A short compilation of results of spectral observations of nonthermal velocities $\xi$ in a wide range of temperatures in X-ray, EUV, UV and visual wave-lengths has been made. Relationship between the $\xi$ and electron temperature T for chromosphere, quiet and active corona, coronal holes (CHs) and flaring plasma is considered.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The standard theory of the solar cycle in terms of an alpha-Omega dynamo hinges on a proper understanding of the nonlinear alpha effect. Boundary conditions play a surprisingly important role in determining the magnitude of alpha. For closed boundaries, the total magnetic helicity is conserved, and since the alpha effect produces magnetic helicity of one sign in the large scale field, it must simultaneously produce magnetic helicity of the opposite sign. It is this secondary magnetic helicity that suppresses the dynamo in a potentially catastrophic fashion. Open boundaries allow magnetic helicity to be lost. Simulations are presented that allow an estimate of alpha in the presence of open or closed boundaries, either with or without solar-like differential rotation. In all cases the sign of the magnetic helicity agrees with that observed at the solar surface (negative in the north, positive in the south), where significant amounts of magnetic helicity can be ejected via coronal mass ejections. It is shown that open boundaries tend to alleviate catastrophic alpha quenching. The importance of looking at current helicity instead of magnetic helicity is emphasized and the conceptual advantages are discussed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The relaxation dynamics of a magnetized plasma system is a subject of fundamental importance in MHD – with applications ranging from laboratory plasma devices like the Toroidal Field Pinch and Spheromaks to astrophysical plasmas, stellar flaring activity and coronal heating. Taylor in 1974 proposed that the magnetic field in a plasma (of small but finite resistivity) relaxes to a minimum energy state, subject to the constraint that its total magnetic helicity is conserved (Woltjer 1958), such that the final magnetic field configuration is a constant $\alpha$ (linear) force-free field – where $\alpha$ is a quantity describing the twist in magnetic field lines. However, a clear signature of this mechanism in astrophysical plasmas remained undetected. Here we report observational detection of a relaxation process, similar to what Taylor (1974, 1986) envisaged, in the magnetic fields of flare-productive solar active regions. The implications of this result for magnetic reconnection and the coronal heating problem are discussed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

During the period from 19 October to 4 November 2003, there was a sudden and high Solar activity. During this period the sunspot area increased from 1110 10E-6 Hemisphere on 19 October to 5690 10E-6 Hemisphere on 30 October, then decreased to 1110 10 E-6 Hemisphere at 4 November 2003. Also, the radio flux of 10.7 cm increased from 120 sfu on 19 October to 298 sfu on 26 October, then decrease to 168 sfu on 4 November 2003. There were two eruptive solar proton flares released on 26 and 28 October 2003, where the last one is the most eruptive flare recorded since 1976 with importance X17/4B. The proton event affecting the Earth's environment, with energy ¿10 MeV is 29500 particle flux units, on 29 October 2003 as recorded by spacecraft SOHO, due to the solar flares of 28 October. The peak of the Solar cycle 21 was at 1979, but high energetic Solar flares, or secondary peaks, occurred at the declining phase in 1981, 1982, and 1984 before the solar activity minimum in 1986. Also, the peak of the solar cycle 22 was at 1989 but high energetic solar flares occurred at the declining phase in 1991, 1992, and 1994, before the solar activity minimum in 1996. Then the secondary peaks were occurred during 2 to 3 years after the first peak, as deduced from the last five solar cycles. The period of 19 Oct. to 4 Nov. 2003 is the second peak of the solar cycle 23, where the main peak of the solar cycle 23 was at 2001. There are many terrestrial influences, due to the solar activity during Oct.-Nov. 2003. These influences are studied in details, especially the geomagnetic storms and their effects on humankind daily activity.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The chromosphere is an intriguing part of the Sun that has stubbornly resisted all attempts at a comprehensive description. Thus, observations carried out in different wavelength bands reveal very different, seemingly incompatible properties. Not surprisingly, a debate is raging between supporters of the classical picture of the chromosphere as a nearly plane parallel layer exhibiting a gentle temperature rise from the photosphere to the transition region and proponents of a highly dynamical atmosphere that includes extremely cool gas. New data are required in order settle this issue. Here a brief overview of the structure and dynamics of the solar chromosphere is given, with particular emphasis on the chromospheric structure of the quiet Sun. The structure of the magnetic field is also briefly discussed, although filaments and prominences are not considered. Besides the observations, contrasting models are also critically discussed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The reconstructions of the open solar magnetic field since 1844 (with use of geomagnetic data) and since 1915 (with use of H$\alpha$-spectroheliograms) are obtained and comparedThe full version of this paper can be found at http://www.gao.spb.ru/personal/ivanov/papers/iv-mil-iaus2004.pdf..To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

VLBI – Very Long Baseline Interferometry – is a radio interferometry technique which provides the highest spatial resolution observations to human kind. But at the present, the accuracy of the astrometry observations is limited by the atmospheric light path variations and instrumental phase errors, and only group delay measurements are used. To overcome these error factors, we have developed the VERA system, which has the first dual beam system. VERA is the first VLBI array to be free from the atmospheric phase fluctuations. It has four VLBI stations with 2300-km maximum baseline length in Japan. To compensate phase fluctuations of interferometer visibilities, which are mainly caused by the atmosphere, the VERA antenna observes two objects simultaneously. In order to do such observations, VERA has a two-receiver system, which tracks a focal plane according to a separation angle between observing objects. By comparing the visibility phase between two beams, simultaneous phase referencing VLBI will be achieved. The goal accuracy of astrometry observations is 10 micro-arcseconds, which makes annual parallax and proper motion measurements of galactic maser objects possible. 10 micro-arcsecond accuracy is equivalent to 10% distance accuracy for the galactic centre. This becomes 20% accuracy at the opposite side of the galaxy. The main scientific targets of VERA are to make a 3-dimensional maser object map of the galaxy and reveal the velocity field of the galaxy. This will show the mass distribution of the galaxy. Currently, construction of four stations is complete, and test observations are underway. We show the scientific goal, current results and instrumental accuracy of VERA.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Multi-wavelength Very Large Array (VLA), SOHO and RHESSI observations have been used to study the three- dimensional structure of evolving coronal loops and related signatures of impulsive and long-lasting energy release above active regions. Here, we discuss recent multiwavelength observations of an impulsive hard X-ray burst that was preceded by gradual changes in the structure of an extended coronal loop connecting the active region to one located on the other side of the solar equator, suggesting pre-burst magnetic evolution at different spatial scales. Changes in the 6 and 20 cm brightness temperature were also detected from the opposite footpoint region suggesting some sort of magnetic connectvity across the solar equator.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

An analysis of polar activity of the Sun was carried out using the observations in the optical range. The secular and cycle peculiarities of the magnetic activity on the high latitudes were found:

1. an increase of the area of polar caps of the Sun, occupied by unipolar magnetic field at the minimum activity during 1878-2000;

2. a decrease of coronal temperature at the high-latitude zones during the last 50 years;

3. the connection between the polar and sunspot activities;

4. outset and duration of the polar activity cycle;

5. drift of the activity to the poles and from the poles after the magnetic field reversal.

Changes of extreme ultraviolet (EUV) Solar flux were registered during the Annular Solar eclipse of May 31 2003, when CORONAS-F satellite (Oraevsky et al., 2002) intersected thrice a zone of the Solar eclipse. During these periods the solar emission was measured in visible and extreme UV spectral regions (near $L_{\alpha} = 121.6$ nm by VUSS instrument). Records by VUSS ($\sim 120$ nm) and the optical (visible) channel of EOS instruments on UTC scale for May 31, 2003 are given on Fig. 1.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

AVS-F instrument (Amplitude-Time Spectrometry of the Sun) is the system of an electronics engineering for onboard data gathering from two detectors: scintillation (CsI (Tl)) detector SONG-D (SOlar Neutrons and Gamma quantums) of complex of detectors SKL (in low and high gamma-band) and from semiconducting detector (X-ray semiconducting spectrometer) XSS-1 (in X-ray band). The experiment is carried out on the satellite CORONAS-F launched on July 31 2001. During more than 2,5 year of apparatus operation more than 30 of solar flares were detected. Characteristics of observed solar flares are presented in this article.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We are currently developing an analytical theory of an artificial satellite of the Moon. It is an interesting problem because the dynamics of a lunar orbiter is quite different from that of an artificial satellite of the Earth, by at least two aspects: the $J_2$ lunar gravity term is only $1/10$ of the $C_{22}$ term and the third body effect of the Earth on the lunar satellite is much larger than the effect of the Moon on a terrestrial satellite. So we have to account at least for these larger perturbations. We use here the method of the Lie Transform as perturbation method. The Hamiltonian of the problem is first averaged over the fast angle, in canonical variables. The solution is developed in powers of the small factors linked to $ n_{\Moon}$, $J_2$, $C_{22}$ and to the Earth's position. The Earth location is determined by the lunar theory ELP2000 (Chapront-Touzé & Chapront 1991) from which we take the leading terms. Series developments are made with our home-made Algebraic Manipulator, the MM (standing for “Moon's series Manipulator”). The results are obtained in a closed form, without any series developments in eccentricity or inclination. So the solution applies for a wide range of values, except for few isolated critical values. We Achieved, among others, second order results for the combined effect of $J_2$ and $C_{22}$. As a side result, we were able to check the second order generator $\mathcal{W}_{2}$ given by Kozai for the effect of the $J_2$ term on an artificial satellite.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Coronal holes (CHs) are large-scale regions of the corona with decreased density of material and temperatures. CHs are characterized by predominantly an open configuration of magnetic field lines. CHs are observed as regions of corona with decreased emission in soft X-rays, and appear simultaneously in different emission lines in distinct regions of solar atmosphere, Zirin (1988). CHs are known to be the source of the fast quasi-stationary solar wind (Nolte et al. 1976). At the same time answers to key questions which are related to the originating (the birth) of coronal holes till now are not obtained. It is known a little works in which the birth of CHs were investigated (Solodina et al. 1977; Bohlin & Sheeley 1978; Watari et al. 1995). The objective of this paper is to study the birth of non-polar CHs. This paper continues our paper Fainshtein et al. (2002), in which one the birth of coronal holes was studied.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Practical measurement of the passage of time requires the notion of a repeating phenomenon. The Earth's rotation has traditionally fulfilled this requirement. To cope with the impracticality of making precise measures of the Sun's hour angle or altitude, particularly in uncooperative weather conditions, various devices have been employed, but all have been calibrated with respect to astronomical phenomena related to the Earth's rotation, or to its orbital motion with respect to the Sun. Modern requirements for timing precision coupled with an increased understanding of the variability of the Earth's rotational speed are likely to bring about a change in the traditional relationship between precise timekeeping and astronomy. The historical background of this relationship and the current definitions are reviewed to show the development of timekeeping capabilities and the growing need for precise timekeeping. Possible future developments are outlined along with their advantages and disadvantages.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present a statistical investigation of soft X-ray (SXR) solar flare occurrence over the last three 11-yr solar cycles (SCs 21-23, corresponding to the period 1976-2003). We studied not only the monthly number of flares, but we also used an index that estimate the energy emitted by flares in the SXR 1-8 Å band ($Q_{x}$) that we find it better defines their importance in the solar activity cycle. The medium and high importance SXR flares (M&X class) seem to reflect the cycle importance given by the smoothed monthly Wolf numbers (W). SXR flare indices show a delay regarding the sunspot numbers for SC 21, while for SC 22 and 23 their time distribution is almost coincident with W. The level of energy emitted by SXR flares, quantified through the $Q_{x}$ index, is about the same for SCs 21-23 despite the difference between the W curves in the cycles. We also point out the SXR flare behaviour on the cycles descendant phases, with short but intense increases in their activity, that might give useful information about the activity level of the next cycle.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We briefly review several aspects of the quasi-stationary structure of the corona in relation with the helio-sheet and, also, of the more confined by the magnetic field structures, including streamers, loops, jets, plumes and narrow linear rays. Both the temperature and the density structures are tentatively considered. Flows deduced from proper motions analysis are discussed. We did not include CMEs and flares in this presentation but other more radial and possibly highly impulsive beams with flows are discussed. We stress the importance of the variations of the coronal magnetic field and inferred currents in explaining the observed structures.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Determinations and measurements of the parallax of the Pleiades, obtained with ground-based studies and with Hipparcos data, are reviewed. A number of uncertainties in both sets of data are found. Although a further correction for abscissa correlations brings the Hipparcos determination closer to the ground-based value, the difference still seems too large. The new Hipparcos parallax determinations seem to reinforce a possible age related effect. A new reduction of the Hipparcos data is in progress. It reduces significantly the contribution of the attitude noise, providing higher accuracies and lower correlation levels for the brighter stars.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A series of coronal magnetograms, related to the active region NOAA 9068 is derived using the effects of the quasi-transverse (QT-) propagation at microwaves. In the assumption that the product of the electron density $N$ and the scale of magnetic divergence $L_d$ is constant and equal to $10^{18}$ cm$^{-2}$, the sensitivity of the measurements peaks at $B(G) \approx 180 \, \lambda^{-4/3} (cm)$, where $\lambda$ is the observational wavelength. The radio maps of the Sun taken with the Solar Siberian Radio Telescope (SSRT) at $\lambda = 5.2$ cm were sampled and converted into the 2D coronal magnetograms supplying absolute values of the total magnetic vector $\vec B$ in the range 10-30 G. Each coronal magnetogram covers the portion of the microwave source in the active region affected by the QT-propagation conditions in the corona.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Modern solar telescope design in the EUV to x-ray range is now capable of producing large images in multiple channels at rapid cadences, with high spatial and temperature resolution. We discuss reconstruction of differential emission measures for solar coronal plasma using two state-of-the-art instruments: the X-Ray Telescope on Solar-B, and the Atmospheric Imaging Assembly on the Solar Dynamics Observatory. We discuss the relative merits of iteration and direct inversion methods for determining DEM($T$). We also consider strategies for automating and visualizing DEM maps, given the high data rates that these instruments will produce. We touch on the scientific potential of high-cadence, spatially resolved DEM data products.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html