corona, including images of polarization brightness, magnetic field line traces, and images of simulated emission in EUV and X-rays. These images can be compared directly with observations of the total eclipse, as well as observations from SDO/AIA, Hinode/XRT, and STEREO/EUVI. Research supported by NASA's Heliophysics Theory and Living With a Star Programs, and NSF/FESD.

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

2012-12-01

98

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

99

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

100

Energy release in a turbulent three-dimensional solar corona  

NASA Astrophysics Data System (ADS)

Recently a lot of theoretical evidence has emerged in support of the hypothesis that coronal dissipation occurs in bursts at very small spatial scales. In this picture, a large number of coherently triggered, unobservable bursts is what appears a one of the many observed solar events (e.g., flares blinkers, flashes, etc.). Most previous computational studies of this process have been limited to two or two an half spatial dimensions. In addition, an incompressible model has been used. This is problematical, since the solar corona is three-dimensional and compressible as well. Furthermore, it is unclear how good an approximation reduced magnetohydrodynamics is in the compressible situation. Here we present the first results of our new compressible MHD coronal dissipation calculations. We solve the MHD equations with CRUNCH3D, a massively parallel, visco-resistive, MHD code with compressibility and thermal conduction. The code employs a Fourier collocation spatial discretization, and uses a second-order RungeKutta temporal discretization. Most simulations we will discuss here are run with 64 X 64 X 64 Fourier modes.

Einaudi, G.; Dahlburg, R.; Velli, M.; Linton, M.

101

On a plasma kinetic model of a 3D solar corona and solar wind at the heliospheric sheet  

Microsoft Academic Search

The dynamical solar corona in 3D consists of transient type magnetic island elements and radial type magnetic flux rope structures in a heliospheric sheet. During the formation and relaxation these elements produce inductive electromagnetic fields where energetic particles are produced. We study the 3D corona formation in the kinetic approach and parametrize it like a hot current-carrying collisionless plasma with

V. M. Gubchenko; M. L. Khodachenko; H. K. Biernat; V. V. Zaitsev; H. O. Rucker

2004-01-01

102

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

103

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

PubMed

During the past 25 years there have been many attempts to detect a possible dust ring around the sun, with contradictory results. Before the 1991 eclipse, infrared eclipse experiments used single-element detectors to scan the corona along the ecliptic for excess surface brightness peaks. The availability of relatively large-format infrared array detectors now provides a considerable observational advantage: two-dimensional mapping of the brightness and polarization of the corona with high photometric precision. The 1991 eclipse path included the high-altitude Mauna Kea Observatory, a further advantage to measure the corona out to large angular distances from the sun. Results are reported from an experiment conducted on Mauna Kea with a HgCdTe-array detector sensitive to wavelengths between 1 and 2.5 micrometers, using broad-band J, H, and K filters. Although the sky conditions were not ideal, the H- and K-band surface brightnesses clearly show the inhomogeneous structure in the K-corona and the elliptical flattening of the F-corona, but no evidence of a circumsolar, local dust component out to 15 solar radii. PMID:17738279

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

1992-09-01

104

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

Microsoft Academic Search

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

Richard Woo

2006-01-01

105

Wroc?aw in Space: X-ray Diagnostics of Solar Corona  

NASA Astrophysics Data System (ADS)

X-ray observations of the solar corona have been undertaken in Solar Physics Division (Space Research Centre of the Polish Academy of Sciences, Wroc?aw) for more than 35 years. Short history of these observations is presented. We focus mainly on the results from the latest experiments. These are hard X-ray photometer onboard the INTERBALL-Tail Probe and two Bragg crystal spectrometers recording solar X-ray spectra from CORONAS-F satellite. Such observations provide useful information on solar coronal plasma heated up to temperatures of several 106 - 107 K.

Siarkowski, M.; K?pa, A.; Sylwester, B.; Sylwester, J.

2006-01-01

106

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

107

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

108

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

109

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

110

Study of the solar corona using radio and space observations  

NASA Technical Reports Server (NTRS)

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

Dulk, G. A.

1984-01-01

111

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

112

Energy?dependent ionization states of shock?accelerated particles in the solar corona  

Microsoft Academic Search

We examine the range of possible energy de- pendence 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, suffi- ciently low in the corona, ions above ~0.1 MeV\\/amu approach an equilibrium charge state that depends primarily upon their speed and only weakly

D. V. Reames; C. K. Ng; A. J. Tylka

1999-01-01

113

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

NASA Technical Reports Server (NTRS)

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

Gopalswamy, N.; Nitta, N.

2011-01-01

114

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

NASA Astrophysics Data System (ADS)

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

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

1999-06-01

115

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

116

A study of the expansion of the solar corona with radiation heat flux  

Microsoft Academic Search

The expansion of the solar corona is studied using the hydrodynamic blast wave theory and the concept of the Roche model, with both solar gravity and radiation heat flux taken into consideration. Similarity solutions are developed when the radiation heat flux is more important than the radiation pressure and energy; the gas in the undisturbed field is assumed to be

J. B. Bhowmick

1980-01-01

117

Azimuthal distribution and escape of accelerated particles from the solar corona  

NASA Astrophysics Data System (ADS)

Coronal effects of solar cosmic rays are examined on the basis of a statistical analysis of the parameters of solar proton events. Calculations are made of the azimuthal-propagation velocity of accelerated particles in the corona and of delays in their escape into interplanetary space. Attention is given to the relationship between the dimensions of regions of fast coronal propagation of fast escape.

Bazilevskaia, G. A.; Sladkova, A. I.

1986-04-01

118

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

119

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

2002-06-14

120

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

SciTech Connect

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

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

2010-02-01

121

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

122

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

123

An attempt to determine the colour of the solar corona during the solar eclipse of 2001 June 21 (preliminary results)  

NASA Astrophysics Data System (ADS)

An attempt to determine the colour of the solar corona during the total solar eclipse of June 21, 2001 using the set of colour filters, telescope of 300 mm and a CCD camera is described. The scattered light both in the telescope and in the CCD camera is a major obstacle to using this method in the future.

Luk?, B.; Minarovjech, M.; Rybansk, M.

2002-12-01

124

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

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

125

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

126

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

127

Heating of accretion disc corona by solar-type flares  

Microsoft Academic Search

We propose a new model for the magnetosphere of a neutron star with accretiondisc for the case when the star's magnetic axis is not aligned with the rotation axis. We calculated the d isc shape and estimated the magnetic field and its gradient in the corona. Using the derived estimates as the initial data, we calculated the model of the

B. V. Somov; A. V. Oreshina; I. V. Oreshina

2002-01-01

128

Evidence for Flux Ropes in the Solar Corona  

Microsoft Academic Search

Although twisted magnetic flux ropes are clearly ejected from the Sun, as demonstrated by LASCO and EIT movies of erupting prominences, there has been some controversy about whether flux ropes exist in the corona before ejection. It has been argued that they are formed only upon ejection. The issue is important because of the need to understand how eruptions are

D. M. Rust

2003-01-01

129

Interaction of non-thermal particles with solar chromosphere and solar corona plasma  

NASA Astrophysics Data System (ADS)

In our paper we present the results of the simultaneous high temporal resolution observations of the solar flares in the active region NOAA 10786 observed on 12 and 13 July 2005. The visual data were collected with the Multi-Channel Subtractive Double Pass (MSDP) spectrograph and Solar Eclipse Coronal Imaging System (SECIS) in Bialkow Observatory (University of Wroclaw, Poland) in H-alpha line with high temporal resolution of 0.04-0.075 s. The radio observations were collected in Ondrejov Observatory (Czech Republic) with 0.1 and 0.01 s cadence in 0.8- 2.0, 3.0 and 2.0-4.5 GHz bands using RT5, RT3 and RT4 radiotelescopes, respectively. The X-ray data were recorded with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) satellite. We found high temporal correlation between the short lived radio emissions of type III, hard X-ray flux variations and short lasting variations of the brightness of the H- alpha flaring kernels observed simultaneously in line center and both wings. High cadence observations of solar flares has been used to investigate the interaction of non-thermal particles with solar chromosphere and solar corona plasma.

Radziszewski, Krzysztof; Rudawy, Pawel; Karlicky, Marian

130

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

131

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

PubMed

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

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

2010-07-01

132

The Heating of the Solar Corona E. R. Priest \\Lambda , C. R. Foley + , J. Heyvaerts ffl , T.D. Arber \\Lambda , D. Mackay \\Lambda , J. L. Culhane + and  

E-print Network

The Heating of the Solar Corona E. R. Priest \\Lambda , C. R. Foley + , J. Heyvaerts ffl , T­scale solar corona. This gives strong evidence against heating concentrated near the loop base for such loops mechanisms are heating the solar corona is a fundamental one in astrophysics that has defied physicists

Priest, Eric

133

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

NASA Technical Reports Server (NTRS)

The large-scale density structure of the white-light solar corona is compared to the organization of the solar magnetic field as identified by the appearance of neutral lines in the photosphere to examine whether any consistent relationship exists between the two. During the period covering Carrington rotations 1717 to 1736 brightness enhancements in the low corona tend to lie over the global neutral sheet identified in the photospheric magnetic field. The brightest of these enhancements are associated with neutral lines throguh active regions. These associations are not 1-1, but do hold both in stable and evolving conditions of the corona. A significant number of long-lived neutral lines is found, including filaments seen in H-alpha, for which there are not coronal enhancements.

Sime, D. G.; Mccabe, M. K.

1990-01-01

134

Energy balance in solar corona from 1.1 to 1.6 solar radius heated through magnetic accelerated regions  

Microsoft Academic Search

Energy balance from 1.1 to 1.6 solar radius is investigated for the inhomogeneous solar-maximum corona. Heating is assumed to arise via energy dissipated by accelerated electrons\\/protons through Coulomb collisions (Levine, 1974). The loss of energy takes place via inward and outward conduction, radiation, and solar wind. It is found that conduction dominates all other losses everywhere except near temperature maximum,

U. Narain; M. Kumar

1986-01-01

135

Current driven low-frequency electrostatic waves in the solar corona: Linear theory and nonlinear saturation  

SciTech Connect

Important solar physical problems such as the heating of the corona, reconnection, and electron acceleration might be related to current-driven plasma waves, especially at low frequencies, where, perhaps, most of the wave power is concentrated. Since a direct observation of plasma waves in the solar corona is impossible, theoretical investigations are needed to clarify the possibilities of their excitation, of their nonlinear evolution, and the possible macroscopic consequences of such waves. A multifluid linear dispersion analysis of current flows parallel to the magnetic field in the solar corona is carried out. For this reason, an appropriate linear dispersion solver is developed, considering all possible propagation directions of the waves with respect to the solar magnetic field. As for the assumed plasma model, an electron distribution drifting in the direction parallel to the ambient magnetic field while the background protons were at rest was considered. Thermal effects are taken into account by means of appropriate energy equations of state. Due to their importance for the heating and anomalous transport in the solar corona, the analysis of low-frequency electrostatic waves is studied. For the limiting cases of parallel and perpendicular propagation, the Buneman and the lower-hybrid waves due to a modified two-stream instability were recovered, respectively. For realistic coronal plasma parameters of the lower corona, the dispersion curves of the two basic unstable wave modes are found to approach each other very closely, and their possible nonlinear saturation level is estimated. It appeared that for solar conditions, the two basic modes contribute a comparable (within an order of magnitude) amount of anomalous dissipation, which is quantified by estimating an ''effective collision rate.''.

Lee, Kuang Wu; Buechner, Joerg; Elkina, Nina [Max-Planck-Institut fuer Sonnensystemforschung, 37191 Katlenburg-Lindau (Germany)

2007-11-15

136

Electromagnetic Influence on Gravitational Mass - Theory, Experiments, and Mechanism of the Solar Corona Heating  

Microsoft Academic Search

Based on the model of Expansive Nondecelerative Universe, the aim of the present contribution is to contribute to the theoretical rationalization of some experiments, in particular of those performed by Podkletnov and de Aquino and devoted to the gravitational mass cessation, to offer a mechanistic explanation of the Solar corona heating, and to propose an experiment to verify the explanation

Miroslav Sukenik; Jozef Sima

2002-01-01

137

Intermittent Heating of the Solar Corona by Heat Flux-generated Ion Cyclotron Waves  

Microsoft Academic Search

Recently, we suggested that the source of ion heating in solar coronal holes is small-scale reconnection events (microflares) at the coronal base. The microflares launch intermittent heat flux up into the corona exciting ion cyclotron waves through a plasma microinstability. The ions are heated by these waves during the microflare bursts and then evolve with no energy input between the

S. A. Markovskii; Joseph V. Hollweg

2004-01-01

138

Electromagnetic Influence on Gravitational Mass - Theory, Experiments, and Mechanism of the Solar Corona Heating  

Microsoft Academic Search

Based on the model of Expansive Nondecelerative Universe, the aim of the present contribution is to contribute to the theoretical ra- tionalization of some experiments, in particular of those performed by Podkletnov and de Aquino and devoted to the gravitational mass ces- sation, to offer a mechanistic explanation of the Solar corona heating, and to propose an experiment to verify

Miroslav Suken

139

ELECTRON DENSITY VARIATION IN OFF-LIMB SOLAR CORONA STRUCTURES I. Ugarte-Urra  

E-print Network

1 ELECTRON DENSITY VARIATION IN OFF-LIMB SOLAR CORONA STRUCTURES I. Ugarte-Urra , J.G. Doyle a study of the electron density variation for off limb observations with the Coronal Diagnostic Spec- trometer (CDS) on board SoHO using the density sensi- tive coronal line ratio Si X (356

140

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

141

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 to the formation of an azimuthal rope of twisted magnetic field embedded within the global field, and to the energy

Fornberg, Bengt

142

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

143

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

Microsoft Academic Search

It has been a puzzle for quite some time that spectroscopic measurements in the inner corona indicate electron temperatures far too low to produce the ion fractions observed in situ in the solar wind. In the present Letter, we show that in order to reconcile the two sets of measurements, a number of conditions have to exist in the inner

Ruth Esser; Richard J. Edgar

2000-01-01

144

IntrAst1 (Petrovay) The Sun THE CHROMOSPHERE AND THE SOLAR CORONA  

E-print Network

IntrAst1 (Petrovay) The Sun THE CHROMOSPHERE AND THE SOLAR CORONA "Chromosphere" = coloured sphere #12;IntrAst1 (Petrovay) The Sun Bottom of chromosphere: at T-minimum, z = 500 km (T = 4200K, = 10: at wavelengths of strong lines or lines of high excitation temperature. #12;IntrAst1 (Petrovay) The Sun H

Petrovay, Kristóf

145

A Space Weather Mission Concept: Observatories of the Solar Corona and Active Regions (OSCAR)  

E-print Network

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$^{\\circ}$ to provide optimum stereoscopic view of the solar corona. We ...

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

2014-01-01

146

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

147

Analysis of IRAS solar system dust data  

NASA Technical Reports Server (NTRS)

Data in the Infrared Astronomical Satellite (IRAS) Zodiacal History File were analyzed to extract dust band locations and peak brightness measurements from approximately 1,000 individual IRAS scans. The study had three goals. One was to show that the prominent solar system dust bands are associated with Hirayama asteroid families and thus that collisions between asteroids account for a significant fraction of the particles in the zodiacal cloud. Recent work suggests that while the Hirayama families are a major source of the dust in the bands, there may also be contributions from two or three smaller, more recently recognized asteroid families. A second goal was to show that there is evidence in the IRAS dust data for the transport of particles from asteroid belt to the Earth by Poynting-Robertson light drag and thus account for the fact that asteroid particles are collected in the Earth's stratosphere. Results of the study will confirm the location of the dust bands within the inner asteroid belt, and show conclusively that the material seen by IRAS is now spread over a wide range of distances from the sun. The third goal was to construct a model of the background zodiacal cloud that satisfies the proper dynamical constraints. Figures are provided to show the scans processed to remove zodiacal background and Galactic signals, and the resulting polynomial fits to the 25 micron scan. The latter provided objective estimates of band widths, peak locations, and peak fluxes. Modelling and analysis of the resulting band data has been presented at several conferences and is the subject of a number of forthcoming papers.

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

1991-01-01

148

The Transient Neutral Flux in Plasma: An Explanation of Heating for the Solar Corona?  

E-print Network

In this short note, we discuss a mechanism for the transport of energy, momentum and dipole moment via transient neutral carriers in plasma. This gives a way to rapidly convert bulk hydrodynamic flow energy into thermal energy over a distance of several mean free paths. In the transition region of the solar corona we estimate various processes and their potential to introduce the high energies needed to to reach the 2 x10^6K observed there. It implies that kinetic methods may be essential for modeling the corona and that there are more gentle but still robust means than reconnection to relax magnetic fields in plasmas.

Chafin, Clifford

2014-01-01

149

Origin of the ten degree Solar System dust bands  

Microsoft Academic Search

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

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

1997-01-01

150

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

151

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

SciTech Connect

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

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

2009-07-15

152

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

2007-01-19

153

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

154

Global Magnetic Topology and Large-Scale Dynamics of the Solar Corona  

NASA Astrophysics Data System (ADS)

We consider the global topology of the coronal magnetic field in relation to the large-scale dynamics of the solar corona. Our consideration includes recent results on the structural analysis of this field determined in two different approximations, namely, potential field source surface model and solar magnetohydrodynamic model. We identify similarities and differences between structural features of the magnetic field obtained in these two models and discuss their implications for understanding various large-scale phenomena in the solar corona. The underlying magnetic topology manifests itself in a variety of observed morphological features such as streamers, pseudo-streamers or unipolar streamers, EUV dimmings, flare ribbons, coronal holes, and jets. For each of them, the related magnetic configuration has specific structural features, whose presence has to be not only identified but also verified on its independence from the used field model in order to reliably predict the impact of such features on physical processes in the corona. Among them are magnetic null points and minima, bald patches, separatrix surfaces and quasi-separatrix layers, and open and closed separator field lines. These features form a structural skeleton of the coronal magnetic field and are directly involved through the ubiquitous process of magnetic reconnection in many solar dynamic phenomena such as coronal mass ejections, solar wind, acceleration and transport of energetic particles. We will pinpoint and elucidate in our overview some of such involvements that have recently received a considerable attention in our ongoing projects at Predictive Science.

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

155

Evolution of interstellar dust and stardust in the solar neighbourhood  

NASA Astrophysics Data System (ADS)

Aims:We studied the evolution of the abundance in interstellar dust species that originate in stellar sources and from condensation in molecular clouds in the local interstellar medium of the Milky Way. We determined from this the input of dust material to the Solar System. Methods: A one-zone chemical evolution model of the Milky Way for the elemental composition of the 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 parametrised form that is gauged by observed abundances of presolar dust grains with a supernova origin. For dust growth in the ISM, a simple method is developed for coupling this with disk and dust evolution models. Results: A chemical evolution model of the solar neighbourhood in the Milky Way is calculated, which forms the basis for calculating a model of the evolution of the interstellar dust population at the galactocentric radius of the Milky Way. The model successfully passes all standard tests for the reliability of such models. In particular the abundance evolution of the important dust-forming elements is compared with observational results for the metallicity-dependent evolution of the abundances for G-type stars from the solar neighbourhood. It is found that the new tables of Nomoto et al. (2006) for the heavy element production give much better results for the abundance evolution of these important elements than the widely used tables of Woosley & Weaver (1995). The time evolution for the abundance of the following dust species is followed in the model: silicate, carbon, silicon carbide, and iron dust from AGB stars and from supernovae, 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; stardust only forms a minor fraction. 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 for dust grains. The observed abundance ratios of presolar dust grains formed in supernova ejecta and in AGB star outflows requires that, for the ejecta from supernovae, the fraction of refractory elements condensed into dust is 0.15 for carbon dust and is quite small (~10-4) for other dust species. Appendix A is only available in electronic form at http://www.aanda.org

Zhukovska, S.; Gail, H.-P.; Trieloff, M.

2008-02-01

156

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

157

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

158

Spatiotemporal organization of energy release events in the quiet solar corona  

E-print Network

Using data from 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 Alfv\\'{e}nic interactions.

Uritsky, Vadim M

2014-01-01

159

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

160

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

SciTech Connect

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

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

2006-09-15

161

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

E-print Network

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 Alfven 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 perturb...

Cranmer, Steven R

2014-01-01

162

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

NASA Astrophysics Data System (ADS)

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

Chai, LiHui; Lee, KuangWu; Bchner, Jrg

2013-04-01

163

Magnetic Reconnection and Particle Acceleration in the Solar Corona  

NASA Astrophysics Data System (ADS)

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

Neukirch, Thomas

164

Electromagnetic Influence on Gravitational Mass - Theory, Experiments, and Mechanism of the Solar Corona Heating  

E-print Network

Based on the model of Expansive Nondecelerative Universe, the aim of the present contribution is to contribute to the theoretical rationalization of some experiments, in particular of those performed by Podkletnov and de Aquino and devoted to the gravitational mass cessation, to offer a mechanistic explanation of the Solar corona heating, and to propose an experiment to verify the explanation of the heating in the Earth conditions.

Miroslav Sukenik; Jozef Sima

2002-06-17

165

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

166

Is the Solar Corona Nonmodally Self-Heated  

Microsoft Academic Search

Recently it was pointed out that nonmodally (transiently and\\/or adiabatically) pre-amplified waves in shear flows, undergoing subsequent viscous damping, can ultimately heat the ambient flow. The key ingredient of this process is the ability of waves to grow, by extracting energy from the spatially inhomogeneous mean flow. In this paper we examine this mechanism in the context of the solar

B. M. Shergelashvili; A. D. Rogava; S. Poedts

2004-01-01

167

High-frequency Faraday rotation observations of the solar corona  

Microsoft Academic Search

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

Elizabeth A. Jensen; Christopher T. Russell

2008-01-01

168

Energy release in a turbulent three-dimensional solar corona  

Microsoft Academic Search

Recently a lot of theoretical evidence has emerged in support of the hypothesis that coronal dissipation occurs in bursts at very small spatial scales. In this picture, a large number of coherently triggered, unobservable bursts is what appears a one of the many observed solar events (e.g., flares blinkers, flashes, etc.). Most previous computational studies of this process have been

G. Einaudi; R. Dahlburg; M. Velli; M. Linton

2002-01-01

169

The relationship between magnetic field expansion factors and solar wind parameters in the corona  

NASA Astrophysics Data System (ADS)

We use the Horizontal Current - Current Sheet (HCCS) magnetic field model to characterize the coronal hole/streamer boundaries in the corona for the Solar Cycle 23 Minimum (1996-1998). The HCCS model describes the interface region much more accurately than traditional PFSS (potential field - source surface) models. Once the models are computed we can compute expansion factors and magnetic field strengths anywhere in a 3D grid. These data are combined with coronal outflow velocities and electron densities from UVCS and LASCO on SOHO to show how the coronal plasma parameters (at 2.3 solar radii) relate to the magnetic field geometry.

Strachan, Leonard; van Ballegooijen, A.; SOHO/UVCS; SOHO/LASCO; Peak, NSO/Kitt

2013-07-01

170

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 OF SOLAR ENERGY by w. M. Gray, W. M. Frank, M. L. Corrin and C. A. Stokes Department of Atmospheric Science interception of solar energy. Growing population pressures and predicted future global food shortages dictate

Gray, William

171

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

NASA Astrophysics Data System (ADS)

During the declining phase of the longest solar minimum in a century, the arrival of the MESSENGER spacecraft at superior conjunction allowed the measurement of magnetohydrodynamic (MHD) waves in the solar corona with its 8 GHz radio frequency signal. MHD waves crossing the line of sight were measured via Faraday rotation fluctuations (FRFs) in the plane of polarization (PP) of MESSENGER's signal. FRFs in previous observations of the solar corona (at greater offset distances) consisted of a turbulent spectrum that decreased in power with increasing frequency and distance from the Sun. Occasionally a spectral line, a distinct peak in the power spectral density spectrum around 4 to 8 mHz, was also observed in these early data sets at offset distances of about 5 to 10 solar radii. The MESSENGER FRF data set shows a spectral line at an offset distance between 1.55 to 1.85 solar radii with a frequency of 0.60.2 mHz. Other possible spectral lines may be at 1.2, 1.7, and 4.5 mHz; MHD waves with these same frequencies have been observed in X-ray data traveling along closed coronal loops at lower offset distances. An initial analysis of the MESSENGER spectral line(s) shows behavior similar to turbulent spectra: decreasing power with increasing frequency and distance from the Sun. Here we detail the steps taken to process the MESSENGER change in PP data set for the MHD wave investigation.

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

2013-07-01

172

Occultation systems in space-borne telescopes dedicated to the observation of the solar corona  

NASA Astrophysics Data System (ADS)

The observation of the solar corona in white light is a challenging task because of the poor contrast of the signal (i.e., the solar corona) to the stray light noise. The main task a coronagraph or heliospheric imager designer shall face is the reduction of the stray light. This is particularly important in space-borne instruments with an external occultation. A large part of the field literature is dedicated to the optimization of the occulting system in order to reduce the total amount of stray light on the instrument focal plane. From the pioneering work of Newkirk and Bohlin in 1965, several solutions have been elaborated in optimizing the occulters shape. Despite a series of classical optimizing shapes has been employed in many solar missions, each optimization shall fit the constraint of the instrument design and of the mission characteristics. Forthcoming solar space missions such as ASPIICS on PROBA3 (formation flight) and Solar Orbiter (approaching the Sun with a perihelion of 0.28 AU) will introduce considerable technological innovations and their characteristics impose demanding efforts on the scientific payloads in order to be compliant with the constraints. This work reviews the most effective occultation systems that have been employed by past coronagraphs, spectrographs and heliospheric imagers. Moreover, it illustrates the innovative solutions that are going to be adopted by the missions to come.

Landini, Federico; Fineschi, Silvano; Moses, Daniel; Romoli, Marco

173

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

174

Is the solar corona nonmodally self-heated?  

Microsoft Academic Search

Recently it was pointed out that nonmodally (transiently and\\/or\\u000aadiabatically) pre-amplified waves in shear flows, undergoing subsequent\\u000aviscous damping, can ultimately heat the ambient flow. The key ingredient of\\u000athis process is the ability of waves to grow, by extracting energy from the\\u000aspatially inhomogeneous mean flow. In this paper we examine this mechanism in\\u000athe context of the solar

B. M. Shergelashvili; A. D. Rogava; S. Poedts

2004-01-01

175

Influence of solar flares on the X-ray corona  

NASA Technical Reports Server (NTRS)

Sequences of X-ray images of solar flares, obtained with the Hard X-ray Imaging Spectrometer on the SMM spacecraft, reveal many dynamical phenomena. Movies of 20 flares recorded with 6-sec time resolution were examined. A preliminary analysis of the events as a group are presented, and some new aspects of the well-studied May 21, 1980 flare and a November 6, 1980 flare are discussed.

Rust, D. M.; Batchelor, D. A.

1986-01-01

176

Comparative Study on Hot Atom Coronae of Solar and Extrasolar Planets  

NASA Astrophysics Data System (ADS)

Solar/stellar forcing on the upper atmospheres of the solar and extrasolar planets via both absorption of the XUV (soft X-rays and extreme ultraviolet) radiation and atmospheric sputtering results in the formation of an extended neutral corona populated by the suprathermal (hot) H, C, N, and O atoms (see, e.g., Johnson et al., 2008). The hot corona, in turn, is altered by an inflow of the solar wind/magnetospheric plasma and local pick-up ions onto the planetary exosphere. Such inflow results in the formation of the superthermal atoms (energetic neutral atoms - ENAs) due to the charge exchange with the high-energy precipitating ions and can affect the long-term evolution of the atmosphere due to the atmospheric escape. The origin, kinetics and transport of the suprathermal H, C, N, and O atoms in the transition regions (from thermosphere to exosphere) of the planetary atmospheres are discussed. Reactions of dissociative recombination of the ionospheric ions CO _{2} (+) , CO (+) , O _{2} (+) , and N _{2} (+) with thermal electrons are the main photochemical sources of hot atoms. The dissociation of atmospheric molecules by the solar/stellar XUV radiation and accompanying photoelectron fluxes and the induced exothermic photochemistry are also the important sources of the suprathermal atoms. Such kinetic systems with the non-thermal processes are usually investigated with the different (test particles, DSMC, and hybrid) versions of the kinetic Monte Carlo method. In our studies the kinetic energy distribution functions of suprathermal and superthermal atoms were calculated using the stochastic model of the hot planetary corona (Shematovich, 2004, 2010; Groeller et al., 2014), and the Monte Carlo model (Shematovich et al., 2011, 2013) of the high-energy proton and hydrogen atom precipitation into the atmosphere respectively. These functions allowed us to estimate the space distribution of suprathermals in the planetary transition regions. An application of these numerical models to study the atmospheric gas flow in the transition region from the collision-dominated thermosphere to collisionless exosphere, and the non-thermal escape will be discussed and illustrated with the simple 1D-models of the hot coronae of the solar and extrasolar planets. This work is supported by the RFBR project No. 14-02-00838a and by the Basic Research Program of the Presidium of the Russian Academy of Sciences (Program 22). begin{itemize} Johnson et al., Sp. Sci.Rev., 2008, v. 139, 355. Shematovich, Solar System Res., 2004, v.38, 28. Shematovich, Solar System Res., 2010, v.44, 96. Shematovich et al., J. Geophys. Res., 2011, v.116, A11320; 2013, v. 118, 1231. Groeller et al., Planet. Space Sci., 2014.

Shematovich, Valery

177

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

178

"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

179

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

180

Evolution of interstellar dust and stardust in the solar neighbourhood  

Microsoft Academic Search

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

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

2008-01-01

181

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

182

Accretional Remanence of Magnetized Dust in the Solar Nebula  

Microsoft Academic Search

Anticipating the results from the Rosetta magnetometer experiment, we present a theoretical study concerning the possible origin of a cometary magnetic field. Assuming the existence of a permanently magnetized iron dust fraction in the primordial solar nebula, we use a numerical model to investigate the outcome of a dust aggregation process involving both magnetic and nonmagnetic preplanetary grains. The growing

Henrik Nbold; Karl-Heinz Glassmeier

2000-01-01

183

Dust to planetesimals - Settling and coagulation in the solar nebula  

Microsoft Academic Search

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

S. J. Weidenschilling

1980-01-01

184

Is the solar corona nonmodally self-heated?  

E-print Network

Recently it was pointed out that nonmodally (transiently and/or adiabatically) pre-amplified waves in shear flows, undergoing subsequent viscous damping, can ultimately heat the ambient flow. The key ingredient of this process is the ability of waves to grow, by extracting energy from the spatially inhomogeneous mean flow. In this paper we examine this mechanism in the context of the solar coronal plasma flows. "Self-heating" (SH) processes are examined when both viscous damping and magnetic resistivity are at work. We show that if the plasma viscosity is in the favorable range of values the asymptotic SH rate in these flows can be quite substantial.

B. M. Shergelashvili; A. D. Rogava; S. Poedts

2004-10-11

185

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

186

Spectral solar irradiance before and during a Harmattan dust spell  

Microsoft Academic Search

Measurements of the ground-level spectral distributions of the direct, diffuse and global solar irradiance between 300 and 1100 nm were made at Akure (7.15N, 5.5E), Nigeria, in December 1991 before and during a Harmattan dust spell employing a spectroradiometer (LICOR LI-1800) with 6 nm resolution. The direct spectral solar irradiance which was initially reduced before the dust storm was further

Z. Debo Adeyefa; Bjrn Holmgren

1996-01-01

187

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

188

Coronagraph observations and analyses of the ultraviolet solar corona  

NASA Technical Reports Server (NTRS)

The major activities on the Spartan Ultraviolet Coronal Spectrometer project include both scientific and experimental/technical efforts. In the scientific area, a detailed analysis of the previously reported Doppler dimming of HI Ly-alpha from the July 1982 rocket flight has determined an outflow velocity at 2 solar radii from sun center to be between 153 and 251 km/s at 67 percent confidence. The technical activities include, several improvements made to the instrument that will result in enhanced scientific performance or in regaining a capability that had deteriorated during the delay time in the launch date. These include testing and characterizing the detector for OVI radiation, characterizing a serrated occulter at UV and visible wavelengths, fabricating and testing telescope mirrors with improved edges, testing and evaluating a new array detector system, modifying the slit mask mechanism and installing a mask in the instrument to block the Ly-alpha resonance line when the electron scattered component is being observed.

Kohl, John L.

1989-01-01

189

Moon Dust Telescopes, Solar Concentrators, and Structures  

NASA Astrophysics Data System (ADS)

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

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

2008-05-01

190

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

191

The Origin of Non-Maxwellian Solar Wind Electron Velocity Distribution Function: Connection to Nanoflares in the Solar Corona  

NASA Astrophysics Data System (ADS)

The formation of the observed core-halo feature in the solar wind electron velocity distribution function is a long-time puzzle. In this Letter, based on the current knowledge of nanoflares, we show that the nanoflare-accelerated electron beams are likely to trigger a strong electron two-stream instability that generates kinetic Alfvn wave and whistler wave turbulence, as we demonstrated in a previous paper. We further show that the core-halo feature produced during the origin of kinetic turbulence is likely to originate in the inner corona and can be preserved as the solar wind escapes to space along open field lines. We formulate a set of equations to describe the heating processes observed in the simulation and show that the core-halo temperature ratio of the solar wind is insensitive to the initial conditions in the corona and is related to the core-halo density ratio of the solar wind and to the quasi-saturation property of the two-stream instability at the time when the exponential decay ends. This relation can be extended to the more general core-halo-strahl feature in the solar wind. The temperature ratio between the core and hot components is nearly independent of the heliospheric distance to the Sun. We show that the core-halo relative drift previously reported is a relic of the fully saturated two-stream instability. Our theoretical results are consistent with the observations while new tests for this model are provided.

Che, H.; Goldstein, M. L.

2014-11-01

192

Measurement of magnetic helicity flux into the solar corona  

NASA Astrophysics Data System (ADS)

We developed a new methodology which can determine magnetic helicity flux across the photosphere based on the magnetograph observation, In order to derive the helicity flux, first the velocity tangential to the solar surface is constructed by applying a correlation tracking technique on the magnetic observation, and secondly the velocity component across the photosphere is derived from the condition that the magnetic evolution must be consistent with the induction equation, Through this procedure, we can determine the helicity flow across the photosphere as a function of time and space, Based on this new method, we analyzed magnetic helicity of the active regions NOAA 9026 and 9077. using the data taken by SOHO/MDI and the vector magnetograph at NAOJ/Tokyo. As a result, it was revealed that positive and negative helicity is supplied in each region simultaneously. In particular, temporary activation of the helicity injection of the both signs was observed prior to X-class flare events in the GOES classification. The investigation on the helicity distribution suggests some relationship between flare onset and the increase of complexity in the helicity structure.

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

193

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

194

Evolucin de la Estructura Trmica Global de la Corona alrededor del ltimo Mnimo de Actividad Solar  

NASA Astrophysics Data System (ADS)

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

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

195

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

196

Particle acceleration by cascading reconnection in the Solar corona  

NASA Astrophysics Data System (ADS)

Recently it has been shown by adaptive mesh refinement MHD simulations that plasma outflows from the Sun decay, forming smaller and smaller scale magnetic islands (Barta et al., 2012). Usually it is conjectured that the resulting reconnection electric fields can accelerate particles to high energies. In this study we use test particle calculations in a guiding center approach to study the consequences of the acceleration of electrons. We show the acceleration in a fragmented current sheet (CS) above a flaring arcade, behind a CME or in the streamer belt of the Sun depends on the resistivity model. In order to compare with the X-ray observation in solar flares, we analyzed the electrons which can reach the chromosphere of the Sun, where they cause X-ray emissions. For them we derive the resulting X-ray spectra with the non-thermal bremsstrahlung method. On the other hand energetic ions are of interest, if they escape into the interplanetary space where they may propagate toward the Earth. We found that the electric fields obtained by applying refined meshes better describe the huge observed energies. Energetic electrons that quickly reach the chromosphere are most efficiently accelerated from the center of the current sheet. All particles gain energies up to MeV energies at a short, sub-second time. As we could explain by simple arguments, the chromospheric footpoints of energetic electrons and positively charged particles are indeed located anti-symmetrically around the current sheet. Independent on the resistivity model, the main acceleration takes place at the same sites. The final particle energy depends mainly on their initial position with respect to the main acceleration sites. We found that initial velocities and pitch angles influence only the low energy electrons, particles with final energies less than 10 keV usually do not reach the chromosphere at all. For the resulting X-ray spectrum we found a reconnection (resistivity) model dependence only for energies around 100keV. For higher reconnection rates (larger electric fields) the spectrum of energetic electrons becomes harder (smaller spectral index), as it can be found using higher mesh resolution runs. In models with a constant enhanced resistivity, switched on for large current carrier velocities, we found a clear break point in the hard X-ray spectrum.

Zhou, Xiaowei; Bchner, Jrg; Gan, Weiqun; Brta, Miroslav; Liu, Siming

197

The C I opacity and physical structure of cool, very dense plasma in the solar corona  

NASA Technical Reports Server (NTRS)

The physical structure of the cool material in the volume of the solar corona is investigated. The observational evidence is summarized in a table giving the brightness contrast in optical and EUV radiations. The state of ionization and the opacity sources are discussed, and a physical model is described that is consistent with the EUV and optical data. It is noted that a comparison of the EUV raster pictures with H-alpha and Ca K photoheliograms indicates that the material is commonly injected from below into relatively low-lying magnetic loops (fibrils) seen near sunspots and plages.

Foukal, P.

1981-01-01

198

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

199

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

200

The Origin of Non-Maxwellian Solar Wind Electron Velocity Distribution Function: Connection to Nanoflares in the Solar Corona  

E-print Network

The formation of the observed core-halo feature in the solar wind electron velocity distribution function is a long-time puzzle. In this letter based on the current knowledge of nanoflares we show that the nanoflare-accelerated electron beams are likely to trigger a strong electron two-stream instability that generates kinetic Alfv\\'en wave and whistler wave turbulence, as we demonstrated in a previous paper. We further show that the core-halo feature produced during the origin of kinetic turbulence is likely to originate in the inner corona and can be preserved as the solar wind escapes to space along open field lines. We formulate a set of equations to describe the heating processes observed in the simulation and show that the core-halo temperature ratio of the solar wind is insensitive to the initial conditions in the corona and is related to the core-halo density ratio of the solar wind and to the quasi-saturation property of the two-stream instability at the time when the exponential decay ends. This rel...

Che, H

2014-01-01

201

STEREO OBSERVATIONS OF FAST MAGNETOSONIC WAVES IN THE EXTENDED SOLAR CORONA ASSOCIATED WITH EIT/EUV WAVES  

SciTech Connect

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

Kwon, Ryun-Young; Ofman, Leon; Kramar, Maxim [Also at Department of Physics, Institute for Astrophysics and Computational Sciences, Catholic University of America, 620 Michigan Avenue, Washington, DC 20064, USA. (United States)] [Also at Department of Physics, Institute for Astrophysics and Computational Sciences, Catholic University of America, 620 Michigan Avenue, Washington, DC 20064, USA. (United States); Olmedo, Oscar [NRC Associate, U.S. Naval Research Laboratory, Washington, DC 20375, USA. (United States)] [NRC Associate, U.S. Naval Research Laboratory, Washington, DC 20375, USA. (United States); Davila, Joseph M.; Thompson, Barbara J.; Cho, Kyung-Suk, E-mail: ryunyoung.kwon@nasa.gov [Also at NASA Goddard Space Flight Center, Solar Physics Laboratory, Code 671, Greenbelt, MD 20771, USA. (United States)] [Also at NASA Goddard Space Flight Center, Solar Physics Laboratory, Code 671, Greenbelt, MD 20771, USA. (United States)

2013-03-20

202

Relative Elemental Abundance and Heating Constraints Determined for the Solar Corona from SERTS Measurement.  

NASA Astrophysics Data System (ADS)

Extreme-ultraviolet (EUV) emission above the quiet solar limb up to 1.2 solar radii was studied using observations made from two different flights of the Goddard Solar EUV Rocket Telescope and Spectrograph (SERTS) covering three different spatial locations. These observations measure the intensities from a number of EUV spectral lines as a function of height. The density scale height was determined from the radial dependence of the intensity of the spectral lines. Line-ratio densities and line-ratio temperatures were determined from ratios of the intensities of iron lines. 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). Emission measures were determined from the Cr XIII, Si XI, Al X and iron lines. Limits on the filling factor were determined from the emission measure and the line-ratio densities for all three regions. The set of relative elemental abundance of silicon, aluminum, and chromium to iron was determined for a quiet coronal region observed by SERTS 1991. The results did not agree with those of Meyer 1985 or 1992, but instead showed aluminum enhancement while silicon was underabundant. For SERTS 1989 the relative elemental abundance of silicon to iron did agree with the Meyer elemental abundances. Heating constraints on the solar corona were determined. The line-ratio temperature increased with height up to at least 1.15 solar radii for all three cases studied. This requires some source of heating at or above that height in the corona. For two of the three cases studied the total radiative power was larger than the maximum heating by heat conduction from above over at least part of the observed region for any filling factor, and, in all three cases, for all filling factor less than or equal to 0.1, so local nonconductive heating is needed.

Falconer, David Allen

1994-01-01

203

Azimuthal structure of the solar wind velocity and K-corona brightness in the heliospheric current sheet  

NASA Astrophysics Data System (ADS)

Solar wind velocity measurements at IMF sector boundary crossings at 1 AU during 1972-1977 are used to infer the azimuthal structure of the solar wind velocity in the heliospheric current sheet (HCS). The solar wind velocity in the in-ecliptic portion of the current sheet is found to vary from longitude to longitude, where it originates from the corona. The yearly average value of solar wind velocity in the HCS is found to vary with the phase of the solar cycle, with a maximum value around 1974. The K-corona brightness on the source surface corresponding to the IMF sector boundary crossings during the period under consideration also exhibits a similar but opposite pattern of variation when the data are averaged over a long period. It is concluded that there exists a longitudinal variation of solar wind velocity in the HCS.

Bala, B.; Prabhakaran Nayar, S. R.

1993-05-01

204

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

205

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

206

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

207

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

PubMed

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

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

2008-11-01

208

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

209

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

E-print Network

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 $(\\sigma/\\lambda)^2$ and $M^{-1}$, where $\\sigma$, $\\lambda$ and $M$ are the half-width of the observed line profile at $1/\\sqrt{e}$, 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...

Zhao, G Q; Wang, C B

2014-01-01

210

Observing and quantifying the solar wind signature of the magnetically complex corona.  

NASA Astrophysics Data System (ADS)

The solar wind exhibits fluctuations over a broad range of timescales characteristic of magnetohydrodynamic (MHD) turbulence evolving in the presence of structures of coronal origin. In- situ spacecraft observations of plasma parameters are at minute (or below) resolution for intervals spanning the solar cycle and provide a large number of samples for statistical studies. The magnetic field power spectrum typically has two characteristic components, an inertial range of turbulence over several orders of magnitude with approximately Kolmogorov power law and at lower frequencies, an approximately '1/f' energy containing range believed to be of direct coronal origin. We focus on the behaviour of in- situ observations of fluctuations in the inner heliosphere as a function of solar cycle and solar wind speed; that is, with respect to coronal structure and dynamics. We employ a recently developed technique that sensitively distinguishes between fractal and multifractal scaling in the timeseries. Our working hypothesis is that since the latter can be characteristic of local MHD turbulence, the former maps more directly to features of coronal origin. We find a strong correlation between the scaling properties of magnetic energy density fluctuations and the magnetic complexity of the coronal magnetic fields. At solar maximum in the ecliptic, where the in- situ observations can be dominated by slow solar wind, the magnetic energy density as seen by WIND and ACE shows a fractal signature, whereas at minimum it is multifractal. This is corroborated by ULLYSES polar observations at solar minimum in quiet, fast solar wind where again, multifractal scaling is found. This high magnetic complexity in the corona corresponds to fractal, rather than multifractal scaling in magnetic energy density; remarkably, this fractal signature dominates the full dynamic range of observations, extending across timescales typically identified with both the '1/f' and 'inertial range'. The correlation of behaviour of other bulk plasma parameters observed in- situ with the magnetic complexity of the coronal will also be discussed. Since we are able to quantify scaling exponents, our results provide constraints on models for the solar wind. In particular, the fractal signature which we discuss here can be captured by a nonlinear Fokker Planck model, with the prospect of a quantitative mapping back to the corona.

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

2008-12-01

211

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

212

Dynamical response of the solar corona. III - Numerical simulation of the 1973 June 10 coronal transient  

NASA Technical Reports Server (NTRS)

A spherically symmetric adiabatic single-fluid model is outlined for simulating the nonlinear time-dependent response of the corona to solar events that are simulated by perturbations in the appropriate physical variables from their steady-state values at the coronal base. Several observed features of the coronal transient that occurred on June 10, 1973, are simulated by using a particular steady-state solar wind, a specific combination of density and temperature perturbations, and a particular time dependence of the perturbations. A different steady-state solar wind, a perturbation of shorter duration, and other perturbation combinations are also employed to simulate the same transient so that the effect of each quantity can be determined. It is found that the model cannot adequately simulate all the observational results for the investigated transient, that the steady-state solar wind is relatively unimportant in such numerical simulations, and that studies which attempt only to reproduce observed shock trajectories may lead to erroneous conclusions regarding the physics of the solar event that produced the transient.

Steinolfson, R. S.; Nakagawa, Y.

1977-01-01

213

Storage, Structure and Reduction of the Solar Data Obtained by the Coronas-I Space Experiment  

NASA Astrophysics Data System (ADS)

An experiment for the investigation of solar X-ray radiation (IRIS) was carried out in the Nuclear Space Physics Laboratory of the A. F. Ioffe Institute of Physics and Technology. The scientific stages of the experiment are: (1) elaboration and creation of a spectrometer device for solar soft and hard X-ray flux measurements; (2) registration of solar X-ray bursts on board the CORONAS-I orbital space station; (3) creation of the Solar Flare Data Base and the development of software for data reduction and physical modeling. These stages are interdependent. Therefore the form of storage, structure and reduction methods of the experimental data are determined by the characteristics of the IRIS spectrometer, by the parameters of the CORONAS-I telemetry system and by the scientific research. The main physical characteristics of the IRIS spectrometer are as follows: energy ranges 2--15 keV and 15--200 keV; dynamic range 10 000; patrol mode time resolution 2.5 s for six energy channels in both X-ray ranges; burst mode time resolution 1.0 s for 32 energy channels in both X-ray ranges and 0.01 s for four energy channels in hard X-ray range only. The reduction of experimental data is performed in two stages. The first stage includes the search for, and selection of, solar X-ray events using a special graphic dialogue computer system. This procedure results in the creation of the Solar Flare Data Base. This database contains the times of solar events, the peak fluxes of soft and hard X-ray radiation, the optical importance, etc. for comparison with the same events in other energy ranges. In the second stage, we study the phenomena of X-ray precursors, the time and energy spectra and the periodicity of flares according to different models. The results obtained are used to produce a database that allows a quick search for any event.

Charikov, Yu. E.; Dmitriyev, P. B.; Kocharov, G. E.; Lasutkov, V. P.; Matveev, G. A.; Nitsora, Yu. N.; Savchenko, M. I.; Skorodumov, D. V.

1997-03-01

214

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

SciTech Connect

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

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

2010-07-20

215

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

SciTech Connect

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

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

2013-08-10

216

Entropy mode at a magnetic null point as a possible tool for indirect observation of nanoflares in the solar corona  

Microsoft Academic Search

Aims: We aim to explore the dynamics of the entropy mode perturbation excited by an energy release in the vicinity of a magnetic null point that is embedded in a gravitationally stratified solar corona. Methods: We solve two-dimensional, time-dependent magnetohydrodynamic equations numerically to find spatial and temporal signatures of the entropy mode that is triggered impulsively by a spatially localized

K. Murawski; T. V. Zaqarashvili; V. M. Nakariakov

2011-01-01

217

Competition of damping mechanisms for the phase-mixed Alfvn waves in the solar corona  

NASA Astrophysics Data System (ADS)

The competition of the linear and nonlinear damping mechanisms for phase-mixed Alfvn waves in the solar corona is studied. It is shown that the nonlinear damping of the phase-mixed Alfvn waves due to their parametric decay is stronger than both collisional and Landau damping for waves with frequencies below a critical frequency which depends on the wave amplitude. This critical frequency is close to the cyclotron frequency ( ~ 105 s-1 in holes) even for small wave amplitudes of the order of 1% of the background value for the magnetic field. This means that the dissipation of the Alfvn wave flux in the corona can be significantly affected by the nonlinear wave dynamics. Nonlinear decay of the low-frequency Alfvn waves transmits a part of the wave energy from the length-scales created by phase mixing to smaller scales, where the waves damp more strongly. However, the direction of the effect can be reversed in the high-frequency domain, 10 s-1

Voitenko, Y.; Goossens, M.

2000-05-01

218

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

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

2014-11-01

220

Astrophysical dust grains in stars, the interstellar medium, and the solar system  

NASA Technical Reports Server (NTRS)

Studies of astrophysical dust grains in circumstellar shells, the interstellar medium, and the solar system may provide information about stellar evolution and about physical conditions in the primitive solar nebula. The following subject areas are covered: (1) the cycling of dust in stellar evolution and the formation of planetary systems; (2) astrophysical dust grains in circumstellar environments; (3) circumstellar grain formation and mass loss; (4) interstellar dust grains; (5) comet dust and the zodiacal cloud; (6) the survival of dust grains during stellar evolution; and (7) establishing connections between stardust and dust in the solar system.

Gehrz, Robert D.

1991-01-01

221

Detection of a corona of fast oxygen atoms during solar maximum  

NASA Astrophysics Data System (ADS)

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

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

1980-07-01

222

Detection of a corona of fast oxygen atoms during solar maximum  

NASA Technical Reports Server (NTRS)

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

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

1980-01-01

223

Significance of adiabatic compression in local heating of the solar corona  

NASA Astrophysics Data System (ADS)

An Investigation of the relative role and contribution of adiabatic compression versus current dissipation to local heating of an X-ray bright point(BP) in the solar corona is carried out. Using a 3D numerical simulation model LINMOD3d, we studied the energy conversion processes due to Lorentz force, pressure gradient force and Ohmic dissipation that increase the thermal energy of an X-ray BP by adiabatic compression. We found the role of compressional effects is quite dominant over the direct Joule heating in changing the temperature. Flux tube volume integration along the magnetic field shows that apart from quantitative comparison, energy conversion rates, total energies and works done by Lorentz and pressure gradient force are sharing the same dynamics. The temperature enhancement follows the same pattern. This indicates that heating this bright point might not need additional sources rather than the adiabatic compression.

Javadi Dogaheh, Setareh; Buechner, Joerg; Otto, Antonius; Carlo Santos, Jean

224

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

225

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

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

226

Monitor PHOKA for solar XUV/EUV irradiation measurement onboard Coronas-Photon mission  

NASA Astrophysics Data System (ADS)

PHOKA is one of the scientific instruments onboard solar satellite Coronas-Photon. The instrument registries fluxes of solar disks radiation in two EUV bands (1-11nm and 27-37nm) and in Ly-?band (121.6nm). Minimum accumulating time of the fluxes is 0.1sec. The silicon Absolute XUV photodiodes AXUV-50(have been fabricated by IRD) are used in PHOKA. AXUV have one hundred percent internal carrier collection efficiency in EUV/XUV region. For blocking of light that is out of the measured EUV band the photodiodes have directly deposited metal filters: Ni-Pd for 1-11nm band and Cr/al for 27-37nm. The Cr/Al devices have at least 7 orders of magnitude visual light blocking. For the Ti/Pd filters the visual light blocking of six order magnitude is achieved. For measuring of visible light background signal the fused silica filters are used. Fused silica filters are placed in filter wheel. Different wheel positions correspond to different PHOKA operation regimes. In Ly-? channel (measuring solar irradiation at 121.6nm) the bare photodiode AXUV and two external filters Acron 122-XN-).5D are used. To ensure the flux measurements with good absolute accuracy the filtered photodiodes are calibrating at synchrotron radiation devices in VNIIOFI (Moscow) and PRB (Germany). The satellite will be launch in autumn season this year to 550km circular orbit with inclination 82.5 degrees. PHOKA instrument Data will be used for studying of development of solar flares and variation of solar irradiation over a long period. During entering and leaving the Earth shadow the instrument will measure solar irradiation passed throw the upper Earth atmosphere (for making occultation measurements to study of the Earth upper atmosphere layers). Detailed description of the instrument, used operation regimes, results of calibration and estimated values of signal/background will be presented and discussed in the report.

Kotov, Yury; Kochemasov, Alexey; Yurov, Vitaly; Korde, Raj

227

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

NASA Astrophysics Data System (ADS)

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

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

2007-05-01

228

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

229

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

230

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

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

231

Improved Constraints on the Preferential Heating and Acceleration of Oxygen Ions in the Extended Solar Corona  

NASA Astrophysics Data System (ADS)

We present a detailed analysis of oxygen ion velocity distributions in the extended solar corona, based on observations made with the Ultraviolet Coronagraph Spectrometer (UVCS) on the SOHO spacecraft. Polar coronal holes exhibit broad line widths and unusual intensity ratios of the O VI ??1032, 1037 emission-line doublet. A traditional interpretation of these features is that oxygen ions have a strong temperature anisotropy, with the temperature perpendicular to the magnetic field being much larger than the temperature parallel to the field. However, recent work by Raouafi and Solanki suggested it may be possible to model the observations using an isotropic velocity distribution. In this paper we analyze an expanded data set to show that the original interpretation of an anisotropic distribution is the only one fully consistent with the observations. It is necessary to search the full range of ion plasma parameters to determine the values with the highest probability of agreement with the UVCS data. The derived ion outflow speeds and perpendicular kinetic temperatures are consistent with earlier results, and there continues to be strong evidence for preferential ion heating and acceleration with respect to hydrogen. At heliocentric heights above 2.1 solar radii, every UVCS data point is more consistent with an anisotropic distribution than with an isotropic distribution. At heights above 3 solar radii, the exact probability of isotropy depends on the electron density chosen to simulate the line-of-sight distribution of O VI emissivity. The most realistic electron densities (which decrease steeply from 3 to 6 solar radii) produce the lowest probabilities of isotropy and most probable temperature anisotropy ratios that exceed 10.

Cranmer, Steven R.; Panasyuk, Alexander V.; Kohl, John L.

2008-05-01

232

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

NASA Astrophysics Data System (ADS)

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

Vilmer, Nicole; Maksimovic, Milan; Rackovic, Kristina

233

The Solar Corona and a CME at the 2010 Total Eclipse  

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

234

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

235

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

236

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

237

Observations of Solar X-ray Spectra by the DIOGENESS and RESIK Spectrometers Onboard the CORONAS-F Satellite  

NASA Astrophysics Data System (ADS)

The first scientific results of the analysis of the X-ray spectra of flares and active regions in the solar corona obtained by Polish-led spectrometers RESIK and DIOGENESS onboard the CORONAS-F satellite are presented. The instruments were designed and made in the Solar Physics Division of the Space Research Center of the Polish Academy of Sciences (SRC PAS, Wroclaw, Poland). The Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation (IZMIRAN, Russia) and the Astronomical Institute of the Czech Academy of Sciences also participated in designing the DIOGENESS spectrometer, while IZMIRAN (Russia), Mullard Space Science Laboratory (MSSL, Great Britain), Rutherford Appleton Laboratory (RAL, Great Britain), and Naval Research Laboratory (NRL, United States) contributed to the development of the RESIK spectrometer. In the paper, we give spectra obtained in a number of previously unstudied spectral ranges and a preliminary identification of new spectral lines. The results for the shifts of the X-ray spectral lines observed with the use of a so-called dopplerometer configuration are also presented. Methods for determining the abundances of the rare elements in the solar corona, including chlorine, potassium, and argon, are described.

Sylwester, J.; Sylwester, B.; Kordylewski, Z.; Phillips, K. J. H.; Kuznetsov, V. D.; Boldyrev, S. I.

2005-11-01

238

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

239

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

240

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

NASA Astrophysics Data System (ADS)

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

Malanushenko, A.; Schrijver, C. J.

2013-10-01

241

Alfvenic Turbulence in the Extended Solar Corona: Kinetic Effects and Proton Heating  

E-print Network

We present a model of magnetohydrodynamic (MHD) turbulence in the extended solar corona that contains the effects of collisionless dissipation and anisotropic particle heating. Measurements made by UVCS/SOHO have revived interest in the idea that ions are energized by the dissipation of ion cyclotron resonant waves, but such high-frequency (i.e., small wavelength) fluctuations have not been observed. A turbulent cascade is one possible way of generating small-scale fluctuations from a pre-existing population of low-frequency MHD waves. We model this 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 parallel wavenumber. 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 fluctuations (with dispersion properties of kinetic Alfven waves) undergo Landau damping, which implies strong parallel electron heating. We discuss the probable nonlinear evolution of the electron velocity distributions into parallel beams and discrete phase-space holes (similar to those seen in the terrestrial magnetosphere) which can possibly heat protons via stochastic interactions.

S. R. Cranmer; A. A. van Ballegooijen

2003-05-08

242

ON THE ANISOTROPY IN EXPANSION OF MAGNETIC FLUX TUBES IN THE SOLAR CORONA  

SciTech Connect

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

Malanushenko, A. [Department of Physics, Montana State University, Bozeman, MT (United States); Schrijver, C. J. [Lockheed Martin Advanced Technology Center, Palo Alto, CA (United States)

2013-10-01

243

Dust in the solar system and in extra-solar planetary systems  

Microsoft Academic Search

Among the observed circumstellar dust envelopes a certain population, planetary debris disks, is ascribed to systems with\\u000a optically thin dust disks and low gas content. These systems contain planetesimals and possibly planets and are believed to\\u000a be systems that are most similar to our solar system in an early evolutionary stage. Planetary debris disks have been identified\\u000a in large numbers

Ingrid Mann; Melanie Khler; Hiroshi Kimura; Andrzej Cechowski; Tetsunori Minato

2006-01-01

244

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

E-print Network

decipherable, then samples of this dust tell us about the conditions in various parts of the solar nebula from of nebula conditions at the boundary between the terrestrial and the giant­planet zones in the solar nebula of their dust is indicative of conditions over a vast swath of the solar nebula between 5­30 AU. Information

Hahn, Joseph M.

245

Modelling the Global Solar Corona: Filament Chirality Observations and Surface Simulations  

E-print Network

The hemispheric pattern of solar filaments is considered in the context of the global magnetic field of the solar corona. In recent work Mackay and van Ballegooijen have shown how, for a pair of interacting magnetic bipoles, the observed chirality pattern could be explained by the dominant range of bipole tilt angles and helicity in each hemisphere. This study aims to test this earlier result through a direct comparison between theory and observations, using newly-developed simulations of the actual surface and 3D coronal magnetic fields over a 6-month period, on a global scale. In this paper we consider two key components of the study; firstly the observations of filament chirality for the sample of 255 filaments, and secondly our new simulations of the large-scale surface magnetic field. Based on a flux-transport model, these will be used as the lower boundary condition for the future 3D coronal simulations. Our technique differs significantly from those of other authors, where the coronal field is either assumed to be purely potential, or has to be reset back to potential every 27 days in order that the photospheric field remain accurate. In our case we ensure accuracy by the insertion of newly-emerging bipolar active regions, based on observed photospheric synoptic magnetograms. The large-scale surface field is shown to remain accurate over the 6-month period, without any resetting. This new technique will enable future simulations to consider the long-term build-up and transport of helicity and shear in the coronal magnetic field, over many months or years.

A. R. Yeates; D. H. Mackay; A. A. van Ballegooijen

2007-07-22

246

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

NASA Astrophysics Data System (ADS)

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

Lee, K. W.; Bchner, J.; Elkina, N.

2008-02-01

247

Coulomb Energy Losses in the Solar Corona and the Proton Energy Budget in Flares  

NASA Astrophysics Data System (ADS)

It has recently been proposed, on the basis of measurements of the flux in the 20Ne 1.634 MeV line, that the energy budget for nonthermal protons in solar flares may be significantly larger than previously assumed. The argument is founded on the fact that the 1.634 MeV feature has a (proton) excitation threshold energy significantly lower than that of the C and O lines in the 4-6 MeV range. Hence the observed enhanced level of emission in the 1.634 MeV line requires a higher flux of low-energy (~1 MeV) protons than would be obtained from a backward extrapolation of the ~10 MeV spectrum using canonical (i.e., modified Bessel function) spectral forms and so a greater overall energy content. In this paper we check the effects on this conclusion of two significant factors omitted from the previous analysis, which was based on a ``cold'' chromospheric target model. While such a model may be appropriate for protons of ~10 MeV energies, protons of ~1 MeV may undergo a significant part of their energy loss in the hot corona, which is ionized and also ``warm'' for beam protons of these energies. The ionization results in a Coulomb logarithm (and energy loss rate) almost 3 times higher than in the neutral chromosphere. On the other hand, the warm target effect results in energy losses a factor of 1-10 times lower than in a cold target. Thus, if beam protons underwent a substantial part of their energy loss in the corona (depending on the column density encountered), previous conclusions from the 20Ne line flux could be either enhanced or negated, depending on which effect dominates. We show that for likely flare coronal temperatures and column densities that the net consequences for the 20Ne flux are in fact small, unless the low-energy protons are preferentially trapped in an improbably hot dense magnetic island.

Emslie, A. Gordon; Brown, John C.; MacKinnon, Alexander L.

1997-08-01

248

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

249

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

SciTech Connect

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

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

2009-10-10

250

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

251

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

252

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

253

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

Microsoft Academic Search

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

J. Rybk; P. Gmry; A. Benz; P. Bogachev; R. Brajsa

2010-01-01

254

Short time variability of solar corona during recent solar cycle minimum  

NASA Astrophysics Data System (ADS)

Sphinx is the X-ray spectrophotometer designed to measure X-ray emission from the Sun in the energy range between 0.8 keV and 15 keV. The instrument is placed onboard Russian KORONAS-PHOTON satellite launched on January 30, 2009. In this paper we present the observations of coronal emission obtained between March-April and August-September 2009, i.e. the times towards the end of the last, very prolonged and deep minimum of solar activity. Prompt analysis of SphinX spectra reveal the variability of the average coronal plasma charac-teristics like the temperature and emission measure. These data are used to compare SphinX and GOES measurements, for selected times. Examples of many sub/microflare events with maxima of the X-ray flux, observed much below the GOES sensitivity threshold level will be presented.

Siarkowski, Marek; Gryciuk, Magdalena; Gburek, Szymon; Sylwester, Janusz; Sylwester, Barbara; Kepa, Anna; Buczkowska, Agnieszka; Kowalinski, Miroslaw

255

Seed Particles in the Solar Corona inferred from the Solar Wind Halo Component of the Proton Spectra measured at 1 AU with ACE  

NASA Astrophysics Data System (ADS)

Recent detailed observations of the halo component of the solar wind, which was discovered by Gloeckler et al. (AIP Conf. Proc., 1039, 367, 2008) using ACE/SWICS measurements of the proton spectrum in the energy range from ~0.6 to ~100 keV/charge, can be used to infer seed particle populations in the solar corona. In the solar wind frame of reference, the halo component is observed at speeds from about 4 to 5 times the thermal speed of the bulk solar wind (well represented by a Maxwellian) to about the flow speed of bulk solar wind, above which the suprathermal tail is observed. During times of strong local acceleration of suprathermal tails, the halo is well represented by a power law spectrum with index ranging from -7 to -8. During times of weak local acceleration of the tails, the halo component appears as a kappa function. The observed halo component can be explained as a remnant of seed particles in the solar corona that are produced by the pump mechanism that also produces the observed -5 power law tails.

Gloeckler, G.; Fisk, L. A.

2013-12-01

256

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

257

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

258

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

259

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

260

Trapping of dust by coherent vortices in the solar nebula  

E-print Network

We develop the idea proposed by Barge & Sommeria (1995) and Tanga et al. (1996) that large-scale vortices present in the solar nebula can concentrate dust particles and facilitate the formation of planetesimals and planets. We introduce an exact vortex solution of the incompressible 2D Euler equation and study the motion of dust particles in that vortex. In particular, we derive analytical expressions for the capture time and the mass capture rate as a function of the friction parameter. Then, we study how small-scale turbulent fluctuations affect the motion of the particles in the vortex and determine their rate of escape by solving a problem of quantum mechanics. We apply these results to the solar nebula and find that the capture is optimum near Jupiter's orbit (as noticed already by Barge & Sommeria 1995) but also in the Earth region. This second optimum corresponds to the transition between the Epstein and the Stokes regime which takes place, for relevant particles, at the separation between telluric and giant planets (i.e near the asteroid belt). At these locations, the particles are efficiently captured and concentrated by the vortices and can undergo gravitational collapse to form the planetesimals.

Pierre-Henri Chavanis

1999-12-06

261

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

NASA Astrophysics Data System (ADS)

We present new Spitzer/IRS spectra of two hot R Coronae Borealis (RCB) stars, one in the Galaxy, V348 Sgr, and one lying in the Large Magellanic Cloud, HV 2671. These two objects may constitute a link between the RCB stars and the late Wolf-Rayet ([WCL]) class of central stars of planetary nebulae (CSPNe), such as CPD -56 8032, that has little or no hydrogen in their atmospheres. HV 2671 and V348 Sgr are members of a rare subclass that has significantly higher effective temperatures than most RCB stars, but shares the traits of hydrogen deficiency and dust formation that define the cooler RCB stars. The [WC] CSPN star, CPD -56 8032, displays evidence of dual-dust chemistry showing both polycyclic aromatic hydrocarbons (PAHs) and crystalline silicates in its mid-IR spectrum. HV 2671 shows strong PAH emission but no sign of having crystalline silicates. The spectrum of V348 Sgr is very different from that of CPD -56 8032 and HV 2671. The PAH emission seen strongly in the other two stars is not present. Instead, the spectrum is dominated by a broad emission centered at about 8.2 ?m. This feature is not identified with either PAHs or silicates. Several other cool RCB stars, novae, and post-asymptotic giant branch stars show similar features in their IR spectra. The mid-IR spectrum of CPD -56 8032 shows emission features that may be associated with C60. The other two stars do not show evidence of C60. The different nature of the dust around these stars does not help us in establishing further links that may indicate a common origin. HV 2671 has also been detected by Herschel/PACS and SPIRE. V348 Sgr and CPD -56 8032 have been detected by AKARI/Far-Infrared Surveyor. These data were combined with Spitzer, IRAS, Two Micron All Sky Survey, and other photometry to produce their spectral energy distributions (SEDs) from the visible to the far-IR. Monte Carlo radiative transfer modeling was used to study the circumstellar dust around these stars. HV 2671 and CPD -56 8032 require both a flared inner disk with warm dust and an extended diffuse envelope with cold dust to fit their SEDs. The SED of V348 Sgr can be fit with a much smaller disk and envelope. The cold dust in the extended diffuse envelopes inferred around HV 2671 and CPD -56 8032 may consist of interstellar medium swept up during mass-loss episodes.

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

2011-08-01

262

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

263

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

NASA Technical Reports Server (NTRS)

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

Fuerstenau, Stephen D.

2006-01-01

264

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

265

Restructuring of Dust Aggregates in the Solar Nebula  

NASA Technical Reports Server (NTRS)

We discuss the results of a recent effort to analyze the mechanical stability of dust aggregates with a detailed model of the physical properties of a contact between grains. This model contains both elastic repulsion forces and attractive van der Waals/dipole/metallic forces along with a description of the energy dissipation due to rolling, sliding, and breaking of contacts. We find that (1) aggregates formed from single sized grains via Particle-Cluster-Aggregation remain fluffy, (2) collisions with other aggregates and with large grains may lead to compaction (3) the velocities of small grains and aggregates in the early solar nebula are too small to produce marked compaction as long as the aggregates are small, and (4) internal restructuring of aggregates is a potentially large sink of energy which could enable the sticking of large bodies even at collision velocities of the order of several hundred cm/s.

Dominik, C.; Tielens, A. G. G. M.

1996-01-01

266

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

267

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

268

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

269

Whie light solar corona: an atlas of 1988 K-coronameter synoptic charts, December 1987 to January 1989  

NASA Astrophysics Data System (ADS)

The synoptic observing project of the High Altitude Observatory's Coronal Dynamics Program began on 30 July 1980. The data obtained for it are gathered by the Mark-III K-coronameter located at the Mauna Loa Solar Observatory, Hawaii, and are published yearly in volumes of The White Light Solar Corona: An Atlas of K-Coronameter Synoptic Charts (Table 1). The data, in the form of synoptic charts, are extended at both the beginning and the end of each year to provide some overlap with the preceding and succeeding volumes. This is also necessary to provide a complete set of the data organized into Carrington rotations covering a specific time period since the rotations do not coincide with the yearly calendar. Further observations are made at the limb, and west limb passage occurs 14 days after east limb passage. Thus, an entire rotation's data requires more than 28 days to collect. Together with the synoptic maps and polar synoptic maps, two additional sections designed to aid the user are included in the volume. As in previous Atlases, the Activity Report Summary for the year is given and the Mauna Loa Solar Observatory Calendar for 1988 (Table III) is also included. This is a list of days on which no coronal observations were achieved. These synoptic data should be regarded as a preliminary presentation in which corrections have not fully been made for the day-to-day variations and scattering of polarized light by the earth's atmosphere. Data from the east and west limbs are presented separately in the synoptic charts, as transient and evolutionary changes in the white light corona can substantially modify the distribution of coronal material over the 14 days between sequential limb passages.

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

1990-03-01

270

ELECTRON DENSITY VARIATION IN OFFLIMB SOLAR CORONA STRUCTURES I. UgarteUrra , J.G. Doyle, and M.S. Madjarska  

E-print Network

1 ELECTRON DENSITY VARIATION IN OFF­LIMB SOLAR CORONA STRUCTURES I. Ugarte­Urra #3; , J.G. Doyle a study of the electron density variation for off limb observations with the Coronal Diagnostic Spec­ trometer (CDS) on board SoHO using the density sensi­ tive coronal line ratio Si X (356

271

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

NASA Astrophysics Data System (ADS)

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

Martiek, K.; Druckmllerov, H.

2011-12-01

272

Nonlinear force-free models for the solar corona. I. Two active regions with very different structure  

NASA Astrophysics Data System (ADS)

Context: With the development of new instrumentation providing measurements of solar photospheric vector magnetic fields, we need to develop our understanding of the effects of current density on coronal magnetic field configurations. Aims: The object is to understand the diverse and complex nature of coronal magnetic fields in active regions using a nonlinear force-free model. Methods: From the observed photospheric magnetic field we derive the photospheric current density for two active regions: one is a decaying active region with strong currents (AR8151), and the other is a newly emerged active region with weak currents (AR8210). We compare the three-dimensional structure of the magnetic fields for both active region when they are assumed to be either potential or nonlinear force-free. The latter is computed using a Grad-Rubin vector-potential-like numerical scheme. A quantitative comparison is performed in terms of the geometry, the connectivity of field lines, the magnetic energy and the magnetic helicity content. Results: For the old decaying active region the connectivity and geometry of the nonlinear force-free model include strong twist and strong shear and are very different from the potential model. The twisted flux bundles store magnetic energy and magnetic helicity high in the corona (about 50 Mm). The newly emerged active region has a complex topology and the departure from a potential field is small, but the excess magnetic energy is stored in the low corona and is enough to trigger powerful flares.

Rgnier, S.; Priest, E. R.

2007-06-01

273

Settling and growth of dust particles in a laminar phase of a low-mass solar nebula  

Microsoft Academic Search

In view of the possibility that vertical convection and turbulence can be suppressed in the early phase of a solar nebula because of a reduction of dust opacity's temperature dependence that is caused by rapid dust particle growth, a reexamination is made of dust particle settling and growth phenomena in the subsequent, laminar phase of the solar nebula. The settling

Y. Nakagawa; M. Sekiya; C. Hayashi

1986-01-01

274

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

275

Growth and sedimentation of dust grains in the primordial solar nebula  

Microsoft Academic Search

The process of dust grain growth and sedimentation in the primordial solar nebula is investigated for a region near the earth's orbit. The growth equation for dust grains that are sinking as well as in thermal motion is solved numerically, in the wide mass range between 10 to the -12th and 10 to the 6th. Turbulent motions in the nebula

Y. Nakagawa; K. Nakazawa; C. Hayashi

1981-01-01

276

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

277

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

SciTech Connect

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

watts, Christopher

2010-01-31

278

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

279

White light solar corona: an atlas of 1987 K-coronameter synoptic charts, December 1986 - January 1988  

NASA Astrophysics Data System (ADS)

The synoptic observing project of the High Altitude Observatory's Coronal Dynamics Program began on 5 August 1980. The data obtained for it are gathered by the Mark 3 K-coronameter located at the Mauna Loa Solar Observatory, Hawaii, and are published yearly in volumes of The White Light Solar Corona: An Atlas of K-Coronameter Synoptic Charts. The data, in form of synoptic charts, are extended at both the beginning and the end of each year to provide some overlap with the preceding and succeeding volumes. This is also necessary to provide a complete set of the data organized into Carrington rotations covering a specific time period, since the rotations do not coincide with the yearly calendar. Further, observations are made at the limb, and west limb passage occurs 14 days after east limb passage. Thus, an entire rotation's data requires more than 28 days to collect. As well as the synoptic maps, two additional sections designed to aid the user are included in the volume. As in previous Atlases, the Activity Report Summary for the year and the Polar Synoptic Charts are included. Also included is the Mauna Loa Solar Observatory Calendar for 1987.

Sime, D. G.; Garcia, C.; Yasukawa, E.; Lundin, E.; Hoffman, F.; Reppert, P.

1988-03-01

280

White light solar corona: an atlas of 1986 K-coronameter synoptic charts, December 1985 - January 1987  

NASA Astrophysics Data System (ADS)

The synoptic observing project of the High ltitude Observatory's Coronal Dynamics Program began on 5 August 1980. The data obtained for it are gathered by the Mark-III K-coronameter located at the Mauna Loa Solar Observatory, Hawaii, and are published yearly in volumes of The White Solar Corona: An Atlas of K-Coronameter Synoptic Charts. The data are extended at both the beginning and the end of each volume to provide some overlap with the preceding and succeeding volumes. This is necessary to provide a complete set of the data organized into Carrington rotations covering a specific time period, since the rotations do not coincide with the yearly calendar. Further, observations are made at the limb, and west limb passage occur 14 days after the east limb passage. Thus, an entire rotation's data requires more than 28 days to collect. As well as the synoptic maps, there are two additional sections designed to aid the user included. As in previous atlases, the Activity Report Summary for the year and the Polar Synoptic Charts are included. Also included is the Mauna Loa Solar Observatory Calendar for 1986. This is a list of days on which no coronal observations were achieved.

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

1987-03-01

281

Fine strand-like structure in the solar corona from MHD transverse oscillations  

E-print Network

Current analytical and numerical modelling suggest the existence of ubiquitous thin current sheets in the corona that could explain the observed heating requirements. On the other hand, new high resolution observations of the corona indicate that its magnetic field may tend to organise itself in fine strand-like structures of few hundred kilometres widths. The link between small structure in models and the observed widths of strand-like structure several orders of magnitude larger is still not clear. A popular theoretical scenario is the nanoflare model, in which each strand is the product of an ensemble of heating events. Here, we suggest an alternative mechanism for strand generation. Through forward modelling of 3D MHD simulations we show that small amplitude transverse MHD waves can lead in a few periods time to strand-like structure in loops in EUV intensity images. Our model is based on previous numerical work showing that transverse MHD oscillations can lead to Kelvin-Helmholtz instabilities that defor...

Antolin, P; Van Doorsselaere, T

2014-01-01

282

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

283

Heating of Chromospheres and Coronae. P. Ulmschneider, Space Solar Physics, Summer School Orsay 1-13.9.97, J.C. Vial, K. Bocchialini, K. Boumier eds. (1997) submitted  

E-print Network

./ } Heating of Chromospheres and Coronae. P. Ulmschneider, Space Solar Physics, Summer School and coronae owe their existence to mechanical heating. In the present work the mechanisms which are thought Orsay 1-13.9.97, J.C. Vial, K. Bocchialini, K. Boumier eds. (1997) submitted 2 Heating of Chromospheres

Ulmschneider, Peter

284

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

285

Validation of Spherically Symmetric Inversion by Use of a Tomographically Reconstructed Three-Dimensional Electron Density of the Solar Corona  

NASA Astrophysics Data System (ADS)

Determination of the coronal electron density by the inversion of white-light polarized brightness (pB) measurements by coronagraphs is a classic problem in solar physics. An inversion technique based on the spherically symmetric geometry (Spherically Symmetric Inversion, SSI) was developed in the 1950s, and has been widely applied to interpret various observations. However, to date there is no study about uncertainty estimation of this method. In this study we present the detailed assessment of this method using a three-dimensional (3D) electron density in the corona from 1.5 to 4 Rsun as a model, which is reconstructed by tomography method from STEREO/COR1 observations during solar minimum in February 2008. We first show in theory and observation that the spherically symmetric polynomial approximation (SSPA) method and the Van de Hulst inversion technique are equivalent. Then we assess the SSPA method using synthesized pB images from the 3D density model, and find that the SSPA density values are close to the model inputs for the streamer core near the plane of the sky (POS) with differences generally less than a factor of two or so; the former has the lower peak but more spread in both longitudinal and latitudinal directions than the latter. We estimate that the SSPA method may resolve the coronal density structure near the POS with angular resolution in longitude of about 50 degrees. Our results confirm the suggestion that the SSI method is applicable to the solar minimum streamer (belt) as stated in some previous studies. In addition, we demonstrate that the SSPA method can be used to reconstruct the 3D coronal density, roughly in agreement with that by tomography for a period of low solar activity. We suggest that the SSI method is complementary to the 3D tomographic technique in some cases, given that the development of the latter is still an ongoing research effort.

Wang, Tongjiang; Davila, Joseph M.

2014-10-01

286

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

NASA Astrophysics Data System (ADS)

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

Jiang, Chaowei; Feng, Xueshang

2012-04-01

287

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

288

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

289

In-situ Monitoring of Interstellar Dust in the Solar System  

NASA Astrophysics Data System (ADS)

The Ulysses spacecraft has been orbiting the Sun on a highly inclined ellipse almost perpendicular to the ecliptic plane (inclination 79 , perihelion distance 1.3 AU, aphelion distance 5.4 AU) since it encountered Jupiter in 1992. The in-situ dust detector on board continuously measures 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 local interstellar cloud (LIC), and the grains act as tracers of the physical conditions in the LIC. The intrinsic size distribution of interstellar grains in the LIC extends to grain sizes larger than those detectable by astronomical observations. The existence of such 'big' interstellar grains is also indicated by observations of radar meteors entering the Earth's atmosphere. The Ulysses measurements showed that the dust-to-gas mass ratio in the local interstellar cloud is several times higher than the standard interstellar value derived from cosmic abundances, implying the existence of inhomogeneities in the diffuse interstellar medium on relatively small length scales. While the Ulysses dust instrument monitored the interstellar dust stream at high ecliptic latitude between 3 and 5 AU, interstellar impactors were also identified in the data sets measured with the in-situ dust detectors on board Cassini, Galileo and Helios, covering a distance range between 0.3 and 3 AU in the ecliptic plane. The data provide evidence for alteration of the interstellar dust stream in the inner solar system, caused by the solar radiation pressure force, gravitaional focussing and interaction of charged grains with the time varying interplanetary magnetic field. We review the insitu interstellar dust measurements obtained from a fleet of four spacecraft in the Solar System and present the latest results from the Ulysses interstellar dust measurements.

Kruger, H.; Altobelli, N.; Grun, E.; Kempf, S.; Landgraf, M.; Srama, R.; Helfert, S.; Moragas-Klostermeyer, G.

290

PLASMA FLOWS GUIDED BY STRONG MAGNETIC FIELDS IN THE SOLAR CORONA Eckart Marsch  

E-print Network

loops, which are clearly visible in the SOHO images and TRACE movies. Most coronal plasma is permanently confined and re- cycled by circulation, but some fraction can escape as tenuous solar wind, being a mixture

Wiegelmann, Thomas

291

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

292

Understanding CME and associated shock in the solar corona by merging multi wavelengths observation  

E-print Network

Using multi-wavelength 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 CME which interact during more than 30 min, and can be considered as physically linked. This was an unusual event. The jet is generated above a typical complex magnetic configuration which 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 large Active Region (AR). 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 which becomes destabilized by magnetic reconnection between the outer part of the jet and the ambient m...

Zucca, Pietro; Demoulin, Pascal; Kerdraon, Alain; Lecacheux, Alain; Gallagher, Peter T

2014-01-01

293

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

294

Dust Models Paint Alien's View of Solar System  

NASA Video Gallery

Dust in the Kuiper Belt, the cold-storage zone that includes Pluto, creates a faint infrared disk potentially visible to alien astronomers looking for planets around the sun. Neptune's gravitationa...

295

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

296

Magnetostatic structures of the solar corona. 2: The magnetic topology of quiescent prominences  

NASA Astrophysics Data System (ADS)

This paper treats the magnetic properties of the quiescent prominence as a part of the larger coronal structure made up of the prominence, cavity, and helmet dome. A rigorous analysis of the mechanical support of a vertical prominence sheet suspended in equilibrium by magnetic fields in uniform gravity shows that the finite vertical extension of the prominence sheet has an important dynamic constraint. For the inverse topology with the prominence magnetic field pointing opposite to the field implied by the bipolar photospheric region below, this constraint requries the prominence sheet to be embedded in a horizontal, nearly force-free, magnetic flux rope which crucially supports a part of the prominence weight by current attraction from above. A similar analysis of the support problem is carried out for the prominence in the normal topology in which both prominence and photospheric magnetic fields point in the same sense. Starting with the observation that most prominences are of the inverse topology, a recent model is extended to show that this topology implies that the prominence sits in a two-flux magnetic system, one flux connecting the bipolar magnetic sources in the photosphere below and the other forming a rope which embeds the prominence and runs above and parallel to the photospheric polarity-inversion line. This model physically relates several pieces of well-known but hitherto disjoint observations. The prominence flux rope manifests itself as the cavity in the corona and as the filament channel in the chromosphere. The chromospheric fibril patterns associated with prominences and filament channels can, for the first time, be modeled faithfully. Several physical implications on the origin of the prominence and questions deriving from the results are discussed.

Low, B. C.; Hundhausen, J. R.

1995-04-01

297

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

298

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

299

Kinetic Instability of Drift-Alfvn Waves in Solar Corona and Stochastic Heating  

Microsoft Academic Search

The solar atmosphere is structured and inhomogeneous, both horizontally and vertically. The omnipresence of coronal magnetic loops implies gradients of the equilibrium plasma quantities such as the density, magnetic field, and temperature. These gradients are responsible for the excitation of drift waves that grow both within the two-component fluid description (both in the presence of collisions and without it) and

J. Vranjes; S. Poedts

2010-01-01

300

Stellar Coronae, Solar Flares: A Detailed Comparison of ? GEM, HR 1099, and the Sun in High-resolution X-Rays  

NASA Astrophysics Data System (ADS)

The Chandra High Energy Transmission Grating Spectrometer (HETG) spectra of the coronally active binary stars ? 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\\,{\\mathring{\\rm{A}}} region (including emission from highly ionized S, Si, Ar, and K) from solar flare spectra to the corresponding ? Gem and HR 1099 spectra. We also model the larger wavelength range of the HETG, from 1.7 to 25\\,{\\mathring{\\rm{A}}}having emission lines from Fe, Ca, Ar, Si, Al, Mg, Ne, O, and Nto determine coronal temperatures and abundances. ? 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 ?20 MK, comparable to the ? Gem and HR 1099 coronae. During the Chandra exposures, ? 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 ? Gem. While ? Gem and HR 1099 differ in their emission measure distributions, they have very similar elemental abundances.

Huenemoerder, David P.; Phillips, Kenneth J. H.; Sylwester, Janusz; Sylwester, Barbara

2013-05-01

301

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

SciTech Connect

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

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

2008-06-09

302

The spectrum of magnetic field irregularities in the solar corona and in interplanetary space  

Microsoft Academic Search

Results are presented of a spectral analysis of Faraday rotation fluctuations observed during the solar occultations of the Helios spacecraft. The temporal spectra of Faraday rotation fluctuations in the frequency range between 10?3 Hz and 10?2 Hz usually assume the form of a power law. The power-law exponent is ?1.6 at heliocentric distances 3 R? < r < 6 R?

I. V. Chashei; A. I. Efimov; L. N. Samoznaev; M. K. Bird; M. Ptzold

2000-01-01

303

Numerical simulation of particle acceleration in the solar corona above active regions  

NASA Astrophysics Data System (ADS)

Recent solar observations have provided important information about particle acceleration above active regions in the course of solar flares. Although many models have been proposed the many questions still remain open. We use different relativistic test particle approaches to study the acceleration mechanisms by magnetic reconnection. We choose to calculate the full particle trajectories by two different codes as well as an approach calculating the motion of the guiding center . The magnetic and electric fields are obtained from MHD simulations of the active region dynamics using subgrid information to calculate the accelerating electric fields. Our MHD simulations are based on the observations. The initial magnetic field is extrapolated from magnetogram of active region. The particles are most efficiently accelerated by the parallel component of electric field. We investigate the particle acceleration in dependence on various subgrid models dependent on the current carrier velocity.. In particular we studied the dependence of the acceleration time and the energy gain of particles as well as their energy distribution needed to calculate the Hard X-ray spectrum to be compared with the observations of the RHESSI solar X-ray telescope.

Zhou, Xiaowei; Skala, Jan; Buechner, Joerg; Gan, Weiqun; Liu, Simimg

2013-04-01

304

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

305

ELECTROMAGNETIC ESCAPE OF DUST FROM THE SOLAR SYSTEM  

E-print Network

configuration of the solar magnetic field, perhaps accounting for particles detected by the Ulysses spacecraft at latitudes up to 80 ffi . When the solar magnetic field is reversed, particles are more strongly confined­sized particles in the solar system can cause these grains to escape along hyperbolic trajectories

Hamilton, Douglas P.

306

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

307

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

308

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

309

Particle Acceleration in a Statistically Modeled Solar Active-Region Corona  

NASA Astrophysics Data System (ADS)

Elaborating a statistical approach to describe the spatiotemporally intermittent electric field structures formed inside a flaring solar active region, we investigate the efficiency of such structures in accelerating charged particles (electrons). The large-scale magnetic configuration in the solar atmosphere responds to the strong turbulent flows that convey perturbations across the active region by initiating avalanche-type processes. The resulting unstable structures correspond to small-scale dissipation regions hosting strong electric fields. Previous research on particle acceleration in strongly turbulent plasmas provides a general framework for addressing such a problem. This framework combines various electromagnetic field configurations obtained by magnetohydrodynamical (MHD) or cellular automata (CA) simulations, or by employing a statistical description of the field's strength and configuration with test particle simulations. Our objective is to complement previous work done on the subject. As in previous efforts, a set of three probability distribution functions describes our ad-hoc electromagnetic field configurations. In addition, we work on data-driven 3D magnetic field extrapolations. A collisional relativistic test-particle simulation traces each particle's guiding center within these configurations. We also find that an interplay between different electron populations (thermal/non-thermal, ambient/injected) in our simulations may also address, via a re-acceleration mechanism, the so called `number problem'. Using the simulated particle-energy distributions at different heights of the cylinder we test our results against observations, in the framework of the collisional thick target model (CTTM) of solar hard X-ray (HXR) emission. The above work is supported by the Hellenic National Space Weather Research Network (HNSWRN) via the THALIS Programme.

Toutounzi, A.; Vlahos, L.; Isliker, H.; Dimitropoulou, M.; Anastasiadis, A.; Georgoulis, M.

2013-09-01

310

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

311

Dynamical models of Kuiper Belt dust in the inner and outer Solar System  

E-print Network

We report several results related to the dynamical evolution of dust produced in the Kuiper Belt (KB). We show that its particle size frequency distribution in space is greatly changed from the distribution at production, as a results of the combined effects of radiation forces and the perturbations of the planets. We estimate the contribution of KB dust to the zodiacal cloud by calculating the radial profile of its number density near the ecliptic. We also study the contribution of KB dust to the population of interplanetary dust particles (IDPs) collected at Earth, by calculating geocentric encounter velocities and capture rates. Our models show, in contrast with previous studies, that KB dust grains on Earth-crossing orbits have high eccentricities and inclinations and, therefore, their encounter velocities are similar to those of cometary grains and not to asteroidal grains. We estimate that at most 25% in number of captured IDPs have cometary or KB origin; the KB contribution may be as low as 1%-2%. We present the velocity field of KB dust throughout the solar system; this, together with the number density radial profile, is potentially useful for planning spacecraft missions to the outer solar system.

Amaya Moro-Martin; Renu Malhotra

2005-06-28

312

Modelling the Global Solar Corona II: Coronal Evolution and Filament Chirality Comparison  

E-print Network

The hemispheric pattern of solar filaments is considered using newly-developed simulations of the real photospheric and 3D coronal magnetic fields over a 6-month period, on a global scale. The magnetic field direction in the simulation is compared directly with the chirality of observed filaments, at their observed locations. In our model the coronal field evolves through a continuous sequence of nonlinear force-free equilibria, in response to the changing photospheric boundary conditions and the emergence of new magnetic flux. In total 119 magnetic bipoles with properties matching observed active regions are inserted. These bipoles emerge twisted and inject magnetic helicity into the solar atmosphere. When we choose the sign of this active-region helicity to match that observed in each hemisphere, the model produces the correct chirality for up to 96% of filaments, including exceptions to the hemispheric pattern. If the emerging bipoles have zero helicity, or helicity of the opposite sign, then this percentage is much reduced. In addition, the simulation produces a higher proportion of filaments with the correct chirality after longer times. This indicates that a key element in the evolution of the coronal field is its long-term memory, and the build-up and transport of helicity from low to high latitudes over many months. It highlights the importance of continuous evolution of the coronal field, rather than independent extrapolations at different times. This has significant consequences for future modelling such as that related to the origin and development of coronal mass ejections.

A. R. Yeates; D. H. Mackay; A. A. van Ballegooijen

2007-11-19

313

Hot oxygen coronas at terrestrial planets  

Microsoft Academic Search

Solar forcing via both influx of the solar wind plasma and absorption of ultraviolet radiation forms the hot oxygen coronas at the terrestrial planets (Shizgal and Arcos, 1996). These coronas were observed in the past and recent planetary space missions (Mariner, Pioneer Venus, IMAGE, Mars Express and etc.). We will dicsuss the relative role of the following energetic processes determining

V. I. Shematovich; R. E. Johnson

2006-01-01

314

Measurements of solar system dust at R < 1 AU and R > 3 AU  

NASA Technical Reports Server (NTRS)

In Situ experiments on space craft yield information about dust parameters such as velocity, flux and size, and mass of particles. In Situ experiments as well as brightness measurements in the inner solar system have been made with Helios from .3 to 1 AU in the ecliptic plane which reveal two different dust populations with different bulk densities and relative velocities to the spacecraft. Zodiacal light measurements from Helios 1 and 2 reveal a radial brightness gradient proportional to R(exp -2.3). Measurements of dust particles in the outer solar system have been made onboard the Pioneer 10 and 11 spacecraft and for the high latitude region with Ulysses. Pioneer 10 and 11 also carried a spin-scan photopolarimeter that was used to map the zodiacal light and background starlight during the cruise to Jupiter in two broad bandpasses centered at .44 and .64 micron. Details of these measurements are briefly discussed.

Mann, Ingrid; Hanner, Martha

1998-01-01

315

Current-driven magnetohydrodynamic thermal instabilities in sheared fields. [of solar corona  

NASA Technical Reports Server (NTRS)

Approximate analytic solutions are sought for the dispersion relation for the MHD stability of magnetized medium in current-driven filamentation modes such as those observed in the solar atmosphere. The magnetic field is assumed to have a self-consistent sheared equilibrium structure. The analysis is carried out in the small wavenumber regime, where shear length is similar to the mode wavelength. Instability is found to depend on the ratio between the thermal and magnetic diffusivities, i.e., the Prandtl number, which identifies the unstable transverse wavenumbers. The instability conditions are expressed in an algebraic equation amenable to numerical solution. Results are provided from use of the model to determine the maximum growth rate and typical scale lengths of instabilities in a precoronal atmosphere and the lower transition region.

Bodo, G.; Ferrari, A.; Massaglia, S.; Rosner, R.

1987-01-01

316

Rocket studies of solar corona and transition region. [X-Ray spectrometer/spectrograph telescope  

NASA Technical Reports Server (NTRS)

The XSST (X-Ray Spectrometer/Spectrograph Telescope) rocket payload launched by a Nike Boosted Black Brant was designed to provide high spectral resolution coronal soft X-ray line information on a spectrographic plate, as well as time resolved photo-electric records of pre-selected lines and spectral regions. This spectral data is obtained from a 1 x 10 arc second solar region defined by the paraboloidal telescope of the XSST. The transition region camera provided full disc images in selected spectral intervals originating in lower temperature zones than the emitting regions accessible to the XSST. A H-alpha camera system allowed referencing the measurements to the chromospheric temperatures and altitudes. Payload flight and recovery information is provided along with X-ray photoelectric and UV flight data, transition camera results and a summary of the anomalies encountered. Instrument mechanical stability and spectrometer pointing direction are also examined.

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

1979-01-01

317

Fragmentation of electric currents in the solar corona by plasma flows  

NASA Astrophysics Data System (ADS)

Aims: We consider a magnetic configuration consisting of an arcade structure and a detached plasmoid, resulting from a magnetic reconnection process, as is typically found in connection with solar flares. We study spontaneous current fragmentation caused by shear and vortex plasma flows. Methods: An exact analytical transformation method was applied to calculate self-consistent solutions of the nonlinear stationary magnetohydrodynamic equations. The assumption of incompressible field-aligned flows implies that both the Alfvn Mach number and the mass density are constant on field lines. We first calculated nonlinear magnetohydrostatic equilibria with the help of the Liouville method, emulating the scenario of a solar eruptive flare configuration with plasmoids (magnetic ropes or current-carrying loops in 3D) and flare arcade. Then a Mach number profile was constructed that describes the upflow along the open magnetic field lines and implements a vortex flow inside the plasmoid. This Mach number profile was used to map the magnetohydrostatic equilibrium to the stationary one. Results: We find that current fragmentation takes place at different locations within our configuration. Steep gradients of the Alfvn Mach number are required, implying the strong influence of shear flows on current amplification and filamentation of the magnetohydrostatic current sheets. Crescent- or ring-like structures appear along the outer separatrix, butterfly structures between the upper and lower plasmoids, and strong current peaks close the lower boundary (photosphere). Furthermore, impressing an intrinsic small-scale structure on the upper plasmoid results in strong fragmentation of the plasmoid. Hence fragmentation of current sheets and plasmoids is an inherent property of magnetohydrodynamic theory. Conclusions: Transformations from magnetohydrostatic into magnetohydrodynamic steady-states deliver fine-structures needed for plasma heating and acceleration of particles and bulk plasma flows in dissipative events that are typically connected to magnetic reconnection processes in flares and coronal mass ejections.

Nickeler, D. H.; Karlick, M.; Wiegelmann, T.; Kraus, M.

2013-08-01

318

Interplanetary Field Enhancements: Further evidence of an interaction between the solar wind and interplanetary dust  

Microsoft Academic Search

Interplanetary field enhancements (IFEs) are highly unusual, sharply-peaked increases in the magnitude of the heliospheric magnetic field. They have been found in the solar wind over a wide range of heliocentric distances. Spatial clustering of IFEs detected near Venus led to a link being found between some IFEs and dust particles co-orbiting with asteroid 2201 Oljato. This link suggested that

G. H. Jones; E. J. Smith; A. Balogh

2003-01-01

319

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

320

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

E-print Network

EUV images of Comet Lovejoy (C/2011 W3) from the AIA 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 6 between neighboring flux tubes over scales of a few thousand km. These density structures imply variations in the Alfven speed on a similar scale. They will drastically affect the propagation and dissipation of Alfven 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 an MHD 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 Alfven waves as the cometary ions...

Raymond, J C; Cranmer, S R; Downs, C

2014-01-01

321

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

322

Properties of Ion-Cyclotron Waves in the Open Solar Corona  

NASA Astrophysics Data System (ADS)

Remote observations of coronal holes have strongly suggested the resonant interactions of ion-cyclotron waves with ions as a principal mechanism for plasma heating and acceleration of the fast solar wind. In order to study these waves, a WKB (Wentzel-Kramers-Brillouin) linear perturbation analysis is used in the frame work of a collisionless multi-fluid model where we consider in addition to protons a second ion component made of alpha particles. We consider a non-uniform background plasma describing a funnel region in the open coronal holes and we use the ray tracing Hamiltonian-type equations to compute the ray path of the waves and the spatial variation of their properties. At low frequency (smaller than the proton cyclotron frequency), the results showed a distinct behavior of the two ion-cyclotron modes found in our calculations, namely the first one propagates anisotropically guided along the magnetic field lines while the second one propagates isotropically with no preferred direction.

Mecheri, R.

2013-01-01

323

CORONAS-F detection of gamma-ray emission from the solar flare on 29 October 2003  

NASA Astrophysics Data System (ADS)

Appreciable HXR/gamma-ray emissions in the 0.015-150 MeV energy range associated with the solar flare on 29 October 2003 (X10/3B) were observed at 20:41-20:58 with the SPR-N and SONG instruments onboard the CORONAS-F mission. Two time intervals were identified which showed major changes in the intensity of these emissions. To specify the details of the spectral changes with time, we fitted the SONG energy loss spectra with a three-component model of incident gamma-ray spectrum: (1) a power law in energy, assumed to be due to electron bremsstrahlung; (2) a broad continuum produced by nuclear de-excitation gamma-lines; and (3) a broad gamma-line generated from pion decay. We study the relationship between non-imaging observations, particularly between time of pion-decay emission onset and motions in this solar flare, using HXR foot points (FP) separation and flare shear temporal behavior presented by (Ji et al., 2008). In this work it was shown that significant FP converging and unshearing motion occurred during the first flare interval. During this interval the primary bremsstrahlung extended to tens of MeV and de-excitation gamma-lines dominated. During the second interval after 20:45 the FPs began to move apart. We found out that starting from 20:46, the gamma-emission spectrum revealed a feature attributed to pion-decay. It means that the effective acceleration of protons to energies above 300 MeV (pion-production threshold) occurred coincidently with a change of the flare magnetic structure. The maximum intensity of the pion-decay gamma emission was observed at 20:49 and proved to be 2.010-4 photons cm-2 s-1 MeV-1 at 100 MeV. This flare was accompanied by GLE-66. Using the data of the world neutron monitor network, we found its onset as 20:59 which corresponds to a reasonable propagation time of protons with ~ 0.5-2 GeV energy on the assumption that proton acceleration began at 20:46.

Kurt, Victoria; Kashapova, Larisa; Yushkov, Boris; Kudela, Karel; Galkin, Vladimir

324

Solar radiation reduction by water and dust in the area of Thessaloniki  

SciTech Connect

In the present work, an attempt is made to present the realistic condition of the atmosphere over the city of Thessaloniki by comparing the direct solar radiation reaching the city centre with the solar radiation reaching the rural areas. The comparison is made possible by making use of the values of direct solar radiation and of turbidity factors, such as the Linke turbidity factor Tg or the Angstrom turbidity coefficient {beta}. The values of direct solar radiation which were measured inside the city were significantly lower than the ones measured out in the rural area. It has been found that the direct solar radiation in the city exhibits a reduction of the order of 10-20%. The reduced values of direct solar radiation measured inside the city are sometimes due to the increased concentration of dust particles and sometimes due to the increased quantities of water vapor coming from Thermaikos bay and diffused in the atmosphere.

Sahsamanoglou, H.S.; Bloutsos, A.A. (Aristotelian Univ. of Thessaloniki (Greece))

1989-01-01

325

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

NASA Astrophysics Data System (ADS)

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

Kla?ka, J.

2013-12-01

326

The Kinematics of a Globally Propagating Disturbance in the Solar Corona  

NASA Astrophysics Data System (ADS)

The kinematics of a globally propagating disturbance (also known as an ``EIT wave'') is discussed using Extreme UltraViolet Imager (EUVI) data from the Solar Terrestrial Relations Observatory (STEREO). We show for the first time that an impulsively generated propagating disturbance has similar kinematics in all four EUVI passbands (304, 171, 195, and 284 ). In the 304 passband the disturbance shows a velocity peak of 238 +/- 20 km s-1 within ~28 minutes of its launch, varying in acceleration from 76 to -102 m s-2. This passband contains a strong contribution from a Si XI line (303.32 ) with a peak formation temperature of ~1.6 MK. The 304 emission may therefore be coronal rather than chromospheric in origin. Comparable velocities and accelerations are found in the coronal 195 passband, while lower values are found in the lower cadence 284 passband. In the higher cadence 171 passband the velocity varies significantly, peaking at 475 +/- 47 km s-1 within ~20 minutes of launch, with a variation in acceleration from 816 to -413 m s-2. The high image cadence of the 171 passband (2.5 minutes compared to 10 minutes for the similar temperature response 195 passband) is found to have a major effect on the measured velocity and acceleration of the pulse, which increase by factors of ~2 and ~10, respectively. This implies that previously measured values (e.g., using EIT) may have been underestimated. We also note that the disturbance shows strong reflection from a coronal hole in both the 171 and 195 passbands. The observations are consistent with an impulsively generated fast-mode magnetoacoustic wave.

Long, David M.; Gallagher, Peter T.; McAteer, R. T. James; Bloomfield, D. Shaun

2008-06-01

327

KINETIC INSTABILITY OF DRIFT-ALFVEN WAVES IN SOLAR CORONA AND STOCHASTIC HEATING  

SciTech Connect

The solar atmosphere is structured and inhomogeneous, both horizontally and vertically. The omnipresence of coronal magnetic loops implies gradients of the equilibrium plasma quantities such as the density, magnetic field, and temperature. These gradients are responsible for the excitation of drift waves that grow both within the two-component fluid description (both in the presence of collisions and without it) and within the two-component kinetic descriptions (due to purely kinetic effects). In this work, the effects of the density gradient in the direction perpendicular to the magnetic field vector are investigated within the kinetic theory, in both electrostatic (ES) and electromagnetic (EM) regimes. The EM regime implies the coupling of the gradient-driven drift wave with the Alfven wave. The growth rates for the two cases are calculated and compared. It is found that, in general, the ES regime is characterized by stronger growth rates, as compared with the EM perturbations. Also discussed is the stochastic heating associated with the drift wave. The released amount of energy density due to this heating should be more dependent on the magnitude of the background magnetic field than on the coupling of the drift and Alfven waves. The stochastic heating is expected to be much higher in regions with a stronger magnetic field. On the whole, the energy release rate caused by the stochastic heating can be several orders of magnitude above the value presently accepted as necessary for a sustainable coronal heating. The vertical stratification and the very long wavelengths along the magnetic loops imply that a drift-Alfven wave, propagating as a twisted structure along the loop, in fact occupies regions with different plasma-{beta} and, therefore, may have different (EM-ES) properties, resulting in different heating rates within just one or two wavelengths.

Vranjes, J.; Poedts, S., E-mail: Jovo.Vranjes@wis.kuleuven.b, E-mail: Stefaan.Poedts@wis.kuleuven.b [Center for Plasma Astrophysics, K. U. Leuven, Celestijnenlaan 200B, 3001 Leuven (Belgium)

2010-08-20

328

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

329

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

330

Observational Evidence of Sausage-pinch Instability in Solar Corona by SDO/AIA  

NASA Astrophysics Data System (ADS)

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 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 snapshots also show the formation of bright knots and narrow regions in-between at the four locations as that of 304 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.; Erdlyi, R.; Tripathi, Durgesh; Fedun, V.; Joshi, N. C.; Kayshap, P.

2013-03-01

331

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

PubMed

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. PMID:11541455

Ockert-Bell, M E; Bell JF 3rd; Pollack, J B; McKay, C P; Forget, F

1997-04-25

332

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

333

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

334

Experiments for in-situ monitoring of dust environments in the Solar System  

NASA Astrophysics Data System (ADS)

"Dust" is present in the Solar System, from planetary surfaces to comets. The in-situ monitoring of its physical and dynamical properties is one of the main scientific tasks to be achieved in order to characterise grains and to correctly understand their role in the evolution of Solar System bodies. A new generation of methods for in-situ exploration of dusty environments in the Solar System has been studied and adopted in different instruments under development or study for future planetary space missions. Mass flux measurements by quartz crystal microbalances, optical detection of single grains and momentum monitoring by piezoelectric transducers are techniques which provide high sensitivity for grains at relatively low (below some hundreds m/s) velocities. The GIADA (Grain Impact Analyser and Dust Accumulator) experiment is part of the payload of the ESA Rosetta orbiter, targeted to a rendez-vous of 46P/Wirtanen comet. Thanks to GIADA, one of the prime scientific objectives of the mission will be fulfilled, i.e. the monitoring of the cometary coma dust environment. The dust flux from different directions vs. time and the momentum and velocity vs. mass of particles will be measured, while comet will approach the Sun. The MAGO (Martian Atmospheric Grain Observer) instrument, under study in the framework of the next Mars exploration opportunities (e.g.: Mars Surveyor Program 2003) adopts similar technical solutions and is aimed at measuring, directly for the first time, the dust mass flux in the Martian atmosphere and the dynamical properties of airborne particles vs. time. Finally, similar measurement techniques can be integrated with other detection/collection systems (e.g. aerogel collectors) to monitor the dust in the near Earth environment, e.g. from the space station.

Colangeli, L.; Bussoletti, E.; Lopez Moreno, J. J.; Epifani, E.; Esposito, F.; Mennella, V.; Palomba, E.; Palumbo, P.; Rotundi, A.; Vergara, S.; Jeronimo, J. M.; Lopez-Jimenez, A. C.; Molina, A.; Morales, R.; Moreno, F.; Olivares, I.; Rodrigo, R.; Rodriguez-Gomez, J. F.; Ruiz-Falco, A.; Sanchez, J.; McDonnell, J. A. M.; Leese, M.; Lamy, P.; Perruchot, S.; Crifo, J. F.; Fulle, M.; Perrin, J. M.; Angrilli, F.; Coradini, A.; Giovane, F.; Gruen, E.; Gustafson, B.; Maag, C.; Weissman, P. R.

1999-09-01

335

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

Microsoft Academic Search

High spatial resolution observations of the ultraviolet solar spectrum reveal high-energy events in the quiet Sun. They can be classified as turbulent events and Jets. The turbulent events show high turbulence (up to 250 km s⁻¹) confined in small areas (<2''), while the jets show upward moving material with velocities (approx.400 Km s⁻¹) exceeding the sound velocity (approx.120 km s⁻¹)

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

1983-01-01

336

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

337

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

E-print Network

CHINA'S DUST AFFECTS SOLAR RESOURCE IN THE U.S.: A CASE STUDY Christian A. Gueymard Nels S The radiative effects of the dust event that hit North America in late April 1998 are studied here as an example radiation nearly as much (e.g., [1]). Earlier studies (e.g., [2, 3]) have shown how a considerable influx

Oregon, University of

338

Cosmic dust  

NASA Technical Reports Server (NTRS)

Dust is a ubiquitous component of our galaxy and the solar system. The collection and analysis of extraterrestrial dust particles is important to exobiology because it provides information about the sources of biogenically significant elements and compounds that accumulated in distant regions of the solar nebula and that were later accreted on the planets. The topics discussed include the following: general properties of interplanetary dust; the carbonaceous component of interplanetary dust particles; and the presence of an interstellar component.

Brownlee, Donald E.; Sandford, Scott A.

1992-01-01

339

Martian Ionospheric Variability as Observed by MARSIS: The Effects of Solar Energetic Particles, Ionizing Radition, Meteors, and Dust Activity  

Microsoft Academic Search

We present evidence for time variability in the martian ionosphere due to solar energetic particles. We also discuss possible ionospheric effects from meteoric material, dust storms, the diurnal ionization cycle, and crustal magnetic fields.

J. R. Espley; W. Farrell; D. A. Brain; D. D. Morgan; M. H. Acua; B. Cantor; J. Plaut; G. Picardi

2007-01-01

340

Martian Ionospheric Variability as Observed by MARSIS: The Effects of Solar Energetic Particles, Ionizing Radition, Meteors, and Dust Activity  

NASA Astrophysics Data System (ADS)

We present evidence for time variability in the martian ionosphere due to solar energetic particles. We also discuss possible ionospheric effects from meteoric material, dust storms, the diurnal ionization cycle, and crustal magnetic fields.

Espley, J. R.; Farrell, W.; Brain, D. A.; Morgan, D. D.; Acua, M. H.; Cantor, B.; Plaut, J.; Picardi, G.

2007-03-01

341

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

Microsoft Academic Search

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: (a) ; that the quiet homogeneous corona'' is in fuct highly

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

1973-01-01

342

Corona Borealis  

NASA Astrophysics Data System (ADS)

(the Northern Crown; abbrev. CrB, gen. Coronae Borealis; area 179 sq. deg.) A northern constellation which lies between Botes and Hercules, and culminates at midnight in mid-May. It represents the crown that in Greek mythology was made by Hephaestus, god of fire, and worn by Princess Ariadne of Crete. Its brightest stars were cataloged by Ptolemy (c. AD 100-175) in the Almagest....

Murdin, P.

2000-11-01

343

To the Problem of the Corona Heating  

Microsoft Academic Search

The adequacy of different models of the corona heating is discussed. The correlation between the brightness of the coronal green line 530.5 nm Fe XIV and the calculated strength of the magnetic field in the corona is shown to be a very useful instrument to solve the problem. This correlation manifests a very strong dependence both on the solar cycle

O. G. Badalyan; V. N. Obridko

2006-01-01

344

Thermal Processing of Silicate Dust in the Solar Nebula: Clues from Primitive Chondrite Matrices  

E-print Network

The most abundant matrix minerals in chondritic meteorites, hydrated phyllosilicates and ferrous olivine crystals, formed predominantly in asteroids during fluid-assisted metamorphism. We infer that they formed from minerals present in three less altered carbonaceous chondrites that have silicate matrices composed largely of micrometer- and nanometer-sized grains of crystalline forsterite, Mg2SiO4, and enstatite MgSiO3, and amorphous, ferromagnesian silicate. Compositional and structural features of enstatite and forsterite suggest that they formed as condensates that cooled below 1300 K at \\~1000 K/h. Most amorphous silicates are likely to be solar nebula condensates also, as matrix, which is approximately solar in composition, is unlikely to be a mixture of genetically unrelated materials with different compositions. Since chondrules cooled at 10-1000 K/h, and matrix and chondrules are chemically complementary, most matrix silicates probably formed close to chondrules in transient heating events. Shock heating is favored as nebular shocks capable of melting millimeter-sized aggregates vaporize dust. The crystalline and amorphous silicates in the primitive chondrite matrices share many characteristic features with silicates in chondritic interplanetary dust particles suggesting that most of the crystalline silicates and possibly some amorphous silicates in the interplanetary dust particles are also nebular condensates. Except for small amounts of refractory oxides that formed with Ca-Al-rich inclusions at the inner edge of the disk and presolar dust, most of the crystalline silicate dust that accreted into chondritic asteroids and long-period comets appears to have formed from shock heating at ~2-10 AU. Forsterite crystals around young stars may have a similar origin.

Edward R. D. Scott; Alexander N. Krot

2005-01-05

345

Evolution of dust particle orbits under the influence of solar wind outflow asymmetries and the formation of the zodiacal dust cloud  

NASA Astrophysics Data System (ADS)

The secular orbital evolution of zodiacal dust particles is mainly influenced by the electromagnetic and the plasma Poynting-Robertson effects. Whereas the first effect is radially symmetric, the second one, caused by the dynamical friction of the dust particles in the ambient solar wind flow, depends on heliographic latitude. This is because the solar wind appears to have pronounced mass and momentum flow variations with respect to heliographic latitudes, with mass flows decreasing by about 50% from the ecliptic toward the poles. We take into account related asymmetries in the plasma Poynting-Robertson effect and study orbital evolution of dust particles orbiting with different inclinations. We derive equations describing the secular changes of the orbital elements under these conditions. We show that the radial migration rates are greater by about 5 to 10% for particles close to the ecliptic as compared to those at higher inclinations. This leads to typical changes in the distribution of inclinations with decreasing semimajor axes of the particles and also shows that the dust distribution function cannot be factored into parts solely dependent on radial distance or inclination alone. Furthermore, the kinetic equation for the distribution function of dust particles is solved numerically, yielding the distribution in orbital element space. The spatial density of the particles can then be found as an integral over this distribution function after application of a Jacobian transformation of element space differentials into configuration space differentials and can be compared with earlier results. Some observational consequences are drawn from this comparison and are discussed in some more detail. It is also pointed out that the plasma Poynting-Robertson effect in a two-temperature solar wind produces normal components of perturbation forces and thus tends to change the inclination of the dust particle orbits. This is of special importance in the solar wind regime inside the critical point where low-Mach-number flows prevail.

Banaszkiewicz, M.; Fahr, H. J.; Scherer, K.

1994-02-01

346

Current Sheets in the Sun's Corona ERIC PRIEST  

E-print Network

the corona is heated to such high temperatures. The energy that is required to heat the corona is about 5000Current Sheets in the Sun's Corona ERIC PRIEST School of Mathematics and Statistics, University an important role in the Sun's atmosphere, especially in coronal heating events and solar ares. They may form

Priest, Eric

347

Current Sheets in the Sun's Corona ERIC PRIEST  

E-print Network

the corona is heated to such high temperatures. The energy that is required to heat the corona is about 5000Current Sheets in the Sun's Corona ERIC PRIEST School of Mathematics and Statistics, University an important role in the Sun's atmosphere, especially in coronal heating events and solar flares. They may form

Priest, Eric

348

Current Sheets in the Sun's Corona ERIC PRIEST  

E-print Network

is then to understand how the corona is heated to such high temperatures. The energy that is required to heat the coronaCurrent Sheets in the Sun's Corona ERIC PRIEST School of Mathematics and Statistics, University an important role in the Sun's atmosphere, especially in coronal heating events and solar ares. They may form

Priest, Eric

349

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

E-print Network

Solar five-minute oscillations have been detected in the power spectra of two six-day time intervals from soft X-ray measurements of the Sun observed as a star using the Extreme Ultraviolet Spectrophotometer (ESP) onboard the Solar Dynamics Observatory (SDO) Extreme Ultraviolet Variability Experiment (EVE). The frequencies of the largest amplitude peaks were found matching within 3.7 microHz the known low-degree (l = 0--3) modes of global acoustic oscillations, and can be explained by a leakage of the global modes into the corona. Due to strong variability of the solar atmosphere between the photosphere and the corona the frequencies and amplitudes of the coronal oscillations are likely to vary with time. We investigate the variations in the power spectra for individual days and their association with changes of solar activity, e.g. with the mean level of the EUV irradiance, and its short-term variations due to evolving active regions. Our analysis of samples of one-day oscillation power spectra for a 49-day ...

Didkovsky, Leonid; Judge, Darrell; Wieman, Seth; Woods, Tom

2012-01-01

350

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

351

Equation of State and Constitutive Models for Numerical Simulations of Dust Impacts on the Solar Probe  

E-print Network

This report presents new EOS and strength models for use in numerical hydrocode simulations of dust impacts on the NASA solar probe space vehicle. This spacecraft will be subjected to impact at velocities up to 300 km/s, producing pressures as high as 100 TPa and temperatures as high as 200 eV. Hence the material models must treat a variety of physical and chemical phenomena, including solid-solid transitions, melting and vaporization, chemical reactions, electronic excitation and ionization. The EOSPro code is used to develop tabular EOS that include these effects. The report discusses the theoretical methods used to create the new EOS tables and constitutive models for six materials--Al2O3, two porous carbon materials, fused SiO2, a silicone elastomer, and germanium--which will be used in the thermal protection shield (TPS) and solar cells, the components most vulnerable to dust impacts. It also presents the results of hydrocode simulations of dust impacts on the TPS and on glass targets. It discusses the i...

Kerley, Gerald I

2013-01-01

352

Combining visibilities from the giant meterwave radio telescope and the Nancay radio heliograph. High dynamic range snapshot images of the solar corona at 327 MHz  

NASA Astrophysics Data System (ADS)

We report first results from an ongoing program of combining visibilities from the Giant Meterwave Radio Telescope (GMRT) and the Nancay Radio Heliograph (NRH) to produce composite snapshot images of the sun at meter wavelengths. We describe the data processing, including a specific multi-scale CLEAN algorithm. We present results of a) simulations for two models of the sun at 327 MHz, with differing complexity b) observations of a complex noise storm on the sun at 327 MHz on Aug. 27, 2002. Our results illustrate the capacity of this method to produce high dynamic range snapshot images when the solar corona has structures with scales ranging from the image resolution of 49'' to the size of the whole sun. We emphasize that snapshot images of a complex object such as the sun, obtained by combining data from both instruments, are far better than images from either instrument alone, because their uv-coverages are very complementary.

Mercier, C.; Subramanian, P.; Kerdraon, A.; Pick, M.; Ananthakrishnan, S.; Janardhan, P.

2006-03-01

353

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

354

Spectral line width decrease in the solar corona: resonant energy conversion from Alfv{\\'e}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.

Zaqarashvili, T V; Ballester, J L

2006-01-01

355

Protons Acceleration in Solar Flares: The Results of the Analysis of Gamma-emission and Neutrons Recorded by the SONG Instrument Onboard the CORONAS-F Satellite  

NASA Astrophysics Data System (ADS)

The SONG instrument onboard CORONAS-F satellite was the only experiment which observed neutral emissions with energies > 20 MeV from solar flares during the 23rd solar activity cycle. High-energy gamma emission was measured by SONG during four major flares, namely: August 25, 2001, October 28, 2003, November 04, 2003, and January 20, 2005. Spectra of this emission were restored in the energy range of 0.05-300 MeV and a broad line at energy range 40-100 MeV produced through ? 0-decay was distinguished. Generation of this line is a direct indication of the appearance of protons accelerated to energies above 300 MeV in the flare volume. In this way we determined the onset of high-energy proton acceleration. The same protons produce simultaneously high-energy neutrons which can leave the Sun. These neutrons were recorded by the SONG instrument after the flares of August 25, 2001, October 28, 2003, and November 04, 2003. Comparison of protons acceleration time during the October 28, 2003 and January 20, 2005 flares with the onset time of Ground Level Enhancement (GLE) leads to a conclusion that protons responsible for the GLE onset escaped from the solar atmosphere without any delay after their acceleration. The obtained results allow one to understand in a new way a process of particle acceleration up to relativistic energy during flare development.

Kuznetsov, S. N.; Kurt, V. G.; Yushkov, B. Yu.; Myagkova, I. N.; Galkin, V. I.; Kudela, K.

356

THE DIGITAL SYSTEM ARTEMIS FOR REAL-TIME PROCESSING OF RADIO TRANSIENT EMISSIONS IN THE SOLAR CORONA  

E-print Network

to build a very large data base of digitized and accurately calibrated solar events, in order to achieveTHE DIGITAL SYSTEM ARTEMIS FOR REAL-TIME PROCESSING OF RADIO TRANSIENT EMISSIONS IN THE SOLAR); it is used to process and record the 120 channels of a multichannel solar radiospectrograph in the frequency

Athens, University of

357

Formation of accretionary dust mantles in the solar nebula: Evidence from preirradiated olivines in CM chondrites  

NASA Astrophysics Data System (ADS)

CM chondrites are regolith breccias consisting of lithic clasts embedded in a fine-grained clastic matrix. The majority of these lithic clasts belongs to a texturally well-defined rock type (primary rock) that can be described as an agglomerate of chondrules and other coarse-grained components, most of which are surrounded by fine-grained rims (dust mantles). Metzler et al. (1992) explain these textures as the result of accretionary processes in the solar nebula, while an alternative model explains them to be the result of regolith processes on the parent body (Sears et al. 1993). The main intention of the present study is to discern between both models by investigating the occurrence, frequency, spatial distribution, and textural setting of preirradiated (track-rich) olivines in CM chondrites. Track-rich olivines were studied in situ in six polished thin sections from 4 different CM chondrites (Cold Bokkeveld, Mighei, Murchison, Nogoya) by optical and scanning electron microscopy (SEM). It was found that their occurrence is restricted to the clastic matrix of these meteorites. The primary rock seems to have formed in an environment shielded from cosmic radiation, since fragments of this rock are free of track-rich grains and solar noble gases. This finding supports the solar nebula model for the formation of dust mantles around chondrules and other coarse-grained components, and points against a regolith origin. In Cold Bokkeveld, a small breccia-in-breccia clast was found, which has been irradiated as an entity within the uppermost millimeters to meters of its parent body for at least about 3 Ma. This clast seems to represent a compacted subsurface layer that was later excavated by impact and admixed to the host breccia. Furthermore, the results of this study may affect the interpretation of compaction ages obtained by fission track methods, since these ages may be mixtures of different contact ages between finegrained, U-rich dust and U-poor olivines. In some cases, they may date the formation of dust mantles in the solar nebula, while in other cases the lithification of the host breccias may be dated.

Metzler, Knut

2004-08-01

358

Origin of isotopic heterogeneity in the solar nebula by thermal processing and mixing of nebular dust  

NASA Astrophysics Data System (ADS)

We have investigated Mo and W isotope compositions in acid leachates and an insoluble residue from the Murchison carbonaceous chondrite. The new data reveal variable enrichments of s- and r-process isotopes and demonstrate that several isotopically diverse presolar components are present in Murchison. The insoluble residue is enriched in s-process Mo and W, evidently due to the enrichment of presolar SiC grains. In contrast, Mo and W released by leaching with weak acids are depleted in s-process isotopes, most likely reflecting the isotope composition of the homogenized portion of the protosolar nebula. The Mo and W isotope compositions of the different leach steps are broadly correlated as expected from s-process nucleosynthesis theory, indicating that Mo and W are presumably hosted in the same carriers. However, at the bulk meteorite scale, no nucleosynthetic W isotope anomalies have been identified (except for IVB iron meteorites) in spite of large Mo isotope heterogeneities among the same samples. This decoupling of Mo and W isotopes in bulk meteorites may reflect physical mixing of varying proportions of isotopically diverse presolar components with a "normal" solar nebula component. Due to the high W/Mo ratio and near-terrestrial W isotope composition of the latter, such mixing has no measurable effect on W isotopes, but results in large Mo isotope variations. Alternatively, thermal processes within the solar nebula imparted Mo isotope heterogeneity on an initially homogeneous mixture of presolar dust, while W was not affected. Removal of volatile Mo oxides during the thermal destruction of fragile presolar components would have created isotopically heterogeneous reservoirs of nebular dust. Accretion of meteorite parent bodies from such variably processed dust would thus result in Mo isotope heterogeneities at the bulk meteorite scale. Other elements such as Os and W were not or only slightly affected because they were more refractory during thermal processing and, therefore, remained isotopically homogeneous. Thermal processing of presolar dust within the solar nebula can thus account for both isotope heterogeneities observed for some elements and the lack of such isotopic heterogeneity for other elements.

Burkhardt, Christoph; Kleine, Thorsten; Dauphas, Nicolas; Wieler, Rainer

2012-12-01

359

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

360

Modeling of Gas and Dust Outflow Dynamics at Active Small Solar System Bodies  

NASA Astrophysics Data System (ADS)

Abstract (2,250 Maximum Characters): We present methodology and results from our recent effort in modeling the gas outflow from the surfaces of primitive/active small solar system bodies, and modeling the dynamics of dust particles entrained by that flow. We based our initial simulation capability on the COMA software package, developed ?1995-1999 for ESA to enable studies preparatory to Rosetta. Rather than integrate the derived software for gas and dust dynamics simulation "into the loop" within high-fidelity 6DOF integration of a rendezvoused spacecraft's dynamics, we created simple tools, or "interfaces", computationally efficient enough to be brought into the loop, yet capturing the variety of ways in which gas and lifted dust can potentially perturb guidance, navigation, and control (GN&C) performance and surface observation performance. For example, these interfaces are called in the loop to compute noise models for degradation by the dust of imagery and lidar navigation observables. The same applies for degradation of science instrument observations of the surface. Accurate spacecraft dynamics propagation is necessary for mission design, while both that and the observables modeling are required for end-to-end simulation and analysis of navigation and control to the designed close-proximity trajectories. We created interfaces with increasing levels of fidelity, ultimately sufficiently approximating the full flow-field of gas and dust activity; both diffuse background activity (with spatial variation in relation to sun direction) and concentrated jet activity (with spatial and temporal variation through masking to the regions of jet activity in the body-fixed frame and modeling body rotation). We show example results using these tools for two representative design reference missions involving 9P/Tempel 1 and 67P/C-G. This work should be of interest to anyone in the DDA community considering involvement in such mission scenarios. It may also be extended in the near future to cases of intentional generation of outgassing, dust, and debris by surface perturbation, ranging from weak (as in comet surface sample collection) to strong (as in experiments involving crater- and ejecta-generating energetic events such as blasts or kinetic impactors).

Fahnestock, Eugene G.

2013-05-01

361

Gradients in dust chemical composition in protoplanetary disks: analogies with the Solar System  

NASA Astrophysics Data System (ADS)

Clues to planet-forming processes are provided by the properties of the dust grains in protoplanetary disks and in cometary nuclei in our own Solar System. We present a compositional analysis of the 10m and 20m silicate emission features for young protoplanetary disks around FGKM stars. We find an increase in the crystallinity levels towards larger radii, such that the median crystalline mass fraction is higher in the outer cold disk region compared to the inner warm parts of the disk. For nearly 80% of the disks, the mass fraction of small ISM-like dust grains is negligible (< 5%) in the outer cold disk region. The median crystalline mass fraction in disks around late-type stars is found to be a factor of ~2 higher than the median for the higher mass FGK type stars. The relatively high abundance of crystalline silicates in the outer cold regions of protoplanetary disks provides an interesting analogy to comets. In this context, we will discuss the applicability of the various mechanisms that have been proposed for comets on the formation and the outward transport of high-temperature material. A (weak) anti-correlation between the X-ray emission strength and the extent of crystallinity in the disk is observed, suggesting X-rays to be an important dust amorphization agent in these disks. This work has highlighted the ubiquity of Solar System like chemical signatures in young protoplanetary disks, and suggests that protoplanets that form closer to a low-mass star can have a different chemical composition from those that formed farther away.

Riaz, Basmah; Kelley, M.; Campins, H.

2014-11-01

362

Plasma Properties and Magnetic Field Structure of the Solar Corona, Based on Coordinated Max 1991 Observations from SERTS, the VLA, and Magnetographs  

NASA Technical Reports Server (NTRS)

The purposes of this investigation are to determine the plasma properties and magnetic field structure of the solar corona using coordinated observations obtained with NASA/GSFC's Solar EUV Rocket Telescope and Spectrograph (SERTS), the Very Large Array (VLA), and magnetographs. The observations were obtained under the auspices of NASA's Max '91 program. The methods of achieving the stated purposes are to use SERTS spectra and spectroheliograms to determine coronal plasma properties such as temperature, density, and emission measure. These properties are subsequently used to calculate the intensity of the thermal bremsstrahlung microwave emission from the coronal plasma (the minimum microwave intensity expected from the emitting plasma). This, in turn, can be used to establish which emission mechanism(s) contribute to the observed microwave emission. Because both mechanisms that may contribute to quiescent active region microwave emission (thermal bremsstrahlung and thermal gyroemission) depend upon the coronal magnetic field in known ways, this information can ultimately be used to derive the coronal magnetic field. Ideally, three-dimensional models of the coronal plasma and magnetic field which are consistent with all of the EUV spectra and spectroheliograms, as well as with the intensity and polarization maps at all of the microwave observing frequencies, can be derived. For completeness, the coronal magnetic field derived from the coordinated multiwaveband observations must be compared with extrapolations from photospheric magnetograms.

Brosius, Jeffrey W.

1996-01-01

363

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

364

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, Jurgen; Beitz, Eike; Bukhari, Mohtashim; Gundlach, Bastian; Hagemann, Jan-Hendrik; Heisselmann, Daniel; Kothe, Stefan; Schrapler, Rainer; von Borstel, Ingo; Weidling, Rene

2014-01-01

365

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

366

A study of H I Lyman-alpha emission from prominences erupting in the intermediate corona and possible future applications for Solar Orbiter/METIS data  

NASA Astrophysics Data System (ADS)

Over almost the last 20 years hundreds of Coronal Mass Ejections (CME) have been observed by the UV Coronagraph Spectrometer (UVCS) onboard SOHO. For many of these events a significant emission in the HI Lyman-alpha lambda 1216 line was sampled during the transit across the slit of the erupting prominences embedded in the core of CMEs. The origin of this emission is completely different from what is typically observed by UVCS: because of the higher density and lower temperatures of such plasmas, the number of neutral H atoms is much larger than under typical coronal conditions, and the plasma is generally not optically thin at these wavelengths, as it is usually true for other coronal structures. Hence, the observed H I Lyman-alpha emission can be explained only if a radiative transport treatment across a moving plasma structure is considered. Once the proper boundary conditions are derived from the UV data, in combination with white light (WL) coronagraphic observations (from LASCO), we will show how the temperature and density of the erupting prominence could be derived even at large altitudes (typically larger than 0.6 solar radii above the limb), thus providing information on heating/cooling and ionization of the CME core during the eruption. These results are very important in the light of coronagraphic observations that will be provided by the METIS instrument onboard the Solar Orbiter: because METIS will contemporary observe the solar corona in WL and in UV (HI Lyman-alpha), it will be possible to derive, with a technique similar to what is shown here, very important information on prominence plasmas embedded in the core of CMEs and crossing the METIS instrument field of view.

Bemporad, Alessandro; Heinzel, Petr; Jejcic, Sonja; Susino, Roberto

367

The quiet corona: Temperature and temperature gradient  

Microsoft Academic Search

A study of the lower corona thermal properties was made using the best examples of solar wind heavy ion spectra obtained with Vela 5 and 6 plasma analyzers at times of quiet solar wind (low speed, low temperature). The multiple Si and Fe ion species peaks in the spectra were fit with solutions of the ionization equilibrium equations to determine

S. J. Bame; J. R. Asbridge; W. C. Feldman; P. D. Kearney

1974-01-01

368

Nearby candidate dust-disk pre-main-sequence solar-mass stars  

E-print Network

I have isolated a population of numerous F stars that appear to be pre-main-sequence (PMS). The candidate PMS stars have been identified using CM diagram, reddening, flux excess in the UV and near-infrared, and luminosity anomaly. Negative luminosity anomaly and excessive UV flux for many of these stars is suggestive of accretion disks, while the NIR excess is indicative in many cases of the presence of dust disk thermal emission. Observed overluminosity of many PMS candidates is consistent with their pre-main-sequence status. The bulk of the PMS candidates is located within 200 pc, exhibiting strong association with regions of star formation that are numerous between ~130 to 180 pc. The number of PMS candidates plummets redward of the spectral type ~ F5. This effect may provide important clues for understanding the evolution of PMS stars in the solar-mass range.

A. A. Suchkov

2002-10-25

369

Formation and Evolution of Planetary Systems (FEPS): Properties of Debris Dust around Solar-type Stars  

E-print Network

We present Spitzer photometric (IRAC and MIPS) and spectroscopic (IRS low resolution) observations for 314 stars in the Formation and Evolution of Planetary Systems (FEPS) Legacy program. These data are used to investigate the properties and evolution of circumstellar dust around solar-type stars spanning ages from approximately 3 Myr to 3 Gyr. We identify 46 sources that exhibit excess infrared emission above the stellar photosphere at 24um, and 21 sources with excesses at 70um. Five sources with an infrared excess have characteristics of optically thick primordial disks, while the remaining sources have properties akin to debris systems. The fraction of systems exhibiting a 24um excess greater than 10.2% above the photosphere is 15% for ages 10 AU. Although the interpretation is not unique, the lack of excess emission shortwards of 16um and the relatively flat distribution of the 24um excess for ages <300~Myr is consistent with steady-state collisional models.

John M. Carpenter; Jeroen Bouwman; Eric E. Mamajek; Michael R. Meyer; Lynne A. Hillenbrand; Dana E. Backman; Thomas Henning; Dean C. Hines; David Hollenbach; Jinyoung Serena Kim; Amaya Moro-Martin; Ilaria Pascucci; Murray D. Silverstone; John R. Stauffer; Sebastian Wolf

2008-10-06

370

Electron acceleration at localized wave structures in the solar corona (German Title: Elektronenbeschleunigung an lokalen Wellenstrukturen in der Sonnenkorona)  

Microsoft Academic Search

Our dynamic Sun manifests its activity by different phenomena: from the 11-year cyclic sunspot pattern to the unpredictable and violent explosions in the case of solar flares. During flares, a huge amount of the stored magnetic energy is suddenly released and a substantial part of this energy is carried by the energetic electrons, considered to be the source of the

Rositsa Stoycheva Miteva

2007-01-01

371

Interplanetary Dust  

NASA Astrophysics Data System (ADS)

The birth of a solar system is enshrouded in gas and dust. A collapsing rotating cloud increases in density until a critical point is reached and a YOUNG STELLAR OBJECT begins its rapid accretion at the center, still surrounded by a disk of gas and dust (figure 1). As stars evolve through a T-Tauri phase, much of this primordial dust cloud is removed by strong stellar winds and radiation forces...

Sykes, M.; Murdin, P.

2000-11-01

372

Mass loading of the solar wind by a sungrazing comet  

NASA Astrophysics Data System (ADS)

Collisionless mass loading was suggested by Biermann et al. (1967) for describing 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 of sunward migrating interplanetary dust particles. In a previous paper, we presented a 3-D MHD model of the solar corona based on the Block-Adaptive-Tree-Solarwind-Roe-Upwind-Scheme code which includes the interaction of dust with the solar wind. We have shown the impact on the solar wind from abrupt mass loading in the coronal region. We apply the model to a sungrazing cometary source, using ejected dust dynamics to generate tail-shaped mass-loading regions. Results help predict the effects on the solar wind acceleration and composition due to sungrazing comets, such as Comet C/2011 W3 (Lovejoy). We show how these effects may be detected by the upcoming Solar Probe Plus Mission.

Rasca, A. P.; Oran, R.; Hornyi, M.

2014-08-01

373

Solar Wind Five  

NASA Technical Reports Server (NTRS)

Topics of discussion were: solar corona, MHD waves and turbulence, acceleration of the solar wind, stellar coronae and winds, long term variations, energetic particles, plasma distribution functions and waves, spatial dependences, and minor ions.

Neugebauer, M. (editor)

1983-01-01

374

A cosmic abundance standard: chemical homogeneity of the solar neighbourhood and the ISM dust-phase composition  

E-print Network

A representative sample of unevolved early B-type stars in nearby OB associations and the field is analysed to unprecedented precision using NLTE techniques. The resulting chemical composition is found to be more metal-rich and much more homogeneous than indicated by previous work. A rms scatter of ~10% in abundances is found for the six stars (and confirmed by six evolved stars), the same as reported for ISM gas-phase abundances. A cosmic abundance standard for the present-day solar neighbourhood is proposed, implying mass fractions for hydrogen, helium and metals of X=0.715, Y=0.271 and Z=0.014. Good agreement with solar photospheric abundances as reported from recent 3D radiative-hydrodynamical simulations of the solar atmosphere is obtained. As a first application we use the cosmic abundance standard as a proxy for the determination of the local ISM dust-phase composition, putting tight observational constraints on dust models.

Norbert Przybilla; Maria-Fernanda Nieva; Keith Butler

2008-09-14

375

The Arrayed Large-Area Dust Detectors in INterplanetray Space (ALADDIN) onboard the IKAROS solar sail demonstrator  

NASA Astrophysics Data System (ADS)

In the summer of 2010, the world's first interplanetary solar sail demonstrator called the Inter-planetary Kite-craft Accelerated by the Radiation of the Sun (IKAROS) will be launched by an H-IIA rocket. On its thin sail membrane, a large-area but still light-weight dust detector made of 8 channels of 9-20 micron-thick PVDF films are attached. This detector is called the Arrayed Large-Area Dust Detectors in INterplanetray Space (AL-ADDIN) and has effective detection area of 0.54 m2 with in order to count and time hyper-velocity impacts by micrometeoroids larger than micron size during its interplanetary cruise. The sensors filter electronic, thermal and vibration noises and record time, peak hold value, and relax duration of signals of micrometeoroid impacts. The first objective of ALADDIN is to test this large PVDF array system on thin sail membrane in the interplanetary operation and the second objective is to hopefully measure dust flux anisotropy in the trailing edge of the Earth, heliocentric flux variance inside the orbit of the Earth (1 AU) down to Venus(0.7 AU), and opportunistic detections of possible cometary dust trails as well as flux enhancement near Venus. It will also compare its results with infrared observation of zodiacal light scattering as a func-tion of the heliocentric distance in order to investigate possible co-relations between these two independent measurements of the inner solar system dust environment.

Yano, Hajime; Tanaka, Makoto; Okamoto, Chisato; Yano, Hajime; Tanak, Makoto; Okamoto, Chisato; Hasegawa, Sunao; Tabata, Makoto; Ogawa, Naoko; Okudaida, Kyoko; Iwai, Takeo

376

DETECTION OF PLASMA FLUCTUATIONS IN WHITE-LIGHT IMAGES OF THE OUTER SOLAR CORONA: INVESTIGATION OF THE SPATIAL AND TEMPORAL EVOLUTION  

SciTech Connect

This work focuses on the first results from the identification and characterization of periodic plasma density fluctuations in the outer corona, observed in STEREO-A COR1 white-light image time series. A two-dimensional reconstruction of the spatial distribution and temporal evolution of the coronal fluctuation power has been performed over the whole plane of the sky, from 1.4 to 4.0 R{sub Sun }. The adopted diagnostic tool is based on wavelet transforms. This technique, with respect to the standard Fourier analysis, has the advantage of localizing non-persistent fluctuating features and exploring variations of the relating wavelet power in both space and time. The map of the variance of the coronal brightness clearly outlines intermittent spatially coherent fluctuating features, localized along, or adjacent to, the strongest magnetic field lines. In most cases, they do not correspond to the visible coronal structures in the brightness maps. The results obtained provide a scenario in which the solar corona shows quasi-periodic, non-stationary density variations characterized by a wide range of temporal and spatial scales and strongly confined by the magnetic field topology. In addition, structures fluctuating with larger power are larger in size and evolve more slowly. The characteristic periodicities of the fluctuations are comparable to their lifetimes. This suggests that plasma fluctuations lasting only one or two wave periods and initially characterized by a single dominant periodicity either rapidly decay into a turbulent mixed flow via nonlinear interactions with other plasma modes, or they are damped by thermal conduction. The periodic non-stationary coronal fluctuations outlined by the closed field lines at low and mid latitudes might be associated with the existence of slow standing magneto-acoustic waves excited by the convective supergranular motion. The fluctuating ray-like structures observed along open field lines appear to be linked either to the intermittent nature of the processes underlying the generation of magnetic reconnection in the polar regions or to the oscillatory transverse displacements of the coronal ray itself.

Telloni, D.; Antonucci, E. [National Institute for Astrophysics (INAF), Astrophysical Observatory of Torino, Via Osservatorio 20, I-10025 Pino Torinese (Italy); Ventura, R.; Romano, P.; Spadaro, D. [National Institute for Astrophysics (INAF), Astrophysical Observatory of Catania, Via S. Sofia 78, I-95123 Catania (Italy)

2013-04-20

377

Global Numerical Modeling of Energetic Proton Acceleration in a Coronal Mass Ejection Traveling through the Solar Corona  

E-print Network

The acceleration of protons and electrons to high (sometimes GeV/nucleon) energies by solar phenomena is a key component of space weather. These solar energetic particle (SEP) events can damage spacecraft and communications, as well as present radiation hazards to humans. In-depth particle acceleration simulations have been performed for idealized magnetic fields for diffusive acceleration and particle propagation, and at the same time the quality of MHD simulations of coronal mass ejections (CMEs) has improved significantly. However, to date these two pieces of the same puzzle have remained largely decoupled. Such structures may contain not just a shock but also sizable sheath and pileup compression regions behind it, and may vary considerably with longitude and latitude based on the underlying coronal conditions. In this work, we have coupled results from a detailed global three-dimensional MHD time-dependent CME simulation to a global proton acceleration and transport model, in order to study time-dependen...

Kozarev, Kamen A; Schwadron, Nathan A; Dayeh, Maher A; Opher, Merav; Korreck, Kelly E; van der Holst, Bart

2014-01-01

378

STARDUST IN FINE-GRAINED CHONDRULE RIMS AND MATRIX IN LAPAZ 031117: INSIGHTS INTO THE CONDITIONS OF DUST ACCRETION IN THE SOLAR NEBULA. P. Haenecour1,2  

E-print Network

OF DUST ACCRETION IN THE SOLAR NEBULA. P. Haenecour1,2 and C. Floss1,3 . 1 Laboratory for Space Sciences is still uncertain. Two main hypotheses have been proposed: formation by accretion in the solar nebula and can be used to better understand conditions in the early solar nebula [e.g., 5]. Presolar silicate

379

The Rayleigh-taylor Instability In The Solar Corona: Prominence Coronal-cavity Interactions And The Evolution To Eruptive States  

NASA Astrophysics Data System (ADS)

We review the discovery and analysis of the Rayleigh-Taylor instability in quiescent solar prominences by the Hinode/SOT and SDO/AIA instruments. The instability is apparently caused by the emergence of magnetic flux near the polarity inversion line below the prominences. The emerging flux is rapidly heated to coronal temperatures of 1 MK or higher and the resulting large temperature gradient with the cool overlying prominence plasma leads to a "magneto-thermal" convective instability that develops into a classic Rayleigh-Taylor system of plumes and downflows. The significance of the discovery is that it offers a mechanism by which magnetic flux and helicity are periodically injected into the coronal cavity flux ropes overlying solar prominences. The increasing flux and helicity in the cavity develop a quasi-steady evolution eventually terminating in the eruption of a slow coronal mass ejection (Fan & Gibson 2007; Zhang, Flyer, & Low 2006). We suggest further investigations using SDO/AIA, ground-based observatories, and the upcoming IRIS mission to verify and extend the SOT and AIA findings.

Berger, Thomas

2012-05-01

380

Numerical simulation of kinetic Alfven waves to study filament formation and their nonlinear dynamics in solar wind and corona  

SciTech Connect

This paper presents a numerical simulation leading to the formation of intense magnetic filaments of kinetic Alfven waves (KAWs) in steady state when the nonlinearity arises due to ponderomotive effects and Joule heating. The nonlinear dynamical equation for the KAW satisfies the modified nonlinear Schroedinger equation. When the plain KAW is perturbed by a transverse perturbation, filamentary structures in solar wind and coronal holes are observed. By changing the parameters of the perturbation (such as the wave number and the phase factor), filamentary structures of KAW magnetic field have been observed. The effect of the change of the dimensionless transverse wave number {gamma} (normalized in terms of electron's collisionless skin depth of the KAW) plays a very important role on filamentary dynamics. Besides the study of the magnetic-field intensity, we have done various diagnostics such as phase portraits and surface plots, and also studied the power spectrum. The effect of changing the value of {gamma} on power spectrum is significant. The motion is found to be quasiperiodic and appears to be chaotic for different parametric regimes. The relevance of these studies in coronal heating and solar wind acceleration/turbulence has also been pointed out.

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

2006-01-15

381

Density fluctuations and the acceleration of electrons by beam-generated Langmuir waves in the solar corona  

E-print Network

Non-thermal electron populations are observed throughout the heliosphere. The relaxation of an electron beam is known to produce Langmuir waves which, in turn, may substantially modify the electron distribution function. As the Langmuir waves are refracted by background density gradients and as the solar and heliospheric plasma density is naturally perturbed with various levels of inhomogeneity, the interaction of Langmuir waves with non-thermal electrons in inhomogeneous plasmas is an important topic. We investigate the role played by ambient density fluctuations on the beam-plasma relaxation, focusing on the effect of acceleration of beam electrons. The scattering of Langmuir waves off turbulent density fluctuations is modeled as a wavenumber diffusion process which is implemented in numerical simulations of the one-dimensional quasilinear kinetic equations describing the beam relaxation. The results show that a substantial number of beam electrons are accelerated when the diffusive time scale in wavenumber...

Ratcliffe, Heather; Kontar, Eduard P

2012-01-01

382

OSO-8 observations of the impulsive phase of solar flares in the transition-zone and corona  

NASA Technical Reports Server (NTRS)

Several solar flares were observed from their onset in C IV 1548.2 A and 1-8 A X-rays using instruments on OSO-8. It is found that impulsive brightening in C IV is often accompanied by redshifts, interpreted as downflows, of the order of 80 km/s. The maximum soft X-ray intensity usually arrives several minutes after the maximum C IV intensity. The most energetic C IV event observed shows a small blueshift just before reaching maximum intensity; estimates of the mass flux associated with this upflow through the transition zone are consistent with the increase of mass in the coronal loops as observed in soft X-rays. Finally, it is suggested that the frequent occurrence of violent dynamical processes at the onset of the flare is associated with the initial energy release mechanism.

Lites, B. W.; Bruner, E. C., Jr.; Wolfson, C. J.

1981-01-01

383

Status of Knowledge after Ulysses and SOHO: Session 2: Investigate the Links between the Solar Surface, Corona, and Inner Heliosphere.  

NASA Technical Reports Server (NTRS)

As spacecraft observations of the heliosphere have moved from exploration into studies of physical processes, we are learning about the linkages that exist between different parts of the system. The past fifteen years have led to new ideas for how the heliospheric magnetic field connects back to the Sun and to how that connection plays a role in the origin of the solar wind. A growing understanding these connections, in turn, has led to the ability to use composition, ionization state, the microscopic state of the in situ plasma, and energetic particles as tools to further analyze the linkages and the underlying physical processes. Many missions have contributed to these investigations of the heliosphere as an integrated system. Two of the most important are Ulysses and SOHO, because of the types of measurements they make, their specific orbits, and how they have worked to complement each other. I will review and summarize the status of knowledge about these linkages, with emphasis on results from the Ulysses and SOHO missions. Some of the topics will be the global heliosphere at sunspot maximum and minimum, the physics and morphology of coronal holes, the origin(s) of slow wind, SOHO-Ulysses quadrature observations, mysteries in the propagation of energetic particles, and the physics of eruptive events and their associated current sheets. These specific topics are selected because they point towards the investigations that will be carried out with Solar Orbiter (SO) and the opportunity will be used to illustrate how SO will uniquely contribute to our knowledge of the underlying physical processes.

Suess, Steven

2006-01-01

384

A close-up of the sun. [solar probe mission planning conference  

NASA Technical Reports Server (NTRS)

NASA's long-range plan for the study of solar-terrestrial relations includes a Solar Probe Mission in which a spacecraft is put into an eccentric orbit with perihelion near 4 solar radii (0.02 AU). The scientific experiments which might be done with such a mission are discussed. Topics include the distribution of mass within the Sun, solar angular momentum, the fine structure of the solar surface and corona, the acceleration of the solar wind and energetic particles, and the evolution of interplanetary dust. The mission could also contribute to high-accuracy tests of general relativity and the search for cosmic gravitational radiation.

Neugebauer, M. (editor); Davies, R. W. (editor)

1978-01-01

385

The Old Feeble Transition Regions and Coronae of Solar-like Dwarf Stars in the Arcturus Moving Group  

NASA Astrophysics Data System (ADS)

Old dwarf stars have generally spun down significantly thus dampening one of the main contributors (rotation) to solar-like alpha-omega magnetic dynamo activity. Studying how stellar activity on stars older than the Sun changes in terms of the chromospheric/transition-region/coronal temperature structure and how much energy is radiated as a function of temperature provides important constraints on how solar-like dynamos work. Stars with different metallicities provide information on how the radiative cooling channels control the temperature structure. We have measured fluxes and profiles of FUV emission lines using the HST COS spectrograph and the broad-band X-ray fluxes using Chandra ACIS-S for a sample of old inactive dwarfs. Our sample comprises five members of the 7-8 Gyr Arcturus Moving Group --- HD90508/LHS2266 (F9 V/M4 V, [Fe/H] = -0.4), HD65583 (G8 V, Fe/H]=-0.7), and HD145417 (K0 V, [Fe/H]=-1.4) --- plus three well-studied comparison stars -- HD103095 (G8 V, [Fe/H]=-1.4), Tau Ceti (G8 V, [Fe/H]=-0.4), and the Quiet Sun (G2 V, [Fe/H]=0.0). In this poster we provide estimates of atmospheric radiative losses as a function of temperature and metallicity. The atmospheres of these low-metallicity stars are more heavily weighted towards cooler temperatures than those of more active stars or even the Sun. Chromospheric emission lines, e.g. C I lines, are far stronger relative transition region lines, e.g C IV. Similarly the X-ray data provide detections for all the targets but with primarily very soft (0.3-0.5 keV) photons and imply "coronal" temperatures of less than 1 MK. While the temperature distributions are cooler, the overall integrated X-ray and FUV luminosities are similar to those of the "Quiet Sun" -- implying that similar amounts of non-radiative energy input are being dissipated. This work is supported by NASA GALEX grant NNX06AB46G, HST grants GO-11555 and GO-11829, and Chandra grants GO6-7018X, GO7-8020X, and GO9-0021X to the University of Colorado.

Brown, Alexander; Hodges-Kluck, E. J.; Ayres, T. R.; Harper, G. M.

2012-05-01

386

2.5D MHD Simulations of the Kelvin-Helmholtz Instability at CME-Boundaries in the Solar Corona  

NASA Astrophysics Data System (ADS)

We discuss the observation of a coronal mass ejection (CME) by the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory from 2011 February 24. This CME with an embedded filament shows periodic vortex-like structures at the northern side of the filament boundary with a wavelength of approximately 14.4 Mm and a propagation speed of about 310 20 km/s. The morphological analysis hints at structures produced by the Kelvin-Helmholtz (KH) instability on the boundary of the filament. We conduct 2.5D numerical simulations of the KH instability, whose results yield qualitative as well as quantitative agreements with the observations. Furthermore, we study the absence of KH vortex-like structures on the southern side of the filament boundary and find that a magnetic field component parallel to the boundary with a strength of about 20% of the total magnetic field has stabilizing effects resulting in an asymmetric development of the instability. This work receives funding from the Austrian Science Fund (FWF): P21051-N16, V195-N16 and P24092-N16.

Mstl, Ute; Temmer, Manuela; Veronig, Astrid

2013-04-01

387

Density Fluctuations and the Acceleration of Electrons by Beam-generated Langmuir Waves in the Solar Corona  

NASA Astrophysics Data System (ADS)

Non-thermal electron populations are observed throughout the heliosphere. The relaxation of an electron beam is known to produce Langmuir waves which, in turn, may substantially modify the electron distribution function. As the Langmuir waves are refracted by background density gradients and as the solar and heliospheric plasma density is naturally perturbed with various levels of inhomogeneity, the interaction of Langmuir waves with non-thermal electrons in inhomogeneous plasmas is an important topic. We investigate the role played by ambient density fluctuations on the beam-plasma relaxation, focusing on the effect of acceleration of beam electrons. The scattering of Langmuir waves off turbulent density fluctuations is modeled as a wavenumber diffusion process which is implemented in numerical simulations of the one-dimensional quasilinear kinetic equations describing the beam relaxation. The results show that a substantial number of beam electrons are accelerated when the diffusive timescale in wavenumber space ? D is of the order of the quasilinear timescale ?ql, while when ? D Lt ?ql, the beam relaxation is suppressed. Plasma inhomogeneities are therefore an important means of energy redistribution for waves and hence electrons, and so must be taken into account when interpreting, for example, hard X-ray or Type III emission from flare-accelerated electrons.

Ratcliffe, H.; Bian, N. H.; Kontar, E. P.

2012-12-01

388

DENSITY FLUCTUATIONS AND THE ACCELERATION OF ELECTRONS BY BEAM-GENERATED LANGMUIR WAVES IN THE SOLAR CORONA  

SciTech Connect

Non-thermal electron populations are observed throughout the heliosphere. The relaxation of an electron beam is known to produce Langmuir waves which, in turn, may substantially modify the electron distribution function. As the Langmuir waves are refracted by background density gradients and as the solar and heliospheric plasma density is naturally perturbed with various levels of inhomogeneity, the interaction of Langmuir waves with non-thermal electrons in inhomogeneous plasmas is an important topic. We investigate the role played by ambient density fluctuations on the beam-plasma relaxation, focusing on the effect of acceleration of beam electrons. The scattering of Langmuir waves off turbulent density fluctuations is modeled as a wavenumber diffusion process which is implemented in numerical simulations of the one-dimensional quasilinear kinetic equations describing the beam relaxation. The results show that a substantial number of beam electrons are accelerated when the diffusive timescale in wavenumber space {tau}{sub D} is of the order of the quasilinear timescale {tau}{sub ql}, while when {tau}{sub D} << {tau}{sub ql}, the beam relaxation is suppressed. Plasma inhomogeneities are therefore an important means of energy redistribution for waves and hence electrons, and so must be taken into account when interpreting, for example, hard X-ray or Type III emission from flare-accelerated electrons.

Ratcliffe, H.; Bian, N. H.; Kontar, E. P., E-mail: h.ratcliffe@astro.gla.ac.uk [School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ (United Kingdom)

2012-12-20

389

Reconstruction of reconnecting magnetic field in both solar corona and geo-magnetosphere and its application to reconnection diagnosis  

NASA Astrophysics Data System (ADS)

Magnetic reconnection is a critical process of energy transfer in the solar-terrestrial plasma. The related 3-D magnetic field geometry and its temporal reconfiguration are important for reconnection diagnosis. For example, we can estimate how fast the coronal magnetic field is reconnected, based on temporal variation of the reconnecting field lines, and we can learn about the micro-physics in the reconnection region with the help of 3-D reconstruction of the magnetic field in geo-space. For a solar micro-flare event, we study the evolution of magnetic field lines, which are ex-trapolated from dynamic footpoints showing convergence motions. We find that the two sets of approaching closed loops were reconfigured to form a joint set of superimposed large-scale closed loops and another set of small-scale closed loops. We estimate the reconnection rate in two ways. One way is to calculate the convective electric field in the photosphere, which is normalized to the product of the plasma jet speed and the coronal magnetic field strength inside the inflow region. Another way is to directly calculate the reconnection rate based on Vin/VA, where Vin is the motion of the convex segments on the reconnecting field lines. The reconnection rate is estimated to range between 0.03 and 0.09. This is the first work illustrat-ing the reconfiguration of the magnetic field geometry, owing to reconnection driven by flux convergence in the photosphere. For a magnetic reconnection event in the geo-magnetotail, we reconstruct the 3D magnetic field structure containing a pair of nulls with a novel method based on Cluster 4-spacecraft measurements. We study the electron dynamics near one null of the pair, and propose a new scenario of micro-physics in the null region. In this scenario, electrons are temporarily trapped in the central reconnection region, accelerated possibly by parallel electric field and electron pressure gradient, and reflected from the magnetic cusp mirrors leading to the bi-directional energetic electron beams, which may excite the high-frequency electrostatic waves. Here, we have demonstrated that reconstruction of the real-time magnetic field structure is quite helpful for magnetic reconnection diagnosis, e.g., estimation of the reconnection rate and analysis of the micro-physics in the inner reconnection region. References: [1]. He, J.-S., Marsch, E., Tu, C.-Y., Tian, H., Guo, L.-J., Reconfiguration of the coronal magnetic field by means of reconnection driven by photospheric magnetic flux convergence, AA, 510, A40, 2010. [2]. He, J.-S., Zong, Q.-G., Deng, X.-H., Tu, C.-Y., et al., Electron trapping around a magnetic null, Geophys. Res. Lett., 35, L14104, 2008.

He, Jiansen; Marsch, Eckart; Tu, Chuanyi; Zong, Qiugang; Tian, Hui; Guo, Lijia

390

Fluid-induced organic synthesis in the solar nebula recorded in extraterrestrial dust from meteorites.  

PubMed

Isotopically anomalous carbonaceous grains in extraterrestrial samples represent the most pristine organics that were delivered to the early Earth. Here we report on gentle aberration-corrected scanning transmission electron microscopy investigations of eight (15)N-rich or D-rich organic grains within two carbonaceous Renazzo-type (CR) chondrites and two interplanetary dust particles (IDPs) originating from comets. Organic matter in the IDP samples is less aromatic than that in the CR chondrites, and its functional group chemistry is mainly characterized by C-O bonding and aliphatic C. Organic grains in CR chondrites are associated with carbonates and elemental Ca, which originate either from aqueous fluids or possibly an indigenous organic source. One distinct grain from the CR chondrite NWA 852 exhibits a rim structure only visible in chemical maps. The outer part is nanoglobular in shape, highly aromatic, and enriched in anomalous nitrogen. Functional group chemistry of the inner part is similar to spectra from IDP organic grains and less aromatic with nitrogen below the detection limit. The boundary between these two areas is very sharp. The direct association of both IDP-like organic matter with dominant C-O bonding environments and nanoglobular organics with dominant aromatic and C-N functionality within one unique grain provides for the first time to our knowledge strong evidence for organic synthesis in the early solar system activated by an anomalous nitrogen-containing parent body fluid. PMID:25288736

Vollmer, Christian; Kepaptsoglou, Demie; Leitner, Jan; Busemann, Henner; Spring, Nicole H; Ramasse, Quentin M; Hoppe, Peter; Nittler, Larry R

2014-10-28

391

On the Intrinsic Difficulty of Producing Stellar Coronae With Acoustic Waves  

E-print Network

candidates for heating not only the chromosphere, but also the corona of the Sun and similar stars. Meanwhile, however, severe empirical limits could be placed on the role that these waves play in heating the solar-corona to heat the open corona, even though such waves are certainly abundant in the photosphere, Finally

Ulmschneider, Peter

392

Interstellar Dust: Contributed Papers  

NASA Technical Reports Server (NTRS)

A coherent picture of the dust composition and its physical characteristics in the various phases of the interstellar medium was the central theme. Topics addressed included: dust in diffuse interstellar medium; overidentified infrared emission features; dust in dense clouds; dust in galaxies; optical properties of dust grains; interstellar dust models; interstellar dust and the solar system; dust formation and destruction; UV, visible, and IR observations of interstellar extinction; and quantum-statistical calculations of IR emission from highly vibrationally excited polycyclic aromatic hydrocarbon (PAH) molecules.

Tielens, Alexander G. G. M. (editor); Allamandola, Louis J. (editor)

1989-01-01

393

Indirect detection of the Martian helium corona  

Microsoft Academic Search

The ion composition mass spectrometer ASPERA on board the PHOBOS 2 spacecraft detected particles with M\\/q=4 in the vicinity of Mars. A significant difference between the measured particle velocity and the solar wind velocity suggests that these ions are of planetary origin, apparently He+ from ionisation within the Martian helium corona. The particles had typical energies of either more than

S. Barabash; O. Norberg

1994-01-01

394

Indirect detection of the Martian helium corona  

Microsoft Academic Search

The ion composition mass spectrometer ASPERA on board the PHOBOS 2 spacecraft detected particles with M\\/q = 4 in the vicinity of Mars. A significant difference between the measured particle velocity and the solar wind velocity suggests that these ions are of planetary origin, apparently He(+) from ionisation within the Martian helium corona. The particles had typical energies of either

S. Barabash; O. Norberg

1994-01-01

395

New Results From Chandra: Abundances in Stellar Coronae  

NASA Technical Reports Server (NTRS)

There is considerable evidence, both solar and stellar, that the chemical compositions of stellar coronae differ from their underlying 1)hotospheres. The differences for solar-type stars appear to be related to FIP, whereas the differences for active stars are more mysterious and perhaps suggest metal depletion. Results to-date will be reviewed and new results from the Chandra X-ray Observatory based on calibration and Emission Line Project observations of late-type stellar coronae, will be presented.

Drake, Jeremy

1999-01-01

396

Micron-Sized Dust Particles Detected in the Outer Solar System by the Voyager 1 and 2 Plasma Wave Instruments  

NASA Technical Reports Server (NTRS)

During the Voyager 1 and 2 flybys of the outer planets it has been demonstrated that the plasma wave instrument can detect small dust particles striking the spacecraft. In this paper, we examine the Voyager plasma wave data for dust impacts in the interplanetary medium at heliocentric radial distances ranging from 6 to 60 astronomical units (AU). The results show that a small but persistent level of dust impacts exists out to at least 30 to 50 AU. The average number density of these particles is about 2 x 10(exp -8)/cu m, and the average mass of the impacting particles is believed to be a few times 10(exp -11) g, which corresponds to particle diameters in the micron range. Possible sources of these particles are planets, moons, asteroids, comets, and the interstellar medium. Of these, comets appear to be the most likely source. The number densities are only weakly dependent on ecliptic latitude, which indicates that the particles probably do not originate from planets, moons, or asteroids. Comparisons with interstellar dust fluxes measured in the inner regions of the solar system by the Ulysses spacecraft indicate that the particles are not of interstellar origin.

Gurnett, D. A.; Ansher, J. A.; Kurth, W. S.; Granroth, L. J.

1997-01-01

397

Micron-Sized Dust Particles Detected in the Outer Solar System by the Voyager 1 and 2 Plasma Wave Instruments  

NASA Technical Reports Server (NTRS)

During the Voyager 1 and 2 flybys of the outer planets it has been demonstrated that the plasma wave instrument can detect small dust particles striking the spacecraft. In this paper, we examine the Voyager plasma wave data for dust impacts in the interplanetary medium at heliocentric radial distances ranging from 6 to 60 astronomical units (AU). The results show that a small but persistent level of dust impacts exists out to at least 30 to 50 AU. The average number density of these particles is about 2 x 10(exp -8)/cu m, and the average mass of the impacting particles is believed to be a few times 10(exp -11) g, which corresponds to particle diameters in the micron range. Possible sources of these particles are planets, moons, asteroids, comets, and the interstellar medium. Of these, comets appear to be the most likely source. ne number densities are only weakly dependent on ecliptic latitude, which indicates that the particles probably do not originate from planets, moons, or asteroids. Comparisons with interstellar dust fluxes measured in the inner regions of the solar system by the Ulysses spacecraft indicate that the particles are not of interstellar origin.

Gurnett, D. A.; Ansher, J. A.; Kurth, W. S.; Granroth, L. J.

1997-01-01

398

Development of a Transparent Self Cleaning Dust Shield for Solar Panels  

Microsoft Academic Search

Development of a transparent electrodynamic shield to protect panels from dust deposition is described. The shield contains a clear panel with embed- ded parallel electrodes connected to a single-phase AC supply for producing an electromagnetic wave. The electromagnetic field produced by the electrodes on the surface of the panel repels dust particles that have already deposited on the panel surface,

R. A. Sims; A. S. Biris; J. D. Wilson; C. U. Yurteri; M. K. Mazumder; C. I. Calle; C. R. Buhler

399

Detection of dust over deserts using satellite data in the solar wavelengths  

Microsoft Academic Search

Dust is a dominant feature in satellite images and is suspected to extract large radiative forcing of climate. While remote sensing of dust over the dark oceans is feasible, adequate techniques for remote sensing over the land still have to be developed. Similar to remote sensing of aerosol over vegetated regions, the authors use a combination of visible and mid-IR

Yoram J. Kaufman; Arnon Karnieli; Didier Tanr

2000-01-01

400

Heating of the corona by magnetic singularities  

NASA Technical Reports Server (NTRS)

Theoretical models of current-sheet formation and magnetic heating in the solar corona are examined analytically. The role of photospheric connectivity in determining the topology of the coronal magnetic field and its equilibrium properties is explored; nonequilibrium models of current-sheet formation (assuming an initially well connected field) are described; and particular attention is given to models with discontinuous connectivity, where magnetic singularities arise from smooth footpoint motions. It is shown that current sheets arise from connectivities in which the photospheric flux structure is complex, with three or more polarity regions and a magnetic null point within the corona.

Antiochos, Spiro K.

1990-01-01

401

ON THE REMOTE DETECTION OF SUPRATHERMAL IONS IN THE SOLAR CORONA AND THEIR ROLE AS SEEDS FOR SOLAR ENERGETIC PARTICLE PRODUCTION  

SciTech Connect

Forecasting large solar energetic particle (SEP) events associated with shocks driven by fast coronal mass ejections (CMEs) poses a major difficulty in the field of space weather. Besides issues associated with CME initiation, the SEP intensities are difficult to predict, spanning three orders of magnitude at any given CME speed. Many lines of indirect evidence point to the pre-existence of suprathermal seed particles for injection into the acceleration process as a key ingredient limiting the SEP intensity of a given event. This paper outlines the observational and theoretical basis for the inference that a suprathermal particle population is present prior to large SEP events, explores various scenarios for generating seed particles and their observational signatures, and explains how such suprathermals could be detected through measuring the wings of the H I Ly{alpha} line.

Laming, J. Martin; Moses, J. Daniel; Ko, Yuan-Kuen [Space Science Division, Naval Research Laboratory, Code 7684, Washington, DC 20375 (United States); Ng, Chee K. [College of Science, George Mason University, Fairfax, VA 22030 (United States); Rakowski, Cara E.; Tylka, Allan J. [NASA/GSFC Code 672, Greenbelt, MD 20771 (United States)

2013-06-10

402

Dust Interactions on Small Solar System Bodies and Technology Considerations for Exploration  

NASA Technical Reports Server (NTRS)

Small-bodies such as asteroids and Mars' moons Phobos and Deimos have relatively unknown regolith environments. It is hypothesized that dust preserved in the regolith on the surfaces will have similar mechanical properties to lunar dust because of similar formation processes from micrometeorite bombardment, low relative gravity for slow settling times, and virtually no weathering because there is no atmosphere. This combination of processes infers that small-body dust particles will be highly angular and retain abrasive properties. The focus of this paper uses the mission architecture and engineering design for an asteroid hopper known as Hedgehog, a spherical spacecraft with several symmetric spikes used to aid with tumbling mobility in a low gravity environment. Dust abrasion considerations are highlighted throughout the paper relating to the lead authors' previous work, but act as an example of one of many important dust or regolith physical properties that need to be considered for future exploration. Measurable regolith properties are summarized in order to identify technologies that may be useful for exploration in terms of scientific return and spacecraft design. Previous instruments are summarized in this paper that could be used on the Hedgehog. Opportunities for hardware payloads are highlighted that include low mass solutions or dualpurpose instruments that can measure regolith or dust properties. Finally, dust mitigation suggestions are made for vehicles of this mobility profile.

Kobrick, Ryan,; Hoffman, Jeffrey; Pavone, Marco; Street, Kenneth; Rickman, Douglas

2014-01-01

403

SIMBA observations of the R Corona Australis molecular cloud  

Microsoft Academic Search

We have mapped the R Corona Australis molecular cloud at 1.2 mm with SIMBA on SEST and detected 25 distinct dust emission peaks. While 7 of them coincide with positions of previously known young stars, 18 are seemingly not associated with any known stellar object. We discuss the nature of individual sources and conclude that there are at least four

K. Kampgen; B. Reipurth; M. Albrecht; E. Kreysa; R. Lemke; M. Nielbock; L. A. Reichertz; A. Sievers; R. Zylka

2003-01-01

404

NUMERICAL SIMULATION OF THREE-DIMENSIONAL TUFT CORONA AND ELECTROHYDRODYNAMICS  

EPA Science Inventory

The numerical simulation of three-dimensional tuft corona and electrohydrodynamics (EHD) is discussed. The importance of high-voltage and low-current operation in the wire-duct precipitator has focused attention on collecting high-resistivity dust. The local current density of in...

405

STATISTICAL DESCRIPTION OF A MAGNETIZED CORONA ABOVE A TURBULENT ACCRETION DISK Dmitri A. Uzdensky and Jeremy Goodman  

E-print Network

. This is perceived to be too hard; certainly the long and arduous struggle to understand the heating of solar coronaSTATISTICAL DESCRIPTION OF A MAGNETIZED CORONA ABOVE A TURBULENT ACCRETION DISK Dmitri A. Uzdensky-based statistical theory of a force-free magnetic field in the corona above a turbulent accretion disk. The field

406

Numerical and Analytical Model of an Electrodynamic Dust Shield for Solar Panels on Mars  

NASA Technical Reports Server (NTRS)

Masuda and collaborators at the University of Tokyo developed a method to confine and transport particles called the electric curtain in which a series of parallel electrodes connected to an AC source generates a traveling wave that acts as a contactless conveyor. The curtain electrodes can be excited by a single-phase or a multi-phase AC voltage. A multi-phase curtain produces a non-uniform traveling wave that provides controlled transport of those particles [1-6]. Multi-phase electric curtains from two to six phases have been developed and studied by several research groups [7-9]. We have developed an Electrodynamic Dust Shield prototype using threephase AC voltage electrodes to remove dust from surfaces. The purpose of the modeling work presented here is to research and to better understand the physics governing the electrodynamic shield, as well as to advance and to support the experimental dust shield research.

Calle, C. I.; Linell, B.; Chen, A.; Meyer, J.; Clements, S.; Mazumder, M. K.

2006-01-01

407

Recent Studies of the Behavior of the Sun's White-Light Corona Over Time  

NASA Technical Reports Server (NTRS)

Predictions of upcoming solar cycles are often related to the nature and dynamics of the Sun's polar magnetic field and its influence on the corona. For the past 30 years we have a more-or-less continuous record of the Sun's white-light corona from groundbased and spacebased coronagraphs. Over that interval, the large scale features of the corona have varied in what we now consider a 'predictable' fashion--complex, showing multiple streamers at all latitudes during solar activity maximum; and a simple dipolar shape aligned with the rotational pole during solar minimum. Over the past three decades the white-light corona appears to be a better indicator of 'true' solar minimum than sunspot number since sunspots disappear for months (even years) at solar minimum. Since almost all predictions of the timing of the next solar maximum depend on the timing of solar minimum, the white-light corona is a potentially important observational discriminator for future predictors. In this contribution we describe recent work quantifying the large-scale appearance of the Sun's corona to correlate it with the sunspot record, especially around solar minimum. These three decades can be expanded with the HAO archive of eclipse photographs which, although sparse compared to the coronagraphic coverage, extends back to 1869. A more extensive understanding of this proxy would give researchers confidence in using the white-light corona as an indicator of solar minimum conditions.

SaintCyr, O. C.; Young, D. E.; Pesnell, W. D.; Lecinski, A.; Eddy, J.

2008-01-01