We analyze the time evolution of microwave spectral indices for 103 solar flares observed by Nobeyama Radio Polarimeters (NoRP) between 1998 and 2005. The microwave spectral index, .t/, is derived from the flux spectral index, ı.t/. We assume a flux frequency dependence of the form S. ;t/=F0 ı.t/ in the optically thin part, i.e., above the turnover frequency, fmax. Here, fmax is defined as the ...

Context. In solar flares, inverse Compton scattering (ICS) of photospheric photons might give rise to detectable hard X-ray photon fluxes from the corona where ambient densities are too low for significant bremsstrahlung or recombination. γ-ray lines and continuum in some large flares imply the presence of the necessary ∼ 100 MeV electrons and positrons, the latter as by-products of GeV energy ...

Solar flare observations in the deka-keV range are performed by the WATCH experiment on board the GRANAT satellite. The WATCH experiment is presented, including the energy calibration as applied in the present work. The creation of the solar burst catalogue covering two years of observation is described and some examples of solar observations are given. The estimated energy releases in the flar...

1. Basic Concepts 2. Sun and Heliosphere at Times of Solar Activity Minimum 2.1. Typical Solar Wind and its Sources 2.2. The Ballerina Model 2.3. Solar Wind Stream Structure 2.4. The Two Basic States of the Solar Wind 2.4.1. Differences 2.4.2. Communities 2.5. Solar Wind Acceleration and Expansion 2.6. Solar Wind Streams and Their Interactions 2.6.1. Corotating Interaction Regions in the Inner ...

Rapid developments in the techniques of interferometry at millimeter wavelengths now permit the use of telescope arrays similar to the Very Large Array at microwave wavelengths. These new arrays represent improvements of orders of magnitude in the spatial resolution and sensitivity of millimeter observations of the Sun, and will allow us to map the solar chromosphere at high spatial resolution ...

It was recently pointed out that the distribution of times between solar flares (the flare waiting-time distribution) follows a power law for long waiting times. Based on 25 years of soft X-ray flares observed by Geostationary Operational Environmental Satellite instruments, it is shown that (1) the waiting-time distribution of flares is consistent with a time-dependent Poisson process and (2) ...

RHESSI measurements relevant to the fundamental processes of energy release and particle acceleration in flares are summarized. RHESSI’s precise measurements of hard X-ray continuum spectra enable model-independent deconvolution to obtain the parent electron spectrum. Taking into account the effects of albedo, these show that the low energy cut-off to the electron power-law spectrum is typicall...

A statistical analysis of a large data set of Hα flares comprising almost 100 000 single events that occurred during the period January 1975 to December 1999 is presented. We analyzed the flares evolution steps, i.e. duration, rise times, decay times and event asymmetries. Moreover, these parameters characterizing the temporal behavior of flares, as well as the spatial distribution on the solar...

The emission of solar flares at millimeter wavelengths is of great interest both in its own right and because it is generated by the energetic electrons which also emit gamma rays. Since high-resolution imaging at gamma-ray energies is not presently possible, millimeter observations can act as a substitute. Except for that class of flares known as gamma-ray flares the millimetric emission is op...

The phenomenon of the double-peak solar cycle structure (Gnevyshev, 1963) is used to study the solar cosmic ray origin. Solar proton events are diminished in number and energetic particle intensity during the maximum solar activity phase. It is shown that during the same time periods the Ground Level Enhancements disappeared almost simultaneously with solar flares of large area and long lasting...