The solar corona is believed to be generally low beta. In a low-beta plasma, energy is mainly stored as magnetic energy or current. To dissipate the stored magnetic energy in the highly conductive corona, anomalous resistivity is needed. Activities of outer layers of X-ray loops in solar flares have been interpreted as the result of reconnection of magnetic field due to anomalous resistivity in a current sheet located above the flaring loop.

However, recent high-cadence EUV observations show many flares without opening up of magnetic field. This means that existence of current sheets above flaring loops is not a necessary element for flares. It is also found for many flares that low temperature prominence plasma are heated in the very early phase of lifting. These observational facts require a new solar flare scenario different from reconnection.

Recent multi-wavelength high-spatial and -temporal resolution observations show that flares originate in the lower atmosphere. We can expect high beta plasma and small curvature magnetic loops in the lower atmosphere. It is also observed high-velocity flows along magnetic loops associated with flares. Bounded motions of charged particles (both thermal motion and flow) along the magnetic lines of force create the centrifugal force. They exceed gravity force under certain conditions (small curvature and high velocity). They can even exceed magnetic tension force depending on beta values of the plasma in the loop.

In the case of the upward acceleration (centrifugal - gravity $>0$), the plasma is balanced by the magnetic tension force if the beta value is not large enough. This is a favorable condition for the interchange instability. Finite beta ($beta \sim 0.1$) plasma in a loop, whose ends are anchored at the photosphere, is unstable against the localized interchange (BALLOONING) mode. It can develop into non-linear phase and explosive phenomena are expected. This is called HIGH-BETA DISRUPTION. The high-beta disruption has many common characteristics to solar flares. Various phenomena related to solar flares such as, high-energy particle acceleration, plasma turbulence, plasma ejections, plasma heating, are interpred as the result of high-beta disruption. High spatial and temporal resolution observations of flares at various wavelengths are used to see the actual instability process. Shibasaki (2001)To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The radio and multi-wavelength signature of coronal loop interaction is discussed in the event on November 28, 1998 with X-class flares and CMEs, observed by Nobeyama Radioheliograph (NoRH), YOHKOH/SXT/HXT, SOHO/EIT/LASCO, and Chinese radio spectrometers (2.6-3.8 GHz). The fluctuations at rising phase with bi-directional drift rates may show the signature of magnetic reconnection caused by loop interaction. There are two or three peaks in radio time profiles and spectra, which show that two or three flares are triggered in the process of loop interaction. The 17 GHz sources are composed of three parts with different time profiles and polarization feature. The formation of twisted loops in post-flare phase may indicate the start time of the CMEs in this event.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Formation and evolution of coronal holes of different type are investigated. Occurrence and evolution of coronal holes in active regions are connected to the processes occurring in these active regions in particular with flares and CMEs. Coronal holes which are not connected to active regions reflect distribution of large-scale solar magnetic fields and their dynamics determined by global solar magnetic field structure changes.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We describe fully consistent NLTE radiation hydrodynamic simulations of the propagation of acoustic waves in sunspot umbrae. In contrast to the case of the quiet internetwork Sun, we find that the observed behavior of the resonance lines of singly ionized calcium (H and K lines) cannot be explained without adding non-acoustic heating. The best agreement with observations is obtained with an extra heating term as a function of height that is constant per volume.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

This paper presents the results of a comprehensive analysis of the dynamics of the sun's global magnetic structure, solar wind parameters, the interplanetary magnetic field and geomagnetic activity during fast global changes of magnetic fields on the Sun.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

TRACE (Transition Region and Coronal Explorer) observations of transverse oscillations in coronal loops have prompted a number of questions to which there are no convincing answers as yet. Only the conclusion that the appearance of oscillations reflects the response of the magnetosphere of an active region to an internal or external magnetohydrodynamic (MHD) disturbance seems beyond question. The sources of such disturbances are solar flares or filament eruptions. The putative correspondence of the observed oscillations to the axisymmetric fundamental kink mode of a single coronal loop raises two questions at once: how to excite this mode and how to explain the rapid damping of the oscillation.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Recent high resolution observations by Lites et al. (2004) show details of facular granules at $0.12^{\prime\prime}$, including dark facular lanes. For an interpretation of these data a basic facular model is constructed, consisting of a magnetic flux sheet embedded in a plane parallel atmosphere. While the maximum contrast originates from the “hot wall” of the flux-sheet depression, the model explains the wide brightening limbward of the facular magnetic field as due to a radiative transfer effect caused by the reduced opacity of the rarefied flux-sheet atmosphere. This model produces a dark, narrow lane centerward of the facular granule even in the absence of granular flow as a consequence of the cool deep layers of the magnetic flux sheet. These results carry over to a self-consistent simulation of a flux concentration in dynamic interaction with convective motion, where the dark lane deepens and broadens.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The solar active regions observations were carried out with facilities for multi-spectral investigations of solar atmosphere on Large solar coronagraph of Sayan observatory. The facilities permits to perform the spectral observations in selected chromospheric and coronal lines simultaneously with obtaining of $H_\alpha$ and He I images.

In this work we analyze the results of spectral observations in the range from 10824 Å to 10835 Å (the He I 10830 Å and Si I 10827 Å lines) and images of the sunspot umbrae in the He I 10830 Å.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

AE Aquarii is a star with unique flaring activity. It is a close binary system, which contains a K3V-K5V red dwarf (secondary) and a magnetized white dwarf rotating with the period of 33 s (primary). It is traditionally classified as a peculiar nova-like star and assigned to the DQ Her subclass of magnetic Cataclysmic Variables (CVs).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

When in 1874 and 1882 Venus passed in front of the face of the Sun, most countries with a scientific reputation to keep or to gain made plans to observe the great event. The United States was no exception. The purpose was primarily to measure the solar parallax, and thereby determine the astronomical unit, the distance between the Earth and the Sun. With a $177000 Congressional appropriation for the 1874 event, and $78000 for 1882, the Americans sent out eight well-equipped expeditions for each transit. Under the U.S. Transit of Venus Commission, the responsibility fell to the U. S. Naval Observatory (Dick 2003). Relying heavily on photographic methods, the Americans returned 350 plates in 1874, and 1380 measurable plates in 1882. Simon Newcomb grew skeptical of the results, but in 1894 William Harkness produced a final value of the solar parallax, after adjustments with other constants, of 8.$\rlap^{\prime\prime}$809, with a probable error of 0.\rlap$^{\prime\prime}$0059, yielding an Earth-Sun distance of 92797000 miles, with a probable error of 59700 miles. This was a significant improvement over previous estimates. How important were the transit of Venus observations? In the end it was Newcomb who had the final say, for it was his system of astronomical constants that was adopted internationally at a Paris conference in 1896. Ironically, just at this time other methods were proving more accurate than Venus transits. In determining a final value for the solar parallax from all methods, Newcomb gave all photographic observations of the 1874 and 1882 transit a weight of 2, compared to a weight of 40 for Pulkovo Observatory's determination of solar parallax from the constant of aberration. Thus the Venus transit observations played little role in the official value used for the astronomical unit in the 20th century.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The active region 8210 (AR 8210) observed on May 1, 1998 is the site of numerous flares. By studying a time series (from 17:00 UT to 21:40 UT) of reconstructed coronal magnetic configurations, we give a scenario of the eruptive phenomena in AR 8210 involving the rotation of the sunspot and the complex topology in a reconnection process. We also study the time evolution of the energy and of the helicity budget. We compute the free energy in the corona, the magnetic energy rate due to transverse photospheric motions. We conclude that the photospheric motions are related to flaring activities and occur before the injections of energy into the corona. In terms of magnetic helicity, we are able to derived the relative magnetic helicity (relative to the potential field) and the helicity of the potential field configuration. The vacuum helicity (or helicity of the potential field) is constant during the time period and characterizes the complex topology. For this time period, the relative magnetic helicity does not show obvious changes related to the flaring activity.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The CCD spectroheliograph-magnetograph is a focal plane ancillary instrument for Pulkovo horizontal solar telescope ACU-5. The instrument is placed at an exit port of an isothermal high-resolution diffraction-grating spectrograph. The modified Leighton optical scheme for registration of sunspot magnetic fields is used. The instrument provides obtaining FITS digital video cards of radial velocities, magnetic fields and spectroheliogram in any line of spectral region 3900A - 11000A. The time of obtaining of one video card by the size 91″ $\times$154″ is equal 10.24sec. The angular resolution of the instrument is 0″.8; spectral resolution is 0.01-0.03A. There is remote access to a solar telescope in real time on the basis of Internet - process engineerings.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Here we show that archaeomagnetic measurement confidence interval ($\alpha_{95}$) may serve as a new proxy for the past solar activity estimation. This proxy is compared with sunspot numbers during 1700-2000 yr and with other proxies during 1500–2000 yr.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The main observable components of coronal mass ejections (CMEs) are the core, cavity and the frontal structure (FS), which is the leading edge of the visible CME. The core of a CME is associated with an eruptive filament whose motion can be followed just from the solar surface. As a rule, the FS is visible in scattered white light (SOHO/LASCO) far from the CME origination site. In few cases in near-the-limb events, the FS was detected closer to the solar surface. However, it appears not possible to detect any manifestations of the FS in a reasonable proximity of the pre-eruptive filament localized on the sun far from the limb. The identification of the FS remains unclear. We propose a method to estimate parameters of the initial volume of a CME based on the comparison of measured height-time plots of its structural components with a self-similar solution of MHD equations describing the expansion of a CME.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The paper presents study of the influence of coronal inhomogeneities on the average temporal pulse profile of radio emission from a compact solar pulse source located near the photosphere of the Sun. To consider both scattering and refraction of the radio emission propagating through the solar corona an integral representation of the wave field in the form of the interference integral is used. Thus formation of regular and random caustics and focuses as well as multipath structure of the radio emission received on the ground are taken into account. A numerical simulation of the average pulse profile, carried out for different parameters of the solar corona turbulence has shown that near-solar plasma can distort the emitted pulse significantly to form several pulses.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In spite of the great progress of solar physics research, complete understanding of the solar activity nature is still lacking. Although everybody can observe the obvious cyclical sunspot variation, recent models of the process can not describe it quite accurately. Thus the official forecast of the 23-rd solar cycle, mainly basing on the dynamical models and precursors, was not proved. Many official predictions considered that the cycle 23 will have an amplitude higher than the previous one. In this case statistical models were neglected as the less reliable but some of those kinematic forecasts are proved to this time. This situation makes evidence that we have to not ignore statistical approaches in the study of the solar behavior at the current stage of the knowledge.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

When Jeremiah Horrocks correctly predicted, and with his friend William Crabtree observed, the Venus transit of 24 November 1639, these two men became more than the first astronomers in history to witness a rare celestial phenomenon. For Horrocks's and Crabtree's achievement constituted in may ways the first major astronomical discovery to be made in Renaissance England. It is also clear from their writings, moreover, that the two men, working in the isolation of rural Lancashire and well away from London or the universities, were fully conversant with contemporary discoveries made in continental Europe by Tycho Brahe, Galileo, Kepler, Gassendi, and others. In many ways, therefore, their work begs more questions than can easily be answered, such as why the rural North-West produced not only Horrocks and Crabtree, but other contemporary astronomers such as the Lancastrians Charles Towneley, Jeremy Shakerley, and their Yorkshire friend William Gascoigne. Yet in addition to whatever regional circumstances might have been present, and how easy it might have been for an educated rural Lancastrian to be fully informed about what astronomers in Paris, Prague, or Florence were doing, what cannot be denied is the outstanding originality of their wider achievement. For Jeremiah Horrocks in particular was a physical scientist of genius. His correct determination of the elliptical shape of the lunar orbit by 1638 when he was about 20 and his wider work on planetary dynamics place him amongst the most creative researchers of the seventeenth century. Central to Horrocks's and Crabtree's achievement was Crabtree's realisation by 1636 that contemporary published astronomical tables were unreliable, and that if one wanted to do serious work in understanding the heavens, then one had to observe and measure them for oneself, and learn to draw original conclusions.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We study the sensitivity to AR of three photospheric lines, comparing experimental results, from THEMIS observations, with spectral synthesis, demonstrating the inappropriateness of using these lines as indicators of quiet sun modifications, because their variations in the active regions. We try to reconstruct the cyclic lines behavior.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

At the footpoints of loops spanning a site of flux emergence, earlier investigated in the papers by Solanki et al. (2003) and Lagg et al. (2004), we find large redshifts in the He 1083 nm line coexisting with an almost unshifted component. The speed associated with these redshifts reaches values as high as 40 km/s. We interpret these downflows in the context of several models: the free-fall downflow of matter along vertical field lines (Schmidt et al. 2000), the redshift by downward propagating acoustic waves (Hansteen 1993) and the motion of condensation regions to either side of loop footpoints (Müller et al. 2003). We present the temporal evolution of these redshifts and reconstruct the magnetic field vector in these regions for both the redshifted and the unshifted atmospheric component.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