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

XSM is a calibration subinstrument of D-CIXS onboard the SMART-1 technology mission to the Moon. SMART-1 was launched in September 2003 from Kourou, French Guyana, and the instruments onboard are now scientifically operational at the time of writing. XSM provides a 52 degree field of view in the energy range of 1-20keV. We have cross calibrated XSM with GOES, and the fidelity of XSM data seems highly likely.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We provide an observational proof of the existence of the global sausage mode oscillations in a flaring loop studying a microwave burst with quasi-periodical pulsations observed with the Nobeyama Radioheliograph (NoRH).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The map of the large-scale chromospheric Doppler velocities ($VD$) on the solar disk, obtained from 2D-spectroscopy within the HeI 10830 Å line for June 4 2002, is presented. Velocity field structures larger than the supergranulation cells are studied. Statistical relations between $VD$ and 1) the intensity in the core of the HeI 10830 Å line and 2) the sign and strength of the longitudinal photospheric magnetic field are obtained and discussed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We describe two flares of GOES class M5.7 and 1.5 which were observed simultaneously by RHESSI (Ramaty High Energy Solar Spectroscopic Imager) and NoRH (Nobeyama Radio Heliograph). Both flares exhibit slow motions suggestive of changing magnetic shear, loop expansion, or gradual reconnection. One flare is clearly a coronal hard X-ray and microwave flare.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We study a simple model for the solar dynamo in the framework of the Parker dynamo, with a nonlinear dynamo saturation mechanism based on magnetic helicity conservation arguments. We find a parameter range in which the model demonstrates a cyclic behaviour with properties similar to that of Parker dynamo with the simplest form of algebraic $\alpha$-quenching. We compare the nonlinear current helicity evolution in this model with data for the current helicity evolution obtained during 10 years of observations at the Huairou Solar Station of China. We conclude that, in spite of the very preliminary state of the observations and the crude nature of the model, the idea of using observational data to constrain our ideas concerning magnetic field generation in the framework of the solar dynamo appears promising.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Analyzing the long-term evolution of active regions (ARs) permits to quantify the link between their atmospheric emission (from optical to X-rays) and the magnetic field. Multi-wavelength studies provide the full story, and not just a snapshot, of the phenomena and they allow us analyze how the atmosphere changes as the field strength decreases (with the dispersion of the AR).

The evolution of the emitted flux in various wavelength ranges contains information on the heating mechanism(s) of the different atmospheric levels. I review what we can learn from such long-term (months) multi-wavelength observations, and compare the results to other solar and stellar studies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We determine a location of a source of a main acceleration of relativistic particles during the flare on July 14, 2000, adopting that the time of acceleration coincides with a burst of the hard linear and continuum gamma-radiation. The process of this effective acceleration starts when one of flare ribbons reaches the large spot of the group, as it follows from the TRACE data. An estimation shows that the source of acceleration locates on the height of 15–20 thousands of km above the photosphere. Comparison these results with those for other large flares allows us to conclude that during almost 30 powerful events in the last three cycles an additional effective “accelerator” of a moderate scale turns on in diluted regions with large magnetic fields and their gradients.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Geomagnetic activity variations are closely related to the global magnetic field of the Sun and could serve as useful proxies to reconstruct the solar wind history and evolution of the inner heliosphere. Historical geomagnetic records reveal trends in the solar wind and interplanetary magnetic field variability resulting from topological changes of the heliospheric current sheet and solar corona viewed from the Earth. Predictions of the solar cycle based on geomagnetic trends are presented.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We have developed the technique and software to observe and process spectral data obtained with the CCD camera. It makes possible to construct two-dimensional maps of Doppler velocity and intensity in solar features simultaneously at two levels in the solar atmosphere. We present some results derived from study of the structure and space-time variations of the Doppler velocity in the region of quiescent filaments in the chromosphere (the $H_{\beta}$ $\lambda 486.1$ nm line) and under filaments in the photosphere (the Fe I $\lambda$ 486.3 nm. and Fe I $\lambda$ 485.9 nm lines). We came to a conclusion that motions in quiescent filaments consist of both the stationary and oscillatory components and follow helical trajectories.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The voyage of the Mexican commission to observe the transit of Venus on 8 December 1874 in Japan is briefly recounted. The five-man expedition was led by Francisco Díaz Covarrubias. They succeeded in establishing two observing stations near Yokohama, one in Nogue-no-Yama and one on a hill called “The Bluff”, and also in determining precise geographical positions for them. Clear skies allowed the observation of the transit at both stations. The results were presented in Paris in 1875, and published on the same year. They were meant as a contribution to be processed along with all other data obtained by different missions. The importance of the expedition for the development of early modern science in Mexico – particularly astronomy – is examined in the broad context of the social and political conditions then prevailing in the country. The relevance of the mission for the establishment of scientific, cultural and even commercial ties between Japan and Mexico is emphasized.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The one-dimensional relaxation of a spatially bounded electron stream in non-uniform background plasma is simulated. The corresponding system of quasi-linear equations is \begin{equation}\frac{\partial f}{\partial t}+V\frac{\partial f}{\partial x}=\frac \partial {\partial V}\left( D\frac{\partial f}{\partial V}\right),\, \frac{\partial W}{\partial t}=2\gamma W,\, \gamma =\frac \pi 2\frac{\omega _p}{n_p}V^2\frac{\partial f}{\partial V},\, D=\frac{8\pi ^2e^2}{m^2}\frac WV. \end{equation} Here $f$ - the electron distribution function, $D$ - diffusion coefficient, and $\gamma$ and $W$ - are the growth rate and spectral energy density of plasma waves respectively, $n$ - background plasma density, $\omega_p$ - plasma frequency. Initial conditions (the electron distribution function at $t = 0$): \begin{equation}f(x,V,t=0)=An_{b}\exp \left(-\frac{(V-V_b)^2}{2V_{Tb}^2}\right)\exp \left(-\left(\frac xd\right)^2\right)\end{equation}To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In Eselevich V. and M. Solar Phys. 195, 319, 2000 is shown that in brightness rays of the streamer belt from time to time there exist additional plasma streams of enhanced density moves antisunward and occupies a separate ray. The duration of additional streams can range from a few hours to several days. For that reason, some of them may be categorized as sporadic SW streams and the others as quasi-stationary SW streams. Preliminary investigations showed that the leading edge of such streams can be extremely small in width. The purpose of this paper is to verify the conclusions about the existence of additional plasma streams with steep fronts in streamer belt rays, based on analyzing the calibrated data from LASCO/SOHO C2 and C3.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Angular positions of the brightest coronal streamers observed during the total solar eclipses (TSEs) in 1870-2001 are compared with calculated tilts of the heliospheric current sheet (HCS) in 1976-2001 and with reconstructed ones in 1870-1976.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The new SOHO/MDI data (1996-2003) reveal an interesting result that the total polar magnetic fluxes do not vary significantly during the polar magnetic field reversals in both hemispheres, while the positive and negative parts of the total fluxes do change.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present calculations of helicity based on our solar dynamo model and show that the results are consistent with observational data.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html