The following aspects of the physics of large-scale solar magnetic fields are discussed: structure of large-scale fields (LSF) and connection with local fields; dynamo and origin of LSF; LSF cycle variation; meridional circulation and LSF; rotation of LSF; fine structure of the field in quiet regions and the concept of the pebble-shaped field; active longitudes, their manifestation in various solar indices, and dependence on the power of solar activity.

There appear indications of more global activity on the Sun which is larger, much beyond the scale of solar active regions (ARs). These indications include formation, flaring and eruption of the trans-equatorial loops seen in EUV and X-rays, formation and eruption of trans-equatorial filaments, global magnetic connectivity in EUV dimming associated with halo-coronal mass ejections, wide spread of radio burst sources in meter wavelength in the solar corona, and quasi-simultaneous magnetic flux emergence in both hemispheres seen during some major solar events. With examples of a few major events in the last solar cycle we discuss the possibility that there is large or global-scale activity on the Sun. Its spatial scale is many times larger than that of AR and temporal scale is over 10 hours. The exemplified trans-equatorial loops are anchored in ARs and their activity is temporally associated with flares in ARs too. In some sense the flares in ARs appear either as a part of or a precursor of the more global activity. It is likely that the combination of the flares in ARs and the associated global activity is responsible to the major solar-terrestrial events. More efforts in understanding the global activity are undertaken.

Free energy stored in the magnetic field is the source that powers solar and stellar activity at all temporal and spatial scales. The energy released during transient atmospheric events is contained in current-carrying magnetic fields that have emerged twisted and may be further stressed via motions in the lower atmospheric layers (i.e. loop-footpoint motions). Magnetic reconnection is thought to be the mechanism through which the stored magnetic energy is transformed into kinetic energy of accelerated particles and mass flows, and radiative energy along the whole electromagnetic spectrum. This mechanism works efficiently at scale lengths much below the spatial resolution of even the highest resolution solar instruments; however, it may imply a large-scale restructuring of the magnetic field inferred indirectly from the combined analysis of observations and models of the magnetic field topology. The aftermath of magnetic energy release includes events ranging from nanoflares, which are below our detection limit, to powerful flares, which may be accompanied by the ejection of large amounts of plasma and magnetic field (so called coronal mass ejections, CMEs), depending on the amount of total available free magnetic energy, the magnetic flux density distribution, the magnetic field configuration, etc. We describe key observational signatures of flares and CMEs on the Sun, their magnetic field topology, and discuss how the combined analysis of solar and interplanetary observations can be used to constrain the flare/CME ejection mechanism.

We have obtained high resolution, high S/N spectra of the RS CVn binary IM Peg using UVES spectrograph at Kueyen 8.2m telescope of ESO VLT. We use Doppler imaging techniques to obtain stellar surface temperature maps from the UVES data. The TempMap code allows us to use surface differential rotation as an input parameter and thus to try to construct the rotation pattern on the stellar surface as part of the inversion process. The UVES observations are combined with spectroscopic observations from another time period obtained at the STELLA observatory. We obtain stellar surface temperature maps also from these spectra. These Doppler images are used to study the magnetic activity and surface differential rotation on IM Peg.

Until recently, the mechanism of the light variability of chemically peculiar (CP) stars was unclear. To improve this situation, we started a theoretical and observational campaign aimed at the nature of the light variability of these stars. We use the TLUSTY model atmospheres calculated for the appropriate surface chemical composition to obtain the emergent flux and to predict the rotationally modulated light curves. We show on example of several well-studied CP stars that their light variations can be explained as a result of i) the uneven surface distribution of the elements (creating overabundant regions), ii) the flux redistribution from the ultraviolet to the visible part of the spectrum (in the overabundant regions), and iii) rotation of the star. We show that the silicon and helium bound-free transitions and iron bound-bound transitions provide the main contribution to the flux redistribution. This result is also a very precise test of modern stellar model atmospheres. We conclude that the mentioned mechanism is a very promising explanation for the light variations in CP stars of earlier spectral types.

The large burst of complex type which occurred at the metric, decimetric and microwave wavelengths from 0203 to 0304 UT on 2004 November 10 is analyzed in this present article, some prominent features of this event are obtained from the correlative analysis of this event with the Hα flare and coronal mass ejection (CME) and the radiation process of this event is discussed based on these observational features.

We analyze Si iv 139.37 nm emission line during solar Explosive Events (EE) near the center of the solar disk with the aim to study the structure of the sources of EEs observed at the VUV. The observations were made by SUMER, on board SoHO, with a raster regime of six EW positions that allowed us to identify the times and EW, NS positions of the maximum amplitude of each EE. Based on one dimensional NS distributions at three different wavelengths (blue, central and red) for times around each maximum we have identified three different shapes of the sources. Also, It was found that the maximum at the blue wing is attained after the maxima at red and central wavelengths.

The solar radio emissions in the decimetric frequency range (above 1 GHz) are very rich in temporal and spectral fine structures due to nonlinear processes occurring in the magnetic structures on the corresponding active regions. In this paper we characterize the singularity spectrum, f(α), for solar bursts observed at 1.6, 2.0 and 3 GHz. We interpret our findings as evidence of inhomogeneous plasma turbulence driving the underlying plasma emission process and discuss the nonlinear multifractal approach into the context of geoeffective solar active regions.

In this paper we analyze soft and hard X-ray emission of the 2002 September 20 M1.8 GOES class solar flare observed by RHESSI and GOES satellites, where soft X-ray emission precedes the onset of the main bulk hard X-ray emission by ~5 min. This suggests that an additional heating mechanism may be at work at the early beginning of the flare. However RHESSI spectra indicate presence of the non-thermal electrons also before impulsive phase. So, we assumed that a dominant energy transport mechanism during rise phase of solar flares is electron beam-driven evaporation. We used non-thermal electron beams derived from RHESSI spectra as the heating source in a hydrodynamic model of the analyzed flare. We showed that energy delivered by non-thermal electron beams is sufficient to heat the flare loop to temperatures in which it emits soft X-ray closely following the GOES 1–8 Å light-curve.

In this work, we analyze observations of the solar radius at 22 and 43 GHz obtained with the 13.7 m antenna of the Itapetinga Radio Observatory (Atibaia, Brazil) and at submillimeter-wave frequencies, 212 and 405 GHz, obtained by the Solar Submillimeter-wave Telescope (SST) (El Leoncito, San Juan, Argentina). The radius is defined as the limb position where the intensity is equal to half of the quiet Sun value. These measured radii are then compared with those predicted by a model of the solar atmosphere proposed by Selhorst, Silva, and Costa (2005). The results show that at 22 and 43 GHz, the emission comes from regions high in the chromosphere. Furthermore, the Itapetinga observations yield radii of 985” ± 5” and 981” ± 6”, at 22 and 43 GHz respectively, consistent with the theoretical positions in the atmosphere. On other hand, the submillimeter observations resulted in a mean radius of 972” ± 3” and 975” ± 5” at 212 and 405 GHz, respectively, considered equal within the uncertainties. The latter results can be explained by the origin of the emission being very close to the region of minimum temperature, between the photosphere and chromosphere. This is a dynamic region largely affected by many solar features, like spicules and plages.

Quasi–periodic pulsations in various wavebands are natural manifestations of emission of stellar flares. We suggest a diagnostic tool of stellar flares based on the coronal seismology and the solar–stellar analogy. Two approaches are used: (I) flare loop as a resonator for MHD oscillations and (II) flare loop as an equivalent electric circuit. Using optical, X–ray, and radio data we obtained flare plasma parameters for the red dwarfs EQ Peg, AT Mic, and AD Leo. The characteristic length of stellar flare loops l ~ R* and their electric currents turned out to be one–two orders of magnitude lager than the solar ones. Advantages of proposed diagnostics in comparison to the scaling law methods are given.

We have analyzed the shape of the solar corona using the data of daily observations with Mark-3/4 (1980-2008) and SOHO/Lasco-2 (1996–2008) telescopes. The angles of deviation of coronal rays from the radial direction Δθ vary cyclically, reaching the maximum deviation towards the solar equator at the minimum of the solar activity. At the minimum of the 24-th cycle of activity, the Δθ angles were smaller than they were at the minimum of the 22-nd and 23-rd cycles.

We also analyzed of the solar structure corona during eclipses for minimum activity from 1870 till 2008. We examined changes in the index, which characterizes the angle of large coronal streamers to the equatorial plane. It has been shown that the index has been smoothly changing during the last 140 years. The maximal value of an index was during 17–19 activity cycles. The minimal values are reached in the end of 19 centuries and at the present time.

We consider the relations between the angles of deviation of coronal rays at the minimum of activity, the parameters of the global magnetic field of the Sun, and the amplitude of the subsequent cycle of activity, and discuss the hypothesis that the variations of the inclination of coronal rays may affect the parameters of the solar wind and the indices of geomagnetic perturbations at the minima of the solar activity cycles.

The formation of an equatorial coronal hole (CH) from 2006 January 9 to 12 was simultaneously observed by GOES-12/SXI, SOHO/EIT and SOHO/MDI instruments. The varieties of soft X-ray and EUV brightness, coronal temperature, and total magnetic flux in the CH were examined and compared with that of a quiet-sun (QS) region nearby. The following results are obtained. (1) A preexisting dark lane appeared on the location of the followed CH and was reinforced by three enhanced networks. (2) The CH gradually formed in about 81 hours and was predominated by positive magnetic flux. (3) During the formation, the soft X-ray and EUV brightness, coronal temperature, and total magnetic flux obviously decreased in the CH, but were almost no change in the QS region. The decrease of the total magnetic flux may be the result of magnetic reconnection between the open and closed magnetic lines, probably indicating the physical mechanism for the birth of the CH.

Early attempts to find how solar activity can influence the Earth's climate involved comparison of many physical processes, such as dynamo mechanism, magnetic reconnection and eruptive activity, irradiance, open flux and particles variations, global atmospheric chemistry and dynamics.. . . However, such direct links seem to be weak even if the solar effects has been found to be stronger during extended maxima or minima of solar activity. Thus, temporal scales ranging from days to thousand of years must be investigated. A description of the most recent results on solar variability and its possible influence on the Earth's climate and atmosphere will be here addressed, with a particular emphasize on modulations of about 120 years (and harmonics). The extrapolation indicates a significant negative decrease of the solar signal, and consequently a decrease of the global Earth's temperature in the forthcoming years. Such a modulation is also testifying by other means, such as spectral observations of temperature sensitive lines indicating a decline of solar activity around 2015 (up to a new prolonged minimum). Prediction of global effects from the Sun's influence over the climate is thus planted in a new way.

The thermosphere is the transition region from the atmosphere to space. Both the solar ultraviolet radiation and the solar wind energy inputs have caused significant thermospheric variations from past to present. In order to understand thermospheric/ionospheric disturbances in association with changes in solar activity, observational and modelling efforts have been made by many researchers. Recent satellite observations, e.g., the satellite CHAMP, have revealed mass density variations in the upper thermosphere. The thermospheric temperature, wind, and composition variations have been also investigated with general/global circulation models (GCMs) which include forcings due to the solar wind energy inputs and the lower atmospheric effects. In particular, we have developed a GCM which covers all the atmospheric regions, troposphere, stratosphere, mesosphere, and thermosphere, to describe variations of the thermospheric temperature and density caused by both effects from the lower atmosphere and the magnetosphere. GCM simulations represent global and localized temperature and density structures, which vary from hour to hour, depending on forcings due to the lower atmosphere, solar and geomagnetic activities. This modelling attempt will enable us to describe the thermospheric weather influenced by solar activity in cooperation with ground-based and satellite observations.

We have analyzed the record of Earth's global temperature variations between 1850 and 2007 looking for signals of periodic variations and compared our results with solar activity variations in the same time period. Significant periods are found at 9.4, 10.6 and 20.9 years. These periodic variations may be caused by solar activity. However, and amazingly enough, we also find at least 17 other significant periodic variations in addition to expected variations with periods of 1 year and of half a year. The result is considered in terms of solar related forcing mechanisms. These may be variable solar heating associated with the small changes in solar irradiance over the solar cycle, or direct effects of interactions between variable magnetic fields carried by the solar wind and particles and fields in interplanetary space or in the Earth's ionosphere.

The coronal mass ejection (CME) link to geomagnetic storms stems from the southward component of the interplanetary magnetic field contained in the CME flux ropes and in the sheath between the flux rope and the CME-driven shock. A typical storm-causing CME is characterized by (i) high speed, (ii) large angular width (mostly halos and partial halos), and (iii) solar source location close to the central meridian. For CMEs originating at larger central meridian distances, the storms are mainly caused by the sheath field. Both the magnetic and energy contents of the storm-producing CMEs can be traced to the magnetic structure of active regions and the free energy stored in them.

Global warming in the troposphere and the decrease of stratospheric ozone concentration has become a major concern to the scientific community. The increase in greenhouse gases and aerosols concentration is believed to be the main cause of this global change in the lower atmosphere and in stratospheric ozone, which is corresponded by a cooling in the middle and upper atmosphere. However, there are natural sources, such as the sun and volcanic eruptions, with the same ability to produce global changes in the atmosphere. The present work will focus on solar variation and its signature in lower and middle atmosphere parameters. The Sun can influence the Earth and its climate through electromagnetic radiation variations and also through changes in the solar wind which causes geomagnetic storms. The effects of both mechanisms over the lower and middle atmosphere and ozone layer will be discussed through an overview of selected papers, which by no means cover this subject that is extremely wide and complex. A fundamental understanding of the atmosphere response to solar variations is required for understanding and interpreting the causes of atmospheric variability. This is an essential focus of climate science, which is seeking to determine the extent to which human activities are altering the planetary energy balance through the emission of greenhouse gases and pollutants.

In this study we investigate the effects of solar activity on the surface air temperature of mid-latitudes. This enables us to understand existence of solar activity effects on the temperature. We used surface air temperature and pressure data as climate parameters, and solar flare index data as solar activity indicator, for the 25 - 50 degree longitude and 30 - 70 degree latitude zone, including Turkey and European part of Russia. We considered the parameters temperature, pressure and flare index data for the period ranging from January 1975 to the end of December 2007, which covers almost three solar cycles, namely 21st, 22nd, and 23rd. We found some significant correlations between solar activity and surface air temperature for cycles 22 and 23 for some zones. We applied multitaper method to obtain the cyclic behavior of surface air temperature data sets. The most pronounced power peaks were found by this transform around 1.2 and 2.5 years which were reported earlier for some solar activity indicators. We concluded that signature of solar activity effect exists on surface air temperature of mid-latitudes where we studied.

The atmospheric response to the 11-year solar cycle is studied using the fully interactive 3-D coupled chemistry-general circulation model LMDz-REPROBUS with a complete seasonal cycle. We will show results concerning a comparison between two series of 20-year runs, one in maximum of activity and the other in minimum. The stratosphere-troposphere system shows partly significant response to a solar cycle enhancement of UV radiation. We show how the changes in stratospheric ozone, temperature and zonal wind are connected.