In this paper, we apply the general theory of Arnold (1965, 1966) and Moffatt et al. (1997). We search sufficient conditions for the linear stability of steady three-dimensional incompressible gravitating flows in ideal magnetohydrodynamics (MHD). The results suggest that the solar and the stellar convection zones must be sensitive to the density stratification.

Hasan et al. (2005) have recently presented 2-D dynamical calculations on wave propagation in in the magnetic network of the Sun. The latter is idealized as consisting of non-potential flux tubes in the quiet solar chromosphere. It is of interest to understand how the nature of wave propagation is influenced by the choice of initial equilibrium configuration of the magnetic field. We examine this by comparing the earlier calculations with those when the network is modelled as a potential structure. Our calculations demonstrate that the nature of the wave propagation is significantly different, particularly the transport of energy which for the potential case, occurs more isotropically than for the non-potential configuration.

Historical records of the Nile water level provide a unique opportunity to investigate the possibility that solar variability influences the Earth's climate. Particularly important are the annual records of the water level, which are uninterrupted for the years 622–1470 A.D. These records are non-stationary, so that standard spectral analyses cannot adequately characterize them. Here the Empirical Mode Decomposition technique, which is designed to deal with non-stationary, nonlinear time series, becomes useful. It allows the identification of two characteristic time scales in the water level data that can be linked to solar variability: the 88 year period and a time scale of about 200 years. These time scales are also present in the concurrent aurora data. Auroras are driven by coronal mass ejections and the rate of auroras is an excellent proxy for solar variabiliy. Analysis of auroral data contemporaneous with the Nile data shows peaks at 88 years and about 200 years. This suggests a physical link between solar variability and the low-frequency variations of the Nile water level. The link involves the influence of solar variability on the North Annual Mode of atmospheric variability and its North Atlantic and Indian Oceans patterns that affect rainfall over Eastren Equatorial Africa where the Nile originates.

Using time-dependent resistive magnetohydrodynamic simulations, we study a flux rope eruption caused by magnetic reconnection with implication in coexistent flare-CME events. Without the resistance the flux rope system presents a double catastrophe. We use the first catastrophic state as the initial condition, in which an isolated flux rope coexists with two current sheets: a vertical one below and a transverse one above the flux rope. The flux rope erupts when reconnection starts in the current sheets, and the flux rope dynamics depends on the reconnection sequence in the two current sheets. We obtain three cases: reconnection occurs (1) simultaneously in the two current sheets, (2) first in the transverse one and then in the vertical, and (3) in an order opposite to case 2. Such a model exhibits characteristics of both magnetic breakout model for CME initiation and standard flare model. We argue that both breakout-like and tether-cutting reconnections may be important for CME eruptions.

A clear case on Dec. 28 2002 is presented. It is about the initiation of two successive CMEs, which were related to an eruptive prominence. In EIT 304 Å and 195 Å observations, we found a long filament severely twisting in a piece of its fragments, which appeared as a prominence on Dec. 26. Then, the prominence converted its twist into writhe. Two days later, the prominence displayed a slow rising motion for hours. There happened internal twisting and mass motion before the prominence rapid acceleration and final eruption. Two successive CMEs recorded by LASCO C2 coronagraph corresponded to the early rising and the subsequently eruptive phases of the prominence, respectively. Evidence of magnetic reconnection, i.e., a cusp structure and post-flare loops in EUV wavebands, and hard X-ray sources in the corona, were observed after the prominence disruption. It appears that the kink instability and the mass drainage in the prominence played important roles in triggering two CMEs' initiation. We suspected that the rather impulsive acceleration of the second CME resulted from magnetic reconnection beneath the prominence.

Mottles and spicules are the most prominent, short-lived, dynamic features residing at the quiet Sun chromospheric network and constitute what is known as chromospheric fine structure. We are reporting a comprehensive study of the dynamical characteristics and physical properties of such structures, from multi-wavelength observations, using line inversion techniques and a wavelet spectral analysis. We are furthermore examining their dynamical evolution and their periodic bi-directional velocity behaviour, their interrelationship and their association with the underlying magnetic field which seems to be their forming and driving mechanism. These studies are crucial to understanding the dynamics of the solar chromosphere, as well as the role such structures play in the mass balance and heating of the overlying solar atmosphere.

We study CMEs observed by LASCO to have plane of the sky velocities exceeding 1500 km/sec. We find that these extremely fast CMEs are typically associated with flares accompanied by erupting prominences. Our results are consistent with a single CME initiation process that consists of three stages. The initial stage is brought about by the emergence of new magnetic flux, which interacts with the pre-existing magnetic configuration and results in a slow rise of the magnetic structure. The second stage is a fast reconnection phase with flaring, filament eruption and a sudden increase of the rise velocity of the magnetic structure (CME). The third stage consists of propagation in the corona. We discuss the sources of these CMEs and the need for improved understanding of the first and third stages.

Wave and oscillatory activity of the solar corona is confidently observed with modern imaging and spectral instruments in the visible light, EUV, X-ray and radio bands, and interpreted in terms of magnetohydrodynamic (MHD) wave theory. The review reflects the current trends in the observational study of coronal waves and oscillations, theoretical modelling of interaction of MHD waves with plasma structures, and implementation of the theoretical results for the mode identification. Also the use of MHD waves for remote diagnostics of coronal plasma - MHD coronal seismology – is discussed.

Very few in situ measurements so far show the details of the interactions between CME and magnetosphere. Here we report a fortuitous observation that the Cluster spacecraft were located at the dusk-side magnetopause, meandering back and forth four times between the ICME and the magnetosphere, and observed part process of the interaction between the CME and the magnetosphere. The primarily analysis showed that: (1) a fast ion beam other than the ambient plasma was observed almost perpendicular to the magnetic field; (2) The left-hand-polarized kinetic Alfvén waves excitation by the ion beam; and (3) the resonances between the kinetic Alfvén waves and part of the beam particles lead to the pitch angle diffusion of resonant particles and formating of a monospheric distribution with nearly constant kinetic energy. The wave-particle resonance may pay an important role in the energy transfer and particle exchange across the magnetopause between the magnetosheath and magnetosphere during the CME impulsion.

It is suggested that we are already in the weak solar cycles series since the start of cycle 23. The interplanetary magnetic filed and the solar wind speed and density are expected to drop considerably during the approaching second weak cycle number 24 and the following ones leading to inflation of the magnetosphere. The corona is also expected to cool down relative to normal cycles corona. A daily background coronal index is proposed. The mechanism of production of weak cycles is tied to the rapid rotation of the photospheric layer which is deeply rooted in the bottom of the convection zone. This rapid surface and subsurface rotation implies slower rotation of the tachocline. Slower dynamo rotation leads to reduction of the strength of the magnetic cycle. One of the very important sequences of the weak cycles, is the expected cooling of the Earths air and sea surface temperatures which would have negative effects on agriculture with increased drought-flood hazards. The reduction of solar UV flux can lead to the closure of the ozone hole on the long run.

We present spectral analysis methods suitable for diagnostics of flaring plasma from RESIK spectra. RESIK is the uncollimated bent crystal spectrometer aboard the Russian CORONAS-F solar mission. It collected many flare and active region spectra in the wavelength range 3.3 Å–6.1 Å, where strong emission lines of Si, S, Ar, and K are present. Based on a careful instrument calibration the absolute fluxes in the individual spectral lines have been obtained. These fluxes have been used for determination of a set of thermodynamic parameters characterizing the emitting plasma and for studies their time behavior during selected flares.

We present a brief description of new complex of space telescopes and spectrographs, TESIS, which will be placed aboard the CORONAS-PHOTON satellite. The complex is intended for high-resolution imaging observation of full Sun in the coronal spectral lines and in the spectral lines of the solar transition region. TESIS will be launched at the end of 2007 – early of 2008. About 25 % of the daily TESIS images will be free for use and for downloading from the TESIS data center that is planned to open 2 months before the TESIS launching at http://www.tesis.lebedev.ru

We review how the so-called flux-transport solar dynamos work and show that such models calibrate well with solar cycle observations, and simulate well the relative peaks of the past 8 cycles. This success provides a basis for forecasting a strong solar cycle 24. We also show that a previous forecast of the timing of onset of cycle 24 is being verified by recent sunspot area statistics and coronal structures.

We present the results of numerical simulations of 3D magnetic reconnection driven by photospheric footpoint motions. The model consists of two positive and two negative sources, which are placed on opposite boundaries of the cubic domain. Two different types of photospheric motions are then considered, namely rotating and twisting of the sources. These different footpoint motions result in a difference in the evolution of the magnetic skeleton and the location and efficiency of the energy build up. Both the dynamical evolution and the corresponding potential evolution of each system is investigated and a comparison is made between the energy storage and release that occurs at separators and separatrix surfaces.

The present work concerns the study of the great solar proton events during the solar cycle 23. For this purpose, the temporal behavior of six solar indices during these great events will be studied. These indices are the radio flux (10.7cm) intensity, the sunspot no., the sunspot area, the GEOS X-ray background flux intensity, and the intensity of the X-ray flares and optical flares.

The stability behaviour of the wave modes that propagate in the solar wind plasma is considered in the framework of the Hall-magnetohydrodynamics. The Hall-MHD theory extends the wave frequency limit up to or higher than the ion cyclotron frequency. Due to the different flow velocities of the adjacent media in the solar wind, a Kelvin–Helmholtz instability is naturally expected to arise. The behaviour of the wave modes due to this particular kind of instability is studied under solar wind conditions typical for 1 AU. This is a preliminary study on the stability problem in the solar wind flowing structures and it could be relevant for the interplanetary and space weather research.

An occulted flare occurred at about 06:07 UT on November 2, 2002. The RHESSI X-ray images show two separate parts. The lower part consists of a complete loop and the upper part a coronal source which well extends above the solar limb. The loop source shrank for about 4 minutes with a speed of $\sim$24 km s$^{-1}$ during the early impulsive phase and then expanded at $\sim$7 km s$^{-1}$, while the coronal source presented an upward motion at about 6 km s$^{-1}$. The temperature of the loop-top is always higher than that near the footpoints. The temperature of the loop increased with altitude, while that of the coronal source just showed opposite variation. These results indicate that the reconnection X-point of this flare is located in between the loop-top source and the coronal source.

We present a statistical investigation of shear motion of the EUV footpoints in two-ribbon solar flares, using the high spatial resolution data obtained in 1998–2005 by the Transition Region and Coronal Explorer (TRACE). In this study we have selected 50 well-observed X- and M- class two-ribbon flares. Our preliminary results are: a) 86% (43 out of 50) of these flares show shear change of footpoints and ribbon separation; b) there is no obvious ribbon separation in those 7 flares which have no shear change of the conjugate footpoints; c) in most events, the cessation of shear change is 0–2 minutes earlier than the end of the impulsive phase.

Using one-minute cadence vector magnetograms of BBSO, we analyze the temporal behavior of the derived vertical electric currents associated with two solar flares on July 26, 2002. One is an M1.0 flare occurred in AR10044, while the other is an M8.7 flare in the adjacent AR 10039. We find that the temporal behaviors of electric currents are very different. For the M1.0 flare, the current density drops rapidly near the flaring neutral line; while for the M8.7 flare, the current density rapidly increases.

We present preliminary results of the study of the photospheric physical conditions about 30 minutes before the 2N/M2 two-ribbon solar flare. The soft X-ray enhancement, $H_{\alpha}$ brightening and microwave bursts occured prior to the flare. We demonstrate the semiempirical models of the preflaring photosphere fot two kernels of the future flare. These models derived from the inversion reproduce the spectral observations in seven Fraunhofer lines. The models consist of two atmospheres: the magnetic flux tube and its nonmagnetic surroundings. The inferred models show strong changes of the photospheric physical conditions in the preflare phase. The preheating was found in the flux tube. Upward motions of the surrounding photospheric material were revealed. Significant discrepancies of the flux-tube temperature and density are found for two sites of the future flare. The inner kernel located near the filament was cooler in the photosphere than the outer kernel.