It was found that filaments observed in EUV could be much more extended than in H$\alpha$. These extended dark structures visible in EUV are named EUV filaments. Their parts seen only in EUV (not observable in H$\alpha$ because of low opacity at the H$\alpha$ wavelength) are called EUV-filament extensions (or simply EUV extensions). For the EUV filament observed by SoHO on 15 October 1999 as northern polar crown filament, only a few small dark structures were seen in H$\alpha$. This suggests that the mass of the EUV extension is larger than, or at least comparable with, the mass of the parts of the filament observed in H$\alpha$. In our previous work we determined the 3D structure of the EUV extension of this EUV filament. In this paper we present the determinations of mass and average density of this EUV extension. For better density estimates we interpret the hydrogen Lyman lines observed by SUMER using non-LTE radiative transfer code. From the best fitting of Lyman lines we obtained a reasonable model of the EUV extension with low gas pressure, temperatures from 2$\times10^4$ K to $10^5$ K and with extended prominence-corona transition regions.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We analyze some of the tens of active regions (AR) each supposed to produce at least one solar flare detected in Gamma- and hard X–rays by the SONG–M spectrometer on board the CORONAS–F satellite. Of special interest is the AR NOAA 9601, which gave rise to the solar flare at 14:30 UT on September 5, 2001 with up to 4 MeV intensity in Gamma and of M6.0 class only in soft X–rays. We examine 1D radio scans of NOAA 9601, taken with the RATAN–600 in Stokes I and V at a set of wavelengths from 1.92 to 10 cm and radio maps taken with the Solar Siberian Radio Telescope (SSRT) at 5.2 cm. The type of this microwave source is classified among the other sources. The some prediction evidences of such type sources are listed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The Fraunhofer spectra were used to study the physical condition variations in the photospheric layers in the course of a bright solar flare. The observations involve both the impulsive and main phases of the flare. The spectral lines are formed in the photosphere at the interval 12–500 km. The modelling was made by fitting the observed and calculated line profiles using the SIR program. The models represent the distributions of temperature, gas density, line-of-sight velocities, etc. on the height. They show some inhomogeneities of these physical parameters at various photospheric levels. Their significant deviations from the VAL-F model may be seen in the course of the flare. The largest heating of the high and middle photospheric levels take place close to two X-ray maxima. At the final flare stage the photosphere is disturbed appreciably while the spectral data testify to the flaring process fading in the chromosphere. This may be an evidence of a disturbance propagation from the upper atmospheric levels to the low ones in the impulsive and main phases.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The preflare plage spectra were obtained with the ATsU-26 solar telescope mounted at the Peak Terskol. The spectra were acquired from 1 h to 20 min before the flare onset. The most prominent peculiarity of all the observed events are the tilted $H_{\alpha}$-emission details which appear less than 40 min before the flare. This result may testify to spiral structure of the ascending $H_{\alpha}$ loops. The ascending velocities in the chromosphere attain more than 10 km/s. Two crossing $H_{\alpha}$ loops were observed to interact before 1n flare. As a result of their interaction, the redistribution of velocities occurs in the both chromosphere and photosphere. This can be a consequence of the preflare reconnection at the lower atmospheric layers. As the flare onset approaches the ascend of photospheric material start to dominate. The preflare line-of-sight velocities exceed considerably those in the neighbouring unperturbed regions.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The renew non-hydrostatic model of electron density, temperature and velocity distribution with height in coronal hole (CH) is build. The presented model is based on the measurements of magnetic field in CH with RATAN-600 observations and on the assumption about equality of magnetic and kinetic energy of upward plasma flows in CH at heights of generation of radio emission in wavelength range 20–30 cm. To construct this model the observational spectrum of brightness temperatures of CH in wavelength range 2–30 cm is used. The first results of modeling are presented.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The time-averaged images of the solar granulation exhibit a slower decrease in contrast with the averaging time than do time-averaged images of numerically simulated granulation and time-averaged random fields with some parameters typical of granulation. This confirms the hints for long-lived structures in the granulation pattern.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the first center-to-limb G-band images synthesized from high resolution simulations of solar magneto-convection. Towards the limb the simulations show “hilly” granulation with dark bands on the far side, bright granulation walls and striated faculae, similar to observations. At disk center G-band bright points are flanked by dark lanes. The increased brightness in magnetic elements is due to their lower density compared with the surrounding intergranular medium. One thus sees deeper layers where the temperature is higher. At a given geometric height, the magnetic elements are cooler than the surrounding medium. In the G-band, the contrast is further increased by the destruction of CH in the low density magnetic elements. The optical depth unity surface is very corrugated. Bright granules have their continuum optical depth unity 80 km above the mean surface, the magnetic elements 200-300 km below. The horizontal temperature gradient is especially large next to flux concentrations. When viewed at an angle, the deep magnetic elements optical surface is hidden by the granules and the bright points are no longer visible, except where the “magnetic valleys” are aligned with the line of sight. Towards the limb, the low density in the strong magnetic elements causes unit line-of-sight optical depth to occur deeper in the granule walls behind than for rays not going through magnetic elements and variations in the field strength produce a striated appearance in the bright granule walls.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We studied the line-of-sight (LOS) velocity field at the photospheric and chromospheric levels in the $H_{\alpha}$-loops in the course of the development of the bright flare. The spectra and filtergrams were acquired with the solar telescope ATsU-26 at the Terskol Peak Observatory. Time variations of the LOS velocities at loop tops and bases were compared to the $H_{\alpha}$ and hard X-ray fluctuations. The intensity variations and $H_{\alpha}$-filtergrams are evidence that elementary X-ray spikes are associated with consecutive disturbances of $H_{\alpha}$-loops in the arcade. The $H_{\alpha}$ intensities and velocities at the loop bases are much higher than at the tops. Different mechanisms can be efficient at the early stages of elementary X-ray spikes and at their maxima: ascent of photospheric matter at loop bases was recorded only when the $H_{\alpha}$ and hard X-ray intensities were minimum, and the intensity maxima were accompanied by descending motions of the photospheric plasma.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We observed a sunspot almost exactly at disc centre on 23 September, 2003, with the Tenerife Infrared Polarimeter (TIP; Martínez Pillet et al. 1999) at the $\phi=70$, cm Vacuum Tower Telescope (VTT) on Tenerife. The highly symmetric spot passed the central meridian just at the time of observations; its solar latitude of $9^\circ$ N was almost perfectly compensated by the inclination of the solar axis $B_0=7^\circ$. We took the full Stokes vector through the line profiles of Fe I 10783 Å, Si I 10784.5 Å and Si I 10786.8 Å. The spatial sampling was adapted to the pixel size of 0.4 arcsec width; the VTT correlation tracker largely compensated image motion. The Stokes spectra were corrected for the dark and the gain matrices, as well as for instrumental polarisation and Stokes cross-talk. The spectral resolution finally achieved with TIP and its detector amounts to 32 mÅ.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Simulations of cellular magnetoconvection in a compressible fluid reveal the formation of magnetic structures with a substantial bipolar component as an inherent property of the topology of cellular flows.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Magnetic and acoustic properties of the complex active region AR 486 are analyzed for two consecutive days: October 28 and October 29, 2003 when two large flares of magnitude X17.2 and X10 were produced, respectively. Using the technique of helioseismic holography we detected seismic waves emitted from these flares at 6 mHz. SOHO-MDI white light images, magnetograms, and Dopplergrams are used to study the physics of the acoustic sources.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

This investigation is devoted to the study of time variations and spatial peculiarities of radio local radio sources associated with the solar active regions (AR) on the basis of microwave observations in September–October 2002. During this period the most interesting results have been obtained for the AR NOAA 0139. So, in this paper an analysis of this radio source is presented. The observations were made with the radio telescopes RT–22 (Crimea), RATAN–600, the Siberian Solar Radio Telescope (SSRT) and Nobeyama. Observations with the RT–22 (wavelengths 2.0, 2.3, 3.5 cm) were carried out by the quasi–zero method with the flux sensitivity of 0.1 s.f.u and the temporal resolution of about 0.1 s. The typical length of realization was about 6.5 hours. The spatial resolution of few arc minutes allowed to limit the analysis by the particular AR but was not enough to distinguish any details. Nevertheless spectral analysis of the AR made using observations with high one–dimensional resolution of the RATAN–600 shows that at short cm wavelengths for this AR at the period of the RT–22 observations dominated thermal cyclotron emission of above the largest sunspot of the group. This result was also confirmed by radio maps of the Nobeyama at wavelength 1.76 cm.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

As based on analysis of radio maps at the wavelength of 1.76 cm obtained from observations at the radio heliograph Nobeyama the parameters of oscillation processes in solar active regions were studied. As a technique for data processing wavelet analysis was used. The inherent periodicity in oscillations submits the existence of a resonance structure for some kinds of MHD waves in the plasma of the solar atmosphere.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Signs of quasi-regular structures in time-averaged photospheric images are described.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Torsional oscillations of sunspots were investigated in a penumbra on the observations in the photosphere of the longitudinal magnetic and velocity fields.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The solar active region No. 10486 can be considered as one of the very large and powerful active regions since 1976. This region has produced the most important two solar flares during the period (1976-2003). The first flare released at 12:15UT on 28 October 2003 with importance X17/4B, and the second flare released at 22:25UT on 4 November 2003 with importance X28/3B. Both flares are the highest level in x-ray production since 1976, when different detectors, onboard various spacecrafts, have taken the data, and since 1996, when SOHO was launched to space. The first flare on 28 October 2003 produced protons events at 6:15UT on 29 Oct. 2003 with energies > 10 MeV. The maximum solar wind speed is 1905 and 1986 km/sec at 29 and 30 October 2003 respectively. The same region after its rotation across the sun was appeared again on the sun's edge at 18 November 2003, and produced high energetic flare at 19 November 2003, which led to increase the solar wind speed to 947 km/sec at 20 November 2003. The evaluation of the active region No. 10486 is very important for understanding the high energetic proton flares. The aim of this study is to follow the morphological and magnetic changes of the active region before, during, and after the high energetic flares were produced. Also, applying the cumulative summation curves method for the different index of the active region to predict the flare of high energy has been carried out. The results are promising and can be used for proton flares and Geomagnetic storms prediction, few days before their occurrence.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present results of an investigation into the coupling between solar-like magnetoconvection and coronal structures using self-consistent numerical simulations of compressible fluids. The model consists of a stratified MHD fluid spanning multiple scale heights, encompassing the transition of the plasma beta from high to low values. The lower portion of the domain, where the beta is high, is convectively unstable while the upper portion is stabilized by the presence of a strong magnetic field and energy losses. As a result, the dynamics associated with evolving magnetic features in the solar atmosphere can be modelled in a manner that is self-consistent with the convective motions that provide the driving. We present simulations of arcade-like reconnection in the presence of supergranular-scale flows.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We investigate the series of the green corona (GC) intensity by the combined catalogues of Rybansky, Tlatov and the original series of Kislovodsk station.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We report the “5+1” dynamical classification of the most frequently observed topologies of the magnetic field in sunspot groups associated with powerful flares (see Fig.1). The classification is based on the analysis of magnetographic and H$\alpha$ observations of more than 600 active regions on the span of 23 years (for detailed description see Ikhsanov 1982, Ikhsanov 1985).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The paper deals with some structural characteristics of sunspot magnetic fields.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html