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1

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

2

Solar wind acceleration in the solar corona  

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

3

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

4

Meteoroid ablation during entry into the solar corona  

NASA Astrophysics Data System (ADS)

The deposition of dust material in the close vicinity of the sun has been discussed before in the context of pick up ion production near the sun and in the context of the FIP (First Ionization Potential) effect. Pick-up ions are ions that are carried with the solar wind but have distinctly different charge states and velocities than the solar wind ions. The FIP effect describes an abundance anomaly observed in the slow speed wind, where elements with FIP below about 10 eV are enhanced in abundance. In order to estimate the possible contribution of dust and meteoroids to these two phenomena, we study the mass deposition during entry of dust and meteoroids into the solar corona. The first-order model that we apply is similar to the one-dimensional ablation models previously developed by other groups for the Earth's atmosphere and for the atmosphere of Venus. We present the results of mass deposition profiles for a wide range of masses and velocities of objects falling into the Sun. Our main focus is in the bigger objects (masses greater than 1 Kg) for which most of the mass is deposited in the lower layers of the solar corona. As a first step, we consider only the ecliptic plane and extrapolate the mass flux from empirical models of the dust and meteoroid flux near Earth orbit. We calculate the mass deposition and estimate its effects on the coronal heavy ion composition. With a simple two-dimensional generalization of the model we can also include the interaction of sungrazing comets with the solar corona. We finally discuss the effect of different material compositions of these objects taking into account refractory and volatile materials.

Lamy, Herv; Mann, Ingrid; Lemaire, Joseph

2010-05-01

5

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

6

Meteoroids in solar corona and planetary atmospheres  

NASA Astrophysics Data System (ADS)

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 the Sun. Several representative chemical compositions of these objects are also considered in-cluding refractory and volatile materials. Our main focus is in the bigger objects (mass 1 Kg) for which most of the mass is deposited in the lower layers of the solar corona. The interaction of sungrazing comets with the solar corona is studied with a two-dimensional generalization of the model. The cumulative profile of mass deposition is calculated and we look for the actual effects on the coronal heavy ions composition. In particular we discuss possible implications for the FIP (First Ionization Potential) effect and for the formation of pick-up ions that are measured in the solar wind. We consider the similarities and differences of the entry process in the Solar corona and in planetary atmospheres and we shortly address the survival probability of molecular species.

Lamy, Herve; Mann, Ingrid; Lemaire, Emeritus Joseph

7

Structure and Dynamics of the Solar Corona  

NASA Technical Reports Server (NTRS)

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

Schnack, D. D.

1994-01-01

8

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

9

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

NASA Technical Reports Server (NTRS)

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

1981-01-01

10

Recycling of the Solar Corona's Magnetic Field  

NASA Astrophysics Data System (ADS)

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

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

2004-09-01

11

Locating current sheets in the solar corona  

E-print Network

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

Joerg Buechner

2007-02-18

12

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

13

Turbulent heating of the corona and solar wind: the heliospheric  

E-print Network

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

14

High Energy Particles in the Solar Corona  

E-print Network

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

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

2008-04-16

15

Variable Winds and Dust Formation in R Coronae Borealis Stars  

E-print Network

We have observed P-Cygni and asymmetric, blue-shifted absorption profiles in the He I 10830 lines of twelve R Coronae Borealis (RCB) stars over short (1 month) and long (3 year) 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 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

2013-01-01

16

Variable Winds and Dust Formation in R Coronae Borealis Stars  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

17

VARIABLE WINDS AND DUST FORMATION IN R CORONAE BOREALIS STARS  

SciTech Connect

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

Clayton, Geoffrey C.; Zhang Wanshu [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 (United States); Geballe, T. R., E-mail: gclayton@fenway.phys.lsu.edu, E-mail: wzhan21@lsu.edu, E-mail: tgeballe@gemini.edu [Gemini Observatory, 670 N. A'ohoku Place, Hilo, HI 96720 (United States)

2013-08-01

18

Thermally Damped Waves in the Solar Corona  

NASA Astrophysics Data System (ADS)

Waves observed by high resolution telescopes in the solar corona are subject to a rapid damping which could be due to non-ideal effects and/or transversal inhomogeneities. The attenuation of modes is currently used to determine, e.g. the value and structure of coronal magnetic field, a fundamental parameter which cannot be measured directly. Here we study the damping of linear MHD modes propagating in a stratified plasma in the presence of thermal conduction. For the chosen particular equilibrium we show the importance of the transversal motion in the process of wave damping.

Marcu, A.; Ballai, I.

2007-09-01

19

R Coronae Borealis dust ejections - A preferred plane?  

NASA Technical Reports Server (NTRS)

Spectropolarimetric observations of R Coronae Borealis obtained during the brightness minimum of 1986 are presented. When combined with previous polarization observations of brightness minima, the distribution of observations in the Q-U plane suggests that ejections of dust clouds occur in a preferred plane about the star, in contrast to the standard model for the R CrB-type stars, which holds that clouds are ejected from all parts of the stellar surface. The possibility of an ejection mechanism connected with nonradial pulsations is discussed as the most likely explanation of the preferred plane.

Stanford, S. A.; Clayton, G. C.; Meade, M. R.; Nordsieck, K. H.; Whitney, B. A.

1988-01-01

20

Magnetic Relaxation in the Solar Corona Kenneth Miller1  

E-print Network

Magnetic Relaxation in the Solar Corona Kenneth Miller1 , Bengt Fornberg2 , Natasha Flyer3 , & B. C- duced in the tenuous solar corona by the turbulent, resistive relaxation of a magnetic field under to a rigid, perfectly conducting base, and, (ii) that em- beds a force-free magnetic field in the form

Fornberg, Bengt

21

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

22

Locating current sheets in the solar corona  

E-print Network

Current sheets are essential for energy dissipation in the solar corona, in particular by enabling magnetic reconnection. Unfortunately, sufficiently thin current sheets cannot be resolved observationally and the theory of their formation is an unresolved issue as well. We consider two predictors of coronal current concentrations, both based on geometrical or even topological properties of a force free coronal magnetic field. First, there are separatrices related to magnetic nulls. Through separatrices the magnetic connectivity changes discontinuously. Coronal magnetic nulls are, however, very rare. At second, inspired by the concept of generalized magnetic reconnection without nulls, quasi-separatrix layers (QSL) were suggested. Through QSL the magnetic connectivity changes continuously, though strongly. The strength of the connectivity change can be quantified by measuring the squashing of the flux tubes which connect the magnetically conjugated photospheres. We verify the QSL and separatrix concepts by com...

Buechner, J

2006-01-01

23

RADIO OBSERVATIONS OF THE SOLAR CORONA DURING AN ECLIPSE  

SciTech Connect

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

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

2011-04-01

24

Rotation of Solar Corona from Tracking of Coronal Bright Points  

Microsoft Academic Search

An automated procedure for identification of coronal bright points is applied to selected EIT images observed at various phases of the solar cycle. The procedure finds about 400 bright points on a single EIT image observed at 195 . The positions of the bright points are tracked to study the profile of solar rotation in the solar corona. It is

Nina Karachik; Alexei A. Pevtsov; Isroil Sattarov

2006-01-01

25

Long-term variations in dust production in R Coronae Borealis  

NASA Technical Reports Server (NTRS)

Several searches for periodicities in the historical visible light curves of RCB stars have found that the intervals between declines are random. This paper reexamines 70 declines of R Coronae Borealis since 1853 using one homogeneous data set, the AAVSO light curve. In this data set, pairs of consecutive declines also show a random distribution of intervals. However, if the sequence of declines is examined, there are semiperiodic variations between times of high- and low-decline activity on a time scale of a few years. Near-IR photometry of RCB stars indicates that there are large semiperiodic variations in the amount of dust being produced which have similar time scales. Possible interpretations of a semiperiodic variation in dust formation rates in RCB stars are presented. One is a magnetic activity cycle resulting in 'spots' on the star over which dust formation takes place. Such a magnetic activity cycle is similar to the solar cycle. Another is the changes in the period and amplitude of the pulsations over several years affecting the efficiency of dust production.

Clayton, Geoffrey C.; Whitney, Barbara A.; Mattei, Janet A.

1993-01-01

26

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

E-print Network

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

California at Berkeley, University of

27

Patchy reconnection in the solar corona  

NASA Astrophysics Data System (ADS)

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

Guidoni, Silvina Esther

2011-05-01

28

Extended Solar Corona Rotation from SOHO/UVCS Observations  

NASA Astrophysics Data System (ADS)

The UVCS instrument aboard SOHO provides almost regular long time series of data for the UV and visible light extended corona covering, with nearly daily observations, a complete solar activity cycle starting from April 1996. The two UV channels data allow the reconstruction of high spatial resolution intensity synoptic maps from 1.5 to 3.0 solar radii for the main spectral lines observed (H I Lyman alpha at 121.6 nm and O VI doublet and at 103.2/103.7 nm), moreover the White Light Channel (WLC), designed to measure the linearly polarized radiance (pB) in the wavelength band from 450 nm to 600 nm, allows to plot the time evolution of the visible corona throughout the solar cycle at 8 different polar angles from 1.75 to 3.0 solar radii. The analysis of the maps shows that some features persist for several solar rotations and so it is possible to analyze the data as a time-series modulated at the period of the solar rotation. Therefore the Lomb-Scargle periodogram and autocorrelation methods are used to extract the most significant frequency components from UVCS data time-series and to investigate the rotation rate of the solar corona at different latitudes, heights and phases of the solar cycle. We find a not rigid latitudinal coronal rotation rate and little evidence of more differential rotation at lower distance from sun center. In general the larger gradients of the rotation rates, both in latitudinal and radial direction, are localized at the boundary between the open and closed magnetic field lines. Moreover the study of the rotation rate as a function of time in the solar cycle shows also that the extended corona rotation is only slightly affected by the slower rotation of the inner corona at the solar maximum.

Giordano, Silvio; Mancuso, Salvatore

29

Probing the solar corona with very long baseline interferometry  

PubMed Central

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

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

2014-01-01

30

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

31

Probing the solar corona with very long baseline interferometry.  

PubMed

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

Soja, B; Heinkelmann, R; Schuh, H

2014-01-01

32

Can slow solar shock waves heat the corona?  

NASA Astrophysics Data System (ADS)

Based on the solution to a generalized Riemann-Kotchine problem, the appearance of dissipative slow shock waves in the plasma of the solar corona, which occur when rotational discontinuities are refracted at a contact discontinuity in the transition region between the chromosphere and corona, is studied. The oblique interaction between a solar rotational discontinuity A and stationary contact discontinuity C in the transition region is considered in the scope of the magnetohydrodynamic model. Here, due to the presence of a large number of nonlinear Alfvn waves, there is a real possibility of the appearance of a rotational discontinuity moving to the solar corona in the chromosphere. The appearance of dissipative slow MHD shock waves with an insignificant change in the magnetic field as a result of refraction of nondissipative rotational discontinuities at a contact discontinuity in the transition region is proved. It is supposed that a wave source of plasma heating can exist in upper layers of the corona because of the motion of slow shock waves undergoing the Landau damping. Thus, a new model of heat transfer from the chromosphere to the solar corona is proposed.

Grib, S. A.; Pushkar', E. A.

2014-12-01

33

Element Abundances in Solar Energetic Particles and the Solar Corona  

NASA Astrophysics Data System (ADS)

This is a study of abundances of the elements He, C, N, O, Ne, Mg, Si, S, Ar, Ca, and Fe in solar energetic particles (SEPs) in the 2 - 15 MeV amu-1 region measured on the Wind spacecraft during 54 large SEP events occurring between November 1994 and June 2012. The origin of most of the temporal and spatial variations in abundances of the heavier elements lies in rigidity-dependent scattering during transport of the particles away from the site of acceleration at shock waves driven out from the Sun by coronal mass ejections (CMEs). Variation in the abundance of Fe is correlated with the Fe spectral index, as expected from scattering theory but not previously noted. Clustering of Fe abundances during the "reservoir" period, late in SEP events, is also newly reported. Transport-induced enhancements in one region are balanced by depletions in another, thus, averaging over these variations produces SEP abundances that are energy independent, confirms previous SEP abundances in this energy region, and provides a credible measure of element abundances in the solar corona. These SEP-determined coronal abundances differ from those in the solar photosphere by a well-known function that depends upon the first ionization potential (FIP) or ionization time of the element.

Reames, Donald V.

2014-03-01

34

Radio Remote Sensing of the Corona and the Solar Wind  

E-print Network

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

Steven R. Spangler; Catherine A. Whiting

2008-09-26

35

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

Microsoft Academic Search

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

L. Svalgaard; J. M. Wilcox

1978-01-01

36

The Magnetic Field of the Solar Corona from Pulsar Observations  

E-print Network

We present a novel experiment with the capacity to independently measure both the electron density and the magnetic field of the solar corona. We achieve this through measurement of the excess Faraday rotation due to propagation of the polarised emission from a number of pulsars through the magnetic field of the solar corona. This method yields independent measures of the integrated electron density, via dispersion of the pulsed signal and the magnetic field, via the amount of Faraday rotation. In principle this allows the determination of the integrated magnetic field through the solar corona along many lines of sight without any assumptions regarding the electron density distribution. We present a detection of an increase in the rotation measure of the pulsar J1801$-$2304 of approximately 160 \\rad at an elongation of 0.95$^\\circ$ from the centre of the solar disk. This corresponds to a lower limit of the magnetic field strength along this line of sight of $> 393\\mu\\mathrm{G}$. The lack of precision in the integrated electron density measurement restricts this result to a limit, but application of coronal plasma models can further constrain this to approximately 20mG, along a path passing 2.5 solar radii from the solar limb. Which is consistent with predictions obtained using extensions to the Source Surface models published by Wilcox Solar Observatory

S. M. Ord; S. Johnston; J. Sarkissian

2007-05-14

37

New Views of the Solar Corona from STEREO and SDO  

NASA Astrophysics Data System (ADS)

In the last few years, we have been treated to an unusual visual feast of solar observations of the corona in EUV wavelengths. The observations from the two vantage points of STEREO/SECCHI are now capturing the entire solar atmosphere simultaneously in four wavelengths. The SDO/AIA images provide us with arcsecond resolution images of the full visible disk in ten wavelengths. All these data are captured with cadences of a few seconds to a few minutes. In this talk, I review some intriguing results from our first attempts to deal with these observations which touch upon the problems of coronal mass ejection initiation and solar wind generation. I will also discuss data processing techniques that may help us recover even more information from the images. The talk will contain a generous portion of beautiful EUV images and movies of the solar corona.

Vourlidas, A.

2012-01-01

38

The origin of interplanetary sectors. [solar corona  

NASA Technical Reports Server (NTRS)

The coronal magnetic models of Altschuler and Newkirk (1969), Schatten, Wilcox, and Ness (1969), and Schatten (1971), that allowed calculation of the coronal magnetic field from the observed photometric magnetic field, are reviewed with reference to coronal holes and the origin of interplanetary magnetic field sectors. Some misconceptions about interplanetary magnetic field sectors are examined. It is suggested that interplanetary sector structure should be confined to studies of the outer corona, interplanetary space, and objects therein, but not the sun itself.

Schatten, K. H.

1980-01-01

39

A study of the background corona near solar minimum  

Microsoft Academic Search

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

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

1977-01-01

40

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

E-print Network

ENERGY DISTRIBUTION OF MICROEVENTS IN THE QUIET SOLAR CORONA Arnold O. Benz Institute of Astronomy of the pixels in quiet regions of the solar corona. The changes in coronal emission measure indicate impulsive can only come from observations of the corona. Of particular interest are time variations in coronal

41

Heating of the Solar Corona and its Loops  

NASA Technical Reports Server (NTRS)

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

Klimchuk, James A.

2009-01-01

42

OBSERVATION OF ULTRAFINE CHANNELS OF SOLAR CORONA HEATING  

SciTech Connect

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

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

2012-05-01

43

Radio Remote Sensing of the Solar Corona with the EVLA  

NASA Astrophysics Data System (ADS)

A number of studies have used the VLA to measure Faraday rotation due to the solar corona, and thus remotely sense the coronal plasma structure (e.g. ApJ 668, 5202, 2007). However, these studies have been limited to a closest angular approach of about 5 solar radii from the Sun (1.25 degrees). At closer heliocentric distances, the system temperature at the 1.4 GHz observing frequency is unacceptably enhanced due to the Sun in the distant sidelobes. In future studies we would like to use the EVLA to probe the inner corona, from 2-5 solar radii. Observations at 5 GHz will be less affected by solar system temperature increase because of smaller antenna beams. We performed test measurements with EVLA antennas to determine the solar contribution to the system temperature as a function of angular distance from the sun at 5 GHz. We report our results in three regions of interest: at 2-3 solar radii (32-48') the system temperature varies from 100-350 K, at 3-5 solar radii (48-80') the system temperature is 50-100 K, and for separations greater than 5 solar radii (80') the system temperature levels off to the cold-sky EVLA Tsys value of 39 K. We also present a model for the system temperature due to the quiet sun in the sidelobes, which adequately reproduces the measured Tsys values. These results demonstrate the feasibility of future EVLA Faraday rotation, and other propagation measurements in the inner corona. This research was supported at the University of Iowa by grant ATM-0354782 from the National Science Foundation.

Whiting, Catherine; Spangler, S. R.

2010-01-01

44

The Structure and Dynamics of the Solar Corona  

NASA Technical Reports Server (NTRS)

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

Mikic, Zoran

2000-01-01

45

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

46

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

47

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

48

A Technique for Measuring Electrical Currents in the Solar Corona  

E-print Network

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

Steven R. Spangler

2007-09-11

49

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

50

Large-scale structure of the solar corona magnetic field  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

51

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

52

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

53

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

54

DIRECT MEASUREMENTS OF MAGNETIC TWIST IN THE SOLAR CORONA  

SciTech Connect

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

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

2011-08-01

55

The EUV Emission in Comet-Solar Corona Interactions  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

56

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.

57

MHD modeling of the solar corona: Progress and challenges  

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

58

Dust Measurements in the Outer Solar System  

Microsoft Academic Search

Dust measurements in the outer solar system are reviewed. Only the plasma wave instrument on board Voyagers 1 and 2 recorded\\u000a impacts in the Edgeworth-Kuiper belt (EKB). Pioneers 10 and 11 measured a constant dust flux of 10-micron-sized particles\\u000a out to 20 AU. Dust detectors on board Ulysses and Galileo uniquely identified micron-sized interstellar grains passing through\\u000a the planetary system.

Eberhard Grn; Harald Krger; Markus Landgraf

1993-01-01

59

Dust Measurements in the Outer Solar System  

Microsoft Academic Search

Dust measurements in the outer solar system are reviewed. Only the plasma wave instrument on board Voyagers 1 and 2 recorded impacts in the Edge- worth-Kuiper belt (EKB). Pioneers 10 and 11 measured a constant dust flux of 10- micron-sized particles out to 20 AU. Dust detectors on board Ulysses and Galileo uniquely identified micron-sized interstellar grains passing through the

Eberhard Grun; Harald Kruger; Markus Landgraf

1994-01-01

60

Wind in the Solar Corona: Dynamics and Composition  

NASA Astrophysics Data System (ADS)

The dynamics of the solar corona as observed during solar minimum with the Ultraviolet Coronagraph Spectrometer, UVCS, on SOHO is discussed. The large quiescent coronal streamers existing during this phase of the solar cycle are very likely composed by sub-streamers, formed by closed loops and separated by open field lines that are channelling a slow plasma that flows close to the heliospheric current sheet. The polar coronal holes, with magnetic topology significantly varying from their core to their edges, emit fast wind in their central region and slow wind close to the streamer boundary. The transition from fast to slow wind then appears to be gradual in the corona, in contrast with the sharp transition between the two wind regimes observed in the heliosphere. It is suggested that speed, abundance and kinetic energy of the wind are modulated by the topology of the coronal magnetic field. Energy deposition occurs both in the slow and fast wind but its effect on the kinetic temperature and expansion rate is different for the slow and fast wind.

Antonucci, Ester

2006-06-01

61

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

NASA Astrophysics Data System (ADS)

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

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

2002-12-01

62

The Structure and Dynamics of the Solar Corona  

NASA Technical Reports Server (NTRS)

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

Mikic, Zoran

1998-01-01

63

Interstellar Dust in the Solar System  

E-print Network

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

Harald Krueger; Markus Landgraf; Nicolas Altobelli; Eberhard Gruen

2007-06-21

64

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

65

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

E-print Network

MAGNETIC FIELD CONFINEMENT IN THE SOLAR CORONA. II. FIELD-PLASMA INTERACTION N. Flyer,1 B. Fornberg) attrib- uted to the failure of the confinement of a magnetic flux rope in the solar corona (see, e study of axisymmetric force-free magnetic fields in the unbounded space outside a unit sphere, presented

Fornberg, Bengt

66

Spitzer Observations of Dust Around R Coronae Borealis Stars  

NASA Astrophysics Data System (ADS)

The RCB stars are rare hydrogen-deficient carbon-rich supergiants, all apparently single stars which are consistent with being post-AGB stars. Their rarity may stem from the fact that they are in an extremely rapid phase of their evolution or in an evolutionary phase that most stars do not undergo. Several evolutionary scenarios have been suggested to account for the RCB stars including, a merger of two white dwarfs, or a final helium shell flash in a Planetary Nebula (PN) central star. Therefore, in the RCB stars, the presence or absence of circumstellar material and the nature of this material provides a fossil record of previous evolutionary stages. We have mapped the shells around four RCB stars, R CrB, UW Cen, SU Tau, and V CrA, with MIPS at 24, 70 and 160 microns. We will model the dust shells using dust grains appropriate to the RCB stars to reproduce the observed morphology. While most RCB stars are relatively cool (<7000; K), a few are significantly hotter ( 20,000 K). Two of these stars, V348 Sgr and HV 2671 show similarities to the [WC] central stars of PNe such as CPD -56 8032. We have obtained IRS spectra of V348 Sgr and HV 2671. We will compare their IR spectra with those of the [WC] stars and the cooler RCB stars. CPD -56 8032 shows emission features of PAHs as well as crystalline silicates, indicating a dual dust chemistry. These systems may all be binaries in which the O-rich silicates are trapped in a disk as a result of a past mass transfer event, with the C-rich particles being widely distributed in the nebula as a result of recent ejections of C-rich material. This work was supported by Spitzer Space Telescope contracts 1287678 and 1287524 issued by Caltech/JPL.

Clayton, Geoffrey C.; De Marco, O.; Gordon, K.; Nordhaus, J.; Bond, H.; Sugerman, B.; Barlow, M.; Lawson, W.; Pollacco, D.

2007-12-01

67

Remote-sensing Observations of the Corona and Solar Wind  

NASA Astrophysics Data System (ADS)

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

Sheeley, Neil R., Jr.

2009-05-01

68

Corongraphic Observations and Analyses of The Ultraviolet Solar Corona  

NASA Technical Reports Server (NTRS)

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

Kohl, John L.

2000-01-01

69

Observational tests for nonequilibrium ionization in the solar corona  

NASA Astrophysics Data System (ADS)

Nonequilibrium ionization may be produced by a variety of processes in the solar corona, for example, by mass flows through the large temperature gradients of the transition region or by impulsive heating and cooling. Any deviation from equilibrium ionization would have a strong effect on the radiation from the corona and on the interpretation of solar observations; hence, it is important to determine observational signatures of nonequilibrium. The temperature-sensitive line ratios can be used as such signatures. We examine the line ratios: C IV I(1548.2 A)/I(312.4 A), O IV I(789.4 A)/I(554.4 A), O V I(629.7 A)/I(172.2 A), O VI I(1031.9 A)/I(173.0 A) and O VI I(1031.9 A)/I(150.1 A). These line ratios are calculated for four coronal loop models that have a steady flow and that are known to have significant departures from equilibrium ionization. Our results indicate that, in general, nonequilibrium causes a considerable reduction in the line ratios, more than an order of magnitude in the downflowing leg of the loop model with the largest mass flows. We find that the C IV line ratio is the most sensitive to nonequilibrium. We discuss the implications of our results for observations, specifically, the observations expected from the upcoming SOHO mission.

Spadaro, D.; Leto, P.; Antiochos, S. K.

1994-05-01

70

Self Organization in the Solar Corona and Interstellar Medium  

NASA Astrophysics Data System (ADS)

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

Spangler, Steven

2009-11-01

71

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

72

The dust around R Coronae Borealis type stars  

NASA Technical Reports Server (NTRS)

Measurements taken by the International Ultraviolet Explorer spacecraft of the stars RY Sgr and R CrB have been analyzed using Mie theory. The extinction data, which show a 2400-2500 A peak, are consistent with a distribution of 5-60 nm glassy or amorphous carbon particles obscuring the stellar flux. The data are also fairly consistent with a cloud ejection model. Since the extinction data lack the commonly observed peak at 2170 A, it is proposed that this difference is due to the conditions present when the dust condenses. Interstellar carbon grains appear to originate in normal carbon stars which are carbon and hydrogen rich. In contrast, the grains around R CrB type stars seem to condense from a carbon-rich and hydrogen-poor vapor.

Hecht, J. H.; Holm, A. V.; Donn, B.; Wu, C.-C.

1984-01-01

73

Very Large Telescope Interferometer observations of the dust geometry around R Coronae Borealis stars  

NASA Astrophysics Data System (ADS)

We are investigating the formation and evolution of dust around the hydrogen-deficient supergiants known as R Coronae Borealis (RCB) stars. We aim to determine the connection between the probable merger past of these stars and their current dust-production activities. We carried out high angular resolution interferometric observations of three RCB stars, namely RY Sgr, V CrA and V854 Cen, with the mid-infrared interferometer (MIDI) on the Very Large Telescope Interferometer (VLTI), using two telescope pairs. The baselines ranged from 30 to 60 m, allowing us to probe the dusty environment at very small spatial scales (50 mas or 400R?). The observations of the RCB star dust environments were interpreted using both geometrical models and one-dimensional radiative transfer codes. From our analysis, we find that asymmetric circumstellar material is apparent in RY Sgr, may also exist in V CrA and is possible for V854 Cen. Overall, we find that our observations are consistent with dust forming in clumps ejected randomly around the RCB star so that over time they create a spherically symmetric distribution of dust. However, we conclude that the determination of whether there is a preferred plane of dust ejection must wait until a time series of observations are obtained. Based on observations made with the Very Large Telescope Interferometer at Paranal Observatory under programme 079.D-0415.

Bright, S. N.; Chesneau, O.; Clayton, G. C.; De Marco, O.; Leo, I. C.; Nordhaus, J.; Gallagher, J. S.

2011-06-01

74

RADIO OBSERVATIONS OF WEAK ENERGY RELEASES IN THE SOLAR CORONA  

SciTech Connect

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

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

2010-08-10

75

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

Microsoft Academic Search

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

Bo Li; Peter A. Robinson; Iver H. Cairns

2006-01-01

76

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

2004-10-26

77

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

78

Clementine Observes the Moon, Solar Corona, and Venus  

NASA Technical Reports Server (NTRS)

In 1994, during its flight, the Clementine spacecraft returned images of the Moon. In addition to the geologic mapping cameras, the Clementine spacecraft also carried two Star Tracker cameras for navigation. These lightweight (0.3 kg) cameras kept the spacecraft on track by constantly observing the positions of stars, reminiscent of the age-old seafaring tradition of sextant/star navigation. These navigation cameras were also to take some spectacular wide angle images of the Moon.

In this picture the Moon is seen illuminated solely by light reflected from the Earth--Earthshine! The bright glow on the lunar horizon is caused by light from the solar corona; the sun is just behind the lunar limb. Caught in this image is the planet Venus at the top of the frame.

1997-01-01

79

Creation of current filaments in the solar corona  

NASA Technical Reports Server (NTRS)

It has been suggested that the solar corona is heated by the dissipation of electric currents. The low value of the resistivity requires the magnetic field to have structure at very small length scales if this mechanism is to work. In this paper it is demonstrated that the coronal magnetic field acquires small-scale structure through the braiding produced by smooth, randomly phased, photospheric flows. The current density develops a filamentary structure and grows exponentially in time. Nonlinear processes in the ideal magnetohydrodynamic equations produce a cascade effect, in which the structure introduced by the flow at large length scales is transferred to smaller scales. If this process continues down to the resistive dissipation length scale, it would provide an effective mechanism for coronal heating.

Mikic, Z.; Schnack, D. D.; Van Hoven, G.

1989-01-01

80

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 prof...

Kraev, U M

2001-01-01

81

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

NASA Astrophysics Data System (ADS)

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

Garca-Hernndez, D. A.; Kameswara Rao, N.; Lambert, D. L.

2013-08-01

82

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

83

Bull. Astr. Soc. India (2013) 00, 1?? The Solar Corona: What Are The Remaining Fundamental  

E-print Network

of beautiful plasma columns our instruments observe in EUV and soft X-rays outline the coronal magnetic field The solar corona has been observed in detail in soft X-rays and EUV for over half a century (Golub tenuous that coronal plasma is almost exclusively optical thin. The magnetic field in the corona typically

Martens, Petrus C.

84

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

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

85

High frequency Faraday rotation observations of the solar corona  

NASA Astrophysics Data System (ADS)

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

Jensen, Elizabeth Annah

86

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

87

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

88

VLTI observations of the dust geometry around R Coronae Borealis stars  

E-print Network

We are investigating the formation and evolution of dust around the hydrogen-deficient supergiants known as R Coronae Borealis (RCB) stars. We aim to determine the connection between the probable merger past of these stars and their current dust-production activities. We carried out high-angular resolution interferometric observations of three RCB stars, namely RY Sgr, V CrA, and V854 Cen with the mid-IR interferometer, MIDI on the VLTI, using two telescope pairs. The baselines ranged from 30 to 60 m, allowing us to probe the dusty environment at very small spatial scales (~ 50 mas or 400 stellar radii). The observations of the RCB star dust environments were interpreted using both geometrical models and one-dimensional radiative transfer codes. From our analysis we find that asymmetric circumstellar material is apparent in RY Sgr, may also exist in V CrA, and is possible for V854 Cen. Overall, we find that our observations are consistent with dust forming in clumps ejected randomly around the RCB star so tha...

Bright, S N; Clayton, G C; De Marco, O; Leo, I C; Nordhaus, J; Gallagher, J S

2011-01-01

89

Dust around R Coronae Borealis stars: II. Infrared emission features in a H-poor environment  

E-print Network

Residual Spitzer/IRS spectra for a sample of 31 R Coronae Borealis (RCB) stars are presented and discussed in terms of narrow emission features superimposed on the quasi-blackbody continuous infrared emission. A broad ~6-10 um dust emission complex is seen in the RCBs showing an extreme H-deficiency. A secondary and much weaker ~11.5-15 um broad emission feature is detected in a few RCBs with the strongest ~6-10 um dust complex. The Spitzer infrared spectra reveal for the first time the structure within the ~6-10 um dust complex, showing the presence of strong C-C stretching modes at ~6.3 and 8.1 um as well as of other dust features at ~5.9, 6.9, and 7.3 um, which are attributable to amorphous carbonaceous solids with little or no hydrogen. The few RCBs with only moderate H-deficiencies display the classical 'unidentified infrared bands (UIRs)' and mid-infrared features from fullerene-related molecules. In general, the characteristics of the RCB infrared emission features are not correlated with the stellar a...

Garcia-Hernandez, D A; Lambert, D L

2013-01-01

90

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

91

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

92

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

93

Heating of the Quiet Corona and Solar Wind  

NASA Astrophysics Data System (ADS)

We have emphasized that the energy flux required to produce the quiet solar corona and the solar wind must have its immediate source in small (`pico'-)flares occurring in the supergranular network. Here the magnetic field is amplified to >100 G and is directed both in- and outwards from the Sun. Evidence for this `furnace' is provided partly by the existence of such magnetic fields (seen in magnetograph observations), transient brightenings, upwards flow and high-speed jets and the general association of bright EUV emissions with the network. The Alfven speed in the furnace must be very large ( 104 km/sec) and, to supply the necessary energy flux of 7x106 ergs/cm2sec, the magnetic flux and energy must be re-supplied with a turnover time of 30 minutes. Pico-flares with total energies 1021 2 ergs should occur at a high rate and appear almost continuous when observed with a spatial resolution 1 arcsec. The transient emfs associated with magnetic field reconnection in the furnace are 106-108 Volts and accordingly ions should be expected to be accelerated to 1-102 MeV/Q, sufficient to produce nuclear reactions on impacting the background plasma. The most interesting secondary particles that can result from such interactions are the radioactive fragments of He, CNO, S, Si and Fe nuclei. These secondary particles should be largely entrained in the high- and low-speed solar wind, reaching the orbit of Earth with energies of only a few keV/nuc. Because of their low fluxes they are difficult to detect with the usual plasma instrumentation. However they accumulate on solid surfaces exposed to the solar wind, penetrating only to a small depth, and can in principle be detected by their distinctive radioactive decay products, notably 10Be and 14C, which have comparatively long lifetimes (i.e. accumulation times). Recent measurements of these isotopes trapped superficially in lunar fines provide the first direct evidence for this scenario. As a result of adiabatic expansion losses in the solar wind, energetic particles that escape directly from the pico-flares along open magnetic field lines should produce a steady `shower' of sub-MeV particles at 1 AU. Such particle fluxes have long been observed with a characteristic anisotropy and large negative radial gradient. In future the possibility should be considered of detecting the corresponding secondary neutrons and nuclear gamma rays directly in space near the Sun, especially in connection with the proposed Solar Orbiter, Solar Probe and Beppi Colombo missions. These missions will also provide an opportunity for the escaping particle flux to be identified from its radial dependence and measured in detail..

Axford, W. I.

94

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

Microsoft Academic Search

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

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

1978-01-01

95

Latitudinal and Radial Variation of Solar Corona Rotation at Solar Minimum  

NASA Astrophysics Data System (ADS)

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 Ly? l216 spectral lines and visible light polarized brightness obtained by the observations of UVCS/SOHO instrument. The time period analyzed range from mid May 1996 to mid May 1997, when, at solar minimum, some features persist for several rotations, thus allowing to analyze the UV and visible emission as time series modulated at the period of the solar rotation. The coronal differential rotation rate significantly differs from that of the photospheric plasma. The estimated equatorial synodic rotation period of the corona at 1.5 Rsolar is 27.48+/-0.15 days. The study of the latitudinal variation shows that the UV corona decelerates towards the photospheric rates from the equator up to the poleward boundary of the mid-latitude streamers, reaching a peak of 28.16+/-0.20 days around +/-30 from the equator at 1.5 Rsolar, while a less evident peak is observed in the northern hemisphere, suggesting a real north-south rotational asymmetry, the northern hemisphere the rotation looks more solid-body-like and slower than in the southern hemisphere. The mid-latitude results are also confirmed by the visible light data available at 1.75 and 2.0 Rsolar. The study of the radial rotation profiles shows that the corona is rotating almost rigidly with height, but we find an abrupt increase by about half a days between 2.3 and 2.5 Rsolar. The larger radial and latitudinal gradients of the rotation rates are localized at the boundary between the open and closed field lines, suggesting that in these regions the differential rotation might be a source of magnetic stress and, consequently, of energy release.

Giordano, S.; Mancuso, S.; Romoli, M.

2007-09-01

96

The Corona of the Young Solar Analog EK Draconis  

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

97

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

98

Dust around R Coronae Borealis Stars. I. Spitzer/Infrared Spectrograph Observations  

NASA Astrophysics Data System (ADS)

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

Garca-Hernndez, D. A.; Kameswara Rao, N.; Lambert, David L.

2011-09-01

99

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

SciTech Connect

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

Garcia-Hernandez, D. A. [Instituto de Astrofisica de Canarias, C/Via Lactea s/n, E-38200 La Laguna (Spain); Rao, N. Kameswara [543, 17th Main, IV Sector, HSR Layout, Bangalore 560102 and Indian Institute of Astrophysics, Bangalore 560034 (India); Lambert, D. L., E-mail: agarcia@iac.es, E-mail: nkrao@iiap.res.in, E-mail: dll@astro.as.utexas.edu [W. J. McDonald Observatory, University of Texas at Austin, 1 University Station, C1400, Austin, TX 78712-0259 (United States)

2013-08-20

100

Dust around R Coronae Borealis stars: I. Spitzer/IRS observations  

E-print Network

Spitzer/IRS spectra from 5 to 37 um for a complete sample of 31 R Coronae Borealis stars (RCBs) are presented. These spectra are combined with optical and near-infrared photometry of each RCB at maximum light to compile a spectral energy distribution (SED). The SEDs are fitted with blackbody flux distributions and estimates made of the ratio of the infrared flux from circumstellar dust to the flux emitted by the star. Comparisons for 29 of the 31 stars are made with the IRAS fluxes from three decades earlier: Spitzer and IRAS fluxes at 12 um and 25 um are essentially equal for all but a minority of the sample. For this minority, the IRAS to Spitzer flux ratio exceeds a factor of three. The outliers are suggested to be stars where formation of a dust cloud or dust puff is a rare event. A single puff ejected prior to the IRAS observations may have been reobserved by Spitzer as a cooler puff at a greater distance from the RCB. RCBs which experience more frequent optical declines have, in general, a circumstellar...

Garcia-Hernandez, D A; Lambert, David L

2011-01-01

101

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

102

Solar Wind Magnetic Field Bending of Jovian Dust Trajectories  

Microsoft Academic Search

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

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

1996-01-01

103

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

104

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

105

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 against expansion into the unbounded space. This property as a basic mechanism for solar coronal mass

Fornberg, Bengt

106

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

107

Interactions of Dust Grains with Coronal Mass Ejections and Solar Cycle Variations of the F-Coronal Brightness  

NASA Technical Reports Server (NTRS)

The density of interplanetary dust increases sunward to reach its maximum in the F corona, where its scattered white-light emission dominates that of the electron K corona above about 3 Solar Radius. The dust will interact with both the particles and fields of antisunward propagating coronal mass ejections (CMEs). To understand the effects of the CME/dust interactions we consider the dominant forces, with and without CMEs. acting on the dust in the 3-5 Solar Radius region. Dust grain orbits are then computed to compare the drift rates from 5 to 3 Solar Radius. for periods of minimum and maximum solar activity, where a simple CME model is adopted to distinguish between the two periods. The ion-drag force, even in the quiet solar wind, reduces the drift time by a significant factor from its value estimated with the Poynting-Robertson drag force alone. The ion-drag effects of CMEs result in even shorter drift times of the large (greater than or approx. 3 microns) dust grains. hence faster depletion rates and lower dust-pain densities, at solar maxima. If dominated by thermal emission, the near-infrared brightness will thus display solar cycle variations close to the dust plane of symmetry. While trapping the smallest of the grains, the CME magnetic fields also scatter the grains of intermediate size (0.1-3 microns) in latitude. If light scattering by small grains close to the Sun dominates the optical brightness. the scattering by the CME magnetic fields will result in a solar cycle variation of the optical brightness distribution not exceeding 100% at high latitudes, with a higher isotropy reached at solar maxima. A good degree of latitudinal isotropy is already reached at low solar activity since the magnetic fields of the quiet solar wind so close to the Sun are able to scatter the small (less than or approx. 3 microns) grains up to the polar regions in only a few days or less, producing strong perturbations of their trajectories in less than half their orbital periods. Finally, we consider possible observable consequences of individual CME/dust interactions. We show that the dust grains very likely have no observable effect on the dynamics of CMEs. The effect of an individual CME on the dust grains, however, might serve as a forecasting tool for the directions and amplitudes of the magnetic fields within the CME.

Ragot, B. R.; Kahler, S. W.

2003-01-01

108

Konus- Wind and Helicon- Coronas-F observations of solar flares  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

109

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

E-print Network

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

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

2014-01-01

110

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

E-print Network

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

Takeru Ken Suzuki

2002-08-06

111

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

112

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

113

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

114

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

115

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

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

116

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

117

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

118

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

119

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

Microsoft Academic Search

We consider the reflection of Alfvn waves in the corona and solar wind, using variables f and g which follow sunward and antisunward characteristics, respectively. We show that the basic equations for f and g have the same structure as the Klein-Gordon equation. Unlike previous studies which used a harmonic analysis, we emphasize the impulse response of the system. This

Joseph V. Hollweg; P. A. Isenberg

2007-01-01

120

The using of large ground-based low frequency radio telescopes for outer solar corona diagnostics  

Microsoft Academic Search

The interplanetary scintillations method is well developed at meter- decimeter wavelength for solar wind study. Potentially the decameter range can be convenient for implementing this method at large elongations, i.e. for studying the outer corona. During last years this method was evaluated by using largest decameter antennas UTR-2 and Nancay Decameter Array at new quantity and quality levels. New methods

A. A. Konovalenko; I. S. Falkovich; N. N. Kalinichenko; M. R. Olyak; I. N. Bubnov; A. Lecacheux; C. Rosolen; J.-L. Bougeret; H. O. Rucker; R. Leitinger

2003-01-01

121

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

SciTech Connect

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

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

2011-11-29

122

Dust in the planetary system: Dust interactions in space plasmas of the solar system  

NASA Astrophysics Data System (ADS)

Cosmic dust particles are small solid objects observed in the solar planetary system and in many astronomical objects like the surrounding of stars, the interstellar and even the intergalactic medium. In the solar system the dust is best observed and most often found within the region of the orbits of terrestrial planets where the dust interactions and dynamics are observed directly from spacecraft. Dust is observed in space near Earth and also enters the atmosphere of the Earth where it takes part in physical and chemical processes. Hence space offers a laboratory to study dust-plasma interactions and dust dynamics. A recent example is the observation of nanodust of sizes smaller than 10 nm. We outline the theoretical considerations on which our knowledge of dust electric charges in space plasmas are founded. We discuss the dynamics of the dust particles and show how the small charged particles are accelerated by the solar wind that carries a magnetic field. Finally, as examples for the space observation of cosmic dust interactions, we describe the first detection of fast nanodust in the solar wind near Earth orbit and the first bi-static observations of PMSE, the radar echoes that are observed in the Earth ionosphere in the presence of charged dust.

Mann, Ingrid; Meyer-Vernet, Nicole; Czechowski, Andrzej

2014-03-01

123

Composition of the Solar Wind  

NASA Technical Reports Server (NTRS)

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

Suess, S. T.

2007-01-01

124

Solar wind driven dust acoustic instability with Lorentzian kappa distribution  

SciTech Connect

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

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

2014-02-15

125

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

E-print Network

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

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

2007-02-13

126

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

127

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

128

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

NASA Astrophysics Data System (ADS)

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.

2006-09-01

129

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

130

Radial Distribution of Compressive Waves in the Solar Corona Revealed by Akatsuki Radio Occultation Observations  

NASA Astrophysics Data System (ADS)

Radial variations of the amplitude and the energy flux of compressive waves in the solar corona were explored for the first time using a spacecraft radio occultation technique. By applying wavelet analysis to the frequency time series taken at heliocentric distances of 1.5-20.5 RS (solar radii), quasi-periodic density disturbances were detected at almost all distances. The period ranges from 100 to 2000 s. The amplitude of the fractional density fluctuation increases with distance and reaches ~30% around 5 RS , implying that nonlinearity of the wave field is potentially important. We further estimate the wave energy flux on the assumption that the observed periodical fluctuations are manifestations of acoustic waves. The energy flux increases with distance below ~6 RS and seems to saturate above this height, suggesting that the acoustic waves do not propagate from the low corona but are generated in the extended corona, probably through nonlinear dissipation of Alfvn waves. The compressive waves should eventually dissipate through shock generation to heat the corona.

Miyamoto, Mayu; Imamura, Takeshi; Tokumaru, Munetoshi; Ando, Hiroki; Isobe, Hiroaki; Asai, Ayumi; Shiota, Daikou; Toda, Tomoaki; Husler, Bernd; Ptzold, Martin; Nabatov, Alexander; Nakamura, Masato

2014-12-01

131

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

132

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

133

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

134

"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

135

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

136

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

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

137

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

NASA Technical Reports Server (NTRS)

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

Von Puttkamer, J.

1973-01-01

138

Solar X-ray and EUV corona and their relation to the magnetic activity  

Microsoft Academic Search

We have studied the solar magnetic cycle in corona using X-ray data from YOHKOH and Extreme Ultraviolet data from SOHO\\/EIT. Soft X-ray data last the period from after the maximum cycle 22 to the maximum cycle 23 (19912001). The SOHO\\/EIT Extreme Ultraviolet data are used for the period from 1996 to 2003. These data provide us a unique opportunity to

Elena E. Benevolenskaya

2007-01-01

139

Solar X-ray and EUV corona and their relation to the magnetic activity  

Microsoft Academic Search

We have studied the solar magnetic cycle in corona using X-ray data from YOHKOH spacecraft. These data last the period from after the maximum cycle 22 to the maximum cycle 23 (1991-2001). We have also considered the SOHO\\/EIT data. The Extreme Ultraviolet data display an evolution of the coronal structures in cycle 23 (1996-2003). These studies reveal a close relation

E. Benevolenskaya

2004-01-01

140

Satellite project "CORONAS-PHOTON" for study of solar hard radiation  

NASA Astrophysics Data System (ADS)

"CORONAS-PHOTON" is the Russian mission for study of the solar hard electromagnetic radiation in the very wide energy range from Extreme UV up to high-energy gamma - radiation. GOAL OF PROJECT: The investigation of energy accumulation and its transformation into energy of accelerated particles processes during solar flares; the study of the acceleration mechanisms, propagation and interaction of fast particles in the solar atmosphere; the study of the solar activity correlation with physical-chemical processes in the Earth upper atmosphere. SCIENTIFIC PAYLOAD CAPABILITY Radiation / Energy region / Detector type: Full solar disk X- radiation / 2keV - 2000MeV / Prop. counter; NaI(Tl); Full solar disk X- and ?-radiation / NaI(Tl)/CsI(Na) phoswich; Full solar disk X- and ?-radiation and solar neutrons / 20 - 300MeV / YalO_3(Ce); CsI(Tl); Hard X-ray polarization in large flares / 20 - 150keV / p-terphenyl scatterer and CsI(Na) absorbers; Full solar disk EUV-radiation monitoring / 6 spectral windows in <10 - 130nm / Filtered photodiodes; Solar images in narrow spectral bands and monochromatic emission lines of hot plasma / Emission of HeII, SiXI, FeXXI, FeXXIII, MgXII ions / Multi-layer and Bregg spherical crystal quartz mirrors with CCDs; Additionally, the temporal and energy spectra of electrons (0.2-14MeV), protons (1-61MeV) and nuclei (Z<26, 2-50MeV/nuclon) at the satellite orbit will be registrated by several instruments. MAIN CHARACTERISTICS OF SPACECRAFT: Spacecraft weight: 1900 kg; Orbit type: Circular; Scientific payload weight: 540 kg; Height: 500 km; Orientation to the Sun [arc min]: better 5; Inclination: 82.5 degree; Instability of orientation [deg/s]: less 0.005; Solar - synchronous orbit is under study. Launching date of "CORONAS-PHOTON" spacecraft is 2006.

Kotov, Yu.; Cor-Phot Team

141

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

142

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

NASA Astrophysics Data System (ADS)

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

Cranmer, Steven R.

2014-08-01

143

Spectroscopic measurements of element abundances in the solar corona: Variations on the FIP theme  

NASA Technical Reports Server (NTRS)

Solar wind and solar energetic particle (SEP) data yield systematic differences between elemental abundances in the corona and in the photosphere related to the first ionization potential (FIP) of the elements: low-FIP elements are preferentially enhanced relative to high-FIP elements by about a factor of four. Spectroscopic studies of the inner corona show that such a pattern may apply on average but not in detail for coronal loops: substantial abundance differences occur between different types of coronal structures, and variations have been found from flare to flare, from one active region to another, and over time in the same region; further, in some flares, anomalies such as enhanced Ne:O ratios, distinctly at odds with the FIP pattern, show that a competing element selection mechanism sometimes operates. Details of the observed abundance variability -- such as the magnitude of the variations, the relevant temporal and spatial scales, and correlations with other properties of the given coronal structure -- may give important clues to the processes which supply and heat the corona, or they may reflect the changing physical conditions or locations where those processes take place. However, many such details remain to be established definitively. At present, abundance variability is primarily a major complication to data analysis and interpretation. However, once it is better understood, it may provide a new diagnostic tool for probing the lower layers of the solar atmosphere.

Saba, J. L. R.

1995-01-01

144

Heating the Solar Corona: Observations for Model Boundary Conditions  

NASA Astrophysics Data System (ADS)

A prominent question in solar physics concerns the sources of coronal heating. This problem can be addressed through observations of closed magnetic loops which have high enough density to provide adequate temporal, spatial, and spectral resolution. Measurements of temperature, density, and velocity throughout the loop can be used for boundary conditions and compared with quantities for model calculations. In this paper, we present Solar Ultraviolet Measurements from Emitted Radiation (SUMER) data from the Solar and Heliospheric Observatory's (SOHO's) JOP 161 program. The SUMER instrument has high spatial and spectral resolution over several different spectral lines and therefore the data cover a large temperature range. The analyzed lines include Mg VIII, Mg IX, N III, N IV, Ne VIII, O IV, O V, S IV, S V, and S X with temperatures ranging from 60,000 K (S IV) to 0.9 MK (Mg IX). The velocity profiles are created using Gaussian fitting with wavelength calibration determined using average quiet Sun velocities from known Doppler velocity shifts. The velocity profiles show important changes in solar foot point plasma speed both spatially and temporally. This analysis builds on previous analysis of solar spectral lines observed with the SOHO Coronal Diagnostic Spectrometer (CDS); the advantage of the SUMER instrument is better resolution, both spectrally and spatially. This work was funded by NASA, Living with a Star Program.

Nestlerode, C. M.; Poland, A. I.

2005-12-01

145

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

PubMed

It is now apparent that there are at least two heating mechanisms in the Sun's outer atmosphere, or corona. Wave heating may be the prevalent mechanism in quiet solar periods and may contribute to heating the corona to 1,500,000?K (refs 1-3). The active corona needs additional heating to reach 2,000,000-4,000,000?K; this heat has been theoretically proposed to come from the reconnection and unravelling of magnetic 'braids'. Evidence favouring that process has been inferred, but has not been generally accepted because observations are sparse and, in general, the braided magnetic strands that are thought to have an angular width of about 0.2?arc seconds have not been resolved. Fine-scale braiding has been seen in the chromosphere but not, until now, in the corona. Here we report observations, at a resolution of 0.2?arc seconds, of magnetic braids in a coronal active region that are reconnecting, relaxing and dissipating sufficient energy to heat the structures to about 4,000,000?K. Although our 5-minute observations cannot unambiguously identify the field reconnection and subsequent relaxation as the dominant heating mechanism throughout active regions, the energy available from the observed field relaxation in our example is ample for the observed heating. PMID:23344359

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

2013-01-24

146

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

NASA Astrophysics Data System (ADS)

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

Szalay, Jamey; Horanyi, M.

2013-10-01

147

The dispersion of radio waves in the solar corona  

Microsoft Academic Search

Different arrival times of the two magnetoionic modes in solar radio bursts have been detected. The bursts are from four decimetric radio events showing narrowband millisecond spikes. They have been observed with 2ms and 0.5ms time resolution, respectively, by the Ikarus and Phoenix spectrometers of ETH Zurich. The four events have been selected because of their low polarization. The arrival

A. O. Benz; P. Pianezzi

1997-01-01

148

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

149

Interference patterns in solar radio spectra: high-resolution structural analysis of the corona  

NASA Astrophysics Data System (ADS)

Aims.We present a new method for high-resolution structural analysis of the solar corona. Methods: .The relationship between the spectral features of various types of solar radio bursts and the physical properties of their sources have been extensively studied by many authors. On the other hand, it is plausible to accept that the spectral properties of the solar radio radiation received on the Earth are - besides the physics of the radio source - influenced by an inter-laying medium that radio waves propagate through. In particular, the regular structures in the solar corona - such as coronal waves, oscillations in shock fronts, the fine structures of coronal loops, streamer current sheets, etc. - might efficiently filter transferred radio radiation just as (broad-band) X-rays are filtered by a periodic atomic structure of crystals; the difference is only in the spatial scale. Using the wave optics methods, we investigate the prospective influence of considered coronal structures on the propagating radio waves originating in an external remote source. Results: .Preliminary results have shown that the resulting modelled radio emission may recall the spectra of observed zebra patterns for the simple 1D density structure considered here and for a reasonable set of parameters. Conversely, it is suggested that the spectra of the zebra patterns might be used for an analysis of those coronal structures that made these traces on the radiation by methods similar to those used in crystallography. The possibility of the presence of such regular small scale structures in the solar corona is demonstrated. For completeness, a brief review of contemporary models of the zebra patterns is provided.

Brta, M.; Karlick, M.

2006-04-01

150

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

151

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

SciTech Connect

We have developed a two-dimensional semiempirical MHD model of the solar corona and solar wind. The model uses empirically derived electron density profiles from white-light coronagraph data measured during the {ital Skylab} period and an empirically derived model of the magnetic field which is fitted to observed streamer topologies, which also come from the white-light coronagraph data. The electron density model comes from that developed by Guhathakurta and coworkers. The electron density model is extended into interplanetary space by using electron densities derived from the {ital Ulysses} plasma instrument. The model also requires an estimate of the solar wind velocity as a function of heliographic latitude and radial component of the magnetic field at 1 AU, both of which can be provided by the {ital Ulysses} spacecraft. The model makes estimates as a function of radial distance and latitude of various fluid parameters of the plasma such as flow velocity {bold {ital V}}, effective temperature T{sub eff}, and effective heat flux q{sub eff}, which are derived from the equations of conservation of mass, momentum, and energy, respectively. The term {open_quotes}effective{close_quotes} indicates that wave contributions could be present. The model naturally provides the spiral pattern of the magnetic field far from the Sun and an estimate of the large-scale surface magnetic field at the Sun, which we estimate to be {approximately}12{endash}15 G. The magnetic field model shows that the large-scale surface magnetic field is dominated by an octupole term. The model is a steady state calculation which makes the assumption of azimuthal symmetry and solves the various conservation equations in the rotating frame of the Sun. The conservation equations are integrated along the magnetic field direction in the rotating frame of the Sun, thus providing a nearly self-consistent calculation of the fluid parameters. The model makes a minimum number of assumptions about the physics of the solar corona and solar wind and should provide a very accurate empirical description of the solar corona and solar wind. Once estimates of mass density {rho}, flow velocity {bold {ital V}}, effective temperature T{sub eff}, effective heat flux q{sub eff}, and magnetic field {bold {ital B}} are computed from the model and waves are assumed unimportant, all other plasma parameters such as Mach number, Alfv{acute e}n speed, gyrofrequency, etc. can be derived as a function of radial distance and latitude from the Sun. The model can be used as a planning tool for such missions as {ital Solar Probe} and provide an empirical framework for theoretical models of the solar corona and solar wind. The model will be used to construct a semiempirical MHD description of the steady state solar corona and solar wind using the {ital SOHO} Large Angle Spectrometric Coronagraph (LASCO) polarized brightness white-light coronagraph data, {ital SOHO} Extreme Ultraviolet Imaging Telescope data, and {ital Ulysses} plasma data. {copyright} {ital {copyright} 1999.} {ital The American Astronomical Society}

Sittler, E.C. Jr.; Guhathakurta, M. [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)] [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

1999-10-01

152

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

153

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

NASA Astrophysics Data System (ADS)

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

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

1999-03-01

154

The filtering of interstellar dust in the solar system  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

155

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

156

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

157

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

158

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

159

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

160

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

NASA Astrophysics Data System (ADS)

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

Biggs, George; Asgari-Targhi, Mahboubeh

2015-01-01

161

A Coherence-Based Approach for Tracking Waves in the Solar Corona  

E-print Network

We consider the problem of automatically (and robustly) isolating and extracting information about waves and oscillations observed in EUV image sequences of the solar corona with a view to near real-time application to data from the Atmospheric Imaging Array (AIA) on the Solar Dynamics Observatory (SDO). We find that a simple coherence / travel-time based approach detects and provides a wealth of information on transverse and longitudinal wave phenomena in the test sequences provided by the Transition Region and Coronal Explorer (TRACE). The results of the search are "pruned" (based on diagnostic errors) to minimize false-detections such that the remainder provides robust measurements of waves in the solar corona, with the calculated propagation speed allowing automated distinction between various wave modes. In this paper we discuss the technique, present results on the TRACE test sequences, and describe how our method can be used to automatically process the enormous flow of data (~1Tb/day) that will be provided by SDO/AIA after launch in late 2008.

Scott W. McIntosh; Bart De Pontieu; Steven Tomczyk

2008-08-21

162

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

NASA Astrophysics Data System (ADS)

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

Uritsky, Vadim; Davila, Joseph

2014-05-01

163

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

SciTech Connect

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

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

2007-07-13

164

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

165

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

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

166

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

167

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

SciTech Connect

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

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

2010-03-10

168

Polar and Equatorial Coronal Hole Winds at Solar Minima: From the Heliosphere to the Inner Corona  

NASA Astrophysics Data System (ADS)

Fast solar wind can be accelerated from at least two different sources: polar coronal holes and equatorial coronal holes. Little is known about the relationship between the wind coming from these two different latitudes and whether these two subcategories of fast wind evolve in the same way during the solar cycle. Nineteen years of Ulysses observations, from 1990 to 2009, combined with ACE observations from 1998 to the present provide us with in situ measurements of solar wind properties that span two entire solar cycles. These missions provide an ideal data set to study the properties and evolution of the fast solar wind originating from equatorial and polar holes. In this work, we focus on these two types of fast solar wind during the minima between solar cycles 22 and 23 and 23 and 24. We use data from SWICS, SWOOPS, and VHM/FGM on board Ulysses and SWICS, SWEPAM, and MAG on board ACE to analyze the proton kinetic, thermal, and dynamic characteristics, heavy ion composition, and magnetic field properties of these two fast winds. The comparison shows that: (1) their kinetic, thermal, compositional, and magnetic properties are significantly different at any time during the two minima and (2) they respond differently to the changes in solar activity from cycle 23 to 24. These results indicate that equatorial and polar fast solar wind are two separate subcategories of fast wind. We discuss the implications of these results and relate them to remote-sensing measurements of the properties of polar and equatorial coronal holes carried out in the inner corona during these two solar minima.

Zhao, L.; Landi, E.

2014-02-01

169

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

170

Charged Dust Dynamics in the Solar System  

Microsoft Academic Search

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

Mihaly Horanyi

1996-01-01

171

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

172

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

173

The Effect of Proton Temperature Anisotropy on the Solar Minimum Corona and Wind  

E-print Network

A semi-empirical, axisymmetric model of the solar minimum corona is developed by solving the equations for conservation of mass and momentum with prescribed anisotropic temperature distributions. In the high-latitude regions, the proton temperature anisotropy is strong and the associated mirror force plays an important role in driving the fast solar wind; the critical point where the outflow velocity equals the parallel sound speed is reached already at 1.5 Rsun from Sun center. The slow wind arises from a region with open field lines and weak anisotropy surrounding the equatorial streamer belt. The model parameters were chosen to reproduce the observed latitudinal extent of the equatorial streamer in the corona and at large distance from the Sun. We find that the magnetic cusp of the closed-field streamer core lies at about 1.95 Rsun. The transition from fast to slow wind is due to a decrease in temperature anisotropy combined with the non-monotonic behavior of the non-radial expansion factor in flow tubes that pass near the streamer cusp. In the slow wind, the plasma beta is of order unity and the critical point lies at about 5 Rsun, well beyond the magnetic cusp. The predicted outflow velocities are consistent with OVI Doppler dimming measurements from UVCS/SOHO. We also find good agreement with polarized brightness (pB) measurements from LASCO/SOHO and HI Ly-alpha images from UVCS/SOHO.

Alberto M. Vasquez; Adriaan A. van Ballegooijen; John C. Raymond

2003-10-29

174

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

175

Energetic particle observations and the abundances of elements in the solar corona  

NASA Technical Reports Server (NTRS)

During the last few years it has become clear that energetic particles in the largest solar events, where abundances are commonly measured, are not accelerated in flares. Rather they are accelerated from the ambient plasma above active regions by shock waves driven by coronal mass ejections. The lowest energy particles from these events have abundances that almost directly reflect those of the source plasma. Residual effects of acceleration, that depend smoothly on the ion's corona Q/A, vanish when abundances are averaged over many events, yielding the characteristic dependence of the average coronal abundances of the First Ionization Potential (FIP) of the elements from H through Fe. In contrast, energetic ions accelerated out of the high speed solar wind from large coronal holes show a reduced FIP effect with a different pattern.

Reames, Donald V.

1992-01-01

176

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

177

Sources of the Solar System Dust Bands and Interplanetary Dust Particles  

NASA Astrophysics Data System (ADS)

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

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

2003-05-01

178

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

179

Direct imaging of a massive dust cloud around R Coronae Borealis  

E-print Network

We present recent polarimetric images of the highly variable star R CrB using ExPo and archival WFPC2 images from the HST. We observed R CrB during its current dramatic minimum where it decreased more than 9 mag due to the formation of an obscuring dust cloud. Since the dust cloud is only in the line-of-sight, it mimics a coronograph allowing the imaging of the star's circumstellar environment. Our polarimetric observations surprisingly show another scattering dust cloud at approximately 1.3" or 2000 AU from the star. We find that to obtain a decrease in the stellar light of 9 mag and with 30% of the light being reemitted at infrared wavelengths (from R CrB's SED) the grains in R CrB's circumstellar environment must have a very low albedo of approximately 0.07%. We show that the properties of the dust clouds formed around R CrB are best fitted using a combination of two distinct populations of grains size. The first are the extremely small 5 nm grains, formed in the low density continuous wind, and the second...

Jeffers, S V; Waters, L B F M; Canovas, H; Rodenhuis, M; Ovelar, M De Juan; Chies-Santos, A L; Keller, C U; 10.1051/0004-6361/201117138

2012-01-01

180

Solar Array Panels With Dust-Removal Capability  

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

181

Direct imaging of a massive dust cloud around R Coronae Borealis  

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

182

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

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

183

A shock associated (SA) radio event and related phenomena observed from the base of the solar corona to 1 AU  

Microsoft Academic Search

We present for the first time an almost complete frequency coverage of a Shock Associated (SA) radio event and related phenomena observed on May 6, 1996 at 9:27 UT. It is observed from the base of the solar corona up to almost 1 Astronomical Unit (AU) from the Sun by the following radio astronomical instruments: the Ondrejov spectrometer operating between

J.-L. Bougeret; P. Zarka; C. Caroubalos; M. Karlick; Y. Leblanc; D. Maroulis; A. Hillaris; X. Moussas; C. E. Alissandrakis; G. Dumas; C. Perche

1998-01-01

184

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

NASA Technical Reports Server (NTRS)

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

Mikic, Zoran; Grebowsky, Joseph (Technical Monitor)

2001-01-01

185

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

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

186

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

SciTech Connect

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

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

2012-01-10

187

An 850 micron survey for dust around solar mass stars  

E-print Network

We present the results of an 850 micron JCMT/SCUBA survey for dust around 13 nearby solar mass stars. The dust mass sensitivity ranged from 0.005 to 0.16 Earth masses. Three sources were detected in the survey, one of which (HD 107146) has been previously reported. One of the other two submillimeter sources, HD 104860, was not detected by IRAS and is surrounded by a cold, massive dust disk with a dust temperature and mass of Tdust = 33 K and Mdust = 0.16 Mearth. The third source, HD 8907, was detected by IRAS and ISO at 60-87 microns, and has a dust temperature and mass Tdust = 48 K and Mdust = 0.036 Mearth. We find that the deduced masses and radii of the dust disks in our sample are roughly consistent with models for the collisional evolution of planetesimal disks with embedded planets. We also searched for residual gas in two of the three systems with detected submillimeter excesses and place limits on the mass of gas residing in these systems. When the properties measured for the detected excess sources are combined with the larger population of submillimeter excess sources from the literature, we find strong evidence that the mass in small grains declines significantly on a ~200 Myr timescale, approximately inversely with age. However, we also find that the characteristic dust radii of the population, obtained from the dust temperature of the excess and assuming blackbody grains, is uncorrelated with age. This is in contrast to self-stirred collisional models for debris disk evolution which predict a trend of radius increasing with age, t ~ R^3. The lack of agreement suggests that processes beyond self-stirring, such as giant planet formation, play a role in the evolutionary histories of planetesimal disks.

Joan Najita; Jonathan P. Williams

2005-08-05

188

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

SciTech Connect

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

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

2011-06-10

189

SDO/AIA Observation of Kelvin-Helmholtz Instability in the Solar Corona  

NASA Technical Reports Server (NTRS)

We present observations of the formation, propagation and decay of vortex-shaped features in coronal images from the Solar Dynamics Observatory (SDO) associated with an eruption starting at about 2:30UT on Apr 8, 2010. The series of vortices formed along the interface between an erupting (dimming) region and the surrounding corona. They ranged in size from several to ten arcseconds, and traveled along the interface at 6-14 km s-1. The features were clearly visible in six out of the seven different EUV wavebands of the Atmospheric Imaging Assembly (AIA). Based on the structure, formation, propagation and decay of these features, we identified these features as the first observations of the Kelvin- Helmholtz (KH) instability in the corona in EUV. The interpretation is supported by linear analysis and by MHD model of KH instability. We conclude that the instability is driven by the velocity shear between the erupting and closed magnetic field of the Coronal Mass Ejection (CME).

Ofman, L.; Thompson, B. J.

2011-01-01

190

Quasi-Harmonic Faraday-Rotation Fluctuations of Radio Waves When Sounding the Outer Solar Corona  

NASA Astrophysics Data System (ADS)

A statistical analysis of the Faraday-rotation fluctuations (FRFs) of linearly polarized radio signals from the Helios 1 and Helios 2 spacecraft shows that the FRF time power spectra can be of three types. Spectra of the first type are well fitted by a single power law in the range of fluctuation frequencies 1-10 mHz. Spectra of the second type are a superposition of a power law and two quasi-harmonic components with fluctuation frequencies of about nu_1 = 4 mHz (fundamental frequency) and nu_2 = 8 mHz (second harmonic). Spectra of the third type exhibit only one of the two quasi-harmonic components against the background of a power law. The spectral density of the quasi-harmonic components can be represented by a resonance curve with a fairly broad [Delta nu =(0.5-1.3) nu_{1,2}] distribution relative to the nu = nu_{1,2} peak. The intensity of the quasi-harmonic FRF has a radial dependence that roughly matches the radial dependence for the background FRF, while their period at the fundamental frequency is approximately equal to the period of the well-known 5-min oscillations observed in the lower solar atmosphere. The fluctuations with 5-min periods in FRF records can be explained by the presence in the outer corona of isolated trains of Alfven waves generated at the base of the chromosphere-corona transition layer and by acoustic waves coming from deeper layers.

Efimov, A. I.; Samoznaev, L. N.; Andreev, V. E.; Chashei, I. V.; Bird, M. K.

2000-08-01

191

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

192

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

193

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

194

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

195

Control analysis for solar panel dust mitigation using an electric curtain  

Microsoft Academic Search

An energy efficiency and control analysis is given for application of a transparent electric curtain for dust mitigation on a solar panel. The electric curtain technique has been proposed by NASA as an effective active method for dust removal from solar panels in planetary and lunar exploration, and this method also has potential for mitigation of dust build-up on terrestrial

D. Qian; J. S. Marshall; J. Frolik

196

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

NASA Astrophysics Data System (ADS)

The problem of phase mixing of shear Alfvn waves is revisited taking into account dissipative phenomena specific for the solar corona. In regions of space plasmas where the dynamics is controlled by the magnetic field, transport coefficients become anisotropic with transport mechanism having different behavior and magnitude depending on the orientation with respect to the ambient magnetic field. Taking into account realistic values for dissipative coefficients we obtain that the previous results derived in context of torsional Alfvn wave phase mixing are actually heavily underestimated so phase mixing cannot be used to explain the damping of torsional Alfvn waves and heating of open coronal structures. The presented results indicate that in order for phase mixing to still be a viable mechanism to explain heating or wave damping unrealistic assumptions have to be made.

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

2008-10-01

197

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

198

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

SciTech Connect

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

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

2013-02-10

199

Spectroscopic Observation of Oscillations in the Corona During the Total Solar Eclipse of 22 July 2009  

NASA Astrophysics Data System (ADS)

We performed high resolution spectroscopy of the solar corona during the total solar eclipse of 22 July 2009 in two emission lines: the green line at 5303 due to Fe xiv and the red line at 6374 due to Fe x, simultaneously from Anji (latitude 3028.1' N; longitude 11935.4' E; elevation 890 m), China. A two-mirror coelostat with 100 cm focal length lens produced a 9.2 mm image of the Sun. The spectrograph using 140 cm focal length lens in Littrow mode and a grating with 600 lines per millimeter blazed at 2 ?m provided a dispersion of 30 m and 43 m per pixel in the fourth order around the green line and third order around the red line, respectively. Two Peltier cooled 1k 1k CCD cameras, with a pixel size of 13 ?m square and 14-bit readout at 10 MHz operated in frame transfer mode, were used to obtain the time sequence spectra in two emission lines simultaneously. The duration of totality was 341 s, but we could get spectra for 270 s after a trial exposure at an interval of 5 s. We report here on the detection of intensity, velocity, and line width oscillations with periodicity in the range of 25 - 50 s. These oscillations can be interpreted in terms of the presence of fast magnetoacoustic waves or torsional Alfvn waves. The intensity ratios of green to red emission lines indicate the temperature of the corona to be 1.65 MK in the equatorial region and 1.40 MK in the polar region, relatively higher than the expected temperature during the low activity period. The width variation of the emission lines in different coronal structures suggests different physical conditions in different structures.

Singh, Jagdev; Hasan, S. S.; Gupta, G. R.; Nagaraju, K.; Banerjee, D.

2011-05-01

200

A 2D dust chemistry of the inner Solar Nebula  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

201

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

202

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

203

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

E-print Network

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

204

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

NASA Astrophysics Data System (ADS)

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

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

2007-08-01

205

Dynamical behaviour of interstellar dust particles in the solar system  

NASA Astrophysics Data System (ADS)

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

Kocifaj, Miroslav; Kla?ka, Jozef

2004-11-01

206

Dust Particles In Pluto System: The Solar Radiation Pressure Effects  

NASA Astrophysics Data System (ADS)

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

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

2010-10-01

207

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

Microsoft Academic Search

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

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

2009-01-01

208

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

SciTech Connect

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

Argo, H.V.

1981-01-01

209

Simultaneous Observation of Solar Oscillations Associated with Coronal Loops from the Photosphere to the Corona  

NASA Astrophysics Data System (ADS)

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 ~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 ~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, Y.; Liu, S.; Zhang, Y. Z.; Zhao, H.; Xu, H. Q.; Xie, W. B.

2013-01-01

210

The solar f-mode as an interfacial mode at the chromosphere-corona transition  

NASA Astrophysics Data System (ADS)

Observations of the solar f-mode at intermediate and high spherical harmonic degree show substantial departures from the dispersion relation expected for a pure surface gravity oscillation. We suggest that the waves are reflected by the high density gradient in the region of the chromosphere-corona transition and are therefore characterized better as interfacial modes localized near the transition. An analytical calculation, for a simple model in which the transition is treated as a discontinuity, shows that such modes have a dispersion relation with the correct qualitative features to explain the observations. However, quantitative agreement is not possible for reasonable parameter values. We next consider a more general atmospheric structure with a continuous stratification for which asymptotic frequency estimates are obtained. These are compared with direct numerical solutions of the differential equations. The frequencies are found to give a much closer quantitative agreement with the observations. We suggest that f-mode seismology might be used to obtain direct information about the average structure of the solar atmosphere and transition region.

Rosenthal, C. S.; Gough, D. O.

1994-03-01

211

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

212

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

NASA Technical Reports Server (NTRS)

In Cram's theory for the formation of the K-coronal spectrum he observed the existence of temperature sensitive anti-nodes, which were separated by temperature insensitive nodes, at certain wave-lengths in the K-coronal spectrum. Cram also showed these properties were remarkably independent of altitude above the solar limb. In this thesis Cram's theory has been extended to incorporate the role of the solar wind in the formation of the K-corona, and we have identified both temperature and wind sensitive intensity ratios. The instrument, MACS, for Multi Aperture Coronal Spectrometer, a fiber optic based spectrograph, was designed for global and simultaneous measurements of the thermal electron temperature and the solar wind velocity in the solar corona. The first ever experiment of this nature was conducted in conjunction with the total solar eclipse of 11 August 1999 in Elazig, Turkey. Here twenty fiber optic tips were positioned in the focal plane of the telescope to observe simultaneously at many different latitudes and two different radial distances in the solar corona. The other ends were vertically stacked and placed at the primary focus of the spectrograph. By isolating the K-coronal spectrum from each fiber the temperature and the wind sensitive intensity ratios were calculated.

Reginald, Nelson L.

2000-01-01

213

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

E-print Network

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

G. Peres; S. Orlando; F. Reale

2004-05-14

214

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

215

Magnetic Field Strength in the Upper Solar Corona Using White-light Shock Structures Surrounding Coronal Mass Ejections  

Microsoft Academic Search

To measure the magnetic field strength in the solar corona, we examined 12 fast (> 1000 km s-1) limb CMEs which show clear shock-like structures in SOHO\\/LASCO observations. By applying 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 to

Roksoon Kim; N. Gopalswamy; Y. Moon; K. Cho; S. Yashiro

2011-01-01

216

Mixing of dust in protoplanetary disks and the solar nebula  

NASA Astrophysics Data System (ADS)

Understanding the small-dust component of protoplanetary disks is key to understanding the conditions for planet formation. Small dust grains, particularly at large distances, provide our primary observational window into the physics of protoplanetary disks, being much more easily observed than the gas component. Furthermore, the distribution of these grains must ultimately control the timing and locations for planetesimal formation, the first major step toward planet formation. For my thesis work, I have used numerical simulations to model the radial distribution of dust grains as they are acted upon by the gas disk, including the evolution of the disk (outward expansion and inward accretion), radial and azimuthal drag of the gas flow on the particle orbits, and turbulent mixing of the particle ensemble radially within the disk. I have run simulations using a range of particle sizes and disk-model parameters and consider primarily two phenomena: the radial diffusion of hot, inner disk particles outward to large AU, relevant to the compositional makeup of bodies within our own solar system, and the time evolution of the global dust-to-gas ratio, which dictates the supply of solid material to the planetesimal- and planet-forming regions. I find that, while the degree out outward mixing depends sensitively on a number of disk-model parameters, the behavior of the global dust-to-gas distribution is relatively uniform between different disk-model simulations, suggesting that, while still mysterious, the conditions for planetesimal formation are commonly met across a range of disk configurations. Observed disk compositions correlate poorly with most observable disk parameters. However, my simulations suggest compositional properties are most-strongly controll= ed by the initial conditions of young disk systems.

Hughes, Anna Louise Haugsjaa

217

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

NASA Astrophysics Data System (ADS)

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

Rusin, V.; Rybansky, M.

1999-03-01

218

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

219

Catalysis by Dust Grains in the Solar Nebula  

NASA Technical Reports Server (NTRS)

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

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

1996-01-01

220

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

221

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

222

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

223

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

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

224

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

225

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

226

The distant future of solar activity: A case study of Beta Hydri. III - Transition region, corona, and stellar wind  

NASA Technical Reports Server (NTRS)

The paper investigates the secular decay of solar-type activity through a detailed comparison of the present sun with the very old solar-type star, Beta Hyi, taken as a proxy of the future sun. Analyses of successive atmospheric layers are presented, with emphasis of the outermost parts. The FUV emission lines for the transition zone are among the faintest so far seen in any solar-type star. The coronal soft X-ray spectrum was measured through different filters on EXOSAT and compared to simulated X-ray observations of the sun seen as a star. The flux from Beta Hyi is weaker than that from the solar corona and has a different spectrum. It is inferred that a thermally driven stellar wind can no longer be supported, which removes the mechanism from further rotational braking of the star through a magnetic stellar wind.

Dravins, D.; Linde, P.; Ayres, T. R.; Linsky, J. L.; Monsignori-Fossi, B.; Simon, T.; Wallinder, F.

1993-01-01

227

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

NASA Technical Reports Server (NTRS)

We report on multi-wavelength observations of the corona taken simultaneously in broadband white light, and in seven spectral lines, H-alpha 656.3 nm, Fe IX 435.9 nm, Fe X 637.4 nm, Fe XI 789.2 nm, Fe XIII 1074.7 nm, Fe XIV 530.3 nm and Ni XV 670.2 nm. The observations were made during the total solar eclipse of 11 July 2010 from the atoll of Tatakoto in French Polynesia. Simultaneous imaging with narrow bandpass filters in each of these spectral lines and in their corresponding underlying continua maximized the observing time during less than ideal observing conditions and yielded outstanding quality data. The application of two complementary image processing techniques revealed the finest details of coronal structures at 1" resolution in white light, and 6.5" in each of the spectral lines. This comprehensive wavelength coverage confirmed earlier eclipse findings that the solar corona has a clear two-temperature structure: The open field lines, expanding outwards from the solar surface, are characterized by electron temperatures near 1 X 10(exp 6) K, while the hottest plasma around 2X 10(exp 6) K resides in loop-like structures forming the bulges of streamers. The first images of the corona in the forbidden lines of Fe IX and Ni XV, showed that there was very little coronal plasma at temperatures below 5 X 10(exp 5) K and above 2.5X 10(exp 6) K. The data also enabled temperature differentiations as low as 0:2 X 10(exp 6) K in different density structures. These observations showed how the passage of CMEs through the corona, prior to totality, produced large scale ripples and very sharp streaks, which could be identified with distinct temperatures for the first time. The ripples were most prominent in emission from spectral lines associated with temperatures around 10(exp 6) K. The most prominent streak was associated with a conical-shaped void in the emission from the coolest line of Fe IX and from the hottest line of Ni XV. A prominence, which erupted prior to totality, appeared in the shape of a hook in the cooler lines of Fe X and Fe XI, spanning 0.5 R(solar) in extent starting at a heliocentric distance of 1.3 R(solar), with a complex trail of hot and cool twisted structures connecting it to the solar surface. Simultaneous Fe X 17.4 nm observations from space by Proba2/SWAP provided an ideal opportunity for comparing emission from a coronal forbidden line, namely Fe X 637.4 nm, with a space-based EUV allowed line. Comparison of the Fe X 17.4 nm and 637.4 nm emission provided the first textbook example of the role of radiative excitation in extending the detectability of coronal emission to much larger heliocentric distances than its collisionally excited component. These eclipse observations demonstrate the unique capabilities of coronal forbidden lines for exploring the evolution of the coronal magnetic field in the heliocentric distance range of 1 - 3 R(solar), which is currently inaccessible to any space-borne or ground-based observatory.

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

2011-01-01

228

A Method to Determine the Heating Mechanisms of the Solar Corona  

NASA Astrophysics Data System (ADS)

One of the paradigms about coronal heating has been the belief that the mean or summit temperature of a coronal loop is completely insensitive to the nature of the heating mechanisms. However, we point out that the temperature profile along a coronal loop is highly sensitive to the form of the heating. For example, when a steady state heating is balanced by thermal conduction, a uniform heating function makes the heat flux a linear function of distance along the loop, while T7/2 increases quadratically from the coronal footpoints; when the heating is concentrated near the coronal base, the heat flux is small and the T7/2 profile is flat above the base; when the heat is focused near the summit of a loop, the heat flux is constant and T7/2 is a linear function of distance below the summit. It is therefore important to determine how the heat deposition from particular heating mechanisms varies spatially within coronal structures such as loops or arcades and to compare it to high-quality measurements of the temperature profiles. We propose a new two-part approach to try and solve the coronal heating problem, namely, first of all to use observed temperature profiles to deduce the form of the heating, and second to use that heating form to deduce the likely heating mechanism. In particular, we apply this philosophy to a preliminary analysis of Yohkoh observations of the large-scale solar corona. This gives strong evidence against heating concentrated near the loop base for such loops and suggests that heating uniformly distributed along the loop is slightly more likely than heating concentrated at the summit. The implication is that large-scale loops are heated in situ throughout their length, rather than being a steady response to low-lying heating near their feet or at their summits. Unless waves can be shown to produce a heating close enough to uniform, the evidence is therefore at present for these large loops more in favor of turbulent reconnection at many small randomly distributed current sheets, which is likely to be able to do so. In addition, we suggest that the decline in coronal intensity by a factor of 100 from solar maximum to solar minimum is a natural consequence of the observed ratio of magnetic field strength in active regions and the quiet Sun; the altitude of the maximum temperature in coronal holes may represent the dissipation height of Alfvn waves by turbulent phase mixing; and the difference in maximum temperature in closed and open regimes may be understood in terms of the roles of the conductive flux there.

Priest, E. R.; Foley, C. R.; Heyvaerts, J.; Arber, T. D.; Mackay, D.; Culhane, J. L.; Acton, L. W.

2000-08-01

229

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

230

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

231

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

232

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

233

Heating and activity of the solar corona. 2. Kink instability in a flux tube  

NASA Astrophysics Data System (ADS)

The development of kink instability in a flux tube is investigated numerically, by solving the resistive MHD equations in three dimensions for a setup where a flux tube is stressed by rotating both ends in opposite directions. Two cases are investigated: one where the tube is initially isolated and in pressure equilibrium with surrounding plasma (external kink) and another with an initially uniform magnetic field, where only a smaller part of the boundaries are used to twist the field (internal kink). The twist angle at the onset of the kink instability depends on several parameters, such as rotation velocity, tube diameter, field strength, and magnetic resistivity, but is generally in the range 4?-8?. Both sets of experiments are followed beyond the point where they become kink unstable into the regime of nonlinear evolution. Of particular interest is the topological evolution. As magnetic dissipation becomes significant, the connectivity between the two boundaries changes from ordered to chaotic, and small-scale current sheets develop. Even though the gross features of the external kink appear to saturate, the total magnetic energy continues to grow, by a steady increase of the free energy in the chaotic region that develops as a result of the kink and by a secular spreading of the magnetic field into the initially field-free region. The internal kink is confined to the cylinder defined by the boundary driving and has only limited influence on the external magnetic field. After the kink, the twist of the magnetic field is reduced, and the internal kink settles into a quasi-steady state where the dissipation on the average balances the Poynting flux input. The average Poynting flux is similar in the external and internal kinks, with a magnitude that corresponds to local winding numbers of the order of unity. Scaling of these results to values characteristic of the solar corona indicate that systematic rotation or shear of the endpoints could be a source of quasi-steady heating in coronal loops.

Galsgaard, Klaus; Nordlund, ke

1997-01-01

234

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

235

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

236

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

237

Current Paths in the Corona and Energy Release in Solar Flares  

NASA Astrophysics Data System (ADS)

Vector magnetogram data show that (1) regions of large current flow, I 1012 A, correlate with the footpoints of flaring coronal loops, and (2) the currents flow up in a region of one magnetic polarity and down in a region of opposite magnetic polarity. It is argued that these properties imply that the currents cannot be generated by shearing or other motions near the photo sphere, and must close deep in the solar atmosphere. It is also argued that the line-tying assumption is inappropriate on timescales of 1 day or longer on which coronal magnetic structures evolve and that an appeal to line tying incorrectly implies that coronal currents close near the photo sphere. The observed shearing of coronal magnetic structures is attributed to the emergence of current-carrying magnetic flux tubes. Energy release in a solar flare is discussed with emphasis on the nonlocal nature of changes in the stored magnetic energy. Energy release occurs in two stages, with nondissipative, local conversion of stored energy into a Poynting flux at Alfvnic fronts, and conversion into particle energy in localized energy release site. The nonlocal nature of the energy release process is described in terms of a circuit model with temporally varying parameters. The power release, IV, occurs at constant total current I 1012 A, due to a large inductive voltage, V 1010 V, and involves changes in the current profile or current path, described by a changing coronal inductance, L, with a coronal resistance, Rc determined by Ldot + Rc = 0. Three ways in which the net inductance can decrease are discussed: like currents moving apart, the current path shortening, and unlike currents moving closer together. Simple models for an erupting filament show that magnetic energy release can drive the eruption only if the current in the filament drains away into a current path lower in the corona. Relocation of the current to a lower height should cause the shearing near the neutral line to increase as a result of a flare, as has been reported recently.

Melrose, D. B.

1995-09-01

238

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

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

239

Electro-optical polarimeters for ground-based and space-based observations of the solar K-corona  

NASA Astrophysics Data System (ADS)

Polarimeters based on electro-optically tunable liquid crystals (LC) represent a new technology in the field of observational astrophysics. LC-based polarimeters are good candidates for replacing mechanically rotating polarimeters in most ground-based and space-based applications. During the 2006 total solar eclipse, we measured the visible-light polarized brightness (pB) of the solar K-corona with a LC-based polarimeter and imager (E-KPol). In this presentation, we describe the results obtained with the E-KPol, and we evaluate its performances in view of using a similar device for the pB imaging of the K-corona from space-based coronagraphs. Specifically, a broad-band LC polarimeter is planned for the METIS (Multi Element Telescope for Imaging and Spectroscopy) coronagraph for the Solar Orbiter mission to be launched in 2017. The METIS science driver of deriving the coronal electron density from pB images requires an accuracy of better than 1% in the measurement of linear polarization. We present the implications of this requirement on the METIS design to minimize the instrumental polarization of the broad-band visible-light (590-650 nm) polarimeter and of the other optics in the METIS visible-light path. Finally, we report preliminary ellipsometric measurements of the optical components of the METIS visible-light path.

Capobianco, G.; Fineschi, S.; Massone, G.; Balboni, E.; Malvezzi, A. M.; Crescenzio, G.; Zangrilli, L.; Calcidese, P.; Antonucci, E.; Patrini, M.

2012-09-01

240

Formation of zebra patterns of solar microwave bursts as a result of propagation of radio waves through the inhomogeneous corona  

NASA Astrophysics Data System (ADS)

The geoefficiency of solar bursts is diagnosed using the dynamic radio emission spectrum. At certain time intervals, the spectrum exhibits nearly parallel narrow-band emission strips termed the zebra pattern. Although there are many hypotheses of its origin, all of them do not take into account changes in the signal parameters upon signal propagation through the solar corona. Our analysis shows that the propagation effects form a dynamic spectrum that contains a zebra pattern. The properties of the modeled spectrum are shown to coincide with the basic properties of the observed spectrum. It is clarified that the spike structure of strips is a natural consequence of the interference of radio waves, and the occurrence of this structure is considered to be evidence in favor of the interference nature of the zebra pattern formation. Consequently, the zebra pattern can be formed not in the radiation source itself, but rather can arise as a result of propagation of radio waves through an inhomogeneous refracting medium of the solar corona.

Yurovsky, Yu. F.

2008-06-01

241

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

NASA Astrophysics Data System (ADS)

An interferometer antenna system to observe polarized radio emission from the solar corona at different frequencies in the range 30 - 110 MHz has been commissioned recently by the Indian Institute of Astrophysics at the Gauribidanur Radio Observatory (latitude 1336'12''N and longitude 7727'07''E), about 100 km north of Bangalore ( http://www.iiap.res.in/centres_radio.htm ). This paper describes the antenna system, associated analog/digital receiver setup, calibration scheme, and preliminary results.

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

2008-12-01

242

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

243

Tomography of the Solar Corona. II. Robust, Regularized, Positive Estimation of the Three-dimensional Electron Density Distribution from LASCO-C2 Polarized White-Light Images  

Microsoft Academic Search

Solar rotational tomography is used to determine the three-dimensional electron density distribution of the solar corona from 2.4 to 6.0 Rsolar. The robust, regularized, positive estimation method, described in a previous paper, is demonstrated on test cases and on LASCO-C2 data. Because the solar rotational pole is inclined to the plane of the ecliptic by about 7, the tomographic inversion

Richard A. Frazin; Paul Janzen

2002-01-01

244

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

245

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

246

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

E-print Network

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

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

2007-05-26

247

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

248

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

249

Solar flare track densities in interplanetary dust particles The determination of an asteroidal versus cometary source of the zodiacal dust cloud  

Microsoft Academic Search

The possibility is explored whether an IDP (interplanetary dust particle) is cometary or asteroidal from measurements of the solar flare track density within its constituent mineral grains. Dust particles that are larger than 1 micron, when injected into the Solar System from comets and asteroids, will spiral into the sun due to the Poynting-Robertson effect. During the process of spiraling

S Sandford

1986-01-01

250

Magnetic Field Strength in the Solar Corona from Type II Band Splitting  

Microsoft Academic Search

The phenomenon of band splitting in type II bursts can be a unique diagnostic for the magnetic field in the corona, which is, however, inevitably sensitive to the ambient density. We apply this diagnostic to the CME-flare event on 2004 August 18, for which we are able to locate the propagation of the type II burst and determine the ambient

K.-S. Cho; J. Lee; D. E. Gary; Y.-J. Moon; Y. D. Park

2007-01-01

251

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

252

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

253

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  

E-print Network

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 LMC, 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 nebula (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 sharing the traits of hydrogen deficiency and dust formation that define the cooler RCB stars. The [WC] CSPNe star, CPD -56 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 -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 c...

Clayton, Geoffrey C; 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

2011-01-01

254

IMPACT OF TEMPERATURE-DEPENDENT RESISTIVITY AND THERMAL CONDUCTION ON PLASMOID INSTABILITIES IN CURRENT SHEETS IN THE SOLAR CORONA  

SciTech Connect

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

Ni Lei; Roussev, Ilia I.; Lin Jun [Yunnan Astronomical Observatory, CAS, P.O. Box 110, Kunming 650011, Yunnan (China); Ziegler, Udo, E-mail: leini@ynao.ac.cn, E-mail: iroussev@ifa.hawaii.edu, E-mail: uziegler@aip.de [Leibniz-Institut fuer Astrophysik Potsdam, D-14482 Potsdam (Germany)

2012-10-10

255

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

256

Growth and sedimentation of dust grains in the primitive solar nebular  

SciTech Connect

Formation of the planets in the solar system is envisioned to occur via a gravitational instability in a thin layer of dust located at the midplane of the primitive solar nebula. The break-up of the dust layer gives rise to seed plants (planetesimals) that, through successive collisions, eventually form the present-day planets. This thesis addresses the problem of the formation of the dust layer, beginning with a configuration in which the dust particles are uniformly mixed with the nebula's turbulent gas. To describe the properties of turbulence in the primitive solar nebula, models by Canuto et al. (1987) and by Cabot et al. (1987) are used. The available results concerning calculation of the velocity of particles embedded in a turbulent fluid were found to be unsatisfactory; therefore, a new formalism was developed to express the latter quantity in terms of the properties of the turbulence in the fluid. Following the space-time evolution of the grains, formalism was developed that simulates the simultaneous processes of collisions and sedimentation of the dust grains in the primitive solar nebula. It is concluded that, for the model of the primitive solar nebula considered, the formation of a dust layer at midplane is very unlikely.

Battaglia, A.

1987-01-01

257

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

SciTech Connect

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

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

2009-07-20

258

Absolute-velocity measurements in the solar-transition region and corona from observations of ultraviolet emission line profiles  

SciTech Connect

This thesis presents an experimental technique to measure absolute velocities of minor ions formed in the solar-transition region and corona. A sounding-rocket experiment July 27, 1987 obtained high-resolution extreme-ultraviolet (EUV) spectra along a solar diameter with spatial resolution of 20 {times} 20 arcseconds. The center-to-limb behavior of four representative lines (Si II {lambda}1533, Fe II {lambda}1563, CIV {lambda}1548, Ne VIII {lambda}770) formed at different heights in the solar atmosphere is discussed. Assuming that horizontal motions cancel statistically so that the line-of-sight velocity approaches zero at the limb, the author find a net radial downflow of approximately 7.5 {plus minus} 1.0 km/s for C IV, 2.7 {plus minus} 1.5 km/s for Fe II {lambda}1563, and upper limits of 0 {plus minus} 1.2 km/s and 0 {plus minus} 4 km/s for Si II and Ne VIII, respectively. The absolute wavelengths of each emission line were determined by direct comparison with wavelengths of known platinum lines generated by an inflight calibration lamp. He then test the assumption of line-of-sight velocity approaching zero at the limb by comparing his wavelengths with recently published laboratory rest wavelengths of the solar emission lines. He finds agreement within the published uncertainties of the laboratory wavelengths, ({plus minus}2 km/s in the case of C IV).

Hassler, D.M.

1990-01-01

259

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

SciTech Connect

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

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

2010-01-10

260

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

SciTech Connect

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

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

2011-12-01

261

Solar heating of the Uranian mesopause by dust of ring origin  

SciTech Connect

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

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

1990-12-01

262

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

263

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

264

The origin and role of dust in the early Solar System  

Microsoft Academic Search

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

Don Brownlee

1994-01-01

265

On the correlation between interplanetary nano dust particles and solar wind properties from STEREO/SWAVES  

NASA Astrophysics Data System (ADS)

Dust particles provide an important fraction of the matter composing the interplanetary medium, their mass density at 1 AU being comparable to the one of the solar wind. Among them, dusts of nanometer size-scale can be detected using radio and plasma waves instruments because they move at roughly the solar wind speed. The high velocity impact of a dust particle generates a small crater on the spacecraft: the dust particle and the crater material are vaporized. This produces a plasma cloud whose associated electrical charge induces an electric pulse measured with radio and plasma instruments. Since their first detection in the interplanetary medium (Meyer-Vernet et al. 2009), nanodusts have been routinely measured using STEREO/WAVES instrument (Zaslavsky et al. 2012) We present the nanodust properties during the 2007-2012 period on STEREO. Since the maximum size of the plasma cloud is larger for smaller local solar wind density, we expect to observe an anticorrelation between the detected voltage amplitude and the ambient solar wind density, as suggested recently by Le Chat et al. (2012). Moreover, the variations in solar wind speed and magnetic field are expected to affect the nano dust dynamics. Using STEREO/WAVES/Low Frequency Receiver (LFR) data, we study correlations of in situ solar wind properties and detection of nanodust impacts as well as some possible effects of Coronal Mass Ejections (CME) on nanodusts acceleration.

Issautier, K.; LE CHAT, G.; Meyer-Vernet, N.; Belheouane, S.; Zaslavsky, A.; Zouganelis, I.; Mann, I.; Maksimovic, M.

2012-12-01

266

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

267

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

268

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

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

269

The envelopes of R Coronae Borealis stars. I - A physical model of the decline events due to dust formation  

Microsoft Academic Search

The paper investigates the conditions of the formation of pure carbon dust in the envelopes of R CrB stars. On the basis of a sketchy equilibrium chemistry of the condensation process, a model is presented which is able to explain the occasional onset of the decline events as well as their development. The descending and the ascending branches of a

A. Goeres; E. Sedlmayr

1992-01-01

270

Effect of Gas Velocity on the Dust Sediment Layer in the Coupled Field of Corona Plasma and Cyclone  

NASA Astrophysics Data System (ADS)

A dust sediment layer was found on the outer tube wall when the ESCP (electrostatic centrifugal precipitator) trapped diesel particulates or ganister sand. The Compton back scatter method was used to measure the sediment thickness during the experiment. The effect of the inlet gas velocity on the dust sediment layer was investigated. PIV (Particle Image Velocimetry) was used to measure the velocity field between the inner barb tube wall and the outer tube wall. Experiments showed that the thickness of the sediment increased with time, and the sediment layer at the lower end was much thicker than that at the upper end. The agglomeration on the outer tube wall could be removed when the inlet gas velocity was increased to a certain value.

Wei, Mingshan; Ma, Chaochen; Li, Minghua; S, N. Danish

2006-09-01

271

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

272

Neutral Solar Wind Generated by Lunar Exospheric Dust at the Terminator  

NASA Technical Reports Server (NTRS)

We calculate the flux of neutral solar wind observed on the lunar surface at the terminator due to solar wind protons penetrating exospheric dust with: (1) grains larger that 0.1 microns and (2) grains larger than 0.01 microns. For grains larger than 0.1 microns, the ratio of the neutral solar wind to solar wind flux is estimated to be approx.10(exp -4)-10(exp -3) at solar wind speeds in excess of 800 km/s, but much lower (less than 10(exp -5) at average to low solar wind speeds. However, when the smaller grain sizes are considered, the ratio of the neutral solar wind flux to solar wind flux is estimated to be greater than or equal to 10(exp -5) at all speeds and at speeds in excess of 700 km/s reaches 10(exp -3)-10(exp -2). These neutral solar wind fluxes are easily measurable with current low energy neutral atom instrumentation. Observations of neutral solar wind from the surface of the Moon could provide a very sensitive determination of the distribution of very small dust grains in the lunar exosphere and would provide data complementary to optical measurements at ultraviolet and visible wavelengths. Furthermore, neutral solar wind, unlike its ionized counterpart, is .not held-off by magnetic anomalies, and may contribute to greater space weathering than expected in certain lunar locations.

Collier, Michael R.; Stubbs, Timothy J.

2007-01-01

273

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 to monitor the broadband turbidity during the event. This dust cloud was characterized by a large ? turbidity

Oregon, University of

274

OBSERVATIONS OF FIVE-MINUTE SOLAR OSCILLATIONS IN THE CORONA USING THE EXTREME ULTRAVIOLET SPECTROPHOTOMETER (ESP) ON BOARD THE SOLAR DYNAMICS OBSERVATORY EXTREME ULTRAVIOLET VARIABILITY EXPERIMENT (SDO/EVE)  

SciTech Connect

We report on the detection of oscillations in the corona in the frequency range corresponding to five-minute acoustic modes of the Sun. The oscillations have been observed using soft X-ray measurements from the Extreme Ultraviolet Spectrophotometer (ESP) of the Extreme Ultraviolet Variability Experiment on board the Solar Dynamics Observatory. The ESP zeroth-order channel observes the Sun as a star without spatial resolution in the wavelength range of 0.1-7.0 nm (the energy range is 0.18-12.4 keV). The amplitude spectrum of the oscillations calculated from six-day time series shows a significant increase in the frequency range of 2-4 mHz. We interpret this increase as a response of the corona to solar acoustic (p) modes and attempt to identify p-mode frequencies among the strongest peaks. Due to strong variability of the amplitudes and frequencies of the five-minute oscillations in the corona, we study how the spectrum from two adjacent six-day time series combined together affects the number of peaks associated with the p-mode frequencies and their amplitudes. This study shows that five-minute oscillations of the Sun can be observed in the corona in variations of the soft X-ray emission. Further investigations of these oscillations may improve our understanding of the interaction of the oscillation modes with the solar atmosphere, and the interior-corona coupling, in general.

Didkovsky, L.; Judge, D.; Wieman, S. [Space Sciences Center, University of Southern California, Los Angeles, CA 90089 (United States); Kosovichev, A. G. [W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305 (United States); Woods, T., E-mail: leonid@usc.edu [Laboratory for Atmospheric and Space Physics, University of Colorado at Boulder, Boulder, CO 80301 (United States)

2011-09-01

275

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

NASA Astrophysics Data System (ADS)

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

Muoz, Olga

2013-04-01

276

Journal of Atmospheric and Solar-Terrestrial Physics 67 (2005) 17341743 Tracing magnetic helicity from the solar corona to the  

E-print Network

and higher magnetic field strength than the surrounding solar wind. Typically, the magnetic field vector, the Solar Wind Experiment and the Magnetic Field Instrument (MFI) on board the Wind spacecraft registered magnetic fields; Solar activity; Interplanetary magnetic clouds 1. Introduction Coronal mass ejections

Dasso, Sergio

277

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

NASA Technical Reports Server (NTRS)

Knowledge of the radial variation of the plasma conditions in the coronal source region of the solar wind is essential to exploring coronal heating and solar wind acceleration mechanisms. The goal of the proposal was to determine as many plasma parameters in the solar wind acceleration region and beyond as possible by coordinating different observational techniques, such as Interplanetary Scintillation Observations, spectral line intensity observations, polarization brightness measurements and X-ray observations. The inferred plasma parameters were then used to constrain solar wind models.

Esser, Ruth

1997-01-01

278

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

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

279

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

280

Homologous sudden disappearances of transequatorial interconnecting loops in the solar corona  

NASA Astrophysics Data System (ADS)

We have found a remarkable sequence of homologous disappearances of transequatorial X-ray loops linking active regions. Each disappearance was closely associated with a major flare and coronal mass ejection (CME). In each case the flarings precede the disappearances and the CMEs. Mass estimates for the X-ray loops are similar to CME masses. This, the timing of the disappearances, their morphology, and the homology of the events in the sequence, provide direct evidence for a new class of CME origins in the low corona. We also briefly report observations of features which we infer to be the soft X-ray counterparts of shock waves emanating from the flare region. The inferred shocks appeared to play a vital role in the disappearances. Our results suggest that flare-generated shock waves may destabilize large transequatorial loops, causing them to erupt.

Khan, Josef I.; Hudson, Hugh S.

2000-04-01

281

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

NASA Technical Reports Server (NTRS)

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

Davila, Joseph M.

1988-01-01

282

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

Microsoft Academic Search

Modeling and observational studies of coronal and interplanetary shocks suggest that they are most effective in accelerating Solar Energetic Particles (SEP) relatively close to the Sun. Interplanetary shocks have been quite well studied, thanks to in situ measurements of energetic articles near Earth and throughout the solar system. Many bursts of energetic charged particles observed close to Earth are not

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

2010-01-01

283

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

284

The effect of radio-wave propagation conditions in the solar corona on the properties of observed type III radio bursts  

NASA Astrophysics Data System (ADS)

Geometrical optics is used to perform a ray-tracing analysis of radio waves in the solar corona in the presence of large-scale ducts. It is shown that some of the characteristic features of type III bursts can be explained by taking into account the effects of radio-wave propagation in the inhomomgenous coronal plasma. In particular, it is possible to explain the fact that the radial coordinates of the point of radio-wave emergence from the corona exceed the level of the fundamental plasma frequency, and the fact that the bursts of decametric storms are observed at the fundamental frequency near the central meridian and at the second harmonic near the solar limb.

Itkina, M. A.; Yashnov, V. A.

1989-10-01

285

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

286

The effect of radio-wave propagation conditions in the solar corona on the properties of observed type III radio bursts  

Microsoft Academic Search

Geometrical optics is used to perform a ray-tracing analysis of radio waves in the solar corona in the presence of large-scale ducts. It is shown that some of the characteristic features of type III bursts can be explained by taking into account the effects of radio-wave propagation in the inhomomgenous coronal plasma. In particular, it is possible to explain the

M. A. Itkina; V. A. Yashnov

1989-01-01

287

Solar flare track densities in interplanetary dust particles The determination of an asteroidal versus cometary source of the zodiacal dust cloud  

NASA Technical Reports Server (NTRS)

The possibility is explored whether an IDP (interplanetary dust particle) is cometary or asteroidal from measurements of the solar flare track density within its constituent mineral grains. Dust particles that are larger than 1 micron, when injected into the Solar System from comets and asteroids, will spiral into the sun due to the Poynting-Robertson effect. During the process of spiraling in, such dust particles accumulate solar flare tracks. The accumulated track density for a given dust grain is a function of the duration of its space exposure and its distance from the sun. Using a computer model, it was determined that the expected track density distributions from grains produced by comets are very different from those produced by asteroids. Individual asteroids produce populations of particles that arrive at 1 AU with scaled track density distributions containing 'spikes,' while comets supply particles with a flatter and wider distribution of track densities.

Sandford, Scott A.

1986-01-01

288

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

289

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

290

Modeling Particle Acceleration and Turbulence Generation in CME-driven Shocks in the Solar Corona and Interplanetary Medium (Invited)  

NASA Astrophysics Data System (ADS)

Large solar energetic particle (SEP) events are associated with fast, wide CMEs driving shock waves through the corona. The process of diffusive shock acceleration is the most plausible acceleration mechanism responsible for these events. We have developed a Monte Carlo simulation model to compute the coupled transport of particles and generation of Alfvnic fluctuation through streaming instabilities in the foreshock region ahead of a CME-driven shock. The model self-consistently computes the fluxes of energetic ions accelerated by the shock front, starting from the ambient ion population that can be modeled as a kappa distribution with spectral indices ranging between 2 and 15. The simulation model computes the density and magnetic field compression ratios from the Rankine-Hugoniot conditions and employs an empirical cross-shock potential in order to model the interaction of the low-energy ions with the shock adequately. We present results of a parameter study simulating a large number of shocks with different speeds and angles of obliquity at different distances from the Sun. A semi-analytical model of the resulting shock-accelerated particle distribution and foreshock transport conditions is generated, based on the theory of diffusive shock acceleration, which captures the simulation results well with a single free parameter fixing the injection efficiency of the shock. The semi-analytical model allows the self-consistent results to be used in analytical modeling of shock acceleration in CME-driven shocks.

Vainio, R. O.; Battarbee, M. C.; Pnni, A.; Laitinen, T. L.

2013-12-01

291

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

SciTech Connect

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

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

2011-06-10

292

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

293

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

294

Solar forced variations of terrestrial high energy particle environment as seen by RESIK PIN detectors on CORONAS-F  

Microsoft Academic Search

RESIK is the bent crystal spectrometer aboard the CORONAS-F satellite. It is equipped with four PIN diode detectors. These detectors were used in order to detect background counts due to energetic particle contamination present within polar regions and SAA belts. At altitudes above 300 km (Coronas-F altitude is about 500 km) the population of charged particles trapped by the Earth's

M. Kowalinski; Z. Kordylewski; J. Sylwester; W. Trzebinski; D. Lisin

2004-01-01

295

Generation of Type III Solar Radio Bursts in Low Corona by Direct Amplification  

Microsoft Academic Search

An alternative scenario to the plasma emission model is proposed for coronal type III solar radio bursts. According to this model, the radio bursts are produced inside a magnetic flux tube with density depletion, by a direct amplification of electromagnetic waves with frequencies near the electron gyrofrequency and its harmonics. The amplification mechanism is the cyclotron-maser instability driven by a

P. H. Yoon; C. S. Wu; H. N. Zheng; S. Wang

2002-01-01

296

Simulations of type III solar radio bursts in the inhomogeneous corona and interplanetary space  

Microsoft Academic Search

It is generally accepted that plasma emission is responsible for type III solar radio bursts which sometimes show harmonic pairs with radiation near the electron plasma frequency and its second harmonic This emission mechanism consists of a sequence of steps i a semi-relativistic electron beam generates primary Langmuir waves via a beam instability ii the primary Langmuir waves undergo electrostatic

B. Li; P. Robinson; I. Cairns

2006-01-01

297

Generation of Type III Solar Radio Bursts in the Low Corona by Direct Amplification  

Microsoft Academic Search

An alternative scenario to the plasma-emission model is proposed for coronal type III solar radio bursts. According to this model, the radio bursts are produced inside a magnetic flux tube with density depletion by a direct amplification of electromagnetic waves with frequencies near the electron gyrofrequency and its harmonics. The amplification mechanism is the cyclotron-maser instability driven by a beam

C. S. Wu; C. B. Wang; Peter H. Yoon; H. N. Zheng; S. Wang

2002-01-01

298

The Inadequacy of Temperature Measurements in the Solar Corona through Narrowband Filter and Line Ratios  

Microsoft Academic Search

We analyze the determination of coronal line-of-sight temperatures with the technique of narrowband filter ratios that is currently employed for data obtained with the Transition Region and Coronal Explorerand the EUV Imaging Telescope on board the Solar and Heliospheric Observatory . We demonstrate that the simple fact that the observed differential emission measure curves in coronal loops have a broad

P. C. H. Martens; J. W. Cirtain; J. T. Schmelz

2002-01-01

299

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

300

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

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

301

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

302

The Interaction of Comet C/2011 W3 (Lovejoy) with the Global Solar Corona: Insight and Perspectives from Realistic Thermodynamic MHD Simulations  

NASA Astrophysics Data System (ADS)

On December 15-16 2011 the perihelion passage of sun-grazing comet C-2011 W3 (Lovejoy) took it perilously close to the sun. Its voyage through the low solar corona was readily observed by the EUV imagers onboard the Solar Dynamics Observatory and the STEREO spacecraft pair. During this time, EUV emission from the cometary tail underwent several significant changes in both intensity and overall inclination and shape, possibly an indication of rapidly changing ambient plasma or magnetic field conditions. To study this phenomenon, we employ a realistic 3D thermodynamic MHD model to obtain a self-consistent picture of the global thermodynamic and magnetic structure of the corona at this time. We use these simulations to examine the ambient plasma parameters along the trajectory and place them in the context of the multi-viewpoint observations, directly connecting the important influence of the global magnetic field structure to comet tail appearance and dynamics. By employing multiple simulations, we demonstrate how such a unique set of observations can be used to probe not only the comet-corona interaction, but also to constrain properties of the coronal plasma and magnetic field.

Downs, C.; Mikic, Z.; Linker, J. A.; Lionello, R.; Schrijver, C.

2012-12-01

303

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

NASA Astrophysics Data System (ADS)

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

Virtanen, I. I.; Mursula, K.

2014-02-01

304

Mean free path and energy loss of electrons in the solar corona and the inner heliosphere  

NASA Astrophysics Data System (ADS)

We have studied the mean free path of electrons in the solar atmosphere in dependence on their initial velocity and their starting height above the photosphere. The net pitch angle change results from the combined effects of Coulomb scattering and the decreasing field strength of the large-scale magnetic field. We show that above a certain velocity all electrons can travel a distance of at least five AU without deflection. This treshold velocity decreases with increasing starting height. Furthermore the loss of kinetic energy due to Coulomb collisions as a function of distance from the Sun has been calculated. At small distances, up to at least 1.5 Rsun (solar radius), the energy component parallel to the magnetic field (assumed as radial from the Sun) decreases but above 1.5 Rsun this component increases though the total particle energy decreases. If we assume that the injected electrons also have a velocity component perpendicular to the magnetic field (pitch angle theta >0), the radial velocity component will increase even at low coronal heights. The theoretical results are compared with observational data of solar type III radio bursts.

Estel, C.; Mann, G.

1999-05-01

305

Solar Wind Speed Structure in the Inner Corona at 3-12 Ro  

NASA Technical Reports Server (NTRS)

Estimates of solar wind speed obtained by Armstrong et al. [1986] based on 1983 VLA multiple-station intensity scintillation measurements inside 12 R(sub o) have been correlated with the electron density structure observed in white-light coronagraph measurements. The observed large- scale and apparently systematic speed variations are found to depend primarily on changes in heliographic latitude and longitude, which leads to the first results on large-scale speed structure in the acceleration region of the solar wind. Over an equatorial hole, solar wind speed is relatively steady, with peak-to-peak variations of 50 km/s and an average of 230 km/s. In contrast, the near-Sun flow speed across the streamer belt shows regular large-scale variations in the range of 100-300 km/s. Based on four groups of data, the gradient is 36 km/s per degree in heliocentric coordinates (corresponding to a rise of 260 km/s over a spatial distance on the Sun of two arcmin) with a standard deviation of 2.4 km/s per degree. The lowest speeds most likely coincide with the stalks of coronal streamers observed in white-light measurements. The detection of significant wind shear over the streamer belt is consistent with in situ and scintillation measurements showing that the density spectrum has a power-law form characteristic of fully developed turbulence over a much broader range of scales than in neighboring regions.

Woo, Richard

1995-01-01

306

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

307

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

308

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

309

Ultra high resolution images of the solar chromosphere and corona using coordinated rocket and balloon observations  

NASA Technical Reports Server (NTRS)

A discussion is presented of the scientific objectives that can be pursued by simultaneous coronal/chromospheric observation with the Multi-Spectral Solar Telescope Array (MSSTA), and a new balloon-borne observatory called the Ultra-High Resolution Vacuum Ultraviolet Spectroheliograph (UHRVS). Attention is given to the proposed UHRVS observatory, which will incorporate two instruments, a 65-cm aperture telescope with narrowband filters for high resolution photographic and photoelectric spectroheliograms, and a very high resolution spectrograph which uses a 40-cm aperture telescope. The capabilities of the MSSTA, and the joint UHRVS/MSSTA observing program that is envisioned are reviewed.

Walker, Arthur B. C., Jr.; Timothy, J. G.; Hoover, Richard B.; Barbee, Troy W., Jr.

1993-01-01

310

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

NASA Astrophysics Data System (ADS)

"EIT waves" are large-scale coronal bright fronts (CBFs) that were first observed in 195 images obtained using the Extreme-ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory ( SOHO). Commonly called "EIT waves", CBFs typically appear as diffuse fronts that propagate pseudo-radially across the solar disk at velocities of 100-700 km s-1 with front widths of 50-100 Mm. As their speed is greater than the quiet coronal sound speed ( c s ?200 km s-1) and comparable to the local Alfvn speed ( v A ?1000 km s-1), they were initially interpreted as fast-mode magnetoacoustic waves (vf=(cs2 + vA2)^{1/2}). Their propagation is now known to be modified by regions where the magnetosonic sound speed varies, such as active regions and coronal holes, but there is also evidence for stationary CBFs at coronal hole boundaries. The latter has led to the suggestion that they may be a manifestation of a processes such as Joule heating or magnetic reconnection, rather than a wave-related phenomena. While the general morphological and kinematic properties of CBFs and their association with coronal mass ejections have now been well described, there are many questions regarding their excitation and propagation. In particular, the theoretical interpretation of these enigmatic events as magnetohydrodynamic waves or due to changes in magnetic topology remains the topic of much debate.

Gallagher, Peter T.; Long, David M.

2011-07-01

311

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

312

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

313

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

E-print Network

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

Kazunari Shibata; Takaaki Yokoyama

2002-06-03

314

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

315

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

316

Mass Motions and Plasma Properties in the 107 K Flare Solar Corona  

NASA Astrophysics Data System (ADS)

In the present work, we analyze Solar Ultraviolet Measurement of Emitted Radiation (SUMER) observations of a solar limb flare that occurred on 1999 May 9. The analyzed data cover a time span of around 6.4 hr, during which an M-7.6 flare erupted and decayed in the field of view. Two selected regions along the SUMER slit have been considered for quantitative analysis. The main purpose of the present analysis is to measure the mass motions and the nonthermal velocities of the postflare plasmas and their temporal evolution. To achieve this we use lines having formation temperatures in the 2.5106 to 2107 K range from which we derive net mass motions and nonthermal velocities and compare them with the properties of the surrounding plasma not affected by the flare activity. To understand the physical conditions of the flaring plasma and of the surrounding material, we derive electron temperature, electron density, and emission measures of the emitting plasma. We find that bulk motions, initially of the order of several hundreds of kilometers per second in both directions, decay within 10 minutes from the flare onset; nonthermal velocities decay to preflare values of around 30 km s-1 in less than 2 hr from the maximum value of around 100 km s-1 at flare onset. The measured electron density does not seem to change during activity, while the flare plasma temperature steadily decays to preflare values. The temperature evolution is consistent with a radiatively cooling plasma, although the uncertainties associated to the measurement of the variation of thermal energy of the flare plasma prevent a definitive conclusion on possible continuous heating of the flaring plasma.

Landi, E.; Feldman, U.; Innes, D. E.; Curdt, W.

2003-01-01

317

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

NASA Technical Reports Server (NTRS)

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

Cruikshank, D. P.

2012-01-01

318

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

319

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

NASA Astrophysics Data System (ADS)

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

Petrie, G. J. D.

2007-05-01

320

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

321

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

322

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

323

Generation of Type III Solar Radio Bursts in Low Corona by Direct Amplification  

NASA Astrophysics Data System (ADS)

An alternative scenario to the plasma emission model is proposed for coronal type III solar radio bursts. According to this model, the radio bursts are produced inside a magnetic flux tube with density depletion, by a direct amplification of electromagnetic waves with frequencies near the electron gyrofrequency and its harmonics. The amplification mechanism is the cyclotron-maser instability driven by a beam of flare-generated streaming electrons. The propagation of an amplified wave is initially confined within the magnetic flux tube until the wave arrives at a point where the local exterior cutoff frequency is equal to the exiting wave frequency. The proposed model is spurred by the consideration that above an active region where the emission is presumed to originate, the ambient magnetic field is strong such that, in contrast to the conventional theories, it cannot be ignored. Numerical analysis leads to some encouraging results, on the basis of which we may resolve a number of longstanding issues raised by observations. The proposed scenario also implies a fundamentally different interpretation of the observed frequency drift in the dynamic spectrum.

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

2002-05-01

324

Generation of Type III Solar Radio Bursts in the Low Corona by Direct Amplification  

NASA Astrophysics Data System (ADS)

An alternative scenario to the plasma-emission model is proposed for coronal type III solar radio bursts. According to this model, the radio bursts are produced inside a magnetic flux tube with density depletion by a direct amplification of electromagnetic waves with frequencies near the electron gyrofrequency and its harmonics. The amplification mechanism is the cyclotron-maser instability driven by a beam of flare-generated streaming electrons. In the present discussion, a depletion factor of approximately 102 near the chromosphere is assumed. The essential point is that in order to produce the electromagnetic waves near the fundamental electron gyrofrequency, the present model requires 0.1<=fp/fg<=0.4 (where fp and fg denote the plasma frequency and gyrofrequency, respectively) in the source region. The propagation of an amplified wave is initially confined within the magnetic flux tube until the wave arrives at a point where the local exterior cutoff frequency is equal to the exiting wave frequency. The proposed model is spurred by the consideration that above an active region where the emission is presumed to originate, the ambient magnetic field is strong enough that, in contrast to conventional theories, it cannot be ignored. Preliminary analysis leads to some encouraging results, on the basis of which we may resolve a number of long-standing issues raised by observations. The proposed scenario also implies a fundamentally different interpretation of the observed frequency drift in the dynamic spectrum.

Wu, C. S.; Wang, C. B.; Yoon, Peter H.; Zheng, H. N.; Wang, S.

2002-08-01

325

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

326

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

327

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

328

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

NASA Technical Reports Server (NTRS)

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

2004-01-01

329

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

NASA Astrophysics Data System (ADS)

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

Kla?ka, J.

2014-09-01

330

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

331

Test of a multilayer-coated EUV grating for I-IV order spectroscopic measurements of the solar corona  

NASA Astrophysics Data System (ADS)

METIS, the Multi Element Telescope for Imaging and Spectroscopy, is a coronagraph selected by the European Space Agency to be part of the payload of the Solar Orbiter mission. The original METIS proposal included four optical paths, for observations in: 1) linearly polarized visible-light (590-650 nm), 2) narrow-band ultraviolet HI Lyman-alpha (121.6 nm), 3) narrow-band extreme-ultraviolet HeII Lyman-alpha (30.4 nm), 4) spectrographic mode for the HI Lyman- alpha and He II Lyman-alpha in corona. The design, coating performances, and test activities of the grating for the spectroscopic path are here described. The grating is optimized to work at near normal incidence and to diffract the 121.6 nm radiation at the first order and the 30.4 nm at its 4th order, consequently the two spectroscopic channels are overlapped on the focal plane. The grating is spherical with variable-line-spaced rulings, 1800 gr/mm central density. The selection of the spectroscopic channel to be acquired, either the 121.6 nm or the 30.4 nm, is made by a suitable filter wheel. The grating is multilayer-coated, to have high efficiency in both the spectral channels. In this paper we describe the tests made on a prototype with flat surface and constant groove spacing. The measures have been carried out at the BEAR beamline at the ELETTRA Synchrotron in Trieste (Italy). The grating was initially coated by gold and successively by a Mo-Si multilayer optimized at 30.4 nm. The efficiencies at the first and fourth order (121.6 and 30.4 nm) have been measured before and after the multilayer deposition. The quality of the multilayer deposition has been tested by atomic force microscope measurements on the grating surface and by reflectivity measurements performed on a test reference mirror. The experimental data are compared with numerical simulations accounting for the coating roughness and the smoothening effect on the blaze profile after the multilayer deposition. To our knowledge, this is the first time that such a grating configuration is proposed.

Poletto, Luca; Frassetto, Fabio; Miotti, Paolo; Giglia, Angelo; Corso, Alain Jody; Zuppella, Paola; Pelizzo, Maria-Guglielmina; Fineschi, Silvano; Antonucci, Ester; Naletto, Giampiero; Nicolosi, Piergiorgio; Romoli, Marco

2013-09-01

332

Three-dimensional study of Mars upper thermosphere/ionosphere and hot oxygen corona: 1. General description and results at equinox for solar low conditions  

NASA Astrophysics Data System (ADS)

Unlike Earth and Venus, Mars with a weak gravity allows an extended corona of hot species and the escape of its lighter constituents in its exosphere. Being the most important reaction, the dissociative recombination of O2+ is responsible for most of the production of hot atomic oxygen deep in the dayside thermosphere/ionosphere. The investigation of the Martian upper atmosphere is therefore complicated by the change in the flow regime from a collisional to a collisionless domain. Past studies, which used simple extrapolations of 1-D thermospheric/ionospheric parameters, could not account for the full effects of realistic conditions, which are shown to be of significant influence on the exosphere both close to and far away from the exobase. In this work, the combination of the new 3-D Direct Simulation Monte Carlo kinetic model and the modern 3-D Mars Thermosphere General Circulation Model is employed to describe self-consistently the Martian upper atmosphere at equinox for solar low conditions. For the first time, a 3-D analysis and shape of the Martian hot corona is provided, along with density and temperature profiles of cold and hot constituents as functions of position on the planet. Atmospheric loss and ion production (found to be more than an order of magnitude lower than the neutral escape), calculated locally all around the planet, provide valuable information for plasma models, refining the understanding of the ion loss, atmospheric sputtering, and interaction with the solar wind, in general.

Valeille, Arnaud; Tenishev, Valeriy; Bougher, Stephen W.; Combi, Michael R.; Nagy, Andrew F.

2009-11-01

333

HighEnergy Aspects of Stellar Coronae 1 HighEnergy Aspects of Stellar Coronae  

E-print Network

, 1997; Accepted ... 1997 Abstract Sun­like stars are the sites of various high­energy processes, many well established) solar flare model, a considerable portion of the solar flare energy is releasedHigh­Energy Aspects of Stellar Coronae 1 High­Energy Aspects of Stellar Coronae M. G¨udel 1 1 Paul

Guedel, Manuel

334

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

335

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

336

Solar energetic particle track densities as an indicator of the origin of interplanetary dust  

NASA Technical Reports Server (NTRS)

An examination of the relation of track densities from solar energetic particles in interplanetary dust grains (IDP's) to the orbital elements of source bodies is made and the positive and negative aspects of using track densities to determine the origin of IDP's are reported. It is found from calculations that predicted track densities for a particle of given size are related logarithmically to the minimum semimajor axis of the source body. Consequently, although track densities measurements may not be capable of distinguishing cometary from asteroidal sources, they should give information on the minimum semimajor axis of the originating bodies.

Blanford, George E.

1994-01-01

337

Using solar flare track densities to determine the origin of interplanetary dust particles  

NASA Technical Reports Server (NTRS)

Sandford theoretically explored the use of solar flare track densities in interplanetary dust particles (IDP's) to distinguish whether they were of cometary or asteroidal origin. He determined that there were differences in the characteristic distributions of track densities that would occur from these two possible sources. Flynn examined the heating of IDP's on atmospheric entry and concluded that IDP's must be predominantly from asteroidal sources because these asteroidal particles would have sufficiently low velocities to survive atmospheric heating with little or no modification whereas cometary particles would ordinarily have velocities that are much higher. This paper looks at what we can learn by combining the approaches of Sandford and Flynn.

Blanford, George E.

1993-01-01

338

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

NASA Astrophysics Data System (ADS)

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

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

2011-09-01

339

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

340

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

341

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  

E-print Network

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 find that we cannot obtain reliable snapshot images for complex objects when the visibilities are sparsely sampled.

Claude Mercier; Prasad Subramanian; Alain Kerdraon; Monique Pick; S. Ananthakrishnan; P. Janardhan

2005-08-31

342

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

343

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.

344

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

345

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

346

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

347

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

NASA Astrophysics Data System (ADS)

Realistic size equivalence and shape of Saharan mineral dust particles are derived from on in-situ particle, lidar and sun photometer measurements during SAMUM-1 in Morocco (19 May 2006), dealing with measured size- and altitude-resolved axis ratio distributions of assumed spheroidal model particles. The data were applied in optical property, radiative effect, forcing and heating effect simulations to quantify the realistic impact of particle non-sphericity. It turned out that volume-to-surface equivalent spheroids with prolate shape are most realistic: particle non-sphericity only slightly affects single scattering albedo and asymmetry parameter but may enhance extinction coefficient by up to 10%. At the bottom of the atmosphere (BOA) the Saharan mineral dust always leads to a loss of solar radiation, while the sign of the forcing at the top of the atmosphere (TOA) depends on surface albedo: solar cooling/warming over a mean ocean/land surface. In the thermal spectral range the dust inhibits the emission of radiation to space and warms the BOA. The most realistic case of particle non-sphericity causes changes of total (solar plus thermal) forcing by 55/5% at the TOA over ocean/land and 15% at the BOA over both land and ocean and enhances total radiative heating within the dust plume by up to 20%. Large dust particles significantly contribute to all the radiative effects reported.

Otto, S.; Trautmann, T.; Wendisch, M.

2010-11-01

348

Interferometry of the e corona.  

PubMed

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

Henderson, G

1970-12-01

349

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

NASA Astrophysics Data System (ADS)

Realistic size equivalence and shape of Saharan mineral dust particles are derived from in-situ particle, lidar and sun photometer measurements during SAMUM-1 in Morocco (19 May 2006), dealing with measured size- and altitude-resolved axis ratio distributions of assumed spheroidal model particles. The data were applied in optical property, radiative effect, forcing and heating effect simulations to quantify the realistic impact of particle non-sphericity. It turned out that volume-to-surface equivalent spheroids with prolate shape are most realistic: particle non-sphericity only slightly affects single scattering albedo and asymmetry parameter but may enhance extinction coefficient by up to 10 %. At the bottom of the atmosphere (BOA) the Saharan mineral dust always leads to a loss of solar radiation, while the sign of the forcing at the top of the atmosphere (TOA) depends on surface albedo: solar cooling/warming over a mean ocean/land surface. In the thermal spectral range the dust inhibits the emission of radiation to space and warms the BOA. The most realistic case of particle non-sphericity causes changes of total (solar plus thermal) forcing by 55/5 % at the TOA over ocean/land and 15 % at the BOA over both land and ocean and enhances total radiative heating within the dust plume by up to 20 %. Large dust particles significantly contribute to all the radiative effects reported. They strongly enhance the absorbing properties and forward scattering in the solar and increase predominantly, e.g., the total TOA forcing of the dust over land.

Otto, S.; Trautmann, T.; Wendisch, M.

2011-05-01

350

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

351

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

352

ON A TRANSITION FROM SOLAR-LIKE CORONAE TO ROTATION-DOMINATED JOVIAN-LIKE MAGNETOSPHERES IN ULTRACOOL MAIN-SEQUENCE STARS  

SciTech Connect

For main-sequence stars beyond spectral type M5, the characteristics of magnetic activity common to warmer solar-like stars change into the brown-dwarf domain: the surface magnetic field becomes more dipolar and the evolution of the field patterns slows, the photospheric plasma is increasingly neutral and decoupled from the magnetic field, chromospheric and coronal emissions weaken markedly, and the efficiency of rotational braking rapidly decreases. Yet, radio emission persists, and has been argued to be dominated by electron-cyclotron maser emission instead of the gyrosynchrotron emission from warmer stars. These properties may signal a transition in the stellar extended atmosphere. Stars warmer than about M5 have a solar-like corona and wind-sustained heliosphere in which the atmospheric activity is powered by convective motions that move the magnetic field. Stars cooler than early-L, in contrast, may have a Jovian-like rotation-dominated magnetosphere powered by the star's rotation in a scaled-up analog of the magnetospheres of Jupiter and Saturn. A dimensional scaling relationship for rotation-dominated magnetospheres by Fan et al. is consistent with this hypothesis.

Schrijver, Carolus J. [Lockheed Martin Advanced Technology Center, 3251 Hanover Street, Palo Alto, CA 94304 (United States)], E-mail: schrijver@lmsal.com

2009-07-10

353

Why is the Sun's Corona so Hot? X-rays and Ultraviolet Emission from the Solar Atmosphere  

Microsoft Academic Search

UNDER ordinary circumstances, the flood of light from the bright disk of the sun overwhelms the weak emis- sion that comes from the solar atmosphere which is thus hidden from view. However, when the sun is totally eclipsed, a white halo appears around the edge of the moon, stretching out to a distance of solar diameter (1,400,000 km) or more.

Anita Mohan; B. N. Dwivedi

2001-01-01

354

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

355

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

356

Intensity of the Fe XV emission line corona, the level of geomagnetic activity, and the velocity of the solar wind  

NASA Technical Reports Server (NTRS)

The method of superposed epochs is used to determine the average solar wind velocity and the Kp index following central meridian passage of coronal weak and bright features identified from OSO 7 isophotograms of the Fe XV (284 A) emission line. It is found that bright coronal regions possess magnetic fields of closed configuration, thus reducing particle escape, while coronal holes possess open magnetic field lines favorable to particle escape or enhanced outflow of the solar wind.

Bell, B.; Noci, G.

1976-01-01

357

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

358

Making the corona and the fast solar wind: a self-consistent simulation for the low-frequency Alfven waves from photosphere to 0.3AU  

E-print Network

We show that the coronal heating and the fast solar wind acceleration in the coronal holes are natural consequence of the footpoint fluctuations of the magnetic fields at the photosphere, by performing one-dimensional magnetohydrodynamical simulation with radiative cooling and thermal conduction. We initially set up a static open flux tube with temperature 10^4K rooted at the photosphere. We impose transverse photospheric motions corresponding to the granulations with velocity = 0.7km/s and period between 20 seconds and 30 minutes, which generate outgoing Alfven waves. We self-consistently treat these waves and the plasma heating. After attenuation in the chromosphere by ~85% of the initial energy flux, the outgoing Alfven waves enter the corona and contribute to the heating and acceleration of the plasma mainly by the nonlinear generation of the compressive waves and shocks. Our result clearly shows that the initial cool and static atmosphere is naturally heated up to 10^6K and accelerated to 800km/s.

Takeru K. Suzuki; Shu-ichiro Inutsuka

2006-05-22

359

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

E-print Network

THE DIGITAL SYSTEM ARTEMIS FOR REAL-TIME PROCESSING OF RADIO TRANSIENT EMISSIONS IN THE SOLAR system named 'ARTEMIS' that was developed and constructed by the Space Research Department (DESPA time signals from multichannel receivers. This system is controlled by a multiprocessor computer based

Athens, University of

360

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

361

On the SORS project of CORONAS I and F  

NASA Astrophysics Data System (ADS)

The scientific experiment SOLAR RADIO SPECTROMETER (abbreviated: SORS) of the CORONAS-I satellite project is described and prospects to the planned mission of CORONAS-F are given. The astrophysical goal of these experiments is the investigation of solar radio emission in a wide frequency band detecting low-frequency solar flare emission outside the terrestrial radio window. The principal capacity of SORS could be demonstrated by observation of dynamic spectra of type III bursts during a relatively short operational period aboard CORONAS-I restricted by low solar activity. Using the experience of CORONAS-I it can be anticipated that a new SORS equipment on CORONAS-F will deliver a broader material for the exploration of coronal and heliospheric plasma processes.

Fomichev, V. V.; Oraevsky, V. N.; Kruger, A.

362

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

Microsoft Academic Search

In our previous paper, we have presented a theory to explain the observed\\u000auniversal correlation between the emission measure ($EM=n^2 V$) and temperature\\u000a(T) for solar\\/stellar flares on the basis of the magnetic reconnection model\\u000awith heat conduction and chromospheric evaporation. Here n is the electron\\u000adensity and V is the volume. By extending our theory to general situations,\\u000awe

Kazunari Shibata; Takaaki Yokoyama

2002-01-01

363

QUASI-PERIODIC PROPAGATING SIGNALS IN THE SOLAR CORONA: THE SIGNATURE OF MAGNETOACOUSTIC WAVES OR HIGH-VELOCITY UPFLOWS?  

SciTech Connect

Since the discovery of quasi-periodic propagating oscillations with periods of order 3-10 minutes in coronal loops with TRACE and SOHO/EIT (and later with STEREO/EUVI and Hinode/EIS), they have been almost universally interpreted as evidence for propagating slow-mode magnetoacoustic waves in the low plasma {beta} coronal environment. Here we show that this interpretation is not unique, and that for coronal loops associated with plage regions (as opposed to sunspots), the presence of magnetoacoustic waves may not be the only cause for the observed quasi-periodicities. We focus instead on the ubiquitous, faint upflows at 50-150 km s{sup -1} that were recently discovered as blueward asymmetries of spectral line profiles in footpoint regions of coronal loops, and as faint disturbances propagating along coronal loops in EUV/X-ray imaging time series. These faint upflows are most likely driven from below and have been associated with chromospheric jets that are (partially) rapidly heated to coronal temperatures at low heights. These two scenarios (waves versus flows) are difficult to differentiate using only imaging data, but careful analysis of spectral line profiles indicates that faint upflows are likely responsible for some of the observed quasi-periodic oscillatory signals in the corona. We show that recent EIS measurements of intensity and velocity oscillations of coronal lines (which had previously been interpreted as direct evidence for propagating waves) are actually accompanied by significant oscillations in the line width that are driven by a quasi-periodically varying component of emission in the blue wing of the line. This faint additional component of blue-shifted emission quasi-periodically modulates the peak intensity and line centroid of a single Gaussian fit to the spectral profile with the same small amplitudes (respectively a few percent of background intensity and a few km s{sup -1}) that were previously used to infer the presence of slow-mode magnetoacoustic waves. Our results indicate that it is possible that a significant fraction of the quasi-periodicities observed with coronal imagers and spectrographs that have previously been interpreted as propagating magnetoacoustic waves are instead caused by these upflows. The different physical cause for coronal oscillations would significantly impact the prospects of successful coronal seismology using propagating disturbances in coronal loops.

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

2010-10-20

364

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

NASA Astrophysics Data System (ADS)

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-dependent effects of SEP acceleration between 1.8 and 8 solar radii in the 2005 May 13 CME. We find that the source population is accelerated to at least 100 MeV, with distributions enhanced up to six orders of magnitude. Acceleration efficiency varies strongly along field lines probing different regions of the dynamically evolving CME, whose dynamics is influenced by the large-scale coronal magnetic field structure. We observe strong acceleration in sheath regions immediately behind the shock.

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

2013-11-01

365

Herschel-resolved Outer Dust Belts of Two-belt Spitzer Debris Disks around Nearby A-type and Solar Type Stars  

NASA Astrophysics Data System (ADS)

We use Herschel dual-band PACS photometry for a unique set of stars that host on-going activity in the terrestrial planet zones and evidence of an outer/colder dust component, to continue the exploration, begun with Spitzer Space Telescope, of their disk structure and composition. The solar- and A-type stars in this sample have combined Spitzer IRS+MIPS (5 to 70 ?m) and Herschel PACS (100 and 160 ?m) SEDs revealing a two-ring disk architecture that mirrors that of the asteroidal-Kuiper belt geometry of our own solar system. Herschel provides the observational sensitivity at PACS 100 ?m required to successfully detect and resolve the outer dust belts. Spatially resolved systems can help breach the degeneracy between the grain properties and the dusts radial location, important for SED modeling. In summary, the PACS observations: 1) establish the location and characteristic dust temperature of the outer/cold dust belts and help constrain the minimum grain size and mass; 2) advance our understanding of dust particle composition by constraining the long wavelength emission; 3) facilitate comparison of dust distributions across stellar spectral range; and 4) establish the overall architecture of the circumstellar dust, perhaps pointing to favorable regions where exoplanets may reside.

Morales, Farisa Y.; Bryden, G.; Werner, M. W.; Stapelfeldt, K. R.

2014-01-01

366

Protoplanetary Dust  

NASA Astrophysics Data System (ADS)

Preface; 1. Planet formation and protoplanetary dust Daniel Apai and Dante Lauretta; 2. The origins of protoplanetary dust and the formation of accretion disks Hans-Peter Gail and Peter Hope; 3. Evolution of protoplanetary disk structures Fred Ciesla and Cornelius P. Dullemond; 4. Chemical and isotopic evolution of the solar nebula and protoplanetary disks Dmitry Semenov, Subrata Chakraborty and Mark Thiemens; 5. Laboratory studies of simple dust analogs in astrophysical environments John R. Brucato and Joseph A. Nuth III; 6. Dust composition in protoplanetaty dust Michiel Min and George Flynn; 7. Dust particle size evolution Klaus M. Pontoppidan and Adrian J. Brearly; 8. Thermal processing in protoplanetary nebulae Daniel Apai, Harold C. Connolly Jr. and Dante S. Lauretta; 9. The clearing of protoplanetary disks and of the protosolar nebula Ilaira Pascucci and Shogo Tachibana; 10. Accretion of planetesimals and the formation of rocky planets John E. Chambers, David O'Brien and Andrew M. Davis; Appendixes; Glossary; Index.

Apai, D.niel; Lauretta, Dante S.

2014-02-01

367

Protoplanetary Dust  

NASA Astrophysics Data System (ADS)

Preface; 1. Planet formation and protoplanetary dust Daniel Apai and Dante Lauretta; 2. The origins of protoplanetary dust and the formation of accretion disks Hans-Peter Gail and Peter Hope; 3. Evolution of protoplanetary disk structures Fred Ciesla and Cornelius P. Dullemond; 4. Chemical and isotopic evolution of the solar nebula and protoplanetary disks Dmitry Semenov, Subrata Chakraborty and Mark Thiemens; 5. Laboratory studies of simple dust analogs in astrophysical environments John R. Brucato and Joseph A. Nuth III; 6. Dust composition in protoplanetaty dust Michiel Min and George Flynn; 7. Dust particle size evolution Klaus M. Pontoppidan and Adrian J. Brearly; 8. Thermal processing in protoplanetary nebulae Daniel Apai, Harold C. Connolly Jr. and Dante S. Lauretta; 9. The clearing of protoplanetary disks and of the protosolar nebula Ilaira Pascucci and Shogo Tachibana; 10. Accretion of planetesimals and the formation of rocky planets John E. Chambers, David O'Brien and Andrew M. Davis; Appendixes; Glossary; Index.

Apai, Dniel; Lauretta, Dante S.

2010-01-01

368

MODELING MAGNETIC FIELD STRUCTURE OF A SOLAR ACTIVE REGION CORONA USING NONLINEAR FORCE-FREE FIELDS IN SPHERICAL GEOMETRY  

SciTech Connect

We test a nonlinear force-free field (NLFFF) optimization code in spherical geometry using an analytical solution from Low and Lou. Several tests are run, ranging from idealized cases where exact vector field data are provided on all boundaries, to cases where noisy vector data are provided on only the lower boundary (approximating the solar problem). Analytical tests also show that the NLFFF code in the spherical geometry performs better than that in the Cartesian one when the field of view of the bottom boundary is large, say, 20 Degree-Sign Multiplication-Sign 20 Degree-Sign . Additionally, we apply the NLFFF model to an active region observed by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory (SDO) both before and after an M8.7 flare. For each observation time, we initialize the models using potential field source surface (PFSS) extrapolations based on either a synoptic chart or a flux-dispersal model, and compare the resulting NLFFF models. The results show that NLFFF extrapolations using the flux-dispersal model as the boundary condition have slightly lower, therefore better, force-free, and divergence-free metrics, and contain larger free magnetic energy. By comparing the extrapolated magnetic field lines with the extreme ultraviolet (EUV) observations by the Atmospheric Imaging Assembly on board SDO, we find that the NLFFF performs better than the PFSS not only for the core field of the flare productive region, but also for large EUV loops higher than 50 Mm.

Guo, Y.; Ding, M. D. [School of Astronomy and Space Science, Nanjing University, Nanjing 210093 (China); Liu, Y.; Sun, X. D. [W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305 (United States); DeRosa, M. L. [Lockheed Martin Advanced Technology Center, 3251 Hanover Street, Palo Alto, CA 94304 (United States); Wiegelmann, T., E-mail: guoyang@nju.edu.cn [Max-Planck-Institut fuer Sonnensystemforschung, Max-Planck-Strasse 2, D-37191 Katlenburg-Lindau (Germany)

2012-11-20

369

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

370

Ultrasonic corona sensor study  

NASA Technical Reports Server (NTRS)

The overall objective of this program is to determine the feasibility of using ultrasonic (above 20 kHz) corona detection techniques to detect low order (non-arcing) coronas in varying degrees of vacuum within large high vacuum test chambers, and to design, fabricate, and deliver a prototype ultrasonic corona sensor.

Harrold, R. T.

1976-01-01

371

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

372

Highly Ionized sodium X-ray line emission from the solar corona and the abundance of sodium  

NASA Astrophysics Data System (ADS)

Context. The Na X X-ray lines between 10.9 and 11.2 have attracted little attention but are of interest since they enable an estimate of the coronal abundance of Na to be made. This is of great interest in the continuing debate on the nature of the FIP (first ionization potential) effect. Aims: Observations of the Na X lines with the Solar Maximum Mission Flat Crystal Spectrometer and a rocket-borne X-ray spectrometer are used to measure the Na/Ne abundance ratio, i.e. the ratio of an element with very low FIP to one with high FIP. Methods: New atomic data are used to generate synthetic spectra which are compared with the observations, with temperature and the Na/Ne abundance ratio as free parameters. Results: Temperature estimates from the observations indicate that the line emission is principally from non-flaring active regions, and that the Na/Ne abundance ratio is 0.07 50%. Conclusions: The Na/Ne abundance ratio is close to a coronal value for which the abundances of low-FIP elements (FIP < 10 eV) are enhanced by a factor of 3 to 4 over those found in the photosphere. For low-temperature (Te ?slant 1.5 MK) spectra, the presence of Fe XVII lines requires that either a higher-temperature component is present or a revision of ionization or recombination rates is needed.

Phillips, K. J. H.; Aggarwal, K. M.; Landi, E.; Keenan, F. P.

2010-07-01

373

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

374

Dust Models Paint Alien's View of Solar System - Duration: 2:47.  

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...

375

Winds in R Coronae Borealis Stars  

Microsoft Academic Search

We present new spectroscopic observations of the He I $\\\\lambda$10830 line in\\u000aR Coronae Borealis (RCB) stars which provide the first strong evidence that\\u000amost, if not all, RCB stars have winds. It has long been suggested that when\\u000adust forms around an RCB star, radiation pressure accelerates the dust away\\u000afrom the star, dragging the gas along with it.

Geoffrey C. Clayton; T. R. Geballe; Luciana Bianchi

2003-01-01

376

Dust production from sub-solar to super-solar metallicity in Thermally Pulsing Asymptotic Giant Branch Stars  

E-print Network

We discuss the dust chemistry and growth in the circumstellar envelopes (CSEs) of Thermally Pulsing Asymptotic Giant Branch (TP-AGB) star models computed with the COLIBRI code, at varying initial mass and metallicity (Z=0.001, 0.008, 0.02, 0.04, 0.06). A relevant result of our analysis deals with the silicate production in M-stars. We show that, in order to reproduce the observed trend between terminal velocities and mass-loss rates in Galactic M-giants, one has to significantly reduce the efficiency of chemisputtering by H2 molecules, usually considered as the most effective dust destruction mechanism. This indication is also in agreement with the most recent laboratory results, which show that silicates may condense already at T=1400 K, instead than at Tcond=1000 K, as obtained by models that include chemisputtering. From the analysis of the total dust ejecta, we find that the total dust-to-gas ejecta of intermediate-mass stars are much less dependent on metallicity than usually assumed. In a broader contex...

Ambra, Nanni; Paola, Marigo; Lo, Girardi; Atefeh, Javadi; Jacco, van Loon

2014-01-01

377

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

378

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

379

Speaking Volumes about Dust  

NSDL National Science Digital Library

This is a lesson about density. Learners will relate the concept of density to the density of dust in space. They will use mission data from the Student Dust Counter (SDC) interface to determine the density of dust grains in a volume of space in the Solar System in order to answer questions concerning the distribution of dust in the solar system. They will discover that space is much more sparsely populated with dust than they may have thought. Students discuss their findings with the class.

380

SINGLE STAGE EVAPORATION OF SOLAR CONDENSATE DUST TO MAKE CAIS. D. S. Ebel and L. , Department of the Geophysical Sciences, 5734 South Ellis Ave., 1  

E-print Network

SINGLE STAGE EVAPORATION OF SOLAR CONDENSATE DUST TO MAKE CAIS. D. S. Ebel and L. Grossman1- tions of the residues which result from isothermal evaporation of CaO-MgO-Al2O3-SiO2 (CMAS) liquids of evaporation was found to increase markedly with P(H2). The evaporation residues exhibit bulk compositions

Grossman, Lawrence

381

Solar photocatalytic disinfection of a group of bacteria and fungi aqueous suspensions with TiO 2, ZnO and Sahara desert dust  

Microsoft Academic Search

This photocatalytic method was aimed to destroy bacteria, to prevent fungi in some industrial products and to create desirable hygienic medium under solar irradiation. The efficiencies of disinfection with the photoactive metal oxides and the Sahara desert dust was investigated. We have studied photocatalytic disinfection of two-groups of microorganisms which are known as bacteria and fungus in pathogenic-organisms: Escherichia coli,

O Seven; B Dindar; S Aydemir; D Metin; M. A Ozinel; S Icli

2004-01-01

382

Collisional evolution of irregular satellite swarms: detectable dust around Solar system and extrasolar planets  

Microsoft Academic Search

Since the 1980s it has been becoming increasingly clear that the Solar system's irregular satellites are collisionally evolved. The current populations are remnants of much more massive swarms that have been grinding away for billions of years. Here, we derive a general model for the collisional evolution of an irregular satellite swarm and apply it to the Solar system and

G. M. Kennedy; M. C. Wyatt

2011-01-01

383

Chemical Signatures of Interstellar Dusts Preserved in Primitive Chondrites and Inner Planets of the Solar System  

NASA Technical Reports Server (NTRS)

We show that the inheritance of interstellar materials by the solar system is not only documented by the presence of presolar grains, various isotopic anomalies, but also expressed in the chemical element distribution in the inner solar system. Additional information is contained in the original extended abstract.

Yin, Qing-Zhu

2002-01-01

384

Abundances of Elements in Stellar Coronae  

NASA Technical Reports Server (NTRS)

Interest in stellar coronal abundances was piqued several years ago by the launch of satellites that were able to study the compositions of coronae on stars other than the sun. Motivated by the possibility that other stellar coronae might share the First Ionization Potential (FIP) Effect solar abundance anomaly, we have in recent years been attempting to determine coronal element abundances in other stars. I will review these results, together with similar results reported in the literature, from a critical perspective of understanding the true uncertainties involved in the measurements. The importance of element abundances for coronal physics will be highlighted, and it will be shown that the differences in the chemical compositions of active stars allow us to draw new conclusions regarding the nature of stellar coronae and coronal heating.

Drake, Jeremy

1998-01-01

385

From asteroids to comets: Gas and dust production of the small-bodies in the solar system  

NASA Astrophysics Data System (ADS)

Comets are considered to be among the most pristine objects in our Solar System. Active comets have been studied for centuries, but the topic of transition objects (TOs) is relatively new in the area of planetary science. In either case, understanding the composition, activity and dynamics of these objects will help us understand the physical and dynamical evolution of comets, their connection to asteroids, and the environment and formation of the early Solar System. The overall theme of this thesis is to search for and study cometary activity on small-bodies in our Solar System. In particular, three separate, but related, projects are presented. Two studies utilized spectroscopic observations from the 1.2 m Elginfield telescope, the 1.8 m Dominion Astrophysical Observatory (DAO), and the 1.5 m Cerro-Tololo Inter-American Observatory (CTIO), to search for TOs and/or to observe active comets at different points in their orbit and of different dynamical ages. A third study used archived images from the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) to search for cometary activity on objects otherwise classified as asteroids. 1. The Elginfield and DAD telescopes were used to test the feasibility of a spectroscopic search program for TOs from these platforms. Even in this initial test mode, the data collected constitutes the largest spectroscopic search for TOs to date. However, previous results could not be improved upon, and this project was not deemed feasible with the current observations. 2. Five active comets were observed spectroscopically with the CTIO. Of particular interest were observations of new Oort cloud comet, 2006 VZ13, which passed perihelion during these observations. Gas and dust production rates and ratios were derived for three molecular species (CN, C2, and C3), and each comet was classified based on criteria from previous studies. 3. Using the CFHTLS, over 950 asteroidal objects were examined for evidence of comae or tail using a three-levet technique, while over 11,000 objects were visually inspected. This is the largest search for main-belt comets (MBCs) of any kind to date, which also examined the general main-belt population. One unknown object was found to show cometary activity. Upper limits were derived for the expected number of weakly and strongly active MBCs in the main-belt. Key words. Comets, asteroids, transition objects, main-belt comets, activated asteroids, solar system, cometary activity, physical evolution, orbit, Jupiter Tisserand parameter, optical spectra, optical observations, emission lines, gas production rate, dust production rate, Elginfield telescope, Dominion Astrophysical Observatory, Cerro-Tololo Inter-American Observatory, Canada-France-Hawaii Telescope, Legacy Survey, spectrograph, CCD camera.

Gilbert, Alyssa M.

386

Radiative properties and direct radiative effect of Saharan dust measured by the C-130 aircraft during SHADE: 1. Solar spectrum  

Microsoft Academic Search

The physical and optical properties of Saharan dust aerosol measured by the Met Office C-130 during the Saharan Dust Experiment (SHADE) are presented. Additional radiation measurements enable the determination of the aerosol optical depth, tau aerlambda, and the direct radiative effect (DRE) of the mineral dust. The results suggest that the absorption by Saharan dust is significantly overestimated in the

Jim Haywood; Pete Francis; Simon Osborne; Martin Glew; Norman Loeb; Eleanor Highwood; Didier Tanr; Gunnar Myhre; Paola Formenti; Edwin Hirst

2003-01-01

387

Case study of a dust storm over Hyderabad area, India: its impact on solar radiation using satellite data and ground measurements.  

PubMed

According to the Earth Observatory dust outbreaks are considered as natural hazards, which affect the ecosystems and human life. The main objective of this study is to assess and monitor the movement of aerosols and pollutants from local or other sources, both natural and anthropogenic, using a combination of ground-based monitoring and satellite data. The turbid and polluted atmosphere in the densely-populated area of Hyderabad, India is further degradated from dust outbreaks originated from Thar desert. A dust event occurred during 10th to 11th April 2006 in the northwest region of India; its plume substantially spreaded across the downwind direction affecting the study region. Using both irradiance measurements and satellite data this dust event is investigated. The analysis shows a significant change in Aerosol Optical Depth (AOD), Aerosol Index (AI) and aerosol-particle size during the dust event. The Aerosol Optical Depth in the dusty day is about 0.2 higher than the previous non-dusty days, while the Angstrm exponent rapidly decreases when the dust plume affected the study area. The surface PM concentrations show enhanced values during the dusty day directly influenced by the dust deposition. There is also a remarkable decrease in ground-reaching global radiation, UV erythemal (UV(ery)) and other irradiance components. The analysis suggested that the use of the diffuse-to-direct-beam ratio is the most appropriate parameter for the dust monitoring since its values at the longer wavelengths are not affected by the solar zenith angle. PMID:17599393

Badarinath, K V S; Kharol, Shailesh Kumar; Kaskaoutis, D G; Kambezidis, H D

2007-10-01

388

Spicules, mass transfer, oscillations, and the heating of the corona  

Microsoft Academic Search

The mass moving in chromospheric spicules is enough to replace the corona in a brief time, so understanding the dynamics of spicules is important for understanding the support and heating of the solar corona. We have undertaken a program involving simultaneous high-resolution observations in various chromospheric visible lines (H-alpha, Ca II H, and G-band, as well as Dopplergrams) using the

J. M. Pasachoff; K. A. Kozarev; D. L. Butts; J. W. Gangestad; D. B. Seaton; B. de Pontieu; L. Golub; E. Deluca; K. Wilhelm; I. Dammasch

2005-01-01

389

Accretionary dust mantles in CM chondrites - Evidence for solar nebula processes  

Microsoft Academic Search

The origin of the various components of 14 carbonaceous chondrites of the CM group, and the evolution of their parent body (or bodies) were examined by studying the texture and the model composition of these chondrites. Evidence is presented for the existence of preaccretionary aqueous alteration of anhydrous primary products in the solar nebula. Based on the results of textural,

K. Metzler; A. Bischoff; D. Stoeffler

1992-01-01

390

An acceleration mechanism for loop transients in the outer corona  

Microsoft Academic Search

The heliocentrifugal motion of coronal loop transients is likely driven largely by the buoyant force exerted by the ambient medium. In the outer corona where the solar wind is well formed, the buoyant force results mainly from the rapid outward decrease in the ambient pressure of the solar wind. The contribution from magnetic buoyancy is not so significant as in

Tyan Yeh; Murray Dryer

1981-01-01

391

Persistent Doppler shift oscillations observed with HINODE/EIS in the solar corona: spectroscopic signatures of Alfvenic waves and recurring upflows  

E-print Network

Using data obtained by the EUV Imaging Spectrometer (EIS) onboard Hinode, we have per- formed a survey of obvious and persistent (without significant damping) Doppler shift oscillations in the corona. We have found mainly two types of oscillations from February to April in 2007. One type is found at loop footpoint regions, with a dominant period around 10 minutes. They are characterized by coherent behavior of all line parameters (line intensity, Doppler shift, line width and profile asymmetry), apparent blue shift and blueward asymmetry throughout almost the en- tire duration. Such oscillations are likely to be signatures of quasi-periodic upflows (small-scale jets, or coronal counterpart of type-II spicules), which may play an important role in the supply of mass and energy to the hot corona. The other type of oscillation is usually associated with the upper part of loops. They are most clearly seen in the Doppler shift of coronal lines with forma- tion temperatures between one and two million degrees. The ...

Tian, Hui; Wang, Tongjiang; Ofman, Leon; De Pontieu, Bart; Innes, Davina E; Peter, Hardi

2012-01-01

392

Low-frequency heliographic observations of the quiet Sun corona  

NASA Astrophysics Data System (ADS)

We present new results of heliographic observations of quiet-Sun radio emission fulfilled by the UTR-2 radio telescope. The solar corona investigations have been made close to the last solar minimum (Cycle 23) in the late August and early September of 2010 by means of the two-dimensional heliograph within 16.5-33 MHz. Moreover, the UTR-2 radio telescope was used also as an 1-D heliograph for one-dimensional scanning of the Sun at the beginning of September 2010 as well as in short-time observational campaigns in April and August of 2012. The average values of integral flux density of the undisturbed Sun continuum emission at different frequencies have been found. Using the data, we have determined the spectral index of quiet-Sun radio emission in the range 16.5-200 MHz. It is equal to -2.10.1. The brightness distribution maps of outer solar corona at frequencies 20.0 MHz and 26.0 MHz have been obtained. The angular sizes of radio Sun were estimated. It is found that the solar corona at these frequencies is stretched-out along equatorial direction. The coefficient of corona ellipticity varies slightly during above period. Its mean magnitudes are equal to ? 0.75 and ? 0.73 at 20.0 MHz and 26.0 MHz, respectively. The presented results for continuum emission of solar corona conform with being ones at higher frequencies.

Stanislavsky, A. A.; Koval, A. A.; Konovalenko, A. A.

2013-12-01

393

Dust to Dust  

NSDL National Science Digital Library

The dust around us is composed of bits of detritus of all manner of things, but it is mostly bits of human skin. This radio broadcast explores the universe through tiny dust particles and discovers what it can tell us about our past as well as our future. The broadcast discusses dust from ice cores that reveal the climate record and the cosmic dust that Earth is gathering every day. There is also explanation of the microscopic composition of the dust around us and the damage dust can do to museum exhibits, especially when the dust interacts with the moisture in the atmosphere. The broadcast is 28 minutes in length.

394

The Origin of Organic Matter in the Solar System: Evidence from Interplanetary Dust Particles  

NASA Technical Reports Server (NTRS)

The origin of the organic matter in interplanetary materials has not been established. A variety of mechanisms have been proposed, with two extreme cases being a Fisher-Tropsch type process operating in the gas phase of the solar nebula or a Miller-Urey type process, which requires interaction with an aqueous fluid, presumably occurring on an asteroid. In the Fisher-Tropsch case, we might expect similar organic matter in hydrated and anhydrous interplanetary materials. However, aqueous alteration is required in the case of the Miller-Urey process, and we would expect to see organic matter preferentially in interplanetary materials that exhibit evidence of aqueous activity, such as the presence of hydrated silicates. The types and abundance of organic matter in meteorites have been used as an indicator of the origin of organic matter in the Solar System. Indigenous complex organic matter, including amino acids, has been found in hydrated carbonaceous chondrite meteorites, such as Murchison. Much lower amounts of complex organic matter, possibly only terrestrial contamination, have been found in anhydrous carbonaceous chondrite meteorites, such as Allende, that contain most of their carbon in elemental form. These results seem to favor production of the bulk of the organic matter in the Solar System by aqueous processing on parent bodies such as asteroids, a Miller-Urey process. However, the hydrated carbonaceous chondrite meteorites have approximately solar abundances of the moderately volatile elements, while all anhydrous carbonaceous chondrite meteorites have significantly lower contents of these moderately volatile elements. Two mechanisms, incomplete condensation or evaporation, both of which involve processing at approx. 1200 C, have been suggested to explain the lower content of the moderately volatile elements in all anhydrous meteorites. Additional information is contained in the original extended abstract.

Flynn, G. J.; Keller, L. P.; Jacobsen, C.; Wirick, S.

2001-01-01

395

Interpretation of the spectral and photometric variations of R Coronae Borealis  

Microsoft Academic Search

A consistent picture explaining both the spectral and photometric (infrared and visual) variations of R Coronae Borealis is developed. It is found that the extreme infrared maximum and minimum can be fitted by dispersion of the same mass of graphite dust. Random clumps of this dust crossing the line of sight both obscure the visual continuum of the object and

L. Hartmann; J. P. Apruzese

1976-01-01

396

Measuring Dust on Mars  

NASA Technical Reports Server (NTRS)

Mars is a dusty planet. Will dust accumulation on solar arrays be a problem for large solar power systems used on long-duration future missions on Mars? NASA Lewis Research Center's Materials Adherence Experiment (MAE) on the Mars Pathfinder Sojourner rover was designed to find out. It measured the dust deposited on the rover's solar array by measuring the change in transparency of a movable glass cover as dust settled on it. This graph shows the results from the first 2 weeks of operation on Mars.

1998-01-01

397

Persistent Doppler Shift Oscillations Observed with HINODE-EIS in the Solar Corona: Spectroscopic Signatures of Alfvenic Waves and Recurring Upflows  

NASA Technical Reports Server (NTRS)

Using data obtained by the EUV Imaging Spectrometer on board Hinode, we have performed a survey of obvious and persistent (without significant damping) Doppler shift oscillations in the corona. We have found mainly two types of oscillations from February to April in 2007. One type is found at loop footpoint regions, with a dominant period around 10 minutes. They are characterized by coherent behavior of all line parameters (line intensity, Doppler shift, line width, and profile asymmetry), and apparent blueshift and blueward asymmetry throughout almost the entire duration. Such oscillations are likely to be signatures of quasi-periodic upflows (small-scale jets, or coronal counterpart of type-II spicules), which may play an important role in the supply of mass and energy to the hot corona. The other type of oscillation is usually associated with the upper part of loops. They are most clearly seen in the Doppler shift of coronal lines with formation temperatures between one and two million degrees. The global wavelets of these oscillations usually peak sharply around a period in the range of three to six minutes. No obvious profile asymmetry is found and the variation of the line width is typically very small. The intensity variation is often less than 2%. These oscillations are more likely to be signatures of kink/Alfven waves rather than flows. In