After briefly summarizing the outstanding achievements and new tendencies witnessed in recent years in the studies of magnetic fields of solar active regions (ARs), we focus on the current understanding on flux appearance and disappearance. On flux appearance, the moving magnetic features (MMFs) stand still as a mystery in solar physics, although the emergence of magnetic flux in the bipolar form are fairly understood. However, the possibly sympathetic flux emergence of several ARs and the appearance of active longitudes or hot spots are poorly understood. The only confirmed model of flux disappearance is the observed flux cancellation. Detailed analysis of the alignments of transverse magnetic fields and the history of magnetic flux evolution suggest that flux cancellation is more likely to be the magnetic reconnection in the lower solar atmosphere. Magnetic and current helicity provide new diagnosis in understanding flux emergence and disappearance, and constrains the energy process in solar activity.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

Helioseismic analysis of solar global oscillations allows investigation of the internal structure and dynamics of the sun. I summarize the recent observational results, putting emphasis on the bands of slower- and faster-than-average rotation migrating in latitude over the solar cycle in a manner similar to the zones of solar activity. I also review theoretical considerations so far proposed as a cause of the periodic oscillation of the rotation profile.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The solar cycle in photosphere and corona reflects the internal dynamics on the Sun. According to the modern understanding the observed behavior of solar activity is related to the dynamo process in convection zone and photosphere and it is closely connected with the evolution of the coronal structures. The observational data from ground and space allow us to investigate the solar cycle as a complex phenomenon and to clarify the most important features such as polar magnetic field reversals, non-uniform distributions of the solar activity complexes and fine structure of the solar cycle.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Using local helioseismology, we construct maps of the horizontal divergence of the velocity field near the solar surface and study the spectrum of solar supergranulation during the period from 1996 to 2002. Supergranulation oscillates and propagates like a wave interference pattern. The variations of the oscillation frequency with latitude and time are less than 5%. We find significant solar-cycle variations in the lifetime and the anisotropic distribution of power. We also measure the time-dependent zonal and meridional flows that advect supergranules.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

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.

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

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

Cyclic variations of the coronal green line brightness (CGLB) are investigated analysing a series of synoptic charts and a special movie assembled of them, covering 1943-2001. Regular changes of the large-scale CGLB distribution in dependence on the phase in the solar cycle are presented. A quantitative relation between the coronal green line intensity $I$ and the total magnetic field strength $B$ is derived for the period 1977-2001; the $B$ was calculated under potential approximation. A simple exponential relation of type $I \propto B^q$ was found to exist between the above two quantities. It is shown that the $q$ exponent may have opposite sign in the equatorial and polar zones. During phases of the solar cycle maxima the $I$ versus $B$ relation is much more complicated and cannot be expressed by such a simple formula.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

The variability of solar radiance over a solar cycle is thought to be a delicate balance between the radiative deficit of sunspots and the extra contribution of plage and network regions. Although the net effect is tiny, it must imply structural and thermal changes in the Sun or in partial layers of it as an unavoidable consequence of the virial theorem. Using the virial theorem for continua including the magnetic field it is shown, how solar radiance variability might be connected to a deeply seated flux-tube dynamo and how this connection is established on a hydrodynamical time-scale.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We consider the Solar Cycle - the variation in any solar, heliospheric or cosmic ray parameter, related to the well-known 22-year dynamo-like process on the Sun - and discuss how it is influenced by the inner (the transformation of the solar activity in the basement of the heliosphere) and the external (the interaction between the solar and interstellar winds) factors. The corresponding approaches to the description of the long-term variations (the Solar Cycle, secular and longer ones) in the galactic cosmic ray intensity are outlined.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

From observations of the Sun as a star made at Kitt Peak it is known that MnI 539.5 nm line exhibits unusually big (for a photospheric line) variations during a solar activity cycle. Doyle et al. 2001 suggested that it is because of optical pumping. This work aims particularly to check this hypothesis with help of observations.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

The $\bf {E \times B}$ drift allows plasma to move through the magnetic field lines and may contribute to various motions inside the Sun (e.g. to explain the adverse gradient of differential rotation in the equatorial zone), at its surface and in the corona. Here we treat an example: using a given azimuthal angular frequency $\omega$(r, $\theta$), rather arbitrary, and the corresponding exact solution for $\bf{B}$, we obtain $\bf{E}$ and the drift velocity. The latter is comparable with the original velocity, but has components in all directionsTo search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The radial surfaces of constant angular frequency may be connected with the upper rest latitude of the filament bands (or boundaries of large-scale unipolar magnetic regions) and with the separation of the sunspot region and the polar region (polar faculae, etc.). The equator-ward evolution of the rest latitudes observed since cycle 12 may be a forebode of a deep minimum.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The oscillations in solar daily soft X-rays (SXR) have been analyzed for 22$^{nd}$ and 23$^d$ solar cycles. The SXR in the 1–8Å passband have been recorded by the GOES-6,8 satellites from January 1986 to April 2003 year. For 22$^{nd}$ cycle the revealed periodicities 24, 43, 54, 65 and 73 days coincide with the 23$^d$ cycle ones within data uncertainty (1 day) and their values may be explained by the differential rotation of the solar chromosphere and corona.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Radio emissions from the solar active regions can be generated by nonlinear coupling of Langmuir waves with Alfvén waves. Multi-wavelength observations can be used to provide evidence for Langmuir-Alfvén turbulence in the solar atmosphere.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In order to verify scenario of solar cycle suggested by Babcock and Leighton, a new index of activity is derived from observational data of bipolar spot groups by taking positions of magnetic poles of the groups into account. In agreement with the Babcock-Leighton scenario, this index reveals substantial correlation with amplitude of the axisymmetric magnetic field of the Sun measured at subsequent minimum of activity.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html