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Author name code: kopp-roger
ADS astronomy entries on 2022-09-14
author:"Kopp, Roger A." 

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Title: Metal Forming: General and Economic Aspects
Authors: Kopp, R.
2011emst.book.5408K    Altcode:
  In a solidified state, metallic materials, which include steel, are
  plastically formed to a permanent set by forces applied externally.

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Title: The Gradual Phase of Flares
Authors: Svestka, Z. F.; Poletto, G.; Fontenla, J.; Hick, P.; Kopp,
   R. A.; Sylwester, B.; Sylwester, J.
1999mfs..conf..409S    Altcode:
  Heating and Cooling in the Gradual Phase Emission Measure-Temperature
  Diagrams Flaring Arches Gradual Phase of Eruptive Flares Postflare
  Giant Arches Giant Arches: Modeling and Interpretation

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Title: Expected Spectroscopic Signatures of Siphon Flows on Coronal
    Loops - Doppler Dimming and Doppler Shifts
Authors: Kopp, R.; Spadaro, D.; Ventura, R.
1996AAS...188.3707K    Altcode: 1996BAAS...28Q.878K
  Coronal magnetic loops may display a wide variety of flow
  configurations, depending upon their geometries and the plasma
  conditions at their footpoints, as well as upon the distribution of
  nonthermal heating along them. Existing models of steady state loop
  flows ("siphon" flows, such as may exist in the closed-field regions
  of large, long-lived helmet streamers) show that the bulk plasma
  streaming velo- city at the top of a loop can easily reach values of
  order the acoustic speed, i.e., in excess of 100 km/s, and may be even
  higher in the supersonic (descending) leg of the loop. In this paper
  we consider some of the observational con- sequences of such siphon
  flows. Using a simple polytropic model to describe the variation of
  plasma parameters along a typical coronal loop, we have calculated the
  expected frequency-dependent emissivities of the resonance-scattered
  H I Lyman-alpha and O VI emission lines as functions of position
  on the loop and of the loop orientation relative to the viewing
  direction. Comparison with similar calculations for a static plasma
  with the same temperature and density provides the degree of Doppler
  dimming to be expected at various points along the loop. This Doppler
  dimming, and the related Doppler shift, comprise important diagnostic
  signatures of loop flows which are potentially observable with the UVCS
  instrument on SOHO. Surprisingly, Doppler dimming, which is ordinarily
  regarded as an indicator of radial outflow from the Sun, does not vanish
  entirely for the horizontal flow at the top of a loop. For a hot (T 2
  MK), nearly isothermal loop extending less than, say, 1 solar radius
  above the limb, the Doppler dimming there can achieve values of more
  than 10 per cent at the loop's summit.

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Title: Working group 3: Coronal streamers
Authors: Kopp, Roger A.
1994SSRv...70..309K    Altcode:
  The working group on coronal streamers convened on the first day of the
  2nd SOHO Workshop, which took place in Marciana Marina, Isola d'Elba,
  27 September 1 October 1993. Recent progress in streamer observational
  techniques and theoretical modeling was reported. The contribution
  of streamers to the mass and energy supply for the solar wind was
  discussed. Moreover, the importance of thin electric current sheets
  for determining both the gross dynamical properties of streamers and
  the fine-scale filamentary structure within streamers, was strongly
  emphasized. Potential advances to our understanding of these areas of
  coronal physics that could be made by the contingent of instruments
  aboard SOHO were pointed out.

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Title: Observational Signatures of Nanoflare Heating
Authors: Poletto, G.; Kopp, R.
1994kofu.symp...71P    Altcode:
  During the past few years it has been suggested that the solar
  corona results from the superposition of a large number of tiny
  impulsive energy-release events, which have come to be known as
  “nanoflares”. However, these events have not yet been observed;
  moreover, it remains to be shown theoretically that the repetitive
  occurrence of nanoflares can eventually build up a plasma at typical
  coronal densities and temperatures. The purpose of this work is to
  describe the temporal evolution of the plasma in a rigid, originally
  cool and nearly empty coronal flux tube with footpoints rooted in
  the chromosphere, when the flux tube is subject to the sporadic
  release of typical nanoflare energies. To this end, by analytically
  integrating the partial differential equations for mass, momentum,
  and energy conservation over the loop's spatial coordinate, we have
  developed a simple model involving only the spatial averages of the
  plasma thermodynamic variables. The model allows us to show how the
  repeated occurrence of low energy events in loops of different sizes
  eventually builds up a higher density, high temperature plasma -
  i.e., a nanoflare-heated corona. The observational consequences of
  our modeling, as well as future work in this area, are also discussed.

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Title: A quasi-steady model of a microflare-heated corona
Authors: Poletto, G.; Kopp, R. A.
1994AdSpR..14d.149P    Altcode: 1994AdSpR..14..149P
  It has been recently proposed that the solar corona is heated via the
  superposition of a large number of tiny energy-release events, the
  so-called nanoflares. In this paper we develop a simple semi-analytical
  model to describe the temporal evolution of the nanoflare plasma,
  confined in rigid magnetic flux tubes and subject to typical nanoflare
  energy releases. Assuming a power law for the nanoflare energy
  distribution and hypothesizing the repeated occurrence of nanoflares
  at random time intervals in an originally cool, low pressure loop, we
  show how a high temperature, high pressure plasma eventually builds up,
  leading to a nanoflare-heated corona. Even if the feasibility of the
  nanoflare mechanism as a coronal heating agent is thus demonstrated,
  we conclude by pointing out that present instrumentaiton cannot provide
  a definitive observational test of this hypothesis.

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Title: Working group 1: Coronal streamers
Authors: Kopp, R. A.
1994STIN...9434091K    Altcode:
  The working group on coronal streamers convened on the first day of the
  2nd SOHO Workshop, which took place in Marciana Marina, Isola d'Elba,
  27 September--1 October 1993. Recent progress in streamer observational
  techniques and theoretical modeling was reported. The contribution
  of streamers to the mass and energy supply for the solar wind was
  discussed. Moreover, the importance of thin electric current sheets
  for determining both the gross dynamical properties of streamers and
  the fine-scale filamentary structure within streamers, was strongly
  emphasized. Potential advances to our understanding of these areas of
  coronal physics that could be made by the contingent of instruments
  aboard SOHO were shown.

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Title: Coronal heating via nanoflares
Authors: Poletto, Giannina; Kopp, Roger
1994LNP...432..161P    Altcode: 1994LNPM...11..161P
  It has been recently proposed that the coronae of single late-type
  main sequence stars represent the radiative output from a large number
  of tiny energy release events, the so-called nanoflares. Although
  this suggestion is attractive and order of magnitude estimates of
  the physical parameters involved in the process are consistent with
  available data, nanoflares have not yet been observed and theoretical
  descriptions of these phenomena are still very crude. In this paper we
  examine the temporal behavior of a magnetic flux tube subject to the
  repeated occurrence of energy release events, randomly distributed in
  time, and we show that an originally empty cool loop may, in fact,
  reach typical coronal density and temperature values via nanoflare
  heating. By choosing physical parameters appropriate to solar conditions
  we also explore the possibilities for observationally detecting
  nanoflares. Although the Sun is the only star where nanoflares might
  be observed, present instrumentation appears to be inadequate for
  this purpose.

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Title: Coronal Heating by Nanoflares: Individual Events and Global
    Energetics
Authors: Kopp, R. A.; Poletto, G.
1993ApJ...418..496K    Altcode:
  Various mechanisms have been proposed to heat the solar corona, but
  none have been completely successful in accounting for its observed
  characteristics. Recently a further candidate has been advanced; namely,
  stochastic heating via a large number of tiny impulsive energy-release
  events, the so-called nanoflares. In this paper we develop a simple
  semianalytical model to describe the temporal evolution of the nanoflare
  plasma and to determine the response of magnetic flux tubes of different
  sizes to typical nanoflare energy releases. This allows us to show how
  the repeated occurrence of low-energy events in an originally cool loop
  may eventually build up a high-temperature plasma a nanoflare-heated
  corona. We also calculate the average nanoflare rate of occurrence,
  as a function of loop size, required to keep the plasma at coronal
  temperatures. The collective effect of this minievent population
  is shown to account for the observed coronal temperature and global
  emission measure. The present estimates may be used as guidelines for
  defining the requisites of future experiments aimed at observationally
  testing the nanoflare heating hypothesis.

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Title: Coronal heating via nanoflares
Authors: Poletto, G.; Kopp, R.
1993STIN...9426696P    Altcode:
  It has been recently proposed that the coronae of single late-type
  main sequence stars represent the radiative output from a large number
  of tiny energy release events, the so-called nanoflares. Although
  this suggestion is attractive and order of magnitude estimates of
  the physical parameters involved in the process are consistent with
  available data, nanoflares have not yet been observed and theoretical
  descriptions of these phenomena are still very crude. The temporal
  behavior of a magnetic flux tube subject to the repeated occurrence
  of energy release events, randomly distributed in time are examined,
  and it was shown that an originally empty cool loop may, in fact, reach
  typical coronal density and temperature values via nanoflare heating. By
  choosing physical parameters appropriate to solar conditions, the
  possibilities for observationally detecting nanoflares were also
  examined. Although the Sun is the only star where nanoflares might
  be observed, present instrumentation appears to be inadequate for
  this purpose.

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Title: Theory of coronal streamer formation.
Authors: Kopp, Roger A.
1992ESASP.348...53K    Altcode: 1992cscl.work...53K
  Conceptually, coronal streamers can form (and disappear) by either of
  two distinct processes: plasma "filling" and outward distention of a
  pre-existing closed magnetic structure; and magnetic reconnection,
  for whatever reason, of an open bipolar field configuration. The
  author argues that the majority of stable-appearing streamers on
  the Sun at any time are in fact of the latter category - namely,
  open-field structures undergoing gradual reconnection. Quasi-steady
  (i.e., "convectively relaxed") reconnection models may be required to
  explain the narrow high-density cores exhibited by most streamers out
  to distances of many solar radii. The author discusses some of the
  observational signatures of reconnection within streamers, which the
  instrumentation aboard SOHO may be capable of detecting.

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Title: Theory of coronal streamer formation
Authors: Kopp, R. A.
1992STIN...9321967K    Altcode:
  Conceptually, coronal streamers can form (and disappear) by either of
  two distinct processes: (1) plasma 'filling' and outward distention of
  a preexisting closed magnetic structure; and (2) magnetic reconnection,
  for whatever reason, of an open bipolar field configuration. We argue
  that the majority of stable-appearing streamers on the Sun at any time
  are in fact of the latter category - namely, open-field structures
  undergoing gradual reconnection. Quasi-steady (i.e., 'convectively
  relaxed') reconnection models may be required to explain the narrow
  high-density cores exhibited by most streamers out to distances of
  many solar radii. Some of the observational signatures of reconnection
  within streamers, which the instrumentation aboard SOHO may be capable
  of detecting are discussed.

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Title: A Semi-analytical Model of Stellar Flares
Authors: Kopp, R. A.; Poletto, G.
1992LNP...397..295K    Altcode: 1992sils.conf..295K
  No abstract at ADS

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Title: Largescale Quasi-Stationary X-Ray Coronal Structures Associated
    with Eruptive Solar Flares
Authors: Kopp, R. A.; Poletto, G.
1992LNP...399..197K    Altcode: 1992esf..coll..197K; 1992IAUCo.133..197K
  No abstract at ADS

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Title: Coronal Heating by Nanoflares: Plasma Dynamics of Elementary
    Events (With 2 Figures)
Authors: Kopp, R. A.; Poletto, G.
1991mcch.conf..634K    Altcode:
  No abstract at ADS

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Title: Formation and cooling of the giant HXIS arches of November
    6 7, 1980
Authors: Kopp, R. A.; Poletto, G.
1990SoPh..127..267K    Altcode:
  Giant arches, first detected by the HXIS instrument aboard SMM, are
  still a poorly understood component of the flare scenario. Their
  origin remains uncertain and their behavior, quite different in
  separate events, has not yet been satisfactorily explained. The
  purpose of the present paper is to analyze the giant arches imaged
  on November 6-7, 1980, which, in contrast to that observed on May
  21, 1980, were not stationary and had shorter cooling times. In
  particular, we use a procedure, already applied to the May 21 case,
  to compute the three-dimensional topology of the magnetic field which
  forms by reconnection over the active region containing the November
  arches. This technique allows us to verify that the observed structures
  are aligned with the computed field lines, lending support to the
  hypothesis that they originate through a reconnection process which
  occurs at progressively larger altitudes. Moreover, a calculation
  of the magnetic energy liberated by reconnection shows that enough
  energy may be thereby released to account for the observed thermal
  energy enhancement of the HXIS arches. Finally, the lifetime of the
  features is shown to be consistent with that predicted by cooling via
  radiation and field-aligned conduction to the underlying chromosphere.

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Title: Coronal heating by nanoflares: Plasma dynamics of elementary
    events
Authors: Kopp, Roger A.; Poletto, Giannina
1990STIN...9110830K    Altcode:
  It has been suggested by Parker Sturrock et al., and others that the
  corona may be stochastically heated, on spatial scales at or below
  current instrumental resolution limits, by a continuous succession of
  many small flarelike events commonly referred to as nanoflares. In this
  paper we extend a semi-analytical point model developed previously for
  solar compact flares, to include gravitational plasma downfall during
  the late decay phase. Applying the model to conditions representative of
  nanoflares allows us to predict the temporal variation of average plasma
  properties in such events and should ultimately facilitate a calculation
  of the spectral characteristics of a nanoflare-heated corona.

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Title: A semi-analytical model of stellar flares
Authors: Kopp, Roger A.; Poletto, Giannina
1990STIN...9110817K    Altcode:
  We present a simplified 'point' model to describe the hydrodynamic
  response of coronal loop plasma to the sudden release of energy
  which occurs at the time of a flare. Our simplification allows the
  full set of partial differential equations for energy, momentum, and
  mass conservation to be replaced by a corresponding set of ordinary
  differential equations for the plasma properties averaged over the
  loop volume. The temporal profiles of plasma temperature, density,
  and velocity are calculated over a time interval long enough to ensure
  that pre-flare conditions are re-established. The model is used for
  the interpretation of stellar flare data. In particular, we derive a
  set of representative loop geometries and flare energy inputs which
  allows us to reproduce the high emission measures typically inferred
  from observations of stellar flares.

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Title: A Simple Model for the Stellar Analogy of Compact Solar Flares
Authors: Kopp, R. A.; Poletto, G.
1990ASPC....9..119K    Altcode: 1990csss....6..119K
  No abstract at ADS

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Title: Hydrodynamics of the inner solar corona
Authors: Kopp, Roger A.
1989MmSAI..60...21K    Altcode:
  An elemental radial magnetic flux tube threading the solar chromospheric
  network and spreading into the overlying corona is considered. The
  dynamical response of the plasma contained in the tube to an occasional
  brief but intense heating of the chromosphere is calculated. It is shown
  that the apparent upward motion of a spicule, as seen in H-alpha, may
  correspond to an outward-propagating radiative cooling wave that follows
  the ejected mass into the corona after one of these heating events. The
  hotter, less dense plasma at still greater heights cools by radiation
  only as it falls back toward the chromosphere over a much longer
  time. The temperature-height histories of individual fluid elements
  appear to be remarkably similar and superpose to define a more-or-less
  common temperature profile for the transition region and inner corona.

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Title: Flare energetics.
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
   Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
   M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
   Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
   G.; Serio, S.; Sylwester, J.; Veck, N. J.
1989epos.conf..377W    Altcode:
  The authors have sought to establish a comprehensive and self-consistent
  picture of the sources and transport of energy within a flare. To
  achieve this goal, they chose five flares in 1980 that were well
  observed with instruments on the Solar Maximum Mission, and with other
  space-borne and ground-based instruments. The events were chosen to
  represent various types of flares. Details of the observations available
  for them and the corresponding physical parameters derived from these
  data are presented. The flares were studied from two perspectives,
  the impulsive and gradual phases, and then the results were compared
  to obtain the overall picture of the energetics of these flares. The
  authors also discuss the role that modeling can play in estimating the
  total energy of a flare when the observationally determined parameters
  are used as the input to a numerical model. Finally, a critique of
  our current understanding of flare energetics and the methods used to
  determine various energetics terms is outlined, and possible future
  directions of research in this area are suggested.

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Title: A simple model for the stellar analogy of compact solar flares
Authors: Kopp, R. A.; Poletto, G.
1989STIN...9015877K    Altcode:
  We have developed a simple point model to describe the average
  thermodynamical properties of a compact flare loop as a function of time
  during the flare decay phase. The model includes thermal conduction,
  chromospheric evaporation, and radiative losses; moreover, it assumes
  lateral (gas + magnetic) pressure balance with the background corona
  at all times. For the case of a low-(beta) plasma (rigid flux tube),
  detailed 1-D hydrodynamical simulations are available in the literature
  for comparison; we show that the temporal variation of average loop
  properties predicted by the point model are in good agreement with
  these numerical simulations for a loop with the same energy input.

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Title: Modeling of coronal magnetic fields during solar flares
Authors: Kopp, R. A.; Poletto, G.
1989MmSAI..60...65K    Altcode:
  Conversion of magnetic energy into diverse forms of plasma energy
  comprises the basic mechanism of flare phenomena. In this process
  magnetic fields undergo major rearrangements which, at least during the
  gradual phase of flares, may be described as a sequence of equilibrium
  configurations. In this paper, the basic techniques used to model
  flaring magnetic configurations are reviewed and results of comparisons
  between predicted and observed topologies are briefly summarized.

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Title: Intercomparison of numerical models of flaring coronal loops.
Authors: Kopp, R. A.; Fisher, G. H.; MacNiece, P.; McWhirter, R. W. P.;
   Peres, G.
1989epos.conf..597K    Altcode:
  The numerical modelling group was concerned with computations relevant
  to the problem of the hydrodynamic and radiative response of a single
  magnetic flux tube to a sudden release of energy in it. The group
  initially considered a simple "benchmark model" in which the physics of
  real loops - radiation, thermal conduction, compressible hydrodynamics,
  gravity and nonthermal heating - could be incorporated with some degree
  of realism. The primary goal of the benchmark model was to intercompare
  code calculations on a standardized, although hypothetical, problem,
  rather than to establish the best possible physical model.

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Title: Modeling of long-duration two-ribbon flares on M dwarf stars.
Authors: Poletto, G.; Pallavicini, R.; Kopp, R. A.
1988A&A...201...93P    Altcode:
  A time-dependent model of magnetic reconnection for the decay phase
  of solar two-ribbon flares is applied to long-duration stellar flares
  observed by the Einstein and Exosat observatories on the stars EQ Peg
  and Prox Cen. It is shown that the model reproduces correctly the
  energy release rate and temporal evolution during the decay phase
  of the observed events. It is concluded that the observed behavior
  is consistent with the interpretation of these flares as stellar
  counterparts of solar two-ribbon flares. In addition, taking into
  account recent measurements of stellar magnetic fields by Saar and
  Linsky (1985), it is shown that the agreement between the data and the
  analytical model results in a well-defined set of physical parameters
  for the emitting region.

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Title: The magnetic geometry and structure of the giant post-flare
    arch of 21 22 May, 1980
Authors: Poletto, G.; Kopp, R. A.
1988SoPh..116..163P    Altcode:
  On 21-22 May, 1980 the HXIS instrument aboard SMM imaged an enormous,
  more-or-less stationary, X-ray arch structure near the position of
  a large two-ribbon flare which immediately preceded it in time. As
  described by Švestka et al. (1982), the arch remained visible for
  up to 10 hours. Previous inferences of the height, orientation, and
  physical parameters of this feature have been based largely on the
  X-ray data and on radio observations of the associated stationary
  Type I noise storm. In the present paper we use the observed
  photospheric line-of-sight magnetic field distribution to compute,
  in the current-free approximation, the three-dimensional topology of
  the coronal field above the flare site. Comparing the HXIS intensity
  contours of the arch to the projected shapes of the field lines suggests
  that the arch is indeed aligned with certain coronal flux tubes and
  allows an independent determination of the geometrical arch parameters
  to be made. This procedure indicates that the true height of the arch
  is about 70000 km, i.e., appreciably less than was suggested previously
  (although it is still certainly to be classified as a `giant" feature
  of the post-flare evolution).

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Title: The determination of coronal fieldline connectivity from
    photospheric flare observations
Authors: Kopp, R. A.; Poletto, G.
1988AdSpR...8k.209K    Altcode: 1988AdSpR...8..209K
  According to current ideas, during the gradual phase of two-ribbon
  flares magnetic reconnection causes the open field configuration created
  at flare onset to relax back to a closed, lower energy state. The shapes
  and orientations of the newly formed loops are indicative of whether
  the reconnected field is potential or force-free and, in the latter
  case, afford a direct evaluation of the amount of shear involved. In
  the present paper we describe an empirical method for deriving the
  footpoint connectivity of the reconnected field lines, based on the
  point-by-point variation of the merging rate above the flare site;
  the latter can in principle be derived from photospheric observations
  alone. As an illustration we apply the method to a simplistic model
  of reconnection above a non-uniform surface field. Future application
  to specific solar events will also be discussed.

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Title: Modeling of long-decay stellar flares on EQ Peg and Prox Cen
Authors: Pallavicini, R.; Poletto, G.; Kopp, R. A.
1988ASSL..143..171P    Altcode: 1988acse.conf..171P
  A magnetic reconnection model of solar 2-ribbon flares is applied to
  long-duration events observed by Einstein and Exosat on the stars
  EQ Peg and Prox Cen. The authors show that the model is capable of
  reproducing the energy release rate and temporal evolution of the decay
  phase of the observed events, strongly supporting their identification
  as stellar counterparts of solar 2-R flares. The model is also used
  to put constraints on the physical parameters of the emitting region.

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Title: Magnetic modelling of giant HXIS arches
Authors: Kopp, R. A.; Poletto, G.
1988AdSpR...8k.203K    Altcode: 1988AdSpR...8..203K
  The HXIS instrument onboard SMM detected for the first time a new type
  of flare-associated phenomenon - the so-called “giant coronal arch”
  - which extends to high altitudes and whose nature has not yet been
  clearly identified. Like post-flare loops, however, giant arches
  apparently occur only after two-ribbon flares, thus suggesting that
  both structures originate from a common mechanism. In order to test
  this hypothesis we examine the possibility that the giant HXIS arches
  observed on 6/7 November 1980 formed by magnetic reconnection high in
  the corona. We conclude that the observed configuration of the HXIS
  structures is indeed consistent with the geometry of magnetic field
  lines reconnecting to a potential configuration.

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Title: Topology of Reconnected Magnetic Fields after Two-Ribbon Flares
Authors: Kopp, R. A.; Poletto, G.
1987sman.work..103K    Altcode:
  Magnetic reconnection is recognized to be responsible for a variety
  of phenomena which occur during flare events. An outstanding example
  of this process is given by the magnetic field restructuring during
  the decay phase of two-ribbon flares. The authors briefly review a 2-D
  analytical model developed by Kopp and Poletto (1984) which has been
  shown to be capable of reproducing the major characteristics of these
  post-flare effects and present an extension of this model to 3-D. For
  this latter case they present, for a simple magnetic configuration
  where the opposite polarities are skewed with respect to one another,
  a set of field line maps which have been obtained under the hypothesis
  that reconnection proceeded up to different heights.

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Title: On the origin of HXIS arches
Authors: Kopp, R. A.; Poletto, G.
1987PAICz..66..249K    Altcode: 1987eram....1..249K
  During SMM operation in 1980 the HXIS instrument detected a few giant
  coronal arches, extending to high altitude (≡10 km) and with widely
  separated footpoints, which always appeared after two-ribbon (2-R)
  flares. In this paper the authors examine the possibility that HXIS
  arches form as a results of magnetic reconnection occurring at high
  levels.

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Title: Coronal Mass Balance and a Time-Dependent Model of
    Transition-Region Downflows in the Chromospheric Network
Authors: Kopp, R. A.
1987BAAS...19..650K    Altcode:
  No abstract at ADS

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Title: Characterization of the Total Flare Energy
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
   Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
   M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
   Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
   G.; Serio, S.; Sylwester, J.; Veek, N. J.
1986epos.conf.5.41W    Altcode: 1986epos.confE..41W
  No abstract at ADS

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Title: Energetics of the Impulsive Phase
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
   Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
   M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
   Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
   G.; Serio, S.; Sylwester, J.; Veek, N. J.
1986epos.conf..5.5W    Altcode: 1986epos.confE...5W
  No abstract at ADS

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Title: Energetics of the Gradual Phase
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
   Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
   M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
   Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
   G.; Serio, S.; Sylwester, J.; Veek, N. J.
1986epos.conf.5.20W    Altcode: 1986epos.confE..20W
  No abstract at ADS

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Title: Magnetic field re-arrangement after prominence eruption.
Authors: Kopp, R. A.; Poletto, G.
1986NASCP2442..235K    Altcode: 1986copp.nasa..235K
  It has long been known that magnetic reconnection plays a fundamental
  role in a variety of solar events. Although mainly invoked in flare
  problems, large scale loops interconnecting active regions, evolving
  coronal hole boundaries, the solar magnetic cycle itself, provide
  different evidence of phenomena which involve magnetic reconnection. A
  further example might be given by the magnetic field rearrangement
  which occurs after the eruption of a prominence. Since most often
  a prominence reforms after its disappearance and may be observed at
  about the same position it occupied before erupting, the magnetic field
  has to undergo a temporary disruption of relax back, via reconnection,
  to a configuration similar to the previous one. The above sequence of
  events is best observable in the case of two ribbon (2-R) flares but
  most probably is associated with all filament eruptions. Even if the
  explanation of the magnetic field rearrangement after 2-R flares in
  terms of reconnection is generally accepted, the lack of a 3-dimensional
  model capable of describing the field reconfiguration, has prevented,
  up to now, a thorough analysis of its topology as traced by H alpha/x
  ray loops. A numerical technique is presented which enables oneto
  predict and visualize the reconnected configuration, at any time, and
  therefore allows one to make a significant comparison of observations
  and model predictions throughout the whole process.

---------------------------------------------------------
Title: Review of Impulsive Phase Phenomena
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
   Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
   M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
   Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
   G.; Serio, S.; Sylwester, J.; Veek, N. J.
1986epos.conf.5.60W    Altcode: 1986epos.confE..60W
  No abstract at ADS

---------------------------------------------------------
Title: Intercomparison of numerical models of flaring coronal loops
Authors: Kopp, R. A.; Fisher, G. H.; MacNeice, P.; McWhirter, R. W. P.;
   Peres, G.
1986epos.conf..7.1K    Altcode: 1986epos.confG...1K
  The proposed Benchmark Problem consists of an infinitesimal magnetic
  flux tube containing a low-beta plasma. The field strength is assumed
  to be so large that the plasma can move only along the flux tube,
  whose shape remains invariant with time (i.e., the fluid motion is
  essentially one-dimensional). The flux tube cross section is taken to
  be constant over its entire length. In planar view the flux tube has a
  semi-circular shape, symmetric about its midpoint s = s<SUB>max</SUB>
  and intersecting the chromosphere-corona interface (CCI) perpendicularly
  at each foot point. The arc length from the loop apex to the CCI is
  10,000 km. The flux tube extends an additional 2000 km below the CCI
  to include the chromosphere, which initially has a uniform temperature
  of 8000 K. The temperature at the top of the loop was fixed initially
  at 2 X 1 million K. The plasma is assumed to be a perfect gas (gamma
  = 5/3), consisting of pure hydrogen which is considered to be fully
  ionized at all temperatures. For simplicity, moreover, the electron
  and ion temperatures are taken to be everywhere equal at all times
  (corresponding to an artificially enhanced electron-ion collisional
  coupling). While there was more-or-less unanimous agreement as to
  certain global properties of the system behavior (peak temperature
  reached, thermal-wave time scales, etc.), no two groups could claim
  satisfactory accord when a more detailed comparison of solutions
  was attempted.

---------------------------------------------------------
Title: Flares Chosen for Energetics Study
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
   Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
   M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
   Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
   G.; Serio, S.; Sylwester, J.; Veek, N. J.
1986epos.conf.5.47W    Altcode: 1986epos.confE..47W
  No abstract at ADS

---------------------------------------------------------
Title: Relationships among the Phases
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
   Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
   M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
   Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
   G.; Serio, S.; Sylwester, J.; Veek, N. J.
1986epos.conf.5.39W    Altcode: 1986epos.confE..39W
  No abstract at ADS

---------------------------------------------------------
Title: Large-scale electric fields resulting from magnetic
    reconnection in the corona.
Authors: Kopp, R. A.; Poletto, G.
1986NASCP2442..469K    Altcode: 1986copp.nasa..469K
  The authors have applied the method of Forbes and Priest to the
  large two-ribbon flare of 29 July, 1973, for which both detailed Hα
  observations and magnetic data are available. One sees from this
  calculation that, as reconnection sets in at the beginning of the
  decay phase, the electric field grows rapidly to reach a maximum value
  of about 2 V/cm within just a few minutes. Thereafter E<SUB>1</SUB>
  declines monotonically with time, as one would expect for any relaxation
  process: as more and more of the magnetic flux disrupted by the flare
  reconnects, the merging rate itself decreases.

---------------------------------------------------------
Title: Modeling of Long Duration Stellar Flares
Authors: Poletto, G.; Pallavicini, R.; Kopp, R. A.
1986BAAS...18Q.962P    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Magnetic reconnection and energy release in a long-duration
    stellar flare
Authors: Poletto, G.; Pallavicini, R.; Kopp, R. A.
1986AdSpR...6h.145P    Altcode: 1986AdSpR...6..145P
  A dynamical model of magnetic reconnection in solar two-ribbon flares
  is applied to EXOSAT observations of a long-decay flare from the star
  EQ Peg. We show that the model is able of reproducing correctly the
  energy release rate and temporal evolution of the decay phase of the
  observed flare. We conclude that the flare was the stellar counterpart
  of solar two-ribbon flares and we derive the physical parameters of
  the emitting region.

---------------------------------------------------------
Title: Flare energetics.
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
   Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
   M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
   Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
   G.; Serio, S.; Sylwester, J.; Veck, N. J.
1986NASCP2439....5W    Altcode:
  In this investigation of flare energetics, the authors establish a
  comprehensive and self-consistent picture of the sources and transport
  of energy within a flare. They chose five flares in 1980 that were
  well observed with instruments on the SMM, and with other space-borne
  and ground-based instruments. Details of the observations available
  for them and the corresponding physical parameters derived from these
  data are presented. The flares were studied from two perspectives,
  the impulsive and gradual phases, and then the results were compared
  to obtain the overall picture of the energetics of these flares. The
  authors also discuss the role that modeling can play in estimating the
  total energy of a flare when the observationally determined parameters
  are used as the input to a numerical model.

---------------------------------------------------------
Title: Intercomparison of numerical models of flaring coronal loops.
Authors: Kopp, R. A.; Fisher, G. H.; MacNiece, P.; McWhirter, R. W. P.;
   Peres, G.
1986NASCP2439....7K    Altcode:
  The authors were concerned with computations relevant to the problem
  of the hydrodynamic and radiative response of a single magnetic flux
  tube to a sudden release of energy in it. They considered a simple
  "Benchmark Model" in which the physics of real loops - radiation,
  thermal conduction, compressible hydrodynamics, gravity and nonthermal
  heating could be incorporated with some degree of realism. The primary
  goal of the Benchmark Model was to intercompare code calculations on a
  standardized, although hypothetical, problem, rather than to establish
  the best possible physical model.

---------------------------------------------------------
Title: Macroscopic electric fields during two-ribbon flares.
Authors: Poletto, G.; Kopp, R. A.
1986lasf.conf..453P    Altcode: 1986lasf.symp..453P
  Large-scale electric fields present during solar flares might provide a
  mechanism for continuously accelerating particles to high energies. The
  authors use the magnetic reconnection model of two-ribbon flares
  (Kopp et al., 1976, 1984) to calculate the temporal variation of the
  coronal electric field for the large flares of 29 July, 1973 and 21
  May, 1980. This calculation shows that the electric field declines
  monotonically during the decay phase. The authors conclude that the
  actual reconnection rate after these two-ribbon flares is being governed
  by the global dynamics of the perturbed coronal field-plasma system,
  rather than by processes within the magnetic diffusion region itself.

---------------------------------------------------------
Title: Three-Dimensional Reconnection after a Prominence Eruption
Authors: Kopp, R. A.; Poletto, G.
1986ASSL..123...65K    Altcode: 1986shtd.symp...65K
  A currently widely held explanation of the diverse phenomena following
  a prominence eruption is that these are the direct result of the ensuing
  reconnection of open magnetic field lines created by the eruption. Kopp
  and Pneuman (1976) and Kopp and Poletto (1984) developed a 2-D model
  wherein an analytical time-dependent magnetic field geometry was used
  to account quantitatively for the major characteristics of many of
  these post-flare effects. In the present paper, after mentioning a
  few situations for which a 2-D treatment would nevertheless clearly be
  inadequate, the authors extend to three dimensions their earlier model.

---------------------------------------------------------
Title: Analysis of loop flows observed on 27 March, 1980 by the UVSP
    instrument during the Solar Maximum Mission
Authors: Kopp, R. A.; Poletto, G.; Noci, G.; Bruner, M.
1985SoPh...98...91K    Altcode:
  In this paper we present the results of an analysis of a set of
  observations in the C IV 1548 Å line obtained on 27 March, 1980 by
  the Solar Maximum Mission Ultraviolet Spectrometer and Polarimeter
  (UVSP). The observed region covers an area of 240 × 240 arc sec
  and includes a system of bright loops at the limb. Simultaneous
  spectroheliograms and dopplergrams of the loop region allowed us to
  derive empirical velocity and emission-measure profiles on individual
  loops. These have been compared with the theoretical profiles for:
  (i) a steady-state loop model with siphon flow, (ii) a steady state
  loop model with downflow in both legs maintained by continuous mass
  addition near the loop summit, (iii) a non-steady loop model with
  downflow, whereby the initial plasma density decays exponentially with
  time (similarity solution). None of these simple models is capable of
  simultaneously representing both the velocity and emission measure
  profiles; thus we still lack a realistic description of cool loop
  dynamics. New observations aimed at determining such parameters as
  the loop lifetime are considered crucial for providing the necessary
  constraints for future modeling efforts.

---------------------------------------------------------
Title: Modeling of reconnection processes in ribbon flares
Authors: Kopp, R. A.; Poletto, G.
1985MmSAI..56..809K    Altcode:
  In a study of how flares are sustained by magnetic energy, the work
  of Hirayama (1974) is extended. Hirayama identified reconnection of
  the open field lines created by filament eruption as the source of
  prolonged energy release observed during the decay phase of two-ribbon
  flares. It is shown that the morphological properties of the decay phase
  of two-ribbon flares may be interpreted in terms of reconnection. A
  two-dimensional model (which can be extended to three dimensions)
  capable of reproducing the large-scale behavior of the observed
  scenario is presented. The capabilities of both models is discussed
  in the context of ongoing research in this area.

---------------------------------------------------------
Title: Extension of the Reconnection Theory of Two-Ribbon Solar Flares
Authors: Kopp, R. A.; Poletto, G.
1984SoPh...93..351K    Altcode:
  The magnetic reconnection theory for two-ribbon flares and flare loops
  hypothesizes that the gradual energy release during the decay phase
  is a direct result of dissipative relaxation of the open coronal
  magnetic configuration created by an eruptive prominence/coronal
  transient precursor. This scenario is here developed quantitatively
  to the point where a realistic comparison with observational data
  can be attempted. Our major refinements are (i) to use an analytical
  description of the reconnecting field geometry specifically chosen
  to characterize the spatial scale of the active region where a flare
  occurs, and (ii) to take account of the fact that the volume occupied
  by X-ray-emitting plasma (hot loops) generally increases with time
  during the flare.

---------------------------------------------------------
Title: Magnetic reconnection in two-ribbon flares - Theory and
    applications
Authors: Kopp, R. A.; Poletto, G.
1984MmSAI..55..737K    Altcode:
  The magnetic reconnection theory of two-ribbon flares and flare loops
  is applied to flares observed both during the Solar Maximum Mission
  and earlier. In order to compare it quantitatively with observational
  data, the original theory is refined in two respects. First, an
  analytical description of the reconnecting field geometry is used
  which is specifically chosen to characterize the actual spatial scale
  of the active region where a flare occurs. Second, the increase in
  coronal volume occupied by the thermal flare plasma is taken into
  account. Application of the modified theory to the large two-ribbon
  flare of July 29, 1973 yields excellent agreement with observations
  of the time variation of the flare plasma energy density, extending
  to rather early times in the flare history. A similar analysis for
  another flare allowed the reconnection process to be directly observed.

---------------------------------------------------------
Title: Observational Evidence for Coronal Magnetic Reconnection
    during the Two-Ribbon Flare of 21 may 1980
Authors: Kopp, R. A.; Poletto, G.
1984uxsa.coll...17K    Altcode: 1984IAUCo..86...17K; 1984uxsa.conf...17K
  No abstract at ADS

---------------------------------------------------------
Title: Intercomparison of numerical flare-loop models during the
    NASA-SMM Workshop series on solar flares
Authors: Kopp, R. A.
1984MmSAI..55..811K    Altcode:
  The flare numerical modeling activity at the Solar Maximum Workshop
  represented the dedicated efforts of several individuals and substantial
  computer resources of their respective institutions. Whereas the
  original intent of this undertaking was to establish a benchmark
  reference calculation for a standard coronal loop configuration, in
  retrospect one can say that its true value was to demonstrate that
  none of the existing codes is without limitations. The author shows
  how difficult it is to intercompare the results obtained with diverse
  and highly complex computer codes.

---------------------------------------------------------
Title: Analysis of active region loop flows as observed from SMM
Authors: Poletto, G.; Kopp, R. A.
1984MmSAI..55..773P    Altcode:
  The physical properties of plasma motions within solar loop structures
  are studied by analyzing and interpreting space observations of
  flows in active regions outside flare conditions. The indirect
  evidence for the presence of plasma motions in loops that derives
  either from observational data or from theoretical arguments is first
  discussed. Direct observations of plasma flows, mostly acquired by
  the SMM USVP experiment, are then reviewed. Finally, the results of
  one recent attempt to compare theory and observations are presented
  and discussed.

---------------------------------------------------------
Title: SMM Observations of Coronal Arcade at the Onset of a Flare
Authors: Strong, K. T.; Bruner, M. E.; Poletto, G.; Kopp, R.
1983BAAS...15..715S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Preliminary Results from an Analysis of SMM Observations of
    Loop Flows.
Authors: Bruner, M.; Kopp, R. A.; Noci, G.; Poletto, G.
1982uxsa.coll....2B    Altcode: 1982IAUCo..73....2B
  No abstract at ADS

---------------------------------------------------------
Title: Heating and acceleration of the solar wind.
Authors: Kopp, R. A.
1981NASSP.450..373K    Altcode: 1981suas.nasa..373K
  The dynamics of the expanding corona are discussed emphasizing the
  physical processes which accelerate the plasma as it flows away from
  the Sun. The solar wind plays a dominant role in the energy balance of
  the part of the corona in which it originates. The wind acceleration
  processes, in large part, with the mechanisms that transport energy
  to the corona in the first place.

---------------------------------------------------------
Title: The Solar Wind Acceleration in Coronal Holes
Authors: Kopp, R. A.
1981sowi.conf...42K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: A Semi-Analytical Approach to Time-Dependent Coronal Expansion
Authors: Kopp, R. A.
1980SoPh...68..307K    Altcode:
  In this paper we point out the existence of a special class of
  solutions to the nonlinear hydrodynamic equations describing the
  time-dependent solar wind, namely that for which the velocity profile
  is time-invariant but the density at each point of the corona changes
  exponentially with time. Theoretical velocity curves are calculated for
  the case of isothermal expansion and compared with the Parker model
  for steady-state expansion. These solutions can be used to obtain
  quantitative estimates for the degree of departure from the latter of
  a real corona undergoing evolution on a finite time scale.

---------------------------------------------------------
Title: Asymmetry and nonradiality in coronal transients
Authors: Sawyer, C.; Illing, R. M. E.; House, L. L.; Wagner, W. J.;
   Kopp, R.
1980BAAS...12Q.899S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Particle acceleration in the process of eruptive opening and
    reconnection of magnetic fields
Authors: Svestka, Z.; Martin, S. F.; Kopp, R. A.
1980IAUS...91..217S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The energy balance in the solar atmosphere above coronal holes.
Authors: McWhirter, R. W. P.; Kopp, R. A.
1979MNRAS.188..871M    Altcode:
  Recent observations from spacecraft have established the correlation
  between high-speed solar wind streams in the vicinity of the earth,
  coronal regions of low density seen in the ATM coronagraph pictures, and
  coronal holes identified from X-ray photographs of the sun. Quantitative
  analysis of these data leads to the conclusion that most, if not all,
  of the solar wind originates in coronal holes and that it experiences
  the main part of its acceleration in the range between two and five
  solar radii. In this paper a simplified model is adopted to show that
  an adequate mechanism for the acceleration is the pressure applied
  to the solar atmosphere by the gradient of the momentum flux carried
  by Alfven waves travelling along the magnetic field lines. The total
  energy requirement of a coronal hole region is then estimated and
  this is shown to be significantly greater than for the other regions
  of the solar atmosphere.

---------------------------------------------------------
Title: Transient Events in Space. (Book Reviews: Study of Travelling
    Interplanetary Phenomena 1977. Proceedings of a symposium, Tel Aviv,
    Israel, June 1977)
Authors: Kopp, Roger A.
1978Sci...200R1142S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Downflow in the supergranulation network and its implications
    for transition region models.
Authors: Pneuman, G. W.; Kopp, R. A.
1978SoPh...57...49P    Altcode:
  Three independent observations by rocket, Skylab, and OSO-8 have
  all indicated the presence of steady downflows of the order of a
  few kilometers per second in the solar transition region overlying
  the chromospheric network. Using density estimates at these heights
  from traditional transition region models, we find that the downward
  mass fluxes associated with these velocities are comparable with
  the estimated upward mass flux in spicules, originating in the same
  regions. Since both observations and theoretical calculations show
  that the solar wind can accept only a small fraction of the upward
  spicule flux, we suggest that the downflow represents spicular
  material returning to the chromosphere after being heated to coronal
  temperatures. In this context, the differential velocity measurement
  of Cushman and Rense is interpreted as indicating a difference in
  downflow speeds rather than a difference in expansion speeds.

---------------------------------------------------------
Title: Downflow of Spicular Material and Transition Region Models
Authors: Pneuman, G. W.; Kopp, R. A.
1977A&A....55..305P    Altcode:
  SUMMARY It has long been recognized that spicules supply material to
  the corona at a rate far in excess to that at which it is removed by
  the solar wind. This surplus material must ultimately return to the
  chromosphere. In fact recent rocket and satellite observations of
  Doppler shifts in transition region lines imply downward mass fluxes
  in the chromospheric network which are roughly comparable to the
  upward spicule flux. The enthalpy flux associated with the downflow
  of coronal material into these regions is shown by various estimates
  to exceed the inward heat flow expected by thermal conduction and it
  may constitute the dominant energy source for the transition region.

---------------------------------------------------------
Title: Models of coronal holes above the transition region.
Authors: Kopp, R. A.; Orrall, F. Q.
1977chhs.conf..179K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Energy Balance and Structure of Active Regions
Authors: Kopp, R.; Orrall, F.
1977ebhs.coll..457K    Altcode: 1977IAUCo..36..457K
  No abstract at ADS

---------------------------------------------------------
Title: Temperature and density structure of the corona and inner
    solar wind.
Authors: Kopp, R. A.; Orrall, F. Q.
1976A&A....53..363K    Altcode:
  A combined theoretical and observational approach is used to construct
  models of the inner corona applicable to quiet open-field regions
  and coronal holes. These models, extending from the top of the
  transition region at about 1.003 solar radii out to 3 solar radii,
  are calculated by employing parameters that describe the coronal
  geometry and heating. Thermal conductivity, heating, radiative losses,
  and solar-wind convection are included in the full energy-balance
  equation, which is integrated to obtain density and temperature models;
  the unknown heating term is parameterized in terms of the mechanical
  flux incident at the base and the characteristic scale height for
  the dissipation of this flux; and boundary conditions at the base are
  fixed by EUV-derived models of the transition region. Two representative
  models, one for a coronal hole and one for a quiet region, are examined
  in detail as illustrative examples of the technique used. It is noted
  that the models obtained predict most of the pertinent observations
  reasonably well but significantly overestimate the radio emission at
  80 and 160 MHz and significantly underestimate the intensity of the
  Fe XV line at 284 A, especially in coronal holes.

---------------------------------------------------------
Title: Magnetic reconnection in the corona and the loop prominence
    phenomenon.
Authors: Kopp, R. A.; Pneuman, G. W.
1976SoPh...50...85K    Altcode:
  Many classes of transient solar phenomena, such as flares, flare sprays,
  and eruptive prominences, cause major disruptions in the magnetic
  geometry of the overlying corona. Typically, the results from Skylab
  indicate that pre-existing closed magnetic loops in the corona are
  torn open by the force of the disruption. We examine here some of the
  theoretical consequences to be expected during the extended relaxation
  phase which must follow such events. This phase is characterized
  by a gradual reconnection of the outward-distended field lines. In
  particular, the enhanced coronal expansion which occurs on open field
  lines just before they reconnect appears adequate to supply the large
  downward mass fluxes observed in Ha loop prominence systems that form
  during the post-transient relaxation. In addition, this enhanced flow
  may produce nonrecurrent high speed streams in the solar wind after
  such events. Calculations of the relaxation phase for representative
  field geometries and the resulting flow configurations are described.

---------------------------------------------------------
Title: Dynamics of coronal hole regions. I. Steady polytropic flows
    with multiple critical points.
Authors: Kopp, R. A.; Holzer, T. E.
1976SoPh...49...43K    Altcode:
  The hydrodynamic properties of a steadily expanding corona are explored
  for situations in which departures from spherically symmetric outflow
  are large, in the sense that the geometrical cross section of a given
  flow tube increases outward from the Sun faster than r<SUP>2</SUP>
  in some regions. Assuming polytropic flow, it is shown that in
  certain cases the flow may contain more than one critical point. We
  derive the criterion for determining which of these critical points is
  actually crossed by the transonic solution which begins at the Sun and
  extends continuously outward. Next, we apply the theory to geometries
  which exhibit rapid spreading of the flow tubes in the inner corona,
  followed by more-or-less radial divergence at large distances. This is
  believed to be the type of geometry found in coronal hole regions. The
  results show that, if this initial divergence is sufficiently large,
  the outflow becomes supersonic at a critical point encountered low in
  the corona in the region of high divergence, and it remains supersonic
  at all greater heights in the corona. This feature strongly suggests
  that coronal hole regions differ from other open-field regions of
  the corona in that they are in a `fast', low density expansion state
  over much of their extent. Such a dynamical configuration makes it
  possible to reconcile the low values of electron density observed in
  coronal holes with the large particle fluxes in the associated high
  speed streams seen in the solar wind.

---------------------------------------------------------
Title: Nonstationary flow resulting from field line reconnection
    following a major coronal transient.
Authors: Kopp, R.; Pneuman, G. W.
1976BAAS....8..293K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Koobi Fora experiment: continuum observations of solar
    spicules during the 30 June 1973 eclipse.
Authors: Kopp, R. A.; White, O. R.; Baur, T. G.
1975A&A....44..299K    Altcode:
  Summary. Limb observations of chromospheric spicules in the continuum
  near 4700 A were obtained during the solar eclipse of 30 June 1973,
  in an experiment conducted close to the edge of the path of totality
  in northern Kenya. The experimental apparatus and observing techniques
  which were employed are described and some results of the data analysis
  are presented. The observations indicate that spicules may extend
  to substantially greater heights in the corona than one infers from
  filtergrams and spectra of the stronger spicule emission lines. The
  derived continuum intensity distribution within a single chromospheric
  emission feature is interpreted as being due to the collective effect
  of one or more spicules within the "blur circle" defined by the
  quality of the seeing during eclipse. This intensity distribution,
  when corrected for the probable number of spicules contributing
  to the observed emission at each height, leads to a straightforward
  determination of the spicule electron density as a function of height,
  since the continuum emission is almost certainly the result of Thomson
  scattering of photospheric radiation by free electrons. The inferred
  densities at heights less than 10000 km are in reasonable agreement with
  previous determinations. Key words: eclipse electron scattering spicules

---------------------------------------------------------
Title: Energy Balance in the Chromosphere-Corona Transition Region
Authors: Kopp, Roger A.
1972SoPh...27..373K    Altcode:
  The classical picture of the transition region is that of a
  thin spherically symmetric shell maintained in a steady average
  thermodynamical state by a balance between conductive heating from
  the hot overlying corona and radiative losses. The further analysis of
  existing extreme ultraviolet flux data casts doubt on the correctness
  of this simple model. It is shown that the downward heat flux between
  the chromosphere and corona cannot be nearly as large as the value 6
  × 10<SUP>5</SUP> erg cm<SUP>−</SUP>)= 13.46 - 2.99 sin<SUP>2</SUP>
  s<SUP>−1</SUP> derived in previous studies by assuming a planar
  atmosphere, and in fact is insufficient to balance transition-region
  radiative losses. An alternative picture is developed, consisting of a
  `transition region network' covering only a small fraction of the solar
  disk. The dissipation of mechanical energy, previously neglected in
  many calculations of theoretical transition region models, appears to
  play a dominant role in the local energy balance of the network.

---------------------------------------------------------
Title: A Gas-Dynamic Calculation of Type II Shock Propagation Through
    the Corona
Authors: Kopp, Roger A.
1972NASSP.308..252K    Altcode: 1972sowi.conf..252K
  No abstract at ADS

---------------------------------------------------------
Title: Gas-Magnetic Field Interactions in the Solar Corona
Authors: Pneuman, G. W.; Kopp, Roger A.
1971SoPh...18..258P    Altcode:
  It is evident from eclipse photographs that gas-magnetic field
  interactions are important in determining the structure and dynamical
  properties of the solar corona and interplanetary medium. Close to
  the Sun in regions of strong field, the coronal gas can be contained
  within closed loop structures. However, since the field in these
  regions decreases outward rapidly, the pressure and inertial forces
  of the solar wind eventually dominate and distend the field outward
  into interplanetary space. The complete geometrical and dynamical
  state is determined by a complex interplay of inertial, pressure,
  gravitational, and magnetic forces. The present paper is oriented
  toward the understanding of this interaction. The `helmet' streamer
  type configuration with its associated neutral point and sheet currents
  is of central importance in this problem and is, therefore, considered
  in some detail.

---------------------------------------------------------
Title: On the interpretation of coronal properties from type III
    radio burst measurements.
Authors: Kopp, R. A.; Pneuman, G. W.
1971BAAS....3Q.262K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Interaction of Coronel Material with Magnetic Fields
Authors: Pneuman, G. W.; Kopp, R. A.
1971IAUS...43..526P    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Emissions from the Sun. (Book Reviews: Introduction to the
    Solar Wind)
Authors: Kopp, Roger A.
1970Sci...169R1195K    Altcode: 1970Sci...169R1195B
  No abstract at ADS

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Title: Coronal Streamers. III: Energy Transport in Streamer and
    Interstreamer Regions
Authors: Pneuman, G. W.; Kopp, Roger A.
1970SoPh...13..176P    Altcode:
  The geometrical and dynamical structure of a corona consisting of
  streamer and interstreamer regions is examined. The present paper is
  an extension of previous works of this series in that energy transport
  processes are included in the theoretical framework of the model. Under
  specified conditions at some reference level above the coronal base,
  the structure at larger distances is determined by simultaneous
  integration of the continuity, momentum, and energy equations for each
  region subject to the condition for a lateral balance of magnetic and
  gas pressure at all levels. Outward thermal conduction and convection
  by the solar wind are assumed to be the processes contributing to the
  energy balance of each region, the magnetic field effectively thermally
  insulating one region from the other.

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Title: Coronal Streamer Configurations with Energy Transport
Authors: Pneuman, G. W.; Kopp, Roger A.
1969BAAS....1T.289P    Altcode:
  No abstract at ADS

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Title: Magnetic Fields and the Temperature Structure of the
    Chromosphere-Corona Interface
Authors: Kopp, Roger A.; Kuperus, Max
1968SoPh....4..212K    Altcode:
  The temperature structure of the transition region between the
  chromosphere and corona is discussed in the context of current ideas
  about magnetic fields in these layers. Magnetic channeling of the
  downward conductive heat flow from the corona into the regions of
  enhanced field at the supergranulation boundaries is proposed as a
  mechanism for explaining the measured intensities of solar ultraviolet
  emission lines which originate in layers with temperatures below
  10<SUP>5</SUP> °K. It is shown that nearly all of the observed
  ultraviolet line emission originates in interspicule regions, and that
  this emission plays an important part in the energy balance of the
  cooler layers of the transition region. It is suggested that certain
  motions observed in the upper chromosphere may represent the earliest
  visual evidence for conversion of inflowing conduction energy into
  kinetic motions.

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Title: Magnetic Fields and the Temperature Structure of the
    Chromosphere-Corona Interface.
Authors: Kopp, Roger A.; Kuperus, Max
1968AJS....73Q..67K    Altcode:
  The temperature structure of the transition region between the
  chromosphere and corona is discussed in the context of current ideas
  about magnetic fields in these layers. Magnetic channeling of the
  downward conductive heat flow from the corona into the regions of
  enhanced field at the supergranulation boundaries is proposed as a
  mechanism for explaining the measured intensities of solar ultraviolet
  lines which are emitted by layers with temperatures below 10~ 0K. It is
  suggested that nearly all of the observed ultraviolet line emission
  originates in interspicule regions, and that this emission plays
  an important part in the energy balance of the cooler layers of the
  transition region.

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Title: The Equilibrium Structure of a Shock-Heated Corona.
Authors: Kopp, Roger Alan
1968PhDT.........2K    Altcode:
  No abstract at ADS

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Title: The Transition to Adiabatic Flow in Hydrodynamic Models of
    the Solar Wind.
Authors: Kopp, Roger A.
1965AJ.....70Q.682K    Altcode:
  Quantitative models of the outer solar corona (R/R0. &gt; 2) and
  interplanetary gas have been constructed by a simultaneous solution
  of the solar wind equations expressing conservation of mass, energy,
  and momentum. These models, all of which exhibit supersonic flow
  beyond some critical distance r~, have vanishing temperature at
  infinity. For a variety of mass and (total) energy fluxes, models
  have been calculated and compared for the following situations:
  (a) Unrestricted heat flow by thermal conduction at all distances
  (i.e., infinitesimal heat flow theory used to evaluate the transport
  coefficient for thermal conduction). (b) Heat flow by conduction
  restricted at large heliocentric distances by the spiralling
  interplanetary magnetic field. (c) Heat flow depressed at large
  distances below that of case (a) due to the fact that the solar
  plasma must support a noninfinitesimal heat flux (or, equivalently,
  that the fractional temperature change over a mean free path becomes
  large at great distances, thereby invalidating the linear heat theory
  approach). (d) Heat flow cut off at large distances by both of the
  effects (b) and (c). The numerical results indicate that, at least for
  the equatorial regions of the solar corona, restrictions (b) and (c)
  on the radial conductive heat flux are sufficient to ensure that the
  gas flow is rapidly becoming adiabatic by the time the plasma reaches
  the vicinity of earth. Turbulence and plasma instabilities, which lead
  to kinking of the magnetic field lines and further reduction of the
  radial heat flow, should enhance this effect.

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Title: The Abundance of Iron in the Solar Photosphere.
Authors: Goldberg, Leo; Kopp, Roger A.; Dupree, Andrea K.
1964ApJ...140..707G    Altcode:
  New laboratory measurements of the absolute f-values of Fe 1 lines by
  Corliss and Warner (1964) have made possible a new determination of
  the abundance of iron in the solar photosphere. Of the 628 lines used
  to obtain the curve of growth by the method of weighting functions,
  the majority fall on the linear branch of the curve and have lower
  excitation potentials in the range 3-5 eV. Since their mean optical
  depths of formation are as large as 0.6, it seems unlikely that the
  lines are significantly affected by departures from LTE. The resulting
  abundances appear to be independent of excitation potential, but seem
  to increase slightly with increasing wavelength. The average value
  of the derived abundance, log NF,/NH + 12 00 = 6.64, is in very good
  agreement with other modern determinations.