Showing papers on "Coronal mass ejection published in 1988"

The Physics of Solar Flares

Abstract: Solar flare phenomena are examined in an introduction for advanced undergraduate and graduate physics students. Chapters are devoted to the history of observations, flare spectroscopy, flare magnetohydrodynamics, flare plasma physics, radiative processes in the solar plasma, preflare conditions, the impulsive phase, the gradual phase, and coronal mass ejections. Diagrams, graphs, and photographs are provided.

The temperature structure, mass, and energy flow in the corona and inner solar wind

Abstract: Remote-sensing and in situ data are used to constrain a radiative energy balance model in order to study the radial variations of coronal temperatures, densities, and outflow speeds in several types of coronal holes and in an unstructured quiet region of the corona. A one-fluid solar wind model is used which takes into account the effects of radiative and inward conductive losses in the low corona and the chromospheric-coronal transition region. The results show that the total nonradiative energy input in magnetically open coronal regions is 5 + or - 10 to the 5th ergs/sq cm, and that most of the energy heating the coronal plasma is dissipated within 2 solar radii of the solar surface.

Dynamics and Structure of Quiescent Solar Prominences

Abstract: 1 Introduction to Quiescent Solar Prominences (E R Priest).- 1.1 Basic Description.- 1.1.1 Different Types.- 1.1.2 Properties.- 1.1.3 Development.- 1.1.4 Structure.- 1.1.5 Eruption.- 1.2 Basic Equations of MHD.- 1.2.1 Magnetohydrostatics.- 1.2.2 Waves.- 1.2.3 Instabilities.- 1.3 Prominence Puzzles.- 2 Overall Properties and Steady Flows (B Schmieder).- 2.1 Basic Properties.- 2.1.1 Description and Classification.- 2.1.2 Fine Structure in H?.- 2.1.3 Evolution of Filaments During the Solar Cycle.- 2.2 Physical Characteristics: Density and Temperature.- 2.2.1 Density and Ionization Degree.- 2.2.2 Non LTE Models.- 2.2.3 Turbulent Velocity and Electron Temperature.- 2.3 Velocity Field and Mass Flux.- 2.3.1 Instrumentation.- 2.3.2 H? Profile Analysis.- 2.3.3 Vertical Motions.- 2.3.4 Horizontal Motions.- 2.3.5 Oscillations.- 2.4 Instability.- 2.4.1 Disparition Brusque of Filaments.- 2.4.2 Model Support.- 2.4.3 Post-Flare Loops and Loop Prominences.- 2.5 Conclusion.- 3 Prominence Environment (O Engvold).- 3.1 Introduction.- 3.2 Helmet Streamers.- 3.2.1 Eclipse Photography.- 3.2.2 Morphology.- 3.2.3 Location of Current Sheet.- 3.2.4 Brightness.- 3.3 Coronal Cavities.- 3.3.1 Brightness and Structure.- 3.3.2 Temperature and Density.- 3.4 Filament Channels.- 3.4.1 Association with Neutral Lines.- 3.4.2 Poleward Migration of Filament Channels.- 3.4.3 Presence of Prominences.- 3.4.4 Temperature and Electron Pressure.- 3.4.5 Cool Matter in the Filament Channels.- 3.5 Prominence-Corona Transition Region.- 3.5.1 Line Emission.- 3.5.2 Empirical Modelling.- 3.5.3 A Fragmented and Dynamic Transition Region.- 3.6 Prominences and Environment.- 3.6.1 Magnetic Fields and Chromospheric Structure.- 3.6.2 Association with Supergranulation Network.- 3.6.3 Dynamics.- 3.6.4 The Mass of Coronal Cavity and Prominence.- 3.6.5 Coronal Voids - a Source of Prominence Mass?.- 3.7 Modelling of the Helmet Streamer/Prominence Complex.- 3.7.1 Helmet Streamer and Cavity.- 3.7.2 Magnetic Field Topology.- 3.7.3 Siphon-Type Models.- 3.8 Conclusions.- 4 Observation of Prominence Magnetic Fields (J L Leroy).- 4.1 Historical Steps.- 4 2 Investigations Based on the Polarimetry of Spectral Lines.- 4.2.1 Zeeman Effect.- 4.2.2 HanleEffect.- 4.2.3 180 1 Introduction to Quiescent Solar Prominences (E R Priest).- 1.1 Basic Description.- 1.1.1 Different Types.- 1.1.2 Properties.- 1.1.3 Development.- 1.1.4 Structure.- 1.1.5 Eruption.- 1.2 Basic Equations of MHD.- 1.2.1 Magnetohydrostatics.- 1.2.2 Waves.- 1.2.3 Instabilities.- 1.3 Prominence Puzzles.- 2 Overall Properties and Steady Flows (B Schmieder).- 2.1 Basic Properties.- 2.1.1 Description and Classification.- 2.1.2 Fine Structure in H?.- 2.1.3 Evolution of Filaments During the Solar Cycle.- 2.2 Physical Characteristics: Density and Temperature.- 2.2.1 Density and Ionization Degree.- 2.2.2 Non LTE Models.- 2.2.3 Turbulent Velocity and Electron Temperature.- 2.3 Velocity Field and Mass Flux.- 2.3.1 Instrumentation.- 2.3.2 H? Profile Analysis.- 2.3.3 Vertical Motions.- 2.3.4 Horizontal Motions.- 2.3.5 Oscillations.- 2.4 Instability.- 2.4.1 Disparition Brusque of Filaments.- 2.4.2 Model Support.- 2.4.3 Post-Flare Loops and Loop Prominences.- 2.5 Conclusion.- 3 Prominence Environment (O Engvold).- 3.1 Introduction.- 3.2 Helmet Streamers.- 3.2.1 Eclipse Photography.- 3.2.2 Morphology.- 3.2.3 Location of Current Sheet.- 3.2.4 Brightness.- 3.3 Coronal Cavities.- 3.3.1 Brightness and Structure.- 3.3.2 Temperature and Density.- 3.4 Filament Channels.- 3.4.1 Association with Neutral Lines.- 3.4.2 Poleward Migration of Filament Channels.- 3.4.3 Presence of Prominences.- 3.4.4 Temperature and Electron Pressure.- 3.4.5 Cool Matter in the Filament Channels.- 3.5 Prominence-Corona Transition Region.- 3.5.1 Line Emission.- 3.5.2 Empirical Modelling.- 3.5.3 A Fragmented and Dynamic Transition Region.- 3.6 Prominences and Environment.- 3.6.1 Magnetic Fields and Chromospheric Structure.- 3.6.2 Association with Supergranulation Network.- 3.6.3 Dynamics.- 3.6.4 The Mass of Coronal Cavity and Prominence.- 3.6.5 Coronal Voids - a Source of Prominence Mass?.- 3.7 Modelling of the Helmet Streamer/Prominence Complex.- 3.7.1 Helmet Streamer and Cavity.- 3.7.2 Magnetic Field Topology.- 3.7.3 Siphon-Type Models.- 3.8 Conclusions.- 4 Observation of Prominence Magnetic Fields (J L Leroy).- 4.1 Historical Steps.- 4 2 Investigations Based on the Polarimetry of Spectral Lines.- 4.2.1 Zeeman Effect.- 4.2.2 HanleEffect.- 4.2.3 180 Ambiguity.- 4.2.4 Instrumental Achievements.- 4.3 Indirect Magnetic Field Determinations.- 4.4 Magnetic Field at the Photospheric Level.- 4.5 Main Features of the Magnetic Field in Quiescent Prominences.- 4.5.1 Field Strength.- 4.5.2 Angle with Horizontal.- 4.5.3 Angle with Prominence Axis.- 4.5.4 Magnetic Structure with Normal or Inverse Polarity.- 4.5.5 Homogeneity of the Field.- 4.6 Some Important Problems.- 4.6.1 Magnetic Field in Sub Arc Second Structures.- 4.6.2 Paradox of Fine Vertical Structures.- 4.6.3 Determination of Currents.- 4.6.4 Evolution of Prominence Magnetic Structure.- 5 The Formation of Solar Prominences (J M Malherbe).- 5.1 Introduction.- 5.2 Overview of Observations.- 5.3 Main MHD Instabilities Involved in Prominence Formation.- 5.3.1 Radiative Thermal Instability.- 5.3.2 Resistive Instabilities.- 5.4 Steady Reconnection in Current Sheets.- 5.4.1 Incompressible and Compressible Theories.- 5.4.2 Unification of Different Regimes.- 5.5 Static Models.- 5.5.1 Condensation in a Loop.- 5.5.2 Condensation in an Arcade.- 5.5.3 Condensation in a Sheared Magnetic Field.- 5.5.4 Condensation in a Current Sheet.- 5.6 Dynamic Models: Injection from the Chromosphere into Closed Loops.- 5.6.1 Surge-Like Models.- 5.6.2 Evaporation Models.- 5.7 Dynamic Models: Condensation in Coronal Current Sheets.- 5.7.1 Numerical Simulations.- 5.7.2 Role of Shock Waves in Condensation Process.- 5.8 Unsolved Problems.- 5.9 Conclusion.- 6 Structure and Equilibrium of Prominences (U Anzer).- 6.1 Introduction.- 6.2 Prominence Models.- 6.2.1 Global Structure.- 6.2.1.1 Two-Dimensional Equilibria.- 6.2.1.1.1 Models with Normal Magnetic Polarity.- 6.2.1.1.2 Models with Inverse Magnetic Polarity.- 6.2.1.1.3 Force-Free Fields.- 6.2.1.2 Quasi-Three-Dimensional Models.- 6.2.1.3 Support by Alfven Waves.- 6.2.2 Internal Structure and Thermal Equilibrium.- 6.2.2.1 Hydrostatic Equilibrium.- 6.2.2.2 Thermal Equilibrium.- 6.3 Concluding Remarks.- 7 Stability and Eruption of Prominences (A W Hood).- 7.1 Introduction.- 7.2 Description of MHD Instabilities.- 7.3 Methods of Solution.- 7.3.1 Normal Modes.- 7.3.2 Energy Method.- 7.3.3 Non Equilibrium.- 7.4 Effect of the Dense Photosphere.- 7.4.1 Physical Arguments.- 7.4.2 Ballooning Modes.- 7.5 Coronal Arcades.- 7.5.1 Distributed Current Models - Eruptive Instability.- 7.5.2 Localised Modes - Small Scale Structure.- 7.5.3 Arcades Containing a Current Sheet.- 7.6 Thermal Stability.- 7.7 Resistive Instabilities - Tearing Modes.- 7.7.1 Introduction.- 7.7.2 Estimate of Tearing Mode Growth Rate.- 7.7.3 Effect of Line Tying.- 7.8 Simple Model of Prominence Eruption and a Coronal Mass Ejection.- 7.9 Conclusions and Future Work.- References.

Filament eruptions and the impulsive phase of solar flares. Report for 18 May 1987-17 May 1988

Abstract: We examine the observed development of filament eruptions in the impulsive phase of flares for evidence of how the eruption is driven. A possibility sometimes adopted as working hypothesis is that the filament eruption and accompanying coronal mass ejection are consequences of energy release in the flare impulsive phase; they are taken to be ejecta in the explosion resulting from the pressure pulse from plasma heating in the flare. Evidence against this view is from four flares in which, in H-alpha movies, a filament eruption was observed during the flare impulsive phase defined by the E = approx. 30 keV hard x-ray emission observed with the U. of Calif. at Berkely detector on the ISEE 3 spacecraft. In each case it was found find that: (1) filament eruption began before onset of the impulsive phase; (2) eruptive motion is consistent with a smooth evolution through the impulsive phase, accelerating, but showing no new acceleration attributable to the impulsive phase; (3) brightening of the H alpha flare ribbons in the impulsive phase occurring in compact areas is much smaller than the overall span of the erupting filament; and (4) the observed projected speed is on the order of 100 km/s atmore » the onset of the impulsive phase. These characteristics indicate that filament eruption is not driven by flare plasma pressure, but instead marks an eruption of magnetic field driven by a global MHD instability of the field configuration in the flare region. It appears that filament eruption and impulsive energy release are coordinated and driven by a common cause, the instability of the whole field configuration. A new mode of energy release, that of the impulsive phase, may be initiated when the eruptive motion surpasses some speed limit of order 100 km/s.« less

Solar and interplanetary control of the location of the Venus bow shock

Abstract: The Venus bow shock location has been measured at nearly 2000 shock crossings, and its dependence on solar EUV, solar wind conditions, and the interplanetary magnetic field determined. The shock position at the terminator varies from about 2.14 Venus radii at solar minimum to 2.40 Venus radii at solar maximum. The location of the shock varies little with solar wind dynamic pressure but strongly with solar wind Mach number. The shock is farthest from Venus on the side of the planet in which newly created ions gyrate away from the ionosphere. When the interplanetary magnetic field is perpendicular to the flow, the cross section of the shock is quite elliptical. This effect appears to be due to the anisotropic propagation of the fast magnetosonic wave. When the interplanetary magnetic field is aligned with the flow, the bow shock cross section is circular and only weakly sensitive to changing EUV flux.

Interplanetary magnetic field draping about fast coronal mass ejecta in the outer heliosphere

Abstract: The possibility that the IMF becomes draped around coronal mass ejections (CMEs) propagating rapidly through the quiescent solar wind into the outer heliosphere is investigated theoretically. The results are presented in diagrams and graphs and discussed in detail. It is found that large sunward-directed structures analogous to the Venus and cometary magnetotails should form when the CME velocity exceeds the solar-wind velocity by more than the local Alfven speed; such structures could hang up swept-up IMF flux for as long as several days. Pioneer 11 magnetic-field measurements at 6.9-9.4 AU from three 20-d periods in 1978 are examined and shown to contain some features consistent with CME draping.

Estimates of solar wind heating inside 0.3 AU

Abstract: Helios 1 proton temperature data have been normalized in order to determine a base temperature-velocity curve at 0.3 AU and to provide quantitative estimates on the close-in heating at different solar wind velocities. The results suggest that the slope of the solar wind temperature gradients for high-speed streams inside 0.3 AU is about half of that found beyond it. The very-low-speed wind is shown to expand adiabatically all the way out. It is also found that intermediate speed winds have enhanced heating rates in proportion to their velocities.

Force-free magnetic fields: Is there a loss of equilibrium

Abstract: This paper examines concept in solar physics that is known as loss of equilibrium in which a sequence of force-free magnetic fields, said to represent a possible quasi-static evolution of solar magnetic fields, reaches a critical configuration beyond which no acceptable solution of the prescribed form exists. This concept is used to explain eruptive phenomena ranging from solar flares to coronal mass ejections. Certain sequences of force-free configurations are discussed that exhibit a loss of equilibrium, and it is argued that the concept is devoid of physical significance since each sequence is defined a way that does not represent an acceptable thought experiment. For example, the sequence may be defined in terms of a global constraint on the boundary conditions, or the evolution of the sequence may require the creation of magnetic flux that is not connected to the photosphere and is not present in the original configuration. The global constraints typically occur in using the so-called generating function method. An acceptable thought experiment is proposed to specify the field configuration in terms of photospheric boundary conditions comprising the normal component of the field and the field-line connectivity. Consider a magnetic-field sequence that, when described in terms of a generatingmore » function, exhibits a loss of equilibrium and show that, when one instead defines the sequence in terms of the corresponding boundary conditions, the sequence is well behaved.« less

Evidence that magnetic energy shedding in solar filament eruptions is the drive in accompanying flares and coronal mass ejections

Abstract: The dependence of the magnetic energy on the field expansion and untwisting of the flux tube in which an erupting solar filament is embedded has been determined in order to evaluate the energy decrease in the erupting flux tube. Magnetic energy shedding by the filament-field eruption is found to be the driving mechanism in both filament-eruption flares and coronal mass ejections. Confined filament-eruption flares, filament-eruption flares with sprays and coronal mass ejections, and coronal mass ejections from quiescent filament eruptions are all shown to be similar types of events.

Expectations for the microphysics of the Mars‐solar wind interaction

Abstract: The two Phobos spacecraft, which will start to orbit Mars early in 1989, will be capable of investigating in detail the microphysics of the Mars-solar wind interaction. Simple scaling arguments and analogies with other planetary bow shocks indicate that the sub-solar shock standoff distance should be small compared with plasma scalelengths, giving the shocked solar wind insufficient space in which to thermalize downstream before encountering the magnetospheric obstacle. Both the magnetosphere and ionosphere can be affected by particles and waves from the solar wind interaction.

Density and white light brightness in looplike coronal mass ejections: Temporal evolution

Abstract: Three ambient coronal models suitable for studies of time-dependent phenomena were used to investigate the propagation of coronal mass ejections initiated in each atmosphere by an identical energy source. These models included those of a static corona with a dipole magnetic field, developed by Dryer et al. (1979); a steady polytropic corona with an equatorial coronal streamer, developed by Steinolfson et al. (1982); and Steinolfson's (1988) model of heated corona with an equatorial coronal streamer. The results indicated that the first model does not adequately represent the general characteristics of observed looplike mass ejections, and the second model simulated only some of the observed features. Only the third model, which included a heating term and a streamer, was found to yield accurate simulation of the mess ejection observations.

Soft X-ray emissions, meter-wavelength radio bursts, and particle acceleration in solar flares

Abstract: A detailed study of the relationship between metric radio bursts and soft X-ray flares has been made using an extensive data set covering 15 yr. It is found that type IV emission is mainly associated with long-duration 1-8 A events that are known to be well associated with coronal mass ejections. In contrast, type II and type III bursts originate primarily in impulsive soft X-ray events that are not necessarily accompanied by mass ejection. Strong type III bursts, in particular, appear to occur only in association with relatively impulsive flares. It is suggested that coronal shocks responsible for type II bursts are blast waves generated in impulsive energy releases.

On the increase of solar activity in the southern hemisphere during solar cycle 21

Abstract: The present paper investigates the north-south asymmetry for major flares (solar cycles 19 and 20), type II radio bursts (solar cycles 19,20 and 21), white light flares (solar cycle 19,20 and 21), and gamma ray bursts, hard X-ray bursts and coronal mass ejections (solar cycle 21). The results are compared with the found asymmetry in favour of the northern hemisphere during solar cycles 19 and 20 in favour of the southern hemisphere during solar cycle 21.

The initiation of solar coronal mass ejections by magnetic nonequilibrium

Abstract: It is suggested that coronal mass ejections (CMEs) may be initiated when the plasma pressure of magnetic shear in a magnetic arcade (or helmet streamer) builds up so much that magnetic equilibrium is no longer possible. The resulting withdrawal of stabilizing magnetic field lines from the underlying prominence, as the CME moves out, then causes the prominence to rise slowly as a secondary effect, stretching out the neighboring field lines until reconnection allows a rapid eruption of the prominence - in the case of an active region prominence, this in turn may initiate a solar flare. Two simple examples of model coronal arcades are studied which suggest that eruption of arcades and therefore initiation of CMEs may be produced if the magnetic flux or axial plasma (or magnetic) pressure become too great or if the external plasma (or magnetic) pressure or temperature become too small. 31 references.

Forward-reverse shock pairs associated with transient disturbances in the solar wind at 1 AU

Abstract: Using color-coded plots of the ISEE-3 solar wind electron data and magnetic field data from ISEE-3 for the period from August 1978 through February 1980, evidence was obtained on two transient disturbances which contained reverse shocks in addition to forward shocks. These disturbances are considered to be associated with coronal mass ejections (CMEs). In the stronger of the two disturbances, the reverse shock was found within the CME and was separated from the forward shock by about 0.2 AU; the pressure between the two shocks was nearly constant. In the weaker disturbance, the reverse shock propagated entirely through the CME, trailing the forward shock by about 0.3-0.4 AU; the pressure between the shocks declined substantially and monotonically. Each disturbance profile can be compared favorably with one of the simple one-dimensional fluid simulations used by Hundhausen (1985) to illustrate the general principles underlying transient disturbance propagation in the solar wind.

Density and white light brightness in looplike coronal mass ejections: Importance of the preevent atmosphere

Abstract: Following studies of Sime et al. (1984), in which some models that simulate coronal mass ejections were found to be inaccurate simulators, two of these models (a model of a static corona in a current-free magnetic field, and a model of a polytropic corona with a coronal streamer) were reexamined, along with a new model, which differed from the second model in that it contained an atmospheric heating term. It is shown that the inclusion of a realistic preevent atmosphere can improve agreement with observations. The essential improvement in the heated atmosphere is that the fast-mode speed is increased to the extent that shocks may not form for typical ejection velocities.

The Formation of Solar Prominences

Abstract: Recent progress in the understanding of the formation of quiescent solar prominences is summarized in this chapter, from both an observational and theoretical point of view. It is now well known that the mass of a quiescent prominence (seen in emission at the solar limb) or a filament (generally seen in absorption above the disk) is an appreciable part of the mass of the entire corona (roughly one tenth or more), which makes it difficult to form these structures by coronal condensation alone. Hence, possible mechanisms proposed recently to account for their formation are divided into two categories reviewed below, namely injection (of the chromospheric material into the corona by siphon flows) and condensation (of the coronal plasma itself).

Temporal 10 Be Variations in Ice: Information on Solar Activity and Geomagnetic Field Intensity

Abstract: Temporal 10Be variations in polar ice are caused by changes of the production rate and the following transport to the ice sheets. The production rate is determined by the cosmic ray flux and its modulation by helio- and geomagnetic shielding effects. The removal of 10Be from the atmosphere is governed by the transport of aerosols to which 10Be is attached. Atmospheric circulation and precipitation rates strongly influence this transport. The 10Be record from Greenlandic ice cores exhibit variations on different time scales. In data from the last millenium, the 11 year solar cycle has been identified. For variations with characteristic times longer than a few centuries, there is the problem to distinguish between the different causes. A possible way to overcome this problem is to compare 10Be with other tracers (14C, 18O) which behave differently. In fact a comparison between the 10Be record from Camp Century, Greenland, and 14C data from tree-rings reveals similar shortterm variations which can be attributed to a variable sun. The agreement between the long-term variations of 10Be with palaeomagnetic data, however, is less good and its interpretation is less conclusive.

Forward‐reverse shock pairs associated with coronal mass ejections

Abstract: For some coronal mass ejections (CMEs), their interaction with the ambient solar wind can produce a forward-reverse shock pair. The high-speed mass ejecta compresses the plasma near the top of the CME on both sides of the tangential discontinuity which separates the CME plasma from the ambient solar wind plasma. The front of the compressed CME plasma propagates in the reverse direction relative to the ejecta flow, it may steepen to form a reverse slow shock. The front of the compressed solar wind plasma also propagates in the foward direction relative to the ambient solar wind and it may steepen to form a forward shock. The forward-reverse shock pair associated with CMEs moves outward in interplanetary space and evolves into a pair of fast shocks. The interplanetary manifestation of some CMEs is pictured as a magnetic cloud accompanied by a shock pair: a forward shock precedes the cloud and a reverse shock either within or behind the cloud. copyright American Geophysical Union 1988

Possible models on disturbances of the plasma tail of comet Halley during the 1985-1986 apparition

Abstract: More than 500 photographs of the plasma tail of comet P/Halley taken from the ground during this apparition are surveyed to study the solar wind-plasma tail interaction. The main disturbances of the plasma tail are tabulated, classifying them as outstanding streamers, rays, condensations helices, arcades, kinks, or disconnection events (DE). Based on the photographs, a standard three-dimensional model of the cometary magnetosphere is proposed. The classified plasma tail disturbances are explained further by possible interaction models taking into account of the IMF observation by Sakigake.

Characterizing solar flare high energy particles in near-Earth orbits

Abstract: The high-latitude radiation environment at 840 km for the solar minimum period from December 1983 to October 1987 was measured, using a dosimeter on the DMSP/F7 satellite to characterize solar proton events and compare them to events from earlier periods near solar maximum. The solar proton spectra agree well. A method of characterizing the high-energy particles in solar proton events is proposed. It uses a power spectrum index and dose number that can be useful in specifying polar radiation environments for the design of spacecraft. Latitudinal cutoff levels for higher-energy (>35 MeV, >55 MeV, and >95 MeV) particles are also given for the solar proton event periods and compared to calculated cosmic ray cutoffs. >

Pick-up ions at Comet P/Halley's bow shock - Observations with the IIS spectrometer on Giotto

Abstract: Gaseous material expanding form the nucleus of comet Halley into space form the neutral coma around the comet. Ionisation in the solar UV radiation removes particles from the coma and injects them into the solar wind plasma. These freshly created ions are accelerated by the interplanetary electric field on cycloidal trajectories with gyrocenters moving with the speed of the magnetic field lines. In the solar wind frame of reference these particles move along the magnetic field lines with a fixed pitchangle. Pitchangle scattering and energy diffusion reduce quickly the initial energy anisotropy which is associated with the narrow pick-up structures. First observations of heavy cometary pick-up ions (water group ions) at the bowshock are presented. The evolution of the distribution function in the vicinity of the shock and radial density profiles are discussed.

The radial dependence of the solar energetic particle flux

Abstract: Researchers discuss the radial dependence of the peak flux and the fluence of solar flare produced energetic particles under the assumption that they propagate diffusively in the heliosphere.

Acceleration of Energetic Particles in Solar Flares

Abstract: A review is given of the basic properties of solar flare accelerated particles and of the solar flare associated electromagnetic emission in the X- and γ-ray region The most widely discussed acceleration processes are acceleration by shocks, by turbulence, and by direct electric fields Currently there is no consensus which of these processes is most ubiquitous and therefore dominant

Two disconnection events in comet P/Halley and possible solar causes

Abstract: Disconnection events in comet P/Halley in April 1986 are discussed Observations were made both from La Palma, Canary Islands and Siding Spring, Australia Different solar phenomena, such as solar flares, coronal mass ejections, coronal holes and the coronal neutral line, are examined as possible causes of the disconnection events The solar wind counterpart of the coronal holes and the coronal neutral lines, the so called high speed plasma streams and the heliospheric current sheet, are the most often suggested causes In our two cases we found the heliospheric current sheet to be the most likely cause, but also a high speed plasma stream might have caused the DE of April 12