The European Grid of Solar Observations (EGSO) is a Solar virtual observatory (see Hill et al., 2002). It has been funded through the 5th Framework Program of the European Community. A dozen of laboratories, mixing Solar Physics and Information Technology, in Great Britain, France, Italy and Swiss have been involved in this project during 3 years. A grid accessing several dozens of databases and archives scattered all around the world has been developped as well as a Solar Event Catalogue and a Solar Feature Catalogue. The original aspect of this work consists in the possibility not only to search through the characteristics of observations, but also search for available data corresponding to specific kinds of events. So it is now very important to be able to follow the Sun 24 hours a day in order to enrich the events database for future queries. More informations on EGSO, catalogues and user interface can be accessd through the web site: http://www.egso.org/

We present a new powerful tool to simulate the streamer belt of the solar corona based on forward modeling. It takes into account the temporal evolution of the corona and provides both qualitative and quantitative results. Starting from the National Solar Observatory photospheric magnetograms, the position of the neutral line at the source surface (2.5 Rsun) is caculated using the potential field source surface model. The plasma sheet of the streamer belt is centered around the current sheet represented as the radial extension of the neutral line. The 3D electron density is represented with octree compression and the radiance images are computed by a ray-tracing algorithm implementing the Thomson scattering. A multi-octree method allows to simulate the temporal evolution of the streamer belt and to compute the synoptic maps from time-series of generated images. The comparison between the synoptic maps of the streamer belt obtained with the SOHO/LASCO-C2 coronagraph and the simulated synoptic maps constructed from our model shows a global agreement for both radiance profiles and global behaviour of the streamer and confirms earlier findings by Wang et al. (1997) that the streamers are associated with folds in the plasma sheet. However, some features cannot be explained using this method and are interpreted by introducing two types of large-scale structures. Our results suggest that the potential field source surface model is not fully adequate for the description of the fine structure of the streamer belt, even during the time of low solar activity. We present new applications of our method to future coronographic observations with SECCHI/COR-2 on STEREO and SILC on Solar Orbiter.

The solar prolateness (also known as Ovalisation, a french origin name) of the extended dynamical chromosphere is established from measurements performed above 2 Mm heights during the years of solar minimum, using the H$\alpha$, Ca II K and HeII 304 line emissions from both ground-based and space-based observations. Coronal X-EUV emissions usually penetrate deep enough into the chromosphere to completely mask this effect on transition region lines and produce the so-called coronal hole effect. However, cool lines like H$\alpha$ and Ca II lines, do NOT show this Coronal Hole (CH) effect. Coronal lines and HeI (D3; 1083 nm) do show CHs but do not show the prolateness effect. We first briefly review different methods which can potentially be used to measure the prolateness. Further we note the similarity of the geometric behaviour of the prolateness and its variation along the solar cycle compared to the behaviour of the fast solar wind. It suggests the same origin possibly related to the emergence of the small scale network and internetwork magnetic field towards the corona and small scale magnetic reconnections. A simple geometric model was proposed to explain the effect of the prolateness of the solar chromosphere by considering that the specific dynamical part of the solar atmosphere above the 2 Mm level, being a mixture of up and down moving jets of chromospheric matter with the coronal plasma between them, is responsible for the solar prolateness (Filippov and Koutchmy, 2000). We however note that polar regions are also showing different types of activity in the low corona, including small prominence eruptions seen e.g. in H$\alpha$ and linear jets seen in SXR and EUV as well as in W-L (eclipses). Some kind of dynamical dissipation of the newly emerged magnetic field is needed. More systematic measurements should be done to build a more complete, possibly 3D, picture to explain the extended in the horizontal direction lifting effect of a large part of the polar chromosphere.

The Kislovodsk series of the green (FeXIV 530.3 nm; KI$_{5303}$) and red (FeX 637.4 nm; KI$_{6374}$) corona has been used to calculate the mean monthly intensities at high latitude (45$^\circ$–90$^\circ$) zones for 1957–2002. The ratio KI$_{6374}$/KI$_{5303}$ was observed during the minimum sunspot activity. It was shown that this ratio increased by more than a factor 2 during the last 45 years at the high latitudes (45$^\circ$–90$^\circ$). This may be interpreted that the fraction of cool regions in the polar corona has more than doubled over these years. We suggest that this increase in the amount of cool regions is related to the increase in the area of the polar zones occupied by magnetic field of a single polarity at the solar minimum and possibly to a corresponding increase in the area occupied by polar coronal holes, while the magnetic field strength itself has not or barely increased.

Total solar eclipses observed on the long baseline allow to obtain the pictures of white-light solar corona with the long temporal distance. New mathematical methods of coronal picture processing allow visualization of very faint coronal structures and enable to compare their position in corona with very high accuracy. We can detect the moving of these faint structures by comparing of pictures obtained on the different places during the same total solar eclipse. Some techniques and results are described in this paper.

Within the framework of the two-layer model the expression for the reflection coefficients of Alfven (torsion) waves propagated from the chromosphere into the corona have been obtained. As a result of reflection the energetic losses of waves with a period less than several tens of seconds are about 70%. This shows evidence in favor of the essential contribution of Alfven waves with a period of 10–40 s to coronal heating of the Sun.

Five series of coronal images have been obtained by V.Kulijanishvili during the total solar eclipse of the June 21, 2001, in Zambia, Lusaka. A photographic mirror-lens coronagraph-polarimeter (D=100 mm, F=1000 mm) was used. The absolute brightness, polarization and direction of polarization of the inner corona were measured. Standard techniques are used for the separation of the F- and K-coronas and for determination of coronal electron densities and temperatures. The background skylight polarization and intensity are calculated.

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.

Major properties of the solar atmosphere and wind are not understood. The energy distribution of the solar atmosphere perturbations, over nearly ten orders of magnitude in energy, is close (within one order of magnitude) to a power-law of index -2, even though there is no agreement on the detailed shape. There is no agreed explanation of the origin of the solar wind, either, nor of the fact that the total wind energy flux is independent of speed, latitude, and phase of solar cycle, with an average base flux of 70 W/m$^2$ – a figure that is similar for a number of other cool stellar winds, and is close to the total observed energy flux of solar atmosphere perturbations. A major theoretical difficulty is that both coronal heating and wind production depend fundamentally on the heat flux, and the solar atmosphere is not collisional enough for classical transport theory to hold. Heat transport thus behaves non classically and the particle velocity distributions may have significant high energy tails, which should dramatically affect coronal heating and solar wind acceleration, in a way that is outside the scope of standard MHD.

It is suggested that we are already in the weak solar cycles series since the start of cycle 23. The interplanetary magnetic filed and the solar wind speed and density are expected to drop considerably during the approaching second weak cycle number 24 and the following ones leading to inflation of the magnetosphere. The corona is also expected to cool down relative to normal cycles corona. A daily background coronal index is proposed. The mechanism of production of weak cycles is tied to the rapid rotation of the photospheric layer which is deeply rooted in the bottom of the convection zone. This rapid surface and subsurface rotation implies slower rotation of the tachocline. Slower dynamo rotation leads to reduction of the strength of the magnetic cycle. One of the very important sequences of the weak cycles, is the expected cooling of the Earths air and sea surface temperatures which would have negative effects on agriculture with increased drought-flood hazards. The reduction of solar UV flux can lead to the closure of the ozone hole on the long run.

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 present work concerns the study of the great solar proton events during the solar cycle 23. For this purpose, the temporal behavior of six solar indices during these great events will be studied. These indices are the radio flux (10.7cm) intensity, the sunspot no., the sunspot area, the GEOS X-ray background flux intensity, and the intensity of the X-ray flares and optical flares.

The main aim of this research is to make direct comparison between the basic structure and dynamics of the photospheric magnetic field, solar wind and geomagnetic characteristics without using theoretical assumptions. The heliospheric and geomagnetic data are found to be divided into two groups characterized by their response to the variability of the latitudinal structures of the photospheric field on short and on long time scales.

Ulysses spacecraft discovered the long-period, outwardly propagating Alfvén waves in the solar polar regions (Balogh et al. 1995). Here we suggest that the waves may be generated in the solar interior due to the pulsation of the Sun in the fundamental radial mode or in low-frequency g-modes. The period of fundamental mode is about 1 hour, while the period of g-modes can be longer. The pulsation causes a periodical variation of density and large-scale magnetic field, this affecting the Alfvén speed in the solar interior. Consequently the Alfvén waves with the half frequency of pulsation (i.e. with the double period) can be parametrically amplified in the interior below the convection zone due to the recently suggested swing wave-wave interaction. Therefore the amplified Alfvén waves have periods of several hours. The waves can propagate upwards through the convection zone to the solar atmosphere and cause the observed long-period Alfvén oscillations in the solar wind.

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.

In this paper we have used the general theory of Arnold (1965,1966) and Vladimirov et al. (1997) to obtain sufficient conditions for linear stability of steady MHD flows of an ideal three-dimensional compressible gravitating flows.

A class of exact analytic solutions to the Grad-Shafranov equation (GSE), in cylindrical geometry under assumption of axial symmetry is obtained. For this configuration all the physical quantities are invariant under rotations about a fixed direction, which we take it to be the direction Oz of a cylindrical polar coordinate system $(r, \theta, z)$. The obtained solutions can be employed to describe isothermal magnetostatic atmosphere.

The stability behaviour of the wave modes that propagate in the solar wind plasma is considered in the framework of the Hall-magnetohydrodynamics. The Hall-MHD theory extends the wave frequency limit up to or higher than the ion cyclotron frequency. Due to the different flow velocities of the adjacent media in the solar wind, a Kelvin–Helmholtz instability is naturally expected to arise. The behaviour of the wave modes due to this particular kind of instability is studied under solar wind conditions typical for 1 AU. This is a preliminary study on the stability problem in the solar wind flowing structures and it could be relevant for the interplanetary and space weather research.

The solar wind is considered as a steady fully ionized hydrogen plasma flow, with rotational symmetry. The Parker-spiral type magnetic field specifies the dependence of the flow speed on the radial distance and meridional angle if the plasma is assumed to be quasi-neutral and currentless. A two-particle kinetic model of the collisionless rotationally symmetrical plasma flow in a magnetic field is formulated and applied to estimate the flux and density of the solar wind. The obtained theoretical results are compared to the observational data.

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.