Narrow Results

One of the key factors of space weather is solar flare activity, the monitoring and prediction of which is an important task of specialized dedicated groups of space experts and solar astronomers. Solar flare forecasts are based on identifying and detecting the so-called precursors, specific processes in solar activity events that occur before flares. Collecting data for space weather analysis and prediction comes down to several types of measurements performed by more than a dozen spacecraft. Ground-based observations and monitoring nowadays are becoming more or less complimentary. One of the reasons for this is the limitation of observation time with ground-based telescopes due to adverse Earth weather conditions. However, solar radio astronomy is immune to almost any weather activity, and the main question here is what new quality it can bring. Observational data accumulated in the 20th century show that solar radio bursts can be associated with flare activity. In addition, the existing network of solar radio telescopes is already well established. As an example, in this paper, we describe the possibilities of a fully steerable 32-meter radio telescope of Ventspils International Radio Astronomy Centre (VIRAC), Latvia, which can be useful for searching for new precursors of solar flares.

Energetic particles recorded in the Earth environment and in interplanetary space have a multitude of origins, i.e. acceleration and propagation histories. At early days practically all sufficiently energetic particles were considered to have come either from solar flares or from interstellar space. Later on, co-rotating interplanetary shocks, the termination shock of the supersonic solar wind, planetary bow shocks and magnetospheres, and also coronal mass ejections (CME) were recognized as energetic particle sources. It was also recognized that less energetic (suprathermal) particles of solar origin and pick-up ions have also a vital role in giving rise to energetic particles in interplanetary disturbances. The meaning of the term "solar energetic particles" (SEP) is now somewhat vague, but essentially it refers to particles produced in disturbances fairly directly related to solar processes. Variation of intensity fluctuations with energy and with the phase of the solar cycle will be discussed. Particular attention will be given to extremes of time variation, i.e. to very quiet periods and to large events. While quiet-time fluxes are expected to shed light on some basic coronal processes, large events dominate the fluctuation characteristics of cumulated fluence, and the change of that fluctuation with energy and with the phase of the solar cycle may also provide important clues. Mainly ISEE-3 and long-term IMP-8 data will be invoked. Energetic and suprathermal particles that may never escape into interplanetary space may play an important part in heating the corona of the sun.

In this work a complete study of 359 solar flares, 111 Halo coronal mass ejections (Halo CMEs) and 45 Partial Halo events occurred from November 2000 to November 2003, is considered. This time period characterized by an unexpected activity of the Sun, was divided into 27-day intervals starting from Bartels Rotation No. 2284 (14.10.2000) to No. 2324 (25.11.2003), generating diagrams of the cosmic ray intensity data recorded at the Athens Neutron Monitor Station. On these qualitative data presented for the first time, a mapping of all available solar and interplanetary events, such as solar flares with importance C, M and X, coronal mass ejections (Halo and Partial) was done. The existence of a connection between solar flares with CMEs and the respective connection to the Forbush effects on yearly and monthly basis are discussed. The role of extreme solar events occurred in March-April 2001 and in October-November 2003 is also considered.

This review paper comprises main concepts, available observational data and recent theoretical results related to astrophysical aspects of particle acceleration at/near the Sun and extreme capacities of the solar accelerator(s). We summarize underground and ground-based observations of solar cosmic rays (SCR) accumulated since 1942, direct spacecraft measurements of solar energetic particles (SEP) near the Earth's orbit, indirect information on the SCR variations in the past, and other relevant astrophysical, solar and geophysical data. The list of the problems under discussion includes: upper limit spectrum (ULS) for solar cosmic rays; maximum energy (rigidity), E_m(R_m), of particles accelerated at/near the Sun; production of the flare neutrinos; energetics of SCR and solar flares; production of flare neutrons and gamma rays; charge states and elemental abundances of accelerated solar ions; coronal mass ejections (CME's) and extended coronal structures in acceleration models; magnetic reconnection in acceleration scenarios; size (frequency) distributions of solar proton events (SPE) and stellar flares; occurrence probability of giant flares; archaeology of solar cosmic rays. The discussion allows us to outline a series of interesting conceptual and physical associations of SCR generation with the high-energy processes at other stars. The most reliable estimates of various parameters are given in each of research fields mentioned above; a set of promising lines of future studies is highlighted. A great importance of SCR data for resolving some general astrophysical problems is emphasized.

Opportunity of the solar flares (SFs) prediction observing the solar neutrino fluxes is investigated. In three neutrino generations, the evolution of the neutrino flux traveling the coupled sunspots (CSs) which are the SF source is considered. It is assumed that the neutrinos possess both the dipole magnetic moment and the anapole moment while the magnetic field above the CSs may reach the values $10^5\text{–}10^6$ Gs, display the twisting nature and posses the nonpotential character. The possible resonance conversions of the solar neutrino flux are examined. Since the ${\nu }_{eL}\to {\nu }_{\mu L}$ resonance takes place before the convective zone, its existence can in no way be connected with the SF. However, when the solar neutrino flux moves through the CSs in the preflare period, then it may undergo the additional resonance conversions and, as a result, depleting the electron neutrinos flux may be observed.

Impulsive energy release events are observed in many natural systems. Solar flares are certainly among the most remarkable examples of such processes. In the last years the study of solar flare statistical properties has received considerable attention in the context of solar flare models based on different approaches, such as Self Organized Criticality (SOC) or magnetohydrodynamic (MHD) turbulence. In this talk the main statistical properties of solar flares will be presented and compared to those of other well known impulsive processes, such as earthquakes and soft γ-ray flashes occurring on neutron stars. It is shown that the these phenomena are characterized by different statistics that cannot be rescaled onto a single, universal curve and that this holds even for the same phenomenon, when observed in different periods or at different locations. Our results indicate apparent complexity of impulsive energy release processes, which neither follow a common behavior nor could be attributed to a universal physical mechanism.

In this work, we present the coexistence of self-organized criticality (SOC) and low-dimensional chaos at solar activity with results obtained by using the intermittent turbulence theory, the nonextensive q-statistics of Tsallis as well as the singular value decomposition analysis. Particularly, we show the independent dynamics of sunspot system related to the convection zone of sun and the solar flare system related to the lower solar atmosphere. However, both systems reveal nonequilibrium phase transition process from a high-dimensional intermittent turbulence state with SOC profile to a low-dimensional and chaotic intermittent turbulence state. The high-dimensional SOC state in both dynamical systems underlying the sunspot and solar flare signal is related with low q-values and low Flatness values (F) while the low-dimensional chaotic state is related with higher q-values and Flatness F-values. The higher q- and F-values reveal strong character of long-range correlations corresponding to system-wide global process while the lower q- and F-values reveal scale invariant local avalanche process. Also, the high-dimensional SOC state corresponds to second order nonequilibrium critical phase transition process while the low-dimensional chaotic state corresponds to first order nonequilibrium phase transition process. Finally, for both dynamics underlying sunspot index and solar flare, at both states of phase transition process, the multiscale and multifractal character was found to exist but with different profile or strength.

The Japanese/US/UK space mission, Hinode, was launched successfully in September 2006. Now, more than a year after the commissioning of the spacecraft and instruments, Hinode is unveiling a new view of the Sun. Hinode's goal is to help us to understand solar activity, and to link activity on (and below) the surface to the outer corona. This review will describe how the initial results are overturning our understanding of the Sun and will look to the future to anticipate what further discoveries might be made. In particular I will describe the areas of basic magnetohydrodynamic (MHD) processes such as magnetic reconnection and Alfvén waves, the formation of both the fast and slow solar winds and the triggering of flares and coronal mass ejections.

An accepted model for magnetospheric substorms is used as the basis for a generic model for magnetic explosions, Emphasis is placed on the role of the inductive electric field and the displacement current. It is pointed out that these are unjustifiably neglected in conventional models, with this neglect being implicit in the assumptions of magnetohydrodynamics. Consequences of including the inductive electric field are identified. Fiducial numbers for the application of the generic model to solar flares and magnetar outbursts are suggested.

The largest amount of antineutrinos detected about the Earth is emitted by the natural radioactive decays of ²³²Th and ²³⁸U chains isotopes and of ⁴⁰K. Other flux components are yielded by cosmic rays interactions in the atmosphere or by possible extra-terrestrial sources such as supernovae explosions, gamma ray bursts, GW events and solar flares. This contribution is aimed to summarise the results obtained by the Borexino experiment about antineutrinos from the Earth and from extraterrestrial sources.

Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is a nine-collimators satellite detecting X–rays and γ–rays emitted by the Sun during flares. We describe a novel method for the construction of electron flux maps at different electron energies from sets of count visibilities measured by RHESSI. The method requires the application of regularized inversion for the synthesis of electron visibility spectra and of imaging techniques for the reconstruction of two-dimensional electron flux maps. From a physical viewpoint this approach allows the determination of spatially resolved electron spectra whose information content is fundamental for the comprehension of the acceleration mechanisms during the flaring events.

The idea of ‘magnetic reconnection’ has been around since the work of Ronald Giovanelli who proposed it while searching for an explanation of solar flares. The idea seems to have received a boost from the work of James Dungey but he made it very clear in his writing that magnetic lines of force were not physical entities and shouldn’t be treated as such. Bearing this point in mind, attention is concerned here with noting the non-physicality of the whole notion of ‘magnetic reconnection’ and suggesting an alternative approach to seeking explanations for such phenomena as solar flares via the study of plasmas.