Author name code: svestka ADS astronomy entries on 2022-09-14 author:"Svestka, Zdenek" ------------------------------------------------------------------------ Title: Sixty Years in Solar Physics Authors: Švestka, Zdeněk Bibcode: 2010SoPh..267..235S Altcode: 2010SoPh..tmp..235S; 2010SoPh..tmp..211S I recount my career in solar physics beginning at Ondřejov Observatory in 1948 and ending with my ∼30 year stay at the Laboratory of Space Research in Utrecht. Title: The Misnomer of ``Post-Flare Loops'' Authors: Švestka, Zdeněk Bibcode: 2007SoPh..246..393S Altcode: Attention is drawn to the fact that the term "post-flare loops" is incorrect and should be avoided, because the loops are parts of the flare itself. Two other names for these loop systems are suggested. Title: Editorial Appreciation Authors: Engvold, Oddbjørn; Harvey, Jack; Leibacher, John; Sakurai, Takashi; Švestka, Zdeněk; van Driel-Gesztelyi, Lidia; Solar Physics editors Bibcode: 2006SoPh..233....1E Altcode: No abstract at ADS Title: Preface Authors: Rottman, G.; Woods, T.; George, V.; Harvey, J.; Švestka, Z.; Engvold, O. Bibcode: 2005SoPh..230....1R Altcode: No abstract at ADS Title: Evidence Linking Slow Solar Wind Streams to Long-Decay X-Ray Events Authors: Švestka, Zdeněk; Fárník, František Bibcode: 2005SoPh..229..305S Altcode: Outflow of slow solar wind from solar active regions has been reported in recent years by many different authors. Therefore, in this paper we have studied synoptic maps of the solar wind density (SWD) based on interplanetary scintillation (IPS) data for available parts of all the years 1991-1994 and 1997-2001 to verify correlations of maxima in SWD with sources in active regions. We have found convincing evidence that eruptive flares in active regions, and thus X-ray long-decay events (LDEs) in general, can produce short-lived enhancements of the SWD. However, we were not able to get statistically convincing evidence that active regions can be permanent sources of slow solar wind, and propose three possible reasons for this negative result. Title: Editorial Authors: Engvold, Oddbjorn; Harvey, Jack; Švestka, Zdenek Bibcode: 2005SoPh..229....1E Altcode: No abstract at ADS Title: Hard x-ray Pulsations in the Initial Phase of Flares Authors: Fárník, F.; Karlický, M.; Švestka, Z. Bibcode: 2003SoPh..218..183F Altcode: When analyzing light curves of hard X-ray bursts recorded by the Hard X-Ray Spectrometer on board the MTI satellite, we have found three events (all associated with major solar flares, two of them in the same active region) which show pulsations in the very initial phase of the burst. Periods of the pulsations range from 25 to 48 s. We compare them with other observations of pulsations of radio waves and in X-rays and conclude that pulsations of this kind have not been observed before. We mention several possible causes and prefer interactions between current-carrying loops as the most likely interpretation of the observed variations. Title: Solar activity Authors: Švestka, Z. Bibcode: 2003dysu.book..237S Altcode: What is the active Sun which is a very important factor in our life? Observations from SOHO and TRACE reveal the highly turbulent nature of Sun's surface and its atmospheric layers: all the time and everywhere we see brightness variations, loop formations and decays, plasma flows and ejections of gas. However, this is not what we call solar activity. The real processes called solar activity appear only in limited parts of the solar surface, and their occurrence varies quasi-periodically with time, creating 11-year cycles of solar activity whose main characteristics are described in this chapter. Particular attention is paid to coronal mass ejections, as the most important phenomenon affecting the Earth. Title: Preface Authors: Lin, R.; Dennis, B.; Benz, A.; Harvey, J.; Engvold, O.; švestka, Z. Bibcode: 2002SoPh..210....1L Altcode: No abstract at ADS Title: X-ray Jets in Interconnecting Loops Authors: Fárník, František; Švestka, Zdeněk. Bibcode: 2002SoPh..206..143F Altcode: We present examples of X-ray jets, observed by the Soft X-ray Telescope on board Yohkoh, which followed trajectories of transequatorial interconnecting loops (TILs). All these TILs were preexisting, seen some time before, but were mostly invisible at the time of the onset of the jet which often made them bright along their total length. With few exceptions, these TIL-associated jets have properties very similar to other jets ejected inside active regions or along open field lines (footpoints in X-ray bright points, recurrence, strong collimation, average speed close to 350 km s−1), but may reach larger lengths, in our examples up to 450 000 km. Exceptions are one jet that moved slower and one that had no brightened area at its supposed source region at the time of its origin (an X-ray bright point appeared there only 3 hours later). It appears that quite a high number of X-ray jets may be of this TIL-associated kind. Title: Flare Changes Associated with Peaks of Hard X-Ray Bursts Authors: Farnik, F.; Svestka, Z.; Karlicky, M. Bibcode: 2002cosp...34E1403F Altcode: 2002cosp.meetE1403F Using the high-resolution records made in four energy channels by the Hard X-Ray Spectrometer (HXRS) on board the MTI spacecraft (launched on 12 March 2000) we try to refine the study made by Dwivedi et al. 18 years ago (Dwivedi, B.N., Hudson, H.S., Kane, S.R., and Svestka, Z.: 1984, Solar Phys. 90, 331) who looked for changes in the flare development associated with changes in the hard X-ray flux. In addition to H-alpha and SOHO data we can, at least for some flares, also use high-resolution TRACE images which make it possible to see fine changes which could not be detected before. We try to find, in particular, which parts of flares produce hard X ray peaks of various hardness in the HXRS records and we also- compare them with peaks in microwave records. Intense peaks often correspond to flaring structures penetrating into strong magnetic fields (penumbrae and umbrae of sunspots) which generally confirms Dwivedi et al.'s findings. However, we can provide more details than they were able to obtain from their data with worse space and time resolution. Title: X-Ray Jets in Interconnecting Loops Authors: Fárník, F.; Švestka, Z. Bibcode: 2002mwoc.conf...81F Altcode: We present several examples of X-ray jets, observed by the SXT onboard Yohkoh, which followed trajectories of transequatorial interconnecting loops (TILs). All these TILs were preexisting, seen some time before, but mostly invisible at the time of the onset of the jet which often made them bright along their total length. With few exceptions, these TIL-associated jets have properties very similar to other jets ejected inside active regions or along open field lines (footpoints in X-ray bright points, recurrence, strong collimation, average speed between 340 and 380 km s-1, but may reach very large lengths, in excess of 450 000 km. Exceptions are one jet that moved slower and one that had no brightened area at its source region at the time of its origin (an X-ray bright point appeared there only 3 hours later). It appears that less than 20% of X-ray jets are of this kind. Title: Locations of Footpoints of Transequatorial Interconnecting Loops Authors: Fárník, František; Karlický, Marian; Švestka, Zdeněk. Bibcode: 2001SoPh..202...81F Altcode: We discuss footpoints of loops seen by Yohkoh in soft X-rays that connect active regions across the equator (transequatorial interconnecting loops - TILs). While most TILs are rooted in moderately strong fields at peripheries of active regions, there are also cases when these loops are anchored in very weak or very strong fields, ranging from < 30 G to several hundred gauss. Some have their footpoints near sunspot penumbrae, creating `X-ray fountains' in a combination with active region loops. But TILs are never rooted in sunspots. The most likely explanation is that magnetic field lines leave spots almost vertically so that TILs rooted in them extend high into the corona and density in them is below the limit of visibility in X-rays. The fact that in force-free modeling some TILs are rooted in sunspots is most probably due to the difference between field-line connections in `vacuum' and in the highly conductive plasma on the Sun. Some TILs end before they reach active regions which sometimes may indicate the real situation, but mostly this `gap' is probably due to a temperature decrease near the loop footpoints which makes them invisible in X-rays. In that case the fact that these cool lowest parts of TILs are never found in TRACE or SOHO EIT images indicates that plasma density in TILs must be very low. Still, the total absence of any counterparts of X-ray TILs in TRACE and EIT images is puzzling and, therefore, other possible interpretations of the `gap' origin are also briefly mentioned. Title: Varieties of Coronal Mass Ejections and Their Relation to Flares Authors: Švestka, Zdeněk. Bibcode: 2001SSRv...95..135S Altcode: Most coronal mass ejections (CMEs) start as coronal storms which are caused by an opening of channels of closed field lines along the zero line of the longitudinal magnetic field. This can happen along any zero line on the Sun where the configuration is destabilized. If the opening includes a zero line inside an active region, one observes a chromospheric flare. If this does not happen, no flare is associated with the CME in the chromosphere, but the process, as well as the response in the corona (a Long Decay Event in X-rays) remains the same. The only difference between flare-associated and non-flare-associated CMEs is the strength of the magnetic field in the region of the field line opening. This can explain essentially all differences which have been observed between these two kinds of CMEs. However, there are obviously also other sources of CMEs, different from coronal storms: sprays (giving rise to narrow, pointed ejections), erupting interconnecting loops (often destabilized by flares), and growing coronal holes. This paper tries to summarize and interpret observations which support this general picture, and demonstrates that both CMEs and flares must be properly discussed in any study of solar-terrestrial relations. Title: Solar Flares: Main Phase Authors: Švestka, Z. Bibcode: 2000eaa..bookE2290S Altcode: After the impulsive phase of a flare is over (see SOLAR FLARES: IMPULSIVE PHASE), we talk about the main phase or gradual phase. Most FLARES (often called compact or confined flares) are short lived and they simply cool during the main phase, decaying within minutes or tens of minutes. However, there is also another kind of flares (eruptive flares) which continue to release energy during their ma... Title: Helioseismic Diagnostics of Solar Convection and Activity Authors: Svestka, Zdenek; Harvey, John W. Bibcode: 2000hdsc.conf.....S Altcode: This book focuses on the recent advances in our understanding of solar convection and activity, and on new methods and results of helioseismic diagnostics of the internal structures and dynamics of solar convection and active regions. The methods of local helioseismology (time-distance tomography, ring-diagram analysis, acoustic imaging, and holography) intensively developed in the past few years have provided promising results on the deep structure of large-scale convection and flows, emerging active regions, and sunspots. The book includes reviews and contributed papers presented at the SOHO-9 Workshop held on July 12-15, 1999, at Stanford University, California, U.S.A. It provides a comprehensive overview of the current status of the field and presents new ideas and approaches to helioseismic diagnostics and theoretical modeling of the physical processes inside the Sun. The book is recommended for graduate students and specialists in solar physics, astrophysics, and geophysics. Link: http://www.wkap.nl/book.htm/0-7923-6520-8 Title: Helioseismic diagnostics of solar convection and activity. Part 1, 2. Proceedings. SOHO-9 Workshop, Stanford, CA (USA), 12 - 15 Jul 1999. Authors: Švestka, Z.; Harvey, J. W.; Kosovichev, A. G.; Duvall, T. L., Jr. Bibcode: 2000SoPh..192....1S Altcode: The following topics were dealt with: theories of solar convection, rotation and activity, helioseismic tomography, acoustic imaging and holography, ring-diagram analysis, magnetic fields and oscillations, solar cycle variations of the internal structure and rotation, solar convective structures and oscillations. Title: Solar activity: An overview Authors: Švestka, Zdenek Bibcode: 1999CSci...77.1503S Altcode: No abstract at ADS Title: G. Burkhardt, U. Esser, H. Hefele, I. Heinrich, W. Hofmann, V. R. Matas, L. D. Schmadel, R. Wielen, and G. Zech (eds.), Astronomy and Astrophysics Abstracts, Volumes 69A and 69B Authors: Švestka, Z. Bibcode: 1999SoPh..188..217S Altcode: No abstract at ADS Title: Quiet solar wind signatures above active regions observed in X-rays Authors: Hick, P.; Svestka, Z.; Jackson, B. V.; Farnik, F.; Hudson, H. Bibcode: 1999AIPC..471..231H Altcode: 1999sowi.conf..231H X-ray images from the Yohkoh satellite, obtained following occurrences of limb flares sometimes show coronal fan-like structures extending above a growing post-flare loop system. We show one such event observed in AR 7270 on the east limb of the Sun on 28/29 August 1992. We suggest that these rays are `ministreamers,' formed as a result of the re-structuring of the corona following the occurrence of a flare-associated CME. Synoptic maps of the solar wind density, constructed from a tomographic analysis of interplanetary scintillation (IPS) measurements, show enhanced scintillation matching the position of AR 7270 if we assume a radial outflow at a reasonable slow solar wind speed of 400 km s-1. From this agreement we argue that outflow of mass occurs from the active region into interplanetary space. Title: Long transequatorial interconnecting loops of the new solar cycle Authors: Fárník, F.; Karlický, M.; Švestka, Z. Bibcode: 1999SoPh..187...33F Altcode: We study two long transequatorial loops connecting high-latitude regions of the new solar cycle. These loops (with lengths of 47 and 61 heliographic degrees) provide evidence that the upper length limit of 37° found by Chase et al. (1976) from Skylab data was determined simply by the typical distances between northern and southern active regions during the period of Skylab observations. We find strong support for the idea that these long interconnecting loops originate through reconnection of field lines extending from the two active regions towards and beyond the equator, and confirm the earlier finding by Canfield, Pevtsov, and McClymont (1996) that only field lines from active regions with the same chirality reconnect. As we are not aware of any longitudinal (E-W) loops of comparable lengths, we suggest that it is mainly the solar differential rotation which drives the reconnection of latitudinal (N-S) field lines. 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: Large-Scale Active Coronal Phenomena in Yohkoh SXT Images IV. Solar Wind Streams from Flaring Active Regions Authors: Švestka, Zdeněk; Fárník, František; Hudson, Hugh S.; Hick, Paul Bibcode: 1998SoPh..182..179S Altcode: We demonstrate limb events on the Sun in which growing flare loop systems are embedded in hot coronal structures looking in soft X-rays like fans of coronal rays. These structures are formed during the flare and extend high into the corona. We analyze one of these events, on 28-29 August 1992, which occurred in AR 7270 on the eastern limb, and interpret these fans of rays either as temporary multiple ministreamers or plume-like structures formed as a result of restructuring due to a CME. We suggest that this configuration reflects mass flow from the active region into interplanetary space. This suggestion is supported by synoptic maps of solar wind sources constructed from scintillation measurements which show a source of enhanced solar wind density at the position of AR 7270, which disappears when 5 days following the event are removed from the synoptic map data. We also check synoptic maps for two other active regions in which existence of these fan-like structures was indicated when the active regions crossed both the east and west limbs of the Sun, and both these regions appear to be sources of a density enhancement in the solar wind. Title: Fan-Like coronal X-ray Structures as Sources of Solar Wind Authors: Hick, P.; Svestka, Z.; Farnik, F.; Hudson, H. S.; Jackson, B. V. Bibcode: 1998AAS...192.1503H Altcode: 1998BAAS...30..840H We show coronal soft X-ray images from the Yohkoh satellite, obtained following occurrences of limb flares. These images show rising post-flare loops, which are embedded in hot coronal structures looking like fans of coronal rays. We analyze the event on 28/29 August 1992, which occurred in AR 7270 on the east limb of the Sun. We suggest that these rays are multiple 'ministreamers', which apparently are formed as a result of the restructuring of the corona following the occurrence of a flare-associated CME. We argue that this configuration allows outflow of mass from the active region into interplanetary space. This is supported by synoptic maps of solar wind sources constructed from scintillation measurements showing a source of enhanced scintillation at the position of AR 7270. Title: Post-Flare Structures Rising with Decreasing or Constant Speed Authors: Svestka, Z.; Farnik, F. Bibcode: 1998ASSL..229..365S Altcode: 1998opaf.conf..365S No abstract at ADS Title: A Window to the West Authors: Svestka, Zdenek Bibcode: 1998fyc..conf...75S Altcode: No abstract at ADS Title: Large-Scale Active Coronal Phenomena in YOHKOH SXT Images. III. Enhanced Post-Flare Streamer Authors: Švestka, Zdeněk; Fárník, František; Hick, Paul; Hudson, Hugh S.; Uchida, Yutaka Bibcode: 1997SoPh..176..355S Altcode: We demonstrate several events where an eruptive flare close to the limb gave rise to a transient coronal streamer visible in X-rays in Yohkoh SXT images, and analyze one of these events, on 28-29 October 1992, in detail. A coronal helmet streamer began to appear 2 hours after the flare, high above rising post-flare loops; the streamer became progressively narrower, reaching its minimum width 7-12 hours after the flare, and widened again thereafter, until it eventually disappeared. Several other events behaved in a similar way. We suggest that the minimum width indicates the time when the streamer became fully developed. All the time the temperature in the helmet streamer structure was decreasing, which can explain the subsequent fictitious widening of the X-ray streamer. It is suggested that we may see here two systems of reconnection on widely different altitudes, one giving rise to the post-flare loops while the other creates (or re-forms) the coronal helmet streamer. A similar interpretation was suggested in 1990 by Kopp and Polettofor post-flare giant arches observed on board the SMM; indeed, there are some similarities between these post-flare helmet streamers and giant arches and, with the low spatial resolution of SMM instruments, it is possible that some helmet streamers could have been considered to be a kind of a giant arch. Title: Solar Physics Announces CD-ROM Authors: Svestka, Zdenek; Howard, Robert F.; Engvold, Oddbjorn Bibcode: 1997SoPh..176..443S Altcode: No abstract at ADS Title: Post-Flare Loops Embedded in a Hot Coronal Fan-Like Structure Authors: Švestka, Z.; Fárnik; Hudson, H. S.; Hick, P. Bibcode: 1997ESASP.415..139S Altcode: 1997cpsh.conf..139S No abstract at ADS Title: Observations of Faint, Outlying Loop Systems in Large Flares Authors: Neidig, Donald F.; Švestka, Zdeněk; Cliver, Edward W.; Airapetian, Vladimir; Henry, Timothy W. Bibcode: 1997SoPh..170..321N Altcode: Faintly visible, darkened regions in Hα lying outside but adjacentto bright flare emissionwere found to occur in 10 of 31 major flares investigated. Without exception, the darkenings occur over `magnetically neutral' areas, and these are usually bordered by ridges ofoppositely-poled field, where one border is shared in common with a flare ribbon. Thedarkenings probably result from the formation of faint, outlying loop systems, similar topost-flare loops seen in absorption, but which are connected to magnetic features outsidethe flare and are unresolved or only marginally resolved in patrol images. Simple modelsfor post-flare loops incorporating the results of statistical equilibrium calculations readilydemonstrate that darkenings of several percent (consistent with our photometric measurements) can be produced by loop structures of cross-sectional diameter ≈ 102 km (unresolved by patrol instruments) and containing gas at densities 5 × 1010-5 × 1011 cm-3 andtemperatures 8000-15000 K. Outlying loop systems might be formed by magnetic fieldreconnection, analogous to the mechanism ascribed to eruptive two-ribbon flares, butassociated with field structures adjacent to the flare. Alternatively, these outlying loopsystems may not erupt but become visible as a result of heating and chromospheric evaporation at the footpoints shared with the flare ribbon. In either case, the observations presented here have interesting implications for both the spatial scale and the topology of thecoronal magnetic fields in which eruptions occur. Title: The first results from SOHO. Authors: Fleck, B.; Švestka, Z. Bibcode: 1997frfs.book.....F Altcode: This volume contains papers reporting the first scientific results from the SOHO mission as well as descriptions of the in-flight performance of some of the instruments. A CD-ROM with multimedia material is included as an integral part of this volume. Reprinted from Sol. Phys., Vol. 170, No. 1 (Jan 1997) (see AAA, Vol. 67) and Vol. 175, No. 2 (Oct 1997) (see AAA, Vol. 68). Title: Speeds of Rising Post-Flare Structures Authors: Švestka, Zdeněk Bibcode: 1996SoPh..169..403S Altcode: There are basically two kinds of post-flare coronal structures: those rising with decreasing speed, and others which rise with constant speed for a long period of time. As a rule, those structures with decreasing speed are post-flare loop systems, while those rising with constant speed are postflare giant arches. However, there are exceptions. We demonstrate several cases of post-flare loop systems which rise with constant speed for many hours, three of them observed by Yohkoh. These observations imply that the Kopp and Pneuman interpretation of post-flare loops as sequentially reconnecting open field lines cannot be generally valid. The most likely interpretation is that all post-flare loop systems start with the Kopp and Pneuman process, but in some of them later-formed loops begin to be continuously heated; thus they cease to cool and begin to expand into the corona. This kind of post-flare loops might represent an intermediate stage between the ordinary post-flare loops and post-flare giant arches. Title: Book reviews Authors: Howard, R. F.; van den Oord, G. H. J.; Švestka, Z. Bibcode: 1996SoPh..169..225H Altcode: No abstract at ADS Title: Large-scale active coronal phenomena in Yohkoh SXT images Authors: Fárník, František; Švestka, Zdeněk; Hudson, Hugh S.; Uchida, Yutaka Bibcode: 1996SoPh..168..331F Altcode: 1996SoPh..168..331U We discuss Yohkoh SXT observations of stationary giant post-flare arches which occurred on 3-6 May, 1992 and study in detail the last arch, associated with the flare at 19:02 UT on 5 May, which extended above the west limb. The arch was similar to the first giant arch discovered on board the SMM, on 21-22 May, 1980. We demonstrate that the long lifetimes of these structures necessarily imply additional energy input from the underlying active region: otherwise, conduction would cool these arches in less than one hour and even with the unlikely assumption of conduction inhibited, pure radiative cooling would not produce the temperature decrease observed. All arch tops, although varying in brightness, stayed for several days at a fairly constant altitude of ∼ 100 000 km, and the arch studied, on 5-6 May, was just a new brightening of the pre-existing decaying structure. The brightening was apparently due to inflow of hot plasma from the flare region. Yohkoh data confirm that these stationary arches are rare phenomena when compared with the rising arches studied in Paper I and with Uchida et al.'s expanding active regions. Title: Flare-like dynamic phenomena Authors: Rompolt, B.; Švestka, Z. Bibcode: 1996AdSpR..17d.115R Altcode: 1996AdSpR..17..115R Using data from Skylab, SMM, and Yohkoh spacecraft, as well as Hα observations on the ground, we summarize the present knowledge about dynamic phenomena on the Sun which usually are not classified as flares, although they resemble processes observed in flares, often are associated with flares, and sometimes can be considered for special kinds of flares. This involves field openings outside active regions (eruptive flares without chromospheric response), loop eruptions, with emphasis on brightenings (and possibly eruptions) of loops which interconnect active regions, sprays, flaring arches (injections of hot and cool plasma into closed field configurations), Hα and X-ray surges (injections of hot and cool plasma into `open' fields), X-ray jets, recently discovered by Yohkoh, as well as Hα jets observed at Wroclaw and Ottawa. We will try to find relationships between all the latter phenomena so that one gets a more homogeneous picture of plasma injections and jets observed on the Sun. There are many active phenomena on the Sun which usually are not classified as flares, although they closely resemble processes observed in flares, or are very often, and quite typically, associated with flares. Some of them are even caused by the same kind of instability that produces flares. Title: Large-Scale Active Coronal Phenomena in YOHKOH SXT Images Authors: Svestka, Z.; Farnik, F.; Hudson, H. S.; Uchida, Y.; Hick, P. Bibcode: 1996ASPC..111..388S Altcode: 1997ASPC..111..388S The authors have checked in Yohkoh SXT images the appearance of giant post-flare arches which were discovered in hard X-ray images from the HXIS and FCS instruments onboard the SMM. They have verified the existence of both the rising and stationary arches. In addition to these two kinds of giant post-flare arches, known before from SMM observations, Yohkoh also reveals other large post-flare coronal structures which might have been considered to be giant arches by the low-resolution SMM instruments. These include coronal helmet streamers above rising flare loops or fans of hot structures in which the rising loops are embedded. Title: Large-Scale Active Coronal Phenomena in YOHKOH SXT Images Authors: Svestka, Z.; Farnik, F.; Hudson, H. S.; Uchida, Y.; Hick, P.; Lemen, J. R. Bibcode: 1996mpsa.conf..609S Altcode: 1996IAUCo.153..609S No abstract at ADS Title: Coronal phenomena associated with flares. Authors: Svestka, Z. Bibcode: 1996joso.proc..135S Altcode: The paper reviews various kinds of large-scale coronal phenomena which are associated with solar flares. Particular attention is paid to Hα and X-ray observations of "post"-flare loops and to recent Yohkoh observations of slowly expanding giant arches and extensive "ray" structures embedding flare loop systems. Title: Large-Scale Active Coronal Phenomena in YOHKOH SXT Images, I Authors: Švestka, Zdeněk; Fárník, František; Hudson, Hugh S.; Uchida, Yutaka; Hick, Paul; Lemen, James R. Bibcode: 1995SoPh..161..331S Altcode: We have found several occurrences of slowly rising giant arches inYohkoh images. These are similar to the giant post-flare arches previously discovered by SMM instruments in the 80s. However, we see them now with 3-5 times better spatial resolution and can recognize well their loop-like structure. As a rule, these arches followeruptive flares with gradual soft X-ray bursts, and rise with speeds of 1.1-2.4 km s−1 which keep constant for >5 to 24 hours, reaching altitudes up to 250 000 km above the solar limb. These arches differ from post-flare loop systems by their (much higher) altitudes, (much longer) lifetimes, and (constant) speed of growth. One event appears to be a rise of a transequatorial interconnecting loop. Title: On `The Solar Flare Myth' postulated by Gosling Authors: Švestka, Zdeněk Bibcode: 1995SoPh..160...53S Altcode: The `Solar Flare Myth' postulated by Gosling (1993) is a misunderstanding. It is true that most sources of coronal mass ejections (CMEs) cannot be classified as flares in the common old sense of that word. However, just for this reason the term `eruptive flare' has been introduced for all solar active phenomena in which an opening of field lines is involved and which lead to magnetic-field and mass ejections resulting in a CME. The process is essentially the same in all events, irrespective of' whether only adisparition brusque without any chromospheric brightening or a major two-ribbon flare is involved in it; the only difference is the different strength of the magnetic field in which the process was accomplished. The major two-ribbon (cosmic-ray) flares clearly represent the most energetic events of this kind, and, therefore, it is very misleading to claim that solar flares in general are phenomena with very little importance for solar-terrestrial physics. Title: A comparison of solar activity during the decline of several solar cycles Authors: Svestka, Z. Bibcode: 1995AdSpR..16i..27S Altcode: 1995AdSpR..16R..27S This review summarizes the general characteristics of solar activity during the declining part of solar cycles and compares the behavior of the Sun during several last cycles. Different characteristics of solar activity are considered and tentative reasons for their different behavior in different cycles are suggested. The activity decline is usually very irregular, characterized by quiet periods interrupted by temporary bursts of activity. These bursts can be quite impressive: actually, as a rule, the most outstanding events of solar activity do not occur at the cycle maximum, but shortly before it, or a few years later. The duration of quiet periods between activity enhancements increases as the cycle declines, but even close to the solar minimum one may still encounter quite interesting flare events. From the point of view of solar-terrestrial relations, these late events are particularly favorable, because their effects in interplanetary space and in planetary magnetospheres can be followed much easier than during high solar activity: one can uniquely ascribe the observed consequencies in space to their isolated sources on the Sun. Title: Book Review: Planetary systems : formation, evolution and detection / Kluwer, 1994 Authors: Solanki, S. K.; Švestka, Zdeněk; Svestka, Z. Bibcode: 1995SoPh..159..403S Altcode: 1995SoPh..159..403B No abstract at ADS Title: Flare-Associated Darkenings in H-Alpha: Possible Evidence for Faint Outlying, Unresolved Loop Systems Authors: Neidig, D. F.; Cliver, E. W.; Svestka, Z.; Airapetian, V.; Henry, T. W. Bibcode: 1995SPD....26.1215N Altcode: 1995BAAS...27..986N No abstract at ADS Title: The Participation of Nuclei in Type-Iii Related Electron Streams Authors: Kallenrode, May-Britt; Svestka, Zdenek Bibcode: 1994SoPh..155..121K Altcode: We study 27 increases of the flux of 300-800 keV electrons on board HELIOS A or B, associated with intense type III radio bursts close to perihelion passages of the two spacecraft, during the solar minimum. Electrons can be detected inside cones with an angular width between 30° and 60°. Though only intense type III bursts are associated with recognizable electron events in space, such an association does not exist for all of them; this fact and great differences in fluxes of the individual events indicate that, apart from the intensity, also some other charactefistic of the type III burst acceleration or propagation process determines the resulting flux of electrons in space; the energy spectrum of the accelerated electrons is one of the likely candidates. A comparison of the electron flux in these events with the flux of 1.7-3.7 MeV nucl−1 helium reveals very large variations of the helium/electron flux ratio, by a factor of at least 15 and possibly much higher. We demonstrate that these variations are not caused by propagation effects in interplanetary space. Therefore, they must be due either to propagation effects in the solar corona or, more likely, to intrinsic variations in the relative production of electrons and nuclei in the type III burst process. An extrapolation of the observed fluxes to 1 AU shows that in only 7 of the 27 electron events studied might a marginal > 1.7 MeV helium flux be recognized ar the Earth distance. Title: On the Occurrence of Blue Asymmetry in Chromospheric Flare Spectra Authors: Heinzel, Petr; Karlicky, Marian; Kotrc, Pavel; Svestka, Zdenek Bibcode: 1994SoPh..152..393H Altcode: We present observations of optical spectra of a flare in which blue line asymmetry was seen for more than 4 min close to the flare onset. The maximum blue asymmetry coincided with the maximum of a hard X-ray and microwave burst. We discuss possible interpretations of the blue asymmetry and conclude that the most plausible one is electron-beam heating with return current. Although this process predicts downflows in the lower transition region and upper chromosphere, its ultimate effect on the line profiles can be blue asymmetry: the upper layers moving away from us absorb the radiation of the red peak thus lowering its intensity in comparison to the blue one. Title: Slow-mode oscillations of large-scale coronal loops Authors: Svestka, Zdenek Bibcode: 1994SoPh..152..505S Altcode: On several occasions, repetitive X-ray brightenings, sometimes accompanied by mass injections into adjacent loops, appeared quasi-periodically with mean periods close to 20 minutes. In all cases when X-ray images were available, the sites of these brightenings were in active regions which were associated with large-scale coronat loops of length (2 − 3) × 105 km. Therefore, the primary source of these long-periodic pulsations might be slow-mode oscillations in these large-scale loops. Free MHD oscillations, proposed earlier by Roberts, Edwin, and Benz (1984), may fit the observed data. Title: Book-Review - Space Science Dictionary Authors: Kleczek, J.; Ckeczkova, H.; Svestka, Z. Bibcode: 1994SoPh..151..203K Altcode: No abstract at ADS Title: Book review Authors: Švestka, Z. Bibcode: 1994SoPh..151..203S Altcode: No abstract at ADS Title: X-Ray Observations of a Major Eruptive Flare Behind the Limb Authors: Smith, Kermit L.; Strong, Keith T.; Švestka, Zdeněk; McCabe, Marie K. Bibcode: 1994SoPh..149..363S Altcode: We analyze X-ray images and spectra of a coronal structure which extended to altitudes over 130 000 km above an eruptive flare located 20° behind the western solar limb. The images were obtained by the Flat Crystal Spectrometer (FCS) and the spectra were obtained by the Bent Crystal Spectrometer (BCS) aboard the SMM spacecraft. Images in OVIII and MgXI lines cover the period from before the flare onset (which occurred at 22:31 UT on 16 February, 1986) through 17 UT on 17 February and were used for determination of temperature and emission measure within the structure. BCS obtained CaXIX spectra of the coronal event, benefiting from the occultation of the active region behind the solar limb. Title: Large-Scale Coronal Structures Associated with Solar Activity (Invited) Authors: Svestka, Z.; Farnik, F. Bibcode: 1994scs..conf..243S Altcode: 1994IAUCo.144..243S The authors summarize observations of filament eruptions, post-flare loops, giant post-flare arches, flaring arches, surges, coronal responses to chromospheric brightenings, and interconnecting loops, made by Skylab and SMM, and confront some of them with soft X-ray observations recently made by Yohkoh. It seems likely that many structures observed by Yohkoh are the same phenomena that were seen before, but it may be sometimes difficult to identify them correctly. Title: Book-Review - Astronomy and Astrophysics Abstracts - Index - V.51-55 Authors: Burkhardt, B.; Esser, U.; Hefele, H.; Heinrich, I.; Hofmann, W.; Krahn, D.; Matas, V. R.; Schmadel, L. D.; Wielen, R.; Zech, G.; Svestka, Z. Bibcode: 1993SoPh..148..177B Altcode: No abstract at ADS Title: Book review Authors: Švestka, Z. Bibcode: 1993SoPh..148..177S Altcode: No abstract at ADS Title: Book-Review - the YOHKOH Solar-A Mission Authors: Svestka, Z.; Uchida, Y.; Farnik, F. Bibcode: 1993SSRv...64..367S Altcode: No abstract at ADS Title: An Analysis of SKYLAB X-Ray Pictures of a Giant Coronal Arch Authors: Simberova, Stanislava; Karlicky, Marian; Svestka, Zdenek Bibcode: 1993SoPh..146..343S Altcode: The limb event of 13/14 August, 1973, imaged by Skylab in soft X-rays, proved to be a giant arch, quite similar to those observed in 1980-1986 on SMM. High spatial resolution (by a factor of 4-5 better than in SMM data) made it possible to see the internal structure of the arch. Its brightest part consisted of loops very similar to, but higher than, post-flare loops, surrounded by a rich system of weak loop structures extending up to altitudes of 260 000 km. While the main brightest structure of the arch was newly formed, the weak very large loops had existed above the active region before and were only enhanced during the event. Title: Responses of large-scale coronal structures to chromospheric activity Authors: Farnik, Frantisek; Hick, Paul; Svestka, Zdenek Bibcode: 1993SoPh..146..313F Altcode: We have followed the transit of two active regions across the western solar limb during June 29 through July 2, 1980, as imaged in 3.5-16 keV X-rays by HXIS aboard the SMM. During frequent brightenings of large-scale coronal structures, hard X-ray emission in the 11-16 keV energy band was recorded up to altitudes of 76 000 km. Soft X-rays could be seen in excess of 250 000 km altitude above the photospheric active region. Many X-ray brightenings low in the corona in the active regions were followed by enhancements high in the corona in the large-scale coronal structures. Although subsequent enhancements rarely appeared in the same position, similar portions of the corona brightened intermittently, indicating that the general configuration of the coronal structures above the active regions did not change much, in spite of the frequent energy inputs. These inputs were of two kinds: nonthermal, with very fast response at high coronal altitudes within seconds or tens of seconds, and thermal, with a delay of several minutes. The nonthermal response is short-lived, reflecting the time profile of the primary source; the thermal response is more gradual and longer lasting than the primary source. In some enhancements of large-scale coronal structures both these kinds of response occur and can be clearly recognized. There are also active-region hrightenings without any response in the high corona and,vice versa, high-corona brightenings without any obvious primary source; in the latter case, it is likely that the source was hidden behind the limb. Title: Book-Review - the YOHKOH Solar-A Mission Authors: Svestka, Z.; Uchida, Y.; Bromage, B. Bibcode: 1993Obs...113..165S Altcode: No abstract at ADS Title: Editorial Authors: de Jager, Cornelis; Howard, Robert F.; švestka, Zdeněk Bibcode: 1993SoPh..143D...7D Altcode: No abstract at ADS Title: Book-Review - Eruptive Solar Flares Authors: Svestka, Z.; Jackson, B. V.; Machado, M. E.; Sylwester, J. Bibcode: 1993SSRv...65..186S Altcode: No abstract at ADS Title: X-Ray Observations of Limb Flare Loops and Post-Flare Coronal Arch Authors: Svestka, Zdenek; Smith, Kermit L.; Strong, Keith T. Bibcode: 1992SoPh..139..405S Altcode: We present observations of another post-flare arch following an eruptive flare, detected in X-ray lines above the western solar limb on 2 May 1985. Title: Book-Review - the YOHKOH / Solar-A Mission Authors: Svestka, Z.; Uchida, Y. Bibcode: 1992JBAA..102R.109S Altcode: No abstract at ADS Title: Book-Review - the YOHKOH Solar-A Mission Authors: Svestka, Z.; Uchida, Y. Bibcode: 1992JBAA..102Q.109S Altcode: No abstract at ADS Title: Book-Review - the YOHKOH Solar-A Mission Authors: Svestka, Z.; Uchida, Y. Bibcode: 1992Sci...256R.253S Altcode: No abstract at ADS Title: The Birth of Giant Post-Flare Arches Authors: Poletto, G.; Svestka, Z. Bibcode: 1992SoPh..138..189P Altcode: Using short accumulation times, we have succeeded in the detection in HXIS images of the initial growth of the giant post-flare arch of 6 November, 1980 at 14:44 UT and part of the initial growth of the giant arch of 7 November, 1980 at 04:30 UT. These observations are relevant to the problem of the origin of giant arches: the fact that the arch of 6 November was imaged more than half an hour before the first flare loops had been recorded in the associated flare, proves that giant arches cannot: be interpreted as upper products of the reconnection process that creates the growing systems of flare loops (as the original interpretation by Švestka et al. (1982a) suggested). However, also the alternative hypothesis by Poletto and Kopp (1988) that these structures originate through a reconnection process in a peripheral, large-scale configuration meets with difficulties: after the initial rise, the maximum brightness in both arches seems to descend, until a much slower rise was resumed about two hours later. Title: Editorial Authors: de Jager, Cornelis; Švestka, Zdeněk; Howard, Robert F. Bibcode: 1992SoPh..137D...5D Altcode: No abstract at ADS Title: History and Basic Characteristics of Eruptive Flares Authors: Svestka, Z.; Cliver, E. W. Bibcode: 1992LNP...399....1S Altcode: 1992esf..coll....1S; 1992IAUCo.133....1S We review the evolution of our knowledge and understanding of the eruptive (dynamic, two-ribbon) flare phenomenon. Starting with the first observation of a white-light flare by Carrington and Hodgson in 1859, we cover in succession the highlights: Hale's invention of the spectroheliograph in 1892 and the spectrohelioscope in 1926 started flare observations in H. The institution of a world-wide flare patrol brought significant advances in knowledge of flares in the 1930s and 1940s and new windows were opened to observe flares at short (SID) and long (radio) wavelengths. In the 1950s and 1960s metric radio bursts were related to trapped energetic electrons and shocks, and two-ribbon flares were associated with energetic protons in space. Radio and X-ray observations gave evidence for two basic types of flare processes: an impulsive phase followed by a long-duration or gradual phase. It was found that flares were often preceded by filament activations, and growing loop prominence systems were recognized as the limb counterpart of two-ribbon disk flares. The early 1970s brought Skylab observations of coronal mass ejections (CMEs) and arcades of coronal soft X-ray loops above two-ribbon flares. In the mid-1970s, the Kopp-Pneuman reconnection model, based on configurations proposed earlier by Carmichael, Sturrock, and Hirayama, provided a framework in which the newly discovered CMEs could be related to the basic characteristics of two-ribbon flares. The 1980s brought, key new results from SMM and Hinotori including images of hard X-ray flares and large-scale coronal structures associated with eruptive flares. In the conclusion, we summarize the basic characteristics of eruptive flares. Title: Eruptive Solar Flares Authors: Svestka, Zdenek; Jackson, Bernard V.; Machado, Marcos E. Bibcode: 1992LNP...399.....S Altcode: 1992IAUCo.133.....S; 1992esf..coll.....S This is an exhaustive survey of present-day solar research including both theory and observations. It deals with eruptive flares, filament eruption in x-rays and radio waves, energy release and transport, and terrestrial response to solar flares. Details of the most recent SOLAR-A project (launched shortly after the conference) are also presented. Title: A Giant Post-Flare Coronal Arch Observed by SKYLAB Authors: Svestka, Z.; Simberova, S. Bibcode: 1992LNP...399..221S Altcode: 1992esf..coll..221S; 1992IAUCo.133..221S The limb event of 13 August 1973, observed by Skylab in soft X-rays, exhibited typical characteristics of the giant post-flare arches observed by HXIS and FCS on board SMM in the 1980s. We present here examples of the processed Skylab images which yield 4 times better angular resolution than the SMM experiments and thus, for the first time, make it possible to distinguish the real fine structure of a giant post-flare arch. Title: A Giant Coronal Arch Observed by Skylab Authors: Švestka, Zdeněk Bibcode: 1991SoPh..135..419S Altcode: The limb event of 13 August 1973, observed by Skylab in soft X-rays, has all the typical characteristics of the giant post-flare arches observed by HXIS and FCS on board SMM in the 1980s. Skylab images provide us with 4-5 times better angular resolution than the SMM experiments and thus, for the first time, make it possible to distinguish the real fine structure of a giant post-flare arch. The image processing of the 13/14 August 1973 event is now in progress. Title: Book-Review - Astronomy and Astrophysics Abstracts V.49A/B Authors: Burghardt, G.; Esser, U.; Hefele, H.; Heinrich, I.; Hofmann, W.; Krahn, D.; Matas, V. R.; Schmadel, L. D.; Wielen, R.; Zech, G.; Svestka, Z. Bibcode: 1991SoPh..134..411B Altcode: No abstract at ADS Title: Book reviews Authors: Švestka, Z. Bibcode: 1991SoPh..134..411S Altcode: No abstract at ADS Title: Flaring Arches - Part Three Authors: Fontenla, Juan M.; Svestka, Zdenek; Farnik, Frantisek; Tang, Frances Y. Bibcode: 1991SoPh..134..145F Altcode: We show detailed observations in X-rays, UV lines, and Hα of an extended arch, about 300000 km long, which developed as a consequence of a compact subflare. This subflare occurred in an `included' magnetic polarity of relatively low magnetic field strength (compared to that of the sunspots). The apparition of this big arch was preceded by that of a smaller arch, about 30000 km long, which masked the polarity inversion line filament in the early phase of the subflare. The big arch which developed later, around the time of the main X-ray and UV spike of the subflare, connected the included polarity and the main leading sunspot of the region, and became fully developed in a few minutes. The fact that both arches were simultaneously observed in all spectral domains as well as their fine structure in Hα can only be explained by considering the arch as composed of several unresolved portions of material having widely different temperatures. The Hα observations can be interpreted as showing the appearance of this cool material as a result of condensation, but a more appealing interpretation is that there was almost simultaneous ejection of superhot (107 K), hot (106 K), mild (105 K), and cool (104 K) material from the subflare site along previously existing magnetic tubes of much lower density. The termination of the subflare was marked by a rather hard X-ray and UV spike which appeared to originate in a different structure than that of the main spike. The material in the arch gradually cooled and drained down after the end of the subflare. Title: Book reviews Authors: Hudson, H. S.; Kleczek, J.; Švestka, Z. Bibcode: 1991SoPh..133..403H Altcode: No abstract at ADS Title: The YOHKOH (Solar-A) Mission : a series of invited contributions Authors: Svestka, Zdenek; Uchida, Yutaka Bibcode: 1991ysam.book.....S Altcode: 1991QB526.F6Y64.... No abstract at ADS Title: Needs and constraints for solar flares space-borne cooperative programs. Authors: Svestka, Z. Bibcode: 1991AdSpR..11e.115S Altcode: 1991AdSpR..11Q.115S There are three basic reasons for cooperation in space observations of flares: (1) observations in different spectral regions, (2) stereoscopic observations, and (3) in situ data. Using experience from the past and considering the planned experiments, problems encountered by flare-related cooperative programs on spacecraft are briefly summarized. Title: The YOHKOH (SOLAR-A) mission. A series of invited contributions. Authors: Švestka, Z.; Uchida, Y. Bibcode: 1991yohk.book.....S Altcode: The SOLAR-A spacecraft was launched by the Institute of Space and Astronautical Science, Japan (ISAS) in August 1991, and, following an ISAS tradition, was renamed YOHKOH. This mission is dedicated principally to the study of solar flares, especially of high-energy phenomena observed in the X- and gamma-ray ranges. With a coordinated set of instruments including hard X-ray and soft X-ray imaging telescopes as well as spectrometers with advanced capabilities, it will reveal many new aspects of flares and help better understand their physics, supporting international collaborations with ground-based observatories as well as theoretical investigations. An overview of this mission, including the satellite, its scientific instruments, and its operation, is given. Title: Evolution of Hot Plasma in Flares Authors: Svestka, Zdenek F. Bibcode: 1991LNP...387..165S Altcode: 1991fpsa.conf..165S This review discusses, in particular, X-ray manifestations of the development of hot flare plasma during the cooling phase of flares. In a preexisting coronal configuration, a small flare source can excite much larger coronal loops and arches, of which only the footpoints become visible if their density is low, or their whole structures can be seen if density is high enough. Flaring arches, through which both cool and, hot plasma flows from the primary flare source to a secondary footpoint, are the most spectacular phenomena of this kind. In other cases the flaring loops did not exist before, but have been newly formed during the flare process. These are the eruptive flares, in which the preflare field lines are first disrupted and subsequently reconnect. The main part of this review is devoted to the development of hot plasma in this particular kind of flaring structures. It is emphasized that X-ray observations of growing systems of loops in eruptive flares, and giant arches following these flares high in the corona, require large fields of view pointed for several hours at the active region in which the flare occurred. This makes their observations with SOLAR-A rather difficult, but one should realize that SOLAR-A represents the only means for studying these coronal components of the most important solar flares until, at least, the end of this century. Title: Real-time simulation of a potential magnetic field in a post-flare arch Authors: Poletto, Giannina; Svestka, Zdenek Bibcode: 1990SoPh..129..363P Altcode: We analyze the X-ray observations on 7-8 November of the last revival of a giant coronal arch first observed in the morning hours of 6 November, 1980. We compare these data with observations of earlier revivals of this arch, in order to determine whether the successive brightenings repeat without any apparent modification, or whether they show a varying behavior as they keep occurring. We also examine the magnetic structure of the revived arches in order to ascertain whether the subsequent phenomena involve the same magnetic configuration. The information about the magnetic structure of the last revival is the best we have, because the revival started close to the time of the Kitt Peak magnetogram which has been used for the magnetic modelling of the whole series of these giant arches. Title: X-Ray Bright Surges Authors: Svestka, Zdenek; Farnik, Frantisek; Tang, Frances Bibcode: 1990SoPh..127..149S Altcode: We present evidence of X-ray emission from surges that are bright in Hα. These surges have many features common to flaring arches of Martin and Švestka (1988); the basic difference between the two is that in flaring arches cold and hot plasma are injected into clearly defined closed magnetic loops, while in the surges the injection goes into large-scale magnetic field structures of which the second footpoint is usually unknown. Because of the steep density gradient in such large-scale structures, the X-ray visibility of bright surges is limited to a few tens of seconds only. A series of repetitive surges, some of them bright and emitting X-rays, occurred on 8 July, 1980 from footpoints of two large-scale coronal structures, which might have been the legs of an enormous arch at least 600 Mm long. Title: Book-Review - Astronomy and Astrophysics Abstracts Authors: Esser, U.; Hefele, H.; Heinrich, I.; Hofmann, W.; Krahn, D.; Matas, V. R.; Schmadel, L. D.; Zech, G.; Svestka, Z. Bibcode: 1990SoPh..126..411E Altcode: No abstract at ADS Title: Book Review: The sun: an introduction / Springer-Verlag Authors: Mewe, R.; Švestka, Z.; Mewe, R. Bibcode: 1990SoPh..126..411M Altcode: 1990SoPh..126..411S No abstract at ADS Title: Book-Review - Astronomy and Astrophysics Abstracts V.44 Authors: Bohme, S.; Svestka, Z. Bibcode: 1989SoPh..119..420B Altcode: No abstract at ADS Title: Book Review: Solar and stellar physics. / Springer-Verlag, 1987 Authors: Poletto, Giannina; Dimitrov, D. L.; Švestka, Z.; Poletto, G. Bibcode: 1989SoPh..119..419P Altcode: 1989SoPh..119..419S No abstract at ADS Title: Flaring Arches - Part Two Authors: Svestka, Zdenek; Farnik, Frantisek; Fontenla, Juan M.; Martin, Sara F. Bibcode: 1989SoPh..123..317S Altcode: We discuss first the development of the coronal arch-shaped structure of ∼ 57000 km length which was born at or before 08:00 UT on 6 November, 1980 and became the site of 13 quasi-periodic brightenings in hard X-rays from 10:00 to 14:30 UT. The same structure became the site of a series of 17 flaring arches between 15:30 and 24:00 UT on that day. The periodicity of ∼ 19 min, defined well for the quasi-periodic variations, seems to be partly retained during the occurrence of the flaring arches. Title: The Footpoints of Giant Arches Authors: Martin, Sara F.; Svestka, Zdenek F.; Bhatnagar, Arvind Bibcode: 1989SoPh..124..339M Altcode: We have detected chromospheric footpoints of the giant post-flare coronal arches discovered by HXIS a few years ago. Hα photographs obtained at Big Bear and Udaipur Solar Observatories show chromospheric signatures associated with 5 sequential giant arch events observed in the interval from 6 to 10 November, 1980. The set of footpoints at one end of the arches consists of enhancements within a plage at the northeast periphery of the active region and the set of footpoints at the other end of the arch consists of brightenings of the chromosphere south of the active region. Both sets of footpoints show very slow brightness variations correlated in time with the brightness variations of the X-ray arches. Current-free modelling of the coronal magnetic field by Kopp and Poletto (1989), based on a Kitt Peak magnetogram, confirms the identification of the two sets of footpoints by showing magnetic field lines connecting them. Title: Solar Flares - the Gradual Phase Authors: Svestka, Zdenek Bibcode: 1989SoPh..121..399S Altcode: 1989IAUCo.104..399S One has to distinguish between two kinds of the gradual phase of flares: (1) a gradual phase during which no energy is released so that we see only cooling after the impulsive phase (a confined flare), and (2) a gradual phase during which energy release continues (a dynamic flare). Title: Book-Review - Astronomy and Astrophysics Abstracts Authors: Esser, U.; Hefele, H.; Heinrich, I.; Hofmann, W.; Krahn, D.; Matas, V. R.; Schmadel, L. D.; Zech, G.; Svestka, Z. Bibcode: 1989SoPh..124..193E Altcode: No abstract at ADS Title: Book-Review - Reports on Astronomy Transactions of the International Astronomical Union Authors: Švestka, Zdeněk Bibcode: 1989SoPh..122..191S Altcode: No abstract at ADS Title: Editorial Authors: de Jager, Cornelis; Švestka, Zdeněk; Howard, Robert F. Bibcode: 1989SoPh..121D...9D Altcode: No abstract at ADS Title: Giant solar arches and coronal mass ejections in November 1980 Authors: Svestka, Zdenek F.; Jackson, Bernard V.; Howard, Russell A.; Sheeley, Neil R., Jr. Bibcode: 1989SoPh..122..131S Altcode: Using data from the SOLWIND coronagraph and photometers aboard HELIOS-A we examine coronal mass ejections from an active region which produced a series of giant post-flare coronal arches. HXIS X-ray observations reveal that in several cases underlying flares did not disrupt these arch structures, but simply revived them, enhancing their temperature, density and brightness. Thus we are curious to know how these quasi-stationary X-ray structures could survive in the corona in spite of recurrent appearances of powerful dynamic flares below them. We have found reliable evidence that two dynamic flares which clearly revived the preexisting giant arch were not associated with any mass ejection. After two other flares, which were associated with mass ejections, the arch might have been newly formed when the ejection was over. In one of these cases, however, the arch had typical characteristics of a revived structure so that it is likely that it survived a powerful mass ejection nearby. In a magnetic configuration of the arch which results from potential-field modelling (Figure 1(b)) such a survival seems possible. Title: Book Review: The physics of solar flares. / CUP, 1988 Authors: Svestka, Z. Bibcode: 1989SoPh..122..192S Altcode: 1989SoPh..122..192T No abstract at ADS Title: Coronal mass ejections and coronal structures. Authors: Hildner, E.; Bassi, J.; Bougeret, J. L.; Duncan, R. A.; Gary, D. E.; Gergely, T. E.; Harrison, R. A.; Howard, R. A.; Illing, R. M. E.; Jackson, B. V.; Kahler, S. W.; Kopp, K.; Low, B. C.; Lantos, P.; Phillips, K. J. H.; Poletto, G.; Sheeley, N. R., Jr.; Stewart, R. T.; Svestka, Z.; Waggett, P. W.; Wu, S. T. Bibcode: 1989epos.conf..493H Altcode: The work of this team was concerned with modelling of post-flare arches, the reconnection theory of flares, the slow variation of coronal structure, and the coronal and interplanetary detection, evolution, and consequences of mass ejections. Title: Book-Review - Astronomy and Astrophysics Abstracts Authors: Bohme, S.; Svestka, Z. Bibcode: 1988SoPh..115..409B Altcode: No abstract at ADS Title: Solar and interplanetary observations of the mass ejection on 7 May, 1979 Authors: Jackson, Bernard V.; Rompolt, Bogdan; Svestka, Zdenek Bibcode: 1988SoPh..115..327J Altcode: We present observations of a mass ejection that was observed by five different instruments along its way from the solar surface to more than 100 solar radii. The instruments involved are the ground-based Hα coronagraph at Wrocław, the white-light SOLWIND coronagraph on board the P78-1 satellite, zodiacal light photometers of the HELIOS B spacecraft, in situ plasma detectors and magnetometers on board the HELIOS B spacecraft, and interplanetary scintillation measurements on the ground. By using a CAT-scan analysis of the images obtained by the SOLWIND coronagraph near the Earth and HELIOS B photometers placed at 0.3 AU perpendicular to the Earth-Sun line, we have been able to get a three-dimensional density reconstruction of the mass ejection and fit the best velocity curve for its propagation. Although problems exist in smoothly joining the height-time curves (for instance, we had to reduce the brightness of the SOLWIND data by more than a factor of two to make the data sets agree photometrically), both this analysis and direct measurements by the other experiments clearly indicate higher speeds at greater distances from the Sun. The plasma acceleration in this case was obviously not limited only to distances within 3 R0, as is usually the case, but continued beyond the outer limit of the coronagraph view at ∼ 8 R0. Title: Book Review: The early universe. / Reidel, 1987 Authors: Kleczek, J.; Švestka, Z.; Kleczek, J. Bibcode: 1988SoPh..115..409K Altcode: 1988SoPh..115..409U No abstract at ADS Title: Book reviews Authors: Schindler, K.; Švestka, Zdeněk Bibcode: 1988SoPh..114..193S Altcode: No abstract at ADS Title: Book Review: The galaxy and the solar system. / U Arizona Press, 1986. Authors: Kotov, V. A.; Kostik, R.; Shchukina, N.; Švestka, Zdeněk; Kotov, V. A. Bibcode: 1988SoPh..115..203K Altcode: 1988SoPh..115..203S No abstract at ADS Title: Flaring Arches - Part One Authors: Martin, Sara F.; Svestka, Zdenek F. Bibcode: 1988SoPh..116...91M Altcode: `Flaring arches" is a name assigned to a particular component of some flares. This component consists of X-ray and Hα emission which traverses a coronal arch from one to the other of its chromospheric footpoints. The primary footpoint is at the site of a flare. The secondary footpoint, tens of thousands of kilometers distant from the source flare, but in the same active region, brightens in Hα concurrent with the beginning of the hard X-ray burst at the primary site. From the inferred travel time of the initial exciting agent we deduce that high speed electron streams travelling through the arch must be the source of the initial excitation at the secondary footpoint. Subsequently, a more slowly moving agent gradually enhances the arch first in X-rays and subsequently in Hα, starting at the primary footpoint and propagating along the arch trajectory. The plasma flow in Hα shows clearly that material is injected into the arch from the site of the primary footpoint and later on, at least in some events, a part of it is also falling back. Title: Book-Review - Solar Radiophysics Authors: McLean, D. J.; Labrum, N. R.; Svestka, Z. Bibcode: 1988SoPh..115R.204M Altcode: No abstract at ADS Title: Book-Review - Progress in Solar Physics Authors: de Jager, C.; Svestka, Z. Bibcode: 1988ApL&C..26..372D Altcode: 1988ApL....26..372D No abstract at ADS Title: Soft X-ray observations of large-scale coronal structures Authors: Svestka, Zdenek Bibcode: 1988AdSpR...8k..81S Altcode: 1988AdSpR...8...81S This paper draws attention to large-scale structures in the solar corona which have been observed only in soft X-rays. Some of them were seen on Skylab in 1973 with poor time resolution, some other aboard the SMM with poor spatial resolution. The Soft X-ray Telescope on SOLAR-A can see them with both kinds of resolution improved by an order of magnitude, provided that it images large enough field of view. Three kinds of structures are of particular interest: (a) Loops that interconnect active regions, even on opposite hemispheres. Observations of their birth may provide information both on the basic characteristics of solar activity and on solar atmospheric processes (reconnection). Their brightenings, losely related to flares, could contribute to our knowledge of instabilities in the solar corona. (b) Flaring arches inside active regions. They appear in extensive coronal structures which may exist for days and intermittently brighten in association with intense X-ray bursts. (c) Giant arches which appear for many hours high in the corona after dynamic flares. Their structure, mode of birth, and their relation to coronal mass ejections, is presently unknown. Title: Thermal Structures Associated with Post-Flare Coronal Arches Authors: Hick, Paul; Svestka, Zdenek Bibcode: 1987SoPh..108..315H Altcode: Shortly after the dynamic flare of 14 ∶ 44 UT on 6 November, 1980, which initiated the second revival in the sequence of post-flare coronal arches of 6-7 November, a moving thermal disturbance was observed in the fine field of view of HXIS. From 15 ∶ 40 UT until about 18 UT, when it left the field of view, the disturbance rose into the corona, as indicated by a projected velocity of 7.4 km s-1 in the south-east direction. The feature was located above the reconnection region of the dynamic flare and was apparently related to the revived coronal arch. Observations in the coarse field of view after 18 UT revealed a temperature maximum in the revived arch, rising with a velocity of 7.0 km s-1 directly in continuation of the thermal disturbance. The rise velocity of the disturbance was initially (at least until 17 ∶ 20 UT) very similar to the rise velocities observed for the post-flare loop tops of the parent flare. This suggests that the rise of the reconnection point, in the Kopp and Pneuman (1976) mechanism responsible for the rise of the loop tops, also dictates the rise of the disturbance. From energy requirements it follows that in this phase the disturbed region is still a separate magnetic `island', thermally isolated from the old arch structure and the post-flare loops. After 18 UT the rise of the post-flare loop tops slowed down to 2 km s-1, which is significantly slower than the rise of the brightness and temperature maxima of the revived arch in the coarse field of view. Thus in this phase the Kopp and Pneuman mechanism is no longer directly responsible for the rise of the thermal structure and the rise possibly reflects the merging of the old and the new arch structures. Title: Post-flare coronal arches observed with the SMM/XRP Flat Crystal Spectrometer Authors: Hick, Paul; Svestka, Zdenek; Smith, Kermit L.; Strong, Keith T. Bibcode: 1987SoPh..114..329H Altcode: The phenomenon of post-flare coronal arches, initially discovered with the Hard X-Ray Imaging Spectrometer (HXIS), was investigated using observations made with the SMM Flat Crystal Spectrometer (FCS) on 20 through 23 January, 1985. Since these observations were made with a different type of instrument from HXIS, they provide independent information on the physical characteristics of the arch phenomenon and extend our knowledge to lower coronal temperatures. Title: Highlights of the Flare Build-Up Study Authors: Gaizauskas, V.; Svestka, Z. Bibcode: 1987SoPh..114..389G Altcode: Years of preparation within the framework of the Flare Build-up Study culminated with intensive observations of solar flares during the Solar Maximum Year (1979-1981). Scientists operating several spacecraft and roughly 70 ground-based observatories participated in an internationally coordinated effort to observe flares with higher spatial, spectral, and temporal resolution over a wider range of wavelengths than heretofore. The FBS stimulated important advances in theories of magnetic reconnection and the growth of plasma instabilities under preflare circumstances. A series of international FBS workshops facilitated data exchanges and collaborative studies for interpreting and synthesizing the wealth of new information about flares. The FBS ended officially at the Symposium on Synopsis of the Solar Maximum Analysis held 2-5 July, 1986 at the COSPAR meeting in Toulouse, France. Here we summarize highlights of its progress towards an understanding of the storage and release of preflare energy. Title: Multi-thermal observations of newly formed loops in a dynamic flare Authors: Švestka, Zdeněk F.; Fontenla, Juan M.; Machado, Marcos E.; Martin, Sara F.; Neidig, Donald F.; Poletto, Giannina Bibcode: 1987SoPh..108..237S Altcode: The dynamic flare of 6 November, 1980 (max ≈ 15:26 UT) developed a rich system of growing loops which could be followed in Hα for 1.5 hr. Throughout the flare, these loops, near the limb, were seen in emission against the disk. Theoretical computations of deviations from LTE populations for a hydrogen atom reveal that this requires electron densities in the loops close to, or in excess of 1012 cm -3. From measured widths of higher Balmer lines the density at the tops of the loops was found to be 4 x 1012 cm -3 if no non-thermal motions were present, or 5 × 1011 cm -3 for a turbulent velocity of ~ 12 km s -1. Title: Cooling of a Coronal Flare Loop Through Radiation and Conduction Authors: Svestka, Zdenek Bibcode: 1987SoPh..108..411S Altcode: A simple method is proposed for a computation of the cooling of coronal flare loops by radiation and conduction, for various temperatures, densities, and lengths of the loops. The relative importance of conductive and radiative losses is briefly discussed. Title: Book-Review - Progress in Solar Physics Authors: de Jager, C.; Svestka, Z.; Jordan, C. Bibcode: 1987Obs...107..130D Altcode: No abstract at ADS Title: Book-Review - Progress in Solar Physics Authors: de Jager, C.; Svestka, Z. Bibcode: 1987Sci...236R1009D Altcode: No abstract at ADS Title: Book Review: Of stars and men: reminiscences of an astronomer. / Adam Hilger, 1986. Authors: Svestka, Z. Bibcode: 1987Ap&SS.133..200S Altcode: 1987Ap&SS.133..200K No abstract at ADS Title: Book reviews Authors: Dyson, John; Švestka, Zdenêk; Kleczek, Josip Bibcode: 1987Ap&SS.133..199D Altcode: No abstract at ADS Title: Book reviews Authors: Hick, Paul; Jackson, B.; Švestka, Zdenek; Křivský, L. Bibcode: 1987SoPh..108..201H Altcode: No abstract at ADS Title: Book-Review - Astronomy and Astrophysics Abstracts V.42:2 Authors: Bohme, S.; Esser, U.; Hefele, H.; Heinrich, I.; Hofmann, W.; Krahn, D.; Matas, V. R.; Schmadel, L. D.; Zech, G.; Svestka, Z. Bibcode: 1987SoPh..114..193B Altcode: No abstract at ADS Title: Relationships among flare images at different wavelengths Authors: Svestka, Zdenek F. Bibcode: 1987SoPh..113...67S Altcode: 1982SoPh..113...67S The talk reviews briefly historical development of the imaging of the Sun, and flare imaging in particular, at different wavelengths. The present state is then critically analyzed, emphasizing and demonstrating problems related to simultaneity of observed data, differences in time resolution, limitations of the imaged field of view, unequal spatial resolution, and alignment of the images. Prospects for the future are briefly sketched, including imaging in very hard X-rays and γ-rays. Title: Flaring arches Authors: Martin, Sara F.; Švestka, Zdenek F. Bibcode: 1987SoPh..113..303M Altcode: 1982SoPh..113..303M No abstract at ADS Title: Solar and Interplanetary Observations of the Mass Ejection on 7 May 1979 Authors: Jackson, B. V.; Rompolt, B.; Svestka, Z. Bibcode: 1987sowi.conf..272J Altcode: No abstract at ADS Title: Book Review: Transactions of the IAU, Vol. XIXB. / Reidel, 1986. Authors: Svestka, Z. Bibcode: 1987SoPh..108..202S Altcode: No abstract at ADS Title: Interplanetary Effects of Coronal Mass Ejections Authors: Hildner, E.; Bassi, J.; Bougeret, J. L.; Duncan, R. A.; Gary, D. E.; Gergely, T. E.; Harrison, R. A.; Howard, R. A.; Illing, R. M. E.; Jackson, B. V.; Kahler, S. W.; Kopp, K.; Low, B. C.; Lantos, P.; Phillips, K. J. H.; Poletto, G.; Sheeley, N. R., Jr.; Steward, R. T.; Svestka, Z.; Waggett, P. W.; Wu, S. T. Bibcode: 1986epos.conf.6.52H Altcode: 1986epos.confF..52H No abstract at ADS Title: Initiations of Coronal Mass Ejections Authors: Hildner, E.; Bassi, J.; Bougeret, J. L.; Duncan, R. A.; Gary, D. E.; Gergely, T. E.; Harrison, R. A.; Howard, R. A.; Illing, R. M. E.; Jackson, B. V.; Kahler, S. W.; Kopp, K.; Low, B. C.; Lantos, P.; Phillips, K. J. H.; Poletto, G.; Sheeley, N. R., Jr.; Steward, R. T.; Svestka, Z.; Waggett, P. W.; Wu, S. T. Bibcode: 1986epos.conf.6.27H Altcode: 1986epos.confF..27H No abstract at ADS Title: The Slowly Varying Corona Near Solar Activity Maximum Authors: Hildner, E.; Bassi, J.; Bougeret, J. L.; Duncan, R. A.; Gary, D. E.; Gergely, T. E.; Harrison, R. A.; Howard, R. A.; Illing, R. M. E.; Jackson, B. V.; Kahler, S. W.; Kopp, K.; Low, B. C.; Lantos, P.; Phillips, K. J. H.; Poletto, G.; Sheeley, N. R., Jr.; Steward, R. T.; Svestka, Z.; Waggett, P. W.; Wu, S. T. Bibcode: 1986epos.conf.6.57H Altcode: 1986epos.confF..57H No abstract at ADS Title: Modelling of Coronal Mass Ejections and POST Flare Arches Authors: Hildner, E.; Bassi, J.; Bougeret, J. L.; Duncan, R. A.; Gary, D. E.; Gergely, T. E.; Harrison, R. A.; Howard, R. A.; Illing, R. M. E.; Jackson, B. V.; Kahler, S. W.; Kopp, K.; Low, B. C.; Lantos, P.; Phillips, K. J. H.; Poletto, G.; Sheeley, N. R., Jr.; Steward, R. T.; Svestka, Z.; Waggett, P. W.; Wu, S. T. Bibcode: 1986epos.conf6.366H Altcode: 1986epos.confF.366H No abstract at ADS Title: Book-Review - Progress in Solar Physics Authors: de Jager, C.; Svestka, Z. Bibcode: 1986S&T....72R.479D Altcode: No abstract at ADS Title: Flaring Arches in Hα and X-Rays Authors: Martin, S. F.; Svestka, Z. Bibcode: 1986BAAS...18Q.898M Altcode: No abstract at ADS Title: X-ray imaging of flare loops and coronal arches Authors: Svestka, Z. Bibcode: 1986sfcp.nasa...41S Altcode: HXIS (Hard X-ray Imaging Spectrometer) results related to preflare, flare-decay, and post-flare phases in the solar corona are summarized. Particularly discussed are miniflares, long-lived X-ray enhancements along filament channels, flare precursors (some signifying the flare position, others possibly related to the onset of mass ejections), growth of post-flare loops, images of sites of field-line reconnections late in the flare development, giant post-flare coronal arches with energy contents comparable to coronal transients, and hot loops interconnecting active regions. The extremely low HXIS background, in particular, made it possible to discover many new, previously unknown features in the solar corona. Also emphasized are some problems that have appeared during the evaluation of HXIS data, for the benefit of those who plan future hard X-ray imaging experiments. Title: Coronal interconnection of two active regions observed in 3.5 8.0 keV X-rays Authors: Farnik, F.; van Beek, H. F.; Svestka, Z. Bibcode: 1986SoPh..104..321F Altcode: Using HXIS data, we have studied the further development of the coronal arch extending towards the SE above active region No. 17255 in November 1980. The arch, studied originally by Švestka (1984) disappeared on 10 November (after pronounced revival), but since 9 November HXIS revealed another arch-like structure towards the SW. We have studied the development of this new structure which appeared to be most likely an arch interconnecting AR 17255 with AR 17251, located nearly 30° to the west. This interconnection revived many times during the following days with intensity varying with the activity in both active regions. We have estimated the physical characteristics in this coronal structure and compared them with observations of interconnecting loops made at lower energies by Skylab in 1973. The temperature (maximum values 7.5-14 × 106 K) and the density (1.1-5.0 × 109 cm−3) are found to be higher than in the Skylab loops (a result that could be expected because the HXIS energy range was harder than that of Skylab) and similar to the values deduced for the earlier arch system extending to the SE. However, much shorter decay times of the brightness variations indicate the presence of conduction in contrast to the SE arch in which conduction was clearly inhibited. This supports the assumption that the SE and SW coronal structures were two different phenomena. Title: Images of Post-Flare Coronal Structures in X-Rays Authors: Svestka, Z.; Hick, P. Bibcode: 1986SoPh..104..187S Altcode: This is an extended abstract of several papers mentioned in the references describing extensive coronal structures related to radio continua and imaged in > 3.5 keV X-rays. Title: Editorial Authors: de Jager, Cornelis; Švestka, Zdeněk Bibcode: 1986SoPh..107..200D Altcode: 1987SoPh..107..200D No abstract at ADS Title: Coronal mass ejection associated with the stationary post-flare arch of 21 22 May 1980 Authors: McCabe, Marie K.; Švestka, Zdeněk F.; Howard, Russell A.; Jackson, Bernard V.; Sheeley, Neil R. Bibcode: 1986SoPh..103..399M Altcode: By using a combination of X-ray (HXIS), Hα (Haleakala), white-light corona (Solwind), and zodiacal light (Helios) images on 21-22 May, 1980 we demonstrate, and try to explain, the co-existence of a coronal mass ejection with a stationary post-flare coronal arch. The mass ejection was seen, both by Solwind and Helios, in prolongation of the path of a powerful spray, whereas the active region filament did not erupt. A tentative comparison is made with other occurrences of stationary, or quasi-stationary post-flare coronal arches. Title: Observations of chromospheric flare dynamics at the next solar maximum specific recommendations of the Chromospheric Flare Dynamics Group. Authors: Canfield, R. C.; Gaizauskas, V.; Kurokawa, H.; Martin, S. F.; Svestka, Z. Bibcode: 1986lasf.conf..489C Altcode: No abstract at ADS Title: White light flares and atmospheric modeling (Working Group report). Authors: Machado, M. E.; Avrett, E. H.; Falciani, R.; Fang, C.; Gesztelyi, L.; Henoux, J. -C.; Hiei, E.; Neidig, D. F.; Rust, D. M.; Sotirovski, P.; Svestka, Z.; Zirin, H. Bibcode: 1986lasf.conf..483M Altcode: The authors give a short summary of their discussions, and a set of recommendations which may help in the study of white light flare emission processes. Title: Coronal mass ejections and coronal structures. Authors: Hildner, E.; Bassi, J.; Bougeret, J. L.; Duncan, R. A.; Gary, D. E.; Gergely, T. E.; Harrison, R. A.; Howard, R. A.; Illing, R. M. E.; Jackson, B. V.; Kahler, S. W.; Kopp, K.; Low, B. C.; Lantos, P.; Phillips, K. J. H.; Poletto, G.; Sheeley, N. R., Jr.; Stewart, R. T.; Svestka, Z.; Waggett, P. W.; Wu, S. T. Bibcode: 1986NASCP2439....6H Altcode: Contents: 1. Introduction. 2. Observations. 3. Initiation of coronal mass ejections - observations. 4. Modelling of coronal mass ejections and post-flare arches. 5. Interplanetary effects of coronal mass ejections. 6. The slowly varying corona near solar activity maximum. 7. Summary. Title: X-ray imaging of flare loops and coronal arches. Authors: Svestka, Z. Bibcode: 1986NASCP2421...41S Altcode: This paper summarizes HXIS results related to preflare, flare-decay, and post-flare phases in the solar corona. Particularly discussed are miniflares, long-lived X-ray enhancements along filament channels, flare precursors (some signifying the flare position, others possibly related to the onset of mass ejections), growth of post-flare loops, images of sites of field-line reconnections late in the flare development, giant post-flare coronal arches with energy contents comparable to coronal transients, and hot loops interconnecting active regions. The extremely low HXIS background, in particular, made it possible to discover many new, previously unknown features in the solar corona. Also emphasized are some problems that have appeared during the evaluation of HXIS data, for the benefit of those who plan future hard X-ray imaging experiments. Title: The physics of solar flares. Proceedings of Symposium 5 of the COSPARTwenty-sixth Plenary Meeting held in Toulouse, France, 30th June - 11th July 1986. Authors: de Jager, C.; Svestka, Z. Bibcode: 1986AdSpR...6f....D Altcode: 1986AdSpR...6.....D Observations and theoretical models of solar-flare phenomena are discussed in reviews and reports presented at the symposium formally marking the end of the international Solar-Maximum-Year/Solar-Maximum-Analysis project. Topics examined include flare buildup, precursors, and onset; the impulsive phase; the gradual phase; and coronal and interplanetary phenomena. Title: On the varieties of solar flares. Authors: Svestka, Zdenek Bibcode: 1986lasf.conf..332S Altcode: 1986lasf.symp..332S An attempt is made to classify flares starting with two axiomatic assumptions: (1) that a flare is a short-lived release of energy in consequence of a rearrangement of the magnetic structure, and (2) the mode of energy release is a reconnection of magnetic field lines. Somewhat surprisingly, in spite of the enormous diversity of the flare phenomena, two classes are derived: dynamic flares and confined flares, where the confined flares may be subdivided in two subclasses. All the other varieties may be due to differences in the boundary conditions of the flare process. The paper discusses the various factors which cause the varieties in flares, and the association of the two basic types of flares with different kinds of radiation and with othere active phenomena on the Sun. Title: Flare build-up study summary Authors: Gaizauskas, V.; Svestka, Z. Bibcode: 1986AdSpR...6f...5G Altcode: 1986AdSpR...6....5G No abstract at ADS Title: Progress in solar physics : review papers invited to celebrate the centennial volume of Solar physics Authors: de Jager, Cornelis; Svestka, Zdenek Bibcode: 1986pspr.book.....D Altcode: 1986QB521.6.P76.... No abstract at ADS Title: A dynamic flare with anomalously dense flare loops Authors: Svestka, Z.; Fontenla, J. M.; Machado, M. E.; Martin, S. F.; Neidig, D. F.; Poletto, G. Bibcode: 1986AdSpR...6f.253S Altcode: 1986AdSpR...6..253S The dynamic flare of 6 November 1980 (max. ~ 15:26 UT) developed a rich system of growing loops which could be followed in Hα for 1.5 hours. Throughout the flare, these loops, near the limb, were seen in emission against the disk. Theoretical computations of b-values for a hydrogen atom reveal that this requires electron densities in the loops to be close to 1012 cm-3. From measured widths of higher Balmer lines the density at the loops of the loops was found to be 4 × 1012 cm-3 if no non-thermal motions were present. It is now general knowledge that flare loops are initially observed in X-rays and become visible in Hα only after cooling. For such a high density a loop would cool through radiation from 107 K to 104 K within a few minutes so that the dense Hα loops should have heights very close to the heights of the X-ray loops. This, however, contradicts the observations obtained by the HXIS and FCS instruments on board SMM which show the X-ray loops at much higher altitudes than the loops in Hα. Therefore, the density must have been significantly smaller when the loops were formed and the flare loops were apparently both shrinking and becoming denser while cooling. Title: The stationary post-flare arch of May 21/22, 1980 Authors: Hick, P.; Svestka, Z. Bibcode: 1985SoPh..102..147H Altcode: On May 21/22, 1980 the Hard X-Ray Imaging Spectrometer aboard the SMM imaged an extensive coronal structure after the occurrence of a two-ribbon flare on May 21, 20:50 UT. The structure was observed from 22:20 UT on May 21 until its disappearence at 09:00 UT on May 22. Title: 21 May 1980 flare review Authors: de Jager, C.; Svestka, Z. Bibcode: 1985SoPh..100..435D Altcode: A review is given of observations and theories relevant to the solar flare of 21 May, 1980, 20 ∶ 50 UT, the best studied flare on record. For more than 30 hr before the flare there was filament activation and plasma heating to above 10 MK. A flare precursor was present ≥6 min before the flare onset. The flare started with filament activation (20 ∶ 50 UT), followed by thick-target heating of two footpoints and subsequent ablation and convective evaporation involving energies of 1 to 2 × 1031 erg. Coronal explosions occurred at 20 ∶ 57 UT (possibly associated with a type-II burst) and at 21 ∶ 04 UT (associated with an Hα spray?). Post-flare loops were first seen at 20 ∶ 57 UT, and their upward motion is interpreted as a manifestation of successive field-line reconnections. A type-IV radio burst which later changed into a type-I noise storm was related to a giant coronal arch located just below the radio noise storm region. Some implications and difficulties these observations present to current flare theories are mentioned. Title: Hard X-ray images of possible reconnection in the flare of 21 May, 1980 Authors: Svestka, Z.; Poletto, G. Bibcode: 1985SoPh...97..113S Altcode: An analysis of the growth of X-ray loops in the flare of 21 May, 1980, observed by HXIS on board SMM spacecraft, has been carried out with high time resolution in six energy channels from 3.5 to 30 keV. This analysis has revealed that the tops of the loops stay for minutes at a given altitude before, quite abruptly, other loop tops begin to appear above them. One of the jumps in altitude, from ∼27 000 to ∼45 000 km if the loops extended radially, which occurred quite late in the flare development, is studied in detail. The fact that the tops, of higher loops were first seen in the 22-30 keV energy channel, and only minutes later at lower energies, suggests a new release of energy in a very small volume high in the corona. An initial temperature of at least 50 × 106 K is indicated by the data, inside a volume which may not exceed a few hundred km in diameter. A magnetic reconnection of previously distended field lines appears to be a likely candidate for the observed phenomenon. Title: Images of a Major Compact Flare in Hard X-rays and H-alpha Authors: Svestka, Z.; Martin, S. F. Bibcode: 1985BAAS...17..628S Altcode: No abstract at ADS Title: Book-Review - Astronomy and Astrophysics Abstracts Authors: Bohme, S.; Svestka, Z. Bibcode: 1984SoPh...94..427B Altcode: No abstract at ADS Title: Book reviews Authors: Valníček, B.; Švestka, Zdeněk Bibcode: 1984SoPh...94..427V Altcode: No abstract at ADS Title: Revivals of a Coronal Arch Authors: Svestka, Z. Bibcode: 1984SoPh...94..171S Altcode: The giant post-flare arch of 6 November 1980 revived 11 hr and 25 hr after its formation. Both these revivals were caused by two-ribbon flares with growing systems of loops. The first two brightenings of the arch were homologous events with brightness maxima moving upwards through the corona with rather constant speed; during all three brightenings the arch showed a velocity pattern with two components: a slow one (8-12 km−1), related to the moving maxima of brightness, and a fast one (∼ 35 km s−1), the source of which is unknown. Title: Hα and Hard X-Ray Development in Two-Ribbon Flares Authors: Dwivedi, B. N.; Hudson, H. S.; Kane, S. R.; Svestka, Z. Bibcode: 1984SoPh...90..331D Altcode: Morphological features of two-ribbon flares have been studied, using simultaneous ISEE-3 hard X-ray records and high-resolution Big Bear Hα movies for more than 20 events. Long-lasting and complex hard X-ray bursts are almost invariably found associated with flares of the two-ribbon type. We find at least three events, namely March 31, 1979, April 10, 1980, and July 1, 1980, where the occurrence of individual spikes in hard X-ray radiation coincides with suddenly enhanced Hα emission covering the sunspot penumbra. There definitely exist important (≥ 1B) two-ribbon Hα flares without significant hard X-ray emission. Title: Imaging of reconnection processes in hard X-rays Authors: Švestka, Zdenek; Poletto, Giannina Bibcode: 1984AdSpR...4g.287S Altcode: 1984AdSpR...4Q.287S The Hard X-ray Spectrometer aboard the SMM detected several events of energy release late in the development of two-ribbon flares. One such event, at 21:12 UT on 21 May, 1980 (~ 20 min after the flare onset and 15 min after the peak of the impulsive phase) is studied in detail. The site of new brightening first became visible in hard X-rays (> 22 keV) and only afterwards showed up at lower energies. It was clearly located high in the corona so that one can identify it with energy release at the tops of newly formed post-flare loops. Thus, if the Kopp and Pneuman model of the loop formation is adopted, we may have imaged here a reconnection process in the solar corona. An attempt is made to estimate physical parameters at the reconnection site. Title: Post-flare thermal waves in the solar corona Authors: Svestka, Z. Bibcode: 1984AdSpR...4g.179S Altcode: 1984AdSpR...4..179S While imaging giant post-flare arches in the solar corona, the Hard X-Ray Spectrometer aboard the SMM detected thermal disturbances propagating through the corona after two-ribbon flares. The speed of propagation is close to, or below, 10 km s-1, and no obvious time-variation of the speed is indicated in the HXIS data. For subsequent two-ribbon flares in the same active region, these thermal disturbances (waves) exhibit highly homologous properties; thus the waves appear to propagate through preexisting arches formed after earlier flares. Temperatures of > 20 × 106 K have been detected in these moving phenomena. We suggest that we see here in X-rays upper products of the consecutive reconnections which create the post-flare loops below. Temperature maps in fine field of view of HXIS offer now a new possibility to detect postflare arches in the corona built during two-ribbon flares. Title: Large post-flare arch-like structures in the solar corona Authors: Svestka, Z. Bibcode: 1984MmSAI..55..725S Altcode: Hard (3.5-10-keV) X-ray observations of large archlike structures in the solar corona, obtained with the SMM HXIS after two-ribbon flares on May 22 and November 6, 1980 (Svestka et al., 1982), are presented in maps and graphs along with Culgoora radioheliograph, Bonn radio-telescope, Nancay radio-interferometer, and GOES-2 X-ray data and analyzed using a theoretical model of postflare loop formation by sequential reconnection of distended field lines (Kopp and Pneuman, 1976). Stationary or slowly expanding arches of temperature 2 x 10 to the 7th K or more, with thermal disturbances propagating upward at about 10 km/s, are observed in association with type I radio noise storms for periods of 10 h or more. The quasi-periodic X-ray and radio flux variations seen above and below the arches in the later stages are attributed to the transition from a system of interconnected loops along the neutral line to groups of isolated plasmoids with repetitive instabilities. Title: Enhanced X-Ray Emission above 3.5-KEV in Active Regions in the Absence of Flares Authors: Schadee, A.; de Jager, C.; Svestka, Z. Bibcode: 1983SoPh...89..287S Altcode: We demonstrate that even in the absence of flares there are very often volumes of hot plasma in the corona above active regions with temperatures in excess of 10 million degrees. Characteristics of this hot plasma and its time variations seem to be different in active regions of different phase of development. These hot plasma regions are sources of very weak, but clearly recognizable, X-ray emission above 3.5 keV. Long-lived X-ray brightenings, 104 times weaker than a flare, but lasting up to 10 hr occur predominantly along the H = 0 line, apparently low in the corona. After major flares, long-lived X-ray emission is also radiated from tops of arches extending high into the corona. Some other long-lived sources, far from the H = 0 line, may be associated with newly emerging flux. Short-lived X-ray sources, with fluxes ranging from subflare levels to 10−3 times the flare flux, last for 2 to more than 30 min and are probably microflares. They seem to be most frequent in growing young active regions and appear often in areas with newly emerging flux. Title: Radio, X-ray, and optical observations of the flare of June 13, 1980, at 6h22m UT Authors: Kattenberg, A.; Allaart, M.; de Jager, C.; Schadee, A.; Schrijver, J.; Shibasaki, K.; Švestka, Z.; van Tend, W. Bibcode: 1983SoPh...88..315K Altcode: A subflare of importance Sf was observed on June 13, 1980 simultaneously by instruments aboard the Solar Maximum Mission (SMM) and various ground based observatories. We describe and compare different kinds of observations, with emphasis on the Hard X-Ray Imaging Spectrometer (HXIS) images and spectra, and on the one-dimensional microwave images with high time and spatial resolution, obtained with the Westerbork Synthesis Radio Telescope (WSRT). The fast electrons causing the X-ray and microwave impulsive bursts had a common acceleration source, but the burst were produced at the opposite footpoints of the loops involved, with microwaves emitted near to a sunspot penumbra. The flare (of a `compact' type) was probably triggered by an emerging flux, and two possible interpretations of this process are briefly discussed. Title: Transient brightenings of interconnecting loops. III. Interpretation. Authors: Spicer, D. S.; Svestka, Z. Bibcode: 1983SoPh...87..271S Altcode: We present two alternative interpretations of the sudden X-ray brightenings observed in loops that interconnect active regions. A fast tearing mode may be excited in those newly formed interconnecting loops within which sufficient magnetic free energy is stored to drive the mode. Alternatively anomalous Joule heating driven by an inductive electric field parallel to the magnetic field varying on a time scale of order of a minute may cause the brightenings. We argue that it is plausible that the fast tearing mode may be the cause of brightenings in the young newly formed interconnecting loops, whereas the anomalous Joule heating might occur in old loop connections when an external disturbance propagates through them. Title: POST Flare Coronal Arches Authors: Svestka, Z. Bibcode: 1983SSRv...35..259S Altcode: The Hard X-ray Imaging Spectrometer aboard the SMM detected gigantic arches in the corona which are formed or, if preexisting, become excited after major two-ribbon flares. They are seen in 3.5 8 keV X-rays and extend along the H = 0 line to altitudes between 105 and 2 × 105 km. These arches are stationary and form the base of a stationary type I radio noise storm initiated by the flare. They are visible in X-rays for ten hours or more and may be revived, in temperature, density, and brightness, if another two-ribbon flare appears below them. We suggest that they are built-up through reconnection process during the flare from the upper reconnected loops in the Kopp and Pneuman model. These loops become interconnected along the H = 0 line in consequence of great shear of the reconnecting loops. Obviously, the coronal transient associated with such flares must be either accomplished prior to the formation of the arch, or it must be formed through a process different from the Anzer-Kopp-Pneuman mechanism. Striking brightness variations occur quasi-periodically in the corona below and above the arch a few hours after the flare. These variations are seen at about the same time in soft X-rays, hard X-rays, and on centimeter microwaves in the low corona, as well as at metric waves in the type I noise-storm region. In spite of their flare-like intensity, however, the variations have little response in the transition layer (O v line) and no response at all in the chromosphere (Hα). We suggest that these semi-periodic brightenings are due to repetitive acceleration processes in plasmoids that encircle the arch perpendicular to the H = 0 line from the low corona through the noise storm region, being completely detached from the lower atmospheric layers. Title: Pre-Flare and Post-Flare X-Ray Variations in Active Regions Authors: Svestka, Z.; Schadee, A. Bibcode: 1983SoPh...86..267S Altcode: Extremely low background noise of the HXIS experiment aboard the SMM made it possible to detect > 3.5 keV X-ray emissions from non-flaring active regions which are 103-104 times weaker than the X-ray flux from flares. Short-lived X-ray bursts and long-lived X-ray enhancements of various intensities seem to characterize active regions in different phases of their development. After major two-ribbon flares, giant X-ray arches are seen in the corona, slowly decaying for many hours after the flare end. Associated with these arches appear to be quasi-periodic flare-like variations of purely coronal nature. Title: Purely Coronal Flare-Like Variations Authors: Svestka, Z.; Schrijver, J.; Somov, B.; Dennis, B. R.; Woodgate, B. E.; Fuerst, E.; Hirth, W.; Klein, L.; Raoult, A. Bibcode: 1983SoPh...85..313S Altcode: A detailed study of the quasi-periodical post-flare variations on November 6, 1980 in X-rays, UV lines, microwaves, and metric waves confirms that these variations were predominantly thermal phenomena and occurred solely in the corona. Only the short-lived impulsive components that preceded all or most of the individual variations were of non-thermal character and penetrated down to the transition layer. The chromosphere (in Hα) did not participate in any part of these events, in contrast to a flare that appeared at the same place a few hours later. However, the X-ray emission of these variations was so strong that the transition layer and the chromosphere definitely should have been enhanced through heat conduction along the magnetic field lines. The expected heat flux at the top of the chromosphere coming from some of these coronal brightenings was 60-80% of the flux expected in the flare at 17:26 which gave rise to a 2B flare in Hα (Figure 8). Therefore, we suggest that the variations were produced in a coronal plasmoid with closed field lines completely detached from the lower atmospheric layers (Figure 9b). We also give reasons why such a detached plasmoid can be expected to be formded in the very late phase (some 4-5 hr after the onset) of a major two-ribbon flare. Title: The Queen's Flare - its Structure and Development - Precursors Pre-Flare Brightenings and Aftermaths Authors: de Jager, Cornelis; Machado, Marcos E.; Schadee, Aert; Strong, Keith T.; Švestka, Zdeněk; Woodgate, Bruce E.; van Tend, W. Bibcode: 1983SoPh...84..205D Altcode: We continue previous research on the limb flare of 30 April, 1980, 20:20 UT, observed in X-rays by several instruments aboard the Solar Maximum Mission (SMM). It is shown quantitatively that the flare originated in an emerging magnetically confined kernel (diameter ∼ 20″) which existed for about ten to fifteen minutes, and from which energetic electrons streamed, in at least two injections, into a previously existing complicated magnetic loop system thus forming a less bright but extended and long-lived tongue. The tongue had a length of ∼ 35 000 km and lasted ∼ 90 min in X-rays (∼ 10 keV); at lower energies (∼ 0.7 keV) it was larger (∼ 80 000 km) and lasted longer. The total number of energetic electrons (≈ 1037) initially present in the kernel is of the same order as the number present in the tongue after the kernel's decline. This gives evidence that the energetic electrons in the tongue originated mainly in the kernel. The electron number densities in the kernel and tongue at maximum brightness were ∼ 4.5 × 1011 and ∼ 1 × 1011 cm#X2212;3, respectively. During the first eight minutes of its existence the tongue was hotter than the kernel, but it cooled off gradually. Its decline in intensity and temperature was exponential; energy was lost by radiation and by conduction through the footpoints of the loop system. These footpoints have a cross-section of only ∼ 3 × 106 km2. This small value, as well as photographs in a CIV UV emission line, suggests a highly filamentary structure of the system; this is further supported by the finding that the tongue had a `filling factor' of ∼ 10#X2212;2. Several faint X-ray brightenings (≲ 0.005 of the flare's maximum intensity) were observed at various locations along the solar limb for several hours before and after the flare. At ∼ 30 min before the flare's onset a faint (≲ 0.02) flare precursor occurred, coinciding in place and shape with the flare. First the kernel precursor was brightest but the tongue precursor increased continuously in brightness and was the brightest part of the precursor some 10-15 min after the first visibility of the kernel precursor, until the start of the main flare. This suggests (weak) continuous electron acceleration in the tongue during a period of at least 30 min. The main flare was caused by strong emergence of magnetic field followed by two consecutive field line reconnections and accelerations in a small loop system, causing footpoint heating. Subsequently plasma streamed (convectively) into a pre-existing system of larger loops, forming the tongue. Title: 3.5 keV X-ray Emission in Absence of Flares Authors: Schadee, A.; de Jager, C.; Svestka, Z. Bibcode: 1983BAAS...15R.704S Altcode: No abstract at ADS Title: Revival of a Coronal Arch Authors: Svestka, Z. Bibcode: 1983BAAS...15..714S Altcode: No abstract at ADS Title: Particle acceleration in two-ribbon flares. Authors: Švestka, Z. Bibcode: 1983POEM...14...69S Altcode: The author points out the basic differences between compact and two-ribbon flares, and discusses observations indicating particle acceleration during a long-enduring reconnection process in the two-ribbon flares. Title: Particle acceleration in two-ribbon flares Authors: Svestka, Z. Bibcode: 1983ebro.conf...69S Altcode: Particle acceleration during a long reconnection process in two-ribbon flares is discussed. The evolution in the understanding of solar flares is summarized, pointing out the contributions of the Skylab mission and other satellite observation missions. A model of a two-ribbon flare is described. Particle acceleration is associated with magnetic reconnection when new loops are formed. Particles are trapped in the loops and produce the hard X-ray, H alpha and white light emission. According to the model, particle acceleration in two-ribbon flares may last for hours, and in filament disruptions, in particular along the boundaries of growing coronal holes, non negligible particle fluxes in space may be produced. Title: Unusual coronal activity following the flare of 6 November 1980 Authors: Švestka, Z.; Dennis, B. R.; Pick, M.; Raoult, A.; Rapley, C. G.; Stewart, R. T.; Woodgate, B. E. Bibcode: 1982SoPh...80..143S Altcode: For almost 30 hr after the major (gamma-ray) two-ribbon flare on 6 November 1980, 03:30 UT, the Hard X-Ray Imaging Spectrometer (HXIS) aboard the SMM satellite imaged in > 3.5 keV X-rays a gigantic arch extending above the active region over the limb. Like a similar configuration on 22 May 1980, this arch formed the lowest part of a stationary post-flare radio noise storm recorded at metric wavelengths at Nançay and Culgoora. 6.5 hr after the flare a coronal region below the arch started quasi-periodic pulsations in X-ray brightness, observed by several SMM instruments. These brightness variations had no response in the chromosphere (Hα), very little in the transition layer (O v), but they clearly correlated with similar variations in brightness at 169 MHz. There were 13 pulses of this kind, with apparent periodicity of about 20 min, until another flare occurred in the active region at ∼ 15:00 UT. All the brightenings appeared within a localized area of about 30000 km2 in the northern part of the active region, but they definitely did not occur all at the same place. Title: Study of the Post-Flare Loops on 1973JUL29 - Part Four - Revision of T and NE Values and Comparison with the Flare of 1980MAY21 Authors: Švestka, Z.; Dodson-Prince, H. W.; Martin, S. F.; Mohler, O. C.; Moore, R. L.; Nolte, J. T.; Petrasso, R. D. Bibcode: 1982SoPh...78..271S Altcode: We present revised values of temperature and density for the flare loops of 29 July 1973 and compare the revised parameters with those obtained aboard the SMM for the two-ribbon flare of 21 May 1980. The 21 May flare occurred in a developed sunspot group; the 29 July event was a spotless two-ribbon flare. We find that the loops in the spotless flare extended higher (by a factor of 1.4-2.2), were less dense (by a factor of 5 or more in the first hour of development), were generally hotter, and the whole loop system decayed much slower than in the spotted flare (i.e. staying at higher temperature for a longer time). We also align the hot X-ray loops of the 29 July flare with the bright Hα ribbons and show that the Hα emission is brightest at the places where the spatial density of the hot elementary loops is enhanced. Title: Observations of a POST Flare Radio Burst in X-Rays Authors: Svestka, Z.; Hoyng, P.; van Tend, W.; Boelee, A.; de Jager, C.; Stewart, R. T.; Acton, L. W.; Bruner, E. C.; Gabriel, A. H.; Rapley, C. G.; de Jager, C.; LaFleur, H.; Nelson, G.; Simnett, G. M.; van Beek, H. F.; Wagner, W. J. Bibcode: 1982SoPh...75..305S Altcode: More than six hours after the two-ribbon flare of 21 May 1980, the hard X-ray spectrometer aboard the SMM imaged an extensive arch above the flare region which proved to be the lowest part of a stationary post-flare noise storm recorded at the same time at Culgoora. The X-ray arch extended over 3 or more arc minutes to a projected distance of 95 000 km, and its real altitude was most probably between 110 000 and 180 000 km. The mean electron density in the cloud was close to 109 cm−3 and its temperature stayed for many hours at a fairly constant value of about 6.5 × 106 K. The bent crystal spectrometer aboard the SMM confirms that the arch emission was basically thermal. Variations in brightness and energy spectrum at one of the supposed footpoints of the arch seem to correlate in time with radio brightness suggesting that suprathermal particles from the radio noise regions dumped in variable quantities into the low corona and transition layer; these particles may have contributed to the population of the arch, after being trapped and thermalized. The arch extended along the H = 0 line thus apparently hindering any upward movement of the upper loops reconnected in the flare process. There is evidence from Culgoora that this obstacle may have been present above the flare since 15-30 min after its onset. Title: Solar Maximum Year; Proceedings of the Symposium, Ottawa, Canada, May 16-June 2, 1982 Authors: Svestka, Z.; Rust, D. M.; Dryer, M. Bibcode: 1982AdSpR...2k....S Altcode: 1982AdSpR...2.....S Results of research conducted during the Solar Maximum Year from August 1979 to through February 1981 are presented, focusing on flare build-up, energy release in flares, and travelling interplanetary phenomena. Topics examined include the relation of solar flares to the evolution and proper motions of magnetic fields, pre-flare heating of filaments, mass motions in a quiescent filament, multiple wavelength observations of flaring active regions, energy transfer in solar flares, direct evidence for chromosphere evaporation in a well-observed compact flare, physics of the impulsive phase of solar flares, and the analysis of ultra-fast fine structures of microwave bursts. Also considered are the effects of electron-cyclotron masers during flares, high energy particle acceleration in flares, particle charge interchange during acceleration in flare regions, diamagnetic aspects of the coronal transient phenomenon, particle acceleration by coronal and interplanetary shock waves, and the propagation of energetic particles in the solar wind. For individual items see A83-35202 to A83-35235 Title: Transient Brightenings of Interconnecting Loops - Part Two - Dynamics of the Brightened Loops Authors: Svestka, Z.; Howard, R. Bibcode: 1981SoPh...71..349S Altcode: We discuss three different kinds of dynamic events related to interconnecting loops observed in soft X-rays aboard Skylab: (1) A newly born transequatorial loop that was either emerging from subphotospheric layers or gradually filled in with hot plasma. (2) Large-scale twists of interconnecting loops which never relax, and often only form, after the loop brightenings. (3) Three events where the loop that later interconnected two active regions had been visible long before one of the interconnecting regions was born. Several impacts this observation might have upon our understanding of the process of flux emergence are suggested. Title: Origin and Location of the Hard X-Ray Emission in a Two-Ribbon Flare Authors: Hoyng, P.; Duijveman, A.; Machado, M. E.; Rust, D. M.; Svestka, Z.; Boelee, A.; de Jager, C.; Frost, K. T.; Lafleur, H.; Simnett, G. M.; van Beek, H. F.; Woodgate, B. E. Bibcode: 1981ApJ...246L.155H Altcode: No abstract at ADS Title: On the outburst of flare activity of 26 November, 1973 Authors: Howard, R.; Svestka, Z. Bibcode: 1981SoPh...71...49H Altcode: We draw attention of flare build-up observers to a strong 30 hour-long outburst of homologous flare activity and unusual growth and brightening of coronal loops, seen on Skylab. We suggest that these events might have been closely associated with newly emerging magnetic flux, in spite of the fact that the flux effects in Hα and EUV were first seen only late after the activity had started, and the flux emerged at the opposite end of the coronal loops from where the flares occurred. Title: Coronal Variations Imaged in 3.5 - 30 keV X-Rays Authors: Svestka, Z. Bibcode: 1981BAAS...13..909S Altcode: No abstract at ADS Title: Giant X-Ray Arches Associated with Post-Flare Radio Noise Storms Authors: Svestka, Z.; Pick, M.; Rapley, C. G.; Stewart, R. T.; Woodgate, B. Bibcode: 1981BAAS...13..555S Altcode: No abstract at ADS Title: X-Ray Observations of Two Different Systems of "Post Flare" Loops Authors: Svestka, Z.; Dodson-Prince, H. W.; Mohler, O. C.; Martin, S. F.; Moore, R. L.; Nolte, J. T.; Petrasso, R. D. Bibcode: 1981BAAS...13R.542S Altcode: No abstract at ADS Title: The limb flare of 1980 April 30 as seen by the hard X-ray imaging spectrometer Authors: van Beek, H. F.; de Jager, C.; Schadee, A.; Svestka, Z.; Boelee, A.; Duijveman, A.; Galama, M.; Hoekstra, R.; Hoyng, P.; Fryer, R.; Simnett, G. M.; Imhof, J. P.; LaFleur, H.; Maseland, H. V. A. M.; Mels, W. M.; Schrijver, J.; van der Laan, J. J. M.; van Rens, P.; van Tend, W.; Werkhoven, F.; Willmore, A. P.; Wilson, J. W. G.; Machado, M. E.; Zandee, W. Bibcode: 1981ApJ...244L.157V Altcode: X-ray imaging of the limb event of 1980 April 30 shows that the flaring involved two distinct components: a pointlike component, which was the source of the initial hard X-ray burst and an extensive tongue reaching some 30,000 km above the limb. The tongue had a higher temperature than the other parts of the structure and seemed to be enhanced by energetic electrons that derived their energy from the initial source. Title: Introduction Authors: De Jager, Cornelis; Švestka, Zdeněk Bibcode: 1981SoPh...72D...7D Altcode: No abstract at ADS Title: Book-Review - Astronomy and Astrophysics Abstracts V.25 & 26 Authors: Bohme, S.; Esser, U.; Fricke, W.; Svestka, Z. Bibcode: 1981SoPh...69..419B Altcode: No abstract at ADS Title: Book review Authors: Švestka, Z. Bibcode: 1981SoPh...69..419S Altcode: No abstract at ADS Title: Structural development of the X-ray limb flare of 30 April 1980 Authors: de Jager, C.; Hoyng, P.; Lafleur, H.; Schadee, A.; Svestka, Z.; van Beek, H. F.; van Tend, W.; Fryer, R.; Simnett, G. M. Bibcode: 1981AdSpR...1m.251D Altcode: 1981AdSpR...1..251D We describe the development of the limb flare of 30 April 1980, 20:20 UT, as observed by the Hard X-ray Imaging Spectrometer (HXIS) aboard the Solar Maximum Mission (SMM). It consisted of a short-lived bright nucleus (FWHM < 10,000 km), just inside the Sun's limb; a longer lasting tongue, extending to a height of ~ 30,000 km, and a more complicated feature, approximately situated at the Sun's limb. The tongue was a pre-existing magnetic structure that started emitting X-rays only a few seconds after the bright nucleus, and which had a slightly higher temperature than the nucleus; its X-ray emission may be caused by electrons escaped from the nucleus. Title: Solar maximum mission experiment: Early results of the hard X-ray imaging experiment Authors: Boelee, A.; de Jager, C.; Duijveman, A.; Galama, M.; Hoekstra, R.; Hoyng, P.; Imhof, J. P.; Lafleur, H.; Maseland, H. V. A. M.; Mels, W. A.; Schadee, A.; Schrijver, J.; Svestka, Z.; van Beek, H. F.; van Rens, P.; van der Laan, J. J. M.; van Tend, W.; Werkhoven, F.; Wiersma, G.; Zandee, W.; Simnett, G. M.; Charlton, C. P.; Fryer, R.; Willmore, A. P.; Wilson, J. W. G.; Machado, M. E. Bibcode: 1981AdSpR...1m.255B Altcode: 1981AdSpR...1R.255B We have selected four widely different flares from the early period of operations of the Hard X-Ray Imaging Spectrometer (HXIS) on SMM to illustrate the characteristic imaging properties of this experiment. For the small flare of April 4, 1980, we demonstrate the instrument's capability for locating a compact source. In the weak, but extensive, flare of April 6 we show how well the instrument can display spatial structure, and also the low level of the instrument background. In the 1B flare of April 7 we are able to locate positions of the X-ray emission in the soft and hard channels, and estimate the positional variations of the emission patches. Finally, in the IN flare of April 10, which produced the strongest hard X-ray burst we have seen so far, we repeat some of the studies made for the April 7 event, and also demonstrate the capability of the HXIS instrument to study the development, with high time resolution, of individual 8'' × 8'' elements of the flare. Title: Flare observations Authors: Svestka, Z. Bibcode: 1981sfmh.book...47S Altcode: The solar flare represents a sudden release of energy in the atmospheric layers of the sun. In tens of seconds or a few minutes the temperature rises throughout the solar atmosphere, reaching its peak, often well above 10 million K, in the solar corona. Flare observations in the H-alpha light are considered along with chromospheric flare spectra, thermal flares in soft X-rays, impulsive hard X-ray and microwave bursts, energy transfer through the transition layer, metric radio bursts, flare ejecta, and the production and effects of high-energy particles in flares. Attention is given to the general characteristics of flares, flare emissions, flare classification, two-ribbon and compact flares, flare theory, flares in relation to magnetic fields, flare occurrence, flares in relation to velocity fields, flare-associated changes in the magnetic field, the EUV spectrum, the EUV flare morphology and density, and flare waves. Title: Structural development of the X-ray limb flare of 30 April 1980. Authors: de Jager, C.; Fryer, R.; Hoyng, P.; Lafleur, H.; Schadee, A.; Simnett, G. M.; Svestka, Z.; van Beek, H. F.; van Tend, W. Bibcode: 1981hea..conf..251D Altcode: No abstract at ADS Title: Solar Maximum Mission experiment: early results of the hard X-ray imaging experiment. Authors: Simnett, G. M.; Boelee, A.; Charlton, C. P.; de Jager, C.; Duijveman, A.; Fryer, R.; Galama, M.; Hoekstra, R.; Hoyng, P.; Imhof, J. P.; Lafleur, H.; Machado, M. E.; Maseland, H. V. A. M.; Mels, W. A.; Schadee, A.; Schrijver, J.; Svestka, Z.; van Beek, H. F.; van Rens, P.; van der Laan, J. J. M.; van Tend, W.; Werkhoven, F.; Wiersma, G.; Willmore, A. P.; Wilson, J. W. G.; Zandee, W. Bibcode: 1981hea..conf..255S Altcode: No abstract at ADS Title: Hα and Hard X-Ray Development in Two-Ribbon Flares Authors: Dwivedi, B. N.; Hudson, H. S.; Kane, S. R.; Svestka, Z. Bibcode: 1980BAAS...12..905D Altcode: No abstract at ADS Title: A Study of the Impulsive Flares and Homologous Flares From AR2372 From April 6-13, Using Hard X-Ray Images Authors: Simnett, G. M.; Machado, M.; Harrison, R. A.; Hoyng, P.; Lafleur, H.; Svestka, Z.; Vanbeek, H. F. Bibcode: 1980BAAS...12S.899S Altcode: No abstract at ADS Title: The Solar Maximum Year and Related Space Experiments Authors: Svestka, Z.; de Jager, C. Bibcode: 1980SSRv...26..317S Altcode: The Solar Maximum Year is a world-wide cooperative project to gain more insight in certain aspects of solar flares. It consists of three sub-programs: The Flare Build-up Study (FBS), the Study of Energy Release from Flares (SERF), and the Study of Travelling Interplanetary Phenomena (STIP). These programs are described. We also describe space observations to be performed during SMY, particularly the Solar Maximum Mission Satellite. Title: Activated Solar Filaments and Flares Authors: Svestka, Z. Bibcode: 1980RSPTA.297..575S Altcode: 1980RSLPT.297..575S Activations and disruptions of dark Hα filaments are very common phenomena on the Sun. They precede the most powerful two-ribbon solar flares, but they also appear far from any active region without any chromospheric flaring. Therefore, until very recently, filament disruptions were considered as interesting, but physically insignificant, flare precursors. Only Skylab observations have shown that the filament disruptions actually represent one of the basic and most important mechanisms of solar activity. These observations have revealed (1) that many coronal transients originate in eruptive filaments without chromospheric flares, (2) that Bruzek's slow-mode waves originate in disrupted filaments and not in flares themselves, and (3) that many coronal X-ray enhancements outside active regions are also tops of newly formed loops, similar to the post-flare loops observed after filament disruptions in active regions. An interpretation of these data stems from Kopp & Pneuman's theory of post-flare loops: the process that disrupts a filament opens the magnetic field and causes a greatly enhanced mass-flow along the field lines. The open field lines subsequently reconnect, starting from the bottom of the corona and proceeding upwards. This process can last for many hours. Hot loops are first seen in X-rays, later in extreme ultraviolet (e.u.v.) lines, and, after an appropriate cooling time, in Hα as the loop prominence systems. The visibility of loops depends on plasma density. Several observed properties of solar flares indicate that the primary acceleration occurs as the field lines reconnect. Thus the process of particle acceleration in two-ribbon flares can last for hours. Because reconnection is accomplished after essentially all filament disruptions, 'disparitions brusques' outside active regions should also accelerate particles. Title: The Dynamics of Brightened Interconnecting Loops Authors: Howard, R.; Svestka, Z. Bibcode: 1980BAAS...12..519H 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 thermal X-ray flare plasma Authors: Moore, R.; McKenzie, D. L.; Svestka, Z.; Widing, K. G.; Dere, K. P.; Antiochos, S. K.; Dodson-Prince, H. W.; Hiei, E.; Krall, K. R.; Krieger, A. S. Bibcode: 1980sfsl.work..341M Altcode: 1980sofl.symp..341M Following a review of current observational and theoretical knowledge of the approximately 10 to the 7th K plasma emitting the thermal soft X-ray bursts accompanying every H alpha solar flare, the fundamental physical problem of the plasma, namely the formation and evolution of the observed X-ray arches, is examined. Extensive Skylab observations of the thermal X-ray plasmas in two large flares, a large subflare and several compact subflares are analyzed to determine plasma physical properties, deduce the dominant physical processes governing the plasma and compare large and small flare characteristics. Results indicate the density of the thermal X-ray plasma to be higher than previously thought (from 10 to the 10th to 10 to the 12th/cu cm for large to small flares), cooling to occur radiatively as much as conductively, heating to continue into the decay phase of large flares, and the mass of the thermal X-ray plasma to be supplied primarily through chromospheric evaporation. Implications of the results for the basic flare mechanism are indicated. Title: Gibt es Cluster von Hellen Punkten? Authors: Kittelberger, G.; Elwert, G.; Svestka, Z. Bibcode: 1980MitAG..50...96K Altcode: No abstract at ADS Title: The needs for prediction and real-time monitoring for the flare build-up study Authors: Svestka, Z. Bibcode: 1979stp.....2..322S Altcode: Similarities between plasma instabilities occurring in the magnetospheric tail and in active regions on the Sun are discussed. Intense observations of the flare build-up processes on the Sun planned for May and June 1980 as a part of the Solar Maximum Year are described. Title: Slowly moving disturbances in the X-ray corona. Authors: Rust, D. M.; Svestka, Z. Bibcode: 1979SoPh...63..279R Altcode: Sequences of soft X-ray pictures, taken aboard Skylab between May and November, 1973, have made it possible to detect slowly moving disturbances originating in disrupted filaments and causing subsequent brightenings of distant coronal structures. With speeds decreasing from ∼400 km s-1 shortly after the filament disruption to ∼10 km s-1 four or five hours later, these disturbances appear to be identical with slow waves earlier inferred by Bruzek, Öhman, and Yajima from chromospheric observations. Title: Transient brightenings of interconnecting loops. Morphology of the sudden brightenings. Authors: Svestka, Z.; Howard, R. Bibcode: 1979SoPh...63..297S Altcode: We study sudden brightenings of coronal loops that interconnect active regions. Such brightenings often occur within one or two days after the birth of a new interconnecting loop, as well as in some old interconnections. The brightenings of young loops are obviously associated with the emergence of new magnetic flux near their footpoints, whereas some enhancements of old loops may be triggered by slowly moving disturbances propagating from other centers of activity. A few loop brightenings are associated with flares, but the loop does not brighten in consequence of energy supply from the flare. Both the flare and the loop brightening are independent consequences of one common agent, presumably newly emerging flux. Title: The birthplaces of active regions and X-ray bright points. Authors: Howard, R.; Fritzova-Svestkova, L.; Svestka, Z. Bibcode: 1979SoPh...63..105H Altcode: A comparison of soft X-ray pictures of the Sun (S-054 experiment of Skylab) with K-line spectroheliograms (Mount Wilson) shows that the X-ray bright points tend to emerge randomly throughout the Ca network pattern. However, all those bright points that developed into active regions emerged at the boundaries of network cells. This suggests that the magnetic flux of active regions comes from greater depths in the convection zone than the shallow flux that gives rise to the random emergence of bright points. Title: Study of the post-flare loops on 29 July 1973. II. Physical parameters in the X-ray loops. Authors: Petrasso, R. D.; Nolte, J. T.; Gerassimenko, M.; Krieger, A. S.; Krogstad, R.; Seguin, F. H.; Svestka, Z. Bibcode: 1979SoPh...62..133P Altcode: We use the filter ratio method of analysis to determine spatially resolved values of plasma parameters in the X-ray emitting post-flare loop system which developed on 29 and 30 July 1973. We find that the loops were hotter and had higher plasma pressure at their tops than near their footpoints. The loop tops were at nearly the same temperature at different places 3 hr after the flare maximum and were also at nearly this same temperature 3 and 8 hr later. Variations in brightness transverse to the loops were due to variations in emission measure. We show by consideration of radiative losses alone that energy must have been added to the hottest part of the flare, at the tops of the loops, late into the decay phase of the flare. Title: Study of the post-flare loops on 29 July 1973. I. Dynamics of the x-ray loops. Authors: Nolte, J. T.; Gerassimenko, M.; Krieger, A. S.; Petrasso, R. D.; Svestka, Z. Bibcode: 1979SoPh...62..123N Altcode: We derive an empirical model of the X-ray emitting post-flare loops observed during the decay phase of the 29 July 1973 flare. We find that the loops are elliptical, with the brightest emitting region at the tops. We determine the height, velocity of growth, and ratio of height to width of the loops at times from 3 to 12 hr after the flare onset. Title: Prominences and Solar Activity. Authors: Svestka, Z. Bibcode: 1979phsp.coll..357S Altcode: 1979phsp.conf..357S; 1979phsp.coll..356S; 1979IAUCo..44..357S Various aspects of solar prominences are discussed. These include (1) filament activation, (2) postflare loops, (3) surges and sprays, (4) coronal transients, (5) disk vs limb observations, (6) solar cycle variations of prominence occurrence, and (7) active prominences patrol service. Title: Slowly-Moving Disturbances in the X-Ray Corona. Authors: Rust, D. M.; Svestka, Z. Bibcode: 1979phsp.coll..276R Altcode: 1979IAUCo..44..276R; 1979phsp.conf..276R A synoptic movie made from nearly 1000 pictures of the solar X-ray corona taken by the S-054 X-ray telescope on Skylab has led to the discovery of disturbances with propagation velocities under 100 km/sec and extending over distances of the order of one solar radius. The disturbances are revealed as brightened coronal structures at progressively greater distances from a central point, usually an active region with an activated or disappearing filament. In a number of cases these coronal brightenings were accompanied by quiescent filament disappearances. The inferred coronal velocities and the rates of damping were found to be in excellent agreement with the velocity curves deduced by Bruzek (1952), in his slow wave hypothesis, and possibly confirmed by Oehman and Oehman (1953) and Yajima (1971) to explain the activation of filaments at great distances from flares. The fact that many of the events showed little or no flaring associated with the filament disappearance at onset leads to the conclusion that the source of the slow disturbances is linked to the initial filament eruption itself, possibly in restructuring of the magnetic fields or in the coronal heating that typically accompanies active region filament eruptions. Title: E. N. Parker first recipient of the George Ellery Hale Prize. Authors: De Jager, Cornelis; Švestka, Zdeněk Bibcode: 1978SoPh...60....3D Altcode: 1978SoPh...60....3. No abstract at ADS Title: Low-energy protons: Gradients in interplanetary space and distribution in the solar corona Authors: Stevens, G. A.; Vanrooijen, J. J.; Svestka, Z.; De Jager, C. Bibcode: 1978clus.nasa..234S Altcode: First and second order anisotropy measurements are proposed as a tool for studying the coronal source function and interplanetary propagation of low energy protons. Optimum orbit and attitude requirements are suggested for a three telescope system. Some limitations with regard to the lower energy limit for a feasible set-up are discussed. Title: Book review Authors: švestka, Z. Bibcode: 1978SoPh...57..483S Altcode: 1978SoPh...57..483. No abstract at ADS Title: X-Ray Analysis of the 29 July 1973 Flare. Authors: Nolte, J.; Geras-Simenko, M.; Krieger, A.; Krogstad, R.; Petrasso, R.; Seguin, F.; Svestka, Z. Bibcode: 1978BAAS...10Q.457N Altcode: No abstract at ADS Title: Erratum: "Development of a complex of activity in the solar corona" [Sol. Phys., Vol. 54, p. 65 - 105 (1977)]. Authors: Howard, R.; Svestka, Z. Bibcode: 1978SoPh...56..471H Altcode: No abstract at ADS Title: Editorial Authors: De Jager, Cornelis; Švestka, Zdeněk Bibcode: 1978SoPh...56....3D Altcode: 1978SoPh...56....3. No abstract at ADS Title: Do changes in coronal emission structure imply magnetic reconnection? Authors: Nolte, J. T.; Gerassimenko, M.; Krieger, A. S.; Petrasso, R. D.; Svestka, Z.; Wentzel, D. G. Bibcode: 1977SoPh...55..401N Altcode: We examine three major possible interpretations of observed reconfigurations of coronal X-ray and XUV emitting structures on a scale comparable to the size of the structures themselves. One possibility is that little change in the large-scale magnetic field configuration is associated with the change in emission. The other two possibilities are processes by which the magnetic field structure can change. Title: Open magnetic fields in active regions. Authors: Svestka, Z.; Solodyna, C. V.; Howard, R.; Levine, R. H. Bibcode: 1977SoPh...55..359S Altcode: Soft X-ray observations confirm that some of the dark gaps seen between interconnecting loops and inner cores of active regions may be loci of open fields, as it has been predicted by global potential extrapolation of photospheric magnetic fields. It seems that the field lines may open only in a later state of the active region development. Title: Development of a complex of activity in the solar corona. Authors: Howard, R.; Svestka, Z. Bibcode: 1977SoPh...54...65H Altcode: Skylab observations of the Sun in soft X-rays gave us the first possibility to study the development of a complex of activity in the solar corona during its whole lifetime of seven solar rotations. The basic components of the activity complex were permanently interconnected (including across the equator) through sets of magnetic field lines, which suggests similar connections also below the photosphere. However, the visibility of individual loops in these connections was greatly variable and typically shorter than one day. Each brightening of a coronal loop in X-rays seems to be related to a variation in the photospheric magnetic field near its footpoint. Only loops (rarely visible) connecting active regions with remnants of old fields can be seen in about the same shape for many days. The interconnecting X-ray loops do not connect sunspots. Title: Introductory Talk (Proceedings of the Meeting `How Can Flares be Understood?', held during the 16th General Assembly of the IAU in Grenoble, France, on 27 August, 1976.) Authors: Švestka, Zdeněk Bibcode: 1977SoPh...53..221S Altcode: No abstract at ADS Title: Transequatorial loops interconnecting McMath regions 12472 and 12474. Authors: Svestka, Z.; Krieger, A. S.; Chase, R. C.; Howard, R. Bibcode: 1977SoPh...52...69S Altcode: We discuss the life-story of a transequatorial loop system which interconnected the newly born active region McMath 12474 with the old region 12472. The loop system was probably born through reconnection accomplished 1.5 to 5 days after the birth of 12474 and the loops were observed in soft X-rays for at least 1.5 days. Transient `sharpenings' of the interconnection and a striking brightening of the whole loop system for about 6 hr appear to be caused by magnetic field variations in the region 12474. A flare might have been related to the brightening, but only in an indirect way: the same emerging flux could have triggered the flare and at the same time strengthened the magnetic field at the foot-points of the loops. Electron temperature in the loop system, equal to 2.1 × 106 K in its quiet phase, increased to 3.1 × 106 K during the brightening. Electron density in the loop system was ≤ 1.3 × 109 cm−3 and it could be estimated to ∼7 × 108 cm−3 prior to the brightening. During the brightening the loops became twisted. There was no obvious effect whatsoever of the activity in 12474 upon the in erconnected old region. The final decay of the loop system reflected the decay of magnetic field in the region 12474. Title: Book reviews Authors: Švestka, Z. Bibcode: 1977SoPh...52..229S Altcode: No abstract at ADS Title: Slowly Moving X-Ray Disturbances from Flares. Authors: Rust, D. M.; Svestka, Z. Bibcode: 1977BAAS....9..329R Altcode: No abstract at ADS Title: Open Magnetic Fields in Active Regions. Authors: Svestka, Z.; Solodyna, C. V.; Howard, R.; Levine, R. H. Bibcode: 1977BAAS....9Q.344S Altcode: No abstract at ADS Title: Solar Flares (Book Review) Authors: Svestka, Z. Bibcode: 1977ApL....18..175S Altcode: No abstract at ADS Title: Low-energy particle events associated with sector boundaries. Authors: Svestka, Z.; Fritzova-Svestkova, L.; Nolte, J. T.; Dodson-Prince, H. W.; Hedeman, E. R. Bibcode: 1976SoPh...50..491S Altcode: Onsets of some 40 to 45 low-energy proton events during the years 1957-1969 coincided in time with transits of well-defined sector boundaries across the Earth. These events can be interpreted as long-lived proton streams filling up some of the magnetic sectors, indicating an acceleration of protons which is not associated with typical proton-producing flares. The sharp onsets of these particle streams, as well as a deficiency of flare-associated particle events shortly before the boundary transit, indicate that in some cases magnetic sector boundaries can inhibit transverse propagation of low-energy particles in the solar corona or in interplanetary space. Title: On the occurrence of sympathetic flares. Authors: Fritzova-Svestkova, L.; Chase, R. C.; Svestka, Z. Bibcode: 1976SoPh...48..275F Altcode: We have tried to determine whether statistical evidence on the occurrence of sympathetic flares, which is negative for whole-disk data, can be found for particular, physically connected, pairs of active regions. Recently, Simnett (1974) and Gergely and Erickson (1975) claimed to have found such evidence, but their results were based on incorrect computations of the random incidence of flares. If the correct formula is applied, the supposed evidence disappears. The results are negative also for pairs of active regions interconnected with magnetic loops visible in soft X-rays during the Skylab mission. The only positive result (with statistical confidence of 3.4 σ) is found for pairs of active regions, which are closer than 30° to each other, without specifying any kind of physical relationship. For such pairs of regions the occurrence of short-time (< 20 min) intervals between flares is increased, but the time interval pattern does not correspond to any mode of propagation of a triggering agent in the solar atmosphere. Therefore, if the increase has real physical significance, it would be indicative of some kind of subphotospheric synchronization of activity in nearby `sympathetic' active regions. Title: Optical Observations of Flares Authors: Svestka, Z. Bibcode: 1976RSPTA.281..435S Altcode: 1976RSLPT.281..435S The lecture describes solar flare effects in the chromosphere and photosphere, particularly emphasizing problems of the energy transfer, and the differences between thermal and non-thermal phases of the flare development. Filamentary and shell models are compared and the depth of the white-light flare emission is discussed. Optical effects possibly associated with other, non-optical flare-associated phenomena are pointed out. Title: What should be observed on the sun. Authors: Svestka, Z. Bibcode: 1976SoPh...47..375S Altcode: Three problems are emphasized in particular: the preflare magnetic field configuration, velocity fields, and the nature of acceleration processes in flares. It is concluded that what we need most urgently are high-resolution hard X-ray, soft X-ray, and EUV-pictures, coronal spectra, and magnetograms with high resolution both in space and time. A space-shuttle equipped with instrumentation of this kind would contribute significantly to our knowledge of the flare process. Title: Low-Energy Particle Events Associated with Sector Boundaries Authors: Svestka, Z.; Fritzova-Svestkova, L.; Nolte, J. T.; Dodson-Prince, H. W.; Hedeman, E. R. Bibcode: 1976BAAS....8R.370S Altcode: No abstract at ADS Title: Flare build-up study Authors: Svestka, Z. Bibcode: 1976SoPh...47.....S Altcode: 1976SoPh...47....1S The papers deal with problems which might be common to solar flares and earth's magnetosphere, problems associated with the initial phases of the flare phenomenon, the acceleration processes that seem to occur in flares and the magnetosphere, as well as the buildup and storage of flare energy in magnetic-field structures. Topics include the active role of magnetic fields in providing flare energy, current-sheet models of solar flares, the role of plasma turbulence in flare development, similarities and differences between magnetospheric substorms and solar flares, observations of magnetic merging in earth's magnetotail during magnetospheric substorms, evidence for magnetic-energy storage in coronal active regions, the possible role of transition-zone instabilities in preflare energy buildup, and flare energy storage and deposition. Other papers discuss energy release through the interaction of coronal magnetic fields, photospheric electric currents as a source of flare energy, magnetic-energy buildup in the solar atmosphere, magnetic and velocity fields in an active region, flare onset at meter wavelengths, laboratory experiments on field-line reconnection, key problems in auroral flare processes, and the solar-physics Shuttle/Spacelab program. Individual items are announced in this issue. Title: Preface Authors: de Jager, Cornelis; Obayashi, Tatsuzo; Švestka, Zdeněk Bibcode: 1976SoPh...47....9D Altcode: No abstract at ADS Title: Solar Flares Authors: Svestka, Z. Bibcode: 1976sofl.book.....S Altcode: 1976STIN...7634103S No abstract at ADS Title: Solar activity (Activité solaire). Authors: Newkirk, G.; Dunn, R. B.; Mehltretter, P.; MacQueen, R.; Bonnet, R. M.; White, O. R.; Fokker, A. D.; Zwaan, C.; Bruzek, A.; Durrant, C.; Grossmann-Doerth, U.; Mehltretter, J. P.; Svestka, Z.; de Feiter, L. D.; Tandberg-Hanssen, E.; Howard, R.; Stix, M.; Pneuman, G. W.; Hundhausen, A. J.; Sawyer, C.; Simon, P. Bibcode: 1976IAUTA..16b..13N Altcode: No abstract at ADS Title: Development of solar active regions. Authors: Svestka, Z. Bibcode: 1976pspe.proc..129S Altcode: 1976pspe.conf..129S The birth, growth, and decay of solar active regions are described. The appearance of active regions in different atmospheric layers is examined, and the coronal extension of active regions is considered. The use of Skylab soft X-ray and extreme UV observations for studying the complex loop structure of active regions in the solar corona and the sensitive reactions of the upper atmospheric layers to newly emerging flux is explained. It was found that well developed active regions are much bigger in the corona than in the underlying sunspot groups and plages, and that many of the active regions are connected with others through systems of magnetic field lines, occasionally visible in soft X-rays. These interconnections, which may survive several solar rotations, indicate bigger complexes on the sun than one individual active region. Title: Skylab observations of X-ray loops connecting separate active regions. Authors: Chase, R. C.; Krieger, A. S.; Svestka, Z.; Vaiana, G. S. Bibcode: 1976spre.conf..917C Altcode: 1976spre.proc..917C One hundred loops interconnecting 94 separate active solar regions detectable in soft X-rays were identified during the Skylab mission. While close active regions are commonly interconnected with loops, the number of such interconnections decreases steeply for longer distances; the longest interconnecting loop observed in the Skylab data connected regions separated by 37 deg. Several arguments are presented which support the point of view that this is the actual limit of the size of magnetic interconnections between active regions. No sympathetic flares could be found in the interconnected regions. These results cast doubt on the hypothesis that accelerated particles can be guided in interconnecting loops from one active region to another over distances of 100 deg or more and eventually produce sympathetic flares in them. Title: Solar flares Authors: Svestka, Z. Bibcode: 1976GAM.....8.....S Altcode: The present book covers all important aspects of solar flares, concentrating mainly on flare morphology. Separate chapters are devoted to low-temperature flares, high-temperature flares, flare-associated optical phenomena, particle emission from flares, and flare models. Flare observations in the H-alpha line are discussed along with flare spectra, thermal and nonthermal emissions from flares, flare waves, and loop prominences. Solar proton and electron emission is examined, particle clouds and interplanetary shock waves are considered, and characteristics of active regions are reviewed. Flare models are described with reference to chromospheric flares, flare synthesis, energy sources, energy release and storage, and particle acceleration. Title: Several aspects of flare-associated particle events. Authors: Svestka, Z. Bibcode: 1976npsa.conf..126S Altcode: No abstract at ADS Title: Book review Authors: Švestka, Z. Bibcode: 1975SoPh...45..543S Altcode: 1975SoPh...45..543. No abstract at ADS Title: Transequatorial Loops Interconnecting McMath 12472 and 12474. Authors: Svestka, Z.; Krieger, A. Bibcode: 1975BAAS....7Q.444S Altcode: No abstract at ADS Title: On the behaviour of the hydrogen Lyman series in flares Authors: de Feiter, L. D.; Svestka, Z. Bibcode: 1975SoPh...41..415D Altcode: The Lyman spectrum of hydrogen has been computed for a number of flare models, characterized by the column density of hydrogen atoms in the ground state (N1), the electron density (ne) and the electron temperature (Te). Broadening by the thermal Doppler effect and by Stark effect has been accounted for. The source functions for the individual lines of the series have been derived from non-LTE calculations of the excitation in hydrogen flares. The aim of the investigation is to evaluate the use of the intensities in between two successive Lyman lines for a determination of the value for N1, which is a physical parameter of the flare for which only indirect determinations are available. Whilst in principle this method could give reliable results, its practical application meets with difficulties which hardly can be overcome. Therefore, one probably has to base the N1 determination on the highest line resolvable in the spectrum. Title: Catalog of solar particle events 1955-1969 Authors: Svestka, Z.; Simon, P. Bibcode: 1975ASSL...49.....S Altcode: 1975cspe.book.....S No abstract at ADS Title: On the Acceleration Process in Solar Flares Authors: Svestka, Z. Bibcode: 1975IAUS...68..427S Altcode: The paper summarizes the data on the acceleration processes on the sun. Four different instabilities are distinguished: (1) one with purely thermal consequences giving rise to the origin of any flare; (2) a nonthermal process at the flash phase of flares giving rise to nearby 100 keV electrons and protons, manifested through hard X-ray and impulsive microwave bursts; (3) an instability giving rise to streams of electrons, without accelerating protons, manifested by type III bursts; when (2) and (3) are linked, flare associated electron events in space are often recorded; and (4) an explosive instability produces a shock wave which manifests itself as a type II burst. This instability leads to a second-step acceleration of particles preaccelerated in (2) and gives origin to more than 10 MeV protons and relativistic electrons. Title: Catalog of solar particles events, 1955 - 1969. Authors: Dodson, H. W.; Hedeman, E. R.; Kreplin, R. W.; Martres, M. -J.; Obridko, V. N.; Shea, M. A.; Smart, D.; Tanaka, H.; Svestka, Z.; Simon, P.; Fritzová-Svestková, L.; Guitart, A. Bibcode: 1975cspe.book.....D Altcode: 1975QB505.C37...... No abstract at ADS Title: Type II Radio Bursts and Particle Acceleration Authors: Švestka, Z.; Fritzová-Švestková, L. Bibcode: 1974SoPh...36..417S Altcode: 328 particle events recorded during 30 months from January 1, 1966 to June 30, 1968 (taken from the new Catalog of Solar Particle Events, 1955-1969) are compared with the occurrence of 166 type II radio bursts during the same period. The results of this comparison give a convincing evidence that proton acceleration to higher energies in flares (the `second acceleration step') is closely connected with the type II burst occurrence. The shock wave appears to originate near the time when the impulsive burst occurs, and the second acceleration step follows immediately the first one; in some cases the second step sets in while the first step is still in progress. Title: The Hα flare as a secondary product of a coronal instability Authors: Švestka, Z. Bibcode: 1973SoPh...31..389S Altcode: The assumption that the flare originates in the corona or transition layer, is confronted with the known properties of chromospheric flares. It is concluded that the basic mode of the energy transport into chromosphere is heat conduction. Only in some flares non-thermal particles contribute to the brightening in lower atmospheric layers: electrons with energy close to 100 keV produce chromospheric bright patches, and protons above 20 MeV cause the photospheric enhancements. The particle-produced brightenings are superposed on the basic quasi-thermal flare and involve only small areas as compared with the extensive regions heated through conduction. Title: A Comment on the Flare Activity in August 1972 Authors: Fritzová-Švestková, L.; Švestka}, Z. Bibcode: 1973SoPh...29..417F Altcode: No abstract at ADS Title: Observational Aspects of Flares Authors: Švestka, Z. Bibcode: 1973str..conf...23S Altcode: No abstract at ADS Title: The Expected Behaviour of the Hydrogen Lyman Lines in Solar Flares Authors: Švestka, Z.; de Feiter, L. D. Bibcode: 1972SSRv...13..824S Altcode: 1972IAUCo..14..824S No abstract at ADS Title: Characteristics of Strong Particle Sources of the Sun (Invited Paper) Authors: Svestka, Z. Bibcode: 1972spen.conf....1S Altcode: No abstract at ADS Title: Editorial Authors: De Jager, Cornelis; Švestka, Zdeněk Bibcode: 1972SoPh...25....3D Altcode: 1972SoPh...25....3. No abstract at ADS Title: Book review Authors: Švestka, Z. Bibcode: 1972SoPh...24..498S Altcode: 1972SoPh...24..498. No abstract at ADS Title: Spectral Analysis of Highly Inhomogeneous Chromospheric Flares Authors: Švestka, Z. Bibcode: 1972SoPh...24..154S Altcode: Analysis of a hydrogen flare spectrum is carried out, assuming that the flare radiation is diluted due to a highly inhomogeneous space distribution of the flare elements in the chromosphere. It is shown that one obtains the correct physical parameters in the flare elements, irrespective of the extent of dilution, if all the elements are optically thin in the spectral regions considered. However, if this is not true for all the elements, the parameters deduced are in error, which increases with the extent of dilution. The worst affected parameter is the linear thickness of the flaring region which is found to be too low by a factor which may be as high as 10. Errors also enter into electron and atom densities which are found to be too high and into the column density of hydrogen atoms which is underestimated. On the other hand, the deduced source function, and in consequence of it the electron temperature as well, remain unaffected, if the analysis is properly carried out. All the errors may increase strikingly if the analysis is performed for optically thick regions. Several kinds of observation are mentioned which indicate that dilution of radiation may occur in flares. However, reasonable estimates of the flare parameters are still possible provided that one avoids spectral regions with τ ≳ 1. Title: Spectra of Solar Flares Authors: Švestka, Zdeněk Bibcode: 1972ARA&A..10....1S Altcode: No abstract at ADS Title: Solar discrete particle events. Authors: Svestka, Z. Bibcode: 1972sstp.conf...72S Altcode: No abstract at ADS Title: Several Solar Aspects of Flare-Associated Particle Events Authors: Švestka, Z. Bibcode: 1972PrAA...30..141S Altcode: No abstract at ADS Title: Neutron and gamma-ray emission from white-light flares. Authors: de Feiter, L. D.; Svestka, Z. Bibcode: 1972spre.conf.1547D Altcode: 1972spre....2.1547D No abstract at ADS Title: Solar Discrete Particle Events Authors: Švestka, Z. Bibcode: 1972ASSL...29...72S Altcode: 1972sun..conf...72S No abstract at ADS Title: Editorial Authors: De Jager, Cornelis; Švestka, Zdeněk Bibcode: 1971SoPh...21....3D Altcode: 1971SoPh...21....3. No abstract at ADS Title: On the Flux of Neutrons from Flares Authors: Švestka, Z. Bibcode: 1971SoPh...19..202S Altcode: Under the assumption that white-light flares are caused by energetic particles penetrating into the photosphere (Švestka, 1970a; Najita and Orrall, 1970) the known number of protons needed for the white-light emission is used to obtain an estimate of the production of neutrons occurring at the same time. In the case of the white-light flare of 23 May, 1967, the peak flux of neutrons at the Earth distance had to exceed 3 neutrons/cm2s, thus being detectable in space. This maximum neutron flux reached the Earth as early as the time of the maximum phase of the flare in the Hα light. However, reasonable estimates show that flares associated with a detectable neutron flux should be fairly rare phenomena, maybe as rare as the white-light flares. Title: Solar Particle Events Authors: Svestka, Z. Bibcode: 1971RSPTA.270..157S Altcode: No abstract at ADS Title: Book Review: Intercorrelated satellite observations related to solar events. Edited by V. MANNO AND D. E. PAGE. Astrophysics and Space Science Library Vol. 19. Springer, New York, and Reidel, Dordrecht, Holland, 1970. xvi + 627 pp. Price $38.20 Authors: Švestka, Z. Bibcode: 1971Icar...14..489S Altcode: No abstract at ADS Title: Editorial Authors: de Jager, Cornelis; Švestka, Zdeněk Bibcode: 1971SoPh...17..287D Altcode: 1971SoPh...17..287. No abstract at ADS Title: Book reviews Authors: Švestka, Z.; Spiegel, E. A.; van Herk, G. Bibcode: 1971SSRv...11..867S Altcode: No abstract at ADS Title: Solar radio astronomy from the optical solar researchers point of view Authors: Svestka, Z. Bibcode: 1971cesra...1...15S Altcode: No abstract at ADS Title: The Phase of Particle Acceleration in the Flare Development Authors: Švestka, Z. Bibcode: 1970SoPh...13..471S Altcode: Evidence is given that the particle acceleration in flares is confined to the initial phase of the flare development preceding the Hα flare maximum and lasting for less than 10 min. The impulsive acceleration process is confined to a relatively small limited volume of about 5 × 1027 cm3 in the region of highest magnetic gradient in the flare, and its size represents about 0.05 or less of the total extent of the hot condensation which produces the soft X-ray and gradual microwave bursts. About one in fifty particles in this volume is accelerated to energy exceeding 100 keV, the total particle density being ≈ 1010 cm−3. The accelerated electrons produce the impulsive hard X-ray burst, but synchrotron losses greatly reduce the number of relativistic electrons participating in the bremsstrahlung process. Protons above 20 MeV penetrate to the lowest chromosphere and upper photosphere and temporarily increase the temperature in the bombarded region. As the result a flash of continuous emission appears, which should be most expressive below 1527 Å. The associated white-light emission shows the bottom of the region where the impulsive acceleration process occurs. Title: Book Review: Astronomy and Astrophysics Abstracts, Vol. 1: Literature 1969, Part 1, Springer-Verlag, Berlin, Heidelberg, New York Authors: Švestka, Z. Bibcode: 1970SoPh...12R.502S Altcode: 1970SoPh...12R.502Z No abstract at ADS Title: Solar Activity. Authors: Svestka, Z. Bibcode: 1970IAUTA..14...71S Altcode: No abstract at ADS Title: Solar particle events. Authors: Svestka, Z. Bibcode: 1970spre.conf..797S Altcode: No abstract at ADS Title: Book Review: Annals of the IQSY, M. I. T. Press, Vols. 1-5 Authors: Švestka, Z. Bibcode: 1970SoPh...12Q.502S Altcode: 1970SoPh...12Q.502Z No abstract at ADS Title: Particle Event Forecasting Authors: Švestka, Z. Bibcode: 1970ASSL...19...90S Altcode: 1970iso..conf...90S No abstract at ADS Title: The solar proton flares of June and November 1968 and February 1969. Authors: Krivský, L.; Svestka, Z. Bibcode: 1970spre.conf..817K Altcode: No abstract at ADS Title: Editorial Authors: De Jager, Cornelis; Švestka, Zdeněk Bibcode: 1969SoPh...10..243D Altcode: 1969SoPh...10..243. No abstract at ADS Title: Proton Flare Project, 1966. Summary of the August/September Particle Events in the McMath Region 8461. (Invited Review Paper) Authors: Švestka, Z.; Simon, P. Bibcode: 1969SoPh...10....3S Altcode: The paper summarizes observations of solar and space phenomena related to the McMath region Number 8461 which passed over the solar disk during the 1966 Proton Flare Project period, from August 21 to September 4, and produced two important solar particle events on August 28 and September 2. The most important results are reviewed and interpretation of some of them is suggested. Title: Comment on the Note by Friedman and Hamberger Authors: Švestka, Z. Bibcode: 1969SoPh....8..400S Altcode: No abstract at ADS Title: Editorial Authors: Švestka, Z.; De Jager, C. Bibcode: 1969SoPh....8....3S Altcode: 1969SoPh....8....3. No abstract at ADS Title: Abstracts of papers from other journals Authors: Pasachoff, Jay M.; Gussmann, E. A.; Stepanyan, N. N.; de Feiter, L. D.; Uchida, Yutaka; Švestka, Z.; Vassilyeva, G. J. Bibcode: 1969SoPh....6..155P Altcode: No abstract at ADS Title: The optical flare Authors: Švestka, Z. Bibcode: 1969sfsr.conf...16S Altcode: No abstract at ADS Title: Solar flares and space research Authors: de Jager, C.; Svestka, Z. Bibcode: 1969sfsr.conf.....D Altcode: 1969sfsr.book.....D No abstract at ADS Title: Effects associated with the sector boundary crossing on 8 July 1966 Authors: Švestka, Z. Bibcode: 1969sfsr.conf..319S Altcode: No abstract at ADS Title: General summary on the results of the first Proton Flare Project period, July 1966. Authors: Simon, P.; Svestka, Z. Bibcode: 1969AIQSY...3..469S Altcode: No abstract at ADS Title: Editorial Authors: De Jager, C.; Švestka, Z. Bibcode: 1968SoPh....5..259D Altcode: 1968SoPh....5..259. No abstract at ADS Title: Effects associated with the Sector Boundary crossing on July 8, 1966 Authors: Švestka, Zdeněk. Bibcode: 1968SoPh....4..361S Altcode: Thirty hours after the proton flare of July 7, 1966, the earth and nearby satellites crossed a sector boundary of the interplanetary magnetic field. This occurred before the flare-associated shockwave arrived at the earth, so that the space was filled with energetic particles ejected from the flare. Satellite measurements have shown that in such a case <20 MeV protons are stored within the range of the sector boundary and with decreasing energy the particles tend to accumulate towards and behind the Eastern boundary limit; low-energy particles, such as <50 keV electrons, are stored exclusively behind this Eastern limit. Title: On Long-Term Forecasts of Proton Flares Authors: Švestka, Zdeněk. Bibcode: 1968SoPh....4...18S Altcode: 174 proton flares which were observed during the period from 1956 to 1965, occurred in 81 different active regions. It is shown that these active regions formed in complexes of activity, which stayed on the solar surface for many months, and in some cases even for several years. Since the proton-flare regions develop very rapidly and reach the proton-flare active stage within a few days, these complexes of activity represent the areas on the sun, where proton-flare regions can form at any time. Reference is made to contributions by Bumba and Howard, who investigated the birth of active regions and detected some properties of complexes of activity; nevertheless, at the present time, we do not know any method to predict when a proton-flare region begins to develop in such a complex of activity. Title: Introduction and Summary Authors: Svestka, Z. Bibcode: 1968IAUS...35..513S Altcode: No abstract at ADS Title: Mass motions in flares indicated by line profiles and filtergrams Introductory lecture Authors: Švestka, Z. Bibcode: 1968mmsf.conf...17S Altcode: No abstract at ADS Title: Loop-Prominence Systems and Proton-Flare Active Regions Authors: Svestka, Z. Bibcode: 1968IAUS...35..287S Altcode: No abstract at ADS Title: Editorial Authors: De Jager, C.; Švestka, Z. Bibcode: 1968SoPh....3....3D Altcode: 1968SoPh....3....3. No abstract at ADS Title: Electron Density in Flares, II: Results of Measurement Authors: Fritzová-Švestková, L.; Švestka, Z. Bibcode: 1967SoPh....2...87F Altcode: Measurements of the electron density in 16 flares are summarized and discussed. For 13 of them the electron density has been determined by the halfwidth method discussed in Part I of this paper. In the flash phase of all disk flares of importance 1 + and higher the electron density exceeds 1013 cm−3 and increases with the flare importance. In the maximum of large flares the electron density exceeds 3 × 1013 cm−3 and declines to 1013 cm−3 and to lower values in about 20 minutes after the flash phase. In limb flares, i.e. higher than 5000 km above the solar limb, the electron density is lower than 5 × 1012 cm−3. This shows a decrease of the electron density in the flare elements situated in higher parts of the chromosphere. On the other hand, however, at least in some flares the electron density remains fairly constant within a wide range of height in the upper chromosphere and the low corona. Title: Electron Density in Flares, I: Discussion of the Halfwidth Method Authors: Švestka, Z.; Fritzová-Švestková, L. Bibcode: 1967SoPh....2...75S Altcode: The halfwidth method used for the determination of the electron density in flares is discussed from the point of view of possible errors which may enter the obtained results. The discussion includes an analysis of errors of measurement as well as errors of the method due to: (1) our incomplete knowledge of the electron damping, (2) the assumption of constant electron temperature, (3) the presence of residual self-absorption in high Balmer lines, and (4) possibly present non-thermal motions. It is shown that the factors (2) to (4) cannot induce any relative error in ne higher than 30 % of the correct value, and the actual error usually is smaller. A comparison is made of the halfwidth-method application to active prominences and limb flares. Title: Editorial Authors: de Jager, C.; Švestka, Z. Bibcode: 1967SoPh....1..303D Altcode: 1967SoPh....1..303. No abstract at ADS Title: Type IV bursts. III. In association with Forbush effects Authors: Švestka, Z. Bibcode: 1967BAICz..18...55S Altcode: No abstract at ADS Title: Editorial Authors: de Jager, C.; Švestka, Z. Bibcode: 1967SoPh....1....3D Altcode: 1967SoPh....1....3. No abstract at ADS Title: Buchbesprechungen über: Solar Physics. Ed. C. DE JAGER, and Z. ŠVESTKA. (Ref. R. O. REDMAN) Authors: de Jager, C.; Švestka, Z. Bibcode: 1967ZA.....67...95D Altcode: No abstract at ADS Title: Optical Observations of Solar Flares Authors: Švestka, Zdeněk Bibcode: 1966SSRv....5..388S Altcode: This paper gives a review of the results of optical observations of solar flares. Observations carried out in the Hα line, flare spectra, and the methods of analysing the flare spectra are briefly discussed. Great attention is paid to the continuous emission of flares in the optical spectral region. In the last section, optical aspects of proton flares are summarized. Title: Type IV bursts. II. In association with PCA events Authors: Fritzová-Švestková, L.; Švestka, Z. Bibcode: 1966BAICz..17..249F Altcode: No abstract at ADS Title: The H- emission in flares Authors: Švestka, Z. Bibcode: 1966BAICz..17..137S Altcode: No abstract at ADS Title: Proton flares before 1956 Authors: Švestka, Z. Bibcode: 1966BAICz..17..262S Altcode: No abstract at ADS Title: A prediction on proton flare occurrence in 1966-1968 Authors: Švestka, Z. Bibcode: 1966BAICz..17...95S Altcode: No abstract at ADS Title: Type IV Bursts. I. List of events Authors: Švestka, Z.; Olmr, J. Bibcode: 1966BAICz..17....4S Altcode: No abstract at ADS Title: Spectral Analysis of Solar Flares Authors: Švestka, Zdeněk Bibcode: 1965AdA&A...3..119S Altcode: No abstract at ADS Title: Spectral anomalies associated with the extraordinary X-ray emission recorded by the SR-1 satellite on August 7, 1960 Authors: Svestka, Z. Bibcode: 1964spre.conf..768S Altcode: No abstract at ADS Title: Electron temperature and bn values in flares Authors: Švestka, Z. Bibcode: 1964BAICz..15...38S Altcode: No abstract at ADS Title: Broadening of high Balmer lines in flares and prominences Authors: Švestka, Z. Bibcode: 1964BAICz..15..162S Altcode: No abstract at ADS Title: Time variation of electron density in a large solar flare Authors: de Feiter, L. D.; Švestka, Z. Bibcode: 1964BAICz..15..117D Altcode: No abstract at ADS Title: Qualitative discussion of 244 flare spectra. IV. Splitting of metal emission lines Authors: Kopecký, M.; Letfus, V.; Blaha, M.; Švestka, Z. Bibcode: 1963BAICz..14..146K Altcode: No abstract at ADS Title: On the spectral analysis of flares Authors: Švestka, Z. Bibcode: 1963BAICz..14...75S Altcode: No abstract at ADS Title: Spectral analysis of the moustache-like flare of August 7, 1960 Authors: Svestka, Z. Bibcode: 1963BAICz..14..234S Altcode: No abstract at ADS Title: Astronomicky a astronauticky slovnik. Authors: Kleczek, Josip; Svestka, Zdenek Bibcode: 1963aaas.book.....K Altcode: 1963QB14.K56....... No abstract at ADS Title: Evidence of Stark broadening of Balmer lines in flares Authors: Svestka, Z. Bibcode: 1962BAICz..13..236S Altcode: No abstract at ADS Title: Qualitative discussion of 244 flare spectra. II. Line asymmetry and helium lines Authors: Švestka, Z.; Kopecký, M.; Blaha, M. Bibcode: 1962BAICz..13...37S Altcode: No abstract at ADS Title: Motions in chromospheric flares Authors: Švestka, Z. Bibcode: 1962BAICz..13..190S Altcode: No abstract at ADS Title: Note on planetary nebulae in the Small Magellanic Cloud Authors: Švestka, Z. Bibcode: 1962BAICz..13...35S Altcode: No abstract at ADS Title: On a peculiar flare spectrum Authors: Švestka, Z. Bibcode: 1962BAICz..13...30S Altcode: No abstract at ADS Title: Qualitative discussion of 244 flare spectra. III. Metal emission lines Authors: Blaha, M.; Kopecký, M.; Švestka, Z. Bibcode: 1962BAICz..13...85B Altcode: No abstract at ADS Title: Qualitative discussion of 244 flare spectra Authors: Švestka, Z.; Kopecký, M.; Blaha, M. Bibcode: 1961BAICz..12..229S Altcode: No abstract at ADS Title: Observations of flares at the Ondřejov Observatory in the year 1959 Authors: Kvičala, F.; Hřebik, F.; Olmr, F.; Švestka, Z.; Křivský, L. Bibcode: 1961BAICz..12...47K Altcode: No abstract at ADS Title: Spectrum of the flare of July 20, 1958 Authors: Švestka, Z. Bibcode: 1961BAICz..12...73S Altcode: No abstract at ADS Title: Measurement of Magnetic Fields in Chromospheric Flares Authors: Blaha, M.; Kopecký, M.; Švestka, Z. Bibcode: 1960Natur.187..224B Altcode: SPECTRA of two great chromospheric flares taken by the flare spectrograph at Ondřejov1 show an evident splitting of the D1 emission line of Na I which is attributed to a magnetic field existing in that part of the chromosphere where the sodium lines are formed. This explanation is supported by the following facts : Title: List of flares observed at Ondrejov observatory during the I.G.Y. Authors: Kvicala, J.; Hrebik, F.; Letfus, V.; Olmr, J.; Svestka, Z.; Krivsky, L. Bibcode: 1960PAICz..43....1K Altcode: No abstract at ADS Title: Hydrogen spectrum of the flare of July 30, 1959 Authors: Švestka, Z. Bibcode: 1960BAICz..11..167S Altcode: No abstract at ADS Title: The flare spectrograph at Ondřejov Authors: Valníček, B.; Letfus, V.; Blaha, M.; Švestka, Z.; Seidl, Z. Bibcode: 1959BAICz..10..149V Altcode: No abstract at ADS Title: Catalogue of Chromospheric Flares observed at Ondřejov during the first half of the year 1957 Authors: Letfus, V.; Růžičková, B.; Švestka, Z. Bibcode: 1959BAICz..10..136L Altcode: No abstract at ADS Title: Damping and Stark broadening of Balmer lines Authors: Švestka, Z. Bibcode: 1959BAICz..10...10S Altcode: No abstract at ADS Title: Polarization of Light of the Comets Arend-Roland (1956h) and Mrkos (1957d) Authors: Blaha, M.; Hruška, A.; Švestka, Z.; Vanýsek, V. Bibcode: 1958Natur.182..331B Altcode: POLARIZATION of the total light of the Comets 1956h and 1957d was studied photographically by simultaneous exposures with three objectives and three `Polaroids'. The planes of polarization of the three `Polaroids' were at 120°. 2-in. objectives were used at ƒ/9 with Agfa `Astro' panchromatic plates. The characteristic curve was determined by comparison with an exposed photometric wedge. Errors due to the instrument were measured by means of light from an artificial source, polarized to a known degree by reflexion from a glass surface. The error of the polarization determined is +/- 2.5 per cent. Title: Catalogue of chromospheric flares observed at Ondřejov during the years 1952-1956 Authors: Letƒus, V.; RůžiČková, B.; Švestka, Z. Bibcode: 1958BAICz...9..178L Altcode: No abstract at ADS Title: 536 Mc/s radio events associated with chromospheric flares during the year 1956 Authors: Budějický, J.; Švestka, Z. Bibcode: 1958BAICz...9...48B Altcode: No abstract at ADS Title: Fysikalni podminky V chromosferickych erupcich. Authors: Svestka, Zdenek Bibcode: 1957PAICz..32.....S Altcode: 1957QB1.C284A3c32.. No abstract at ADS Title: Mezihvezdna hmota. Authors: Svestka, Zdenek; Vanysek, Valdimir Bibcode: 1956mehm.book.....S Altcode: 1956QB500.S9....... No abstract at ADS Title: Several Notes on the Statistics of Chromosferic Flares Authors: Švestka, Z. Bibcode: 1956BAICz...7....9S Altcode: No abstract at ADS Title: The Optical Thickness of Flares and the Broadening of Balmer Lines in their Spectra Authors: Švestka, Z. Bibcode: 1956BAICz...7..130S Altcode: No abstract at ADS Title: The Width of Hα in Solar Flares Authors: Švestka, Z.; Fritzová, L. Bibcode: 1956BAICz...7...30S Altcode: No abstract at ADS Title: Secondary Periods of Long-periodic Variables Authors: Fritzová, L.; Pěkný, Z.; Švestka, Z. Bibcode: 1954BAICz...5...49F Altcode: No abstract at ADS Title: Hvezdne atmosfery. Authors: Svestka, Zdenek Bibcode: 1954hvat.book.....S Altcode: 1954QB809.S85...... No abstract at ADS Title: Catalogue des crateres lunaire Authors: Bouska, J.; Hrebik, F.; Svestka, Z. Bibcode: 1953PAICz..25..107B Altcode: No abstract at ADS Title: Recurrent and Revived Active Regions on the Sun Authors: Švestka, Z. Bibcode: 1953BAICz...4..186S Altcode: No abstract at ADS Title: Slunce a jeho vlivy NA zemi. Authors: Link, Frantisek; Svestka, Zdenek Bibcode: 1953sajv.book.....L Altcode: 1953QB521.L72...... No abstract at ADS Title: The Hα-Emission from Chromospheric Flares: Central Intensity and Line-Width Authors: Švestka, Z. Bibcode: 1951BAICz...2..165S Altcode: No abstract at ADS Title: The Hα-Emission from Chromospheric Flares: The Flare of August 5, 1949 Authors: Švestka, Z. Bibcode: 1951BAICz...2..153S Altcode: No abstract at ADS Title: The Hα-Emission from Chromospheric Flares: Expanding Source of Radiation Authors: Švestka, Z. Bibcode: 1951BAICz...2..150S Altcode: No abstract at ADS Title: The Hα-Emission from Chromospheric Flares: Course of the Asymmetry Authors: Švestka, Z. Bibcode: 1951BAICz...2..120S Altcode: No abstract at ADS Title: The Hα-Emission from Chromospheric Flares: General Features of the Asymmetry Authors: Švestka, Z. Bibcode: 1951BAICz...2..100S Altcode: No abstract at ADS Title: The Hα-Emission from Chromospheric Flares: Observations Authors: Švestka, Z. Bibcode: 1951BAICz...2...81S Altcode: No abstract at ADS Title: On a Possible Development of Planetary Nebulae Authors: Švestka, Z. Bibcode: 1950BAICz...2...52S Altcode: No abstract at ADS Title: The Reason of Validity of the Bode's Law Authors: Švestka, Z. Bibcode: 1950BAICz...2...45S Altcode: No abstract at ADS Title: A Note on the Brightness of Lunar Eclipses Authors: Švestka, Z. Bibcode: 1950BAICz...2...41S Altcode: No abstract at ADS Title: On the Variations of the Enlargement of the Earth's Shadow during the Lunar Eclipses Authors: Švestka, Z. Bibcode: 1950BAICz...2....6S Altcode: No abstract at ADS Title: The Influence of Clouds on the Density of the Central Part of the Earth's Shadow Authors: Švestka, Zdeněk. Bibcode: 1949BAICz...1..131S Altcode: No abstract at ADS Title: On the Variation of the Coma-Diameter of Encke's Comet Authors: Bouška, Jiří.; Švestka, Zdeněk. Bibcode: 1949BAICz...1..123B Altcode: No abstract at ADS Title: On the Observed Density of the Earth's Shadow near its Centre Authors: Švestka, Zdeněk. Bibcode: 1949BAICz...1..109S Altcode: No abstract at ADS Title: On the Real Number of Solar Flares Authors: Švestka, Zdeněk. Bibcode: 1949BAICz...1...95S Altcode: No abstract at ADS Title: Observations of Solar Flares and High-speed Prominences from July to December 1948 Authors: Švestka, Zdeněk. Bibcode: 1949BAICz...1...73S Altcode: No abstract at ADS Title: The Illumination by Diffusion in the Centre of the Earth's Shadow Authors: Švestka, Zdeněk. Bibcode: 1948BAICz...1...48S Altcode: No abstract at ADS Title: The Density of the Earth's Shadow near its Centre Authors: Švestka, Zdeněk. Bibcode: 1948BAICz...1...29S Altcode: No abstract at ADS