The mathematical analysis of the Alfven Wave equation in inhomogeneous magnetic fields which explain the resonance absorption of Alfven surface waves near a resonant layer can also be used to show that magnetic reconnection process can arise near the zero frequency resonant layer driven by very low frequency Alfven surface waves. The associated phenomena of resonant absorption and magnetic reconnection in inhomogeneous plasmas can explain the recent obsrevations of intense magnetic activity in the long period geomagnetic micropulsations range, at magnetospheric cusp latitudes, during the time of occurence of flux transfer events.

Fringe profiles of Fabry-Perot interferograms taken in the λ 5303 line during the total solar eclipses of 1980 and 1983 are studied in relation to coronal structures observed in white-light pictures. Evidence for doppler-shifted discrete components and large random velocity components in specific regions is presented here.

In this paper we report preliminary results from a study of the inner corona based on the direct comparison of XUV resonance emission line λ174.53 FeX with that of the white-light emission from the K corona. The data sets were obtained 17718th of March, 1988, during a total solar eclipse of the sun and consists of co-spatial and co-temporal measurements of these two quantities as a function of position angle and height above the solar limb. The local emission of a coronal resonance line is proportional to the electron density squared, the chemical abundance, and the electron kinetic temperature, while the white-light emission (arising from Thomson scattering by electrons) depends directly on the electron density and the local radiation field. Taken together these measurements yield an estimate of the quantity where n is the electron density. This quantity, called “X the coronal irregularity factor” by C.W. Allen, is found to be >1.

The earlier concept of average solar wind speed has changed with time. Besides quiet periods of low/average solar wind speeds, two different kinds of solar sources (solar flares and coronal holes) have been identified to produce high speed solar wind streams. In an earlier investigation, it was reported that the high speed streams associated to these sources produce distinctly different effects on the cosmic ray intensity (Venkatesan, et. al., 1982).

The sun as a star has been studied by many observers by monitoring the calcium K line profile. Skumanich et al (1984) proposed a three component model of the solar cycle variability of calcium K emission using extant contrast and fractional area parameters for (1) cell (2) network and (3) plage components. The computed line profile agreed well with the observed one at the solar minimum by taking the contribution of only cell and network features and using extant limb-darkening laws. The occurrence of plages during the growth of the solar cycle was found to be insufficient to account for the increase in K emission and therefore, they introduced an additional network component, ‘Active network’ in excess of the quiet sun value to explain the observed excess emission during the maximum phase.

The conditions under which the hydromagnetic interface waves can exist at a magnetic interface is deduced. Using these conditons, it is shown that a slow interface wave with a phase velocity about 5Km/s and a fast interface wave with a phase velocity 6.5 to 8km/s at the photospheric level can exist.

We extended Stein's hydrodynamic theory of acoustic wave generation to accommodate the effect of a vertically uniform magnetic field. It is shown that in the presence of a uniform vertical field with pure horizontal field fluctuations the acoustic waves are produced both from a non-magnetic monopole source of the Reynolds stress and by the magnetic field fluctuations. The computed acoustic flux is found to be confined to the topmost of the spot's convection zone with a small range of depth.

There are two regions of rapid dissipation when Alfvén waves propagate from the transition region to the corona. They occur respectively in a range of several hundred kilometers above the base of the transition region and in the corona at about 1-3Ro. The heating of the atmosphere by wave dissipation could be one order of magnitude larger than heat conduction in the coronal part with a lower temperature and density and stronger magnetic field. Wave heating could also become more important when the magnetic field divergence becomes stronger.

Magnetic reconnection is a fundamental process in astrophysics which plays many different roles on the Sun. The classical theory of fast steady reconnection due to Sweet, Parker, Petschek and Sonnerup has been unified in a theory which possesses many new regimes that depend on the boundary conditions at large distances. For example, the flux pile-up regime possesses diverging flows, a long central diffusion region and a reconnection rate that is much larger than the Petschek value. Recent numerical experiments however, often possess three features that are not present in the earlier theoretical models, namely highly curved inflow field lines, separatrix jets and reversed current spikes, and so an attempt is described to include these features in a new theoretical model.

Several solar phenomena where reconnection is believed to be operating are described. Cancelling magnetic features in photospheric magnetograms are probably evidence of reconnection submergence. Most prominences are of inverse polarity and have upflows driven by reconnection below them. Coronal heating may well be due to reconnection in many small current sheets. In solar flares reconnection may be driven below an eruptiing active-region prominence and hence power the high-temperature flare loops and chromospheric ribbons.

Magnetic Reconnection is often invoked as the primary mechanism for driving a flare or a prominence eruption. Here I argue that a catastrophic loss of mechanical equilibrium, rather than reconnection, is probably the primary mechanism for driving these phenomena. However, reconnection is still essential in order for any significant amount of energy to be released. To illustrate this idea we present some recent results from an MHD simulation based on a catastrophe mechanism first proposed by Van Tend and Kuperus. In order for this mechanism to be effective a substantial amount of reconnection must occur within a few Alfvén-scale times. Such rapid reconnection is plausible since the loss of mechanical equilibrium can generate flows which drive the reconnection at a rapid rate.

In “closed” magnetic structures (i.e., coronal loops) the random shuffling of magnetic footpoints in the photosphere causes twisting and braiding of field lines in the corona. If the motions are sufficiently slow, the coronal field evolves through a sequence of force-free equilibrium states. Numerical simulations are presented for a simplified model in which the overall curvature of the coronal loop is neglected. It is shown that magnetic fine structures develop on spatial scales significantly smaller than those of the imposed “photospheric” velocity field.

Several theoretical studies have proposed that, in response to photospheric foot-point motions, current sheets can be generated in the solar corona without the presence of a null point in the initial potential magnetic field. In these analytic models, current sheets form wherever the coronal field dips down and is parallel to the photosphere. A fundamental assumption in these analyses — commonly referred to as the line-tying assumption — is that all coronal field lines are anchored to a boundary surface representing the top of the dense, gas-pressure-dominated photosphere. In theoretical arguments presented elsewhere (Karpen, Antiochos, and DeVore 1989), however, we show that line-tying is not valid for “dipped” coronal fields, and hence that the conclusions of the line-tied models are incorrect. We contend that current sheets will not form if the photosphere-corona interface is represented by a physically valid model. Here we summarize a numerical investigation of the response of a “dipped” potential magnetic field in a hydrostatic-equilibrium atmosphere to shearing motions of the foot points. Our results show that, in the absence of artificial line-tying conditions, a current sheet indeed does not form at the location of the dip. Rather, the dipped magnetic field rises, causing upflows of photospheric and chromospheric plasma.

For a 3D force-free field occupying a half-space D = {z > 0}, we discuss: i) the storage of free magnetic energy when the field evolves quasi-statically as a consequence of motions imposed to its footpoints on the plane {z = 0}; ii) the release of this energy during a reconnection process implying a rearrangement of the lines which is either local, occuring in the neighbourhood of spontaneously formed current sheets, or global, occuring in an explosive flare-like way.

Magnetic tension posseses low values at regions of large magnetic “shear” on the polarity inversion line. The low tension allows for a non-force-free field that depends on the density of the medium. Instabilities which can modify the density may then possibly evolve into solar flares. Heuristic arguments are given to favour instability driven flare scenarios.

The downward tension force is known to be extremely small at the locations of highly sheared magnetic fields. The free energy in such tension free fields is shown to be dependent on the plasma density. The excess of this free energy over that available in a force free configuration is estimated and shown to be sufficient to drive instabilities which could possibly initiate a solar flare.

Prominences are sheets of cold (< 104 K) plasma totally imbedded in the hot (> 106 K) coronal plasma. A Prominence-Corona Transition Region (PCTR) is therefore present all around it.

Responses of the solar atmosphere and interplanetary medium to simulated solar disturbances were studied by time-dependent, MHD numerical simulations. This deterministic initial-boundary value problem was attacked in the classical way: a representative steady state is first established, then input parameters at the lower near-Sun boundary are perturbed. We discuss a number of 2- and 3-dimensional examples of coronal mass ejection (CME) simulations and some current controversies concerning the basic process of CME initiation. Footpoint shearing motion is tested to see whether it can provide a reasonable mechanism for CME development from arch filament configurations.

We also demonstrate possible interplanetary consequences to CME-like disturbances by using 3-D simulations to determine the dynamic response of the solar wind to a plasmoid injection from an eruptive filament or prominence. We also discuss the separate possibility whereby a plasmoid may be generated in the interplanetary medium by a solar-generated shock that propagates through a heliospheric current sheet. Application of the 3-D model for the interpretation of interplanetary scintillation observations is also discussed.