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