Author name code: kopp-roger ADS astronomy entries on 2022-09-14 author:"Kopp, Roger A." ------------------------------------------------------------------------ Title: Metal Forming: General and Economic Aspects Authors: Kopp, R. Bibcode: 2011emst.book.5408K Altcode: In a solidified state, metallic materials, which include steel, are plastically formed to a permanent set by forces applied externally. Title: The Gradual Phase of Flares Authors: Svestka, Z. F.; Poletto, G.; Fontenla, J.; Hick, P.; Kopp, R. A.; Sylwester, B.; Sylwester, J. Bibcode: 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 Title: Expected Spectroscopic Signatures of Siphon Flows on Coronal Loops - Doppler Dimming and Doppler Shifts Authors: Kopp, R.; Spadaro, D.; Ventura, R. Bibcode: 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. Title: Working group 3: Coronal streamers Authors: Kopp, Roger A. Bibcode: 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. Title: Observational Signatures of Nanoflare Heating Authors: Poletto, G.; Kopp, R. Bibcode: 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. Title: A quasi-steady model of a microflare-heated corona Authors: Poletto, G.; Kopp, R. A. Bibcode: 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. Title: Working group 1: Coronal streamers Authors: Kopp, R. A. Bibcode: 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. Title: Coronal heating via nanoflares Authors: Poletto, Giannina; Kopp, Roger Bibcode: 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. Title: Coronal Heating by Nanoflares: Individual Events and Global Energetics Authors: Kopp, R. A.; Poletto, G. Bibcode: 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. Title: Coronal heating via nanoflares Authors: Poletto, G.; Kopp, R. Bibcode: 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. Title: Theory of coronal streamer formation. Authors: Kopp, Roger A. Bibcode: 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. Title: Theory of coronal streamer formation Authors: Kopp, R. A. Bibcode: 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. Title: A Semi-analytical Model of Stellar Flares Authors: Kopp, R. A.; Poletto, G. Bibcode: 1992LNP...397..295K Altcode: 1992sils.conf..295K No abstract at ADS Title: Largescale Quasi-Stationary X-Ray Coronal Structures Associated with Eruptive Solar Flares Authors: Kopp, R. A.; Poletto, G. Bibcode: 1992LNP...399..197K Altcode: 1992esf..coll..197K; 1992IAUCo.133..197K No abstract at ADS Title: Coronal Heating by Nanoflares: Plasma Dynamics of Elementary Events (With 2 Figures) Authors: Kopp, R. A.; Poletto, G. Bibcode: 1991mcch.conf..634K Altcode: No abstract at ADS Title: Formation and cooling of the giant HXIS arches of November 6 7, 1980 Authors: Kopp, R. A.; Poletto, G. Bibcode: 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. Title: Coronal heating by nanoflares: Plasma dynamics of elementary events Authors: Kopp, Roger A.; Poletto, Giannina Bibcode: 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. Title: A semi-analytical model of stellar flares Authors: Kopp, Roger A.; Poletto, Giannina Bibcode: 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. Title: A Simple Model for the Stellar Analogy of Compact Solar Flares Authors: Kopp, R. A.; Poletto, G. Bibcode: 1990ASPC....9..119K Altcode: 1990csss....6..119K No abstract at ADS Title: Hydrodynamics of the inner solar corona Authors: Kopp, Roger A. Bibcode: 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. 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. Bibcode: 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. Title: A simple model for the stellar analogy of compact solar flares Authors: Kopp, R. A.; Poletto, G. Bibcode: 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. Title: Modeling of coronal magnetic fields during solar flares Authors: Kopp, R. A.; Poletto, G. Bibcode: 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. Title: Intercomparison of numerical models of flaring coronal loops. Authors: Kopp, R. A.; Fisher, G. H.; MacNiece, P.; McWhirter, R. W. P.; Peres, G. Bibcode: 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. Title: Modeling of long-duration two-ribbon flares on M dwarf stars. Authors: Poletto, G.; Pallavicini, R.; Kopp, R. A. Bibcode: 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. Title: The magnetic geometry and structure of the giant post-flare arch of 21 22 May, 1980 Authors: Poletto, G.; Kopp, R. A. Bibcode: 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). Title: The determination of coronal fieldline connectivity from photospheric flare observations Authors: Kopp, R. A.; Poletto, G. Bibcode: 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. Title: Modeling of long-decay stellar flares on EQ Peg and Prox Cen Authors: Pallavicini, R.; Poletto, G.; Kopp, R. A. Bibcode: 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. Title: Magnetic modelling of giant HXIS arches Authors: Kopp, R. A.; Poletto, G. Bibcode: 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. Title: Topology of Reconnected Magnetic Fields after Two-Ribbon Flares Authors: Kopp, R. A.; Poletto, G. Bibcode: 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. Title: On the origin of HXIS arches Authors: Kopp, R. A.; Poletto, G. Bibcode: 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. Title: Coronal Mass Balance and a Time-Dependent Model of Transition-Region Downflows in the Chromospheric Network Authors: Kopp, R. A. Bibcode: 1987BAAS...19..650K Altcode: No abstract at ADS 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. Bibcode: 1986epos.conf.5.41W Altcode: 1986epos.confE..41W No abstract at ADS 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. Bibcode: 1986epos.conf..5.5W Altcode: 1986epos.confE...5W No abstract at ADS 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. Bibcode: 1986epos.conf.5.20W Altcode: 1986epos.confE..20W No abstract at ADS Title: Magnetic field re-arrangement after prominence eruption. Authors: Kopp, R. A.; Poletto, G. Bibcode: 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. Bibcode: 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. Bibcode: 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 = smax 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 E1 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1982uxsa.coll....2B Altcode: 1982IAUCo..73....2B No abstract at ADS Title: Heating and acceleration of the solar wind. Authors: Kopp, R. A. Bibcode: 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. Bibcode: 1981sowi.conf...42K Altcode: No abstract at ADS Title: A Semi-Analytical Approach to Time-Dependent Coronal Expansion Authors: Kopp, R. A. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1977chhs.conf..179K Altcode: No abstract at ADS Title: Energy Balance and Structure of Active Regions Authors: Kopp, R.; Orrall, F. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 r2 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 × 105 erg cm)= 13.46 - 2.99 sin2 s−1 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. Bibcode: 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. Bibcode: 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. Bibcode: 1971BAAS....3Q.262K Altcode: No abstract at ADS Title: Interaction of Coronel Material with Magnetic Fields Authors: Pneuman, G. W.; Kopp, R. A. Bibcode: 1971IAUS...43..526P Altcode: No abstract at ADS Title: Emissions from the Sun. (Book Reviews: Introduction to the Solar Wind) Authors: Kopp, Roger A. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 105 °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 Bibcode: 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 Bibcode: 1968PhDT.........2K Altcode: No abstract at ADS Title: The Transition to Adiabatic Flow in Hydrodynamic Models of the Solar Wind. Authors: Kopp, Roger A. Bibcode: 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. Title: The Abundance of Iron in the Solar Photosphere. Authors: Goldberg, Leo; Kopp, Roger A.; Dupree, Andrea K. Bibcode: 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.