A new information resource to study solar magnetic field variations and their influence on the Earth extending ordinary lengths of some traditional indices of solar activity is introduced.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

New methods of local area helioseismology provide three-dimensional maps of sound-speed variations and mass flows in the upper convection zone, giving important insight into the internal structure and dynamics of sunspots and active regions. Most of these results are obtained from SOHO/MDI data using the method of time-distance helioseismology (or acoustic tomography). Robustness of this method has been significantly improved by incorporating most important wave propagation effects and stochastic properties of solar oscillations. Time-distance helioseismology reveals that developed sunspots have a two layer structure: a relatively thin sub-photospheric layer of lower sound speed, and a deeper layer of higher sound speed. The mass flows in the upper layer are typically converging and directed downward, while in the deeper interior the flows are mostly diverging. These results support the cluster model of sunspots suggested by Parker. New observations also provide interesting information about emerging magnetic flux, formation and evolution of active regions and complexes of activity, and allow us to investigate effects of sub-photospheric dynamics of active regions on the global circulation of the Sun and also small-scale rapid shear flows associated with flares and CME.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

High resolution optical spectra of hydrogen and calcium lines observed with the Echelle spectrograph of the VTT at Sacramento Peak Observatory were analyzed. The observed line profiles in some parts of dark chromospheric mottles are to be matched with theoretical ones using the cloud model and several parameters (e.g. the temperature, gas pressure, flow velocity) are to be derived. Individual steps of the procedure, as well as crucial problems are discussed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The black-drop effect bedeviled attempts to determine the Astronomical Unit from the time of the transit of Venus of 1761, until dynamical determinations of the AU obviated the need for transit measurements. By studying the 1999 transit of Mercury, using observations taken from space with NASA's Transition Region and Coronal Explorer (TRACE), we have fully explained Mercury's black-drop effect, with contributions from not only the telescope's point-spread function but also the solar limb darkening. Since Mercury has no atmosphere, we have thus verified the previous understanding, often overlooked, that the black-drop effect does not necessarily correspond to the detection of an atmosphere. We continued our studies with observations of the 2004 transit of Venus with the TRACE spacecraft in orbit and with ground-based imagery from Thessaloniki, Greece. We report on preliminary reduction of those data; see http://www.transitofvenus.info for updated results. Such studies are expected to contribute to the understanding of transits of exoplanets. Though the determination of the Astronomical Unit from studies of transit of Venus has been undertaken only rarely, it was for centuries expected to be the best method. The recent 8 June 2004 transit of Venus provided an exceptionally rare opportunity to study such a transit and to determine how modern studies can explain the limitations of the historical observations.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

Archival full disk observations of the central depth of Mn 539.467, a photospheric line, have been found to correlate with chromospheric Ca K intensity. In this paper we present spectroheliograms taken in Mn I 539.467 and 542.32 nm lines and other nearby lines to see if the other photospheric lines show chromospheric structures. We see both Mn images and also Si I 542.118 mimic magnetograms the similar way, while strong Fe and Ti lines only faintly reveal magnetic features, and weak Fe lines of comparable strength to Mn show nothing.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the review of temporal variations of the solar neutrino flux, including our original results of investigations of the solar neutrino flux variations in 1970–1997.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Gaia is a mission to map the positions and determine the velocities of 1 billion stars in the Galaxy, in order to determine how it was formed and how it has evolved. Spectroscopy provides one component of the space velocities for 200 million objects, and, in addition, astrophysical information such as temperature and metallicity for the brighter 40 million stars in a large unbiased Galactic sample. Together the instruments on Gaia will transform our knowledge of the Galaxy. We describe here a sample of the science that will be done with Gaia concentrating on aspects in which the spectroscopy plays a central role.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

The solar results from CORONAS-F satellite have been reviewed. The observations with the DIFOS multi-channel photometer in a broad spectral range from 350 to 1500 nm have allowed to determine the dependence of the relative amplitudes of p-modes of the global solar oscillations on the wavelength. The EUV observations in SPIRIT experiment have enabled the study of various manifestations of solar activity and high-temperature events on the Sun. The data from the flare instruments-gamma spectrometer HELICON, flare spectrometer IRIS, amplitude-time spectrometer AVS-F, and X-ray spectrometer RPS-1 have been used to analyze the hard emission from solar flares and to carry out the diagnostics of the solar flare plasma. The Solar Cosmic Ray Complex has investigated the solar flare effects in the Earth's environment. The UV emission variations during solar flares in the vicinity of the 120-nm wavelengh have been recorded and the relative variation amplitude has been determined.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

An erupting prominence seen by SOHO/EIT was tracked into the field of view of the LASCO C2 and C3 coronagraphs where it developed into the core of a structured CME. The erupting prominence was deflected by an angle of $\sim 20^{\circ}$ towards the north pole whereas the consequent core of the CME and it's leading edge propagated in the outer corona at constant position angle. The prominence material underwent a constant acceleration phase until a height of $\sim$1.5 solar radii before it started to decelerate up to a distance of 5.0 solar radii. An inflow of plasma with a speed of about 70-80 km/s was discovered in the EIT observations at a height of 1.5-1.2 solar radii in the course of the prominence eruption, matching in time the prominence deceleration phase. The downflowing material followed a curved path, suggestive of the apex of a contracting magnetic loop sliding down along other field lines.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Results of modern multi-wavelength observations of large solar non-stationary events are briefly summarized. Such events consist of a puls, an eruption (surge or CME) and a long-living system of giant arches.

Observations demonstrate often that the pulse arises as a result of “avalanche” of interaction of small-scale magnetic elements, while the dynamic system transforms into a state of self-organizing criticality (SOC) on the post-eruptive phase. We developed new code for the avalanche model where it is possible to consider a transition of the active region as a dynamic system in a state of SOC. Derived solutions show, firstly, that the avalanche is naturally developed nearby spots during the pulse. Secondly, during long-duration events, occuring along the neutral line of the longitudinal magnetic field, behaviour of the large-scale coronal magnetic field is characterized by a state of SOC.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We represent results of experiments on investigation of solar wind plasma by the method of radio sounding, when the signal from the radio source paths through the solar wind plasma and then it's received at ground-based radiointerferometer.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We summarize the recent results and prospective work in two parallel studies (Komitov; Bonev, Penev and Sello) of the long-term trends in solar variability that can be deduced from both indirect data and optical records. Analysis of data from $^{14}C$ measurements (Stuiver et al. 1998), aurorae (Schove series: Shove 1983), and direct astronomical records (group sunspot number) (Hoyt & Schatten 1998) focus on the stability and changes in amplitude of the cycles with duration near one and two centuries. Although these two projects have been carried independently and different methods have been used. We present them in a joint fashion in order to emphasize the common direction of their work.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

According to daily observation SOHO/MDI during 1996-2003 and NSO/KP Vacuum Telescope during 1978-2003 magnetic elements with intensity of the magnetic field above background have been allocated. The knots were then identified that allowed to trace their displacement comparatively of heliographic grid. Thus, fields of speeds for the period with 1978 on 2003 have been constructed. Variations of speed meridional circulation are found out. The basic direction of speed meridional drift is directed to poles. At the same time it is shown, that during a maximum of activity at latitude less than $20^o$ arise currents in the direction of equator. Streams in the direction to equator arise and during a minimum of activity at latitude about $40-60^o$. Fields of speeds on various phases of solar cycle are constructed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

This paper utilizes a searchable Solar Feature Catalogue (SFC) for sunspots created from the SOHO/MDI whitelight images and magnetograms in 2001-2003 using the automated pattern recognition techniques described at http://www.cyber.brad.ac.uk/egso/. Comparison of sunspot areas taklen from the SFC with the daily sunspot numbers published in the Sunspot Index Data Centre (SIDC) shows very good correlation of 78–86%. The total magnetic flux from sunspot areas, measured from a single solar image, is shown to have a strong northern-southern asymmetry revealing magnetic flux decrease in the northern hemisphere and an increase in the southern one with the solar cycle descendence towards the period end (year 2003). The resulting, or excess, flux has also demonstrated very significant asymmetry being negative in the southern hemisphere and positive in the northern at the beginning of the period (solar maximum, 2001)with its amplitude descreasing towards the the period end (2003), or the solar minimum. Also, in 2003 there are signs of change in the excess flux polarity between the northern and southern hemispheres.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

We report on a novel investigation of the complex magnetism of the quiet Sun which is based on a realistic three-dimensional modeling of the Hanle effect.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

On the base of the interferometric observations during the total solar eclipse on 11 August 1999 magnetic field strength in a coronal volume at the height of 10$^5$ km above the solar limb has been evaluated using an indirect method. A cold coronal emission (CCE), seen in the lines of $H_{\alpha}$ and K CaII, existed there. The conclusion is made that the magnetic field strength in this bulk, before the investigated CCE-region formed, was about 100-200 G.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html