The solar magnetic field that extends through the chromosphere is thought to expand through the transition region into the corona. The strong flux concentrations are located within the boundaries of supergranular convection cells. These boundaries form network lanes, observed in emission lines as bright lanes with varying width throughout the solar atmosphere. These network field concentrations are surrounded by mixed-polarity magnetic field with a scale of the granule diameter, as suggested by observations. We use potential magnetic field extrapolations on synthetic magnetograms to study the magnetic network topology and the effects of background magnetic field on the network expansion through the solar atmosphere. We find that the background magnetic field has a considerable effect on the ratio of network area over field of view. Furthermore we find that the expansion of the network boundaries with height deviate significantly from well-assumed funnel model expansion.

I first review: a) the current state of knowledge of ion acceleration in solar flares; b) the physics of positron production and annihilation; and c) recent RHESSI data on solar flare annihilation radiation. I then show how the modeling of the positron production and annihilation in the chromosphere, coupled with the newly available high-resolution data on the 511 keV annihilation line, can have important physical implications w. r. t. the models: a) information on the temperature and density of the chromosphere; b) constraints on some of the physical characteristics of the flare and to some extent on the acceleration process.

Although I do mention past instruments (SMM and Yohkoh), this review focuses on the RHESSI satellite, considering the quantum leap it has constituted in the quality of the data it is providing and consequently the constraints it can place on models (of ion acceleration, annihilation environment, etc.).

The solar magnetism, its origin, and its impact on the earth are of primary interest for solar physicists. The understanding of the solar dynamo in the convection zone and the coupling of the magnetic fields up to the corona and the heliosphere calls for synoptic as well as for high spatial resolution observations of the Sun. Understanding the interactions between radiative and magneto-convective processes at the interface between the solar interior and the atmosphere requires spectro-polarimetric observations at high spatial and spectral resolution with high polarimetric accuracy. Thus large-aperture telescopes are needed to resolve the small scales and to collect enough photons to study the evolution of the magnetic processes. For assembling the mosaic of the solar dynamo and its magnetic coupling out to the heliosphere, large scale properties and hence synoptic observations play a crucial role. I present my personal perspective of the prospects in ground-based solar physics, and comment on the planned and upcoming new facilities including SOLIS, GREGOR, NST, SUNRISE, and ATST, as well as ALMA and FASR, but also mention the upcoming space missions HMI@SDO and SOLAR-B.

Magnetohydrodynamic equilibria for a plasma in a gravitational field are investigated analytically. For equilibria with one ignorable spatial coordinate, the equations reduce to a single nonlinear elliptic partial differential equation for the magnetic potential A, known as the Grad-Shafranov equation. Specifying the arbitrary functions in the latter equation, one gets a nonlinear elliptic partial differential equation (the sinh Poisson equation). Analytical solutions of this equation are obtained for the case of an isothermal atmosphere in a uniform gravitational field. The solutions are obtained by using the tanh method, and are adequate for describing parallel filaments of diffuse, magnetized plasma suspended horizontally in equilibrium in a uniform gravitational field.

In this paper, we have presented high resolution magnetograms around sunspot at CaI $6102.7 \AA$ photospheric line and in $H\alpha$ chromospheric line.

Futher, more the longitudinal magnetic field difference in two wings(red and blue)around central line in photosphere and chromosphere has been studied.

The performance of the solar cell is influenced by the spectral solar distribution. The silicon solar cell spectral response does not totally coincide with the solar spectrum. In the case of sun light exposure at outdoor conditions, the shapes of the cell spectral response curves are slightly different than that of under simulated light exposure. This paper is interested in studying the effect of variation of solar radiation during the partial eclipse on the output short circuit current and open circuit voltage of the monocrystalline and amorphous silicon solar cells. Also, the spectral cell behaveiour in terms of the solar eclipse was investigated. The ultimate goal is to explain some of an interesting natural phenomenon by using the solar cell spectral response.

We review what we have learnt about flares and prominences using multi-wavelength observations in the perspective of testing theoretical models.

This article is a study of a family of nonlinear force-free magnetic fields (FFMFs), in Cartesian geometry under assumption of translational symmetry, as simple models of the magnetic fields in the solar corona. For this configuration all the physical quantities are invariant under translations in a fixed direction to be the direction Oz of a Cartesian coordinate system. Two classes of exact analytic solutions for the steady state are obtained. These solutions may be helpful in understanding the physics involved in the transition from the low-confinement to the high-confinement mode in tokamaks. In particular, they can be employed for stability investigations, which would be of relevance to magnetic confinement systems. Further, the obtained solutions may have several applications in the study of solar photosphere, the solar corona, as well as astrophysical plasmas.

Solar flares are of great fundamental and practical interest. In some events the energy release might exceed 1026 J Tsurutani et al. (2003) and accompanying CME courses extremely severe magnetic storm. Because of very rare occurrence of such global flares a laboratory simulation appears to be an alternative that could provide experimental data necessary for physical understanding of this phenomenon and for verifying theoretical models. Flare involves processes on many widely varying spatial and time scales. In laboratory only some parts of the whole evolution could be attempted for simulation. The present work is focused on the last stage of eruption when a magnetic loop filled with heated plasma is ejected away from the Sun, either itself or pushed by an upcoming jet. The geometry of a flare loop suggests that a magnetic dipole and laser-produced plasma could be used to simulate this structure Nikitin & Ponomarenko (1995). In the present work similarity criteria that relate laboratory parameters to the natural phenomena, experimental set up and preliminary results are presented.

The magnetic field of the Sun and the plasma properties of its atmosphere, such as temperature, density and waves in the solar corona, determine the origin, energetics and evolution of the solar wind. The solar wind comes in three main kinds, as steady fast streams, variable slow flows and transient fast coronal mass ejections, with all being closely associated with the structure and activity of the coronal magnetic field that evolves on a multitude scales. This tutorial paper places emphasis on the observed and measured characteristics of the solar wind sources and their magnetic structure. The boundary conditions in the magnetically closed corona, in the transiently opening corona, and in the lastingly open corona (funnels and holes) will be discussed, and their influences on and consequences for the interplanetary solar wind be addressed. The resulting three-dimensional structure of the solar wind and its evolution over the solar cycle are also briefly discussed.

The dynamic process of magnetic flux emergence from the solar interior to the outer atmosphere may well be related with eruptive phenomena and intense events of the Solar activity. However, the physics of the emergence is not still well understood. Thus, we have performed 3D MHD simulations to study the rising motion of a twisted flux tube from the convection zone of the Sun and its interaction with a preexisting coronal magnetic field. The results show that the reconnection process depends criticaly on the initial relative orientation between the two magnetic flux systems into contact. On the other hand, the overal process of emergence depends mostly on the dynamics of the sub-photospheric plasma.

Solar coronal heating is a complex problem due to the variety of scales and physical phenomena involved, and intricacy of “boundary conditions”. Lattice models and self-organized criticality provide means to model phenomenologically some of the physics involved over a wide range of scales, and reproduce certain statistical features of solar flares. Furthermore, these models offer a basis for the study of Parker's hypothesis of coronal heating by nanoflares. We provide a short review of this approach pioneered by Lu & Hamilton (1991) and related more recent works involving lattice models.

Helioseismic holography is a technique used to image the sources of seismic disturbances observed at the solar surface. It has been used to detect acoustic emission, known as sun quakes, radiated from X-class solar flares. Since the seismic power emitted by the X-class flares has proved to be independent of the strength of the flare, we have undertaking a systematic search for seismic signatures from M-class solar flares, observed by SOHO-MDI.

We have detected significant acoustic emission from a few M-class solar flares. Preliminary results of the survey of M-type solar flares studied so far is available at: aira.astro.ro/~deanna/M.html.

The Kelvin-Helmholtz instability (KHI) could be a potential source for some of the Alfvénic fluctuations observed in the solar wind. The nonlinear evolution of KHI is examined in 2+1 dimensions in the context of magnetohydrodynamics. We derived a nonlinear Schródinger equation (NLSE) and we obtained soliton solutions of this 2+1 dimensions NLSE.

We have examined the effect of small- and large-scale structures in the solar wind on the topology and dynamics of the Earth's magnetosphere during magnetic storms. To do so, we ran global magnetohydrodynamic (MHD) simulations of a magnetic storm that occurred on 23-24 May 2000 by using upstream solar wind data from the ACE, IMP-8, and Wind spacecraft to run separate simulations of the global magnetosphere. This study suggests that the presence of small-scale structures in the solar wind can affect the global configuration of the magnetosphere.

The Rayleigh-Taylor instability (RTI) of a continuously stratified fluid has implications on the stability of solar and planetary interiors. A nonlinear stage of the two-dimensional RTI is studied by including various effects. By using the multiple scale method, we derived a nonlinear Schrödinger equation (NLSE) in 2+1 dimensions. We show the general soliton solutions of the NLSE and this allows to discuss their stability.

Kinematic solar dynamo models (KSDM) that use a solar like differential rotation profile usually fail to reproduce the latitudinal distribution of the toroidal magnetic fields. Usually, it is assumed that it is the larger radial shear present in the solar tachocline at higher latitudes that is the responsible for such results. We here consider variations in the shape and thickness of the tachocline and find that a better distribution of the toroidal fields is obtained when the thickness of the tachocline is $d_1=0.02R_{\odot}$, a smaller value than that conventionally used.

Using Big Bear Solar Observatory (BBSO) magnetograms and H${\alpha}$ images in a quiet region and a coronal hole, observed on 9 14 and 16, 2004, respectively, we have explored the magnetic flux emergence, disappearance and distribution in the two regions. The following results are obtained: (1) The evolution of magnetic flux in the quiet region is much faster than that in the coronal hole, as the flux appeared in the form of ephemeral regions in the quiet region is four times as large as that in the coronal hole, and the flux disappeared in the form of flux cancellation, three times as fast as in the coronal hole. (2) More magnetic elements with opposite polarities in the quiet region are connected by arch filaments. (3) The flux distribution of network and intranetwork (IN) elements is similar in both polarities in the quiet region. For network fields in the coronal hole, the number of negative elements is much more than that of positive elements. However for the IN fields, the number of positive elements is much more than that of negative elements. (4) In the coronal hole, the fraction of negative flux change obviously with different threshold flux density. 73% of the magnetic fields with flux density larger than 2 Gauss is negative polarity, and 95% of the magnetic fields is negative, if we only measure the fields with their flux density larger than 20 Gauss. These results display that in a coronal hole, stronger fields is occupied by one predominant polarity; however the majority of weaker fields, occupied by the other polarity.

Differential rotational rate of the magnetic field measured in the photosphere was calculated and its temporal dependence was studied using two independent methods. It was found that the rotational rate has a character of torsional waves running to the equator with 11 year periodicity. At high latitudes the rotation is getting slower during minimum of activity when the field measured there is stronger.

Based upon the similar time profiles of the hard x-ray and microwave emissions on 21 April 2002 flare-CME event, we argue that: (1) in the impulsive phase of the flare, the fast loop-loop reconnection triggered the quasi periodic magnetic energy release and particle acceleration with duration of the order of minute, (2) in the extended phase of the flare (01:40-01:50UT), the quasi period reconnection in current sheet produced the impulsive energetic electrons injection and modulated the microwave emissions with duration of 10-30 s, (3) the current driven instability enhances the magnetic energy releasing rate and scatters the energetic electrons, which may be used to explain the power index of the hard X-ray and microwave emissions.