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  • Chemical Engineering  (708)
  • Engineering General  (497)
  • SOLAR PHYSICS  (396)
  • 1985-1989  (1,601)
  • 1975-1979
  • 1986  (1,601)
Collection
Keywords
Publisher
Years
  • 1985-1989  (1,601)
  • 1975-1979
Year
  • 1
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    Formation of a compound stream between 0.85 AU and 6.2 AU and its effects on solar energetic particles and galactic cosmic rays (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: This paper describes the formation of a compound stream as a result of the interaction and coalescence of a series of five streams (a slow transient stream, two corotating streams, and two exceptionally fast transient streams) observed by the Helios B (HB) satellite near 0.85 AU. The compound stream and two merged interaction regions were also observed by the Voyager 1 satellite near 6.2 AU when it was nearly radially aligned with the HB. Closely associated with this compound stream was one of the largest solar energetic particle events observed beyond 5 AU. The relationship of this compound stream and its magnetic fields to the intensity profiles of solar energetic particles and galactic cosmic rays is discussed.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 13331-13
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  • 2
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    The composition of solar energetic particles (1986)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The present measurements of elemental abundances in 15 large solar energetic particle events confirm the existence of two major effects: systematic differences between solar energetic particle abundances and photospheric abundances that are approximately correlated with first ionization potential (implying that the solar corona is the likely source population for these particles), and an enhancement of heavy ion abundances relative to a baseline of solar energetic particle abundances whose magnitude increases with rising atomic number. These data suggest the possibility that the degree of heavy ion enhancement has some correlation with spectral slope, and confirm that the aforementioned effects are not due to time or energy variations within individual events. The maximum column density above the solar acceleration region is less than 0.1 g/sq cm, on the basis of these data.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 301; 938-961
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  • 3
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    Particle formation and interaction (1986)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: A wide variety of experiments can be conducted on the Space Station that involve the physics of small particles of planetary significance. Processes of interest include nucleation and condensation of particles from a gas, aggregation of small particles into larger ones, and low velocity collisions of particles. All of these processes could be investigated with a general purpose facility on the Space Station. The microgravity environment would be necessary to perform many experiments, as they generally require that particles be suspended for periods substantially longer than are practical at 1 g. Only experiments relevant to planetary processes will be discussed in detail here, but it is important to stress that a particle facility will be useful to a wide variety of scientific disciplines, and can be used to address many scientific problems.
    Keywords: SOLAR PHYSICS
    Type: NASA. Lyndon B. Johnson Space Center Space Station Planetology Experiments (SSPEX); 4 p
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  • 4
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    Simultaneous Solar Maximum Mission (SMM) and very large array observations of solar active regions (1986)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The research deals mainly with Very Large Array and Solar Maximum Mission observations of the ubiquitous coronal loops that dominate the structure of the low corona. As illustrated, the observations of thermal cyclotron lines at microwave wavelengths provide a powerful new method of accurately specifying the coronal magnetic field strength. Processes are delineated that trigger solar eruptions from coronal loops, including preburst heating and the magnetic interaction of coronal loops. Evidence for coherent burst mechanisms is provided for both the Sun and nearby stars, while other observations suggest the presence of currents that may amplify the coronal magnetic field to unexpectedly high levels. The existence is reported of a new class of compact, variable moving sources in regions of apparently weak photospheric field.
    Keywords: SOLAR PHYSICS
    Type: NASA-CR-177187 , NAS 1.26:177187
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  • 5
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    Solar flare X-ray polarimetry (1986)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The motivation for high quality solar flare X-ray polarization measurements are discussed in general. The design of the proposed instrument is described and then the sensitivity and energy response are discussed. The laboratory work which demonstrates that the earlier lithium contamination problem was solved, is described.
    Keywords: SOLAR PHYSICS
    Type: NASA-CR-179899 , NAS 1.26:179899
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  • 6
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    Solar Flares and Coronal Physics Using P/OF as a Research Tool (1986)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This NASA Conference Publication contains the proceedings of the Workshop on Solar High-Resolution Astrophysics Using the Pinhole/Occulter Facility held at NASA Marshall Space Flight Center, Alabama, on May 8 to 10, 1985. These proceedings include primarily the invited tutorial papers, extended abstracts of contributed poster papers, and summaries of subpanel (X-Ray and Coronal Physics) discussions. Both observational and theoretical results are presented. Although the emphasis of the Workshop was focused primarily on topics peculiar to solar physics, one paper is included that discusses the P/0F as a tool for X-ray astronomy.
    Keywords: SOLAR PHYSICS
    Type: NASA-CP-2421 , M-523 , NAS 1.55:2421 , May 08, 1985 - May 10, 1985; Huntsville, AL; United States
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  • 7
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    Ionic charge distributions of energetic particles from solar flares (1986)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The effects which solar flare X-rays have on the charge states of solar cosmic rays is determined quantitatively. Rather than to characterize the charge distribution by temperature alone, it is proposed that the X-ray flux at the acceleration site also is used. The effects of flare X-rays are modeled mathematically.
    Keywords: SOLAR PHYSICS
    Type: NASA-CR-176610 , NAS 1.26:176610
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  • 8
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    The possible importance of synchrotron/inverse Compton losses to explain fast MM-wave and hard X-ray emission of a solar event (1986)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The solar burst of 21 May 1984 presented a number of unique features. The time profile consisted of seven major structures (seconds), with a turnover frequency or approx. 90 GHz, well correlated in time to hard X-ray emission. Each structure consisted of multiple fast pulses (.1 seconds), which were analyzed in detail. A proportionality between the repetition rate of the pulses and the burst fluxes at 90 GHz and or approx. 100 keV hard X-rays, and an inverse proportionality between repetition rates and hard X-rays power law indices have been found. A synchrotron/inverse Compton model has been applied to explain the emission of the fast burst structures, which appear to be possible for the first three or four structures.
    Keywords: SOLAR PHYSICS
    Type: NASA-TM-88659 , NAS 1.15:88659 , INPE-3809-PRE/895 , SMM Topical Workshop on Rapid Fluctuations in Solar Flares; Sep 30, 1985 - Oct 04, 1985; Lanham, MD; United States
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  • 9
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    The structure of the static corona and transition region (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Static models of coronal loops are investigated. For loops that are low-lying with heights above the chromosphere below about 5000 km, it is shown that a new type of solution appears to the static equations, in addition to the well-known coronal loop solution. The new solution is characterized by a maximum plasma temperature less than about 100,000 K. The structure and properties of these cool solutions are discussed. The differential emission measure Q(T) expected for a magnetic arcade, which must naturally contain both hot and cool loops, is calculated. It is shown that the cool loops have a dramatic effect on the form of Q(T) in the lower transition region. In particular, they can account for the observed rise in Q at low T, which has long been thought to be incompatible with the static-loop model. Finally, the implications of the cool loops on other observations of both the solar and stellar coronae and transition regions are discussed.
    Keywords: SOLAR PHYSICS
    Type: AD-A169499 , Astrophysical Journal, Part 1 (ISSN 0004-637X); 301; 440-447
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  • 10
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    A comparison of photospheric electric current and ultraviolet and X-ray emission in a solar active region (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: This paper presents an extensive set of coordinated observations of a solar active region, taking into account spectroheliograms obtained with the aid of the Solar Maximum Mission (SMM) Ultraviolet Spectrometer Polarimeter (UVSP) instrument, SMM soft X-ray polychromator (XRP) raster maps, and high spatial resolution ultraviolet images of the sun in Lyman-alpha and in the 1600 A continuum. These data span together the upper solar atmosphere from the temperature minimum to the corona. The data are compared to maps of the inferred photospheric electric current derived from the Marshall Space Flight Center (MSFC) vector magnetograph observations. Some empirical correlation is found between regions of inferred electric current density and the brightest features in the ultraviolet continuum and to a lesser extent those seen in Lyman-alpha within an active region.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 300; 428-437
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  • 11
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    Transition region, corona, and solar wind in coronal holes (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The formation of wind-driven solar model based on a new hypothesis for nonlinear wave dissipation is described. The equations and solutions used to derive the model are examined. The corona and solar wind are analyzed. The model is applied to observations and it is detected that it displays the proper steep temperature rise to a maximum coronal temperature in excess of 10 to the 6th K, a solar wind flux in excess of 3.5 x 10 to the 8th/sq cm per sec at 1 AU, and nonthermal velocities are observed at the bases of coronal holes; however, the model does not produce enough detail.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 4111-412
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  • 12
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    Solar wind Fe and CNO measurements in high-speed flows (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Solar wind characteristics in driver plasma and coronal hole-associated flow types are analyzed. Measurements of solar wind Fe charge states and densities in well-defined driver plasma and coronal hole-associated high-speed streams, and charge distributions of CNO ions in high speed streams collected with the ultra low energy charge analyzer on ISEE 3 are examined. The Fe-H velocity differences and Fe/H abundance ratios are studied. The data reveal that the driver plasma solar wind has charge states of 15 or 16 with a coronal temperature = 4 x 10 to the 6th K, and the Fe charge states distributions in coronal hole-associated streams = 9 or 10 with a coronal temperature = 1.4 x 10 to the 6th K; the ionization temperature for the CNO group = (1.3 + or - 0.3) x 10 to the 6th K.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 4133-414
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  • 13
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    Solar flare ionization in the mesosphere observed by coherent-scatter radar (1986)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: The coherent-scatter technique, as used with the Urbana radar, is able to measure relative changes in electron density at one altitude during the progress of a solar flare when that altitude contains a statistically steady turbulent layer. This work describes the analysis of Urbana coherent-scatter data from the times of 13 solar flares in the period from 1978 to 1983. Previous methods of measuring electron density changes in the D-region are summarized. Models of X-ray spectra, photoionization rates, and ion-recombination reaction schemes are reviewed. The coherent-scatter technique is briefly described, and a model is developed which relates changes in scattered power to changes in electron density. An analysis technique is developed using X-ray flux data from geostationary satellites and coherent scatter data from the Urbana radar which empirically distinguishes between proposed D-region ion-chemical schemes, and estimates the nonflare ion-pair production rate.
    Keywords: SOLAR PHYSICS
    Type: NASA-CR-176649 , NAS 1.26:176649 , AR-118 , UILU-ENG-86-2501 , (ISSN 0568-0581)
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  • 14
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    The heavy-ion compositional signature in He-3-rich solar particle events (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A survey of the approx. 1 MeV/nucleon heavy ion abundances in 66 He-3-rich solar particle events was performed using the Max-Planck-Institut/University of Maryland and Goddard Space Flight Center instruments on the ISEE-3 spacecraft. The observations were carried out in interplanetary space over the period 1978 October through 1982 June. Earlier observations were confirmed which show an enrichment of heavy ions in He-3-rich events, relative to the average solar energetic particle composition in large particle events. For the survey near 1.5 MeV/nucleon the enrichments compared to large solar particle events are approximately He4:C:O:Ne:Mg:Si:Fe = 0.44:0.66:1.:3.4:3.5:4.1:9.6. Surprising new results emerging from the present broad survey are that the heavy ion enrichment pattern is the same within a factor of approx. 2 for almost all cases, and the degree of heavy ion enrichment is uncorrelated with the He-3 enrichment. Overall, the features established appear to be best explained by an acceleration mechanism in which the He-3 enrichment process is not responsible for the heavy ion enrichment, but rather the heavy ion enrichment is a measure of the ambient coronal composition at the sites where the He-3-rich events occur.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 303; 849-860
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  • 15
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    Time-dependent coronal shock acceleration of energetic solar flare particles (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A global time-dependent model is presented for the coronal and interplanetary shock acceleration and propagation of energetic solar flare particles. The calculations are carried out to help prove that coronal shock acceleration of solar flare particles is responsible for energetic solar flare event data gathered in interplanetary space. The model is based on the theory of diffusive shock acceleration, and requires particle speeds to be much greater than bulk velocities. Also, sufficient scattering must occur upstream and downstream of the shock for the particle scattering mean free path to be smaller than the characteristic scale lengths, which causes the same particles to encounter the shock repeatedly. A spherically symmetric shock wave is assumed, which leads to the same emission configuration for impulsively and monoenergetically emitted particles. Consideration is given to acceleration by compression at the shock front, adiabatic deceleration in the divergent downstream flow, the temporal evolution of the shock and the three-dimensional geometry of the corona. The model is used to generate normalized proton omnidirectional distributions at 1 AU and at the shock front. The spectral exhibit trends similar to those in observational data, especially proton acceleration times and the proton distribution profiles at 1 AU.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 303; 829-842
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  • 16
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    Rapid acceleration of energetic particles in the 1982 February 8 solar flare (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Hard X-ray and gamma-ray measurements of the February 8, 1982 (1250 UT) solar flare made with spectrometers aboard the ISEE 3 and SMM spacecraft show that bursts of photons from 40 keV to 40 MeV are coincident within + or - 1 s. This indicates that the acceleration of particles to relativistic velocities can occur promptly (within 1 s). As far as the energetic particles interacting at the sun are concerned, the 'two-phase' process, which requires several minutes for particle acceleration to relativistic velocities, cannot account for the present gamma-ray observations. Even the 'two-step' acceleration process, which is assumed to occur in a small magnetic loop, is severely constrained by the present observations.
    Keywords: SOLAR PHYSICS
    Type: AD-A199486 , AFGL-TR-88-0219 , Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 300; L95-L98
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  • 17
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    The role of nonclassical electron transport in the lower solar transition region (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: One problem in solar physics is concerned with an understanding of the observed brightness of the quiet solar atmosphere in spectral lines which are formed in the lower solar transition region. The present paper has the objective to examine the possibility that the observed line emission results from nonclassical electron transport effects which are associated with the inherently steep temperature gradients in the solar transition region. The height variation of the electron temperature is parameterized to enable correspondence with a variety of one-dimensional constant pressure transition region models. The models include empirical models, theoretical models, and the constant classical heat fluxx model used by Shoub (1983). The electron velocity distribution function is considered along with the effect on collisional excitation and ionization rates, and effects on heat transport.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 300; 420-427
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  • 18
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    Possible explanation of the solar-neutrino puzzle (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A new derivation of the Mikheyev and Smirnov (1985) mechanism for the conversion of electron neutrinos into mu neutrinos when traversing the sun is presented, and various hypotheses set forth. It is assumed that this process is responsible for the detection of fewer solar neutrinos than expected, with neutrinos below a minimum energy, E(m), being undetectable. E(m) is found to be about 6 MeV, and the difference of the squares of the respective neutrino masses is calculated to be 6 X 10 to the - 5th sq eV. A restriction on the neutrino mixing angle is assumed such that the change of density near the crossing point is adiabatic. It is predicted that no resonance conversion of neutrinos will occur in the dense core of supernovae, but conversion of electron neutrinos to mu neutrinos will occur as they escape outward through a density region around 100.
    Keywords: SOLAR PHYSICS
    Type: Physical Review Letters (ISSN 0031-9007); 56; 1305-130
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  • 19
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    A shock condensation mechanism for loop prominences (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Self-consistent, numerical solutions of the resistive MHD equations in two dimensions show that a quasi-stationary, fast-mode shock is a characteristic feature of the reconnection dynamics of the Kopp-Pneuman model of two-ribbon flares. A preliminary analysis of the effects of radiative cooling and thermal conduction suggests that the fast shock can help trigger a thermal condensation (i.e., a loop prominence)if the reconnecting magnetic fields are sufficiently strong.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 302; L67-L70
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  • 20
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    The influence of faculae on total solar irradiance and luminosity (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The reported investigation of the facular contribution to the total solar irradiance is based on the data provided by the Active Cavity Radiometer Irradiance Monitor (ACRIM) for 1980-1982, and on the Earth Radiation Budget (ERB) radiometry for 1978-1982. It is found that the solar irradiance records from the ACRIM and the ERB radiometers, after subtraction of the calculated sunspot-blocking contribution, exhibit a short-term modulation which is better explained by faculae than be errors in the sunspot-blocking function. The evidence indicates that faculae produce an important contribution to short-term modulation of the total solar irradiance.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 302; 826-835
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  • 21
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    On magnetic field stochasticity and nonthermal line broadening in solar flares (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Observations of nonthermal line broadening seen in solar flares by the Solar Maximum Mission satellite are discussed in light of recent results on the generation of magnetic field stochasticity. It is shown that a consistent model for the data can be constructed by assuming that the observations signal the destruction of an ambient magnetohydrodynamic equilibrium.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 301; 975-980
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  • 22
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    Two classes of solar energetic particle events associated with impulsive and long-duration soft X-ray flares (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: For the period 1978 September to 1983 December, 67 solar particle events have been identified for which the instruments detected electrons above 3 MeV and for which there are soft X-ray observations. The events are divided into two classes impulsive and long-duration - based on their signature in soft X-rays, and it is found that they have different properties. The events originating with impulsive flares are associated with intensed meter-wavelength type III bursts with associated type V continuum. The events associated with long-duration flares can originate anywhere on the solar disk, extend to much higher proton energies, and are well associated with coronal and interplanetary shocks; for about half of the long-duration events, the associated meter-wavelength events do not include type III bursts. The results discovered by Evenson et al. (1984) and by Kahler et al. (1984) are extended.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 301; 448-459
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  • 23
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    On the behavior of hydromagnetic surface waves (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The behavior of velocity, magnetic field, and pressure perturbations about a continuously varying interface in pressure equilibrium is investigated in detail within ideal incompressible magnetohydrodynamics. A specific initial value problem is solved in quadrature for a thin interface and compared with the solution for a discontinuous interface. The unattenuated surface wave about a discontinuous interface is replaced at a thin interface by a collective surface disturbance which decays, with the associated energy density flowing into local oscillations within the interface. At long times the envelope of the local oscillations is concentrated within a small fraction of the thin interface (gradients within the envelope increase linearly with time, eventually resulting in a breakdown of the linearized ideal theory). Thus, the derived decay rate of the surface disturbance gives a mode-conversion rate rather than a heating rate. In applications to the propagation and dissipation of surface waves in the solar corona, this rate cannot in general be interpreted as a coronal heating rate.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 301; 430-439
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  • 24
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    Solar activity and the coupling of g-mode oscillations (1986)
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    Publication Date: 2019-07-12
    Description: The solar g-mode oscillations depend strongly on the difference between actual and adiabatic temperature gradients in the solar interior. Solar activity anchored at the base of the convection zone disturbs this difference and couples modes with similar eigenfrequencies. This coupling is computed, and the possible observational effects at the photosphere are discussed. These include a scatter in the frequencies deduced for weakly coupled modes and the apparent temporal behavior of strongly coupled modes.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 300; 824-829
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  • 25
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    Two-frequency imaging of microwave impulsive flares near the solar limb (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: VLA observations of two impulsive microwave and hard X-ray flares close to the solar limb on November 21 and 22, 1981 are presently interpreted in terms of an inhomogeneous flare volume, with the magnetic field strength and orientation varying with position both transverse to, and along, the line-of-sight. The 15 GHz radiation of the flares on both days may be due to electrons of E = 300 keV in weak nonthermal tail; the absence of 4.9 GHz radiation from these sources is attributed to absorption along the ray path from the flare to the earth, on the basis of the fact that thermal bremsstrahlung and gyrosynchrotron radiation mechanisms generate more low than high frequency radiation.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 300; 438-441
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  • 26
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    Fast-shock formation in line-tied magnetic reconnection models of solar flares (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: In a previous study by the author, an approximately stationary fast shock was tentatively identified in a numerical experiment designed to study line-tied magnetic reconnection. Here the evidence for the occurrence of a stationary fast shock is reexamined, and the previous identification is confirmed. In the numerical experiment, line-tied reconnection is modeled by a configuration which produces two supermagnetosonic outflow jets - one directed upward, away from the photosphere, and one directed downward, toward an arcade of closed magnetic loops tied to the photosphere. The fast shock occurs when the downward-directed jet encounters the obstacle formed by the closed loops. Although the existence of a stationary, or nearly stationary, fast shock is confirmed, the transition from the supermagnetosonic flow region upstream of the shock to the nearly static region downstream of the shock is more complicated than was previously thought. Immediately downstream of the shock, there exists a deflection sheath in which the submagnetosonic flow coming out of the shock is diverted around the region of static closed loops. The MHD jump conditions are used to investigate the characteristics of the fast shock and to show that a stationary shock cannot exist unless accompanied by a deflection sheath. Analysis of the shock's location and dimensions suggests that such fast shocks may contribute to particle acceleration and to thermal condensation in flares.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 305; 553-563
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  • 27
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    A mechanism for deep chromospheric heating during solar flares (1986)
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    Publication Date: 2019-07-12
    Description: The role of the negative hydrogen ion, H(-), in the energy balance of the deep solar chromosphere is reexamined and it is found, in contrast with earlier authors, that H(-) is a source of heating at these levels. The response of this region to an ionizing flux of flare-associated UV radiation (1500 to 1900 A) is then addressed: it is found that the excess ionization of Si to Si(+) increases the local electron number density considerably, since most species are largely neutral at deep chromospheric levels. This in turn increases the electron-hydrogen atom association rate, the H(-) abundance, and the rate of absorption of photospheric radiation by this ion. It is found that the excess absorption by this process may lead to a substantial temperature enhancement at temperature minimum levels during flares.
    Keywords: SOLAR PHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 159; 1-2
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    A two-fluid solar wind model with Alfven waves - Parameter study and application to observations (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The effects of Alfven waves from the inner corona on the solar wind density profile, flow velocity and on the random motion of protons are studied. Different base densities, temperatures, and wave velocity amplitudes, as well as different flow geometries, are considered. The model calculations are compared to simultaneous observations of the electron density profile and the resonantly scattered Lyman alpha line. Present observations, out to 4 solar radii, can be used to place limits on the coronal base density and temperature, and put an upper limit on the wave amplitude. It is pointed out that future observations of the electron density and the Lyman alpha line, out to larger heliocentric distances, and of lines from heavier elements, should be used to place more stringent constraints on the amplitudes of MHD waves in the corona.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 2950-296
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  • 29
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    The dynamics of magnetically trapped fluids. I - Implications for umbral dots and penumbral grains (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A study of the magnetohydrodynamic system in which a nonmagnetized fluid in a gravitational field is surrounded by a fluid carrying a vertical magnetic field is presented. It is pointed out that this study can throw some light on the fine-structural features of a sunspot. The equilibrium configuration of the field-free fluid is a tapering column ending at an apex. The regions away form the apex can be studied by the slender flux tube approximation. A scheme developed to treat the apex indicates that, just below the apex, the radius of the tapering column opens up with a 3/2 power dependence on the depth below the apex. If the internal pressure of the field-free fluid is increased, the apex rises, and a static equilibrium may not be possible beyond a limit if the magnetic pressure drops quickly above a certain height. The nature of steady-flow solutions beyond this limit is investigated. Under conditions inside a sunspot, a column of field-free gas is found to rise with a velocity of about 100 km/hr. If umbral dots and penumbral grains are interpreted as regions where the field-free gas ultimately emerges, a very natural explanation of most of their observed properties is obtained.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 302; 809-825
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  • 30
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    Electron density diagnostics in the 10-100 A interval for a solar flare (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Electron density measurements from spectral-line diagnostics are reported for a solar flare on July 13, 1982, 1627 UT. The spectrogram, covering the 10-95 A interval, contained usable lines of helium-like ions C V, N VI, O VII, and Ne IX which are formed over the temperature interval 0.7-3.5 x 10 to the 6th K. In addition, spectral-line ratios of Si IX, Fe XIV, and Ca XV were compared with new theoretical estimates of their electron density sensitivity to obtain additional electron density diagnostics. An electron density of 3 x 10 to the 10th/cu cm was obtained. The comparison of these results from helium-like and other ions gives confidence in the utility of these tools for solar coronal analysis and will lead to a fuller understanding of the phenomena observed in this flare.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 301; 981-988
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  • 31
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    Viscous normal modes on coronal inhomogeneities and their role as a heating mechanism (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Viscous damping of Alfven surface waves is examined both analytically and numerically using incompressible MHD. Normal modes are shown to exist on discontinuous as well as continuously varying interfaces in Alfven speed. The waves experience negligible decay below the transition zone. High-frequency waves damp just above the transition region, while those of lower frequency lose energy further out. A comparison of dissipative decay rates shows that wave damping by viscosity proceeds approximately two orders of magnitude faster than by resistivity.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 304; 526-531
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  • 32
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    Fourier transform spectrometer observations of solar carbon monoxide. II - Simultaneous cospatial measurements of the fundamental and first-overtone bands, and Ca II K, in quiet and active regions (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Fourier transform spectrometry has yielded simultaneous cospatial measurements of important diagnostics of thermal structure in the high solar photosphere and low chromosphere. It is noted that the anomalous behavior of the fundamental bands of CO in quiet areas near the limb is accentuated in an active region plage observed close to the limb. The difference between the core temperatures of the CO fundamental bands in a plage and a nearby quiet region at the limb is larger than the corresponding brightness temperature differences in the inner wings of the Ca II line measured in a quiet region and several plages closer to the disk center. Numerical simulations indicate that the disparate behavior of the CO bands with respect to Ca II K cannot be reconciled with existing single component thermal structure models; a two-component atmosphere is required.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 304; 542-559
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  • 33
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    Energetics of the gradual phase of solar flares (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The Solar Maximum Mission (SMM) has operated since 1980 with a package of instruments that cover the solar spectrum from optical to gamma-ray wavelengths. While these instruments were not specifically designed to gather data on flare energetics, the SMM can measure many of the terms in the energy budget of a flare that have not been possible to determine in the past, especially when SMM data are combined with complementary data from other spacecraft and ground-based observatories, as was done as part of the SMY. During the recent SMM workshops on solar flares, the energetics of the gradual phase of several well-observed flares were investigated. The results of these studies are reviewed in this presentation. The advances that have resulted from the SMM flare energetics studies are discussed in context of what still must be done observationally and theoretically to define the complete energy budget of a flare.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 6 19; 257-266
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  • 34
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    Do we understand coronal mass ejections yet? (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Though many more coronal mass ejections (CMEs) were observed, and though much more has been learned about them during the Solar Maximum Analysis period, they are not yet fully understood. A few recent observational results are reviewed; conclusions and implications drawn from these observations are presented. An emerging picture of the magnetic character of CMEs is sketched; the variations of CMEs' frequency and latitudes over most of a solar cycle are shown. A strong caution about the present lack of concensus on the definition of CMEs is illustrated with examples of the consequences of using different definitions. Finally, some remaining questions about coronal mass ejections are posed.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 6 19
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  • 35
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    Classification of solar flares and the relationship between the first and second phases (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A large data base on solar flares obtained during the last solar maximum years makes it necessary to revise the views on the relationship between the impulsive phase and the second phase of flares. Contrary to the view most popular before the launch of the Solar Maximum Mission, it is now known that relativistic electrons and gamma-ray-producing protons and ions are accelerated during the impulsive phase. Because flares producing nuclear gamma-rays are different from ordinary flares, it is concluded that additional processes take place in gamma-ray-line flares. Recent studies have shown that flares with gradual hard X-ray time profiles not only produce nuclear gamma-rays during the impulsive phase but also develop full-fledged second-phase phenomena. It is proposed that filament eruption plays a key role in gamma-ray-line flares. When an erupting filament interacts with an overlaying flare loop, relativistic electrons and energetic protons are produced during the impulsive phase. When the erupting filament fully distends the overlying flare loop, full-fledged second-phase phenomena, such as shocks, interplanetary energetic particles, mass ejections and etc. are observed. When the overlying flare loop is compact and strong enough to suppress the activated filament, gamma-rays are emitted during the first phase but no second-phase phenomena occur.
    Keywords: SOLAR PHYSICS
    Type: AD-A184300 , Advances in Space Research (ISSN 0273-1177); 6; 6 19
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  • 36
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    Solar gradual hard X-ray bursts - Observations and an interpretation (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A recent study of solar gradual hard X-ray bursts is summarized. The data are interpreted in terms of a model involving the acceleration and trapping of electrons in post flare loop systems following coronal mass ejections. A controversy about the classification of the metric continuum that typically accompanies gradual hard X-ray events is addressed.
    Keywords: SOLAR PHYSICS
    Type: AD-A186861 , AFGL-TR-87-0293 , Advances in Space Research (ISSN 0273-1177); 6; 6 19
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  • 37
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    The over-the-limb hard X-ray events (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Over-the-limb hard X-ray events offer a uniquely direct view of the hard X-ray emission from the solar corona during a major flare. Limb occultation at angles greater than about 10 deg (an arbitrary definition of this class of events) excludes any confusion with brighter chromospheric sources. Published observations of seven over-the-limb events, beginning with the prototype flare of March 30, 1969, are reviewed. The hard X-ray spectra appear to fall into two classes: hard events, with power-law index of about 2.0; and soft events, with power-law index about 5.4. This tendency towards bimodality is only significant at the 90-percent confidence level due to the smallness of the number of events observed to date. If borne out by future data, the bimodality would suggest the existence of two different acceleration mechanisms.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 6 19
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  • 38
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    The interaction of solar p-modes with a sunspot. I - Observations (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Time series of velocity maps of two isolated sunspots and their surroundings were recorded in the Fe I line and the umbral line Ti I. Both 3 and 5 min umbral oscillations were detected at photospheric heights. The 5 min oscillations have reduced amplitude in the umbra, which appears to act as a filter in transmitting selected frequencies in the power spectrum of 5 min p-mode oscillations of the surrounding convection zone. The k-omicron power spectrum of the umbral oscillations shows this selective transmission and also shows a shift of power to longer horizontal wavelengths. This behavior is exhibited by a simple theoretical model of the interaction of p-modes with a sunspot. The 3 min umbral oscillations are concentrated in the dark central part of the umbra. In both sunspots, the kinetic energy density of the 3 min umbral oscillation in the photosphere is much greater than the corresponding kinetic energy density at chromospheric heights measured in other sunspots.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 311; 1015-102
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  • 39
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    Observations concerning the generation and propagation of Type III solar bursts (1986)
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    Publication Date: 2019-07-12
    Description: A number of Type III bursts were observed during the Helios missions in which the burst exciter passed over the spacecraft, as evidenced by strong electric field fluctuations near the plasma frequency. Six of these were suitable for detailed study. Of the six events, one was ambiguous, one showed what is interpreted as a switchover from harmonic to fundamental, and the rest all generated fundamental at onset. This would be expected if both fundamental and harmonic are generated, as, at a fixed frequency, the fundamental will be generated earlier. For the event which seems to show both fundamental and harmonic emission, the frequency ratio is not exactly 2. This is explained in terms of a time delay of the fundamental, due to scattering and diffusion in the source region. A time delay of the order of 600 seconds at 1 AU and 20 kHz, and inversely proportional to frequency, is required to explain the observations. Crude estimates show that delay times at least this long may be attributed to trapping and scattering.
    Keywords: SOLAR PHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 169; 1-2
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  • 40
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    A method for determining corotating interaction regions in the equatorial plane of the heliosphere from solar wind velocity data (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 13689-13
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  • 41
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    Heliospheric current sheet and its solar cycle variations (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The three-dimensional structure of the heliospheric current sheet is constructed for Carrington rotations 1647, 1654, 1661, 1667, 1693, 1699, and 1719. These rotations are chosen from different epochs during the sunspot cycle 21, so that geometrical changes of the current sheet during a sunspot cycle can be inferred. Only for relatively simple neutral lines on the source surface, do the structures of the current sheet approximate those envisaged by Svalgaard and Wilcox (1976) and Thomas and Smith (1981).
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 13679-13
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  • 42
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    The coalescence of two merged interaction regions between 6.2 and 9.5 AU - September 1979 event (1986)
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    Publication Date: 2019-07-12
    Description: A simulation study, based on an unsteady, one-dimensional, one-fluid MHD model, and using the plasma and magnetic field data from the Voyager 1 at 6.2 AU, was conducted on the evolution and interaction of solar wind structures to explain the two interaction regions observed by Voyager 1 within a large-scale interplanetary compound stream that was recorded at a heliocentric distance of 6.2 AU. A strong forward shock F(D) with a speed of 960 km/s was present at the front of the second interaction region, and two reverse shocks, R1 and R2, were at the end of the first interaction region. The model shows that the forward shock passed through the two reverse shocks and into the first interaction region, becoming weaker in each of these interactions. The reverse shocks coalesced to form a stronger reverse shock R; thus, the shock signature changed from R1-R2-F(D) to F(D)-R between 6.2 and 9.5 AU. The major stream structures at 9.5 AU predicted by the simulation model agree well with those directly observed from Pioneer 11.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 13341-13
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  • 43
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    Interplanetary shocks preceded by solar filament eruptions (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The solar and interplanetary characteristics of six interplanetary shock and energetic particle events associated with the eruptions of solar filaments lying outside active regions are discussed. The events are characterized by the familiar double-ribbon H-alpha brightenings observed with large flares, but only very weak soft X-ray and microwave bursts. Both impulsive phases and metric type II bursts are absent in all six events. The energetic particles observed near the earth appear to be accelerated predominantly in the interplanetary shocks. The interplanetary shock speeds are lower and the longitudinal extents considerably less than those of flare-associated shocks. Three of the events were associated with unusual enhancements of singly-ionized helium in the solar wind following the shocks. These enhancements appear to be direct detections of the cool filament material expelled from the corona. It is suggested that these events are part of a spectrum of solar eruptive events which include both weaker events and the large flares. Despite their unimpressive and unreported solar signatures, the quiescent filament eruptions can result in substantial space and geophysical disturbances.
    Keywords: SOLAR PHYSICS
    Type: AD-A188238 , AFGL-TR-87-0312 , Journal of Geophysical Research (ISSN 0148-0227); 91; 13321-13
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  • 44
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    Solar chromospheric modeling based on submillimeter limb brightness profile (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A method of modeling the solar chromosphere is developed, based on submillimeter continuum observations of the solar limb. Submillimeter radiation from the solar limb emanates from the chromosphere in local thermodynamic equilibrium, making it an important chromospheric diagnostic. Also, the use of high-resolution limb profiles allows for atmospheric modeling independent of gravitational hydrostatic equilibrium. The chromospheric model is constructed to match high-resolution solar limb profiles at 30, 50, 100, and 200 microns, determined by an occultation of the solar limb observed from the Kuiper Airborne Observatory during the total solar eclipse of July 31, 1981. This matching is achieved by 'stretching' the solar model atmosphere of Vernazza, Avrett, and Loesser (1981) vertically out of hydrostatic equilibrium, while maintainingn its vertical temperature-optical depth profile.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 310; 907-911
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  • 45
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    Extreme limb profiles of the sun at far-infrared and submillimeter wavelengths (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Thirty, 50, 100, and 200 microns solar limb intensity profiles determined with arcsecond resolution from airborne observations of the occultation of the solar limb during the total eclipse of July 31, 1981, are presented. Two points of particular importance emerge: (1) the longer-wavelength (100 and 200 micron) limbs are significantly brighter than disk center. At 200 microns the extreme limb is about 1.22 times the brightness of disk center. This is consistent with the 6000 K temperature-plateau structure of the model chromospheres of Vernazza, Avrett, and Loeser (1973, Ap. J., 184, 605; 1981; Ap. J. Suppl., 45, 635); and (2) the longer wavelength limbs are extended significantly further above the visible limb than Vernazza, Avrett, and Loeser predict. These results provide a strong basis for modeling of the solar chromosphere free from the assumption of gravitational-hydrostatic equilibrium.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 308; 448-458
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  • 46
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    Interaction of the solar wind with interstellar neutral hydrogen - Three-fluid model (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: It is commonly assumed in models of the solar wind-interstellar neutral hydrogen interaction that the ionized interstellar particles are quickly assimilated into the solar wind proton population and 'become indistinguishable' from the original solar wind. This assumption leads to the prediction that the solar wind proton temperature should increase with radius in the outer heliosphere. This temperature increase has not been observed. It is pointed out that assimilation of the interstellar particles to the point of indistinguishability takes place on the very long Coulomb collision time scale, and is not expected to occur within the heliosphere. Results are presented of a three-fluid model of the solar wind which consists of comoving thermal populations of protons of solar origin, protons produced by ionization of interstellar hydrogen, and electrons. The steady-state results yield a solar wind with a 'core' proton distribution which cools adiabatically, and a 'halo' of interstellar pickup protons which is maintained near 10 to the 7th K by the energy input of continued ionization and pickup. Such a distribution will not be observed to manifest the temperature increase at large heliocentric distances which is predicted from a one-fluid analysis. Further time-dependent calculations show a strong correlation between the densities of the solar wind and the interstellar pickup protons. It is suggested that the interstellar pickup population may be observable by the Voyager plasma instruments in low resolution mode during periods of high solar wind density and low solar wind temperature.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 9965-997
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  • 47
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    Sensitivity of the curve-to-growth technique utilized in rocket experiments to determine the line shape of solar He I resonance lines (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The sensitivity of the curve-of-growth (COG) technique utilized in rocket measurements to determine the line profiles of the solar He I resonance emissions is theoretically examined with attention to the possibility of determining the line core shape using this technique. The line at 584.334 A is chosen as an illustration. Various possible source functions of the solar line have been assumed in the computation of the integrated transmitted intensity. A recent observational data set obtained by the present researchers is used as the constraint of the computation. It is confirmed that the COG technique can indeed provide a good measurement of the solar line width. However, to obtain detailed knowledge of the solar profile at line center and in the core region, (1) it is necessary to be able to carry out relative solar flux measurements with a 1-percent or better precision, and (2) it must be possible to measure the He gas pressure in the absorption cell to lower than 0.1 mtorr. While these numbers apply specifically to the present geometry, the results are readily scaled to other COG measurements using other experimental parameters.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 9957-996
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  • 48
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    The electron-cyclotron maser instability as a source of plasma radiation (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The generation of continuum bursts from the sun at dm and m wavelengths (in particular, type IV bursts) via the electron-cyclotron-maser instability is examined. The maser instability can be driven by an electron distribution with either a loss-cone anisotropy or a peak at large pitch angles. For omega(p)/Omega(e) much greater than 1, the maser emission is produced by electrons interacting through a harmonic (cyclotron) resonance and is electrostatic, being in the upper hybrid mode at frequencies approximately equal to omega(p). Coalescence processes are required to convert the electrostatic waves into transverse radiation which can escape from the source region. Whether the resultant spectrum is nearly a smooth continuum or has a zebra-stripe pattern (both of which occur in type IV bursts) depends on the form of the electron distribution, inhomogeneities in the density and magnetic field, and whether the maser reaches saturation. For at least the case of some type IV dm bursts with fine structure, comparison with observations seems to indicate that the electrons producing the emission are more likely to have a loss-cone distribution, and that the maser instability is not at saturation.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 307; 808-819
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  • 49
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    Viscosity and the Chew-Goldberger-Low equations in the solar corona (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A general discussion of the dominant terms in the stress tensor in a magnetized plasma such as the solar corona is presented. The importance of dissipative terms such as electrical resistivity, heat conduction, and interspecies collisions is assessed. For average coronal conditions, the proton stress tensor is found to reduce to the dominant terms in the classical expression for the viscous stress. The classical expression can fail in the transition region, however. In the diffusion region of reconnection, classical viscosity will be appropriate if the resistivity is very large, so that the diffusion region is broad, but in that case the viscous heating is small compared to the resistive heating. On the other hand, the more general expression for the stress tensor is required if the diffusion region is thin; the stress tensor will be important in this case. The electron stress tensor is also considered, and it is shown how the classical expression for electron viscosity can fail in the transition region and lower corona.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 306; 730-739
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  • 50
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    Flare stars and solar bursts - High resolution in time and frequency (1986)
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    Publication Date: 2019-07-12
    Description: Coronal loops on the sun and nearby stars are studied using observations at 20-cm wavelength with high resolution in time and frequency. Observations of the dwarf M star AD Leonis with high time resolution led to the discovery of a quasi-periodic train of circularly polarized spikes with a mean periodicity of 32 + or - 5 ms and a total duration of 150 ms. Observations at closely spaced wavelengths using the VLA revealed a narrow-band structure in solar bursts and in the slowly varying radiation of the dwarf M star YZ Canis Minoris. This narrow-band emission may be attributed to electron-cyclotron maser radiation. Maser action at the second or first harmonic of the gyrofrequency implies magnetic field strengths of 250 and 500 G, respectively. Hence, observations with high resolution in time and frequency suggest coherent processs in the coronas of the sun and dwarf M stars. It is noted that the scientific potential suggested by the present data can be realized by the development of a solar-stellar synthesis radiotelescope. This instrument would be dedicated to solar and stellar observations with high angular, temporal, and frequency resolution.
    Keywords: SOLAR PHYSICS
    Type: AD-A171982 , Solar Physics (ISSN 0038-0938); 104; 227-233
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  • 51
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    Electron-cyclotron maser emission from the sun and stars Variations with plasma temperature and density (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Very bright and highly circularly polarized radio bursts from the sun, the planets, flare stars, and close binary stars are attributed to the electron-cyclotron maser instability. The mode and frequency of the dominant radiation from the maser instability is shown to be dependent on the plasma temperature and the ratio omega(p)/Omega(e) of the plasma frequency to the electron-frequency. For the emission from the sun omega(p)/Omega(e) is probably greater than 0.3 and for omega(p)/Omega(e) greater than 0.3 and less than the square root of 2, the emission can be either in the x-mode at the second harmonic or in the 0- and/or z-modes at the fundamental. For higher omega(p)/Omega(e), the emission moves to higher harmonics of Omega(e) with the emission being predominately in the z-mode when omega(p)/Omega(e) is greater than about the square root of 3.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 104; 93-97
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  • 52
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    Temperature diagnostic line ratios of Fe XVII (1986)
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    Publication Date: 2019-07-12
    Description: Based on extensive calculations of the excitation rates of Fe XVII, four temperature-sensitive line ratios are investigated, paying special attention to the contribution of resonances to the excitation rates and to the contributions of dielectronic recombination satellites to the observed line intensities. The predictions are compared to FPCS observations of Puppis A and to Solar Maximum Mission (SMM) and SOLEX observations of the sun. Temperature-sensitive line ratios are also computed for emitting gas covering a broad temperature range. It is found that each ratio yields a differently weighted average for the temperature and that this accounts for some apparent discrepancies between the theoretical ratios and solar observations. The effects of this weighting on the Fe XVII temperature diagnostics and on the analogous Fe XXIV/Fe XXV satellite line temperature diagnostics are discussed.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 306; 762-766
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  • 53
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    Decimeter continuum radio emission from a post-flare loop (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: It is shown how radio observations permitted the estimation of magnetic fields in the postflare loop associated with the May 19, 1979 long-lasting burst. The strongest 20-cm burst source is associated with H-alpha brightening at 20:41 UT. A comparison of spatially-resolved microwave and soft X-ray emission connected with the flare loop event showed that, at the time of maximum 20-cm flux from the source associated spatially with the declining X-ray flare, as much as one-half of the 20-cm flux could be thermal bremsstrahlung from the X-ray postflare groups. It is suggested that this 20-cm burst emission is produced either by a thermal free-free process or by thermal/nonthermal gyroradiation.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 104; 223-226
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  • 54
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    Relative timing of hard X-rays and radio emissions during the different phases of solar flares - Consequences for the electron acceleration (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 104; 145-163
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  • 55
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    The decay of the mean solar magnetic field (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The effects that differential rotation and a hypothetical meridional flow would have on the evolution of the sun's mean line-of-sight magnetic field as seen from earth have been analyzed. By winding the large-scale field into strips of alternating positive and negative polarity, differential rotation causes the mean-field amplitude to decay and the mean-field rotation period to acquire the value corresponding to the latitude of the surviving unwound magnetic flux. For a latitudinally broad two-sector initial field such as a horizontal dipole, the decay is rapid for about 5 rotations, and slow with a t exp-1/2 dependence thereafter. If a poleward meridional flow is present, it will accelerate the decay by carrying the residual flux to high latitudes where the line-of-sight components are small. The resulting decay is exponential with an e-folding time of 0.75 yr (10 rotations) for an assumed 15 m/s peak meridional flow speed.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 103; 2 19; 203-224
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  • 56
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    The solar flare extreme ultraviolet to hard X-ray ratio (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Simultaneous measurements of the peak 10-1030 A extreme ultraviolet (EUV) flux enhancement and more than 10 keV hard X-ray (HXR) peak flux of many solar flare bursts, ranging over about four orders of magnitude in HXR intensity, are studied. A real departure from linearity is found in the relationship between the peak EUV and HXR fluxes in impulsive flare bursts. This relationship is well described by a given power law. Comparison of the predictions of the impulsive nonthermal thick-target electron beam model with observations shows that the model satisfactorily predicts the observed time differences between the HXR and EUV peaks and explains the data very well under given specific assumptions. It is concluded that the high-energy fluxes implied by the invariant area thick-target model cannot be completely ruled out, while the invariant area model with smaller low cutoff requires impossibly large beam densities. A later alternative thick-target model is suggested.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 305; 936-946
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  • 57
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    Solar gradual hard X-ray bursts and associated phenomena (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: White-light coronagraph, H-alpha and radio data are presented as well as hard X-ray data for a sample of 10 gradual hard X-ray bursts (GHBs) in an attempt to better understand the nature of these events. It is found that: (1) the hard X-ray photon energy spectrum began to harden near the onset of the GHBs and continued in this fashion during the decay phase; (2) a coronal mass ejection (CME) occurred in association with at least nine of the GHBs; (3) the GHBs occurred in the late phase of major flares; (4) the centimeter wavelength bursts associated with the GHBs had relatively low frequency spectral maxima, and in relation to the observed hard X-ray emission, they were microwave-rich; (5) the associated decimetric bursts showed significant intensity variations on time scales ranging from 0.1 to approximately greater than 1 minute; and (6) the GHBs were most strongly associated with type IV events. It is concluded that the acceleration and trapping of radiating electrons occurs in the postflare loop systems following CMEs.
    Keywords: SOLAR PHYSICS
    Type: AD-A173330 , AFGL-TR-86-0215 , Astrophysical Journal, Part 1 (ISSN 0004-637X); 305; 920-935
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  • 58
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    A spatially confined long-lived stream of solar particles (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The intensities of low-energy solar-interplanetary electrons and ions at 1 AU occasionally change in a 'square-wave' fashion. The changes may be increases or decreases and they have duration of a few hours. In one such example following a solar flare, particles flow away from the sun in a well-defined channel 2.5 x 10 to the 6th km in width for twenty hours or longer. It is believed that the interplanetary magnetic lines defined by this channel connect to an active region at 16 deg N solar latitude. At this time the earth was located at a solar latitude of 2 deg S. Evidently the particle channel connects to a region of the solar atmosphere which supplies particles over these long times either via storage of the flare accelerated particles or else by continuous acceleration. Arguments are given against the latter possibility. A model for coronal storage which is consistent with the observations is discussed.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 103; 165-175
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  • 59
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    A study of hard X-ray associated meter-decameter bursts observed on December 19, 1979 (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The results of a study of the relationship of a complex meter-decameter wavelength radio burst observed with the Clark Lake E-W and N-S interferometers, with a hard X-ray burst observed with the X-ray spectrometer aboard ISEE-3 are presented. The radio burst consisted of several type III's, reverse drift type III's, a U burst, and type II and type IV bursts. The X-ray emission was also complex. The radio as well as hard X-ray emissions were observed before the flash phase of the flare; they were not always associated and it is conjectured that this may constitute evidence for acceleration of electrons high in the corona. On the other hand, all components of the reverse drift burst were associated with hard X-ray subpeaks, indicating multiple injection of electron beams along field lines with different density gradients. While the type II burst appeared to be related to the hard X-ray burst, a detailed correspondence between individual features of the radio and hard X-ray burst emissions could not be found. The type IV burst started after all hard X-ray emissions ceased. Its source appeared to be a magnetic arch, presumably containing energetic electrons reponsible for the gyrosynchrotron radiation of type IV.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 103; 153-164
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  • 60
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    Delta-configurations - Flare activity and magnetic-field structure (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Complex sunspots in four active regions of April and May 1980, all exhibiting regions of magnetic classification delta, were studied using data from the NASA Marshall Space Flight Center vector magnetograph. The vector magnetic field structure in the vicinity of each delta was determined, and the location of the deltas in each active region was correlated with the locations and types of flare activity for the regions. Two types of delta-configuration were found to exist, active and inactive, as defined by the relationships between magnetic field structure and activity. The active delta exhibited high flare activity, strong horizontal gradients of the longitudinal (line-of-sight) magnetic field component, a strong transverse (perpendicular to line-of-sight) component, and a highly nonpotential orientation of the photospheric magnetic field, all indications of a highly sheared magnetic field. The inactive delta, on the other hand, exhibited little or no flare production, weaker horizontal gradients of the longitudinal component, weaker transverse components, and a nearly potential, nonsheared orientation of the magnetic field. It is concluded that the presence of such sheared fields is the primary signature by which the active delta may be distinguished, and that it is this shear which produces the flare activity of the active delta.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 103; 111-128
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  • 61
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    The structure of high-temperature flare plasma. II Comparison with observations (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: In Emslie, (1985) scaling law's which relate peak loop temperature to injected nonthermal electron flux in electron-heated models of the flare corona are derived. These predicted relationships are compared with recent coordinated observations in hard X-rays and soft X-rays. Satisfactory agreement is found for large events, while for smaller events the plasma electron temperature determined by soft X-ray spectral fitting is too high. A possible resolution of this apparent discrepancy through careful examination of the method used to determine the temperature of the soft X-ray emitting plasma is discussed. It is concluded that temperatures determined by spectral fitting over a series of lines are not necessarily representative of the true temperature of the plasma, since the fitting technique is plagued by the same difficulties as a more straightforward technique involving a single spectral line or portion of continuum (Craig and Brown, 1976). The differences between actual and derived temperatures are sufficiently large to remove the above discrepancy between observations and modeling of electron-heated coronae.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 103; 103-110
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  • 62
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    The excitation of the iron K-alpha feature in solar flares (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The relationship between the hard X-ray photon spectrum and the flux of iron K-alpha emission in a thick-target electron bombardment model is evaluated. Results are presented for various power-law hard X-ray spectra. These results are applied to two events observed with the Hard X-Ray Burst Spectrometer and the K-alpha channel of the X-Ray Polychromator Bent Crystal Spectrometer on the Solar Maximum Mission satellite. For one of the events, on March 29, 1980, at 09:18 UT, the K-alpha flux predicted for a thick-target nonthermal process is significant compared to the background fluorescent component, and the data are indeed consistent with an enhancement of the predicted amount. For the other event, on October 14, 1980 at 0.6:09 UT, the hard X-ray spectrum is so steep that no significant K-alpha flux is predicted for this process, and no enhancement is seen. It is concluded that the agreement between the predicted K-alpha flux and the observed magnitude of the K-alpha enhancement above the fluorescent background at the time of the large hard X-ray bursts lends support to a thick-target nonthermal interpretation of impulsive hard X-ray emission in solar flares.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 103; 89-102
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  • 63
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    Solar irradiance variations from photometry of active regions (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The Extreme Limb Photometer (ELP) has been used to measure the irradiance fluctuation of the sun due to selected active regions. Forty-five active regions that were completely scanned at various disk positions are included in the analysis. The contribution of these active regions to a global solar irradiance fluctuation has been correlated with photometric sunspot and facular indices (PSI and PFI) using published values of sunspot and calcium plage areas. The measured ELP fluctuations are converted to a global brightness fluctuation, Delta B/B. The sunspot component of Delta B/B correlates with PSI with r = 0.95. The facular component of Delta B/B correlates with PFI with r = 0.72. The expression for PFI is important to the question of energy balance between sunspots and faculae and the results presented here are not incompatible with energy balance between the two phenomena; that is the energy deficit of sunspots may be balanced by the energy excess of faculae.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 103; 21-31
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  • 64
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    Latitude and depth variation of solar rotation (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: New measurements of frequencies of various modes of acoustic waves trapped within the sun are reported for degrees up to 98 which allow the convective envelope to be isolated. For degrees between 20 anad 98, no evidence is found that internal rotation differs significantly with depth or latitude from the rotation of surface magnetic field patterns. Modes covering a wide latitude range have systematically lower frequencies than those confined near the equator, indicating the existence of a structural asymmetry within the sun.
    Keywords: SOLAR PHYSICS
    Type: Nature (ISSN 0028-0836); 321; 500
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  • 65
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    Absolute solar flux measurement shortward of 575 A (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A rare-gas ionization chamber was used to obtain an accurate measurement of the absolute solar EUV flux in the 50- to 575-A region. The instrument, operating in total and near-total absorption, was flown on a solar-pointing sounding rocket on August 16, 1983. For the day of the flight, the solar activity indices were F sub 10.7 = 132.1 and R sub I = 80, and the integrated solar irradiance at the earth, corrected for atmospheric absorption, was found to be 4.31 + or - 0.31 x 10 to the 10th photons sq cm s. Almost exactly a year earlier (August 10, 1982) the same instrument measured an integrated solar flux of 5.71 + or - 0.42 x 10 to the 10th photons/sq cm s during a time of enhanced solar activity (F sub 10.7 = 209.5 and R sub I = 155).
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 7089-709
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  • 66
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    White-light movies of the solar photosphere from the SOUP instrument on Spacelab (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Initial results are presented on solar granulation, pores and sunspots from the white-light films obtained by the Solar Optical Universal Polarimeter (SOUP) instrument in Spacelab 2. Several hours of movies were taken at various disk and limb positions in quiet and active regions. The images are diffraction-limited at 0.5 arcsec resolution and are, of course, free of atmospheric seeing and distortion. Properties of the granulation in magnetic and nonmagnetic regions are compared and are found to differ significantly in size, rate of intensity variation, and lifetime. In quiet sun, on the order of fifty-percent of the area has at least one 'exploding granule' occurring in it during a 25-min period. Local correlation tracking has detected several types of transverse flows, including systematic outflow from the penumbral boundary of a spot, motion of penumbral filaments, and cellular flow patterns of supergranular and mesogranular size. Feature tracking has shown that, in the quiet sun, the average granule fragment has a velocity of about one kilometer/second.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 8 19
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  • 67
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    Energy balance in solar active regions - The dip of April, 1985 (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The presence of a solar active region affects the luminosity of the sun. Sunspots directly produce 'dips' in the total solar irradiance approximately proportionally to their projected area, while faculae produce excess energy. These effects were discovered during the solar maximum period of 1980, and the sunspot effect during solar minimum is examined. The 'dip' due to an active region in April, 1985, as observed in the total solar irradiance by the ACRIM instrument on the Solar Maximum Mission is examined. These data (obtained after the spacecraft repair in May, 1984) have simple variations, relative to those observed in 1980, because of the reduced level of activity approaching solar minimum. It is found that the PSI index of projected sunspot area as defined in 1980 appears to describe this 'dip' satisfactorily.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 8 19
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  • 68
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    The relationship of shock-associated kilometric radio emission with metric type II bursts and energetic particles (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Shock-associated (SA) events from 1978 to 1982 are compared with metric type II bursts and solar energetic particle (SEP) events. Most metric type II bursts are not obviously associated with SA events at 1980 kHz. Metric type II bursts associated with magnetically well connected flares and SA emission are well correlated with SEP events; those without SA emission are poorly correlated with SEP events. The largest SEP events from flares at any longitude are well correlated with SAs. These results are consistent with the hypothesis that the escaping electrons giving rise to SA emission are accelerated in coronal shocks.
    Keywords: SOLAR PHYSICS
    Type: AD-A187791 , AFGL-TR-87-0310 , Advances in Space Research (ISSN 0273-1177); 6; 6 19
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  • 69
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    A dynamic flare with anomalously dense flare loops (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The dynamic flare of November 6, 1980 developed a rich system of growing loops which could be followed in H-alpha for 1.5 hours. Throughout the flare, these loops, near the limb, were seen in emission against the disk. Theoretical computations of b-values for a hydrogen atom reveal that this requires electron densities in the loops to be close to 10 to the 12th per cu cm. From measured widths of higher Balmer lines the density at the tops of the loops was found to be 4 x 10 to the 12th per cu cm if no nonthermal motions were present. It is now general knowledge that flare loops are initially observed in X-rays and become visible in H-alpha only after cooling. For such a high density a loop would cool through radiation from 10 to the 7th K to 10 to the 4th K within a few minutes so that the dense H-alpha loops should have heights very close to the heights of the X-ray loops. This, however, contradicts the observations obtained by the HXIS and FCS instruments on board SMM which show the X-ray loops at much higher altitudes than the loops in H-alpha. Therefore, the density must have been significantly smaller when the loops were formed and the flare loops were apparently both shrinking and becoming denser while cooling.
    Keywords: SOLAR PHYSICS
    Type: AD-A193926 , AFGL-TR-88-0077 , Advances in Space Research (ISSN 0273-1177); 6; 6 19; 253-256
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    Evidence against chromospheric evaporation from the 21 May 1980 flare (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Antonucci et al. (1985) have presented observations of the large two-ribbon flare of May 21, 1980 and interpreted the Ca XIX X-ray line profiles, hard X-ray observations, and X-ray images to support the standard model of electron-beam-driven chromospheric evaporation. Here it is shown that an active filament which erupted at flare onset can also explain the observations, and that a closer look at the evidence of Antonucci et al. leads to discrepancies with the chromospheric evaporation model.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 6 19
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  • 71
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    The evolution of the spatial structure of thick-target hard X-ray emission in solar flares (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The spatial distribution of hard X-ray bremsstrahlung emission from an electron-heated target is examined, using a self-consistent calculation of the hydrodynamic response of the atmosphere to heating by the electrons to compute the density-height structure of the target atmosphere at various times. In this way the temporal evolution of the hard X-ray spatial structure at various photon energies is predicted. These results are compared with existing observations from the SMM Hard X-Ray Imaging Spectrometer to give a prognosis for the type of structure to be expected at the subarcsec resolution planned for future instrumentation.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 6 19
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  • 72
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    Evidence for solar flare directivity from the Gamma-Ray Spectrometer aboard the SMM satellite (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A number of observations from the SMM Gamma-Ray Spectrometer are presented that altogether strongly indicate that the high-energy emission from flares is anisotropic. They are: (1) the fraction of events detected at energies above 300 keV near the limb is significantly higher than is expected for isotropically emitting flares; (2) there is a statistically significant center-to-limb variation in the 300-1000-keV spectra of flares; and (3) nearly all of the events detected at above 10 MeV are located near the limb.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 6 19; 123-126
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    A high spatial resolution study of microwave flare precursors (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Several examples of preflare changes are provided from VLA high-resolution microwave data, which show that in general the active region increases in intensity and polarization over a period of several tens of minutes prior to the onset of a flare in that region. However, this phenomenon by itself does not appear to be sufficient to trigger a flare. It is shown that at 10 min or less before flare onset something else happens, usually in the form of one of the following three features: (1) sudden change of polarization of the flaring region, (2) change of orientation of the neutral plane separating one polarity from another in a bipolar region, and (3) appearance of new sources in the immediate vicinity of some preexisting structure of the active region. All three features are consistent with the emergence of new flux, which interacts with a preexisting region to form a neutral or current sheet. The formation of the latter is ultimately responsible for triggering the onset of a flare.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 6 19
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  • 74
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    X-ray imaging of a filament eruption with the Solar Maximum Mission satellite (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Soft X-ray observations of a filament located near NOAA AR 4640 were obtained with the Flat Crystal Spectrometer (FCS) on board the Solar Maximum Mission satellite on April 3-12, 1985. On April 7 the filament partially lifted off. At the same time and location an enhancement was imaged in soft X-rays. A total of 16 h of FCS observations, including 25 raster images, were made of the filament prior to the eruption, and over 40 h of observations, including 57 raster images, were made following the eruption. Careful alignment of H-alpha images taken during the same period has made possible the calculation of the integrated soft X-ray emission around the filament channel before, during, and after the eruption. Kitt Peak magnetograms have also been examined for this period to determine the corresponding magnetic field structure. A time history of the eruption in X-ray and optical wavelengths, and the development of the magnetic-field structure are presented. Evidence is seen for X-ray brightening in preexisting magnetic-field loops over the filament.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 6 19
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  • 75
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    Numerical simulation of flare energy build-up and release via Joule dissipation (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A new numerical MHD model is developed to study the evolution of an active region due to photospheric converging motion, which leads to magnetic-energy buildup in the form of electric current. Because this new MHD model has incorporated finite conductivity, the energy conversion occurs from magnetic mode to thermal mode through Joule dissipation. In order to test the causality relationship between the occurrence of flare and photospheric motion, a multiple-pole configuration with neutral point is used. Using these results it is found that in addition to the converging motion, the initial magnetic-field configuration and the redistribution of the magnetic flux at photospheric level enhance the possibility for the development of a flare.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 6 19
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  • 76
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    The electron-cyclotron maser instability as the source of solar type V continuum (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: In this paper, it is proposed that the electron-cyclotron (EC) maser instability can be the source of solar type V bursts. The propagation of electrons up an open field line is examined, and it is shown that the resultant distribution can be subject to the bump-in-tail (BIT) or the EC maser instabilities, or both. The characteristics of the emission from the BIT and EC maser instabilities when they are driven by such distributions are compared. It is proposed that type V bursts are produced by the coalescence of the upper hybrid waves produced by the maser instability, while type IIIs are produced by the BIT instability.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 310; 432-443
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  • 77
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    Magnetic field corrections to solar oscillation frequencies (1986)
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    Publication Date: 2019-07-12
    Description: It is argued that the frequencies of both the solar p- and g-modes of oscillation are modified by a magnetic field. In particular, the decrease in p-mode frequencies is attributed to a magnetic field within the solar interior evolving over the solar cycle. Field strengths at the base of the convection zone of at least 500,000 G are required.
    Keywords: SOLAR PHYSICS
    Type: Nature (ISSN 0028-0836); 323; 603-605
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  • 78
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    The synchrotron-maser theory of type II solar radio emission processes - The physical model and generation mechanism (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A theory is proposed to explain the generation mechanism of type II solar radio bursts. It is suggested that the shock wave formed at the leading edge of a coronal transient can accelerate electrons. Because of the nature of the acceleration process, the energized electrons can possess a 'hollow-beam' type distribution function. When the electron beam propagates along the ambient magnetic field to lower altitudes and attains larger pitch angles, a synchrotron-maser instability can set in. This instability leads to the amplification of unpolarized or weakly polarized radiation. The present discussion incorporates a model which describes the ambient magnetic field and background plasma by means of MHD simulation. The potential emission regions may be located approximately, according to the time-dependent MHD simulation. Since the average local plasma frequency in the source region can be evaluated from the MHD model, the frequent drift associated with the radiation may be estimated. The result seems to be in good agreement with that derived from observations.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 309; 392-401
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  • 79
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    Analysis of the prominence associated with the coronal mass ejection of August 18, 1980 (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: This paper develops a diagnostic method based on the observed H-alpha and continuum brightness to derive the electron density, line of sight thickness, and degree of ionization of hydrogen as functions of the temperature of the prominence filaments. Analysis of data from the event of August 18, 1980, illustrates that the rising prominence material has decreased density, increased temperature, and increased ionization of hydrogen relative to quiescent prominences in the lower corona. Hydrogen is found to be 90-99 percent ionized, electron densities are near 10 to the 8th/cu cm, and the temperature is near 20,000 K. The increased ionization is due mainly to the decreased density.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 10961-10
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  • 80
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    Disruption of a coronal streamer by an eruptive prominence and coronal mass ejection (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The coronal mass ejection of August 18, 1980 is analyzed using images from the coronagraph on the Solar Maximum Mission (SMM) satellite. The event occurred at the site of a large coronal helmet streamer and evolved into the three-part structure of a bright frontal shell, followed by a relatively dark space surrounding a bright filamentary core as seen in many mass ejections of the SMM epoch. The bright core can be identified as material from a prominence whose eruption was observed from the ground. The mass of the frontal shell is equal to that of the coronal helmet streamer, indicating that the shell is the coronal material previously in the helmet streamer, displaced and set into motion by the erupting prominence and surrounding cavity. The mass ejected in the bright core (or prominences) is estimated to be 50 percent larger than the 'coronal' material in the front loop.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 10951-10
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  • 81
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    Electron acceleration in flares inferred from radio and hard X-ray emissions (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Properties of electron acceleration in flares, especially the density structure in the acceleration region, are deduced from a correlation study between decimetric type III, spike, and hard X-ray (HXR) bursts. The high association rate found (71 percent) strongly suggests that spikes also originate from energetic electrons. Spikes and type III bursts have been found to be easily identified by their different polarizations. The two types of emission generally do not overlap in frequency. A reliable lower limit to the density is derived from the starting frequency of type III and U bursts. The spike emission very likely yields an upper limit. The density inhomogeneity in the acceleration region spans more than one order of magnitude and is more than one order of magnitude larger in the associated type U sources. A peak-to-peak correlation does not always exist between type III, spike and HXR bursts. This discrepancy can be interpreted in terms of the different source conditions and propagation properties. Whereas spikes need special conditions to become visible, type III and peaks of HXR may be the product of many elementary accelerations.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 104; 179-185
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  • 82
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    Particle propagation, wave growth and energy dissipation in a flaring flux tube (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Wave amplification by downgoing particles in a common flare model is investigated. The flare is assumed to occur at the top of a coronal magnetic flux loop, and results in the heating of plasma in the flaring region. The hot electrons propagate down the legs of the flux tube towards increasing magnetic field. It is simple to demonstrate that the velocity distributions which result in this model are unstable to both beam instabilities and cyclotron maser action. An explanation is presented for the propagation effects on the distribution, and the properties of the resulting amplified waves are explored, concentrating on cyclotron maser action, which has properties (emission in the z mode below the local gyrofrequency) quite different from maser action by other distributions considered in the context of solar flares. The z mode waves will be damped in the coronal plasma surrounding the flaring flux tube and lead to heating there. This process may be important in the overall energy budget of the flare. The downgoing maser is compared with the loss cone maser, which is more likely to produce observable bursts.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 6 19
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  • 83
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    The relative contribution of beam versus thermally produced X-rays in the large loop of the 5 November 1980 flare (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Observations of the temporal evolution of loop BC in soft X-rays in the November 5, 1980 flare are reviewed. Calculations are performed to model this evolution. The most consistent interpretation involving a minimum amount of energy is the following: thermal heating near B gives rise to a conduction front which moves out along the loop uninhibited for about 27 s, and beam heating near C gives rise to a second conduction front which moves in the opposite direction and prevents any energy reaching C by thermal conduction from B.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 6 19
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  • 84
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    Solar burst precursors and energy build-up at microwave wavelengths (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: We summarize high-resolution microwave observations (VLA) of heating and magnetic triggering in coronal loops. Magnetic changes that precede solar eruptions on time scales of tens of minutes involve primarily emerging coronal loops and the interaction of two or more loops. Thermal cyclotron lines have been detected in coronal loops, suggesting the presence of hot current sheets that enhance emission from relatively thin layers of enhanced temperature and constant magnetic field. These current sheets may play a role in the excitation of solar bursts. A filament-associated source with a high brightness temperature and steep radiation spectrum occurs above a region of apparently weak photospheric field. This source might be attributed to currents that enhance coronal magnetic fields. Compact (phi=5 sec) transient sources with lifetimes of 30 to 60 minutes have also been detected in regions of apparently weak photospheric field. We conclude by comparing VLA observations of coronal loops with simultaneous SMM-XRP observations.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 6 19; 97-100
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  • 85
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    Solar flare precursors (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Recent progress in the study of flare precursors and onset is reviewed. New theoretical results on filament formation and erution are presented, including especially the dynamical effects of magnetic fields. Ample evidence is found that energetic processes are already at work in the onset phase, a few minutes before the rapid rise of the hard-radiation impulse. In particular, the prevalence of soft and hard X-ray preheating (to less than 100 million K) is detailed, along with a connection to the launch of coronal mass ejections. A possible interpretation of the empirical time profiles near onset is that 'preheating' signifies that the flare has slowly started, and the transition to the impulsive stage then represents a change of phase in the flare-instability process. Finally, the problem of the interpretation of microwave preflare data is delineated.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 6 19
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  • 86
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    Dynamical behaviour in coronal loops (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Rapid variability has been found in two active region coronal loops observed by the X-ray Polychromator (XRP) and the Hard X-ray Imaging Spectrometer (HXIS) onboard the Solar Maximum Mission (SMM). There appear to be surprisingly few observations of the short-time scale behavior of hot loops, and the evidence presented herein lends support to the hypothesis that coronal heating may be impulsive and driven by flaring.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 6 19
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  • 87
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    Evidence for coronal turbulence in a quiescent active region (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The first evidence for nonthermal broadening of X-ray lines in a quiescent active region was based on a single observation of a limb active region by the Flat Crystal Spectrometer (FCS) on the SMM satellite, reported by Acton et al. (1981). With the renewal of SMM operations, the FCS has been used to further investigate this phenomenon. On April 28, 1984 a map of Mg XI resonance line profiles was made for a bright area in NOAA Active Region 4474 during a nonflaring period. The narrowest line profiles are consistent with the nominal instrumental width plus a thermal width equivalent to about 3 million K, the temperature derived from line ratios of O VIII, Ne IX, and Mg XI. The broadest line profiles are consistent with the instrumental width plus a thermal width equivalent to about 7 million K, but a substantial amount of plasma at this temperature would result in much greater flux in the FCS higher-temperature channels than was seen. If the excess width is attributed solely to plasma turbulence, the corresponding velocity would be about 40 + or - 10 km/s.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 6 19; 37-40
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  • 88
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    A study of solar filaments from high resolution microwave observations (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The Very Large Array was used to observe several solar filaments at 1.5 and 5 GHz. The maximum temperature depressions appear to be associated with H-alpha filaments. Comparison with He 10,830 A spectroheliogram shows that 20 cm temperature depressions correspond to the regions of reduced intensity in the He 10,830 A around filaments, which correspond to coronal cavities. The temperature and density structure of the transition sheath between the filament and the surrounding corona was studied assuming that the energy radiated away is balanced by the energy conducted from the corona. It is found that the observations can be better explained by a model having a pressure gradient in the transition sheath around the filament.
    Keywords: SOLAR PHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 167; 1 c
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  • 89
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    Two classes of gamma-ray/proton flares - Impulsive and gradual (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Various observational properties of gamma-ray/proton (GR/P) flares are investigated. The question whether gamma ray line (GRL) flares are different from other flares is reevaluated, and flares with gradual hard X-ray time profiles are searched for and shown to share many common characteristics. Among the gradual flares, the only difference between those with observable nuclear gamma rays and those without is that hard X-ray burst spectrometer peak rates are greater than 4500 counts/s for the former, and less for the latter. It is proposed that GR/P flares be classified into impulsive and gradual flares. The differences between the two classes ofo GR/P flares are studied in phenomena occurring in the high corona and interplanetary medium. By examining the ratio of the number of interplanetary protons to the number of gamma-ray producing protons, it is found that it is small for impulsive GR/P flares but relatively large for gradual GR/P flares.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 308; 912-928
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  • 90
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    Radio evidence for a delayed acceleration process in solar flares (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Observations of six delayed solar radio bursts at dm and mm frequencies are analyzed. The events included five Type II bursts. The data comprise 17 GHz interferometer data and ISEE-3 and SMM hard X-ray spectrometry data which peaked 0.5-1.0 hr after the main radio bursts. The data indicate the electrons with energies in the MeV range continue to be excited for tens of minutes after the impulsive phase acceleration. The continuing acceleration occurs in a large magnetic structure extending to at least 200,000 km altitude. The radio signals arise from a columnar source, the microwave signals being emitted near a leg or legs and meterwave emissions originating from the top of the magnetic structure.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 105; 383-398
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  • 91
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    Focusing anisotropy of solar cosmic rays (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Analysis of 50-MeV particle data from ICE and 1-GeV data from eight high-latitude neutron monitors of the February 16, 1984 solar cosmic ray event indicates that an exponential with scattering mean free path of greater than 2 AU and with index in the 1.3-1.7 range provides a better description of particle anisotropies than the first-order form, confirming the prediction from cosmic ray transport theories which incorporate the effect of adiabatic focusing into the usual pitch angle scattering formalism. The time profile of the event is largely a reflection of coronal transport processes, with good fits provided by a coronal diffusion coefficient of about 10 to the 18th sq cm/s and with velocity-dependent escape. The simple method of predicting the interplanetary scattering parameters has application where particle injection is nearly continuous, but where previously accelerated particles have filled the heliosphere with a large omnidirectional background.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 8713-872
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  • 92
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    Properties of metre-wavelength solar bursts associated with coronal mass ejections (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: An investigation is made to determine the relationship between a coronal mass ejection (CME) and the characteristics of associated metre-wave activity. It is found that (1) the CME width and leading edge velocity can be highly influential in determining the intensity, spectral complexity and frequency coverage of both type II and continuum burst; (2) the presence of a CME is possibly a necessary condition for the production of a metric continuum event and (3) metric continuum bursts as well as intense, complex type II events are preferentially associated with strong, long lasting soft X-ray events.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 105; 149-171
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  • 93
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    An atlas of photospheric magnetic field observations and computed coronal magnetic fields: 1976-1985 (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Daily magnetogram observations of the large-scale photospheric magnetic field have been made at the John M. Wilcox Solar Observatory at Stanford since May of 1976. These measurements provide a homogeneous record of the changing solar field through most of solar cycle 21. Using the photospheric data, the configuration of the coronal and heliospheric fields can be calculated using a Potential Field-Source Surface model. This provides a three-dimensional picture of the heliospheric field evolution during the solar cycle. This paper announces the publication of UAG Report No. 94, an Atlas containing the complete set of synoptic charts of the measured photospheric magnetic field, the computed field at the source surface, and the coefficients of the multipole expansion of the coronal field. The general underlying structures of the solar and heliospheric fields, which determine the environment for solar-terrestrial relations and provide the context within which solar activity related events occur, can be approximated from these data.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 105; 205-211
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  • 94
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    Properties of r-modes in the sun (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Global oscillations of the sun (r-modes) with very long periods of about 1 month are reviewed and studied. Such modes would be trapped in an acoustic cavity formed either by most of the convective envelope or by most of the radiative interior. A turning point frequency giving cavity boundaries is defined and the run of eigenvalues for angular harmonics l less than or equal to 3 are plotted for a conventional solar convection zone. The r-modes show equipartition of oscillatory energy among shells which each contain one antinode in the radial dimension. Toroidal motion is dominant to at least the 14th radial harmonic mode. Viscosity from convective turbulence is strong and would damp any mode in just a few solar rotations if it were the only significant nonadiabatic effect. 'Radial fine splitting' which lifts the degeneracy in n is very small (20 nHz or less) for all n less than or equal to 14 trapped in the envelope. But if splitting could be detected, there would be a valuable new constraint on solar convection theories.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 105; 1-15
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  • 95
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    On the magnetic structure of the quiet transition region (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Existing models of the quiet chromosphere-corona transition region predict a distribution of emission measure over temperature that agrees with observation for a T greater than about 100,000 K. These 'network' models assume that all magnetic field lines that emerge from the photosphere extend into and are in thermal contact with the corona. It is shown that the observed fine-scale structure of the photospheric magnetic network instead suggests a two-component picture in which magnetic funnels that open into the corona emerge from only a fraction of the network. The gas that makes up the hotter transition region is mostly contained within these funnels, as in standard models, but, because the funnels are more constricted in our picture, the heat flowing into the cooler transition region from the corona is reduced by up to an order of magnitude. The remainder of the network is occupied by a population of low-lying loops with lengths less than about 10,000 km. It is proposed that the cooler transition region is mainly located within such loops, which are magnetically insulated from the corona and must, therefore, be heated internally. The fine-scale structure of ultraviolet spectroheliograms is consistent with this proposal, and theoretical models of internally heated loops can explain the behavior of the emission measure below a T of aobut 100,000 K.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 105; 35-45
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  • 96
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    The origin of the 28- to 29-day recurrent patterns of the solar magnetic field (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Numerical simulations of the sun's mean line-of-sight magnetic field suggest an origin for the 28- to 29-day recurrent patterns of the field and its associated interplanetary phenomena. The patterns are caused by longitudinal fluctuations in the eruption of new magnetic flux, the transport of this flux to mid latitudes by supergranular diffusion and meridional flow, and the slow rotation of the resulting flux distributions at the 28- to 29-day periods characteristic of those latitudes.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 104; 425-429
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  • 97
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    New high-resolution rocket-ultraviolet filtergrams of the solar disc (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A rocket-borne solar ultraviolet telescope named Transition Region Camera was launched successfully for the third on July 13, 1982. High quality calibrated photographic images of the sun were obtained at Lyman alpha and in the continuum at 160 nm and 220 nm. The angular resolution achieved is better than one arcsec. A flare, active regions, sunspots, the 8 Mm mesostructure, the chromospheric network, bright UV grains and coronal loops were observed during the flight. The results are presented and the evolution with height in the solar atmosphere of the various structures observed is followed from one wavelength to the other, showing distinct differences. The value of the field's intensity of magnetic flux tubes is deduced from the observations.
    Keywords: SOLAR PHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 162; 1-2; 292-306
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  • 98
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    Analysis of coronal H I Lyman-alpha measurements in a polar region of the sun observed in 1979 (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Measurements of the intensities and spectral line profiles of resonantly scattered hydrogen Ly-alpha radiation have been used to determine hydrogen kinetic temperatures and electron densities between r = 1.5 and 2.2 solar radii in a polar region of the corona observed in 1979 near solar maximum. The mean temperature, 1.8 x 10 to the 6th K, in this region is significantly higher, by about 60 percent, than that obtained in a similar region observed in a 1980 rocket flight. The densities in these two polar regions are similar and are a factor of about 4 larger than in polar coronal holes observed at solar minimum. The flow velocities in both regions are most likely subsonic for r less than about 4 solar radii. The results reported here support the hypothesis that polar coronal holes observed at different times during the solar cycle can have different temperatures, densities, and possibly flow velocities.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 307; 381-388
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  • 99
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    Clumpy Langmuir waves in type III solar radio bursts (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A model is developed for type III radio emission in the interplanetary medium based on recent data on Langmuir waves, associated with ion sound waves, density fluctuations in the interplanetary plasma, streaming electrons and radio emission. In this model, Langmuir wave growth is suppressed by refraction in field-aligned density irregularities except near density minima where clumps of Langmuir waves form. Quasi-linear relaxation limits the growth of the Langmuir waves in the clumps. The radio emission, which is attributed to coalescence of the Langmuir waves with associated ion sound waves, saturates at a brightness temperature equal to the effective temperature of the Langmuir waves, estimated to be between 10 to the 15th and 10 to the 16th K from obserrvational data. The model is consistent with all the relevant data on type III events. In particular, it accounts naturally for observed brightness temperatures of type III bursts.
    Keywords: SOLAR PHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 163; 1-2
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  • 100
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    Infrared helioseismology - Detection of the chromospheric mode (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Time-series observations of an infrared solar OH absorption line profile have been obtained on two consecutive days using a laser heterodyne spectrometer to view a 2 arcsec portion of the quiet sun at disk center. A power spectrum of the line center velocity shows the well-known photospheric p-mode oscillations very prominently, but also shows a second feature near 4.3 mHz. A power spectrum of the line intensity shows only the 4.3 mHz feature, which is identified as the fundamental p-mode resonance of the solar chromosphere. The frequency of the mode is observed to be in substantial agreement with the eigenfrequency of current chromospheric models. A time series of two beam difference measurements shows that the mode is present only for horizontal wavelengths greater than 19 Mm. The period of a chromospheric p-mode resonance is directly related to the sound travel time across the chromosphere, which depends on the chromospheric temperature and geometric height. Thus, detection of this resonance will provide an important new constraint on chromospheric models.
    Keywords: SOLAR PHYSICS
    Type: Nature (ISSN 0028-0836); 322; 232-234
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