Science.gov

Sample records for solar dust corona

  1. The colour of the solar corona and dust grains in it

    NASA Astrophysics Data System (ADS)

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

    1980-02-01

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

  2. The New Solar Corona

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

  3. The New Solar Corona

    NASA Astrophysics Data System (ADS)

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

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

  4. Solar corona top heating

    NASA Astrophysics Data System (ADS)

    Molotkov, I. A.; Ryabova, N. A.

    2016-05-01

    The solar magnetic field fragmentation into thin magnetic tubes above the photosphere makes it possible to transform and factorize MHD equations analytically and to obtain explicit expressions for Alfvén and magnetosonic fields. A physical model that enables an explanation of the effect of strong heating of the solar chromosphere and corona has been proposed. This model makes it possible to estimate analytically a powerful Alfvén disturbance entering the chromosphere due to convective motions of the photosphere and a thermal release due to a three-wave interaction within the chromosphere.

  5. Global Magnetohydrodynamic Modeling of the Solar Corona

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

  6. Corona solar blind ultraviolet image detecting method

    NASA Astrophysics Data System (ADS)

    Yin, Li-min; Tang, Wen-qing; Zhang, Yu

    2009-07-01

    Corona is one of important reasons of electrical energy loss in the electric power. According to incomplete statistics, corona loss electrical energy has achieved two thousands and fifty millions kW.h in our nation every year. Sometimes corona also can have some disturbance to radio and communication. Therefore to discover and examine corona promptly has the extremely vital significance for conserving energy and realizing high quality communication. Ultraviolet image detecting technology is a preferred corona detection method in electric power. It may realize all-weather reliable survey to corona. The solar blind ultraviolet signal discharged by corona is quite weak. Moreover the ultraviolet image quality has been affected seriously by the detection system noise. A corona solar blind ultraviolet image processing method is proposed in this paper. Ultraviolet image has so small target, low contrast image, district characteristic and real-time demand that it is processed by multi-scale ultraviolet morphology filter technology based on mathematics morphology in this paper. Results show that the method can stretch image contrast, enhance target and weaken noise. The algorithm is easy to deal in parallel and it can be realized easily by hardware. It will be accurately demarcated when the condition of device need to be absolutely measured. The paper proposes a kind of mathematics morphology algorithm. Solar blind ultraviolet image will be further processed according to temperature and humidity in order to remove the infection of corona discharge demarcation and solve correct demarcation question when equipment condition need to be absolutely measured.

  7. Solar Corona on 08.01.2010

    NASA Video Gallery

    The solar corona on 2010/08/01, observed by SDO’s AIA. The false colors represent images taken with different filters that are sensitive to distinct coronal temperatures: blue- 1 million degrees...

  8. Solar Corona on 10.21.2010

    NASA Video Gallery

    The solar corona on 2010/10/21, observed by SDO’s AIA. The false colors represent images taken with different filters that are sensitive to distinct coronal temperatures: blue for one million de...

  9. Global Magnetohydrodynamic Modeling of the Solar Corona

    NASA Technical Reports Server (NTRS)

    Linker, Jon A.

    1998-01-01

    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

  10. Meteoroid ablation during entry into the solar corona

    NASA Astrophysics Data System (ADS)

    Lamy, Hervé; Mann, Ingrid; Lemaire, Joseph

    2010-05-01

    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.

  11. Global Magnetohydrodynamic Modeling of the Solar Corona

    NASA Technical Reports Server (NTRS)

    Linker, Jon A.

    1997-01-01

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

  12. Meteoroids in solar corona and planetary atmospheres

    NASA Astrophysics Data System (ADS)

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

    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.

  13. Seeing the solar corona in three dimensions

    NASA Astrophysics Data System (ADS)

    Vásquez, Alberto M.

    2016-03-01

    The large availability and rich spectral coverage of today's observational data of the solar corona, and the high spatial and temporal resolution provided by many instruments, has enabled the evolution of three-dimensional (3D) physical models to a great level of detail. However, the 3D information provided by the data is rather limited as every instrument observes from a single angle of vision, or two at the most in the case of the STEREO mission. Two powerful available observational techniques to infer detailed 3D information of the solar corona from empirical data are stereoscopy and tomography. In particular, the technique known as differential emission measure tomography (DEMT) allows determination of the 3D distribution of the coronal electron density and temperature in the inner corona. This paper summarizes the main technical aspects of DEMT, reviews all published work based on it, and comments on its future development and applications.

  14. Global Magnetohydrodynamic Modeling of the Solar Corona

    NASA Technical Reports Server (NTRS)

    Linker, Jon A.

    2001-01-01

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

  15. The F and K components of the solar corona.

    NASA Technical Reports Server (NTRS)

    Calbert, R.; Beard, D. B.

    1972-01-01

    Numerical calculations of the F component are conducted for a large range of parameters, particle size distribution, minimum particle size, minimum approach to the sun, albedo, and spatial distribution. Various parametrized functional forms for the electron spatial distribution are assumed, and the parametrical elongation dependence of the K component is calculated. New and old data are analyzed by fitting the theoretical parametrized elongation dependence to observations of the total intensity of the solar corona. The orbital behavior of the dust is estimated together with the temperature and thermal emission.

  16. STOCHASTIC COUPLING OF SOLAR PHOTOSPHERE AND CORONA

    SciTech Connect

    Uritsky, Vadim M.; Ofman, Leon; Davila, Joseph M.; Coyner, Aaron J.

    2013-05-20

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

  17. Probing the Solar Corona with VLBI

    NASA Astrophysics Data System (ADS)

    Soja, Benedikt; Sun, Jing; Heinkelmann, Robert; Schuh, Harald; Böhm, Johannes

    2013-04-01

    Radio observations close to the Sun are sensitive to the dispersive effects of the Sun corona. This has been used to determine (among other parameters) the electron density in the corona during solar conjunctions with spacecrafts. Although geodetic Very Long Baseline Interferometry (VLBI) observations close to the Sun have already been performed before 2002 (but suspended afterwards) they have not yet been used for calculations of corona electron densities. Almost 10 years later the International VLBI Service for Geodesy and Astrometry (IVS) decided to schedule twelve 24 hours VLBI sessions in 2011 and 2012 including observations closer than 15 degrees to the heliocenter. Both the recent and the earlier sessions are analysed in order to determine electron densities of the Sun corona. Based on the ionospheric delay corrections derived from two-frequency VLBI measurements, other dispersive effects like instrumental biases and, most important of all, the Earth's ionosphere effects are estimated and then eliminated. The residual delays are used to successfully determine power-law parameters of the electron density of the Sun corona for several of these sessions. In some cases, scheduled observations close to the Sun had failed, making it impossible to derive meaningful results from them. Both, the successful and the lost observations were analysed including external information like Sunspot numbers and flare occurrences. The estimated electron densities were compared to previous models of the Sun corona derived by radio measurements to spacecrafts during solar conjunctions. Our investigations show that it is possible to use geodetic VLBI sessions with observations close to the Sun to determine electron densities of the corona. The success depends on the geometry, i.e. the source position with respect to the Sun, and on the schedule, which can be optimized for such investigations. Unpredictable disturbances at the Sun's surface, such as flares, play also a role. So far

  18. MASC: Magnetic Activity of the Solar Corona

    NASA Astrophysics Data System (ADS)

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

    We present MASC, an innovative payload designed to explore the magnetic activity of the solar corona. It is composed of three complementary instruments: a Hard-X-ray spectrometer, a UV / EUV imager, and a Visible Light / UV polarimetric coronagraph able to measure the coronal magnetic field. The solar corona is structured in magnetically closed and open structures from which slow and fast solar winds are respectively released. In spite of much progress brought by two decades of almost uninterrupted observations from several space missions, the sources and acceleration mechanisms of both types are still not understood. This continuous expansion of the solar atmosphere is disturbed by sporadic but frequent and violent events. Coronal mass ejections (CMEs) are large-scale massive eruptions of magnetic structures out of the corona, while solar flares trace the sudden heating of coronal plasma and the acceleration of electrons and ions to high, sometimes relativistic, energies. Both phenomena are most probably driven by instabilities of the magnetic field in the corona. The relations between flares and CMEs are still not understood in terms of initiation and energy partition between large-scale motions, small-scale heating and particle acceleration. The initiation is probably related to magnetic reconnection which itself results magnetic topological changes due to e.g. flux emergence, footpoints motions, etc. Acceleration and heating are also strongly coupled since the atmospheric heating is thought to result from the impact of accelerated particles. The measurement of both physical processes and their outputs is consequently of major importance. However, despite its fundamental importance as a driver for the physics of the Sun and of the heliosphere, the magnetic field of our star’s outer atmosphere remains poorly understood. This is due in large part to the fact that the magnetic field is a very difficult quantity to measure. Our knowledge of its strength and

  19. Nanoflare Heating of Solar and Stellar Coronae

    NASA Technical Reports Server (NTRS)

    Klimchuk, James A.

    2010-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

    1981-01-01

    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.

  1. Radio seismology of the outer solar corona

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  3. Recycling of the Solar Corona's Magnetic Field

    NASA Astrophysics Data System (ADS)

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

    2004-09-01

    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 ~3×1020 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.

  4. VARIABLE WINDS AND DUST FORMATION IN R CORONAE BOREALIS STARS

    SciTech Connect

    Clayton, Geoffrey C.; Zhang Wanshu; Geballe, T. R. E-mail: wzhan21@lsu.edu

    2013-08-01

    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.

  5. Scintillation effects on radio wave propagation through solar corona

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

    When RF waves pass through the solar corona and solar wind regions close to the Sun, strong scintillation effects appear at their amplitude, frequency and phase, especially in the regions very close to the Sun (less than 4 solar radius).

  6. RADIATIVE HEATING OF THE SOLAR CORONA

    SciTech Connect

    Moran, Thomas G.

    2011-10-20

    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.

  7. Globally propagating waves in the solar corona

    NASA Astrophysics Data System (ADS)

    Warmuth, Alexander

    2011-12-01

    High-cadence space-based observations, available for over a decade now, have revealed globally propagating wave-like disturbances in the solar corona. These coronal waves have now been imaged in a wide range of spectral channels, yielding a wealth of information. Still, no consensus on their physical nature has been reached yet. While many findings are consistent with fast-mode MHD waves and/or shocks, other characteristics have given rise to alternative models which involve magnetic reconfiguration in the framework of an erupting coronal mass ejection. In this paper, the observational signatures of coronal waves will be reviewed, and the different physical interpretations of coronal waves and how they are motivated by observations will be discussed. Finally, the potential of using coronal waves as a diagnostic tool for the corona will be shown.

  8. Green corona and solar sector structure

    NASA Technical Reports Server (NTRS)

    Antonucci, E.; Svalgaard, L.

    1974-01-01

    Analysis of the green-line corona for the interval 1947-1970 suggests the existence of large-scale organization of the emission. The green-line emission at high northern latitudes (approximately 40 to 60 deg) is correlated with the emission at high southern latitudes 6, 15, and 24 days later, while the low-latitude green corona seems to be correlated on both sides of the equator with no time lag. These coronal features are recurrent with a 27-day period at all latitudes between plus or minus 60 deg, and these large-scale structures are believed to be associated with the solar magnetic sector structure. The high correlation between northern and southern high-latitude emission at 15 days time lag is explained as a signature of a two-sector structure, while four sectors are associated with the 6- and 24-day peaks.

  9. Torsional oscillations in the solar corona

    NASA Astrophysics Data System (ADS)

    Makarov, V. I.; Tlatov, A. G.

    1997-07-01

    The dependence of the differential rotation of the solar corona on latitude and time is investigated using observations in the Fe XIV 5303 Angstrom line from 1940 to 1992. Five bands of fast and slow rotation relative to the average value are distinguished. The bands of slow rotation arise after the reversal of the polar magnetic field of the Sun and migrate toward the equator over the course of 8 to 15 years along the `butterfly' patterns of polar faculae and of the sunspots of the following cycle. The bands of fast rotation arise 5-6 years later and also migrate toward the equator parallel to the bands of slow rotation. The fastest latitude drift of the bands was observed from 1945 to 1955, and preceded the maximum of the 19th solar activity cycle (1955-1965). The amplitude of the azimuthal component of the coronal rotation relative to the mean rotation varied within 30 m/s. The equatorial drift velocity varied from 3 to 5 m/s. The latitude-time distribution of the zones with slow coronal rotation is associated with the appearance of high-latitude and middle-latitude coronal holes after the reversal of the solar polar magnetic field and during the solar activity maximum of the next sunspot cycle. The origin of the zones of anomalous rotation in the corona and their dynamics in the global activity cycle are discussed.

  10. Torsional oscillations in the solar corona

    NASA Astrophysics Data System (ADS)

    Makarov, V. I.; Tlatov, A. G.

    1997-08-01

    The dependence of the differential rotation of the solar corona on latitude and time is investigated using observations in the Fe XIV 5303 A line from 1940 to 1992. Five bands of fast and slow rotation relative to the average value are distinguished. The bands of slow rotation arise after the reversal of the polar magnetic field of the sun and migrate toward the equator over the course of eight to 15 years along the 'butterfly' patterns of polar faculae and of the sunspots of the following cycle. The bands of fast rotation arise 5-6 years later, and also migrate toward the equator parallel to the bands of slow rotation. The fastest latitude drift of the bands was observed from 1945 to 1955 and preceded the maximum of the 19th solar activity cycle (1955-1965). The amplitude of the azimuthal component of the coronal rotation relative to the mean rotation varied within +/- 30 m/s. The equatorial drift velocity varied from 3 to 5 m/s. The latitude-time distribution of the zones with slow coronal rotation is associated with the appearance of high-latitude and middle-latitude coronal holes after the reversal of the solar polar magnetic field and during the solar activity maximum of the next sunspot cycle. The origin of the zones of anomalous rotation in the corona and their dynamics in the global activity cycle are discussed.

  11. Faraday Rotation Observations of the Solar Corona

    NASA Astrophysics Data System (ADS)

    Mancuso, S.; Spangler, S. R.

    1998-05-01

    Faraday rotation measures the path integral of the product of electron density and line of sight component of the magnetic field from the observer to a source of linearly polarized radio emission. For our observations, the line of sight passes through the solar corona. These observations were made with the NRAO Very Large Array at frequencies of 1465 and 1635 MHz. Observations at two frequencies can confirm the lambda (2) dependence of position angle rotation characteristic of Faraday rotation. We observed the extended radio source 0036+030 (4C+03.01) on March 28, 1997, when the source was 8.6 Rsun from the center of the Sun. Nearly continuous observations were made over an 11 hour period. Our observations measure an average rotation measure (RM) of about +7 radians/m(2) attributable to the corona. The RM showed slow variations during the observing session, with a total change of about 3 radians/m(2) . This variation is attributed to large scale gradients and static plasma structures in the corona, and is the same for two source components separated by 30 arcseconds (22000 km). We have also detected RM variations on time scales of 15 minutes to one hour, which may be coronal Alfven waves. We measure an rms variation of 0.57 radians/m(2) for such fluctuations, which is comparable to previous reports.

  12. The Solar Corona at the 2015 Total Solar Eclipse

    NASA Astrophysics Data System (ADS)

    Pasachoff, Jay M.; Carter, Allison L.

    2015-04-01

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

  13. Dynamics and energetics of the solar corona

    NASA Technical Reports Server (NTRS)

    Steinolfson, R. S.

    1992-01-01

    The primary objective of this research program is to improve our understanding of the dynamics and energetics of the solar corona both in the quiescent dynamic equilibrium state when coronal structure is dominated by the equatorial streamer belt and in the eruptive state when coronal plasma is ejected into the interplanetary medium. Numerical solutions of the time-dependent magnetohydrodynamic (MHD) equations and comparisons of the computed results with observations form the core of the approach to achieving this objective. Some of the specific topics that have been studied are: (1) quiescent coronal streamers in an atmosphere dominated by a dipole magnetic field at large radii, (2) the formation of coronal mass ejections (CMEs) in quiescent streamers due to the emergence of new magnetic flux and due to photospheric shear motion, (3) MHD shock formation near the leading edge of CMEs, (4) coronal magnetic arcade eruption as a result of applied photospheric shear motion, and (5) the three-dimensional structure of CMEs.

  14. Untwisting magnetic fields in the solar corona

    NASA Astrophysics Data System (ADS)

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

    2012-07-01

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

  15. Exploring dynamic events in the solar corona

    NASA Astrophysics Data System (ADS)

    Downs, Cooper James

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

  16. A study of the background corona near solar minimum

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

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

  17. Solar corona/prominence seen through the White Light Coronograph

    NASA Technical Reports Server (NTRS)

    1974-01-01

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

  18. RADIO OBSERVATIONS OF THE SOLAR CORONA DURING AN ECLIPSE

    SciTech Connect

    Kathiravan, C.; Ramesh, R.; Barve, Indrajit V.; Rajalingam, M. E-mail: ramesh@iiap.res.in E-mail: rajalingam@iiap.res.in

    2011-04-01

    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.

  19. Radio Observations of the Solar Corona During an Eclipse

    NASA Astrophysics Data System (ADS)

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

    2011-04-01

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

  20. Heating of the Solar Corona: Review

    NASA Astrophysics Data System (ADS)

    Erdélyi, R.

    2005-06-01

    The heating of solar and stellar chromospheres and coronae are one of the key fundamental and yet unresolved questions of modern space and plasma physics. In spite of the multi-fold efforts spanning over half a century including the many superb technological advances and theoretical developments (both analytical and computational) the unveiling of the subtles of coronal heating still remained an exciting job for the 21st century! In the present paper I review the various popular heating mechanisms put forward in the existing extensive literature. The heating processes are, somewhat arbitrarily, classified as hydrodynamic (HD), magnetohydrodynamic (MHD) or kinetic based on the model medium. These mechanisms are further divided based on the time scales of the ultimate dissipation involved (i.e. AC and DC heating, turbulent heating). In particular, attention is paid to discuss shock dissipation, Landau damping, mode coupling, resonant absorption, phase mixing, and, reconnection. Finally, I briefly review the various observational consequences of the many proposed heating mechanisms and confront them with high-resolution ground-based and satellite data currently available.

  1. Results of observations of the dust distribution in the F-corona of the sun

    NASA Astrophysics Data System (ADS)

    Shestakova, L. I.; Demchenko, B. I.

    2016-03-01

    The results of modeling of the distribution of dust in the circumsolar zone are presented. The dust distribution was retrieved from observations of the line-of-sight velocities in the F-corona to the distances of 7-11 solar radii during the total eclipses of the Sun in different years: on July 31, 1981; August 11, 1991; March 29, 2006; and August 1, 2008. Comparison of the results has shown that the dust composition varies from year to year and the dust is dynamically nonuniform. In addition to the dust related to the zodiacal cloud and concentrating to the ecliptic plane, the dust of retrograde motion and the ejections and accretion in the polar regions are observed. From the results of observations of eclipses on July 31, 1981, August 11, 1991, and August 1, 2008, the east-west asymmetry in a sign of the line-of-sight velocities was detected: they are negative to the east of the Sun and positive to the west. Such distribution of the velocities is indicative of the nearecliptic orbital dust motion, whose direction coincides with that of the motion of the planets. In the course of the eclipse of March 29, 2006, almost no dynamical connection with the zodiacal cloud was found. At the same time, the direction, where the observed velocities are largest in value and opposite in sign on opposite sides of the Sun, was determined, which provides evidence of the orbital motion deviating from the ecliptic plane. The results of observations in 2006 reveal a clear genetic connection of the observed orbital motion of dust with the parent comets of the Kreutz family found near the Sun close to the eclipse date. The velocities observed near the symmetry line in the plane of the sky grow by absolute value with increasing the elongation, which may take place, if the line of sight croßses an empty zone that is free of dust. The modeling of the data of observations near the symmetry plane allowed the parameters of the dust distribution near the sublimation zone to be obtained. In

  2. Peculiarities of propagation of charged particles in solar corona

    NASA Technical Reports Server (NTRS)

    Pisarenko, N. F.; Mikryukova, N. A.; Shafer, Y. G.; Morozova, E. I.; Klimenko, V. V.; Timofeev, V. E.

    1985-01-01

    The influence of boundaries of the large scale unipolar magnetic regions (UMR) on the Sun upon the charged particle propagation in the solar corona and interplanetary space is investigated. Increases of the charged particle fluxes from solar flares on November 4 and 20, 1978 detected by Venera-11 and Prognoz-1 and on December 7, 1982 by Venera-13 and "GMS-2" were analyzed.

  3. Topological Structure of the Magnetic Solar Corona

    NASA Astrophysics Data System (ADS)

    Maclean, R. C.

    2007-12-01

    The solar corona is a highly complex and active plasma environment, containing many exotic phenomena such as solar flares, coronal mass ejections, prominences, coronal loops, and bright points. The fundamental element giving coherence to all this apparent diversity is the strong coronal magnetic field, the dominant force shaping the plasma there. In this thesis, I model the 3D magnetic fields of various coronal features using the techniques of magnetic charge topology (MCT) in a potential field. Often the real coronal field has departures from its potential state, but these are so small that the potential field method is accurate enough to pick out the essential information about the structure and evolution of the magnetic field. First I perform a topological analysis of the magnetic breakout model for an eruptive solar flare. Breakout is represented by a topological bifurcation that allows initially enclosed flux from the newly emerging region in my MCT model of a delta sunspot to reconnect out to large distances. I produce bifurcation diagrams showing how this behaviour can be caused by changing the strength or position of the emerging flux source, or the force-free parameter α. I also apply MCT techniques to observational data of a coronal bright point, and compare the results to 3D numerical MHD simulations of the effects of rotating the sources that underlie the bright point. The separatrix surfaces that surround each rotating source are found to correspond to locations of high parallel electric field in the simulations, which is a signature of magnetic reconnection. The large-scale topological structure of the magnetic field is robust to changes in the method of deriving point magnetic sources from the magnetogram. Next, I use a Green's function expression for the magnetic field to relax the standard topological assumption of a flat photosphere and extend the concept of MCT into a spherical geometry, enabling it to be applied to the entire global coronal

  4. The magnetic field structure in the active solar corona.

    NASA Technical Reports Server (NTRS)

    Schatten, K. H.

    1971-01-01

    The structure of the magnetic field of the active solar corona is discussed with reference to optical and radio observations of the solar atmosphere. Eclipse observations provide evidence of fine scale structures in the solar atmosphere that appear to relate to the coronal magnetic field. The coronal magnetic field used for comparison is calculated from potential theory; the influence of solar activity upon the potential theory field is discussed with reference to observations of the Faraday rotation of a microwave signal from Pioneer 6 as it was occulted by the solar atmosphere. Evidence has been found suggesting the existence of expanding magnetic bottles located at 10 solar radii above flaring active regions. The dynamics of these events is discussed. It is further suggested that these magnetic bottles are an important component in the solar corona.

  5. Patchy reconnection in the solar corona

    NASA Astrophysics Data System (ADS)

    Guidoni, Silvina Esther

    2011-05-01

    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

  6. THE 2008 AUGUST 1 ECLIPSE SOLAR-MINIMUM CORONA UNRAVELED

    SciTech Connect

    Pasachoff, J. M.; Rusin, V.; Saniga, M.; Minarovjech, M.; Druckmueller, M.; Aniol, P.

    2009-09-10

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

  7. HIGH SPATIAL RESOLUTION OBSERVATIONS OF LOOPS IN THE SOLAR CORONA

    SciTech Connect

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

    2013-08-01

    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.

  8. Probing the solar corona with very long baseline interferometry

    PubMed Central

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

    2014-01-01

    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

  9. Probing the solar corona with very long baseline interferometry

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

    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.

  10. Probing the solar corona with very long baseline interferometry.

    PubMed

    Soja, B; Heinkelmann, R; Schuh, H

    2014-01-01

    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

  11. A theory of heating of quiet solar corona

    SciTech Connect

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

    2015-03-15

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

  12. A theory of heating of quiet solar corona

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  13. Modeling the multi-ion structure of the solar corona

    NASA Astrophysics Data System (ADS)

    Ofman, Leon; Provornikova, Elena; Wang, Tongjiang

    2014-06-01

    The solar corona is typically observed in EUV by SDO/AIA and other instruments using the heavy ion emission lines such as Fe IX, Fe XII, and other ion emission lines. However, the relative (to protons) abundance of the emitting ions is very low and the collisional coupling between the Fe ions and electrons decreases rapidly with height in the low corona, while gravitational settling may become significant in quiescent long-lived magnetic structures, such as streamers. Thus, the structure of the weakly collisional solar corona imaged in Fe IX (and other heavy ions) may differ significantly from the structure of the main electron-proton constituents of the corona. The electron structure is observed by white light coronagraphs, and during solar eclipses in the low corona. I present the results of multi-fluid modeling of coronal streamers and other magnetic structures that demonstrate the effects of weak coupling between the heavy ions and the coronal electron-proton components, and show that the multi-ion coronal structure must be taken into account in interpretation of EUV observations.

  14. Element Abundances in Solar Energetic Particles and the Solar Corona

    NASA Astrophysics Data System (ADS)

    Reames, Donald V.

    2014-03-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Cirtain, Jonathan Wesley

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

  16. Imaging and Processing Images of the Solar Corona

    NASA Astrophysics Data System (ADS)

    Espenak, Fred

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

  17. Modeling Jets in the Corona and Solar Wind

    NASA Astrophysics Data System (ADS)

    Torok, Tibor; Lionello, Roberto; Titov, Viacheslav S.; Leake, James E.; Mikic, Zoran; Linker, Jon A.; Linton, Mark G.

    2016-04-01

    Coronal jets are transient, collimated eruptions that occur in regions of open or semi-open magnetic fields in the solar corona. Our understanding of these events has significantly improved in recent years, owing to improved observational capabilities and numerical simulations. Yet, several important questions concerning coronal jets remain largely unanswered. For example: What exactly are the physical mechanisms that heat and accelerate the plasma? And to what extent do jets contribute to the heating of the corona and in providing mass and energy to the fast solar wind? Here we present a "new generation" of coronal-jet simulations that will allow us to address such questions in more detail than before. In contrast to previous simulations, our code models the large-scale corona in a spherical domain, uses an advanced description of the energy transfer in the corona ("thermodynamic MHD"), and includes the solar wind. As a first application, we consider a purely radial coronal magnetic field and a simple coronal heating function that decreases exponentially with height above the surface. We produce so-called standard and blowout jets by continuously driving the system at the lower boundary with data extracted from flux-emergence simulations. We discuss the formation, dynamics, and evolution of the jets, as well as their contribution to coronal heating and the solar wind.

  18. New Views of the Solar Corona from STEREO and SDO

    NASA Astrophysics Data System (ADS)

    Vourlidas, A.

    2012-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

  20. New Synoptic Maps of the Solar Corona from UVCS Observations

    NASA Astrophysics Data System (ADS)

    Strachan, L.; Panasyuk, A. V.; Miralles, M.; Kohl, J. L.; Baham, M.

    2005-05-01

    We present for the first time synoptic maps of the extended solar corona (r/Ro > 1.5) based on eight years of data from the SOHO Ultraviolet Coronagraph Spectrometer (UVCS). The data reveal the changes in the physical properties of the large scale features in the corona. Maps of O VI line intensities, line widths, and line ratios for the O VI 1032/1037 doublet and intensities and line widths for the H I Ly-alpha line reveal information about the evolution of coronal densities, temperatures, and outflow velocities over the solar cycle. In particular these data are used in support of program to understand the solar cycle variation of coronal holes and coronal streamers. This work is supported by NASA Grant NAG5-12781 to the Smithsonian Astrophysical Observatory and NASA subcontract OGSP21010200061SAO awarded to SAO through a grant to Southern Universty at Baton Rouge.

  1. Heating of the Solar Corona and its Loops

    NASA Technical Reports Server (NTRS)

    Klimchuk, James A.

    2009-01-01

    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.

  2. Measuring the IR solar corona during the 2017 eclipse

    NASA Astrophysics Data System (ADS)

    Bryans, Paul; Hannigan, James; Philip, Judge; Larson, Brandon; Sewell, Scott; McIntire, Lauren

    2016-05-01

    On 21 August 2017 a total solar eclipse will pass across the continental United States, offering a unique opportunity to conduct scientific research of the solar atmosphere. With the light from the Sun eclipsed, the solar corona becomes visible in a way not possible when swamped by the light from the photosphere. The infrared (IR) spectrum of the corona, in particular, is predicted to contain some of the most magnetically sensitive spectral lines. However, no comprehensive survey of this spectral range has been carried out to date. Here, we describe a Fourier Transform Spectrometer, currently under construction at NCAR, to measure the IR spectrum from 2 to 12 microns. We will discuss the operation of the experiment, which will be deployed along the path of totality in Wyoming, and the scientific results we hope to obtain.

  3. Plasma Compression in Magnetic Reconnection Regions in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Provornikova, E.; Laming, J. M.; Lukin, V. S.

    2016-07-01

    It has been proposed that particles bouncing between magnetized flows converging in a reconnection region can be accelerated by the first-order Fermi mechanism. Analytical considerations of this mechanism have shown that the spectral index of accelerated particles is related to the total plasma compression within the reconnection region, similarly to the case of the diffusive shock acceleration mechanism. As a first step to investigate the efficiency of Fermi acceleration in reconnection regions in producing hard energy spectra of particles in the solar corona, we explore the degree of plasma compression that can be achieved at reconnection sites. In particular, we aim to determine the conditions for the strong compressions to form. Using a two-dimensional resistive MHD numerical model, we consider a set of magnetic field configurations where magnetic reconnection can occur, including a Harris current sheet, a force-free current sheet, and two merging flux ropes. Plasma parameters are taken to be characteristic of the solar corona. Numerical simulations show that strong plasma compressions (≥4) in the reconnection regions can form when the plasma heating due to reconnection is efficiently removed by fast thermal conduction or the radiative cooling process. The radiative cooling process that is negligible in the typical 1 MK corona can play an important role in the low corona/transition region. It is found that plasma compression is expected to be strongest in low-beta plasma β ˜ 0.01–0.07 at reconnection magnetic nulls.

  4. OBSERVATION OF ULTRAFINE CHANNELS OF SOLAR CORONA HEATING

    SciTech Connect

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

    2012-05-01

    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.

  5. The Structure and Dynamics of the Solar Corona

    NASA Technical Reports Server (NTRS)

    Mikic, Zoran

    2000-01-01

    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.

  6. The Structure and Dynamics of the Solar Corona

    NASA Astrophysics Data System (ADS)

    Mikic, Zoran

    2000-03-01

    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.

  7. Observational capabilities of solar satellite "Coronas-Photon"

    NASA Astrophysics Data System (ADS)

    Kotov, Yu.

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

  8. The Structure and Dynamics of the Solar Corona

    NASA Technical Reports Server (NTRS)

    Mikic, Zoran

    1998-01-01

    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.

  9. The Structure and Dynamics of the Solar Corona

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

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

    SciTech Connect

    McIntosh, Scott W.; De Pontieu, Bart

    2012-12-20

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

  11. Magnetic tornadoes as energy channels into the solar corona.

    PubMed

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

    2012-06-28

    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

  12. Energy distribution of nanoflares in the quiet solar corona

    NASA Astrophysics Data System (ADS)

    Ulyanov, Artyom

    2012-07-01

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

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

    SciTech Connect

    Schmelz, J. T.; Reames, D. V.; Von Steiger, R.; Basu, S.

    2012-08-10

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

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

    NASA Technical Reports Server (NTRS)

    Svalgaard, L.; Wilcox, J. M.

    1978-01-01

    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 interplanetary magnetic field, coronal holes, geomagnetic activity, cosmic rays, and polar fields of the sun. It is pointed out that the present understanding of coronal and interplanetary morphology is based on data acquired during the descending part and the minimum of the considered sunspot cycle.

  15. Particle acceleration processes in the solar corona

    NASA Astrophysics Data System (ADS)

    Melrose, D. B.

    A review is presented of some theoretical ideas on particle acceleration associated with solar flares. Various acceleration mechanisms are discussed, including forms of stochastic acceleration, shock drift acceleration, resonant acceleration, diffusive acceleration at shock fronts, acceleration during magnetic reconnection, and acceleration by parallel electric fields in double layers or electrostatic shocks. Particular attention is given to first phase acceleration of electrons in solar flares, which is usually attributed to bulk energization of electrons. It is proposed that the dissipation cannot be due to classical resistivity and entails anomalous resistivity or hyperresistivity, such as in multiple double layers. A model is developed for bulk energization due to the continual formation and decay of weak double layers.

  16. Release timescales of solar energetic particles in the low corona

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    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.

  17. Basic results of the CORONAS-F solar observations

    NASA Astrophysics Data System (ADS)

    Kuznetsov, V. D.

    2006-08-01

    142190 Troitsk, Moscow Region, Russia V.D. Kuznetsov N.V.Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Troitsk, Russia The report contains a review of the basic results of the CORONAS-F solar observations during the period of orbital operation of the satellite (from July 31, 2001 to December 6, 2005). Basic results are related with helioseismic observations of the Sun, with localization and study of the morphology of numerous active phenomena in the Sun, including the outstanding events in the declining phase of the solar cycle; with spectroscopic diagnostics of the coronal and flare-generated plasma; with the study of the atomic and nuclear processes in solar flares; with detection of the fluxes of solar cosmic rays, gamma-rays, and neutrons from the major flares reaching the Earth's orbit.

  18. Imaging the Transition from Corona to Solar Wind

    NASA Astrophysics Data System (ADS)

    DeForest, Craig; Howard, Tim A.; Howard, Russell A.; Tenerani, Anna

    2016-05-01

    The region around the Alfvén surface -- the last frontier of the solar system -- is largely unexplored, mostly because of the difficulty of detecting the surface itself. Many important transitions happen between the mid-to-outer corona and the innermost heliosphere, including: the transition to superAlfvénic flow; the transition from structured, highly anisotropic structure to nearly isotropic turbulent structures; and the formation of identifiable, separable fast and slow wind streams. We will report new results from two recent imaging campaigns -- one with STEREO and one with SOHO/LASCO (coincidentally performed on the 20th anniversary of the first SOHO campaign) -- to explore and image the transition to turbulent flow and the outer boundary of the corona.

  19. Solar Cycle Variations of O VI and H I Lyman Alpha Intensities in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Miralles, M. P.; Panasyuk, A. V.; Strachan, L.; Gardner, L. D.; Suleiman, R. M.; Smith, P. L.; Kohl, J. L.

    2000-05-01

    UVCS/SOHO measurements of O VI (103.2 and 103.7 nm) and H I Lyman alpha intensities in the solar corona have been made from 1996 to the present spanning the rising phase of cycle 23. During solar minimum the corona consisted of large coronal holes at the poles and quiescent streamers at the equator. During the ascending phase of the cycle, the corona presented high latitude streamers and finally polar streamers as the Sun approached solar maximum. Recent observations of the solar corona show the presence of coronal holes at the equator and streamers at the poles. Our observations provide descriptions of these structures over the rising phase of the solar cycle. We compare the properties of quiescent equatorial streamers which occurred at solar minimum to high latitude and polar streamers observed toward solar maximum. We also compare solar minimum polar coronal holes to equatorial coronal holes present at solar maximum. We discuss how these results are related to the plasma properties. This work is supported by NASA under Grant NAG5-7822 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency and by PRODEX (Swiss contribution).

  20. RGB color photometry of the solar corona from total solar eclipses

    NASA Astrophysics Data System (ADS)

    Shopov, Y. Y.; Varonov, A.; Stoykova, D. A.

    2016-02-01

    In the following article we present some of our results from observations of two total solar eclipses (TSE). By combining appropriate photographic equipment and post-processing techniques we show that numerous solar phenomena can be captured in details during TSE. We use color slide RGB photometry technique to visualize invisible regions of the solar corona and to highlight some of the solar phenomena that are very difficult for observation by Earth-based observatories. In fact it reveals more details of the far solar corona than any original image taken from ground-based observations. RGB photometry visualizes different components of the solar corona in one image, which is impossible using conventional observations. This makes it valuable tool for studies of the solar corona. Here we first observe peculiar near infrared emission regions around the upper part of the solar limb during the 1999 TSE. So far its origin is unknown and they need further studies including observations during other solar eclipses. Our observational experiment was designed for other purposes and their registration was completely unexpected.

  1. Solar Activity in the Green Corona Over Cycle 23

    NASA Astrophysics Data System (ADS)

    Rušin, V.

    2006-12-01

    The intensity of the green coronal line (5303Å, Fe {\\sc xiv), which is directly proportional to the electron density as well as the temperature of the corona, is a good and sensitive indicator of the reflection of the photospheric activity in the emission corona, mapping also the evolution of the magnetic fields in the active regions on the solar surface. In cycle 23 (1996 -2007), the average intensity of the green corona was of about 30% less when compared with that of the preceding cycle; this, however, does not necessarily imply a lower temperature of the corona, but rather a smaller number of active regions and/or smaller strength of local magnetic fields in the latter. The maximum of the intensity of the green corona was observed in August 2001, preceding for about one and a half year that of sunspot number. Moreover, the increased intensities were not observed continuously in time and heliographic latitude, but rather in particular latitudes, with a slight time-lag between the north and south hemispheres. It is well known that a time-latitudinal distribution of the intensity of the green corona features two kinds of large-scale motions. The first is the so-called polar branch, which separates from the "main flow" in the middle latitudes in the cycle minimum, lasts for about 3 -4 years and disappears at the time of the maxima of solar activity near the poles. The other is the equatorial (or principal) branch, which after separation in middle-latitudes moves first towards the poles, then roughly 2 years after the polar branch reached the poles makes a U-turn at upper heliographic latitudes of ±70 degrees, and migrates towards the equator where it disappears in the next minimum; the life-time of this branch is about 18 years. Given the time of the splitting of the two branches, we can guess the time of the maximum and minimum of the forthcoming cycle - cycle 24: the corresponding numbers are 2011 and 2012.5 for the time of the "double" maximum and 2019 for

  2. The EUV Emission in Comet-Solar Corona Interactions

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

    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.

  3. Diagnosing the Prominence-Cavity Connection in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Schmit, D. J.

    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 χ2 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

  4. Solar Corona Simulation Model With Positivity-preserving Property

    NASA Astrophysics Data System (ADS)

    Feng, X. S.

    2015-12-01

    Positivity-preserving is one of crucial problems in solar corona simulation. In such numerical simulation of low plasma β region, keeping density and pressure is a first of all matter to obtain physical sound solution. In the present paper, we utilize the maximum-principle-preserving flux limiting technique to develop a class of second order positivity-preserving Godunov finite volume HLL methods for the solar wind plasma MHD equations. Based on the underlying first order building block of positivity preserving Lax-Friedrichs, our schemes, under the constrained transport (CT) and generalized Lagrange multiplier (GLM) framework, can achieve high order accuracy, a discrete divergence-free condition and positivity of the numerical solution simultaneously without extra CFL constraints. Numerical results in four Carrington rotation during the declining, rising, minimum and maximum solar activity phases are provided to demonstrate the performance of modeling small plasma beta with positivity-preserving property of the proposed method.

  5. Exploring the prominence-corona connection and its expansion into the outer corona using total solar eclipse observations

    SciTech Connect

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

    2014-10-01

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

  6. Numerical Simulations of Helicity Condensation in the Solar Corona

    NASA Technical Reports Server (NTRS)

    Zhao, L.; DeVore, C. R.; Antiochos, S. K.; Zurbuchen, T. H.

    2015-01-01

    The helicity condensation model has been proposed by Antiochos (2013) to explain the observed smoothness of coronal loops and the observed buildup of magnetic shear at filament channels. The basic hypothesis of the model is that magnetic reconnection in the corona causes the magnetic stress injected by photospheric motions to collect only at those special locations where prominences form. In this work we present the first detailed quantitative MHD simulations of the reconnection evolution proposed by the helicity condensation model. We use the well-known ansatz of modeling the closed corona as an initially uniform field between two horizontal photospheric plates. The system is driven by applying photospheric rotational flows that inject magnetic helicity into the system. The flows are confined to a finite region on the photosphere so as to mimic the finite flux system of, for example, a bipolar active region. The calculations demonstrate that, contrary to common belief, coronal loops having opposite helicity do not reconnect, whereas loops having the same sense of helicity do reconnect. Furthermore, we find that for a given amount of helicity injected into the corona, the evolution of the magnetic shear is insensitive to whether the pattern of driving photospheric motions is fixed or quasi-random. In all cases, the shear propagates via reconnection to the boundary of the flow region while the total magnetic helicity is conserved, as predicted by the model. We discuss the implications of our results for solar observations and for future, more realistic simulations of the helicity condensation process.

  7. 3- and 5- Minute Oscillatory Behavior in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Calabro, Brandon; McAteer, James; Pevtsov, Alexander

    2011-10-01

    We study the spatially- and temporally-localized oscillatory behavior of the solar corona using a 6-hour sequence of narrowband 171A (extreme ultraviolet) image from the SWAP instrument onboard Proba2. We use a Morlet wavelet transform to extract oscillation parameters from the temporal evolution of emission in each pixel and study the variation in space and time of oscillatory power in the 3- and 5-minute band. We extract and compare these parameters between active Sun, quiet Sun and coronal hole regions. In each region of the corona studied the 5-minute periodicity is more prevalent than the 3-minute periodicity by a factor of 2--3. All areas of the corona exhibit a similar temporal behavior in the 5-minute band, suggesting a global driving mechanism. However, the dominance of the 5-minute periodicity is stronger in active regions than in other areas of the Sun. The 3-minute periodicity in active regions tends to be localized in the sunspot umbra, whereas the 5-minute is more prevalent in the penumbra.

  8. Solar-Panel Dust Accumulation and Cleanings

    NASA Technical Reports Server (NTRS)

    2005-01-01

    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.

  9. The Structure and Dynamics of the Solar Corona

    NASA Technical Reports Server (NTRS)

    Mikic, Zoran

    1998-01-01

    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.

  10. The Structure and Dynamics of the Solar Corona

    NASA Astrophysics Data System (ADS)

    Mikic, Zoran

    1998-06-01

    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.

  11. Numerical Simulations of Helicity Condensation in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Zhao, L.; DeVore, C. R.; Antiochos, S. K.; Zurbuchen, T. H.

    2015-05-01

    The helicity condensation model has been proposed by Antiochos to explain the observed smoothness of coronal loops and the observed buildup of magnetic shear at filament channels. The basic hypothesis of the model is that magnetic reconnection in the corona causes the magnetic stress injected by photospheric motions to collect only at those special locations where prominences are observed to form. In this work we present the first detailed quantitative MHD simulations of the reconnection evolution proposed by the helicity condensation model. We use the well-known ansatz of modeling the closed corona as an initially uniform field between two horizontal photospheric plates. The system is driven by applying photospheric rotational flows that inject magnetic helicity into the corona. The flows are confined to a finite region on the photosphere so as to mimic the finite flux system of a bipolar active region, for example. The calculations demonstrate that, contrary to common belief, opposite helicity twists do not lead to significant reconnection in such a coronal system, whereas twists with the same sense of helicity do produce substantial reconnection. Furthermore, we find that for a given amount of helicity injected into the corona, the evolution of the magnetic shear is insensitive to whether the pattern of driving photospheric motions is fixed or quasi-random. In all cases, the shear propagates via reconnection to the boundary of the flow region while the total magnetic helicity is conserved, as predicted by the model. We discuss the implications of our results for solar observations and for future, more realistic simulations of the helicity condensation process.

  12. Solar Cycle 23: Variation of the Solar Corona in the Ultraviolet from Solar Minimum to Solar Maximum

    NASA Astrophysics Data System (ADS)

    Miralles, M. P.; Panasyuk, A. V.; Strachan, L.; Gardner, L. D.; Suleiman, R.; Cranmer, S. R.; Kohl, J. L.

    2001-06-01

    UVCS/SOHO measurements of H I Ly-alpha and O VI (103.2 nm and 103.7 nm) intensities in the solar corona have been made from solar Cycle 23's minimum in 1996 to its current maximum. At solar minimum, the corona consisted of large coronal holes at the poles and quiescent streamers at the equator. During the approach to solar maximum, equatorial coronal holes and high latitude streamers became more conspicuous. Recently, coronal holes at higher latitudes have reappeared, allowing a comparison to be made of O VI intensities and line widths of coronal holes at different latitudes. We also characterize the variation of coronal hole properties with height, and location over the solar cycle. This work is supported by NASA under Grant NAG5-10093 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency and by PRODEX (Swiss contribution)

  13. Faraday Rotation Probing of the Solar Corona in 1997

    NASA Astrophysics Data System (ADS)

    Mancuso, S.; Spangler, S. R.

    1999-05-01

    Faraday rotation observations of polarized radiation from natural radio sources yield a unique diagnostic of the coronal magnetic field and electron density at heliocentric distances not reached by spacecraft. Dual frequency polarization measurements yield the rotation measure, which is proportional to int n_e vec {B} * ds, where n_e is the electron density, vec {B} is the magnetic field, and the integral is along the line of sight. We made linear polarization observations with the NRAO Very Large Array of several polarized radio sources occulted by the solar corona. The observations were made at frequencies of 1465 and 1665 MHz on four days in May, 1997. The observations cover a full solar rotation and sample solar elongations ranging from about 5 to 14 solar radii. The magnitudes of the rotation measures observed range from 11 to less than 1 radians/m(2) . We attribute the relatively low values for the rotation measures to the magnetohydrodynamic state of the corona at the time of the observations. The coronal magnetic field was quasi-dipolar with the lines of sight to the sources generally not crossing sector boundaries. The highest plasma density was at the streamer belt at low latitudes, which was missed by many of the lines of sight. The largest rotation measure was observed for the source 3C79 on May 11, 1997, and corresponds to a case in which the line of sight passed through the streamer belt at small solar elongation. This research was supported by grant ATM96-16721 from the National Science Foundation.

  14. Globally propagating waves in the solar corona -an introduction

    NASA Astrophysics Data System (ADS)

    Warmuth, Alexander

    Globally propagating wave-like disturbances have been observed in the solar chromosphere since the 1960s. These "Moreton waves" were interpreted as the ground tracks of dome-shaped waves that expand through the corona and sweep over the chromosphere. However, only the recent decade has seen detailed analysis of these phenomena, prompted by the availability of coronal imaging data from numerous spaced-based instruments, most famously SOHO/EIT. Globally propagating coronal waves have now been observed in a wide range of spectral channels, yielding a wealth of information. Still, no consensus on their physical nature has been reached. While many findings have supported the "classical" interpretation of the disturbances -fast-mode MHD waves which are propagating in the solar corona and which may be shocked -other characteristics have given rise to alternative models which involve magnetic reconfiguration in the framework of a CME eruption. I will review the different observational signatures of coronal waves, as well as associated phenomena such as metric type II radio bursts. Furthermore, I will discuss the different physical interpretations of coronal waves and how they are supported by observations. Finally, I will consider how some of the lingering controversies might be resolved by observations.

  15. Corongraphic Observations and Analyses of The Ultraviolet Solar Corona

    NASA Technical Reports Server (NTRS)

    Kohl, John L.

    2000-01-01

    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.

  16. Radiative transfer of X-rays in the solar corona

    NASA Technical Reports Server (NTRS)

    Acton, L. W.

    1978-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

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

  18. A study of acoustic heating and forced convection in the solar corona

    NASA Technical Reports Server (NTRS)

    Foukal, P. V.

    1980-01-01

    The S055 EUV spectra was used to perform emission measure and line intensity ratio analyses of loop plasma conditions in a study on the thermodynamics of magnetic loops in the solar corona. The evidence that loops contain plasma hotter than the background corona, and thus, require enhanced local dissipation of magnetic or mechanical energy is discussed. The S055 EUV raster pictures were used to study physical conditions in cool ultraviolet absorbing clouds in the solar corona, and optical data were used to derive constraints on the dimension, time scales and optical depths in dark opaque clouds not seen in H alpha and CaK as filaments or prominences. Theoretical modelling of propagation of magnetically guided acoustic shocks in the solar chromosphere finds it still unlikely that high frequency acoustic shocks could reach the solar corona. Dynamic modelling of spicules shows that such guided slow mode shocks can explain the acceleration of cool spicular material seen high in the corona.

  19. Constant cross section of loops in the solar corona

    NASA Astrophysics Data System (ADS)

    Peter, H.; Bingert, S.

    2012-12-01

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

  20. RADIO OBSERVATIONS OF WEAK ENERGY RELEASES IN THE SOLAR CORONA

    SciTech Connect

    Ramesh, R.; Kathiravan, C.; Barve, Indrajit V.; Beeharry, G. K.; Rajasekara, G. N.

    2010-08-10

    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.

  1. Observation of the corona between 1-2 solar radii at the total solar eclipses

    NASA Astrophysics Data System (ADS)

    Hanaoka, Yoichiro

    2016-07-01

    The observation of the solar corona is now being carried out extensively with spaceborne instruments, but there is a blank gap of the height coverage of the current instruments; the corona between 1-2 Rsun is difficult to be observed. However, this height range is crucially important to understand the initiation of coronal mass ejections (CMEs). At present, solar eclipses are the best chance to observe this height range (and beyond) with a wide dynamic range and a high signal-to-noise ratio. We have carried out white-light imaging observations of the corona at solar eclipses and obtained coronal images seamlessly combining the eclipse observations and the observations with space instruments such as the LASCO of the SOHO. Particularly, at the total solar eclipse on 13 November 2012, we found manifestations of CMEs in their initial phase in the height range of 1-2 Rsun. Continuous observations of the corona including the height range 1-2 Rsun in addition to those with the current spaceborne instruments are very important to observe the initial state of the CMEs, and the eclipse observation is a pathfinder for future space observations which fill the blank gap.

  2. R Coronae Borealis Stars Are Viable Factories of Pre-solar Grains

    NASA Astrophysics Data System (ADS)

    Karakas, Amanda I.; Ruiter, Ashley J.; Hampel, Melanie

    2015-08-01

    We present a new theoretical estimate for the birthrate of R Coronae Borealis (RCB) stars that is in agreement with recent observational data. We find the current Galactic birthrate of RCB stars to be ≈25% of the Galactic rate of Type Ia supernovae, assuming that RCB stars are formed through the merger of carbon-oxygen and helium-rich white dwarfs. Our new RCB birthrate (1.8 × 10-3 yr-1) is a factor of 10 lower than previous theoretical estimates. This results in roughly 180-540 RCB stars in the Galaxy, depending on the RCB lifetime. From the theoretical and observational estimates, we calculate the total dust production from RCB stars and compare this rate to dust production from novae and born-again asymptotic giant branch (AGB) stars. We find that the amount of dust produced by RCB stars is comparable to the amounts produced by novae or born-again post-AGB stars, indicating that these merger objects are a viable source of carbonaceous pre-solar grains in the Galaxy. There are graphite grains with carbon and oxygen isotopic ratios consistent with the observed composition of RCB stars, adding weight to the suggestion that these rare objects are a source of stardust grains.

  3. Milli-Arcsecond Imaging of the Solar Corona

    NASA Astrophysics Data System (ADS)

    Davila, Joseph; Kamalabadi, Farzad; Oktem, Figen S.

    2016-07-01

    Dissipation in the solar corona is believed to occur in extremely thin current sheets of order 1-100 km. Emission from these hot but thin current sheets is visible in coronal EUV emission lines, however, this spatial scale is unresolved in existing imaging instruments. Conventional optics cannot be easily manufactured with sufficient surface figure accuracy to obtain the required resolution. A photon sieve, a diffractive imaging element similar to a Fresnel zone plate, can be manufactured to provide a few milli-arcsec (mas) resolution, with much more relaxed tolerances than conventional imaging technology. Images from photon sieves will not only show the structure of the corona at a resolution never before obtained, they will also allow a study of the temperature structure in the dissipation region. Several photon sieves have been designed, fabricated, and tested by us at Goddard Space Flight Center. To fully exploit the potential of these devices two new technologies, (1) formation flying and (2) computational image deconvolution must be used. Recent progress on photon sieve development as well as these issues will be discussed. A simple design for a sounding rocket payload is presented that obtains 80 mas (0.080 arcsec) imaging with a 100 mm diameter photon sieve to image Fe XIV 334 and Fe XVI 335 which would provide a demonstration of this technology.

  4. Milli-Arcsecond (MAS) Imaging of the Solar Corona

    NASA Astrophysics Data System (ADS)

    Davila, Joseph M.; Oktem, Figen S.; Kamalabadi, Farzad; O'Neill, John; Novo-Gradac, Anne-Marie; Daw, Adrian N.; Rabin, Douglas M.

    2016-05-01

    Dissipation in the solar corona is believed to occur in extremely thin current sheets of order 1-100 km. Emission from these hot but thin current sheets should be visible in coronal EUV emission lines. However, this spatial scale is far below the resolution of existing imaging instruments, so these dissipation sites have never been observed individually. Conventional optics cannot be manufactured with sufficient surface figure accuracy to obtain the required spatial resolution in the extreme-ultraviolet where these hot plasmas radiate. A photon sieve, a diffractive imaging element similar to a Fresnel zone plate, can be manufactured to provide a few milli-arcsec (MAS) resolution, with much more readily achievable tolerances than with conventional imaging technology. Prototype photon sieve elements have been fabricated and tested in the laboratory. A full-scale ultra-high resolution instrument will require formation flying and computational image deconvolution. Significant progress has been made in overcoming these challenges, and some recent results in these areas are discussed. A simple design for a sounding rocket concept demonstration payload is presented that obtains 80 MAS (0.080 arcsec) imaging with a 100 mm diameter photon sieve to image Fe XIV 334 and Fe XVI 335. These images will show the structure of the corona at a resolution never before obtained, and they will also allow a study of the temperature structure in the dissipation region.

  5. Solar system exposure histories of interplanetary dust particles

    NASA Technical Reports Server (NTRS)

    Nier, Alfred O.

    1994-01-01

    The topics discussed include the following: stratospheric collection of interplanetary dust particles (IDP's); sources of interplanetary dust particles; and solar wind and noble gas isotopic ratios in IDP's.

  6. The MiniMax24 corona at the November 14, 2012 total solar eclipse in Australia

    NASA Astrophysics Data System (ADS)

    Stoeva, Penka; Kuzin, Sergey; Benev, Boyan; Stoev, Alexey

    We discuss the results from observations of the white-light corona conducted half a year before the MiniMax24, during the November 14, 2012 total solar eclipse in Australia, in the region of Mount Molloy, 150km from Palm Cove, Cairns, Queensland. WL images show the continuum K-corona that result from scattering of photospheric light by electrons in the corona. Solar corona was observed with 300 mm objective and 2000 mm Macsutov-Cassegrain telescope. Photos were made with different exposures in order to obtain high-resolution composite image of the white light corona, which allows us to reveal its small- and large-scale structures. The eclipse observations were compared with near-simultaneous SOHO EUV and SOHO LASCO visible-light coronagraphic images. Analysis of the Ludendorf flattening index (0.024) and phase of the solar cycle (+0.87) shows that white light corona is solar maximum type - the shape is spherical with many streamers located at all azimuths around the occulted disk. Observations of the November 14, 2012 total solar eclipse give us the possibility to investigate solar corona structure during this unique minimal maximum of the solar activity cycle and compare it with previous eclipse observations during maximum.

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

    NASA Astrophysics Data System (ADS)

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

    2012-05-01

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

  8. Creation of current filaments in the solar corona

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

    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.

  9. Clementine Observes the Moon, Solar Corona, and Venus

    NASA Technical Reports Server (NTRS)

    1997-01-01

    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.

  10. Magnetic loops, downflows, and convection in the solar corona

    NASA Technical Reports Server (NTRS)

    Foukal, P.

    1978-01-01

    Optical and extreme-ultraviolet observations of solar loop structures show that flows of cool plasma from condensations near the loop apex are a common property of loops associated with radiations whose maximum temperature is greater than approximately 7000 K and less than approximately 3,000,000 K. It is suggested that the mass balance of these structures indicates reconnection by means of plasma motion across field lines under rather general circumstances (not only after flares). It is shown that the cool material has lower gas pressure than the surrounding coronal medium. The density structure of the bright extreme ultraviolet loops suggests that downflows of cool gas result from isobaric condensation of plasma that is either out of thermal equilibrium with the local energy deposition rate into the corona, or is thermally unstable. The evidence is thought to indicate that magnetic fields act to induce a pattern of forced convection.

  11. The Temperature of the Corona as Derived from Total Solar Eclipse Observations

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    Multiwavelength imaging observations in a suite of coronal forbidden lines of the corona during total solar eclipses enables the empirical inference of the spatial distribution of temperature in the solar corona up to a few solar radii above the limb. The temperature sensitivity of coronal emission lines is such that temperature differences of 105 K can be detected in the images. Using high resolution multiwavelength and white light eclipse images acquired since 2006, covering almost a solar cycle, we show evidence for (1) how the distribution of the temperature in the corona is bimodal, with closed coronal structures dominated by 2 106 K plasma, while structures streaming away from the Sun are dominated by 106 K emission, (2) prominences are invariably enshrouded by the hottest material in the corona, and (3) that the dominance of one temperature versus the other is solar-cycle dependent.

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

    NASA Astrophysics Data System (ADS)

    Rušin, V.; Saniga, M.; Komžík, R.

    2014-10-01

    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.

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

    PubMed

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

    1992-09-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

    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.

  15. Solar Corona and plasma effects on Radio Frequency waves

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

  16. Current Sheet Formation and Reconnection Dynamics in the Solar Corona

    NASA Astrophysics Data System (ADS)

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

    2009-05-01

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

  17. THE EXPANSION OF ACTIVE REGIONS INTO THE EXTENDED SOLAR CORONA

    SciTech Connect

    Morgan, Huw; Jeska, Lauren; Leonard, Drew

    2013-06-01

    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.

  18. Diagnostics of the solar corona from comparison between Faraday rotation measurements and magnetohydrodynamic simulations

    SciTech Connect

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

    2014-07-10

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

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

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

    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.

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

    SciTech Connect

    Garcia-Hernandez, D. A.; Lambert, D. L. E-mail: nkrao@iiap.res.in

    2013-08-20

    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.

  1. The State of the Corona During the Weak Solar Cycle 24: the View from LASCO Images

    NASA Astrophysics Data System (ADS)

    Barlyaeva, T.; Lamy, P.; Llebaria, A.; Boclet, B.

    2016-04-01

    The LASCO-C2 coronagraph onboard SOHO continues its white-light imaging of the corona from 1.5 to 6.0 solar radii, thus allowing investigating the consequences of the weak Solar Cycle 24 on the corona and comparing it to the previous cycle (23). Temporal variations of the global radiance of the corona are presented. We pay particular attention to the mid-term variations which are distinctly different between the two cycles and highlight the similarities and differences. Finally, we rely on our ARTEMIS II catalog of coronal mass ejections (CMEs) to compare their global rates during these two cycles.

  2. Dust removal from solar cells

    NASA Technical Reports Server (NTRS)

    Ashpis, David E. (Inventor)

    2011-01-01

    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."

  3. Dust Removal from Solar Cells

    NASA Technical Reports Server (NTRS)

    Ashpis, David E. (Inventor)

    2015-01-01

    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."

  4. Laboratory identification of MHD eruption criteria in the solar corona

    NASA Astrophysics Data System (ADS)

    Myers, Clayton E.

    2015-11-01

    Ideal magnetohydrodynamic (MHD) instabilities such as the kink and torus instabilities are believed to play an important role in driving ``storage-and-release'' eruptions in the solar corona. These instabilities act on long-lived, arched magnetic flux ropes that are ``line-tied'' to the solar surface. In spite of numerous observational and computational studies, the conditions under which these instabilities produce an eruption remain a subject of intense debate. In this paper, we use a line-tied, arched flux rope experiment to study storage-and-release eruptions in the laboratory. An in situ array of miniature magnetic probes is used to assess the equilibrium and stability of the laboratory flux ropes. Two major results are reported here: First, a new stability regime is identified where torus-unstable flux ropes fail to erupt. In this ``failed torus'' regime, the flux rope is torus-unstable but kink-stable. Under these conditions, a dynamic ``toroidal field tension force'' surges in magnitude, causing the flux rope to contract. This tension force, which is missing from existing eruption models, is the J × B force between self-generated poloidal currents in the flux rope and the toroidal (guide) component of the vacuum field. Secondly, a clear torus instability threshold is observed in the kink-unstable regime. This latter result, which is consistent with existing theoretical and numerical results, verifies the key role of the torus instability in driving solar eruptions. In collaboration with M. Yamada, H. Ji, J. Yoo, W. Fox, J. Jara-Almonte, A. Savcheva, and E. E. DeLuca. This research is supported by DoE Contract No. DE-AC02-09CH11466 and by the NSF/DoE Center for Magnetic Self-Organization (CMSO).

  5. The Corona of the Young Solar Analog EK Draconis

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

    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

  6. Inbound waves in the solar corona: A direct indicator of Alfvén surface location

    SciTech Connect

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

    2014-06-01

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

  7. Dynamics of Solar System Dust

    NASA Technical Reports Server (NTRS)

    Dermott, Stanley F.

    2002-01-01

    The ongoing aim of the research is to investigate the dynamical and physical evolution of interplanetary dust particles in order to produce a detailed global model of the zodiacal cloud and its constituent components that is capable of predicting thermal fluxes in mid-infrared wave bands to an accuracy of 1% or better; with the additional aim of exploiting this research as a basis for predicting structure in exozodiacal clouds that may be signatures of unseen planets.

  8. Circumstellar Dust Shells: Clues to the Evolution of R Coronae Borealis Stars

    NASA Astrophysics Data System (ADS)

    Montiel, Edward J.; Clayton, Geoffrey C.

    2016-06-01

    R Coronae Borealis (RCB) stars are an exotic group of extremely hydrogen- deficient, carbon-rich supergiants that are known for their spectacular declines in brightness (up to 8 mags) at irregular intervals. Two scenarios are currently competing to explain the origins of these stars. One suggests that RCB stars are the products after a binary white dwarf (WD) system merges. The other takes a single, evolved star and has it undergo a final, helium-shell flash (FF) and becoming a cool giant. Recently, observations of elemental abundances in RCB stars have strongly swung the argument in favor of the WD merger model. The FF scenario has maintained its relevancy by seemingly being the only model able to offer a suitable explanation for one RCB feature that merger model has historically struggled with explaining: the presence of cold, circumstellar dust envelopes which might be fossil planetary nebulae (PNe). In reality, the shells could actually be fossil PNe, material left over from the WD merger, or mass lost during the RCB phase, itself. I will present the results of my dissertation, which is to try and discern the nature and history of the far-IR dust shells around RCB stars to help understand the origin of these enigmatic stars. I will discuss our efforts to determine the mass, size, temperature, and morphology of these diffuse structures surrounding a sample of RCB stars using multi-wavelength observations ranging from the ultraviolet to the submillimeter. These observations have provided unprecedented wavelength coverage for both the central stars and their CSM. They have been examined by eye for morphology and have been used in the construction of maximum-light spectral energy distributions (SEDs). I will present the results of our Monte Carlo radiative transfer of the maximum-light SEDs. Finally, I will highlight our work investigating the HI abundance of the envelope of R Coronae Borealis, itself, using archival 21—cm observations from the Arecibo

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

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Benz, A. O.; Guedel, M.

    1994-01-01

    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.

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

    PubMed

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

    2011-07-28

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

  12. Sun-grazing comets as probes of the physics of the solar corona

    NASA Astrophysics Data System (ADS)

    Schrijver, C.

    2012-12-01

    In 2011, two Sun-grazing comets were observed at EUV wavelengths as they descended into the inner solar corona. The first, C/2011 N3 (SoHO), was observed by the Atmospheric Imaging Assembly of the Solar Dynamics Observatory up to the point at which it terminated its existence very near to its orbital perihelion. Its tail emission was visible to within 0.146 solar radii of the solar surface. The second comet in the inner corona, C/2011 W3, was observed by a fleet of observatories, including the STEREO spacecraft which saw it during its approach to, and subsequent voyage away from, its orbital perihelion behind the Sun as seen from Earth. C2011 W3 survied for only about 1.6 more days when the last of its material sublimated. The variable cometary tails, observed in a multiple EUV passbands, were seen to be deflected by the interaction with the solar magnetic field as the comets flew through the corona. In this talk, I will discuss lessons about the solar corona learned from the cometary emission and absorption features and from the interaction of the ionizing cometary material with the magnetized corona through which it traveled.

  13. Laboratory Identification of MHD Eruption Criteria in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Yamada, M.; Myers, C. E.; Ji, H.; Yoo, J.; Fox, W. R., II; Jara-Almonte, J.; Savcheva, A. S.; DeLuca, E. E.

    2015-12-01

    Ideal magnetohydrodynamic (MHD) instabilities such as the kink [1] and torus [2] instabilities are believed to play an important role in driving "storage-and-release" eruptions in the solar corona. These instabilities act on long-lived, arched magnetic flux ropes that are "line-tied" to the solar surface. In spite of numerous observational and computational studies, the conditions under which these instabilities produce an eruption remain a subject of intense debate. In this paper, we use a line-tied, arched flux rope experiment to study storage-and-release eruptions in the laboratory [3]. An in situ array of miniature magnetic probes is used to assess the equilibrium and stability of the laboratory flux ropes. Two major results are reported here: First, a new stability regime is identified where torus-unstable flux ropes fail to erupt. In this "failed torus" regime, the flux rope is torus-unstable but kink-stable. Under these conditions, a dynamic "toroidal field tension force" surges in magnitude and causes the flux rope to contract. This tension force, which is missing from existing eruption models, is the J×B force between self-generated poloidal currents in the flux rope and the toroidal (guide) component of the vacuum field. Secondly, a clear torus instability threshold is observed in the kink-unstable regime. This latter result, which is consistent with existing theoretical [4] and numerical [5] findings, verifies the key role of the torus instability in driving some solar eruptions. This research is supported by DoE Contract No. DE-AC02-09CH11466 and by the NSF/DoE Center for Magnetic Self-Organization (CMSO). [1] Hood & Priest, Geophys. Astrophys. Fluid Dynamics 17, 297 (1981) [2] Kliem & Török, Phys. Rev. Lett. 96, 255002 (2006) [3] Myers, Ph.D. Thesis, Princeton University (2015) [4] Olmedo & Zhang, Astrophys. J. 718, 433 (2010) [5] Török & Kliem, Astrophys. J. 630, L97 (2005)

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

    NASA Astrophysics Data System (ADS)

    Kuznetsov, V. D.

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

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

    NASA Technical Reports Server (NTRS)

    Gopalswamy, N.; Nitta, N.

    2011-01-01

    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.

  16. Study of the solar corona using radio and space observations

    NASA Technical Reports Server (NTRS)

    Dulk, G. A.

    1984-01-01

    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.

  17. The Writhe of Helical Structures in the Solar Corona

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

  18. Solar flares in soft X-rays detected in the Coronas-F experiment

    NASA Astrophysics Data System (ADS)

    Pankov, V. M.; Prokhin, V. L.; Khavenson, N. G.; Gusev, A. A.

    2009-12-01

    The RPS-1 spectrometer on the board of the Coronas-F satellite detecting solar X-rays in the range of 3-31.5 keV using a CdTe detector is described and some results of the observation of weak solar flares are presented.

  19. A New Solar System Dust Band

    NASA Astrophysics Data System (ADS)

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

    2007-10-01

    The relative proportions of asteroidal and cometary material in the zodiacal cloud is an evolving debate. The determination of the asteroidal component is constrained through the study of the dust bands (the fine-structure component superimposed on the broad background cloud), since they have been confidently linked to specific, young, asteroid family disruptions in the main belt. These disruptions represent recent injections of dust into the cloud and thus hold the key to determining at least a minimum value of the asteroidal contribution. There are currently known to be three dust band pairs, one at approximately 10 degrees corresponding to the Veritas family and two central band pairs near the ecliptic, one of which corresponds to the Karin cluster of the Koronis family. However, through careful co-adding of almost all the pole-to-pole intensity scans in the mid infrared wavebands of the IRAS data set, a new solar system dust band has been found at approximately 17 degrees inclination. We think this is a confirmation of the M/N partial band pair suggested by Sykes (1988). The new dust band appears to be mostly, yet not completely formed, which we attribute to the young age of the likely sources. We will present dynamical modeling of the new band which allows us to determine the most likely source and amount of cross-sectional area of dust in the band. This is turn allows us to put constraints on the size of the precursor and amount of dust contributed by this source to the background cloud. Since the band is incomplete, the dynamics of the distribution of the node will allow us to put loose constraints on the time of formation of this band and compare with the ages of the potential sources. This work is funded by NASA GSRP.

  20. Simulated kinetic effects of the corona and solar cycle on high altitude ion transport at Mars

    NASA Astrophysics Data System (ADS)

    Curry, S. M.; Liemohn, M.; Fang, X.; Brain, D.; Ma, Y.

    2013-06-01

    We present results from the Mars Test Particle (MTP) simulation as part of a community‒wide model comparison in order to quantify the role of different neutral atmospheric conditions in planetary ion transport and escape. This study examines the effects of individual ion motion by simulating particle trajectories for three cases: solar minimum without the neutral corona, solar minimum with the inclusion of the neutral corona, and solar maximum with the inclusion of the neutral corona. The MTP simulates 1.5 billion test particles through background electric and magnetic fields computed by a global magnetohydrodynamic model. By implementing virtual detectors in the simulation, the MTP has generated velocity space distributions of pickup ions and quantifies the ion acceleration at different spatial locations. The study found that the inclusion of a hot neutral corona greatly affects the total O+ production and subsequent loss, roughly doubling the total escape for solar minimum conditions and directly contributing to high energy sources above 10 keV. The solar cycle influences the amount of O+ flux observed by the virtual detectors, increasing the O+ flux and total escape by an order of magnitude from solar minimum to maximum. Additionally, solar maximum case induces greater mass loading of the magnetic fields, which decreases the gyroradius of the ions and redirects a significant ion population downtail to subsequently escape.

  1. Coordinated UVCS/SOHO and VLA Observations of the Solar Corona

    NASA Astrophysics Data System (ADS)

    Miralles, M. P.; Cranmer, S. R.; Raymond, J. C.; Spangler, S. R.; Kohl, J. L.

    2003-12-01

    Coordinated UVCS/SOHO and VLA coronal observations took place during August 16--19, 2003. The radio source 3C 228 passed behind a streamer in the northeast at a heliocentric distance of about 7 solar radii, and behind the north coronal hole at about 4 solar radii in the latter part of the radio observation. The goal of this campaign is to combine the analysis of radio polarimetric sounding measurements of the corona with ultraviolet spectroscopy of the same regions, in order to obtain qualitatively new information about the properties of the solar coronal plasma. The Ultraviolet Coronagraph Spectrometer (UVCS) aboard SOHO observed O VI (103.2 and 103.7 nm) and H I Lyman alpha (121.6 nm) emission lines to determine kinetic temperatures, average densities and outflow speeds in the corona. UVCS observations provide unique information on the heating and acceleration processes in the corona. The Very Large Array (VLA) observations reveal the Faraday rotation of polarized radio waves due to passage through the magnetized plasma of the corona. These measurements provide limits on the coronal magnetic field strength and constrain the properties of magnetohydrodynamic (MHD) waves. Radio propagation techniques are a useful complementary tool to ultraviolet coronagraphic spectroscopy in determining the physical processes that are responsible for the heating of the extended corona and the acceleration of the solar wind. This work is supported by NASA under Grant NAG5-12865 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency and by PRODEX (Swiss contribution).

  2. Solar corona synoptic observations from SOHO with an extreme ultraviolet imaging telescope

    NASA Technical Reports Server (NTRS)

    Delaboudiniere, Jean-Pierre; Gabriel, A. H.; Artzner, G. E.; Dere, Ken; Howard, Russell A.; Michels, D.; Catura, Richard; Lemen, J.; Stern, R.; Gurman, Joseph B.

    1992-01-01

    The major scientific objective of the EUV Imaging Telescope (EIT) is to study the evolution of coronal structure over a wide range of spatial and temporal scales and temperatures. A second strategic objective is to provide full disk synoptic maps of the global corona to aid in unifying SOHO (Solar and Heliospheric Observatory)/Cluster investigations. EIT will also provide images to support the planning of detailed spectroscopic investigations by the CDS (Coronal Diagnostic Spectrometer) and SUMER spectrometers in SOHO. EIT observations will be made in four narrow spectral bands, centered at 171 A (Fe 9), 195 A(Fe 12), 284 A (Fe 15), and 304 A (He 2) representing restricted temperature domains within a wide temperature range from 40,000 to 3,000,000 K. The results will be images of the solar atmosphere from the upper chromosphere and transition region to the active region corona. These maps, made at appropriate time intervals, will be used to study the fine structures in the solar corona and to relate their dynamic properties to the underlying chromosphere and photosphere. Dynamic events in the inner corona will be related to white light transients in the outer corona, and observations of the internal structure of coronal holes will be used to investigate origins of the solar wind.

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

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

    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

  4. Modeling the Acceleration Process of Dust in the Solar Wind

    NASA Astrophysics Data System (ADS)

    Jia, Y. D.; Lai, H.; Russell, C. T.; Wei, H.

    2015-12-01

    In previous studies we have identified structures created by nano-dust in the solar wind, and we have observed the expected draping and diverting signatures of such structures using well-spaced multi-spacecraft observations. In this study, we reproduce such an interaction event with our multi-fluid MHD model, modeling the dust particles as a fluid. When the number density of dust particles is comparable to the solar wind ions, a significant draping in the IMF is created, with amplitude larger than the ambient fluctuations. We note that such a density is well above several nano dust particles per Debye sphere and a dusty fluid is appropriate for modeling the dust-solar wind interaction. We assume a spherical cloud of dust travelling with 90% solar wind speed. In addition to reproducing the IMF response to the nano-dust at the end-stage of dust acceleration, we model the entire process of such acceleration in the gravity field of the inner heliosphere. It takes hours for the smallest dust with 3000 amu per proton charge to reach the solar wind speed. We find the dust cloud stretched along the solar wind flow. Such stretching enhances the draping of IMF, compared to the spherical cloud we used in an earlier stage of this study. This model will be further used to examine magnetic perturbations at an earlier stage of dust cloud acceleration, and then determine the size, density, and total mass of dust cloud, as well as its creation and acceleration.

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

    NASA Technical Reports Server (NTRS)

    Woo, Richard

    2006-01-01

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

  6. Observational studies of reconnection in the solar corona

    SciTech Connect

    McKenzie, David E.

    2011-11-15

    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.

  7. The Structure and Dynamics of the Solar Corona and Inner Heliosphere

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

    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.

  8. A new model of amplitude fluctuations for radio propagation in solar corona during superior solar conjunction

    NASA Astrophysics Data System (ADS)

    Xu, Guanjun; Song, Zhaohui

    2016-02-01

    Radio communication links through the solar corona are disturbed by electron density fluctuations caused by coronal turbulence. This has become a problem for deep space exploration when the spacecraft is near superior conjunction with the Sun. With a forecast of the signal fluctuations the link could be adapted to compensate for these impairments in real time. Motivated by this need, we present a theoretical study of the signal fluctuations including an analytical expression for the amplitude fluctuations. The proposed model includes an anisotropic spectrum of density fluctuations, the solar wind "outer scale," and the spectral exponent. The performance of this analytical solution is demonstrated by comparison with published data from spacecraft and with other existing analytical methods.

  9. Modeling electron density, temperature distribution in the solar corona based on solar surface magnetic field observations

    NASA Astrophysics Data System (ADS)

    Lago, A.; Rodríguez, J. M.; Vieira, L.; Coelho Stekel, T. R.; Costa, J. E. R.; Pinto, T. S. N.

    2015-12-01

    Magnetic fields constitute a natural link between the Sun, the Earth and the Heliosphere in general. The solar dynamo action maintains and strengthens the magnetic field in the solar interior. The structure of the solar corona is mostly determined by the configuration and evolution of the magnetic field. While open magnetic field lines carry plasma into the heliosphere, closed field lines confine plasma. Additionally, key physical processes that impact the evolution of Earth's atmosphere on time-scale from days to millennia, such as the soft X-ray and EUV emission, are also determined by the solar magnetic field. However, observations of the solar spectral irradiance are restricted to the last few solar cycles and are subject to large uncertainties. Here we present a physics-based model to reconstruct in near-real time the evolution of the solar EUV emission based on the configuration of the magnetic field imprinted on the solar surface and assuming that the emission lines are optically thin. The structure of the coronal magnetic field is estimated employing a potential field source surface extrapolation based on the synoptic charts. The coronal plasma temperature and density are described by a hydrostatic model. The emission is estimated to employ the CHIANTI database. The performance of the model is compared to the emission observed by EVE instrument on board SDO spacecraft. The preliminary results and uncertainties are discussed in details. Furthermore, we examine the possibility of delivery the reconstruction of the solar spectral irradiance in near-real time using the infrastructure provided by the Brazilian Space weather program (EMBRACE/INPE). This work is partially supported by CNPq/Brazil under the grant agreement no. 140779/2015-9.

  10. Observaciones de la corona solar interior con un coronógrafo de espejo

    NASA Astrophysics Data System (ADS)

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

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

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

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

  13. Research on dual spectrum solar-blind ultraviolet corona detection system

    NASA Astrophysics Data System (ADS)

    Yang, Feng; Gu, Yan; Sun, Jianning; Pan, Jingsheng; Zhu, Bo; Wang, Qi; Lu, Xiaoqing

    2015-04-01

    A dual spectrum solar-blind ultraviolet (UV) corona detection system is designed in this paper. A common optical axis using a dichroic mirror is applied to this system in order to make visible light and ultraviolet light spectroscopy to ultraviolet detector and visible detectors. A high speed circuit of image processing based on TMS320DM642 DSP and a circuit that is used into system control and power management based on microcontroller are designed for the presented system. On the basis of the multi-threaded programming ideas, real-time image acquisition of ultraviolet and visible detectors, ultraviolet image noise reduction, image registration, dual spectral integration, Characteristic superimposing, serial communication and image display are achieved by using the DSP image processing circuit. Experimental results show that the dual spectrum solar-blind ultraviolet corona detection system has a good performance of corona detection based on ultraviolet and visible image fusion.

  14. The corona near the time of the 1983 June 11 total solar eclipse

    NASA Technical Reports Server (NTRS)

    Sime, D. G.; Fisher, R. R.; Mccabe, M. K.; Mickey, D. L.

    1984-01-01

    Observations are presented of the corona during the June 11, 1983 total solar eclipse, together with preliminary results of a coordinated observing program conducted to investigate the relationship between the corona and the lower parts of the solar atmosphere. Synoptic observations of the white light corona and disk in H-alpha are compared with the eclipse image, together with the inferred longitudinal component of the photospheric magnetic field measured using the magnetically sensitive Fe line at 6303 A. Using these data, an interpretation of the global three-dimensional coronal structure is attempted; showing that the eclipse image contains bright features which are far from the plane of the sky, and that it is dominated by streamers over polar filament neutral lines.

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

    NASA Technical Reports Server (NTRS)

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

    2007-01-01

    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.

  16. Threaded-Field-Line Model for the Transition Region and Solar Corona

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    In numerical simulations of the solar corona, both for the ambient state and especially for dynamical processes the most computational resources are spent for maintaining the numerical solution in the Low Solar Corona and in the transition region, where the temperature gradients are very sharp and the magnetic field has a complicated topology. The degraded computational efficiency is caused by the need in a highest resolution as well as the use of the fully three-dimensional implicit solver for electron heat conduction. On the other hand, the physical nature of the processes involved is rather simple (which still does not facilitate the numerical methods) as long as the heat fluxes as well as slow plasma motional velocities are aligned with the magnetic field. The Alfven wave turbulence, which is often believed to be the main driver of the solar wind and the main source of the coronal heating, is characterized by the Poynting flux of the waves, which is also aligned with the magnetic field. Therefore, the plasma state in any point of the three-dimensional grid in the Low Solar Corona can be found by solving a set of one-dimensional equations for the magnetic field line ("thread"), which passes through this point and connects it to the chromosphere and to the global Solar Corona. In the present paper we describe an innovative computational technology based upon the use of the magnetic-field-line-threads to forlmulate the boundary condition for the global solar corona model which traces the connection of each boundary point to the cromosphere along the threads.

  17. A Dust Characterization Experiment for Solar Cells Operating on Mars

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

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

  19. Mass and Energy Transfer Between the Solar Photosphere and Corona

    NASA Astrophysics Data System (ADS)

    Peter, H.

    2015-12-01

    The problem of chromospheric and coronal heating is also a problem of mass supply to the corona. On average we see redshifts at transition region temperatures of the order of 10 km/s. If interpreted as downflows, this would quickly empty the corona, and fresh material has to be transported into the corona. Several models have been proposed to understand this mass cycle between the different atmospheric layers. However, as of yet all these proposals have serious shortcomings. On the observational side open questions remain, too. With the new IRIS mission we can observe the transition region at unprecedented spatial and spectral resolution, but the observational results are still puzzling. In particular the finding that the spatial distribution of line widths and Doppler shifts do not change with increasing resolution is against physical intuition. This shows that even with IRIS we still have significant velocity gradients along the line-of-sight, indicating that shocks might play a significant role. Likewise the temporal evolution might be a key for our understanding of the mass cycle. It might well be that the filling and draining of hot plasma occurs on significantly different time scales, which might be part of the difficulty to arrive at a conclusive observational picture. Considering the progress made for the quiet Sun, it seems clear that the processes responsible for the mass exchange are not resolved (yet). Therefore one might wonder to what extent one could use larger and resolved individual events in more active parts of the Sun to understand the details of the mass transport. In particular a common understanding of reconnection events such as Ellerman bombs in the photosphere, explosive events in the transition region and the recently discovered IRIS bombs in-between might provide the key to better understand the mass cycle throughout the atmospheric layers from the photosphere to the corona.

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

  1. THE CYCLING OF MATERIAL BETWEEN THE SOLAR CORONA AND CHROMOSPHERE

    SciTech Connect

    Guerreiro, N.; Hansteen, Viggo; De Pontieu, B.

    2013-05-20

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

  2. The Structure and Dynamics of the Solar Corona and Inner Heliosphere

    NASA Technical Reports Server (NTRS)

    Mikic, Zoran

    2002-01-01

    This report covers technical progress during the second quarter of the first year of NASA Sun-Earth Connections Theory Program (SECTP) contract 'The Structure and Dynamics of the Solar Corona and Inner Heliosphere,' NAS5-99188, between NASA and Science Applications International Corporation. and covers the period November 16, 1999 to February 15, 2000. Under this contract SAIC and the University of California, Irvine (UCI) have conducted research into theoretical modeling of active regions, the solar corona, and the inner heliosphere, using the MHD (magnetohydrodynamic) model. The topics studied include: the effect of emerging flux on the stability of helmet streamers, coronal loops and streamers, the solar magnetic field, the solar wind, and open magnetic field lines.

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

  4. Evolution of interstellar dust and stardust in the solar neighbourhood

    NASA Astrophysics Data System (ADS)

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

    2008-02-01

    Aims:We studied the evolution of the abundance in interstellar dust species that originate in stellar sources and from condensation in molecular clouds in the local interstellar medium of the Milky Way. We determined from this the input of dust material to the Solar System. Methods: A one-zone chemical evolution model of the Milky Way for the elemental composition of the disk combined with an evolution model for its interstellar dust component similar to that of Dwek (1998) is developed. The dust model considers dust-mass return from AGB stars as calculated from synthetic AGB models combined with models for dust condensation in stellar outflows. Supernova dust formation is included in a simple parametrised form that is gauged by observed abundances of presolar dust grains with a supernova origin. For dust growth in the ISM, a simple method is developed for coupling this with disk and dust evolution models. Results: A chemical evolution model of the solar neighbourhood in the Milky Way is calculated, which forms the basis for calculating a model of the evolution of the interstellar dust population at the galactocentric radius of the Milky Way. The model successfully passes all standard tests for the reliability of such models. In particular the abundance evolution of the important dust-forming elements is compared with observational results for the metallicity-dependent evolution of the abundances for G-type stars from the solar neighbourhood. It is found that the new tables of Nomoto et al. (2006) for the heavy element production give much better results for the abundance evolution of these important elements than the widely used tables of Woosley & Weaver (1995). The time evolution for the abundance of the following dust species is followed in the model: silicate, carbon, silicon carbide, and iron dust from AGB stars and from supernovae, as well as silicate, carbon, and iron dust grown in molecular clouds. It is shown that the interstellar dust population is

  5. Zero-beta MHD simulations of a solar eruption driven by a solar wind in the corona

    NASA Astrophysics Data System (ADS)

    Lee, Hwanhee; Magara, Tetsuya; Kang, Jihye

    2016-05-01

    Solar winds always exist in the corona, continuously carrying out magnetized plasmas from the solar surface toward the interplanetary space. We assume that a solar wind also plays an important role in producing a solar eruption. To confirm this hypothesis, we construct a solar eruption model in which a solar wind upflow is imposed at the top boundary of three-dimensional zero-beta magnetogydrodynamic (MHD) simulations. The initial magnetic field is given by nonlinear force-free field (NLFFF) reconstruction that is applied to the surface field provided by a flux emergence simulation. The simulation demonstrates that a solar eruption occurs due to the imbalance between magnetic pressure gradient force and magnetic tension force caused by a solar wind that gradually transports the envelope flux outward. This result provides important insights into the role of solar winds in producing solar eruptions.

  6. Dynamics and Thermodynamics of the Corona Observed During the Total Solar Eclipse of 20 March 2015

    NASA Astrophysics Data System (ADS)

    Habbal, S. R.; Ding, A.; Druckmuller, M.; Johnson, J.; Morgan, H.; Arndt, M. B.; Alzate, N.; Hutton, J.

    2015-12-01

    Total solar eclipse observations are snapshots of the instantaneous dynamic state of the corona, and each observation never fails to yield surprises. Occurring at the declining phase of solar cycle 24, the 20 March 2015 total solar eclipse was no exception. Images taken through narrow bandpass filters centered on the Fe XIV 530.3 nm and Fe XI 789.2 nm coronal emission lines, showed a corona dominated by strong Fe XIV emission, with a peak ionization temperature of 1.8 MK, and with weak Fe XI emission at 1.1 MK, present mostly over the two poles. Simultaneous imaging spectroscopy through a dual channel high-resolution spectrometer, centered on these two wavelengths, revealed Doppler red shifts exceeding 1000 km/s in the extended corona, covering a distance range of up to 1.5 solar radii above the solar surface. These redshifts together with the observed Doppler broadening could be assigned to specific coronal structures, which were observed simultaneously in high resolution white light images. By comparing these observations with contemporaneous observations from SDO, SWAP/Proba2 and LASCO/C2 and C3, the dynamics of the coronal plasma, as well as its thermodynamics, could be mapped in a region of space, untenable to present-day observatories. These latest eclipse observations underscore the unique scientific opportunities accessible with similar instrumentation during the all-american 21 August 2017 total solar eclipse.

  7. Nonlinear interaction between wave and convective disturbances in the solar corona

    NASA Astrophysics Data System (ADS)

    Veselovsky, I. S.; Mikhalyaev, B. B.; Bembitov, D. B.

    2015-12-01

    During more than two decades, many non-stationary events have been observed in the solar corona by different ground and space instruments, namely: oscillations and flows. These events play a crucial role in a solving two important problems of the solar physics: coronal heating and solar wind acceleration. Numerous observational data and theoretical works demonstrate the nonlinear interaction between waves and flows in the solar atmosphere. On other hand, nonlinear effects can also be used in coronal seismology, where a significant success leaded to many original works on linear disturbances in the coronal plasma. The nonlinear approach should make it possible to achieve more precise results.

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

    NASA Astrophysics Data System (ADS)

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

    2011-11-01

    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 (>~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.

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

    SciTech Connect

    Sterken, V. J.; Altobelli, N.; Schwehm, G.; Kempf, S.; Srama, R.; Strub, P.; Gruen, E.

    2011-11-29

    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.

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

    NASA Astrophysics Data System (ADS)

    Hayashi, K.

    2013-11-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

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

  12. The temperature structure, mass, and energy flow in the corona and inner solar wind

    NASA Technical Reports Server (NTRS)

    Withbroe, George L.

    1988-01-01

    Remote-sensing and in situ data are used to constrain a radiative energy balance model in order to study the radial variations of coronal temperatures, densities, and outflow speeds in several types of coronal holes and in an unstructured quiet region of the corona. A one-fluid solar wind model is used which takes into account the effects of radiative and inward conductive losses in the low corona and the chromospheric-coronal transition region. The results show that the total nonradiative energy input in magnetically open coronal regions is 5 + or - 10 to the 5th ergs/sq cm, and that most of the energy heating the coronal plasma is dissipated within 2 solar radii of the solar surface.

  13. Corona during the total solar eclipse on March 20, 2015, and 24 cycle development

    NASA Astrophysics Data System (ADS)

    Yazev, Sergey; Mordvinov, Aleksandr; Dvorkina-Samarskaya, Antonina

    2016-06-01

    We analyzed the structure of coronal features, using data on the March 20, 2015 total solar eclipse. The Ludendorff index characterizing the flattening of the corona is 0.09. The solar corona structure in the Northern and Southern hemispheres corresponds to the maximum and post-maximum phases of solar activity, respectively. The asynchronous development of magnetic activity in the Sun's Northern and Southern hemispheres caused a substantial asymmetry of coronal features observed at the reversal of polar magnetic fields in the current cycle. The polar ray structures in the Southern Hemisphere are associated with the polar coronal hole, while in the Northern Hemisphere a polar hole has not been formed yet. We examine the relation between large-scale magnetic fields and location of high coronal structures.

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

    NASA Astrophysics Data System (ADS)

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

    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.

  15. On Shock Wave Formation in the Solar Corona

    NASA Astrophysics Data System (ADS)

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

    In order to investigate the formation of radio emitting shock waves above flaring active regions, we combine spectral and imaging observations of type II radio events with X-ray imaging and full-Sun observations and, in one case, with the extrapolated magnetic field configuration in the corona. We confirm and extend earlier findings that type II bursts develop above active region loops seen in soft X-ray images. Sources at successively lower frequencies are non-radially displaced from the axis of the active region loops. Two new radio features identified in high resolution spectrograms establish a possible link between the type II emission and the preceding activity in the underlying corona: 1. Fast-drift bursts and pulsations with a restricted bandwidth are observed in coronal loops from the impulsive flare phase until the onset of the type II emission. Envelope features of this burst group (starting frequency and/or cut-off frequency) drift gradually to lower frequencies, at a normalized drift rate similar to the following type II lanes. The source sites are located between the sites of H_alpha emission and of the type II emission. The envelope features of theburst group therefore appear as an early manifestation of the disturbance which later gives rise to the type II emission. We refer to these envelope features as a type II precursor. 2. Immediately before the type II emission a short (<= 1 min duration) series of narrow-band bursts occurs at frequencies between the split bands of the type II lanes. As a whole, the burst sequence has an inverted U--shaped spectral envelope. We therefore call it an arc. It has fundamental-harmonic structure as the subsequent type II burst, but no band splitting. The source is located near or above the summits of the coronal loops where the precursor emission occurred before, and close to the site where the type II emission starts. The arc feature occurs especially prior to high-frequency type II bursts, i.e. type II shocks

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

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

    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.

  17. DISCOVERY OF FINELY STRUCTURED DYNAMIC SOLAR CORONA OBSERVED IN THE Hi-C TELESCOPE

    SciTech Connect

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

    2014-05-20

    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.

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

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

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

  19. Radial distribution of compressive waves in the solar corona revealed by Akatsuki radio occultation observations

    SciTech Connect

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

    2014-12-10

    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 R{sub S} (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 R{sub S} , 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 R{sub S} 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 Alfvén waves. The compressive waves should eventually dissipate through shock generation to heat the corona.

  20. Spatiotemporal organization of energy release events in the quiet solar corona

    SciTech Connect

    Uritsky, Vadim M.; Davila, Joseph M.

    2014-11-01

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

  1. Spatiotemporal Organization of Energy Release Events in the Quiet Solar Corona

    NASA Technical Reports Server (NTRS)

    Uritsky, Vadim M.; Davila, Joseph M.

    2014-01-01

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

  2. Ultraviolet and extreme ultraviolet spectroscopy of the solar corona at the Naval Research Laboratory.

    PubMed

    Moses, J D; Ko, Y-K; Laming, J M; Provornikova, E A; Strachan, L; Beltran, S Tun

    2015-11-01

    We review the history of ultraviolet and extreme ultraviolet spectroscopy with a specific focus on such activities at the Naval Research Laboratory and on studies of the extended solar corona and solar-wind source regions. We describe the problem of forecasting solar energetic particle events and discuss an observational technique designed to solve this problem by detecting supra-thermal seed particles as extended wings on spectral lines. Such seed particles are believed to be a necessary prerequisite for particle acceleration by heliospheric shock waves driven by a coronal mass ejection. PMID:26560611

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

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

    The PI (Cranmer) and Co-I (A. van Ballegooijen) made significant progress toward the goal of building a "unified model" of the dominant physical processes responsible for the acceleration of the solar wind. The approach outlined in the original proposal comprised two complementary pieces: (1) to further investigate individual physical processes under realistic coronal and solar wind conditions, and (2) to extract the dominant physical effects from simulations and apply them to a one-dimensional and time-independent model of plasma heating and acceleration. The accomplishments in the report period are thus divided into these two categories: 1a. Focused Study of Kinetic MHD Turbulence. We have developed a model of magnetohydrodynamic (MHD) turbulence in the extended solar corona that contains the effects of collisionless dissipation and anisotropic particle heating. A turbulent cascade is one possible way of generating small-scale fluctuations (easy to dissipate/heat) from a pre-existing population of low-frequency Alfven waves (difficult to dissipate/heat). We modeled the cascade as a combination of advection and diffusion in wavenumber space. The dominant spectral transfer occurs in the direction perpendicular to the background magnetic field. As expected from earlier models, this leads to a highly anisotropic fluctuation spectrum with a rapidly decaying tail in the parallel wavenumber direction. The wave power that decays to high enough frequencies to become ion cyclotron resonant depends on the relative strengths of advection and diffusion in the cascade. For the most realistic values of these parameters, though, there is insufficient power to heat protons and heavy ions. The dominant oblique waves undergo Landau damping, which implies strong parallel electron heating. We thus investigated the nonlinear evolution of the electron velocity distributions (VDFs) into parallel beams and discrete phase-space holes (similar to those seen in the terrestrial magnetosphere

  4. Solar wind driven dust acoustic instability with Lorentzian kappa distribution

    SciTech Connect

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

    2014-02-15

    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.

  5. Solar wind magnetic field bending of Jovian dust trajectories.

    PubMed

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

    1996-11-29

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

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

    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.

  7. On the Generation and Dissipation of Ion Cyclotron Waves in the Extended Solar Corona

    NASA Astrophysics Data System (ADS)

    Cranmer, S. R.

    1999-12-01

    The dissipation of high frequency (10 to 10,000 Hz) ion cyclotron resonant Alfven waves has been proposed as a leading candidate for the heating of the extended solar corona and the acceleration of the high speed solar wind. The competition between various wave generation mechanisms and resonant wave damping is examined in detail, and a database of more than 2000 low-abundance ion species is taken into account for completeness. Also, the Sobolev approximation from the theory of hot star winds is applied to the gyroresonant wave-particle interaction in the solar wind, and the surprisingly effective damping ability of ``minor'' ions is explained in simple terms. High frequency waves (propagating parallel to open magnetic field lines) that originate at the base of the corona are damped significantly when they resonate with ions having charge-to-mass ratios of about 0.1. Thus, if the waves came solely from the coronal base, there would be negligible wave power available to resonate with higher charge-to-mass ratio ions at larger heights. This result confirms preliminary suggestions from earlier work that the waves that heat and accelerate the high speed solar wind must be generated throughout the extended corona. This work is supported by the National Aeronautics and Space Administration under grant NAG5-7822 to the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana, and by the ESA PRODEX program (Swiss contribution).

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

    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.

  10. The Structure and Dynamics of the Solar Corona and Inner Heliosphere

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

  11. Diffusion in the chromosphere and the composition of the solar corona and energetic particles

    NASA Technical Reports Server (NTRS)

    Vauclair, S.; Meyer, J. P.

    1985-01-01

    Composition observations, in the solar photosphere, and in the upper transition region (TR) and corona imply a change of composition of the solar atmosphere somewhere between the photosphere and the upper TR. Heavy elements with first ionization potential (FIP) 9 eV (high-FIP element) are approx. 4 times less abundant in the TR and corona than in the photosphere, as compared to both hydrogen and heavy elements with lower low-FIP elements. A separation is suggested between neutral and ionized elements in a region where the high-FIP elements are mostly neutral, and the low-FIP elements ionized. This occurs in the chromosphere at altitudes above 600 km and below 2000 km above Photosphere. Whether the diffusion processes can explain the observed change in composition is investigated.

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

    NASA Technical Reports Server (NTRS)

    Von Puttkamer, J.

    1973-01-01

    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.

  13. The Source of Alfven Waves That Heat the Solar Corona

    NASA Technical Reports Server (NTRS)

    Ruzmaikin, A.; Berger, M. A.

    1998-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2013-01-01

    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.

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

    SciTech Connect

    Mirzoeva, I. K.

    2013-04-15

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

  16. Filament Channels: Isolated Laboratories of Plasma Heating in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Panasenco, O.; Velli, M.

    2015-12-01

    Solar filament channels are complex systems comprising photospheric, chromospheric and coronal components. These components include magnetic neutral lines, supergranule cells, fibrils (spicules), filaments (prominences when observed on the limb), coronal cells, filament cavities and their overlying coronal arcades. Filaments are very highly structured and extend in height from the photosphere to the corona. Filament cores have chromospheric temperatures - 10,000 K (even at coronal heights ~ 100 Mm), surrounded by hotter plasma with temperature up to ~50,000 K. The whole filament is isolated from the rest of the solar corona by an envelope - the filament channel cavity - with temperatures of about 2,000,000 K. The filament channel cavity is even hotter than the solar corona outside the filament channel arcade. The compactness and big temperature variations make filament channels unique ready-to-go laboratories of coronal plasma heating and thermodynamics. In this work we discuss possible sources and mechanisms of heating in the filament channel environment. In particular, we address the mechanisms of magnetic canceling and current sheet dissipation.

  17. Low Frequency Radio Observations of Bi-directional Electron Beams in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Carley, E.; Reid, H.; Vilmer, N.; Gallagher, P.

    2015-12-01

    The radio signature of a shock travelling through the solar corona is known as a type II solar radio burst. In rare cases, these bursts can exhibit a fine structure known as 'herringbones' which are a direct indicator of particle acceleration occurring at the shock front. However, few studies have been performed on herringbones and the details of the underlying particle acceleration processes are unknown. Here, we use an image processing technique known as the Hough transform to statistically analyse the herringbone fine structure in a radio burst at 20-90MHz observed from the Rosse Solar-Terrestrial Observatory on 2011 September 22. We identify 188 individual bursts which are signatures of bi-directional electron beams continuously accelerated to speeds of 0.16 c. This occurs at a shock acceleration site initially at a constant altitude of 0.6 Rsun in the corona, followed by a shift to 0.5 Rsun. The anti-sunward beams travel a distance of 170 Mm (and possibly further) away from the acceleration site, while those travelling toward the sun come to a stop sooner, reaching a smaller distance of 112 Mm. We show that the stopping distance for the sunward beams may depend on the total number density and the velocity of the beam. Our study concludes that a detailed statistical analysis of herringbone fine structure can provide information on the physical properties of the corona which lead to these relatively rare radio bursts.

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

    NASA Technical Reports Server (NTRS)

    Saba, J. L. R.

    1995-01-01

    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.

  19. SUPRATHERMAL ELECTRONS IN THE SOLAR CORONA: CAN NONLOCAL TRANSPORT EXPLAIN HELIOSPHERIC CHARGE STATES?

    SciTech Connect

    Cranmer, Steven R.

    2014-08-20

    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 Alfvén 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.

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

    NASA Astrophysics Data System (ADS)

    Kotov, Yu.; Cor-Phot Team

    "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 γ-radiation / NaI(Tl)/CsI(Na) phoswich; Full solar disk X- and γ-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.

  1. Solar activity and its evolution across the corona: recent advances

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

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

    PubMed

    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

    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

  3. The flow of interstellar dust into the solar system

    NASA Astrophysics Data System (ADS)

    Sterken, V. J.; Altobelli, N.; Kempf, S.; Schwehm, G.; Srama, R.; Grün, E.

    2012-02-01

    Context. Interstellar dust (ISD) is a major component in the formation and evolution of stars, stellar systems, and planets. Astronomical observations of interstellar extinction and polarization, and of the infrared emission of the dust, are the most commonly used technique for characterizing interstellar dust. Besides this, the interstellar dust from the local interstellar cloud enters the solar system owing to the relative motion of the Sun with respect to this cloud. Once in the solar system, in-situ observations can be made by spacecraft using impact ionization detectors and time-of-flight spectrometers like the ones flown on the Cassini, Ulysses, and Galileo, spacecrafts. Also a sample return can be done, as in the Stardust mission. Once in the solar system, the trajectories of these dust grains are shaped by gravitational, solar radiation pressure, and Lorentz forces. The Lorentz forces result from the interaction of the charged dust particles with the interplanetary magnetic field. The ISD densities in the solar system thus depend both on the location in the solar system and on time, correlated to the solar cycle. Aims: This paper aims at giving the reader insight into the flow patterns of ISD when it moves through the solar system. This is useful for designing future in-situ or sample return missions or for knowing whether for specific missions, simplified assumptions can be used for the dust flux and direction, or whether full simulations are needed. Methods: We characterize the flow of ISD 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. Dust densities, fluxes, and directionalities are derived from the trajectory simulations. Different graphics representations are used to gain insight

  4. Conditions for electron-cyclotron maser emission in the solar corona

    NASA Astrophysics Data System (ADS)

    Morosan, D. E.; Zucca, P.; Bloomfield, D. S.; Gallagher, P. T.

    2016-05-01

    Context. The Sun is an active source of radio emission ranging from long duration radio bursts associated with solar flares and coronal mass ejections to more complex, short duration radio bursts such as solar S bursts, radio spikes and fibre bursts. While plasma emission is thought to be the dominant emission mechanism for most radio bursts, the electron-cyclotron maser (ECM) mechanism may be responsible for more complex, short-duration bursts as well as fine structures associated with long-duration bursts. Aims: We investigate the conditions for ECM in the solar corona by considering the ratio of the electron plasma frequency ωp to the electron-cyclotron frequency Ωe. The ECM is theoretically possible when ωp/ Ωe< 1. Methods: Two-dimensional electron density, magnetic field, plasma frequency, and electron cyclotron frequency maps of the off-limb corona were created using observations from SDO/AIA and SOHO/LASCO, together with potential field extrapolations of the magnetic field. These maps were then used to calculate ωp/Ωe and Alfvén velocity maps of the off-limb corona. Results: We found that the condition for ECM emission (ωp/ Ωe< 1) is possible at heights <1.07 R⊙ in an active region near the limb; that is, where magnetic field strengths are >40 G and electron densities are >3 × 108 cm-3. In addition, we found comparatively high Alfvén velocities (>0.02c or >6000 km s-1) at heights <1.07 R⊙ within the active region. Conclusions: This demonstrates that the condition for ECM emission is satisfied within areas of the corona containing large magnetic fields, such as the core of a large active region. Therefore, ECM could be a possible emission mechanism for high-frequency radio and microwave bursts.

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

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

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

  6. The FIP and Inverse FIP Effects in Solar and Stellar Coronae

    NASA Astrophysics Data System (ADS)

    Laming, J. Martin

    2015-09-01

    We review our state of knowledge of coronal element abundance anomalies in the Sun and stars. We concentrate on the first ionization potential (FIP) effect observed in the solar corona and slow-speed wind, and in the coronae of solar-like dwarf stars, and the "inverse FIP" effect seen in the corona of stars of later spectral type; specifically M dwarfs. These effects relate to the enhancement or depletion, respectively, in coronal abundance with respect to photospheric values of elements with FIP below about 10 eV. They are interpreted in terms of the ponderomotive force due to the propagation and/or reflection of magnetohydrodynamic waves in the chromosphere. This acts on chromospheric ions, but not neutrals, and so can lead to ion-neutral fractionation. A detailed description of the model applied to closed magnetic loops, and to open field regions is given, accounting for the observed difference in solar FIP fractionation between the slow and fast wind. It is shown that such a model can also account for the observed depletion of helium in the solar wind. The helium depletion is sensitive to the chromospheric altitude where ion-neutral separation occurs, and the behavior of the helium abundance in the closed magnetic loop strongly suggests that the waves have a coronal origin. This, and other similar inferences may be expected to have a strong bearing on theories of solar coronal heating. Chromospheric waves originating from below as acoustic waves mode convert, mainly to fast-mode waves, can also give rise to ion-neutral separation. Depending on the geometry of the magnetic field, this can result in FIP or Inverse FIP effects. We argue that such configurations are more likely to occur in later-type stars (known to have stronger field in any case), and that this explains the occurrence of the Inverse FIP effect in M dwarfs. We conclude with a discussion of possible directions for future work.

  7. Comparative Study on Hot Atom Coronae of Solar and Extrasolar Planets

    NASA Astrophysics Data System (ADS)

    Shematovich, Valery

    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

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

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

    We present results from 14 exceptionally high-reaching large solar jets observed in the polar coronal holes. EUV movies from SDO/AIA show that each jet is similar to many other similar-size and smaller jets that erupt in coronal holes, but each is exceptional in that it goes higher than most other jets, so high that it is observed in the outer corona beyond 2.2 R(sub Sun) in images from the SOHO/LASCO/C2 coronagraph. For these high-reaching jets, we find: (1) the front of the jet transits the corona below 2.2 R(sub Sun) at a speed typically several times the sound speed; (2) each jet displays an exceptionally large amount of spin as it erupts; (3) in the outer corona, most jets display oscillatory swaying having an amplitude of a few degrees and a period of order 1 hour. We conclude that these jets are magnetically driven, propose that the driver is a magnetic-untwisting wave that is grossly a large-amplitude (i.e., nonlinear) torsional Alfven wave that is put into the reconnected open magnetic field in the jet by interchange reconnection as the jet erupts, and estimate from the measured spinning and swaying that the magnetic-untwisting wave loses most of its energy in the inner corona below 2.2 R(sub Sun). From these results for these big jets, we reason that the torsional magnetic waves observed in Type-II spicules should dissipate in the corona in the same way and could thereby power much of the coronal heating in coronal holes.

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

    SciTech Connect

    Sittler, E.C. Jr.; Guhathakurta, M.

    1999-10-01

    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

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

    NASA Astrophysics Data System (ADS)

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

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

  12. The effects of restricted “EIT wave” propagation on the low solar corona

    NASA Astrophysics Data System (ADS)

    Long, David; Perez-Suarez, David

    2015-08-01

    We present observations of an “EIT wave” associated with an X-class flare from 2012-July-6, the propagation of which was severely restricted by the magnetic structure of the solar corona surrounding the erupting active region. The “EIT wave” was observed by both SDO and STEREO-A, allowing a three-dimensional examination of how the propagation of the disturbance was affected both by a neighbouring coronal hole and a trans-equatorial loop system. In addition, the eruption was observed at the limb by the ground-based CoMP instrument, allowing the Doppler motion associated with the eruption and resulting coronal loop oscillation to be investigated in detail. This combination of data-sets provides a unique insight into the three-dimensional evolution of the “EIT wave” and its effects on the surrounding corona.

  13. A Simple Dynamical Model for Filament Formation in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Litvinenko, Y.

    2005-12-01

    Filament formation in the solar corona is considered in the case of a slowly evolving force-free magnetic field. The strong-field approximation is used, which takes into account the magnetohydrodynamic equations of motion, induction, and compressibility. Methods for solving the relevant equations are presented and applied to filament modeling. A three-dimensional calculation is presented, which uses linear force-free magnetic fields. The boundary conditions are chosen to resemble the qualitative linkage model for the formation of filaments, suggested by Martens and Zwaan (2001). Consistent with this model, dense formations, reminiscent of filament pillars, are shown to appear in the corona above the region of converging and canceling magnetic bipoles. The results demonstrate the principal role of magnetic field in the dynamical processes of dense plasma accumulation and support in filaments. The model can be useful for clarifying the role of flux emergence in coronal mass ejection initiation.

  14. Simultaneous VLA and UVCS/SOHO Observations of the Solar Corona

    NASA Astrophysics Data System (ADS)

    Spangler, S. R.; Miralles, M. P.; Cranmer, S. R.; Raymond, J. C.

    2004-12-01

    Measurement of Faraday rotation of radio waves which propagate through the solar corona is one of the best ways of measuring the coronal magnetic field. Faraday rotation can provide information on both the large scale, static component of this field as well as the fluctuating, turbulent component, but the technique requires supplementary information on the coronal plasma. On August 16, 2003, the line of sight to the extended, polarized radio source 3C228 passed through the corona, with a closest heliocentric distance of 7 to 8 solar radii. Polarimetric observations with the Very Large Array of the National Radio Astronomy Observatory were made at 21 and 18 cm. These data yielded measurements of the rotation measure (proportional to the path integral of plasma density and line-of-sight component of the magnetic field) along several, closely-spaced lines of sight through the corona. Simultaneous observations of the OVI and HI Lyman alpha emission lines with the Ultraviolet Coronagraph Spectrometer (UVCS) aboard SOHO were used to determine kinetic temperature, average densities, and outflow speeds in the corona. On that day, the line of sight passed close to a coronal streamer. The VLA data show a very large Faraday rotation event during the eight hour observing session, in which the rotation measure changed by 62 rad/m2. This large variation seems to be associated with passage of the coronal current sheet through the line of sight. We will present models of the coronal magnetic field consistent with our observations. This work was supported at the University of Iowa by grant ATM03-54782 from the Division of Atmospheric Sciences, National Science Foundation. At Smithsonian Astrophysical Observatory, this work is supported by NASA under grant NNG04GE84G, by the Italian Space Agency, and by PRODEX (Swiss contribution).

  15. Formation and Evolution of Large-Scale Magnetic Funnels in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Panasenco, Olga; Velli, Marco

    2016-05-01

    The existence of open coronal magnetic fields with peculiar geometry - large-scale magnetic funnels - can be attributed to three factors: (i) the presence of two or more corona holes of the same polarity (or pseudostreamers - PSs), (ii) specific configurations of closed magnetic field in the low corona up to 1.3 Rs (filament channels) and (iii) the presence of strong active regions in the vicinity of the pseudostreamer. The important property of magnetic funnels is their strongly non-monotonic expansion factor below 2 Rs. The case study presented here is a pseudostreamer near the equator, formed between two isolated coronal holes of the same polarity, and harboring a pair of twin filaments in its base. Following the evolution of these coronal holes we find that the PS topology changes when two coronal holes merged together. Using a potential field source-surface (PFSS) extrapolation to compute the coronal field from photospheric maps (SDO/HMI), we show that the funnel-like geometry of the open magnetic field changes to a regular one with monotonic expansion factor after the merging of coronal holes. The presence of coronal magnetic funnels becomes directly visible when sufficient plasma accumulates inside them: when the plasma density grows to become observable coronal cloud prominences appear in the corona. The plasma suspension at heights of 0.3 Rs coincides with the largest gradients in the field which naturally leads to a diamagnetic hypothesis for the force counteracting gravity. We study the evolution of the funnel-like open fields during several solar rotations and find a direct relation between funnels and the presence of coronal clouds at great heights in the solar corona.

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

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

    We have developed a two-dimensional semiempirical MHD model of the solar corona and solar wind. The model uses empirically derived electron density profiles from white-light coronagraph data measured during the Skylub period and an empirically derived model of the magnetic field which is fitted to observed streamer topologies, which also come from the white-light coronagraph data The electron density model comes from that developed by Guhathakurta and coworkers. The electron density model is extended into interplanetary space by using electron densities derived from the Ulysses plasma instrument. The model also requires an estimate of the solar wind velocity as a function of heliographic latitude and radial component of the magnetic field at 1 AU, both of which can be provided by the Ulysses spacecraft. The model makes estimates as a function of radial distance and latitude of various fluid parameters of the plasma such as flow velocity V, effective temperature T(sub eff), and effective heat flux q(sub eff), which are derived from the equations of conservation of mass, momentum, and energy, respectively. The term effective indicates that wave contributions could be present. The model naturally provides the spiral pattern of the magnetic field far from the Sun and an estimate of the large-scale surface magnetic field at the Sun, which we estimate to be approx. 12 - 15 G. The magnetic field model shows that the large-scale surface magnetic field is dominated by an octupole term. The model is a steady state calculation which makes the assumption of azimuthal symmetry and solves the various conservation equations in the rotating frame of the Sun. The conservation equations are integrated along the magnetic field direction in the rotating frame of the Sun, thus providing a nearly self-consistent calculation of the fluid parameters. The model makes a minimum number of assumptions about the physics of the solar corona and solar wind and should provide a very accurate

  17. New View of Gas and Dust in the Solar Nebula

    NASA Astrophysics Data System (ADS)

    Taylor, G. J.

    2010-08-01

    The recognizable components in meteorites differ in their relative abundances of the three oxygen isotopes (16O, 17O, and 18O). In particular, the amount of 16O varies from being like that of the Earth to substantially enriched compared to the other two isotopes. The current explanation for this interesting range in isotopic composition is that dust and gas in the solar nebula (the cloud of gas and dust surrounding the primitive Sun) began with the same 16O-rich composition, but the solids evolved towards the terrestrial value. A new analysis of the problem by Alexander Krot (University of Hawaii) and colleagues at the University of Hawaii, the University of Chicago, Clemson University, and Lawrence Livermore National Laboratory leads to the bold assertion that primordial dust and gas differed in isotopic composition. The gas was rich in 16O as previously thought (possibly slightly richer in 16O than the measurements of the solar wind returned by the Genesis Mission), but that the dust had a composition close to the 16O-depleted terrestrial average. In this new view, the dust had a different history than did the gas before being incorporated into the Solar System. Solids with compositions near the terrestrial line may have formed in regions of the solar nebula where dust had concentrated compared to the mean solar dust/gas ratio (1 : ~100). The idea has great implications for understanding the oxygen-isotope composition of the inner Solar System and the origin of materials in the molecular cloud from which the Solar System formed.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1999-03-01

    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.

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

    SciTech Connect

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

    2013-03-10

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

  1. 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)

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

    2008-01-01

    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.

  2. Dust inventory through the Solar System: From Earth to Pluto

    NASA Astrophysics Data System (ADS)

    Piquette, M. R.; Horanyi, M.; Stern, A.; Bagenal, F.; Szalay, J.; Poppe, A. R.; Weaver, H. A., Jr.; Young, L. A.; Olkin, C.; Ennico Smith, K.

    2015-12-01

    The Student Dust Counter (SDC) is an impact dust detector onboard the New Horizons spacecraft, observing the dust density distribution since April 2006 across the Solar System. SDC measures 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 compared to model predictions following the orbital evolution of dust grains originating from the Edgeworth-Kuiper Belt and migrating inward due to Poynting-Robertson drag. SDC's results, as well as data taken by the Pioneer 10 dust detector, are compared to model predictions to estimate the mass production rate and the ejecta size distribution power law exponent. On July 14, 2015, the New Horizons spacecraft passed through the Pluto system and is now continuing to take measurements in the solar system's third zone, the Kuiper Belt. The measurements SDC has taken throughout the solar system, including in the Pluto-Charon system, will be discussed in this presentation, as well as predictions for the dust distribution it will measure as it explores the Kuiper Belt.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    Faraday rotation (FR) techniques have been used to probe variations of coronal plasma velocity, density and magnetic field. The plane of polarization for an electromagnetic wave rotates in proportion to the integrated product of parallel magnetic field components and electron density along the radio signal line-of-sight as directed towards the receiving antenna. Fluctuations in FR through the corona thus represent the evolution of these line-integrated plasma parameters, providing a unique measurement of regional corona physics. The MESSENGER spacecraft radio 8 GHz radio beacon, transmitting through the corona at offsets 1.6 to 1.9 solar radii and near-equatorial heliolatitude, was recorded on the Green Bank radio telescope during the solar minimum of 2009. Here we reanalyze at higher temporal resolution the data previously published (Jensen et al 2013, Solar Physics 285:83-95). Combinations of coherent and incoherent integration were used to estimate Stokes parameters, from which the FR phase differences were obtained for serial one-second frames. Results were concatenated and corrected for phase wrap-around to produce a continuous FR phase curve. The general FR phase curve was broad and sweeping, with greatest spectral power observed in periods of hours. Also, finer wave-like fluctuations were noted with periods on the order of 100's of seconds. With the lowest-frequency components removed by detrending techniques, spectral analysis revealed a power spectrum of form P=kνα with spectral index α = -2.25 over frequencies ν = 2-20 milliHertz (mHz), and a flat noise spectrum at higher frequencies. Imposed upon the general power spectrum were trends of enhanced spectral power around 3.5 and 6 mHz, corresponding to approximately 5- and 3-minute period waves. Temporal evolution plots demonstrated that the increased power in these spectral bands appeared intermittently and irregularly. Our results reinforce the findings of prior coronal FR studies, and now extend the

  4. Coronagraph observations and analyses of the ultraviolet solar corona

    NASA Technical Reports Server (NTRS)

    Kohl, John L.

    1989-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

    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.

  6. Heating of the solar and stellar coronae: a review

    NASA Astrophysics Data System (ADS)

    Erdélyi, R.; Ballai, I.

    2007-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  8. Expansion of the solar wind from a two-hole corona

    NASA Technical Reports Server (NTRS)

    Whang, Y. C.

    1983-01-01

    A one-fluid model is employed to study the global expansion of the solar wind from a two-hole corona, under the assumptions that the holes are confined to polar caps within 30 deg of heliographic colatitude, the flow is steady and axisymmetric, and the geometry of streamlines is prescribed. The boundary conditions are adjusted in such a way that the calculated solar-wind properties at 1 AU are in reasonable agreement with observational results. A series of numerical solutions are obtained, the series produces a maximum terminal speed of 829 km/s at the pole. The calculated solar-wind speeds are strongly latitude-dependent and are positively correlated with local divergence factor of a stream tube. The solutions imply that most plasma properties are highly inhomogeneous at the polar caps. The flow velocity, the temperature, the proton-number flux and the conduction-heat flux all increase towards the hole center.

  9. Proton Heating in the Extended Solar Corona Resulting From Kinetic Alfven Turbulence

    NASA Astrophysics Data System (ADS)

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

    2002-12-01

    Spectroscopic observations of the solar corona have made it clear that the ``coronal heating problem'' comprises not only the local deposition of heat immediately above the transition region, but also extended heat deposition throughout the (collisionless) acceleration region of the solar wind. The dissipation of magnetohydrodynamic (MHD) waves and/or turbulence has been considered as a likely heating mechanism in the solar wind for several decades. However, it is still not well understood how MHD fluctuations are generated, how they evolve in frequency and wavenumber, or how their damping leads to the observed proton, electron, and ion properties of the fast wind. We present a model of MHD turbulence that specifically addresses the issue of kinetic dissipation and particle heating in the collisionless extended corona. The nonlinear cascade is modeled as a combination of advection and diffusion in wavenumber space, with the dominant cascade occurring in the direction perpendicular to the background magnetic field. This leads to a highly anisotropic fluctuation spectrum (as expected, based on many earlier simulations and scaling models) with a rapidly decreasing power-law tail in the parallel wavenumber direction. In the low-plasma-beta corona, the dominant oblique fluctuations (with dispersion properties of kinetic Alfven waves) are dissipated by electron Landau damping, with only a tiny fraction of the energy going to high-frequency ion cyclotron waves. This implies strong parallel electron heating and weak proton and ion heating, which is not what is observed. We discuss the probable nonlinear evolution of the electron velocity distributions into parallel beams and discrete phase-space holes (similar to those seen in the terrestrial magnetosphere) which can possibly heat protons via stochastic interactions.

  10. Low frequency radio observations of bi-directional electron beams in the solar corona

    NASA Astrophysics Data System (ADS)

    Carley, Eoin P.; Reid, Hamish; Vilmer, Nicole; Gallagher, Peter T.

    2015-09-01

    The radio signature of a shock travelling through the solar corona is known as a type II solar radio burst. In rare cases these bursts can exhibit a fine structure known as "herringbones", which are a direct indicator of particle acceleration occurring at the shock front. However, few studies have been performed on herringbones and the details of the underlying particle acceleration processes are unknown. Here, we use an image processing technique known as the Hough transform to statistically analyse the herringbone fine structure in a radio burst at ~20-90 MHz observed from the Rosse Solar-Terrestrial Observatory on 2011 September 22. We identify 188 individual bursts which are signatures of bi-directional electron beams continuously accelerated to speeds of 0.16-0.10+0.11 c. This occurs at a shock acceleration site initially at a constant altitude of ~0.6 R⊙ in the corona, followed by a shift to ~0.5 R⊙. The anti-sunward beams travel a distance of 170-97+174 Mm (and possibly further) away from the acceleration site, while those travelling toward the Sun come to a stop sooner, reaching a smaller distance of 112-76+84 Mm. We show that the stopping distance for the sunward beams may depend on the total number density and the velocity of the beam. Our study concludes that a detailed statistical analysis of herringbone fine structure can provide information on the physical properties of the corona which lead to these relatively rare radio bursts.

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

    NASA Technical Reports Server (NTRS)

    Titov, V. S.

    2007-01-01

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

  12. Electrodynamic Dust Shield for Solar Panels on Mars

    NASA Technical Reports Server (NTRS)

    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

    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.

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

    SciTech Connect

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

    2013-11-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

    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.

  15. Induced emission of Alfvén waves - the missing source of solar corona heating and solar wind acceleration

    NASA Astrophysics Data System (ADS)

    Galinsky, Vitaly; Shevchenko, Valentin

    2013-10-01

    The solar corona is considerably hotter than Sun's surface or photosphere. However, the mechanism that heats it to millions of degrees is still under debates. Recent observations revealed presence of the ubiquitous outward-propagating Alfvénic motions with amplitudes up to 25 km s-1 and periods of the order of 100-500s throughout the quiescent atmosphere, thus suggesting the possible source of energy for acceleration of the fast solar wind and heating the quiet corona. Nevertheless, the challenge remains to understand how these waves are dissipated in the solar atmosphere, and how that dissipation delivers energy to the ions and electrons that comprise the coronal plasma and solar wind. Here we report a method that extends and extrapolates these observational data up to the level suitable for constraining and verification of heating and acceleration models. The macro-scale instability of the marginally stable particle distribution function compliments the resonant frequency sweeping dissipation of transient Alfvén waves by their induced emission in inhomogeneous streaming plasma that provides enough energy for keeping the plasma temperature decaying not faster than r-1 - in close agreement with in situ heliospheric observations.

  16. Short-period intensity oscillations in the solar corona observed during the total solar eclipse of 26 February 1998

    NASA Astrophysics Data System (ADS)

    Cowsik, Ramanath; Singh, Jagdev; Saxena, A. K.; Srinivasan, R.; Raveendran, A. V.

    1999-08-01

    Encouraged by the detection of high-frequency, low-amplitude continuum intensity oscillations in the solar corona during the total solar eclipse of 1995, we designed and fabricated a six-channel photometer incorporating low-noise Hamamatsu R647 photomultipliers. Fast photometry at five different locations in the solar corona was performed at Don Bosco Mission, Venezuela during the total solar eclipse of 26 February 1998. Three interference filters with passbands of about 150 Å and centered around 4700, 4900, and 5000 Å were used. The photometric data were recorded at a rate of 20 Hz in three channels and 50 Hz in the remaining three channels. The power spectrum analysis of one of the channels that recorded appreciable counts indicates the existence of intensity oscillations in the frequency range 0.01-0.2 Hz. A least-squares analysis yields 90.1, 25.2, and 6.9 s periods for the three prominent components which have amplitudes in the range 0.5-3.5% of the coronal brightness. These periods and their amplitudes are similar to those detected in the coronal intensity oscillations during the 1995 eclipse.

  17. Observations of the brightness temperature distribution of the quiet solar corona at decametric wavelengths

    NASA Technical Reports Server (NTRS)

    Sastry, Ch. V.

    1987-01-01

    The brightness temperature distribution of the quiet solar corona at a wavelength of 8.9 meters is measured by two types of radio telescope: (1) a 'T' type array with a resolution of 26'X38', and (2) a fan beam interferometer with an E-W resolution of 3'. It is found that the persistent bright regions do not have any angular structure on scales of 6' or less. The daily variations of the brightness temperature of different regions are studied and the possible interpretation discussed.

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

    SciTech Connect

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

    2007-07-13

    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.

  19. Numerical Modeling of the Solar Chromosphere and Corona: What Has Been Done? What Should Be Done?

    NASA Astrophysics Data System (ADS)

    Hansteen, V.; Carlsson, M.; Gudiksen, B.

    2015-10-01

    A number of increasingly sophisticated numerical simulations spanning the solar atmosphere from below the photosphere in the convection zone to far above in the corona have shed considerable insight into the role of the magnetic field in the structure and energetics of the Sun's outer layers. This development is strengthened by the wealth of observational data now coming on-line from both ground and space based observatories. In this talk we will concentrate on the successes and failures of the modeling effort thus far and discuss the inclusion of various effects not traditionally considered in the MHD description such as time dependent ionization, non-LTE radiative transfer, and generalized Ohm's law.

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

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

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

  1. Dust to planetesimals - Settling and coagulation in the solar nebula

    NASA Technical Reports Server (NTRS)

    Weidenschilling, S. J.

    1980-01-01

    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 mechanisms between the inner and outer nebula. A numerical model for computing simultaneous coagulation and settling is described.

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

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

    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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    SciTech Connect

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

    2013-03-20

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

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

    SciTech Connect

    Habbal, Shadia Rifai; Morgan, Huw; Druckmueller, Miloslav; Ding, Adalbert

    2010-03-10

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

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

  7. Polar and equatorial coronal hole winds at solar minima: From the heliosphere to the inner corona

    SciTech Connect

    Zhao, L.; Landi, E.

    2014-02-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Zhao, L.; Landi, E.

    2014-02-01

    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.

  9. Kinetic Simulation of Slow Magnetosonic Waves and Quasi-Periodic Upflows in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Ruan, Wenzhi; He, Jiansen; Zhang, Lei; Vocks, Christian; Marsch, Eckart; Tu, Chuanyi; Peter, Hardi; Wang, Linghua

    2016-07-01

    Quasi-periodic disturbances of emission-line parameters are frequently observed in the corona. These disturbances propagate upward along the magnetic field with speeds of ∼100 km s‑1. This phenomenon has been interpreted as evidence of the propagation of slow magnetosonic waves or has been argued to be a signature of intermittent outflows superposed on the background plasmas. Here we aim to present a new “wave + flow” model to interpret these observations. In our scenario, the oscillatory motion is a slow-mode wave, and the flow is associated with a beam created by the wave–particle interaction owing to Landau resonance. With the help of a kinetic model, we simulate the propagation of slow-mode waves and the generation of beam flows. We find that weak periodic beam flows can be generated by to Landau resonance in the solar corona, and the phase with the strongest blueward asymmetry is ahead of that with the strongest blueshift by about 1/4 period. We also find that the slow wave damps to the level of 1/e after the transit time of two wave periods, owing to Landau damping and Coulomb collisions in our simulation. This damping timescale is similar to that resulting from thermal conduction in the MHD regime. The beam flow is weakened/attenuated with increasing wave period and decreasing wave amplitude since Coulomb collisions become more and more dominant over the wave action. We suggest that this “wave + flow” kinetic model provides an alternative explanation for the observed quasi-periodic propagating perturbations in various parameters in the solar corona.

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

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

    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.

  11. The potential of hydrogen lines for the spectropolarimetry of the solar corona

    NASA Astrophysics Data System (ADS)

    Vial, Jean-Claude; Chane-Yook, Martine

    2016-07-01

    Neutral Hydrogen lines have been detected in the hot and ionized solar corona as early as 1970 (Gabriel et al. 1971) and since then with the Spartan and UVCS/SoHO space experiments. Moreover, because of the sensitivity of the Lyman lines to the Hanle effect (Bommier and Sahal-Brechot 1982, Trujillo Bueno et al. 2005), polarization measurements in these lines could lead to the diagnostic of weak magnetic fields in the corona (Derouich et al. 2010), a challenge which has led to various space mission proposals such as LYOT/SMESE or MASC. Our investigation concerns the computation of the emission in 10 selected lines of Hydrogen (Lyman, Balmer, and Paschen) taking into account the proper computation of the NonLTE H ionization and atomic levels populations. We present the results for three different coronal models (streamer, quiet Sun and coronal hole) in terms of profiles and absolute intensities at altitudes varying from 1.05 to 1.9 solar radius. These spectrophotometric results could help for the determination of the space and ground-based polarimetric instrumentation best suited for the measurement of the coronal magnetic field.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    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 ( σ/ λ)2 and M -1, where σ, λ 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″.

  14. A Simple Dynamical Model for Filament Formation in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Litvinenko, Yuri E.; Wheatland, M. S.

    2005-09-01

    Filament formation in the solar atmosphere is considered. In the limit of sub-Alfvénic but supersonic motion, plasma flow in the solar corona is driven via the induction equation by a slow evolution of force-free magnetic fields. Methods for solving the relevant magnetohydrodynamic equations are presented and applied to filament modeling in two and three dimensions. An illustrative two-dimensional example is given, which is based on a potential magnetic field with a dip. The example describes the formation of a normal filament between two bipolar regions on the Sun. Next a detailed three-dimensional calculation is presented, which uses linear force-free magnetic fields. The boundary conditions are chosen to resemble the qualitative ``head-to-tail'' linkage model for the formation of filaments, suggested by Martens & Zwaan. Consistent with this model, dense formations, reminiscent of filament pillars, are shown to appear in the corona above the region of converging and canceling magnetic bipoles. The numerical results are consistent with the principal role of magnetic field in the dynamical processes of dense plasma accumulation and support in filaments, advocated by Martens & Zwaan.

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

    PubMed

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

    2008-11-01

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

  16. Synthetic spectral analysis of a kinetic model for slow-magnetosonic waves in solar corona

    NASA Astrophysics Data System (ADS)

    Ruan, Wenzhi; He, Jiansen; Zhang, Lei; Vocks, Christian; Marsch, Eckart; Tu, Chuanyi; Peter, Hardi; Wang, Linghua

    2016-03-01

    We propose a kinetic model of slow-magnetosonic waves to explain various observational features associated with the propagating intensity disturbances (PIDs) occurring in the solar corona. The characteristics of slow mode waves, e.g, inphase oscillations of density, velocity, and thermal speed, are reproduced in this kinetic model. Moreover, the red-blue (R-B) asymmetry of the velocity distribution as self-consistently generated in the model is found to be contributed from the beam component, as a result of the competition between Landau resonance and Coulomb collisions. Furthermore, we synthesize the spectral lines and make the spectral analysis, based on the kinetic simulation data of the flux tube plasmas and the hypothesis of the surrounding background plasmas. It is found that the fluctuations of parameters of the synthetic spectral lines are basically consistent with the observations: (1) the line intensity, Doppler shift, and line width are fluctuating in phase; (2) the R-B asymmetry usually oscillate out of phase with the former three parameters; (3) the blueward asymmetry is more evident than the redward asymmetry in the R-B fluctuations. The oscillations of line parameters become weakened for the case with denser surrounding background plasmas. Similar to the observations, there is no doubled-frequency oscillation of the line width for the case with flux-tube plasmas flowing bulkly upward among the static background plasmas. Therefore, we suggest that the "wave + beam flow" kinetic model may be a viable interpretation for the PIDs observed in the solar corona.

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

    NASA Technical Reports Server (NTRS)

    Reames, Donald V.

    1992-01-01

    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.

  18. Optimization of a motion tracking and mapping method based on images of the solar corona

    NASA Astrophysics Data System (ADS)

    Pavlova, Petya; Garnevski, Dimitar; Koleva, Kostadinka

    2016-01-01

    The study presents the current stage of development and application of a motion tracking and mapping method, based on solar corona images. The object of discussion is the problem of image processing during the extraction of features of interest in the sequence of solar prominences images. At first the method requires calculating techniques that ensure processing time-period commensurable with the time-period of the fastest developing part of the prominence body. That defines the necessity of optimization of the basic algorithms. The paper describes results of test procedures on accepted approaches for reducing the operation time by parallel processing of the images. The method also requires presentation of the lightness information independently of the sensor of particular coronagraph and image file format. This investigation proposes two techniques for achievement the identity of images from different instruments/sensors.

  19. Synthetic Hydrogen Spectra of Oscillating Prominence Slabs Immersed in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Zapiór, M.; Oliver, R.; Ballester, J. L.; Heinzel, P.

    2016-08-01

    We study the behavior of Hα and Hβ spectral lines and their spectral indicators in an oscillating solar prominence slab surrounded by the solar corona, using an MHD model combined with a 1D radiative transfer code taken in the line of sight perpendicular to the slab. We calculate the time variation of the Doppler shift, half-width, and maximum intensity of the Hα and Hβ spectral lines for different modes of oscillation. We find a non-sinusoidal time dependence of some spectral parameters with time. Because Hα and Hβ spectral indicators have different behavior for different modes, caused by differing optical depths of formation and different plasma parameter variations in time and along the slab, they may be used for prominence seismology, especially to derive the internal velocity field in prominences.

  20. THE ORIGIN OF NON-MAXWELLIAN SOLAR WIND ELECTRON VELOCITY DISTRIBUTION FUNCTION: CONNECTION TO NANOFLARES IN THE SOLAR CORONA

    SciTech Connect

    Che, H.; Goldstein, M. L.

    2014-11-10

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

  1. The Time-Dependent Chemistry of Cometary Debris in the Solar Corona

    NASA Technical Reports Server (NTRS)

    Pesnell, W. D.; Bryans, P.

    2015-01-01

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

  2. The time-dependent chemistry of cometary debris in the solar corona

    SciTech Connect

    Pesnell, W. D.; Bryans, P.

    2014-04-10

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

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

    NASA Astrophysics Data System (ADS)

    Pesnell, W. D.; Bryans, P.

    2014-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

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

  6. Solar wind mass-loading due to dust

    NASA Astrophysics Data System (ADS)

    Rasca, A. P.; Horányi, M.

    2013-06-01

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

  7. Solar Wind Mass-Loading Due to Dust

    NASA Astrophysics Data System (ADS)

    Rasca, A.; Horanyi, M.

    2011-12-01

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

  8. Large Area Dust Detector onboard Solar Power Sail Spacecraft

    NASA Astrophysics Data System (ADS)

    Yano, Hajime

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

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

    NASA Technical Reports Server (NTRS)

    Gehrz, Robert D.

    1991-01-01

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

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

    SciTech Connect

    Nuevo, Federico A.; Vasquez, Alberto M.; Huang Zhenguang; Frazin, Richard; Manchester, Ward B. IV; Jin Meng

    2013-08-10

    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.

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

    SciTech Connect

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

    2010-07-20

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

  12. International Solar Cycle Studies [ISCS] Working Group 2: solar magnetic field variability - from the lower atmosphere through the inner corona

    NASA Astrophysics Data System (ADS)

    Harrison, Richard A.; Michels, Donald

    This report is a summary of activities and plans relating to the International Solar Cycle Studies (ISCS) Working Group 2, which is concerned with solar magnetic field variability, from the lower atmosphere through the inner corona. Whilst the Working Group carries a rather general title, the activities are focusing on several well defined topics - in particular the onset of coronal mass ejection events. Recognising the large number of scientific meetings worldwide, the working style of this group is aimed at improving communication, information exchange and collaboration making use of existing meetings and with a minimum of red tape. The core of the activity is through the use of the World Wide Web and e-mail. In this way, this Working Group does not introduce extra effort, but provides a better focus for on-going projects.

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

    NASA Technical Reports Server (NTRS)

    Mikic, Zoran; Grebowsky, Joseph (Technical Monitor)

    2001-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

    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.

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

    SciTech Connect

    Tajfirouze, E.; Safari, H.

    2012-01-10

    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.

  18. Three-Dimensional Reconstruction of the Electron Density in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Burnett, L. W.; Nychka, D. W.; Gibson, S. E.; Dalmasse, K.

    2015-12-01

    The need to understand the Sun's magnetic field motivates much of present-day solar physics research. Our ultimate goal is to quantitatively validate models of the global coronal magnetic field by comparing forward models of synthetic data to real observations. As a necessary first step, we seek to build a three-dimensional (3D) model of the electron density in the solar corona, based on white-light coronagraph data. Given that these observations are two-dimensional snapshots, we employ a new application of statistical tomography to piece together the full 3D picture. In an initial step, we demonstrate that our method is capable of reconstructing geometrically-simple density formations. We next turn to more realistic coronal density structures as represented by the global magnetohydrodynamic models made available by Predictive Science Inc., and integrated to create synthetic data using the FORWARD SolarSoft codes. Finally, we consider the application of our method to Mauna Loa Solar Observatory K-Coronagraph observations, and discuss the strengths and limitations of our method.

  19. THE ENERGETICS OF A GLOBAL SHOCK WAVE IN THE LOW SOLAR CORONA

    SciTech Connect

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

    2015-02-01

    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 × 10{sup 31} erg to produce the ''EIT wave'', which is approximately 10% the kinetic energy of the associated CME (shown to be ≈2.5 × 10{sup 32} 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.

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

    NASA Technical Reports Server (NTRS)

    Ofman, L.; Thompson, B. J.

    2011-01-01

    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).

  1. Solar Array Panels With Dust-Removal Capability

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

    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.

  2. Enhanced damping of Alfven waves in the solar corona by a turbulent wave spectrum

    NASA Technical Reports Server (NTRS)

    Kleva, Robert G.; Drake, J. F.

    1992-01-01

    The effect of a background spectrum of Alfven waves on the rate of dissipation of a test shear Alfven wave is numerically calculated. The results demonstrate that as the classical resistivity eta and classical viscosity mu become small, the damping rate of the Alfven wave remains large and depends only on the amplitude for the scalar potential of the wave spectrum and the wavenumber of the Alfven wave. The damping rate is virtually independent of eta and mu. The wave spectrum need not be turbulent or stochastic to affect the damping rate. The dissipation rate is nonlinear enhanced by nonstochastic spectra as well as by stochastic spectra if two conditions are met. First, the perpendicular magnetic field associated with Alfven wave spectrum must exceed a certain collision-frequency threshold and second, for nonstochastic spectra only, the magnetic field must exceed a threshold proportional to the parallel wavenumber of the shear Alfven wave. These conditions can be easily satisfied in the solar corona.

  3. X-ray spectrometer spectrograph telescope system. [for solar corona study

    NASA Technical Reports Server (NTRS)

    Bruner, E. C., Jr.; Acton, L. W.; Brown, W. A.; Salat, S. W.; Franks, A.; Schmidtke, G.; Schweizer, W.; Speer, R. J.

    1979-01-01

    A new sounding rocket payload that has been developed for X-ray spectroscopic studies of the solar corona is described. The instrument incorporates a grazing incidence Rowland mounted grating spectrograph and an extreme off-axis paraboloic sector feed system to isolate regions of the sun of order 1 x 10 arc seconds in size. The focal surface of the spectrograph is shared by photographic and photoelectric detection systems, with the latter serving as a part of the rocket pointing system control loop. Fabrication and alignment of the optical system is based on high precision machining and mechanical metrology techniques. The spectrograph has a resolution of 16 milliangstroms and modifications planned for future flights will improve the resolution to 5 milliangstroms, permitting line widths to be measured.

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

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1986-10-01

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

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

    SciTech Connect

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

    1986-10-01

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

  9. Magnetohydrodynamic Oscillations in the Solar Corona and Earth's Magnetosphere: Towards Consolidated Understanding

    NASA Astrophysics Data System (ADS)

    Nakariakov, V. M.; Pilipenko, V.; Heilig, B.; Jelínek, P.; Karlický, M.; Klimushkin, D. Y.; Kolotkov, D. Y.; Lee, D.-H.; Nisticò, G.; Van Doorsselaere, T.; Verth, G.; Zimovets, I. V.

    2016-04-01

    Magnetohydrodynamic (MHD) oscillatory processes in different plasma systems, such as the corona of the Sun and the Earth's magnetosphere, show interesting similarities and differences, which so far received little attention and remain under-exploited. The successful commissioning within the past ten years of THEMIS, Hinode, STEREO and SDO spacecraft, in combination with matured analysis of data from earlier spacecraft (Wind, SOHO, ACE, Cluster, TRACE and RHESSI) makes it very timely to survey the breadth of observations giving evidence for MHD oscillatory processes in solar and space plasmas, and state-of-the-art theoretical modelling. The paper reviews several important topics, such as Alfvénic resonances and mode conversion; MHD waveguides, such as the magnetotail, coronal loops, coronal streamers; mechanisms for periodicities produced in energy releases during substorms and solar flares, possibility of Alfvénic resonators along open field lines; possible drivers of MHD waves; diagnostics of plasmas with MHD waves; interaction of MHD waves with partly-ionised boundaries (ionosphere and chromosphere). The review is mainly oriented to specialists in magnetospheric physics and solar physics, but not familiar with specifics of the adjacent research fields.

  10. Shock Acceleration and Transport of Solar Energetic Particles in the Corona

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  11. Periodicities in the X-ray emission from the solar corona

    SciTech Connect

    Chowdhury, Partha; Jain, Rajmal; Awasthi, Arun K. E-mail: parthares@gmail.com E-mail: awasthi@prl.res.in

    2013-11-20

    We have studied the time series of full disk integrated soft and hard X-ray emission from the solar corona during 2004 January to 2008 December, covering the entire descending phase of solar cycle 23 from a global point of view. We employ the daily X-ray index derived from 1 s cadence X-ray observations from the Si and CZT detectors of the 'Solar X-ray Spectrometer' mission in seven different energy bands ranging between 6 and 56 keV. X-ray data in the energy bands 6-7, 7-10, 10-20, and 4-25 keV from the Si detector are considered, while 10-20, 20-30, and 30-56 keV high energy observations are taken from the CZT detector. The daily time series is subjected to power spectrum analysis after appropriate correction for noise. The Lomb-Scargle periodogram technique has shown prominent periods of ∼13.5 days, ∼27 days, and a near-Rieger period of ∼181 days and ∼1.24 yr in all energy bands. In addition to this, other periods like ∼31, ∼48, ∼57, ∼76, ∼96, ∼130, ∼227, and ∼303 days are also detected in different energy bands. We discuss our results in light of previous observations and existing numerical models.

  12. Thermal structure of current sheets and supra-arcade downflows in the solar corona

    SciTech Connect

    Hanneman, Will J.; Reeves, Katharine K. E-mail: kreeves@cfa.harvard.edu

    2014-05-10

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

  13. Latitudinal properties of the Lyman alpha and O VI profiles in the extended solar corona

    NASA Astrophysics Data System (ADS)

    Zangrilli, L.; Nicolosi, P.; Poletto, G.; Noci, G.; Romoli, M.; Kohl, J. L.

    1999-02-01

    We have analysed the latitudinal properties of the profiles of the H I Lyman alpha line at 1215.6 protect Angstroms and of the O VI doublet at 1031.9 protect Angstroms and 1037.6 protect Angstroms in the extended solar corona, between 1.5 R_sun and 2.0 R_sun. Observations have been performed with the UltraViolet Coronagraph Spectrometer (UVCS) on board the ESA-NASA solar satellite SOHO (SOlar and Heliospheric Observatory). The results show that these lines have quite a different behaviour with latitude: the Ly alpha line has larger full width at half maximum (FWHM) values in the streamer region and narrower ones towards polar latitudes, while the O VI lines have a minimum FWHM at the center of the streamer, which almost steadily increases towards polar regions. The observations have been analysed looking also for an interpretation in terms of selective heating mechanisms. The implications of our results for coronal heating theories are also examined. In particular we discuss the possibility for the presence of the ion-cyclotron coronal heating mechanism. Moreover, we point out an interesting correlation between the intensity of the coronal lines and their widths, which may be relevant to the open question of the different morphological features visible in the Ly alpha and O VI lines.

  14. Dust Hazard Management in the Outer Solar System

    NASA Technical Reports Server (NTRS)

    Seal, David A.

    2012-01-01

    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.

  15. Dust in the Solar System - Properties and Origins

    NASA Technical Reports Server (NTRS)

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

    2013-01-01

    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

  16. 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)

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

    2000-01-01

    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

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

    NASA Astrophysics Data System (ADS)

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

    Absorption in the atmosphere below 500 km results in attenuation of the solar EUV flux, variation of its spectra and distortion of solar images acquired by solar EUV instruments operating on LEO satellites even on solar synchronous orbits. Occultation measurements are important for planning of solar observations from these satellites, and can be used for monitoring the upper atmosphere as well as for studying its response to the solar activity. We present the results of the occultation measurements of the solar EUV radiation obtained by the CORONAS-F/SPIRIT telescope at high solar activity (2002), by the CORONAS-Photon/TESIS telescope at low activity (2009), and by the SWAP telescope and LYRA radiometer onboard the PROBA 2 satellite at moderate activity (2010). The measured attenuation profiles and the retrieved linear extinction coefficients at the heights 200-500 km are compared with simulations by the NRLMSIS-00 and DTM2013 atmospheric models. It was shown that the results of simulations by the DTM2013 model are well agreed with the data of measurements at all stages of solar activity and in presence of the geomagnetic storm, whereas the results of the NRLMSISE-00 model significantly diverge from the measurements, in particular, at high and low activity. The research leading to these results has received funding from the European Union’s Seventh Programme for Research, Technological Development and Demonstration under Grant Agreement “eHeroes” (project № 284461, www.eheroes.eu).

  18. Solar wind-generated current in the Lunar Dust Experiment

    NASA Astrophysics Data System (ADS)

    Xie, Lianghai; Zhang, Xiaoping; Zheng, Yongchun; Guo, Dawei

    2016-04-01

    Measurements from the Lunar Dust Experiment (LDEX) show that the current associated with lofted lunar dust lacks an altitude dependence, implying that the current may come from other sources. Here we present some evidences for solar wind (SW)-generated current. Direct SW influx on the nightside can cause a large current, and the backscattered energetic neutral atoms (ENAs) on the dayside can bring a good correlation between the current and SW density. It is found that the current favors a lower SW speed and a smaller SW incident angle, but the dependences are also affected by the solar zenith angle (SZA) and the scattering function of ENAs. Picked-up ions can enhance the current when the angle between the convection electric field and LDEX's normal is larger than 90°. But when the angle is smaller than 90°, the enhancement is negligible.

  19. Electrostatic lofting variability of lunar dust under solar wind and solar uv irradiance

    NASA Astrophysics Data System (ADS)

    Cihan Örger, Necmi; Rodrigo Cordova Alarcon, Jose; Cho, Mengu; Toyoda, Kazuhiro

    2016-07-01

    It has been considered that lunar horizon glow is produced by forward scattering of the sunlight above the terminator region by the electrically charged dust grains. Previous lunar missions showed that lunar horizon glow is highly varying phenomenon; therefore, it is required to understand how this physical mechanism fundamentally occurs in order to be able to observe it. Therefore, terminator region and the dayside of the moon are the focus areas of this study in order to explain forward scattering of the sunlight towards night side region in the future steps of this work. In this paper, the results of lunar dust height calculations are presented as a function of solar zenith angle and solar wind properties. First, equilibrium surface potential, Debye length and surface electric field have been calculated to be used in the dust model to predict the lofting of lunar dust under various solar wind conditions. Dependence of the dust lofting on different parameters such as electron temperature or plasma density can be explained from the initial results. In addition, these results showed that zero potential occurs between subsolar point and terminator region as it is expected, where the maximum height of dust particles are minimum, and its position changes according to the solar wind properties and photoemission electron temperature. Relative to this work, a CubeSat mission is currently being developed in Kyushu Institute of Technology to observe lunar horizon glow.

  20. Origin of the solar system dust bands discovered by IRAS

    NASA Technical Reports Server (NTRS)

    Dermott, S. F.; Nicholson, P. D.; Burns, J. A.; Houck, J. R.

    1984-01-01

    It is shown that distinctive longitudinal variations in thermal flux and mean latitude can be used to determine the typical orbits of the grains comprising the Solar System bands. In particular, how the bands should vary if they are debris associated with the three principal asteroid families is predicted. Based on these ideas, IRAS observations may allow discrimination between asteroidal and cometary origins of the dust bands and, perhaps, of the entire zodiacal cloud.

  1. Catalysis by dust grains in the solar nebula.

    NASA Astrophysics Data System (ADS)

    Kress, M. E.; Tielens, A. G. G. M.

    1996-10-01

    In order to determine whether grain-catalyzed reactions played an important role in the chemistry of the solar nebula, the authors applied their time-dependent model of methane formation via Fischer-Tropsch catalysis to pressures from 10-5 to 1 bar and temperatures from 450 to 650K. 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.

  2. Transient F Ring Dust Features in Cassini UVIS Solar Occultations

    NASA Astrophysics Data System (ADS)

    Becker, T. M.; Colwell, J. E.; Esposito, L. W.; Attree, N.; Murray, C.

    2015-12-01

    We present results from an investigation of the variable particle size distribution in Saturn's dynamic F ring. We analyze 13 solar occultations observed by the Cassini Ultraviolet Imaging Spectrograph (UVIS), of which 4 occultations show a clear signature of diffracted sunlight. The magnitude and scattering angle of the diffraction signal suggest the presence of a significant population of micron-sized dust particles; however, the lack of a detection of diffracted light in other solar occultations implies that such a population is transient or spatially variable. Initial comparisons with images from the Cassini Imaging Science Subsystem (ISS) suggest that a diffraction signal is detected in UVIS occultations that coincide with a recent collisional event in the F ring core, as seen in the ISS images. This implies that such events release a significant population of dust, which can then be measured by the diffraction signature in the UVIS data. We use a forward-modeling approach to place constraints on the particle size distribution of the F ring during each solar occultation. We present these measurements of the size distribution and our comparisons of the F ring dust population as measured by UVIS with the ISS images of the ring.

  3. Solar Corona/Wind Composition and Origins of the Solar Wind

    NASA Astrophysics Data System (ADS)

    Lepri, S. T.; Gilbert, J. A.; Landi, E.; Shearer, P.; von Steiger, R.; Zurbuchen, T.

    2014-12-01

    Measurements from ACE and Ulysses have revealed a multifaceted solar wind, with distinctly different kinetic and compositional properties dependent on the source region of the wind. One of the major outstanding issues in heliophysics concerns the origin and also predictability of quasi-stationary slow solar wind. While the fast solar wind is now proven to originate within large polar coronal holes, the source of the slow solar wind remains particularly elusive and has been the subject of long debate, leading to models that are stationary and also reconnection based - such as interchange or so-called S-web based models. Our talk will focus on observational constraints of solar wind sources and their evolution during the solar cycle. In particular, we will point out long-term variations of wind composition and dynamic properties, particularly focused on the abundance of elements with low First Ionization Potential (FIP), which have been routinely measured on both ACE and Ulysses spacecraft. We will use these in situ observations, and remote sensing data where available, to provide constraints for solar wind origin during the solar cycle, and on their correspondence to predictions for models of the solar wind.

  4. The Solar Helium Abundance in the Outer Corona Determined from Observations with SUMER/SOHO

    NASA Astrophysics Data System (ADS)

    Laming, J. M.; Feldman, U.

    2000-05-01

    At altitudes of about 1.05 solar radii or more, the corona above quiet solar regions becomes essentially isothermal. This obviates many of the difficulties associated with the inverse problem of determining emission measure distributions, and allows for fairly straightforward relative element abundance measurements. We present new values for the He abundance. The first is based on a reanalysis of the He/O ratio studied by previously by Feldman (1998) using data acquired by SUMER. We use a revised value of the O abundance, and a more thorough evaluation of the atomic physics for He II to derive an He/H abundance ratio of 0.092, (mass fraction, Y=0.27), with an error of ~ 17% coming mainly from the O abundance uncertainty. We demonstrate that this result may be affected by gravitational settling of O relative to He. We also derive an abundance for He by direct comparison to emission lines of the H I Lyman series, with the result He/H =0.083 +/- 10% (Y=0.25). Gravitational settling, if present, has the opposite effect on this result to that above. Combining the two measurements leads to a final result of He/H =0.084+/- 0.008. This work was supported by the NRL/ONR Solar Magnetism and the Earth's Environment 6.1 Research Option and by NASA Contract W19473. The SUMER project is financially supported by DARA, CNES, NASA and the ESA PRODEX program (Swiss contribution). SUMER is a part of SOHO, the Solar and Heliospheric Observatory, of ESA and NASA.

  5. The Solar Corona and a CME at the 2010 Total Eclipse

    NASA Astrophysics Data System (ADS)

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

    2011-05-01

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

  6. Thermal Structure of Current Sheets and Supra-Arcade Downflows in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Hanneman, Will; Reeves, K.

    2013-01-01

    Data has been collected from the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) to determine the thermal structure of supra-arcade downflows (SADs) in the solar corona. SADs, first discovered by Yohkoh in 1999 January 20 (McKenzie & Hudson 1999) can be described as inward flowing density depletions, often observed in post flare current sheets. Some models of this phenomenon have suggested that the plasma in the dark lanes is heated to temperatures of ~8 MK (Maglione et al. 2011). The three flares examined here took place on 2011 October 22, 2012 January 14 and 2012 January 27. Using the relation between temperature and the different sensitivity of the 94Å, 131Å, and 171Å channels, colour-temperature maps are made for each flare, and contours are added to indicate the distribution of very hot plasma (> 5.5 MK) and slightly cooler plasma (> 3 MK). We find that the hottest areas in the current sheet are located near the top of the arcade. We also compare the colour-temperatures in the SADs to that of the surrounding plasma. Cross sections of emission in the AIA bandpasses through the dark lanes are quantitatively measured and compared with the predictions made by Maglione et al. The levels of emission in relation to background determine whether these predictions can be ruled out.

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

    SciTech Connect

    Su, J. T.; Liu, S.; Zhang, Y. Z.; Zhao, H.; Xu, H. Q.; Xie, W. B.; Liu, Y.

    2013-01-01

    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.

  8. Hard X-ray Detectability of Small Impulsive Heating Events in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Glesener, L.; Klimchuk, J. A.; Bradshaw, S. J.; Marsh, A.; Krucker, S.; Christe, S.

    2015-12-01

    Impulsive heating events ("nanoflares") are a candidate to supply the solar corona with its ~2 MK temperature. These transient events can be studied using extreme ultraviolet and soft X-ray observations, among others. However, the impulsive events may occur in tenuous loops on small enough timescales that the heating is essentially not observed due to ionization timescales, and only the cooling phase is observed. Bremsstrahlung hard X-rays could serve as a more direct and prompt indicator of transient heating events. A hard X-ray spacecraft based on the direct-focusing technology pioneered by the Focusing Optics X-ray Solar Imager (FOXSI) sounding rocket could search for these direct signatures. In this work, we use the hydrodynamical EBTEL code to simulate differential emission measures produced by individual heating events and by ensembles of such events. We then directly predict hard X-ray spectra and consider their observability by a future spaceborne FOXSI, and also by the RHESSI and NuSTAR spacecraft.

  9. Electron Acceleration by Cascading Reconnection in the Solar Corona. II. Resistive Electric Field Effects

    NASA Astrophysics Data System (ADS)

    Zhou, X.; Büchner, J.; Bárta, M.; Gan, W.; Liu, S.

    2016-08-01

    We investigate electron acceleration by electric fields induced by cascading reconnections in current sheets trailing coronal mass ejections via a test particle approach in the framework of the guiding-center approximation. Although the resistive electric field is much weaker than the inductive electric field, the electron acceleration is still dominated by the former. Anomalous resistivity η is switched on only in regions where the current carrier’s drift velocity is large enough. As a consequence, electron acceleration is very sensitive to the spatial distribution of the resistive electric fields, and electrons accelerated in different segments of the current sheet have different characteristics. Due to the geometry of the 2.5-dimensional electromagnetic fields and strong resistive electric field accelerations, accelerated high-energy electrons can be trapped in the corona, precipitating into the chromosphere or escaping into interplanetary space. The trapped and precipitating electrons can reach a few MeV within 1 s and have a very hard energy distribution. Spatial structure of the acceleration sites may also introduce breaks in the electron energy distribution. Most of the interplanetary electrons reach hundreds of keV with a softer distribution. To compare with observations of solar flares and electrons in solar energetic particle events, we derive hard X-ray spectra produced by the trapped and precipitating electrons, fluxes of the precipitating and interplanetary electrons, and electron spatial distributions.

  10. Early Evaluation of the Corona at the 2016 March 9 Total Solar Eclipse

    NASA Astrophysics Data System (ADS)

    Pasachoff, Jay M.; Seaton, Daniel B.; Sterling, Alphonse C.

    2016-05-01

    We observed the corona on 2016 March 9 with a variety of assets on the ground and in space. The umbra of the total eclipse swept across Indonesia and into the Pacific, with totality at our Indonesian observation sites lasting 2 min 45 s at Ternate in the Spice Islands (Malukus) and 2 min 10 at Belitung. We compare our ground-based results with the coronal configurations observed with PROBA2/SWAP and Hinode XRT. One of our scientific goals is to follow the coronal configuration over the solar-activity cycle, with the sunspot number now half its maximum of either its 2012 or 2014 peak. We are evaluating temporal changes by comparing eclipse observations made at several ground-based sites along the path, with the longest span being 75 min from Belitung to the Woleia atoll in mid-Pacific, 1:25 UTC to 2:40 UTC; we are evaluating whether the airborne observations made at 3:35 UTC on March 8 (across the International Dateline) are of suitable quality to provide further comparison at high spatial resolution. We also compare our images with the near-simultaneous coronal observations made with SOHO/LASCO, SDO/AIA, STEREO-A/SECCHI, and the Mauna Loa Solar Observatory's K-cor coronagraph. ACS received support for image analysis from the Hinode project.

  11. Neon and Oxygen Abundances and Abundance Ratio in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Landi, E.; Testa, P.

    2015-02-01

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

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

    SciTech Connect

    Argo, H.V.

    1981-01-01

    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.

  13. Dynamical behaviour of interstellar dust particles in the solar system

    NASA Astrophysics Data System (ADS)

    Kocifaj, Miroslav; Klačka, Jozef

    2004-11-01

    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 μm, 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: /T2, where T is orbital period and is time average of cubed solar distance over the period T. The value of the quantity /T2 is 0.673 ± 0.002 [AU3 /year2 ].

  14. Spectral solar irradiance before and during a Harmattan dust spell

    SciTech Connect

    Adeyefa, Z.D.; Holmgren, B.

    1996-09-01

    Measurements of the ground-level spectral distributions of the direct, diffuse and global solar irradiance between 300 and 1100 nm were made at Akure (7.15{degree}N, 5.5{degree}E), Nigeria, in December 1991 before and during a Harmattan dust spell employing a spectroradiometer (LICOR LI-1800) with 6 nm resolution. The direct spectral solar irradiance which was initially reduced before the dust storm was further attenuated by about 50% after the spell. Estimated values of the Angstrom turbidity coefficient {beta} indicated an increase of about 146% of this parameter while the Angstrom wavelength-exponent {alpha} decreased by about 65% within the 2-day study period. The spectral diffuse-to-direct and diffuse-to-global ratios suggest that the main cause of the significant reduction in solar irradiance at the surface was the scattering by the aerosol which led to an increase in the diffuse component. The global irradiance though reduced, was less sensitive to changing Harmattan conditions. It is recommended that solar energy devices that use radiation from Sun and sky be used under fluctuating Harmattan conditions. There are some deviations from the Angstrom formula under very turbid Harmattan conditions which could be explained by the relative increase of the particle sizes. 31 refs., 12 figs., 3 tabs.

  15. 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)

    Reginald, Nelson L.

    2000-01-01

    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.

  16. Interchange Reconnection and Slow Solar Wind Formation at the boundaries of open field regions in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Rappazzo, A. F.; Matthaeus, W. H.; Ruffolo, D. J.; Servidio, S.; Velli, M.

    2014-12-01

    ). We examine a reduced MHD model of a simplified interfaceregion between open and closed corona. We extend previous results to quantify the flux of mass density,heat and momentum from the closed to the adjacent open regionthrough their shared boundary, and model the impact of this fluxon the acceleration of the slow component of the solar wind.

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

    NASA Astrophysics Data System (ADS)

    Rusin, V.; Rybansky, M.

    1999-03-01

    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

  18. Imaging observation of quasi-periodic disturbances' amplitudes increasing with height in the polar region of the solar corona

    SciTech Connect

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

    2014-08-01

    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 Å, 193 Å, and 211 Å 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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    Total solar eclipses offer a unique opportunity to study the white light and emission coronae at high resolution. Magnetohydrodynamic (MHD) models have been used to predict the structure of the corona prior to eclipses, using measurements of photospheric magnetic fields on the Sun. In particular, such an MHD model was used to predict the structure of the corona for the July 11, 2010 total solar eclipse, using SOHO/MDI photospheric magnetic field data. We will compare observed images of the total solar eclipse with features from the MHD model, including magnetic field line traces and simulated polarization brightness images. We will also compare images of simulated emission in EUV and X-rays with observations from SOHO/EIT, Hinode/XRT, STEREO/EUVI, and SDO/AIA. Such comparisons of observed emission with predictions from global coronal MHD models provide a very sensitive constraint on coronal heating models. Research supported by NASA's Heliophysics Theory and Living With a Star Programs, and NSF/CISM.

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

    NASA Astrophysics Data System (ADS)

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

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

  1. Influence of solar wind ions on photoemission charging of dust

    NASA Astrophysics Data System (ADS)

    Nouzak, Libor; Richterova, Ivana; Pavlu, Jiri; Safrankova, Jana; Nemecek, Zdenek

    2016-04-01

    The lunar surface covered by a layer of dust grains is exposed to solar wind particles and photons coming from the Sun on the sunlit side. Solar wind ions cause sputtering of dust grains or can be implanted into grains. We suppose that as a consequence of ion implantation, an additional energy is transferred to grains, more valence band electrons are excited, and the photoelectron yield is increased. An increase of the photoelectron current causes the enhanced density of electrons that form a sheet above the illuminated lunar surface. Thus, an influence of solar wind ions on the Debye length and photoelectron sheet formation is expected. We present laboratory estimations of work functions and photoelectron yields of a single micron-sized silica grain before and after ion implantation. The silica grain used as a lunar simulant is caught in the electrodynamic trap. Grain's specific charge is evaluated by an analysis of the grain motion within the trap, while its work function is determined from observations of a time evolution of the charge-to-mass ratio when the grain is irradiated by photons of different emission lines. By comparison of the photoelectron current (from grain) with photon flux (from UV source), we establish the photoelectron yield of the trapped object. The influence of ion implantation is thoroughly analyzed and discussed.

  2. OBSERVATIONAL EVIDENCE OF RESONANTLY DAMPED PROPAGATING KINK WAVES IN THE SOLAR CORONA

    SciTech Connect

    Verth, G.; Goossens, M.; Terradas, J. E-mail: marcel.goossens@wis.kuleuven.b

    2010-08-01

    In this Letter, we establish clear evidence for the resonant absorption damping mechanism by analyzing observational data from the novel Coronal Multi-Channel Polarimeter. This instrument has established that in the solar corona there are ubiquitous propagating low-amplitude ({approx}1 km s{sup -1}) Alfvenic waves with a wide range of frequencies. Realistically interpreting these waves as the kink mode from magnetohydrodynamic wave theory, they should exhibit a frequency-dependent damping length due to resonant absorption, governed by the Terradas-Goossens-Verth relation showing that transverse plasma inhomogeneity in coronal magnetic flux tubes causes them to act as natural low-pass filters. It is found that the observed frequency dependence on damping length (up to about 8 mHz) can be explained by the kink wave interpretation; and furthermore, the spatially averaged equilibrium parameter describing the length scale of transverse plasma density inhomogeneity over a system of coronal loops is consistent with the range of values estimated from Transition Region and Coronal Explorer observations of standing kink modes.

  3. Solar Micro-Type III Burst Storms and Long Dipolar Magnetic Field in the Outer Corona

    NASA Astrophysics Data System (ADS)

    Morioka, A.; Miyoshi, Y.; Iwai, K.; Kasaba, Y.; Masuda, S.; Misawa, H.; Obara, T.

    2015-08-01

    Solar micro-type III radio bursts are elements of the so-called type III storms and are characterized by short-lived, continuous, and weak emissions. Their frequency of occurrence with respect to radiation power is quite different from that of ordinary type III bursts, suggesting that the generation process is not flare-related, but due to some recurrent acceleration processes around the active region. We examine the relationship of micro-type III radio bursts with coronal streamers. We also explore the propagation channel of bursts in the outer corona, the acceleration process, and the escape route of electron beams. It is observationally confirmed that micro-type III bursts occur near the edge of coronal streamers. The magnetic field line of the escaping electron beams is tracked on the basis of the frequency drift rate of micro-type III bursts and the electron density distribution model. The results demonstrate that electron beams are trapped along closed dipolar field lines in the outer coronal region, which arise from the interface region between the active region and the coronal hole. A 22 year statistical study reveals that the apex altitude of the magnetic loop ranges from 15 to 50 RS. The distribution of the apex altitude has a sharp upper limit around 50 RS suggesting that an unknown but universal condition regulates the upper boundary of the streamer dipolar field.

  4. Temperature and ionization balance dependence of O VII line ratios. [in solar corona

    NASA Technical Reports Server (NTRS)

    Acton, L. W.; Brown, W. A.

    1978-01-01

    The forbidden-plus-intersystem to resonance line ratio (G) for the heliumlike ion O VII is calculated, taking into account cascades, blended satellite lines, and radiative plus dielectric recombination. It is noted that G is of particular use for investigating radiative-transfer effects and nonequilibrium ionization in the solar corona and that the calculations are applicable to a low-density optically thin Maxwellian plasma. The temperature dependence of G is considered for the case of a steady-state equilibrium plasma, and the effect of departures from ionization equilibrium on G is examined. It is found that G is quite insensitive to temperature over the range from 600,000 to 6 million K for a steady-state plasma, but that recombinations may be suppressed or dominant, depending on the relative abundance of O VIII, for a plasma in which the state of ionization is not in equilibrium with the electron temperature. This latter effect is shown to be capable of causing large variations in G that are dependent on electron temperature.

  5. 3D Solar Corona from Soho/eit to Stereo/secchi

    NASA Astrophysics Data System (ADS)

    Portier-Fozzani, Fabrice; Stereo Team

    While taking into account the difficulties encountered by 3D imaging specialists with usual objects over the last 20 years we derived apropriate stereoscopic methods that we could use for the very specific case of the solar corona. Tomographic methods which should be better for such optically thin EUV lines need lots of different quasi-simultaneous viewpoints which is not possible. Usual objects reconstructed by stereovision are mainly optical thick objects such as buildings with variable external luminosity. Direclty applied classical algorithms give at least big uncertainties due to the light emission integration along the line of sight. Also structures extractions and maching between images are very difficult to derived. Epipolar geometry has to be determined before all other steps and decomposing each image in wavelet spatial frequencies with Multiscale Vision Model for example improves a lot the extract/match step. Results of such automatization of the method are presented in the paper. Shorter methods for 3D loops descriptions with applications for helicity measurement of coronal structures evolutions and links to space weather are also presented.

  6. Excitation of magnetohydrodynamic waves by plasmoids ejection in the solar corona

    NASA Astrophysics Data System (ADS)

    Yang, Liping; Zhang, Lei; He, Jiansen; Peter, Hardi; Tu, Chuanyi; Wang, Linghua; Feng, Xueshang

    2016-03-01

    In this study, we numerically investigate the excitation of MHD waves in the interchange reconnection scenario in the solar corona. The modeling results show that as a result of tearing instability, the magnetic reconnection occurs, accompanying the creation of plasmoids. The created plasmoids are quickly shot, and strongly collide with the magnetic field in the outflow regions, which consecutively triggers the perturbations of velocity component Vx, Vy, and Vz. The perturbations of Vy satisfy the polarity relations of slow-mode wave, and their propagating speed approaches the sonic speed in the model, while the perturbations of Vz satisfy the polarity relations of Alfvén wave, and their propagating speed is about the Alfvén speed, thus verifying that they are slow-mode waves and Alfvén waves, respectively. These simulation results indicate that not only fast-mode wave but also slow-mode wave and Alfvén wave can be simultaneously excited by plasmoid ejections and releases.

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

    SciTech Connect

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

    2010-08-20

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2000-08-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

    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

  11. Catalysis by Dust Grains in the Solar Nebula

    NASA Technical Reports Server (NTRS)

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

    1996-01-01

    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.

  12. GRAIN SORTING IN COMETARY DUST FROM THE OUTER SOLAR NEBULA

    SciTech Connect

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

    2012-12-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Landis, Geoffrey; Jenkins, Phillip P.

    1996-01-01

    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.

  15. On the effects of magnetic field line topology on the energy propagation in the solar corona

    NASA Astrophysics Data System (ADS)

    Candelaresi, Simon

    2016-05-01

    Using the MHD approximation, we study the propagation of energy from photospheric footpoint motions into the corona. Our model consists of a magnetic carpet with closed and open magnetic field lines. Magnetic null points are present close at the surface. The applied photospheric driver twists the field into a topologically non-trivial configuration which leads to reconnection and a change in field line topology. Prior to this event, the energy propagation into the corona is largely inhibited due to closed field lines. After such events the energy is free to propagate into the corona.

  16. Solar wind implication on dust ion acoustic rogue waves

    NASA Astrophysics Data System (ADS)

    Abdelghany, A. M.; Abd El-Razek, H. N.; Moslem, W. M.; El-Labany, S. K.

    2016-06-01

    The relevance of the solar wind with the magnetosphere of Jupiter that contains positively charged dust grains is investigated. The perturbation/excitation caused by streaming ions and electron beams from the solar wind could form different nonlinear structures such as rogue waves, depending on the dominant role of the plasma parameters. Using the reductive perturbation method, the basic set of fluid equations is reduced to modified Korteweg-de Vries (KdV) and further modified (KdV) equation. Assuming that the frequency of the carrier wave is much smaller than the ion plasma frequency, these equations are transformed into nonlinear Schrödinger equations with appropriate coefficients. Rational solution of the nonlinear Schrödinger equation shows that rogue wave envelopes are supported by the present plasma model. It is found that the existence region of rogue waves depends on the dust-acoustic speed and the streaming temperatures for both the ions and electrons. The dependence of the maximum rogue wave envelope amplitude on the system parameters has been investigated.

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

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

    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.

  18. 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)

    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

    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

  19. Intermittent Energy Dissipation in Magnetohydrodynamic Turbulence: Applications to the Solar Corona and Solar Wind

    NASA Astrophysics Data System (ADS)

    Zhdankin, Vladimir

    2015-11-01

    Energy dissipation is highly intermittent in large-scale turbulent plasmas, being localized in space and in time. This intermittency is manifest by the presence of coherent structures such as current (and vorticity) sheets, which account for a large fraction of the overall energy dissipation and may serve as sites for magnetic reconnection and particle acceleration. The statistical analysis of these dissipative structures is a robust and informative methodology for probing the underlying dynamics, both in numerical simulations and in observations. In this talk, the statistical properties of current sheets in numerical simulations of driven magnetohydrodynamic (MHD) turbulence are described, including recent results obtained from applying new methods for characterizing their morphology. Instantaneously, the overall energy dissipation is found to be evenly spread among current sheets spanning a continuum of energy dissipation rates and inertial-range sizes, while their thicknesses are localized deep inside the dissipation range. The temporal dynamics are then investigated by tracking the current sheets in time and considering the statistics of the resulting four-dimensional spatiotemporal structures, which correspond to dissipative events or flares in astrophysical systems. These dissipative events are found to exhibit robust power-law distributions and scaling relations, and are often highly complex, long-lived, and weakly asymmetric in time. Based on the distribution for their dissipated energies, the strongest dissipative events are found to dominate the overall energy dissipation in the system. These results are compared to the observed statistics of solar flares, and some possible implications for the solar wind are also described.

  20. Dust Detection Using Radio and Plasma Wave Instruments in the Solar System

    NASA Astrophysics Data System (ADS)

    Ye, S.; Gurnett, D. A.; Kurth, W. S.; Averkamp, T. F.; Kempf, S.; Hsu, S.; Srama, R.; Grün, E.; Morooka, M. W.; Sakai, S.; Wahlund, J. E.

    2014-12-01

    Nanometer to micrometer sized dust particles pervade our solar system. The origins of these dust particles include asteroid collisions, cometary activity, and geothermal activity of the planetary moons, for example, the water dust cloud ejected from Saturn's moon Enceladus. Radio and plasma wave instruments have been used to detect such dust particles via voltage pulses induced by impacts on the spacecraft body and antennas. The first detection of such dust impacts occurred when Voyager 1 passed through Saturn's ring plane. Since then, dust impacts have been detected by radio and plasma wave instruments on many spacecraft, including ISEE-3, Cassini, and STEREO. In this presentation, we review the detection of dust particles in the solar system using radio and plasma wave instruments aboard various spacecraft since the Voyager era. We also show characteristics of the dust particles derived from recent observations by Cassini RPWS in Saturn's magnetosphere. The dust size distribution and density are consistent with those measured by the conventional dust detectors. A new method of measuring the electron density inside the Enceladus plume based on plasma oscillations observed after dust impacts will also be discussed. The dust measurement by radio and plasma wave instruments complements that by conventional dust detectors and provide important information about the spatial distribution of dust particles due to less pointing constraints and the larger detection area.

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

    SciTech Connect

    Kim, R.-S.; Gopalswamy, N.; Cho, K.-S.; Yashiro, S.; Moon, Y.-J.

    2012-02-20

    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.

  2. Inward Motions in the Outer Solar Corona Between 6 And 12 R : Evidence For Waves or Magnetic Reconnection Jets?

    NASA Astrophysics Data System (ADS)

    Velli, Marco; Tenerani, Anna; DeForest, Craig

    2016-05-01

    DeForest et al. (2014) used synoptic visible-light image sequences from the COR2 coronagraph on board the STEREO-A spacecraft to identify inbound wave motions in the outer corona beyond 6 solar radii and inferred, from the observation, that the Alfven surface separating the magnetically dominated corona from the ow dominated wind must be located at least 12 solar radii from the Sun over polar coronal holes and 15 solar radii in the streamer belt. Here we will discuss both this and previous observations of inflows further down and attempt identification of the observed inward signals. We will theoretically reconstruct height-speed diagrams and compare them to the observed profiles. Interpretation in terms of Alfven / magnetoacouatic modes or Alfvenic turbulence appears to be ruled out by the fact that the observed signal shows a deceleration of inward motion when approaching the Sun. Fast magnetoacoustic waves are not directly ruled out in this way, as it is possible for inward waves observed in quadrature, but not propagating exactly radially, to suffer total reflection as the Alfven speed rises close to the Sun. However, the reconstructed signal in the height speed diagram has the wrong concavity. A final possibility is decelerating reconnection jets, most probably from component reconnection, in the accelerating wind: the profile in this case appears to match the observations very well. This interpretation does not alter the conclusion that the Alfven surface must be at least 12 solar radii from the photosphere.

  3. Short time variability of solar corona during recent solar cycle minimum

    NASA Astrophysics Data System (ADS)

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

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

  4. From Solar to Stellar Corona: The Role of Wind, Rotation, and Magnetism

    NASA Astrophysics Data System (ADS)

    Réville, Victor; Brun, Allan Sacha; Strugarek, Antoine; Matt, Sean P.; Bouvier, Jérôme; Folsom, Colin P.; Petit, Pascal

    2015-12-01

    Observations of surface magnetic fields are now within reach for many stellar types thanks to the development of Zeeman-Doppler Imaging. These observations are extremely useful for constraining rotational evolution models of stars, as well as for characterizing the generation of the magnetic field. We recently demonstrated that the impact of coronal magnetic field topology on the rotational braking of a star can be parameterized with a scalar parameter: the open magnetic flux. However, without running costly numerical simulations of the stellar wind, reconstructing the coronal structure of the large-scale magnetic field is not trivial. An alternative—broadly used in solar physics—is to extrapolate the surface magnetic field assuming a potential field in the corona, to describe the opening of the field lines by the magnetized wind. This technique relies on the definition of a so-called source surface radius, which is often fixed to the canonical value of 2.5{R}⊙ . However this value likely varies from star to star. To resolve this issue, we use our extended set of 2.5D wind simulations published in 2015 to provide a criterion for the opening of field lines as well as a simple tool to assess the source surface radius and the open magnetic flux. This allows us to derive the magnetic torque applied to the star by the wind from any spectropolarimetric observation. We conclude by discussing some estimations of spin-down timescales made using our technique and compare them to observational requirements.

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

    SciTech Connect

    Pinto, Rui F.; Brun, Allan Sacha; Grappin, Roland

    2011-08-20

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

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

    SciTech Connect

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

    2013-07-10

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

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

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

    PubMed

    Galinsky, V L; Shevchenko, V I

    2013-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-10-01

    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, η ~ T -3/2, the decrease in plasma temperature at the X-points leads to (1) an increase in the magnetic diffusivity until the characteristic time for magnetic diffusion becomes comparable to that of thermal conduction, (2) an increase in the reconnection rate, and (3) more efficient conversion of magnetic energy into thermal energy and kinetic energy of bulk motions. These results provide further explanation of the rapid release of magnetic energy into heat and kinetic energy seen during flares and coronal mass ejections. In this work, we demonstrate that the consideration of anisotropic thermal conduction and Spitzer-type, temperature-dependent magnetic diffusivity, as in the real solar corona, are crucially important for explaining the occurrence of fast reconnection during solar eruptions.

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

    NASA Technical Reports Server (NTRS)

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

    1978-01-01

    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.

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

    SciTech Connect

    Shen, Yuandeng; Liu, Yu

    2012-06-20

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

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

    NASA Technical Reports Server (NTRS)

    Fuerstenau, Stephen D.

    2006-01-01

    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.

  13. Restructuring of Dust Aggregates in the Solar Nebula

    NASA Technical Reports Server (NTRS)

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

    1996-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2008-01-01

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

  15. THE DYNAMICS OF DUST GRAINS IN THE OUTER SOLAR SYSTEM

    SciTech Connect

    Belyaev, Mikhail A.; Rafikov, Roman R. E-mail: rrr@astro.princeton.ed

    2010-11-10

    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.

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

    NASA Technical Reports Server (NTRS)

    Turgay, Eren H.

    2004-01-01

    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

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

    SciTech Connect

    Clayton, Geoffrey C.; Gallagher, J. S.; Freeman, W. R.; Camp, K. A. E-mail: wfreem2@lsu.edu

    2011-08-15

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

  18. Inward Motions in the Outer Solar Corona between 7 and 12 R ⊙: Evidence for Waves or Magnetic Reconnection Jets?

    NASA Astrophysics Data System (ADS)

    Tenerani, Anna; Velli, Marco; DeForest, Craig

    2016-07-01

    DeForest et al. used synoptic visible-light image sequences from the COR2 coronagraph on board the STEREO-A spacecraft to identify inbound wave motions in the outer corona beyond 7 solar radii and inferred, from the observation, that the Alfvén surface separating the magnetically dominated corona from the flow dominated wind must be located beyond at least 12 solar radii from the Sun over polar coronal holes and beyond 15 solar radii in the streamer belt. Here, we attempt identification of the observed inward signal by theoretically reconstructing height-speed diagrams and comparing them to the observed profiles. Interpretation in terms of Alfvén waves or Alfvénic turbulence appears to be ruled out by the fact that the observed signal shows a deceleration of inward motion when approaching the Sun. Fast magnetoacoustic waves are not directly ruled out in this way, as it is possible for inward waves observed in quadrature, but not propagating exactly radially, to suffer total reflection as the Alfvén speed rises close to the Sun. However, the reconstructed signal in the height-speed diagram has the wrong concavity. A final possibility is decelerating reconnection jets, most probably from component reconnection, in the accelerating wind: the profile in this case appears to match the observations very well. This interpretation does not alter the conclusion that the Alfvén surface must be at least 12 solar radii from the photosphere. Further observations should help constrain this process, never identified previously in this way, in the distance range from 7 to 12 solar radii.

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

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  20. 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)

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

    2015-01-01

    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.

  1. Two-fluid and magnetohydrodynamic modelling of magnetic reconnection in the MAST spherical tokamak and the solar corona

    NASA Astrophysics Data System (ADS)

    Browning, P. K.; Cardnell, S.; Evans, M.; Arese Lucini, F.; Lukin, V. S.; McClements, K. G.; Stanier, A.

    2016-01-01

    Twisted magnetic flux ropes are ubiquitous in laboratory and astrophysical plasmas, and the merging of such flux ropes through magnetic reconnection is an important mechanism for restructuring magnetic fields and releasing free magnetic energy. The merging-compression scenario is one possible start-up scheme for spherical tokamaks, which has been used on the Mega Amp Spherical Tokamak (MAST). Two current-carrying plasma rings or flux ropes approach each due to mutual attraction, forming a current sheet and subsequently merge through magnetic reconnection into a single plasma torus, with substantial plasma heating. Two-dimensional resistive and Hall-magnetohydrodynamic simulations of this process are reported, including a strong guide field. A model of the merging based on helicity-conserving relaxation to a minimum energy state is also presented, extending previous work to tight-aspect-ratio toroidal geometry. This model leads to a prediction of the final state of the merging, in good agreement with simulations and experiment, as well as the average temperature rise. A relaxation model of reconnection between two or more flux ropes in the solar corona is also described, allowing for different senses of twist, and the implications for heating of the solar corona are discussed.

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

    SciTech Connect

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

    2013-10-10

    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 β 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 β falls off with height; and (3) the variations of the local fast magnetosonic speed and plasma β 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.

  3. The influence of absorbed solar radiation by Saharan dust on hurricane genesis

    NASA Astrophysics Data System (ADS)

    Bretl, Sebastian; Reutter, Philipp; Raible, Christoph C.; Ferrachat, Sylvaine; Poberaj, Christina Schnadt; Revell, Laura E.; Lohmann, Ulrike

    2015-03-01

    To date, the radiative impact of dust and the Saharan air layer (SAL) on North Atlantic hurricane activity is not yet known. According to previous studies, dust stabilizes the atmosphere due to absorption of solar radiation but thus shifts convection to regions more conducive for hurricane genesis. Here we analyze differences in hurricane genesis and frequency from ensemble sensitivity simulations with radiatively active and inactive dust in the aerosol-climate model ECHAM6-HAM. We investigate dust burden and other hurricane-related variables and determine their influence on disturbances which develop into hurricanes (developing disturbances, DDs) and those which do not (nondeveloping disturbances, NDDs). Dust and the SAL are found to potentially have both inhibiting and supporting influences on background conditions for hurricane genesis. A slight southward shift of DDs is determined when dust is active as well as a significant warming of the SAL, which leads to a strengthening of the vertical circulation associated with the SAL. The dust burden of DDs is smaller in active dust simulations compared to DDs in simulations with inactive dust, while NDDs contain more dust in active dust simulations. However, no significant influence of radiatively active dust on other variables in DDs and NDDs is found. Furthermore, no substantial change in the DD and NDD frequency due to the radiative effects of dust can be detected.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

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

    SciTech Connect

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

    1982-01-01

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

  6. Coronal mass ejection speeds measured in the solar corona using LASCO C2 and C3 images

    NASA Astrophysics Data System (ADS)

    Dal Lago, A.; Schwerin, R.; Stenborg, G.; Gonzalez, W. D.

    In this work we present height-time diagrams of 2 halo coronal mass ejections, observed on September 28th, 1997 and June 29th, 1999. The CMEs were observed by the Large Angle and Spectroscopic Coronagraph (LASCO), which observes the solar corona from 2 to 32 solar radii. To obtain these diagrams we divide the LASCO images of a given sequence in angular slices, transform them into rectangular slices (their width chosen proportional to the time distance to the next image) and place them side by side. Thus, the speed profile of any pattern moving in the particular latitudinal slice can be derived. With this method we were able to identify even minor speed changes in several angular positions for the chosen events. This technique is particularly appropriate to identify acceleration or deceleration of structures in halo CMEs.

  7. An improved model for interplanetary dust fluxes in the outer Solar System

    NASA Astrophysics Data System (ADS)

    Poppe, Andrew R.

    2016-01-01

    We present an improved model for interplanetary dust grain fluxes in the outer Solar System constrained by in situ dust density observations. A dynamical dust grain tracing code is used to establish relative dust grain densities and three-dimensional velocity distributions in the outer Solar System for four main sources of dust grains: Jupiter-family comets, Halley-type comets, Oort-Cloud comets, and Edgeworth-Kuiper Belt objects. Model densities are constrained by in situ dust measurements by the New Horizons Student Dust Counter, the Pioneer 10 meteoroid detector, and the Galileo Dust Detection System (DDS). The model predicts that Jupiter-family comet grains dominate the interplanetary dust grain mass flux inside approximately 10 AU, Oort-Cloud cometary grains may dominate between 10 and 25 AU, and Edgeworth-Kuiper Belt grains are dominant outside 25 AU. The model also predicts that while the total interplanetary mass flux at Jupiter roughly matches that inferred by the analysis of the Galileo DDS measurements, mass fluxes to Saturn, Uranus, and Neptune are at least one order-of-magnitude lower than that predicted by extrapolations of dust grain flux models from 1 AU. Finally, we compare the model predictions of interplanetary dust oxygen influx to the giant planet atmospheres with various observational and photochemical constraints and generally find good agreement, with the exception of Jupiter, which suggests the possibility of additional chemical pathways for exogenous oxygen in Jupiter's atmosphere.

  8. A solar escalator on Mars: Self-lifting of dust layers by radiative heating

    NASA Astrophysics Data System (ADS)

    Daerden, F.; Whiteway, J. A.; Neary, L.; Komguem, L.; Lemmon, M. T.; Heavens, N. G.; Cantor, B. A.; Hébrard, E.; Smith, M. D.

    2015-09-01

    Dust layers detected in the atmosphere of Mars by the light detection and ranging (LIDAR) instrument on the Phoenix Mars mission are explained using an atmospheric general circulation model. The layers were traced back to observed dust storm activity near the edge of the north polar ice cap where simulated surface winds exceeded the threshold for dust lifting by saltation. Heating of the atmospheric dust by solar radiation caused buoyant instability and mixing across the top of the planetary boundary layer (PBL). Differential advection by wind shear created detached dust layers above the PBL that ascended due to radiative heating and arrived at the Phoenix site at heights corresponding to the LIDAR observations. The self-lifting of the dust layers is similar to the "solar escalator" mechanism for aerosol layers in the Earth's stratosphere.

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

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

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

  10. Photometric analysis of the corona during the 20 March 2015 total solar eclipse: density structures, hydrostatic temperatures and magnetic field inference.

    NASA Astrophysics Data System (ADS)

    Bazin, C.; Vilinga, J.; Wittich, R.; Koutchmy, S.; Mouette, J.; Nitschelm, C.

    2015-12-01

    We present some new accurate CCD photometry analysis of the white light solar corona at the time of the last 20 March 2015 total eclipse (airborne observations on a Falcon 7X and at ground-based- Svalbard). We measured coronal brightness profiles taken along radial directions from 1.001 to 3 solar radii in the northern, southern and equatorial regions, after removing the F-corona and the sky background. These studies allow to evaluate the density gradients, structures and temperature heterogeneity, by considering the Thomson scattering in white light of the K- corona and also emissions of the EUV Fe XII 193A (1 to 2 MK) and Fe XI 171/174 (lower temperature) simultaneously observed by SDO/AIA and SWAP/Proba2 space missions. Some dispersion between the regions is noticed. The limitation of the hydrostatic equilibrium assumption in the solar atmosphere is discussed as well as the contribution of the magnetic field pressure gradients as illustrated by a comparison with the model stationary magnetic corona from Predictive Sc. Inc. These results are compared with the results of the quieter 2010 total solar eclipse corona analyzed with the same method. This photometric analysis of the inner and intermediate white light corona will contribute to the preparation of the Aspiics/Proba 3 flying formation future coronagraphic mission of ESA for new investigation at time of artificial eclipses produced in Space. Note that Aspiics will also observe in the He I D3 line at 5876 A, and will record intensities of the Fe XIV line 5303A simultaneously with the analysis of the orange white- light continuum, including precise polarimetry analysis. .

  11. 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)

    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

    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.

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

    SciTech Connect

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

    1990-03-01

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

  13. White Light Solar Corona: An Atlas of 1988 K-Coronameter Synoptic Charts, December 1987-January 1989. Technical note

    SciTech Connect

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

    1990-03-01

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

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

    SciTech Connect

    Ni Lei; Roussev, Ilia I.; Lin Jun; Ziegler, Udo E-mail: iroussev@ifa.hawaii.edu

    2012-10-10

    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.

  15. Interstellar and Solar System Organic Matter Preserved in Interplanetary Dust

    NASA Technical Reports Server (NTRS)

    Messenger, Scott; Nakamura-Messenger, Keiko

    2015-01-01

    Interplanetary dust particles (IDPs) collected in the Earth's stratosphere derive from collisions among asteroids and by the disruption and outgassing of short-period comets. Chondritic porous (CP) IDPs are among the most primitive Solar System materials. CP-IDPs have been linked to cometary parent bodies by their mineralogy, textures, C-content, and dynamical histories. CP-IDPs are fragile, fine-grained (less than um) assemblages of anhydrous amorphous and crystalline silicates, oxides and sulfides bound together by abundant carbonaceous material. Ancient silicate, oxide, and SiC stardust grains exhibiting highly anomalous isotopic compositions are abundant in CP-IDPs, constituting 0.01 - 1 % of the mass of the particles. The organic matter in CP-IDPs is isotopically anomalous, with enrichments in D/H reaching 50x the terrestrial SMOW value and 15N/14N ratios up to 3x terrestrial standard compositions. These anomalies are indicative of low T (10-100 K) mass fractionation in cold molecular cloud or the outermost reaches of the protosolar disk. The organic matter shows distinct morphologies, including sub-um globules, bubbly textures, featureless, and with mineral inclusions. Infrared spectroscopy and mass spectrometry studies of organic matter in IDPs reveals diverse species including aliphatic and aromatic compounds. The organic matter with the highest isotopic anomalies appears to be richer in aliphatic compounds. These materials also bear similarities and differences with primitive, isotopically anomalous organic matter in carbonaceous chondrite meteorites. The diversity of the organic chemistry, morphology, and isotopic properties in IDPs and meteorites reflects variable preservation of interstellar/primordial components and Solar System processing. One unifying feature is the presence of sub-um isotopically anomalous organic globules among all primitive materials, including IDPs, meteorites, and comet Wild-2 samples returned by the Stardust mission.

  16. Interstellar and Solar System Organic Matter Preserved in Interplanetary Dust

    NASA Astrophysics Data System (ADS)

    Messenger, Scott R.; Nakamura-Messenger, Keiko

    2015-08-01

    Interplanetary dust particles (IDPs) collected in the Earth’s stratosphere derive from collisions among asteroids and by the disruption and outgassing of short-period comets. Chondritic porous (CP) IDPs are among the most primitive Solar System materials. CP-IDPs have been linked to cometary parent bodies by their mineralogy, textures, C-content, and dynamical histories. CP-IDPs are fragile, fine-grained (< um) assemblages of anhydrous amorphous and crystalline silicates, oxides and sulfides bound together by abundant carbonaceous material. Ancient silicate, oxide, and SiC stardust grains exhibiting highly anomalous isotopic compositions are abundant in CP-IDPs, constituting 0.01 - 1 % of the mass of the particles. The organic matter in CP-IDPs is isotopically anomalous, with enrichments in D/H reaching 50x the terrestrial SMOW value and 15N/14N ratios up to 3x terrestrial standard compositions. These anomalies are indicative of low T (10-100 K) mass fractionation in cold molecular cloud or the outermost reaches of the protosolar disk. The organic matter shows distinct morphologies, including sub-um globules, bubbly textures, featureless, and with mineral inclusions. Infrared spectroscopy and mass spectrometry studies of organic matter in IDPs reveals diverse species including aliphatic and aromatic compounds. The organic matter with the highest isotopic anomalies appears to be richer in aliphatic compounds. These materials also bear similarities and differences with primitive, isotopically anomalous organic matter in carbonaceous chondrite meteorites. The diversity of the organic chemistry, morphology, and isotopic properties in IDPs and meteorites reflects variable preservation of interstellar/primordial components and Solar System processing. One unifying feature is the presence of sub-um isotopically anomalous organic globules among all primitive materials, including IDPs, meteorites, and comet Wild-2 samples returned by the Stardust mission. We will present

  17. The Temperature and Density Structure of the Solar Corona. I. Observations of the Quiet Sun with the EUV Imaging Spectrometer on Hinode

    NASA Astrophysics Data System (ADS)

    Warren, Harry P.; Brooks, David H.

    2009-07-01

    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.

  18. Sixteen Years of Ulysses Interstellar Dust Measurements in the Solar System. II. Fluctuations in the Dust Flow from the Data

    NASA Astrophysics Data System (ADS)

    Strub, Peter; Krüger, Harald; Sterken, Veerle J.

    2015-10-01

    The Ulysses spacecraft provided the first opportunity to identify and study interstellar dust (ISD) in situ in the solar system between 1992 and 2007. Here we present the first comprehensive analysis of the ISD component in the entire Ulysses dust data set. We analyzed several parameters of the ISD flow in a time-resolved fashion: flux, flow direction, mass index, and flow width. The general picture is in agreement with a time-dependent focusing/defocusing of the charged dust particles due to long-term variations of the solar magnetic field throughout a solar magnetic cycle of 22 years. In addition, we confirm a shift in dust direction of 50° ± 7° in 2005, along with a steep, size-dependent increase in flux by a factor of 4 within 8 months. To date, this is difficult to interpret and has to be examined in more detail by new dynamical simulations. This work is part of a series of three papers. This paper concentrates on the time-dependent flux and direction of the ISD. In a companion paper we analyze the overall mass distribution of the ISD measured by Ulysses, and a third paper discusses the results of modeling the flow of the ISD as seen by Ulysses.

  19. Exploring Small Spatial Scales in the Transition Region and Solar Corona with the Very High Angular Resolution Imaging Spectrometer (VERIS)

    NASA Astrophysics Data System (ADS)

    Chua, D. H.; Korendyke, C. M.; Vourlidas, A.; Brown, C. M.; Tun-Beltran, S.; Klimchuk, J. A.; Landi, E.; Seely, J.; Davila, J. M.; Hagood, R.; Roberts, D.; Shepler, E.; Feldman, R.; Moser, J.; Shea, J.

    2012-12-01

    Theoretical and experimental investigations of the transition region and coronal loops point to the importance of processes occurring on small spatial scales in governing the strong dynamics and impulsive energy release in these regions. As a consequence, high spatial, temporal, and temperature resolution over a broad temperature range, and accuracy in velocity and density determinations are all critical observational parameters. Current instruments lack one or more of these properties. These observational deficiencies have created a wide array of opposing descriptions of coronal loop heating and questions such as whether or not the plasma within coronal loops is multi-thermal or isothermal. High spectral and spatial resolution spectroscopic data are absolutely required to resolve these controversies and to advance our understanding of the dynamics within the solar atmosphere. We will achieve this with the Very High Angular Resolution Imaging Spectrometer (VERIS) sounding rocket payload. VERIS consists of an off-axis paraboloid telescope feeding a very high angular resolution, extreme ultraviolet (EUV) imaging spectrometer that will provide the first ever, simultaneous sub-arcsecond (0.16 arcsecond/pixel) spectra in bright lines needed to study plasma structures in the transition region, quiet corona, and active region core. It will do so with a spectral resolution of >5000 to allow Doppler velocity determinations to better than 3 km/s. VERIS uses a novel two-element, normal incidence optical design with highly reflective, broad wavelength coverage EUV coatings to access a spectral range with broad temperature coverage (0.03-15 MK) and density-sensitive line ratios. Combined with Hinode Solar Optical Telescope (SOT) and ground based observatories, VERIS will deliver simultaneous observations of the entire solar atmosphere from the photosphere to the multi-million degree corona at sub-arcsecond resolution for the first time ever, allowing us to understand the

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

    SciTech Connect

    Habbal, S. Rifai; Morgan, H.; Scholl, I.; Druckmueller, M.; Daw, A.; Johnson, J.; Ding, A.; Arndt, M.; Esser, R.; Rusin, V.

    2010-01-10

    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

  1. Height of Shock Formation in the Solar Corona Inferred from Observations of Type II Radio Bursts and Coronal Mass Ejections

    NASA Technical Reports Server (NTRS)

    Gopalswamy, N.; Xie, H.; Makela, P.; Yashiro, S.; Akiyama, S.; Uddin, W.; Srivastava, A. K.; Joshi, N. C.; Chandra, R.; Manoharan, P. K.

    2013-01-01

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

  2. Latitudinal and Solar-Cycle Variations of the White-Light Corona from SOHO/LASCO Observations

    NASA Astrophysics Data System (ADS)

    Fainshtein, V. G.; Tsivileva, D. M.; Kashapova, L. K.

    2010-11-01

    SOHO/LASCO data were used to obtain the latitudinal and radial distributions of the brightness of the K- and F-corona in the period of 1996 - 2007, and their solar-cycle variations were studied. Then an inversion method was employed to obtain the radial distributions of the electron density N e( R, θ) for various latitude values on the coronal images. Our values of N e( R, θ) are in good agreement with the findings of other authors. We found that in an edge-on streamer belt the electron density, like the K-corona brightness, varies with distance more slowly in the near-equatorial rays than in near-polar regions. We have developed a method for assessing the maximum values of the electron density at the center of the face-on streamer belt in its bright rays and depressions between them. Not all bright rays observed in the face-on streamer belt are found to be associated with an increased electron density in them. Mechanisms for forming such rays have been suggested.

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

    SciTech Connect

    Martisek, K.; Druckmuellerova, H.

    2011-12-01

    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.

  4. Possible signature of Alfvén wave dissipation in the localized magnetic funnels of the equatorial solar corona

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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 Å 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 Alfvén 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 Å line-width along it. Therefore, it exhibits the most likely signature of Alfvén 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 Alfvén 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 Alfvén waves can change the non-thermal component and thus the full width at half-maximum of the Fe XII 195.120 Å line. We find the clues of Alfvén 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.

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

    NASA Astrophysics Data System (ADS)

    Lorenz, Ralph D.; Reiss, Dennis

    2015-03-01

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

  6. Numerical model for the acceleration of a dust cloud by the solar wind

    NASA Astrophysics Data System (ADS)

    Jia, Y.-D.; Russell, C. T.; Lai, H. R.; Wei, H. Y.

    2015-10-01

    In this study we investigate the behavior of two massive fluids: protons in the solar wind and charged dust. For simplification we temporarily ignore the charging process of dust particles. The mass of charged dust can be 103 amu to grams, but we only model the lighter ones because the behavior of grains more massive than 105 are similar. A multi-fluid MHD code is used to simulate the large scale structure formed around a dust cloud released into the solar wind, and its evolution. Dust clouds as we are simulating can be made by meteoroid-meteoroid collisions with size from 1 to 100 m in diameter. These are dangerous if they hit the Earth's atmosphere. Detecting them in space can help detect where such objects are in near Earth space.

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

    SciTech Connect

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

    2012-12-10

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

    Existing, competing theories for coronal and interplanetary type III solar radio bursts appeal to one or more of modulational instability, electrostatic (ES) decay processes, or stochastic growth physics to preserve the electron beam, limit the levels of Langmuir-like waves driven by the beam, and produce wave spectra capable of coupling nonlinearly to generate the observed radio emission. Theoretical constraints exist on the wavenumbers and relative sizes of the wave bandwidth and nonlinear growth rate for which Langmuir waves are subject to modulational instability and the parametric and random phase versions of ES decay. A constraint also exists on whether stochastic growth theory (SGT) is appropriate. These constraints are evaluated here using the beam, plasma, and wave properties (1) observed in specific interplanetary type III sources, (2) predicted nominally for the corona, and (3) predicted at heliocentric distances greater than a few solar radii by power-law models based on interplanetary observations. It is found that the Langmuir waves driven directly by the beam have wavenumbers that are almost always too large for modulational instability but are appropriate to ES decay. Even for waves scattered to lower wavenumbers (by ES decay, for instance), the wave bandwidths are predicted to be too large and the nonlinear growth rates too small for modulational instability to occur for the specific interplanetary events studied or the great majority of Langmuir wave packets in type III sources at arbitrary heliocentric distances. Possible exceptions are for very rare, unusually intense, narrowband wave packets, predominantly close to the Sun, and for the front portion of very fast beams traveling through unusually dilute, cold solar wind plasmas. Similar arguments demonstrate that the ES decay should proceed almost always as a random phase process rather than a parametric process, with similar exceptions. These results imply that it is extremely rare for

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

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

    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.

  10. Time delays in the nonthermal radiation of solar flares according to observations of the CORONAS-F satellite

    NASA Astrophysics Data System (ADS)

    Tsap, Yu. T.; Stepanov, A. V.; Kashapova, L. K.; Myagkova, I. N.; Bogomolov, A. V.; Kopylova, Yu. G.; Goldvarg, T. B.

    2016-07-01

    In 2001-2003, the X-ray and microwave observations of ten solar flares of M- and X-classes were carried out by the CORONAS-F orbital station, the RSTN Sun service, and Nobeyama radio polarimeters. Based on these observations, a correlation analysis of time profiles of nonthermal radiation was performed. On average, hard X-ray radiation outstrips the microwave radiation in 9 events, i.e., time delays are positive. The appearance of negative delays is associated with effective scattering of accelerated electrons in pitch angles, where the length of the free path of a particle is less than the half-length of a flare loop. The additional indications are obtained in favor of the need to account for the effect of magnetic mirrors on the dynamics of energetic particles in the coronal arches.

  11. 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)

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

    1979-01-01

    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.

  12. The Plasma and Field Perturbation Around a Charged Dust Cloud in the Solar Wind

    NASA Astrophysics Data System (ADS)

    Jia, Y. D.; Russell, C. T.; Lai, H.; Wei, H.

    2014-12-01

    When asteroids and meteoroids collide at their typical speeds of 20km/s at 1AU, they can totally disrupt each other if their mass ratios are within a factor of 106. The resulting charged dust and gas can be picked up by the solar wind, resulting in a large magnetic structure containing over 106kg of mass, accelerated to almost the solar wind speed. This dust is invisible to our Earth-based detectors as are the impactors and targets but they can be detected by our interplanetary spacecraft and they do create ground-level magnetospheric disturbances when they impact the Earth. Moreover we can identify the parent bodies for these impacting bolides by determining which asteroids cross the ecliptic plane along the path of these disturbances carried by the solar wind. Hence, these structures can be used in a planetary defense strategy. Since they have a very practical application we need to understand their formation and evolution better. We apply our multi-fluid code to model this interaction, to show how the field is affected by charged dust. We assume a cloud of charged dust moving close to the solar wind speed, but a small velocity difference exists between the dust and ions. Gravity pulls horizontally opposite to the solar wind plasma, maintaining the concentration of dust cloud.

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

    NASA Astrophysics Data System (ADS)

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

    2006-09-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  15. Solar heating of the Uranian mesopause by dust of ring origin

    SciTech Connect

    Rizk, B.; Hunten, D.M. )

    1990-12-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Miteva, Rositsa Stoycheva

    2007-07-01

    Our dynamic Sun manifests its activity by different phenomena: from the 11-year cyclic sunspot pattern to the unpredictable and violent explosions in the case of solar flares. During flares, a huge amount of the stored magnetic energy is suddenly released and a substantial part of this energy is carried by the energetic electrons, considered to be the source of the nonthermal radio and X-ray radiation. One of the most important and still open question in solar physics is how the electrons are accelerated up to high energies within (the observed in the radio emission) short time scales. Because the acceleration site is extremely small in spatial extent as well (compared to the solar radius), the electron acceleration is regarded as a local process. The search for localized wave structures in the solar corona that are able to accelerate electrons together with the theoretical and numerical description of the conditions and requirements for this process, is the aim of the dissertation. Two models of electron acceleration in the solar corona are proposed in the dissertation: I. Electron acceleration due to the solar jet interaction with the background coronal plasma (the jet--plasma interaction) A jet is formed when the newly reconnected and highly curved magnetic field lines are relaxed by shooting plasma away from the reconnection site. Such jets, as observed in soft X-rays with the Yohkoh satellite, are spatially and temporally associated with beams of nonthermal electrons (in terms of the so-called type III metric radio bursts) propagating through the corona. A model that attempts to give an explanation for such observational facts is developed here. Initially, the interaction of such jets with the background plasma leads to an (ion-acoustic) instability associated with growing of electrostatic fluctuations in time for certain range of the jet initial velocity. During this process, any test electron that happen to feel this electrostatic wave field is drawn to co

  17. FINE STRAND-LIKE STRUCTURE IN THE SOLAR CORONA FROM MAGNETOHYDRODYNAMIC TRANSVERSE OSCILLATIONS

    SciTech Connect

    Antolin, P.; Yokoyama, T.; Van Doorsselaere, T.

    2014-06-01

    Current analytical and numerical modeling suggest the existence of ubiquitous thin current sheets in the corona that could explain the observed heating requirements. On the other hand, new high resolution observations of the corona indicate that its magnetic field may tend to organize itself in fine strand-like structures of few hundred kilometers widths. The link between small structure in models and the observed widths of strand-like structure several orders of magnitude larger is still not clear. A popular theoretical scenario is the nanoflare model, in which each strand is the product of an ensemble of heating events. Here, we suggest an alternative mechanism for strand generation. Through forward modeling of three-dimensional MHD simulations we show that small amplitude transverse MHD waves can lead in a few periods time to strand-like structure in loops in EUV intensity images. Our model is based on previous numerical work showing that transverse MHD oscillations can lead to Kelvin-Helmholtz instabilities that deform the cross-sectional area of loops. While previous work has focused on large amplitude oscillations, here we show that the instability can occur even for low wave amplitudes for long and thin loops, matching those presently observed in the corona. We show that the vortices generated from the instability are velocity sheared regions with enhanced emissivity hosting current sheets. Strands result as a complex combination of the vortices and the line-of-sight angle, last for timescales of a period, and can be observed for spatial resolutions of a tenth of loop radius.

  18. Fine Strand-like Structure in the Solar Corona from Magnetohydrodynamic Transverse Oscillations

    NASA Astrophysics Data System (ADS)

    Antolin, P.; Yokoyama, T.; Van Doorsselaere, T.

    2014-06-01

    Current analytical and numerical modeling suggest the existence of ubiquitous thin current sheets in the corona that could explain the observed heating requirements. On the other hand, new high resolution observations of the corona indicate that its magnetic field may tend to organize itself in fine strand-like structures of few hundred kilometers widths. The link between small structure in models and the observed widths of strand-like structure several orders of magnitude larger is still not clear. A popular theoretical scenario is the nanoflare model, in which each strand is the product of an ensemble of heating events. Here, we suggest an alternative mechanism for strand generation. Through forward modeling of three-dimensional MHD simulations we show that small amplitude transverse MHD waves can lead in a few periods time to strand-like structure in loops in EUV intensity images. Our model is based on previous numerical work showing that transverse MHD oscillations can lead to Kelvin-Helmholtz instabilities that deform the cross-sectional area of loops. While previous work has focused on large amplitude oscillations, here we show that the instability can occur even for low wave amplitudes for long and thin loops, matching those presently observed in the corona. We show that the vortices generated from the instability are velocity sheared regions with enhanced emissivity hosting current sheets. Strands result as a complex combination of the vortices and the line-of-sight angle, last for timescales of a period, and can be observed for spatial resolutions of a tenth of loop radius.

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

    SciTech Connect

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

    1987-03-01

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

  20. White Light Solar Corona: An ATLAS of 1987 K-coronameter Synoptic Charts, December 1986-January 1988. Technical note

    SciTech Connect

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

    1988-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Wang, Tongjiang; Davila, Joseph M.

    2014-01-01

    Determining the coronal electron density by the inversion of white-light polarized brightness (pB) measurements by coronagraphs is a classic problem in solar physics. An inversion technique based on the spherically symmetric geometry (spherically symmetric inversion, SSI) was developed in the 1950s and has been widely applied to interpret various observations. However, to date there is no study of the uncertainty estimation of this method. We here present the detailed assessment of this method using a three-dimensional (3D) electron density in the corona from 1.5 to 4 solar radius as a model, which is reconstructed by a tomography method from STEREO/COR1 observations during the solar minimum in February 2008 (Carrington Rotation, CR 2066).We first show in theory and observation that the spherically symmetric polynomial approximation (SSPA) method and the Van de Hulst inversion technique are equivalent. Then we assess the SSPA method using synthesized pB images from the 3D density model, and find that the SSPA density values are close to the model inputs for the streamer core near the plane of the sky (POS) with differences generally smaller than about a factor of two; the former has the lower peak but extends more in both longitudinal and latitudinal directions than the latter. We estimate that the SSPA method may resolve the coronal density structure near the POS with angular resolution in longitude of about 50 deg. Our results confirm the suggestion that the SSI method is applicable to the solar minimum streamer (belt), as stated in some previous studies. In addition, we demonstrate that the SSPA method can be used to reconstruct the 3D coronal density, roughly in agreement with the reconstruction by tomography for a period of low solar activity (CR 2066). We suggest that the SSI method is complementary to the 3D tomographic technique in some cases, given that the development of the latter is still an ongoing research effort.

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

    PubMed

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

    2007-05-25

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

  4. Dynamics of a Prominence-horn Structure during Its Evaporation in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Wang, Bing; Chen, Yao; Fu, Jie; Li, Bo; Li, Xing; Liu, Wei

    2016-08-01

    The physical connections among and formation mechanisms of various components of the prominence-horn cavity system remain elusive. Here we present observations of such a system, focusing on a section of the prominence that rises and separates gradually from the main body. This forms a configuration sufficiently simple to yield clues regarding the above issues. It is characterized by embedding horns, oscillations, and a gradual disappearance of the separated material. The prominence-horn structure exhibits a large-amplitude longitudinal oscillation with a period of ∼150 minutes and an amplitude of ∼30 Mm along the trajectory defined by the concave horn structure. The horns also experience a simultaneous transverse oscillation with a much smaller amplitude (∼3 Mm) and a shorter period (∼10–15 minutes), likely representative of a global mode of the large-scale magnetic structure. The gradual disappearance of the structure indicates that the horn, an observational manifestation of the field-aligned transition region separating the cool and dense prominence from the hot and tenuous corona, is formed due to the heating and diluting process of the central prominence mass; most previous studies suggested that it is the opposite process, i.e., the cooling and condensation of coronal plasmas, that formed the horn. This study also demonstrates how the prominence transports magnetic flux to the upper corona, a process essential for the gradual build-up of pre-eruption magnetic energy.

  5. Dynamics of a Prominence-horn Structure during Its Evaporation in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Wang, Bing; Chen, Yao; Fu, Jie; Li, Bo; Li, Xing; Liu, Wei

    2016-08-01

    The physical connections among and formation mechanisms of various components of the prominence-horn cavity system remain elusive. Here we present observations of such a system, focusing on a section of the prominence that rises and separates gradually from the main body. This forms a configuration sufficiently simple to yield clues regarding the above issues. It is characterized by embedding horns, oscillations, and a gradual disappearance of the separated material. The prominence-horn structure exhibits a large-amplitude longitudinal oscillation with a period of ˜150 minutes and an amplitude of ˜30 Mm along the trajectory defined by the concave horn structure. The horns also experience a simultaneous transverse oscillation with a much smaller amplitude (˜3 Mm) and a shorter period (˜10–15 minutes), likely representative of a global mode of the large-scale magnetic structure. The gradual disappearance of the structure indicates that the horn, an observational manifestation of the field-aligned transition region separating the cool and dense prominence from the hot and tenuous corona, is formed due to the heating and diluting process of the central prominence mass; most previous studies suggested that it is the opposite process, i.e., the cooling and condensation of coronal plasmas, that formed the horn. This study also demonstrates how the prominence transports magnetic flux to the upper corona, a process essential for the gradual build-up of pre-eruption magnetic energy.

  6. On the structure of solar and stellar coronae - Loops and loop heat transport

    NASA Technical Reports Server (NTRS)

    Litwin, Christof; Rosner, Robert

    1993-01-01

    We discuss the principal constraints on mechanisms for structuring and heating the outer atmospheres - the coronae - of stars. We argue that the essential cause of highly localized heating in the coronae of stars like the sun is the spatially intermittent nature of stellar surface magnetic fields, and that the spatial scale of the resulting coronal structures is related to the spatial structure of the photospheric fields. We show that significant constraints on coronal heating mechanisms derive from the observed variations in coronal emission, and, in addition, show that the observed structuring perpendicular to coronal magnetic fields imposes severe constraints on mechanisms for heat dispersal in the low-beta atmosphere. In particular, we find that most of commonly considered mechanisms for heat dispersal, such as anomalous diffusion due to plasma turbulence or magnetic field line stochasticity, are much too slow to account for the observed rapid heating of coronal loops. The most plausible mechanism appears to be reconnection at the interface between two adjacent coronal flux bundles. Based on a model invoking hyperresistivity, we show that such a mechanism naturally leads to dominance of isolated single bright coronal loops and to bright coronal plasma structures whose spatial scale transverse to the local magnetic field is comparable to observed dimensions of coronal X-ray loops.

  7. Yohkoh/SXT soft x-ray observations of sudden mass loss from the solar corona

    NASA Technical Reports Server (NTRS)

    Hudson, H. S.; Acton, L. W.; Alexander, D.; Freeland, S. L.; Lemen, J. R.; Harvey, K. L.

    1995-01-01

    Direct X-ray observations allow us to estimate the hot coronal mass before and after a flare or other disturbance of the type leading to a coronal mass ejection. The sudden disappearance of a large coronal structure (scale greater than 105 km) gives evidence that an ejection has occurred, if the time scales are much shorter than the conductive or radiative cooling times for such structures. A flare also typically adds large amounts of new material to the corona via evaporation resulting from the coronal energy release. This provides a competing mechanism that makes the estimation of the total mass loss somewhat difficult. We note that the X-ray observations have the advantage of covering the entire corona rather than the limb regions unlike the coronagraph observations. We have identified two examples of coronal mass disappearances. before and during long duration flare events on 21 Feb. 1992 (on the E limb) and 13 Nov. 1994 (near disk center). In latter case the total mass amounted to some 4 x 10(exp 14) g with a density of 3 x 10(exp 8)cm(exp -3) and a temperature of 2.8 MK before its disappearance. This corresponds to a radiative cooling time of some 104 S. much longer than the observed time of disappearance. We therefore suggest that these sudden mass disappearances correspond with coronal mass ejections (CMEs), and suggest that further data analysis will be able to confirm this by comparison with optical observations of specific CMEs.

  8. HEATING OF THE SOLAR CHROMOSPHERE AND CORONA BY ALFVEN WAVE TURBULENCE

    SciTech Connect

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

    2011-07-20

    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.

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

    NASA Astrophysics Data System (ADS)

    Miteva, Rositsa Stoycheva

    2007-07-01

    Our dynamic Sun manifests its activity by different phenomena: from the 11-year cyclic sunspot pattern to the unpredictable and violent explosions in the case of solar flares. During flares, a huge amount of the stored magnetic energy is suddenly released and a substantial part of this energy is carried by the energetic electrons, considered to be the source of the nonthermal radio and X-ray radiation. One of the most important and still open question in solar physics is how the electrons are accelerated up to high energies within (the observed in the radio emission) short time scales. Because the acceleration site is extremely small in spatial extent as well (compared to the solar radius), the electron acceleration is regarded as a local process. The search for localized wave structures in the solar corona that are able to accelerate electrons together with the theoretical and numerical description of the conditions and requirements for this process, is the aim of the dissertation. Two models of electron acceleration in the solar corona are proposed in the dissertation: I. Electron acceleration due to the solar jet interaction with the background coronal plasma (the jet--plasma interaction) A jet is formed when the newly reconnected and highly curved magnetic field lines are relaxed by shooting plasma away from the reconnection site. Such jets, as observed in soft X-rays with the Yohkoh satellite, are spatially and temporally associated with beams of nonthermal electrons (in terms of the so-called type III metric radio bursts) propagating through the corona. A model that attempts to give an explanation for such observational facts is developed here. Initially, the interaction of such jets with the background plasma leads to an (ion-acoustic) instability associated with growing of electrostatic fluctuations in time for certain range of the jet initial velocity. During this process, any test electron that happen to feel this electrostatic wave field is drawn to co

  10. 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

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

    2011-09-01

    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.

  11. A U-type solar radio burst originating in the outer corona.

    NASA Technical Reports Server (NTRS)

    Stone, R. G.; Fainberg, J.

    1971-01-01

    The observation of a U-type solar radio burst with a reversing frequency of approximately 0.7 MHz suggests the presence of a magnetic bottle extending out to about 35 solar radii. A possible model of this loop structure is developed from the data. The occurrence of low-frequency U-bursts seems to be extremely rare although magnetic bottles may develop frequently during solar maximum.

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

    NASA Astrophysics Data System (ADS)

    Hayashi, K.; Hoeksema, J. T.; Liu, Y.; Bobra, M. G.; Sun, X. D.; Norton, A. A.

    2015-05-01

    Time-dependent three-dimensional magnetohydrodynamics (MHD) simulation modules are implemented at the Joint Science Operation Center (JSOC) of the Solar Dynamics Observatory (SDO). The modules regularly produce three-dimensional data of the time-relaxed minimum-energy state of the solar corona using global solar-surface magnetic-field maps created from Helioseismic and Magnetic Imager (HMI) full-disk magnetogram data. With the assumption of a polytropic gas with specific-heat ratio of 1.05, three types of simulation products are currently generated: i) simulation data with medium spatial resolution using the definitive calibrated synoptic map of the magnetic field with a cadence of one Carrington rotation, ii) data with low spatial resolution using the definitive version of the synchronic frame format of the magnetic field, with a cadence of one day, and iii) low-resolution data using near-real-time (NRT) synchronic format of the magnetic field on a daily basis. The MHD data available in the JSOC database are three-dimensional, covering heliocentric distances from 1.025 to 4.975 solar radii, and contain all eight MHD variables: the plasma density, temperature, and three components of motion velocity, and three components of the magnetic field. This article describes details of the MHD simulations as well as the production of the input magnetic-field maps, and details of the products available at the JSOC database interface. To assess the merits and limits of the model, we show the simulated data in early 2011 and compare with the actual coronal features observed by the Atmospheric Imaging Assembly (AIA) and the near-Earth in-situ data.

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

    NASA Technical Reports Server (NTRS)

    Esser, Ruth

    1997-01-01

    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.

  14. The effect of ballooning modes on thermal transport and magnetic field diffusion in the solar corona

    NASA Technical Reports Server (NTRS)

    Strauss, H. R.

    1989-01-01

    Presently favored mechanisms of coronal heating (current sheet dissipation and Alfven wave resonant heating) deposit heat in thin layers. Classical thermal conduction cannot explain how heat is transported across the magnetic field. If heating occurs in thin layers, large pressure gradients can be created which can give rise to ballooning modes. These instabilities are caused by the pressure gradient and the curvature of the magnetic field, and are stabilized by magnetic tension. The modes are broad band in wavelength and should produce turbulence. A mixing length expression for the turbulent heat transport shows that it is more than adequate to rapidly convect heat into much broader layers. Furthermore, the turbulent resistivity implies that heating occurs over most of the width of these broadened layers. The broadening also implies that much shorter time scales are required for heating. The beta values in the corona suggest that 1-10 turbulent layers are formed in typical loop or arch structures.

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

    NASA Technical Reports Server (NTRS)

    Davila, Joseph M.

    1988-01-01

    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.

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

    SciTech Connect

    Jiang Chaowei; Feng Xueshang E-mail: fengx@spaceweather.ac.cn

    2012-04-20

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

  17. A model for absorption of solar radiation by mineral dust within liquid cloud drops

    NASA Astrophysics Data System (ADS)

    Zhang, Qing; Thompson, Jonathan E.

    2015-10-01

    Models of light scattering and absorption that consider the effect of insoluble inclusions present within liquid cloud droplets may assume the inclusion occupies random locations within the droplet. In certain cases, external forces can lead to certain orientations or alignments that are strongly preferred. Within this modeling study, we consider one such case in which an insoluble mineral dust inclusion (ρ=2.6 g/cm3) is placed within a liquid water drop (ρ=1.0 g/cm3). Such an instance mimics mineral dust aerosols being incorporated within cloud drops in Earth's atmosphere. Model results suggest super-micron mineral dust settles to the bottom of cloud droplets. However, Brownian motion largely randomizes the position of sub-micron mineral dust within the droplet. The inherent organization of the particles that result has important consequences for light absorption by mineral dust when present within a cloud drop. Modeled results suggest light absorption efficiency may be enhanced by as much as 4-6 fold for an isolated droplet experiencing direct solar illumination at solar zenith angles of <20°. For such an isolated droplet, the absorption efficiency enhancement falls rapidly with increasing solar zenith angle indicating a strong angle of incidence dependence. We also consider the more common case of droplets that contain dust inclusions deep within optically dense clouds. Absorption efficiency enhancements for these locales follow a dramatically different pattern compared to the optically isolated droplet due to the presence of diffuse rather than direct solar irradiation. In such cases, light absorption efficiency is decreased through including super-micron dust within water droplets. The study has important implications for modeling the absorption of sunlight by mineral dust aerosol within liquid water clouds. The angle of incidence dependence also reveals that experimental measurement of light absorption for cases in which particle alignment occurs may not

  18. Dust Models Paint Alien's View of Solar System

    NASA Video Gallery

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

  19. 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)

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

    2011-06-01

    We report on the first multi-wavelength coronal observations, taken simultaneously in white light, Hα 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.

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

    SciTech Connect

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

    2011-06-20

    We report on the first multi-wavelength coronal observations, taken simultaneously in white light, H{alpha} 656.3 nm, Fe IX 435.9 nm, Fe X 637.4 nm, Fe XI 789.2 nm, Fe XIII 1074.7 nm, Fe XIV 530.3 nm, and Ni XV 670.2 nm, during the total solar eclipse of 2010 July 11 from the atoll of Tatakoto in French Polynesia. The data enabled temperature differentiations as low as 0.2 x 10{sup 6} K. The first-ever images of the corona in Fe IX and Ni XV showed that there was very little plasma below 5 x 10{sup 5} K and above 2.5 x 10{sup 6} K. The suite of multi-wavelength observations also showed that open field lines have an electron temperature near 1x 10{sup 6} K, while the hottest, 2x 10{sup 6} K, plasma resides in intricate loops forming the bulges of streamers, also known as cavities, as discovered in our previous eclipse observations. The eclipse images also revealed unusual coronal structures, in the form of ripples and streaks, produced by the passage of coronal mass ejections and eruptive prominences prior to totality, which could be identified with distinct temperatures for the first time. These trails were most prominent at 10{sup 6} K. Simultaneous Fe X 17.4 nm observations from Proba2/SWAP provided the first opportunity to compare Fe X emission at 637.4 nm with its extreme-ultraviolet (EUV) counterpart. This comparison demonstrated the unique diagnostic capabilities of the coronal forbidden lines for exploring the evolution of the coronal magnetic field and the thermodynamics of the coronal plasma, in comparison with their EUV counterparts in the distance range of 1-3 R{sub sun}. These diagnostics are currently missing from present space-borne and ground-based observatories.

  1. Neutral Solar Wind Generated by Lunar Exospheric Dust at the Terminator

    NASA Technical Reports Server (NTRS)

    Collier, Michael R.; Stubbs, Timothy J.

    2007-01-01

    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.

  2. Validation of Earth atmosphere models using solar EUV observations from the CORONAS and PROBA2 satellites in occultation mode

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    Aims: Knowledge of properties of the Earth's upper atmosphere is important for predicting the lifetime of low-orbit spacecraft as well as for planning operation of space instruments whose data may be distorted by atmospheric effects. The accuracy of the models commonly used for simulating the structure of the atmosphere is limited by the scarcity of the observations they are based on, so improvement of these models requires validation under different atmospheric conditions. Measurements of the absorption of the solar extreme ultraviolet (EUV) radiation in the upper atmosphere below 500 km by instruments operating on low-Earth orbits (LEO) satellites provide efficient means for such validation as well as for continuous monitoring of the upper atmosphere and for studying its response to the solar and geomagnetic activity. Method: This paper presents results of measurements of the solar EUV radiation in the 17 nm wavelength band made with the SPIRIT and TESIS telescopes on board the CORONAS satellites and the SWAP telescope on board the PROBA2 satellite in the occulted parts of the satellite orbits. The transmittance profiles of the atmosphere at altitudes between 150 and 500 km were derived from different phases of solar activity during solar cycles 23 and 24 in the quiet state of the magnetosphere and during the development of a geomagnetic storm. We developed a mathematical procedure based on the Tikhonov regularization method for solution of ill-posed problems in order to retrieve extinction coefficients from the transmittance profiles. The transmittance profiles derived from the data and the retrieved extinction coefficients are compared with simulations carried out with the NRLMSISE-00 atmosphere model maintained by Naval Research Laboratory (USA) and the DTM-2013 model developed at CNES in the framework of the FP7 project ATMOP. Results: Under quiet and slightly disturbed magnetospheric conditions during high and low solar activity the extinction coefficients

  3. Coronal mass ejection speeds measured in the solar corona using LASCO C2 and C3 images

    NASA Astrophysics Data System (ADS)

    dal Lago, A.; Schwenn, R.; Stenborg, G.; Gonzalez, W.

    In this work we present height-time diagrams of 3 halo coronal mass ejections, observed on July 25th,1999, September 28th,1997, and June 29th,1999. The CMEs were observed by the Large Angle and Spectroscopic Coronagraph (LASCO) which is an instrument on board of the Solar and Heliospheric Observatory (SOHO observing the solar corona from 2 to 32 solar radii. To obtain these diagrams we divide the LASCO images of a given sequence in angular slices, transform them into rectangular slices (their width chosen proportional to the time distance to the next image) and place them side by side. Thus, the speed profile of any pattern moving in the particular latitudinal slice can be derived. With this method we were able to identify even minor speed changes in several angular positions for the chosen events. This technique is particularly appropriate to identify acceleration or deceleration of structures in halo CMEs. This information may be used to improve predictions of CME travel times to earth. From the analysis of these 3 events we conclude that: (a) the CME observed on September 28th,1997, started very slowly, with initial speeds ranging from 107 to 178 km/s, and accelerated in the C2 field of view reaching final constant speeds of 352 to 400 km/s in the C3 field of view; (b) the CMEs observed on July 25th,1999, and June 29th,1999 started with initial speeds from 310 to 650 km/s and 435 to 650 km/s, respectively. They decelerated smoothly in the C3 field of view and reached a variety of speeds ranging from 150 to 330 km/s, depending on the direction around the sun.

  4. Laboratory study of the equilibrium and eruption of line-tied magnetic flux ropes in the solar corona

    NASA Astrophysics Data System (ADS)

    Myers, Clayton Edward

    2015-03-01

    Ideal magnetohydrodynamic (MHD) instabilities such as the kink instability and the torus instability are leading candidates to explain the sudden onset of eruptive events in the solar corona. These instabilities act on line-tied magnetic flux ropes--long-lived arched structures anchored to the solar surface. In spite of substantial observational and numerical research, however, the role of these instabilities in the corona remains a subject of intense debate. For this thesis, we have constructed and operated a new line-tied flux rope experiment that permits for the first time the study of both the kink and torus instabilities in the laboratory. This experiment has the following key features: (1) the arched flux rope is line-tied to two conducting footpoints; (2) the system is magnetically dominated (low-beta) with significant stored energy; (3) the system is driven quasi-statically, producing a long-lived equilibrium; and (4) the flux rope is generated within a potential (vacuum) magnetic field arcade whose decay index---the predicted torus instability control parameter---can be externally controlled. The flux ropes are diagnosed using a two-dimensional in situ magnetic probe array whose cross-section covers a substantial portion of the plasma. The central result of this thesis is that toroidal field forces, which are traditionally neglected in the analysis of coronal flux ropes, are identified for the first time as an essential contributor to both the equilibrium and the stability of line-tied flux ropes. Most importantly, experimental measurements show that a tension force derived from a self-generated paramagnetic toroidal field exerts a restoring force on the line-tied plasma and suppresses eruptive behavior in a significant portion of the parameter space. This suppression extends to regimes that are both kink and torus unstable. We find that, in order to explain the measured tension force, low aspect ratio and line-tying effects must be considered. Finally

  5. Solar Wind Speed Structure in the Inner Corona at 3-12R(sub)O

    NASA Technical Reports Server (NTRS)

    Woo, R.

    1995-01-01

    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 compared with white light coronagraph measurements.

  6. Signatures of Exo-Solar Planets in Dust Debris Disks

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

    We have developed a new numerical approach to the dynamics of minor bodies and dust particles, which enables us to increase, without using a supercomputer, the number of employed particle positions in each model up to 10(exp 10) - 10(exp 11), a factor of 10(exp 6) - 10(exp 7) higher than existing numerical simulations. We apply this powerful approach to the high-resolution modeling of the structure and emission of circumstellar dust disks, incorporating all relevant physical processes. In this Letter, we examine the resonant structure of a dusty disk induced by the presence of one planet of mass in the range of (5 x 10(exp -5) - 5 x 10(exp -3))M. It is shown that the planet, via resonances and gravitational scattering, produces (i) a central cavity void of dust; (ii) a trailing (sometimes leading) off-center cavity; and (iii) an asymmetric resonant dust belt with one, two, or more clumps. These features can serve as indicators of planet(s) embedded in the circumstellar dust disk and, moreover, can be used to determine the mass of the planet and even some of its orbital parameters. The results of our study reveal a remarkable similarity with various types of highly asymmetric circumstellar disks observed with the JCMT around Epsilon Eridani and Vega.

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

    NASA Astrophysics Data System (ADS)

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

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

  8. Structure, Dynamics, and Spectra of the Solar Corona at the 2013 and 2015 Total Eclipses and Plans for 2017's American Totality

    NASA Astrophysics Data System (ADS)

    Pasachoff, Jay M.; Dantowitz, Ronald; Voulgaris, Aristeidis

    2016-01-01

    We observed the total solar eclipses of 3 November 2013 from Gabon and of 20 March 2015 from Svalbard in clear skies with cameras to image the solar corona at high resolution and with spectrographs for coronal emission lines. We report on the composite images showing coronal structure and (in comparison with other sites' images) dynamics, as well as the relation of our inner- and middle-corona composite images with surface EUV images from SDO and SWAP and with the outer-corona images from the coronagraphs on SOHO/LASCO. Our spectra show not only the common forbidden lines of Fe XIV (green line) and Fe X (red line) but also rarer species such as Ca XV. Finally, we describe our planned suite of observations for the 21 August 2017 solar eclipse, whose path of totality will cross the United States from Pacific to Atlantic, with more-favorable cloudiness statistics for western sites.Our Gabon and Svalbard expeditions were supported by grants from the Committee for Research and Exploration of the National Geographic Society.

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

    NASA Technical Reports Server (NTRS)

    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

    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

  10. LADEE UVS Observations of Solar Occultation by Exospheric Dust Above the Lunar Limb

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

    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 greater than 500) for 20-30 ms integration times. The 1-degree solar viewer field of view subtends a diameter of approximately 8 km at a distance of 400-450 km.

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

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

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

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

    SciTech Connect

    Pomoell, J.; Vainio, R.

    2012-02-01

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

  13. ANALYTIC APPROXIMATE SEISMOLOGY OF PROPAGATING MAGNETOHYDRODYNAMIC WAVES IN THE SOLAR CORONA

    SciTech Connect

    Goossens, M.; Soler, R.; Arregui, I.

    2012-12-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

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

  16. Extreme ultraviolet spectra of solar flares from the extreme ultraviolet spectroheliograph SPIRIT onboard the CORONAS-F satellite

    SciTech Connect

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

    2014-01-01

    We present detailed extreme ultraviolet (EUV) spectra of four large solar flares: M5.6, X1.3, X3.4, and X17 classes in the spectral ranges 176-207 Å and 280-330 Å. These spectra were obtained by the slitless spectroheliograph SPIRIT onboard the CORONAS-F satellite. To our knowledge, these are the first detailed EUV spectra of large flares obtained with a spectral resolution of ∼0.1 Å. We performed a comprehensive analysis of the obtained spectra and provide identification of the observed spectral lines. The identification was performed based on the calculation of synthetic spectra (the CHIANTI database was used), with simultaneous calculations of the differential emission measure (DEM) and density of the emitting plasma. More than 50 intense lines are present in the spectra that correspond to a temperature range of T = 0.5-16 MK; most of the lines belong to Fe, Ni, Ca, Mg, and Si ions. In all the considered flares, intense hot lines from Ca XVII, Ca XVIII, Fe XX, Fe XXII, and Fe XXIV are observed. The calculated DEMs have a peak at T ∼ 10 MK. The densities were determined using Fe XI-Fe XIII lines and averaged 6.5 × 10{sup 9} cm{sup –3}. We also discuss the identification, accuracy, and major discrepancies of the spectral line intensity prediction.

  17. Understanding coronal mass ejections and associated shocks in the solar corona by merging multiwavelength observations

    SciTech Connect

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

    2014-11-01

    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 Alfvén speed.

  18. Performance Analysis of the Nano Dust Analyzer Under Solar UV Illumination

    NASA Astrophysics Data System (ADS)

    O'Brien, L. E.; Gruen, E.; Sternovsky, Z.

    2014-12-01

    The Nano Dust Analyzer (NDA) is a linear time-of-flight mass analyzer developed to measure the distribution and elemental composition of nanometer-sized dust particles originating in the inner Heliosphere. The temporal variability of the flux and angular distribution is governed by the complex interaction with the interplanetary magnetic field within 1 AU and provides the means also to learn about solar wind conditions. As part of a heliospheric mission, measurements made by the NDA will determine the size-dependent flux of nano-dust and its variations, it will characterize the composition of nano-dust, and may determine their source processes. The nano-dust particles arrive at 1 AU approximately from the direction of the Sun, thus, the NDA is designed specifically to operate while being exposed directly to solar UV radiation. Here, we report on the performance analysis of the NDA under UV illumination. Solar UV radiation is most likely the largest source of noise for the instrument. A fraction of incident photons will scatter into the ion detector and generate background noise, reducing the instrument's sensitivity. The detailed modeling is conducted using a commercial ray-tracing program. The instrument's performance while exposed to UV radiation is optimized in terms of instrument geometry and surface materials/optical properties, and the requirements on all optical surfaces that are necessary to reduce the effect of UV to the required level are defined and presented here.

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

    SciTech Connect

    Huenemoerder, David P.; Phillips, Kenneth J. H.; Sylwester, Janusz; Sylwester, Barbara E-mail: kennethjhphillips@yahoo.com E-mail: bs@cbk.pan.wroc.pl

    2013-05-10

    The Chandra High Energy Transmission Grating Spectrometer (HETG) spectra of the coronally active binary stars {sigma} Gem and HR 1099 are among the highest fluence observations for such systems taken at high spectral resolution in X-rays with this instrument. This allows us to compare their properties in detail to solar flare spectra obtained with the Russian CORONAS-F spacecraft's RESIK instrument at similar resolution in an overlapping bandpass. Here we emphasize the detailed comparisons of the 3.3-6.1 A region (including emission from highly ionized S, Si, Ar, and K) from solar flare spectra to the corresponding {sigma} Gem and HR 1099 spectra. We also model the larger wavelength range of the HETG, from 1.7 to 25 A - having emission lines from Fe, Ca, Ar, Si, Al, Mg, Ne, O, and N-to determine coronal temperatures and abundances. {sigma} Gem is a single-lined coronally active long-period binary which has a very hot corona. HR 1099 is a similar, but shorter period, double-lined system. With very deep HETG exposures we can even study emission from some of the weaker species, such as K, Na, and Al, which are important since they have the lowest first ionization potentials, a parameter well known to be correlated with elemental fractionation in the solar corona. The solar flare temperatures reach Almost-Equal-To 20 MK, comparable to the {sigma} Gem and HR 1099 coronae. During the Chandra exposures, {sigma} Gem was slowly decaying from a flare and its spectrum is well characterized by a collisional ionization equilibrium plasma with a broad temperature distribution ranging from 2 to 60 MK, peaking near 25 MK, but with substantial emission from 50 MK plasma. We have detected K XVIII and Na XI emission which allow us to set limits on their abundances. HR 1099 was also quite variable in X-rays, also in a flare state, but had no detectable K XVIII. These measurements provide new comparisons of solar and stellar coronal abundances, especially at the lowest first ionization

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

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

    The Chandra High Energy Transmission Grating Spectrometer (HETG) spectra of the coronally active binary stars σ 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 σ 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 N—to determine coronal temperatures and abundances. σ 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 σ Gem and HR 1099 coronae. During the Chandra exposures, σ 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

  1. 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)

    Sandford, Scott A.

    1986-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  3. Polarimetric Studies of Solar Light Scattered by Interplanetary Dust Particles and the Eye-Sat Project

    NASA Astrophysics Data System (ADS)

    Levasseur-Regourd, A. C.; Lasue, J.

    2014-12-01

    Studying intensity and linear polarization of the solar light scattered by interplanetary dust is of interest for various reasons. This so-called zodiacal light constitutes a faint polarized glow that constitutes a changing foreground for observations of faint extended astronomical sources. Besides, analysis of its polarization provides information on properties of the dust particles, such as spatial density, morphology and complex refractive index. Previous observations, mostly from the Earth and with a resolution in the 10° range, have been used to infer that the local polarization at 90° phase angle increases with increasing solar distance. Numerical simulations suggest that, in the inner solar system, interplanetary dust particles consist of a mixture of absorbing and less absorbing materials, and that radial changes originate in a decrease of organic materials with decreasing solar distance under alteration or evaporation processes. To improve the quality of data on zodiacal light polarimetry, Eye-Sat nanosat is being developed in the context of the JANUS CNES cubesats program for students. The project is now in phase C-D, for a piggy-back launch in 2016. Eye-Sat triple cubesat is anticipated to demonstrate the feasibility of a series of new on-board technologies. Moreover, during its one-year mission, zodiacal light intensity and polarization are to be measured, for the first time with a spatial resolution of about 1° over a wide portion of the sky and in four different wavelengths (visible to near-IR), leading to a better assessment of interplanetary dust properties. Finally, a significant fraction of the interplanetary dust is estimated to come from comets, the most pristine objects to be found in the inner solar system. While similarities have indeed been noticed between polarimetric properties of interplanetary and cometary dust particles, the latter being currently extensively documented by the Rosetta mission to comet 67P

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

    SciTech Connect

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

    2008-06-09

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

  5. The Structure of the Solar Corona above Sunspots as Inferred from Radio, X-Ray, and Magnetic Field Observations

    NASA Astrophysics Data System (ADS)

    Vourlidas, A.; Bastian, T. S.; Aschwanden, M. J.

    1997-11-01

    We present observations of a solar active region, NOAA/USAF no. 7123, during 1992 April 3-10. The database includes high-angular-resolution radio, soft X-ray, magnetograph, and Hα observations. The radio observations include VLA maps in the Stokes I and V parameters at 4.7 and 8.4 GHz. The soft X-ray observations were obtained by the Soft X-Ray Telescope on board the Yohkoh satellite, the magnetograms were obtained at Kitt Peak, Mt. Wilson, and Big Bear, and the Hα data were obtained at Big Bear. The lead sunspot in the active region is studied here. In particular, the polarization properties and brightness temperature spectrum are used to constrain the thermal structure of the corona over the sunspot. It is found that the 4.7 GHz emission of the sunspot is polarized in the sense of the ordinary mode, in contradiction with simple gyroresonance models that predict that the spot should be polarized in the sense of the extraordinary mode. We model the spectral and temporal evolution of the polarization structure in two frequencies, 4.7 and 8.4 GHz, using gyroresonance models to fit one-dimensional brightness temperature profiles across the spot in each polarization and frequency. The constraints provided by the X-ray and magnetic field observations help us to derive a qualitatively self-consistent picture for the daily evolution of the spot. We attribute the excess of the o-mode emission to the magnetic field configuration and to the temperature inhomogeneities across the spot. Namely, we find that (1) the umbral and penumbral environments are distinct, with the X-rays and the o-mode radio emission coming from the hotter penumbral loops, while the observed x-mode emission originates from the cooler umbral loops; (2) there exist temperature inhomogeneities in both the radial and vertical direction over the spot; and (3) the umbral magnetic field remains more confined in the corona than that predicted by a dipole model. Instead, a field configuration based on the

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

    NASA Astrophysics Data System (ADS)

    Virtanen, I. I.; Mursula, K.

    2014-02-01

    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°.

  7. North-south asymmetric solar cycle evolution: Signatures in the photosphere and consequences in the corona

    SciTech Connect

    Virtanen, I. I.; Mursula, K.

    2014-02-01

    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{sub 2}{sup 0} 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{sub 2}{sup 0}-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{sub 2}{sup 0}-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°.

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

    NASA Technical Reports Server (NTRS)

    Falconer, David A.

    1994-01-01

    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.

  9. MESSENGER soft X-ray observations of the quiet solar corona

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

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

    NASA Technical Reports Server (NTRS)

    Woo, Richard

    1995-01-01

    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.

  11. 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)

    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

    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

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

    SciTech Connect

    Van Doorsselaere, Tom; Wardle, Nick; Jansari, Kishan; Verwichte, Erwin; Nakariakov, Valery M.; Del Zanna, Giulio

    2011-02-01

    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.

  13. Comparing the solar magnetic field in the corona and in the inner heliosphere during solar cycles 21-23

    NASA Astrophysics Data System (ADS)

    Virtanen, I. I.; Mursula, K.

    2009-04-01

    We compare the open solar magnetic field estimated by the PFSS model based on the WSO photospheric field observations, with the inner heliospheric magnetic field. We trace the observed radial HMF into the coronal PFSS boundary at 2.5 solar radii using the observed solar wind velocity, and determine the PFSS model field at the line-of-sight footpoint. Comparing the two field values, we calculate the power n of the apparent decrease of the radial field. According to expectations based on Maxwell's equations, also reproduced by Parker's HMF model, the radial HMF field should decrease with n=2. However, comparison gives considerably lower values of n, indicating the effect of HCS in the PFSS model and the possible superexpansion. The n values vary with solar cycle, being roughly 1.3-1.4 at minima and about 1.7 at maxima. Interestingly, the n values for the two HMF sectors show systematic differences in the late declining to minimum phase, with smaller n values for the HMF sector dominant in the northern hemisphere. This is in agreement with the smaller field value in the northern hemisphere and the southward shifted HCS, summarized by the concept of the bashful ballerina. We also find that the values of n during the recent years, in the late declining phase of solar cycle 23, are significantly larger than during the same phase of the previous cycles. This agrees with the exceptionally large tilt of the solar dipole at the end of cycle 23. We also find that the bashful ballerina appears even during SC 23 but the related hemispheric differences are smaller than during the previous cycles.

  14. The R Coronae Borealis Stars

    NASA Astrophysics Data System (ADS)

    Clayton, Geoffrey C.

    1996-03-01

    This year marks the bicentennial of the discovery of the variability of R Coronae Borealis. The R Coronae Borealis (RCB) stars are distinguished from other hydrogen-deficient objects by their spectacular dust formation episodes. They may decline by up to 8 magnitudes in a few weeks revealing a rich emission-line spectrum. Their atmospheres have unusual abundances with very little hydrogen and an overabundance of carbon and nitrogen. The RCB stars are thought to be the product of a final helium shell flash or the coalescence of a binary white-dwarf system. Dust may form in non-equilibrium conditions created behind shocks caused by pulsations in the atmospheres of these stars. The RCB stars are interesting and important, first because they represent a rare, or short-lived stage of stellar evolution, and second because these stars regularly produce large amounts of dust so they are laboratories for the study of dust formation and evolution. (SECTION: Invited Review Paper)

  15. Particle Acceleration in a Statistically Modeled Solar Active-Region Corona

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

    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.

  16. The Role and Implications of Non-Thermal Distributions in the Solar Corona/Wind

    NASA Astrophysics Data System (ADS)

    Scudder, J. D.

    2014-12-01

    Astrophysical plasmas contain ubiquitous non-thermal velocity distribution functions (VDF's) down to the mean energies of the plasma. These non-thermal particles represent a non-negligible part of the solar wind density, gas pressure, and heat flow. The usual fluid treatments ignore the information in non-Gaussian VDF's, while kinetic treatments suggest they play an essential role for the observed wind expansion. The existence of the such kurtotic VDF's contradict the very Spitzer-Braginskii (SB) approximations made to motivate low order closures approximations of the quasi-neutral fluid equations for the plasma (1). Their routine observation implies the usual continuum description of the plasma must change from the SB framework. The origin of such kurtotic distributions has been traced (1) to the consequences of gravity's violating the assumptions of the SB framework, giving any astrophysical plasma fluid description a non-local character. The quasi-steady character of the observed solar wind implies that this non-local character is resolved by spatial variation of the kurtotic distribution functions moving along the tubes of magnetic force as they enforce the higher goals of quasi-neutrality and zero current. This insight suggests an unusual equation of state for the plasma. A minimal fluid model will be introduced for the coronal expansion that (i) suggests the origin and strength of kurtotic VDF's, (ii) explains their ubiquity; (iii) provides a continuum description, (iv) allows variations of kurtosis and velocity filtration-like variations of T; and (v) retains coulomb collisions. The non-thermal electrons of the solar wind VDF's will be shown to closely resemble the conduction band in a metal, being the global regulators of quasi-neutrality, electric and heat currents and behaving as a second electron fluid which, together with the protons forms the minimal 3 fluid description. (1) Scudder, J.D. and H. Karimabadi, Ap J., 770:26, 2013

  17. On Determination of 3D Morphology and Plasma Properties of the Solar Corona

    NASA Technical Reports Server (NTRS)

    Gary, G. Allen; Davis, John M.; Moore, Ronald; Six, N. Frank (Technical Monitor)

    2002-01-01

    An earlier analysis preformed and published will be revisited and applied to SECCHI's observations. Using coronal models and imaging-rendering techniques we will investigate several important facts regarding the solar stereographic mission. A synthesized image will be presented formed from integrating the emission from the volume elements along the line-of-sight path through a three-dimensional volume. We used analysis of pairs of these synthesized images with various angular perspectives to investigate the effect of angular separation on mission objectives. The resulting images and analysis provide guidelines for developing a stereographic mission analysis program.

  18. The effect of the hot oxygen corona on the interaction of the solar wind with Venus

    NASA Technical Reports Server (NTRS)

    Belotserkovskii, O. M.; Mitnitskii, V. IA.; Breus, T. K.; Krymskii, A. M.; Nagy, A. F.

    1987-01-01

    A numerical gasdynamic model, which includes the effects of mass loading of the shocked solar wind, was used to calculate the density and magnetic field variations in the magnetosheath of Venus. These calculations were carried out for conditions corresponding to a specific orbit of the Pioneer Venus Orbiter (PVO orbit 582). A comparison of the model predictions and the measured shock position, density and magnetic field values showed a reasonable agreement, indicating that a gasdynamic model that includes the effects of mass loading can be used to predict these parameters.

  19. Forbidden lines of the solar corona and transition zone - 975-3000 A

    NASA Technical Reports Server (NTRS)

    Sandlin, G. D.; Brueckner, G. E.; Tousey, R.

    1977-01-01

    Forbidden lines characteristic of plasmas at temperatures of 50,000 to 3 million K are observed in ATM UV spectra. Identifications, accurate wavelengths, ionization classes, intensities, and half-widths are presented. Coronal blends with He II at 1640 A are noted. Variations in nonthermal velocities with limb distance are observed. Doppler shifts in the coronal lines observed on the disk may be related to the solar wind. The coincidence of two lines with F IV(3P-5S) is evidence for atomic fluorine in the sun.

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

    PubMed

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

    1997-04-25

    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

  1. Using the ionospheric response to the solar eclipse on 20 March 2015 to detect spatial structure in the solar corona.

    PubMed

    Scott, C J; Bradford, J; Bell, S A; Wilkinson, J; Barnard, L; Smith, D; Tudor, S

    2016-09-28

    The total solar eclipse that occurred over the Arctic region on 20 March 2015 was seen as a partial eclipse over much of Europe. Observations of this eclipse were used to investigate the high time resolution (1 min) decay and recovery of the Earth's ionospheric E-region above the ionospheric monitoring station in Chilton, UK. At the altitude of this region (100 km), the maximum phase of the eclipse was 88.88% obscuration of the photosphere occurring at 9:29:41.5 UT. In comparison, the ionospheric response revealed a maximum obscuration of 66% (leaving a fraction, Φ, of uneclipsed radiation of 34±4%) occurring at 9:29 UT. The eclipse was re-created using data from the Solar Dynamics Observatory to estimate the fraction of radiation incident on the Earth's atmosphere throughout the eclipse from nine different emission wavelengths in the extreme ultraviolet (EUV) and X-ray spectrum. These emissions, having varying spatial distributions, were each obscured differently during the eclipse. Those wavelengths associated with coronal emissions (94, 211 and 335 Å) most closely reproduced the time varying fraction of unobscured radiation observed in the ionosphere. These results could enable historic ionospheric eclipse measurements to be interpreted in terms of the distribution of EUV and X-ray emissions on the solar disc.This article is part of the themed issue 'Atmospheric effects of solar eclipses stimulated by the 2015 UK eclipse'. PMID:27550766

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

    NASA Astrophysics Data System (ADS)

    Gallagher, Peter T.; Long, David M.

    2011-07-01

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

  3. Probability of solar panel clearing events at the Insight landing sites (Mars) from a dust devil track survey

    NASA Astrophysics Data System (ADS)

    Reiss, D.; Lorenz, R. D.

    2015-10-01

    The InSight robotic lander is scheduled to land on Mars in September 2016. InSight was designed to perform the first comprehensive surface-based geophysical investigation of Mars [1]. Passage of vortices may have a number of influences on the geophysical measurements to be made by InSight. Seismic data could be influenced by dust devils and vortices via several mechanisms such as loading of the elastic ground by a surface pressure field which causes a local tilt [e.g. 2]. In addition, the power supply of the InSight instruments is provided by solar arrays. Solar-powered missions on Mars like the Sojourner rover in 1997 were affected by a decline in electrical power output by 0.2-0.3 %per day caused by steadily dust deposition on its horizontal solar panel [3]. The solar-powered Mars Exploration Rovers (MERs) Spirit and Opportunity experienced similar dust deposition rates [4] which led to steady power decrease over time endangering longer rover operation times. The much longer operation times of the rovers were made possible by unanticipated 'dust clearing events' of the solar arrays by wind gust or dust devils [5]. Recent studies imply that dust devils are primarily responsible for those recurrent 'dust clearing events' [6]. In this study we investigate the potential frequency of intense dust devil occurrences at the InSight landing site regions, which are able to remove dust from its solar panels. We analyzed newly formed dust devil tracks within a given time span using multi-temporal HiRISE image data covering the same surface area. Based on these measurements we will give encounter rate predictions of intense (high tangential speed and high pressure drop) dust devils with the InSight lander.

  4. Particle acceleration in 3D single current sheets formed in the solar corona and heliosphere: PIC approach

    NASA Astrophysics Data System (ADS)

    Zharkova, V. V.; Siversky, T.

    2015-09-01

    Acceleration of protons and electrons in a reconnecting current sheet (RCS) is investigated with the test particle and particle-in-cell (PIC) approaches in a 3D magnetic topology. PIC simulations confirm a spatial separation of electrons and protons with respect to the midplane depending on the guiding field. Simulation reveals that the separation occurs in magnetic topologies with strong guiding fields and lasts as long as the particles are kept dragged into a current sheet. This separation produces a polarisation electric field induced by the plasma feedback to a presence of accelerated particles, which shape can change from symmetric towards the midplane (for weak guiding field) to fully asymmetric (for strong guiding field). Particles are found accelerated at a midplane of any current sheets present in the heliosphere to the energies up to hundred keV for electrons and hundred MeV for protons. The maximum energy gained by particles during their motion inside the current sheet is defined by its magnetic field topology (the ratio of magnetic field components), the side and location from the X-nullpoint, where the particles enter a current sheet. In strong magnetic fields of the solar corona with weaker guiding fields, electrons are found circulating about the midplane to large distances where proton are getting accelerated, creating about the current sheet midplane clouds of high energy electrons, which can be the source of hard X-ray emission in the coronal sources of flares. These electrons are ejected into the same footpoint as protons after the latter reach the energy sufficicent to break from a current sheet. In a weaker magnetic field of the heliosphere the bounced electrons with lower energies cannot reach the midplane turning instead at some distance D before the current sheet midplane by 180 degrees from their initial motion. Also the beams of accelerated transit and bounced particles are found to generate turbulent electric fields in a form of Langmuir

  5. Core and wing densities of asymmetric coronal spectral profiles: Implications for the mass supply of the solar corona

    SciTech Connect

    Patsourakos, S.; Klimchuk, J. A.; Young, P. R. E-mail: james.a.klimchuk@nasa.gov

    2014-02-01

    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{sup –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 Å 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.

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

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

    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 approximately equal to 50 km per sec. 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(sub XIV) lines at 264.78 and 274.20 Angstroms 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(sub 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

    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 Å 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.

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

    NASA Technical Reports Server (NTRS)

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

    1979-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

    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.

  10. The thermal structure of solar coronal loops and implications for physical models of coronae

    NASA Technical Reports Server (NTRS)

    Raymond, J. C.; Foukal, P.

    1982-01-01

    EUV spectra of three active region loops observed above the solar limb with the SO55 spectrometer on Skylab are analyzed. It is noted that the lengths, peak temperatures, and pressures of the loops are typical of the X-ray coronal loops to which static models have been applied. It is found that the physical parameters of the coronal loop plasma derived from EUV spectra and raster pictures are not well represented by the static models. Although the loops also contain a significant quantity of cool plasma, no physical reason is found to differentiate them from other active region loops of similar length, pressure, and temperature. Several line ratios in the loop spectrum suggest departures from ionization equilibrium caused by rapid cooling. The source of this cooling material is discussed with reference to several models of loop dynamics.

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

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

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

  12. Fragmentation of electric currents in the solar corona by plasma flows

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    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.

  15. Spectroscopic Constraints on Models of Ion-Cyclotron Resonance Heating in the Polar Solar Corona and Fast Solar Wind

    NASA Astrophysics Data System (ADS)

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

    1998-12-01

    We present preliminary results from a theoretical model of the heating of minor ions in the fast solar wind. We examine the compatibility between these models and spectroscopic determinations of velocity distribution functions from the UVCS and SUMER instruments aboard SOHO. By examining the dependence of line shapes (which probe the perpendicular velocity distribution) on ion charge and mass, detailed information can be extracted about the preferential heating and the Coulomb collisional coupling. The primary momentum and energy deposition mechanism we investigate is the dissipation of high-frequency (ion-cyclotron resonant) Alfven waves, which can accelerate and heat ions differently depending on their charge and mass. Minor ions which do not appreciably damp the resonant wave amplitudes can be used to constrain the slope of the fluctuation spectrum. SUMER measurements of several ions at heliocentric heights between 1.02 and 1.07 solar radii allow the ``base'' spectrum to be analyzed, and UVCS O VI line widths measured between 1.5 and 3.5 solar radii provide information about the radial evolution of the spectrum. This work is supported by the National Aeronautics and Space Administration under grant NAG5-3192 to the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana, and by the ESA PRODEX program (Swiss contribution).

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

    NASA Astrophysics Data System (ADS)

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

    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 2.0•10-4 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  18. Explaining Inverted Temperature Loops in the Quiet Solar Corona with Magnetohydrodynamic Wave Mode Conversion

    NASA Astrophysics Data System (ADS)

    Schiff, Avery; Cranmer, Steven R.

    2016-05-01

    We simulate the temperature profiles along coronal loops measured with AIA DEM tomography and field-line extrapolation by Nuevo et al (2013). By varying the strength and nature of the heating mechanism, we modeled steady-state, gravitationally stable loops that have temperature profiles with local maxima below the loop apex. Because these loops have negative vertical temperature gradients over much of their length, they have been called "down loops" and were seen to exist primarily in equatorial quiet regions near solar minimum. In our models, the amount of heat deposited in the loop is attributed to two sources: (1) the dissipation of Alfven waves in a turbulent cascade, and (2) the dissipation of compressive waves over a variable length. The compressive waves are generated in a nonlinear process by which some fraction of the Alfven waves undergo mode conversion instead of contributing directly to the heating process. We found that when a large percentage (> 99%) of the Alfven waves underwent this conversion, the heating was greatly concentrated at the base of the loop and stable "down loops" were created. In some cases, we found loops with three extrema that are gravitationally stable. We map the full parameter space to explore which conditions lead to which loop types, and we demonstrate that the simulated characteristics of the loops -- including magnetic field strength, pressure, and temperature -- are consistent with values measured by Nuevo et al. (2013).

  19. VERTICAL KINK OSCILLATION OF A MAGNETIC FLUX ROPE STRUCTURE IN THE SOLAR CORONA

    SciTech Connect

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

    2014-12-20

    Vertical transverse oscillations of a coronal magnetic rope, observed simultaneously in the 171 Å and 304 Å 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 Å and 304 Å 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 Å bandpass shows an oscillatory motion with the period of about 1000 s.

  20. The solar corona as probed by comet Lovejoy (C/2011 W3)

    SciTech Connect

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

    2014-06-20

    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 Alfvén speed on a similar scale. They will drastically affect the propagation and dissipation of Alfvén 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 Alfvén waves as the cometary ions isotropize.

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

    NASA Astrophysics Data System (ADS)

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

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

  2. Dynamics and distribution of nano-dust particles in the inner solar system

    NASA Astrophysics Data System (ADS)

    JuháSz, A.; HoráNyi, M.

    2013-06-01

    Dust particles in the approximate mass range of 10-22dust particles, have been shown to become entrained in the solar wind plasma flow. When these so-called nano-dust particles (NDPs) impact a spacecraft, they have been suggested to produce sufficiently large plasma clouds to cause a detectable signal in the onboard electric antennas. NDPs have been identified on the twin STEREO spacecraft, and the observed intermittent nature of their fluxes were suggested to represent the stochastic nature of their sources near the Sun. Here we show that even if the generation of NDPs remains a constant in time, their detectability near the ecliptic plane becomes intermittent due their interaction with the interplanetary magnetic fields.

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

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

  4. 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)

    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

    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.

  5. Fast Magnetoacoustic Wave Trains of Sausage Symmetry in Cylindrical Waveguides of the Solar Corona

    NASA Astrophysics Data System (ADS)

    Shestov, S.; Nakariakov, V. M.; Kuzin, S.

    2015-12-01

    Fast magnetoacoustic waves guided along the magnetic field by plasma non-uniformities, in particular coronal loops, fibrils, and plumes, are known to be highly dispersive, which lead to the formation of quasi-periodic wave trains excited by a broadband impulsive driver, e.g., a solar flare. We investigated the effects of cylindrical geometry on the fast sausage wave train formation. We performed magnetohydrodynamic numerical simulations of fast magnetoacoustic perturbations of a sausage symmetry, propagating from a localized impulsive source along a field-aligned plasma cylinder with a smooth radial profile of the fast speed. The wave trains are found to have pronounced period modulation, with the longer instant period seen in the beginning of the wave train. The wave trains also have a pronounced amplitude modulation. Wavelet spectra of the wave trains have characteristic tadpole features, with the broadband large-amplitude heads preceding low-amplitude quasi-monochromatic tails. The mean period of the wave train is about the transverse fast magnetoacoustic transit time across the cylinder. The mean parallel wavelength is about the diameter of the wave-guiding plasma cylinder. Instant periods are longer than the sausage wave cutoff period. The wave train characteristics depend on the fast magnetoacoustic speed in both the internal and external media, the smoothness of the transverse profile of the equilibrium quantities, and also the spatial size of the initial perturbation. If the initial perturbation is localized at the axis of the cylinder, the wave trains contain higher radial harmonics that have shorter periods.

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

    SciTech Connect

    Srivastava, A. K.; Joshi, N. C.; Kayshap, P.; Erdelyi, R.; Fedun, V.; Tripathi, Durgesh

    2013-03-10

    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.

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

    NASA Technical Reports Server (NTRS)

    Bagenal, Fran

    2001-01-01

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

  8. Solar System dynamics and global-scale dust storms on Mars

    NASA Astrophysics Data System (ADS)

    Shirley, James H.

    2015-05-01

    Global-scale dust storms occur during the southern summer season on Mars in some Mars years but not in others. We present an updated catalog of Mars years including such storms (n = 9) and Mars years without global-scale storms (n = 11) through the year 2013. A remarkable relationship links the occurrence and non-occurrence of global-scale dust storms on Mars with changes in the orbital angular momentum of Mars with respect to the Solar System barycenter (LMars). All of the global-scale dust storms became planet-encircling in both latitude and longitude during periods when LMars was increasing or near maxima. Statistical significance at the 1% level is obtained for the clustering tendency of LMars phases for the 5 mid-season storms with Ls ranging from 208° to 262° (1956, 1971, 1982, 1994, and 2007). The 11 Mars years without global-scale dust storms exhibit mainly decreasing and minimum values of LMars during the first half of the dust storm season; this tendency is statistically significant at the 5% level. A systematic progression is present in the phasing of the solar irradiance and LMars waveforms for the global-scale storm years. LMars phases for the early season global-scale storms of 1977 and 2001 are advanced in phase with respect to those of the mid-season storms, while the phase for the late season storm of 1973 is delayed with respect to those of the mid-season storms cluster. Factors internal to the Mars climate system, such as a spatial redistribution of surface dust from year to year, must be invoked to account for the non-occurrence of global-scale dust storms in five years (1986, 2003, 2005, 2009, and 2013) when the LMars phase was otherwise favorable. Our results suggest that the occurrence of increasing or peak values of LMars immediately prior to and during the Mars dust storm season may be a necessary-but-not-sufficient condition for the initiation of global-scale dust storms on Mars.

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

    NASA Technical Reports Server (NTRS)

    Cruikshank, D. P.

    2012-01-01

    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

  10. Sixteen Years of Ulysses Interstellar Dust Measurements in the Solar System. I. Mass Distribution and Gas-to-dust Mass Ratio

    NASA Astrophysics Data System (ADS)

    Krüger, Harald; Strub, Peter; Grün, Eberhard; Sterken, Veerle J.

    2015-10-01

    In the early 1990s, contemporary interstellar dust penetrating deep into the heliosphere was identified with the in situ dust detector on board the Ulysses spacecraft. Between 1992 and the end of 2007 Ulysses monitored the interstellar dust stream. The interstellar grains act as tracers of the physical conditions in the local interstellar medium (ISM) surrounding our solar system. Earlier analyses of the Ulysses interstellar dust data measured between 1992 and 1998 implied the existence of a population of “big” interstellar grains (up to 10-13 kg). The derived gas-to-dust-mass ratio was smaller than the one derived from astronomical observations, implying a concentration of interstellar dust in the very local ISM. In this paper we analyze the entire data set from 16 yr of Ulysses interstellar dust measurements in interplanetary space. This paper concentrates on the overall mass distribution of interstellar dust. An accompanying paper investigates time-variable phenomena in the Ulysses interstellar dust data, and in a third paper we present the results from dynamical modeling of the interstellar dust flow applied to Ulysses. We use the latest values for the interstellar hydrogen and helium densities, the interstellar helium flow speed of {v}{ISM∞ }=23.2 {km} {{{s}}}-1, and the ratio of radiation pressure to gravity, β, calculated for astronomical silicates. We find a gas-to-dust mass ratio in the local interstellar cloud of {R}{{g}/{{d}}}={193}-57+85, and a dust density of (2.1 ± 0.6) × 10-24 kg m-3. For a higher inflow speed of 26 {km} {{{s}}}-1, the gas-to-dust mass ratio is 20% higher, and, accordingly, the dust density is lower by the same amount. The gas-to-dust mass ratio derived from our new analysis is compatible with the value most recently determined from astronomical observations. We confirm earlier results that the very local ISM contains “big” (i.e., ≈1 μm sized) interstellar grains. We find a dust density in the local ISM that is a

  11. Cosmic dust

    NASA Technical Reports Server (NTRS)

    Brownlee, Donald E.; Sandford, Scott A.

    1992-01-01

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

  12. Revealing Exo-Zody and Exo-Planets from Solar System Dust Measurements: ALADDIN-2 for the Solar Power Sail Mission

    NASA Astrophysics Data System (ADS)

    Yano, Hajime; Hirai, Takayuki

    2016-07-01

    The dust structure of our Solar System provides a benchmark information of dust disks of other exo-planetary systems in general, just like the Sun as the closest main sequence G-star that we can study with the most details. Heliocentric dust distributions and gravitational and orbital interactions with planets such as mean motion resonances (MMRs) of dust flux of our Solar System are what we can transfer the knowledge of our Solar System dust apply to infer anisotropic exo-zodiacal brightness, or spatial structures within a exo-planetary dust disks with information about potentially embedded planets inside. In the coming era of disk resolved observations by ALMA, TMT and other new telescopes, we will be able to apply what we find in the Solar System to the rest of planetary systems. In 2010-11, the IKAROS solar sail spacecraft carried the ALADDIN large area dust detector array to study large meteoroids between the Earth and Venus orbits. Yano et al. directly detected both the Earth's and Venus' MMRs dust structures, being consistent with numerical simulations that predict the existence of such local enhancements of dust distribution around these terrestrial planets, as well as Neptune. JAXA's Solar Power Sail mission plans to carry even larger dust detector inherited the technology onboard IKAROS, namely ALADDIN-2 in order to search for such MMRs in the Mars and Jupiter orbits, as predicted by Kuchner et al.(2000), in addition to make a continuous measurement of large dust flux from 1.0 to 5.2 AU crossing the main asteroid belt up to Jupiter Trojan region. It is also noted that recent reanalysis of the Pioneer 10 and 11 photo polarimeter data suggests a small enhancement of the brightness towards the anti-solar direction near Jupiter the largest planet of our Solar System, implying a possible existence of a dust belt related to the planet. The spatial density of dust particles directly measured by the ALADDIN-2 will provide a more conclusive and direct proof due to

  13. Weak Solar Flares in 3 -31.5 keV X-rays Detected in the Coronas-F Experiment

    NASA Astrophysics Data System (ADS)

    Gusev, Anatoly; Pugacheva, Galina; Martin, Inácio M.; Spjeldvik, Walther

    The RPS-1 spectrometer on the board of the Coronas-F satellite detecting solar X-rays in the range of 3-31.5 keV using a CdTe detector is described and some results of the observation of weak solar flares are presented. The detector has a high detection efficiency and radiation damage resistance necessary for long time space experiments. It has an active area of 46 mm2, a thickness of 1.4 mm, an operation voltage of 100 V, an energy resolution of 0.88 keV (13.87 keV Am241), a power consumption of 8.5 W, and a mass of 1.8 kg. The width of the first 12 channels (3-9 keV) is 0.5 keV, the width of the next 12 channels is 1 keV, and the width of the last 8 channels (21-31.5 keV) is 1.3 keV. The spectrum accumulation time in 32 channels is 16 s. The spectrometer provides vast experimental data on the spectra of soft X-ray emission of solar flares. The high spectral resolution of the instrument allows an investigation of the dynamics of the temperature in the source using the direct comparison of the spectrum shape with some models, for example, with the CHIANTI 5.2 model. It was noted that hardness of the spectrum in the flare maximum increases with the flare class and solar activity level. The magnetic heating of the corona was confirmed by the spectra of the background solar X ray radiation for various numbers of sunspots: the more sunspots, the harder the spectrum of the X-ray background radiation was registered and, respectively, the stronger was the impact on the Earth's atmosphere. Near the solar activity maximum, the background radiation intensity increased by more than an order of magnitude and the maximum energy increased from 6 to 20 keV. (To the memory of Drs. V.M. Pankov and V.L. Prokhin, colleagues and coworkers in the Coronas-F mission.)

  14. Arecibo radar micrometeor studies: Interplanetary dust in the solar system and the atmospheric fate of this dust

    NASA Astrophysics Data System (ADS)

    Mathews, J.; Briczinski, S.; Meisel, D.; Zhou, Q.; Janches, D.

    Radar