An eruptive prominence of June 10, 1973

An eruptive prominence of June 10, 1973, showing ascending and expanding motions, has been recorded spectroscopically at Oslo Solar Observatory.The Ca ii H line yields broadening velocities ranging from 5 km s^-1 to 20 km s^-1. An extreme ratio of 1/30 was measured for line-broadening to expansion velocity.Flare activity succeeded the start of the observed disparition brusque phase of the prominence. The eruption is related to coronal disturbances recorded approximately 1 hr later by ATM, Skylab.     

Kinematics of a loop prominence

The kinematics of a loop system has been studied from high resolution Ca ii K line spectra and H filtergrams recorded at Oslo Solar Observatory.Emission features are seen to fall at supersonic velocities from the top of the arches towards the chromosphere. Our data are in agreement with the assumption of matter falling freely along a dipole type magnetic field of maximum height 100–150 thousand km. There is a slight asymmetry between positive and negative line shifts which can be accounted for as a tilt of the individual loops relative to the plane of the sky of 5–10°. The planes of the loops are also inclined by a small angle of approximately 15°. It appears that matter starts from rest at the top of the loops. An observed tilt of some emission features in the K line spectra may be explained by a gradient in the line-of-sight velocity with height caused by the curvature of the dipole type loops.     

Dynamics and internal structure of an eruptive prominence

The kinematics and the development of the internal structure in the eruptive prominence of August 16, 1988 are described. The prominence exposed helical structure, and the pitch of the fine structure filaments was measured. The evolution of the pitch was measured in the legs of the prominence and at its summit from the pre-eruptive phase up to the late phases of the eruption. The pitch angle was decreasing in the legs as well as at the summit. However, the observations indicate that the integral twist remained constant. The prominence was twisted more at the summit where it was wider than in the legs. The effective twist at the prominence summit was approximately 20 and in the legs it amounted to about 8 . Such a ratio did not change during the eruption, i.e., no redistribution of the twist was observed within the accuracy of measurements. The nature of the instability causing the eruption is discussed and the energetics of the process is considered.     

The growth of electric current in the eruptive prominence of June 8, 1974

The observed twisting of bright threads during the eruption of a limb prominence is described in terms of the transfer of energy from the large-scale to the small-scale magnetic field. Modeling the process by means of an inductive circuit, the time constant for the growth of current along the bundle of threads appears to be consistent with the observed rate of twisting.Visiting astronomer on leave from the Department of Astro-Geophysics, University of Colorado, Boulder, Colorado 80309, U.S.A.     

About the prominence heating mechanisms during its eruptive phase

Recent EUV observations reveal that the `image' of the prominence overlaying coronal emission sometimes suddenly changes from absorption of EUV radiation to emission during the eruptive phase. This change reveals fast heating of the plasma within the prominence. We propose a kinetic mechanism of heating the fluid particles that transforms magnetic energy of the pre-eruptive magnetic configuration stored in the filament electric current into heat through collision processes of counteracting flows. The shape of the flux that the filament is made of should include upward concave segments to provide the counter flows within the erupting prominence. A typical twisted flux rope easily meets this requirement. Gas dynamic calculations are offered in addition to permit a quantitative evaluation of the relevant parameters and their time variations.     

An eruptive prominence and associated cm-mm emission outside the solar limb

We present radio maps at 22 and 44 GHz which show the emission before and after the eruption of a quiescent prominence located at the west limb. The observed radiation following the eruption is not consistent with thermal bremsstrahlung mechanism. It can be interpreted as due to gyrosynchrotron emission of nonthermal electrons. Our observations appear to be similar to the microwave radiation observed in post-flare loops; this radiation is due to nonthermal electrons trapped in the closed magnetic structures formed after the prominence eruption.     

A remarkable eruptive prominence on the solar disk on January 29, 1968

Observations of a remarkable dynamic H phenomenon in projection on the solar disk are reported. An eruptive prominence in the shape of large loops was ejected to a great distance from the point of origin.     

Simultaneous multifrequency observations of an eruptive prominence at millimeter wavelengths

Radio images and spectra of an eruptive prominence were obtained from simultaneous multifrequency observations at 36 GHz, 89 GHz, and 110 GHz on May 28, 1991 with the 45-m radio telescope at Nobeyama Radio Observatory (NRO), the National Astronomical Observatory, Japan (NAOJ). The radio spectra indicated that the optical depth is rather thick at 36 GHz whereas it is thin at 89 and 110 GHz. The H data, taken at Norikura Solar Observatory, NAOJ, suggest that the eruption of an active region filament was triggered by an H flare. The shape and position of the radio prominence generally coincided with those of H images. The radio emission is explained with an isothermal cool thread model. A lower limit for the electron temperature of the cool threads is estimated to be 6100 K. The range of the surface filling factors of the cool threads is 0.3–1.0 after the H flare, and 0.2–0.5 in the descending phase of the eruptive prominence. The column emission measure and the electron number density are estimated to be of the order of 10²⁸ cm^–5 and 10¹⁰ cm^–3, respectively. The physical parameters of a quiescent prominence are also estimated from the observations. The filling factors of the eruptive prominence are smaller than those of the quiescent prominence, whereas the emission measures and the electron densities are similar. These facts imply that each cool thread of the prominence did not expand after the eruption, while the total volume of the prominence increased.     

Dynamic regimes of prominence evolution

The dynamical model of a solar prominence taking into account plasma motion in the form of a cumulative flux was developed. Of great importance is the fact that the prominence plasma is partially ionized. Ion-neutral collisions in nonsteady flux conditions radically change the energetics and dynamics of the prominence model. In this case the equilibrium state described by the Kippenhahn-Schlüter solutions becomes unstable, and various dynamic regimes of plasma compression, as well as monotonic or quasi-periodic expansion of the plasma can exist in the prominence.     

The dynamical process of a coronal transient associated with an eruptive prominence

The statistical correlation between an eruptive prominence and the coronal transient associated with this prominence implies that there should be a relationship between these two kinds of dynamical processes. This paper analyzes the dynamical effect of a plasma ‘piston’ in the corona, consisting of an eruptive prominence and/or a magnetic flux region (loop or arcade, or blob) in front of the prominence. Ahead of the piston, there is a compressed flow, which produces a shock front. This high-density region corresponds to the bright feature of the transient. Behind the piston, there is a rarefaction region, which corresponds to the dark feature of the transient. Therefore, both the bright and dark features of the transient may be explained at the same time by the dynamical process of the moving piston. Two local solutions, one perpendicular and one parallel to the direction of solar gravitational field, are discussed. The influence of gravity on the gas-dynamical process driven by the piston is discussed in terms of characteristic theory, and the flow field is given quantitatively. For a typical piston trajectory similar to the one for an eruptive prominence, the velocity of the shock front which locates ahead the transient front is nearly constant or slightly accelerated, and the width of the compressed flow region may be kept nearly constant or increased linearly, depending on the velocity distribution of the piston. Based on these results, the major features of the transient may be explained. Some of the fine structure of the transient is also shown, which may be compared in detail with observations.     

Positional measurements on the eruptive loop prominence of 27 April 1981 and comparison with the X-ray sources

Using the Hα observational data from Yunnan Observatory, we have made position measurements on the eruptive loop prominence of 27 April 1981, and have compared the results with the positions of X-ray sources obtained by the hard X-ray telescope (SXT) on board the HINOTORI satellite. From the results of measurement and comparison, it is suggested that 1) The two mounds A and C at 0830 UT are extensions of two ribbons in the flare near the limb, which started before 0758 UT. 2) The central positions of two X-ray sources at 0756 UT are just situated at the top of the mound A and the mound C, respectively. The Hα footpoint corresponding to the main source of X-rays was behind the solar limb. The second source of X-rays corresponds to C₁ and C₂. 3) The X-ray sources were probably located near the footpoints of loops.     

The magnetic configuration of the November 18, 1968 loop prominence system

Computed current-free magnetic fields are compared to the loop prominence associated with the west limb proton flare of 18 November 1968. Successive sets of fitting fieldlines closely resemble the loop prominence system throughout its growth and lifetime. The successive position bases of the fieldlines reproduce the drift rate of spreading two-ribbon flares.     

Effects of magnetic shear,spot, and plage rotation on prominence evolution

We have studied the evolution of two dark H filaments as prominences during their disk passage from 12 to 19 February, 1992 and 6 to 17 March, 1992, using Kodaikanal Observatory H and Caii K spectroheliograms. Both the filaments were well outside the spot regions. However, they were connected to sunspots by small threads. Outside the spot regions, the filaments were also anchored between opposite polarity plage regions. Both the filaments were almost straight in the beginning. However, they acquired a curved shape (inverted U-shape) as the spot and plages underwent rotation. It is shown that rotation of the plage and spot plays an important role in the evolution of prominences, one serving as the anchor and the other imparting necessary shear. Once the shear reaches a critical value it starts unwinding the filaments, resulting in the fine structure of the two prominences studied.     

Study of a large helical eruptive prominence associated with double CME on 21 April 2001

Here we present a preliminary analysis of a helical eruptive prominence at the east limb of the Sun on 21 April 2001. Unusually this eruption is associated with a double CME. We have tried to study the morphology of the event, energy budget of the prominence and associated CMEs. Our analysis shows that the prominence and first CME started simultaneously from the limb and prominence carries sufficient energy to feed both the CMEs. Moreover, it is also concluded that CMEs are magnetically driven and internally powered.     

Magnetic field evolution during prominence eruptions and two-ribbon flares

Simple models for the MHD eruption of a solar prominence are presented, in which the prominence is treated as a twisted magnetic flux tube that is being repelled from the solar surface by magnetic pressure forces. The effects of different physical assumptions to deal with this magneto-hydrodynamically complex phenomenon are evaluated, such as holding constant the prominence current, radius, flux or twist or modelling the prominence as a current sheet. Including a background magnetic field allows the prominence to be in equilibrium initially with an Inverse Polarity and then to erupt due to magnetic non-equilibrium when the background magnetic field is too small or the prominence twist is too great. The electric field at the neutral point below the prominence rapidly increases to a maximum value and then declines. Including the effect of gravity also allows an equilibrium with Normal Polarity to exist. Finally, an ideal MHD solution is found which incorporates self-consistently a current sheet below the prominence and which implies that a prominence will still erupt and form a current sheet even if no reconnection occurs. When reconnection is allowed it is, therefore, driven by the eruption.     

The loop prominence of 11 August 1972: A coronal continuum event

Observations of a loop prominence formed after the flare of 11 August 1972 are discussed. Estimates of electron density are obtained from (a) the line ratio of the Ca xv forbidden lines and (b) a Thompson scattering model. Both methods give an approximate value of n _e = 10¹¹ cm^-3. This density was high enough to render the loop structures visible as continuum features, corresponding to the Ca xv structures as seen in the plane of the sky. By a double exposure technique, it was found that the loop structures seen in H and Fe xiv differ significantly.     

Large Proton Anisotropies in the 18 August 2010 Solar Particle Event

The solar particle event observed at STEREO Ahead on 18?August 2010 displayed a rich variety of behavior in the particle anisotropies. Sectored rates measured by the Low Energy Telescope (LET) on STEREO showed very large bidirectional anisotropies in 4??C?6?MeV protons for the first ???17?hours of the event while inside a magnetic cloud, with intensities along the field direction several hundred to nearly 1000 times greater than those perpendicular to the field. At the trailing end of the cloud, the protons became isotropic and their spectrum hardened slightly, while the He/H abundance ratio plunged by a factor of approximately four for about four hours. Associated with the arrival of a shock on 20?August was a series of brief (<?10?minute duration) intensity increases (commonly called ??shock spikes??) with relatively narrow angular distributions (???45^° FWHM), followed by an abrupt decrease in particle intensities at the shock itself and a reversal of the proton flow to a direction toward the Sun and away from the receding shock. We discuss the STEREO/LET observations of this interesting event in the context of other observations reported in the literature.     

The eruptive evolution of the Galilean satellites: Implications for the ancient magnetic field of Jupiter

The hypothesis considering the Jupiter-Sun system as a limiting case of a close binary star implies the initial relative ice abundances in all the Galilean satellites to be essentially equal. The satellites move in the Jovian magnetosphere; thus the unipolar current flowing through their bodies subjected their ices to volumetric electrolysis. Explosions of the electrolysis products resulted in a loss of ices. While Callisto did not explode at all, Ganymede exploded once, Europa twice, and Io two or three times. An analysis of the magnetic field changes needed to create the modern ice abundances in the satellite shows:

1. the initial field of Jupiter was ～10² times stronger when compared with the present-day field, and
2. the field had to decrease exponentially with τ_2| ≈ (0.6?1), which means its relic nature.