The purpose of this paper is to outline a model of mode-coupled MHD compressional waves in the corona and solar wind. The eventual aim of this work is to be able to compute how MHD waves propagate through the corona and into the solar wind beginning with a source of Alfven or fast mode waves at the base of the corona. The necessity for consideration of mode coupling arises because of typical scalelengths in the corona. For wave sources, such as supergranulation, with wave periods of about a day, the different modes do no propagate independently, as in the WKB approximation, but are coupled because the ratio of wavelength to scalelength is of the order of one or greater.

The observations of MHD turbulence in the solar wind indicate that this is in a state characterized, to a good degree by the absence of non linear interactions. It is argued that this is a general property of incompressible MHD turbulence in a magnetized plasma.

Solar wind flow quantities such as matter flux, momentum flux and energy flux, may be closely related to the mechanism responsible for the evolution of the solar wind. In the highly supersonic flow regime their study is facilitated by the fact that the contribution of thermal motions to the momentum and energy fluxes is negligibly small, and thus all three quantities are expressible in terms of proton density n and flow velocity u. If a relation between n, u and heliocentric distance r can be established, the study of these quantities is further simplified. In the following we point out that such a relation does in fact exist, and comment on its implications.

Results of solar wind measurements by different spacecraft are not always in full accord. Such measurements are in general not from one and the same distance r from the sun, nor are they taken at the same phase of the solar activity cycle. One would like to be able to discriminate between spacecraft calibration effects on the one hand, and solar wind variations which reflect true spatial gradients or changing boundary conditions at the sun on the other hand. Accordingly, we examine in this paper the possibility of reconciling the apparent discrepancies.

Solar wind protons impinging on interplanetary dust grains are trapped, deionized, and subsequently desorbed. The steady state distribution of desorbed neutral hydrogen inside of 0.4 AU can be deduced by observation of resonantly scattered solar 121.6 nm radiation. Calculated integral intensities and spectral profiles are given, showing the clear spectral separation of the different radiation components. Given a specific solar wind proton flux, the interplanetary dust distribution can be determined. Conversely, dust density profiles from zodiacal light measurements can be used to deduce solar wind proton fluxes at heliocentric distances of 0.4 to 0.15 AU. Observations of latitudinal and short-term temporal proton flux variations seem feasible.

Collective interactions of the solar wind and newly ionized interstellar gas cause turbulent electron heating to ionizing energies analogous to laboratory experiments on the critical ionization velocity effect. Implications for solar wind and interstellar gas dynamics are calculated by simultaneously solving continuity equations for solar wind protons, interstellar hydrogen atoms, and energetic electrons. Electron impact ionization is shown to be practically as important as photoionization, giving rise to a stronger deceleration and heating of the distant solar wind, a weaker terminating shock, a smaller stand-off distance of the helio pause, and implying higher densities of the outer solar wind and the interstellar neutral gas.

The brightnesses of Titan and Neptune have been monitored photo-electrically at 472 and 551 nm since 1972 at the Lowell Observatory, yielding annual mean magnitudes accurate to 0.3 percent (0.003 mag). Both objects increased steadily in brightness until 1976 and declined thereafter (Lockwood 1977, Lockwood and Thompson 1979). The range of variation was about 0.08 mag for Titan and 0.03 mag for Neptune.

Interplanetary magnetic field data from the different satellites obtained during the period 1963-1973 at 1 A.U. and compiled by J. King have been analysed in heliocentric ecliptic coordinates. The peculiarities of the background interplanetary magnetic field (BIMF) are discussed in relation to the orientation of the solar system in the Galaxy and the variable helioefficiency of the planets. The results of the direct cosmic experiments are evidence of the solar activity being a complex phenomenon of the solar system as a whole.

The dynamic nature of the outer corona has been revealed in recent years by improved techniques of studying the corona with ground based instruments and from space. Rapid changes in the coronal brightness pattern takes the form of mass ejections in which the outward moving material generally appears to escape the Sun. These events are called coronal transients. Observations have shown that the excess mass and energy in coronal transients are supplied by material expelled from the chromosphere and lower corona in conjunction with Hα surface activity. The transients are the coronal response to release of mass and energy which are manifested by flares and eruptive prominences.

Flares are believed to derive their energy from localized nonpotential magnetic fields; this energy is somehow stored and initially released in the low corona. Therefore, knowledge of coronal conditions prior to flares is essential to our understanding of the flare process. The coronal plasma is constrained by the magnetic field and its characteristic emission is easily observed at soft X-ray wavelengths. Therefore, X-ray imagery is well suited for observing changes in emission influenced by nonpotential magnetic fields in the low corona. This study used soft X-ray images from the Skylab AS&E telescope to search for evidence of coronal preflare emission.

The transition zone overheating model and the melon seed model are compared with observations of spicules, macrospicules, surges and sprays.

Extreme ultraviolet observations of the chromospheric network in a coronal hole obtained in 1973 by the Harvard College Observatory experiment aboard Skylab are analyzed. Upper and lower limits to the actual emission measure in UV spicules have been obtained, and the consistency of the derived values with the hypothesis that UV spicules are Hα spicules falling back after being heated is discussed.

Hα observations of a peculiar type of filament activation are presented and discussed. Ejected filament material was stopped at a distant position and formed a new stable filament for 1/2− 1 hour until it returned to its source or faded in situ. A similar event has been observed at the solar limb.

We present direct observational evidence for the preflare magnetic field configuration, the nature of the filament destabilization and triggering of the flare, and the magnetic field configuration after the filament eruption in the large, well-ordered, expanding two-ribbon flare of July 29, 1973.

The topic of this paper is to present some results concerning the dynamics of quiescent filaments. Observations with the Meudon Heliograph in three wavelengths in the Hα line have already shown two kinds of perturbations : (1) a fast one lasting about 10 minutes and (2) a slow one which lasts a few hours. These qualitative observations have been completed recently with the Multichannel Subtractive Double Pass Spectrograph (MSDP) which operates on the Solar Tower in Meudon. This instrument allows a good spatial and temporal resolution which gives quantitative results.

In a series of papers on the flare of 29 July 1973 (Nolte et al., 1979; Martin, 1979; Švestka et al., 1979) it has been shown that Hα “post-flare” loops are the cooled aftermath of previously hot coronal loops which were visible in x-rays in the same position earlier in the flare. Kopp and Pneuman (1976) have proposed that these post-flare loops are formed by a process of successive magnetic field reconnections of previously distended magnetic field lines as illustrated in Figure 1. Each successive reconnection of the magnetic field yields a closed magnetic loop that forms above and concentric with previously formed loops. A shock wave created during each sudden reconnection travels down both legs of each loop and provides energy for ionizing chromospheric mass at the footpoints of the loop. Subsequent condensation of the ionized mass at the tops of the loops renders them visible as this mass falls to the chromosphere.

An interesting microwave event at 2800 MHz was recorded at Ahmedabad on September 19, 1977 at 1026 UT at the same time as the H-Alpha solar flare of importance 3B. The microwave burst was of impulsive nature, with as many as twenty impulses in seventy minutes with a quasi-periodicity of 1 to 5 minutes. An X-ray burst recorded by GOES Satellite in 1-8A band showed at the same time a smooth soft X-ray profile with apparently no sign of hard X-ray bursts. This indicates that the acceleration of discrete electron streams which produced impulsive microwave bursts was not sufficient to produce the hard X-ray component but got thermalised to produce soft X-ray emission, with a gradual rise and a slow decay covering a long duration of more than 2 1/2 hours.

It has been apparent for the last few years that a large fraction of the total energy released during a solar flare appears initially in the form of energetic electrons accelerated during the impulsive phase. An estimate of the energy of these electrons is based on the observed hard x-ray spectra as well as the assumed form (thermal or non-thermal) of the electron distribution. Even after the basic form of the electron distribution is assumed, additional assumptions, such as the low energy cut-off in the case of the power law energy spectrum or existence of a multi-thermal source in the case of the thermal spectrum, are usually required. In order to test these assumptions, measurements of the hard x-ray spectrum with spatial resolution and covering a wide range of x-ray energy are essential. In absence of good spatial resolution, as is the case with most of the presently available hard x-ray observations, the impulsive x-ray emission at energies hv ≲ 10 keV is often unobservable because of the presence of a large background of relatively intense gradual emission associated with most flares. Observations made in the past suffered either because of the lack of a clearly identifiable impulsive x-ray emission at low energies (Peterson et al, 1973) or an adequate spectral resolution (Kahler, 1973). Thus so far it has not been possible to measure unambiguously the spectrum of impulsive x-rays ≲ 10 keV and hence to deduce a possible low energy cut-off in the energetic electron spectrum. Here we report briefly such an observation made with the ISEE-3 x-ray spectrometer experiment and its implications with regard to the characteristics of energetic electrons in solar flares.

The flare energy is generally considered to be stored in stressed (twisted or sheared) magnetic fields. Origin of the stress may be either intrinsic or due to horizontal shear motion (Tanaka and Nakagawa 1973) or due to propagation of twist from below (Piddington 1974). Characteristic magnetic configurations in the great activities (inverted, twisted δ-configuration; Zirin and Tanaka 1973) suggest an inherent shape of fluxtube for these regions: a twisted magnetic knot. Further, evolutionary characteristics such as rapid growths of spots and growth of twist in parallel with apparent shear motion of spot, together with the fact that the shear motion is associated with upward velocity (Tanaka and LaBonte 1979), suggest a continuous emergence of such a twisted knot from below throughout the activity (Tanaka 1979). In this model (Fig. 1) the flare energy may be supplied directly into the corona as the twisted portion of the fluxtube emerges out. The amount of energy supplied between t0 and t may be equated to the energy contained in the twist (ɸ) between z1 and z2,

Observations and analysis of solar flare activated ascending “Fountain type” prominence of 1 February 1979 are presented. This “Fountain” prominence rose to 180,000 km above the solar surface and gave rise to a number of ascending loops and helical structure. These “helicals” are clear manifestation of magnetic field configuration. From these observations it is shown that, as the “Fountain” prominence rises, it carries along with it the complex magnetic field which unfolds as the prominence material expands into distinct magnetic field lines. Several type III radio bursts were also seen associated with this event. No type II or IV radio emission was reported.