Solar flares involve the sudden release of magnetic energy in the solar corona. Accelerated nonthermal electrons have been often invoked as the primary means for transporting the bulk of the released energy to the lower solar atmosphere. However, significant challenges remain for this scenario, especially in accounting for the large number of accelerated electrons inferred from observations. Propagating magnetohydrodynamics (MHD) waves, particularly those with subsecond/second-scale periods, have been proposed as […]
Solar flares are sudden explosive processes, that convert the energy of the magnetic field into the kinetic energy of electrons and ions. Since the beginning of the century, millimeter observations of solar flares became routinely possible at a few frequencies with limited spatial resolution (see Kaufmann 2012, as a review). One of the most puzzling aspects of the observations at millimeter wavelengths (200-400 GHz) is the presence, in some flares, […]
The new generations of multiwavelength radioheliographs with high spatial resolution will employ microwave imaging spectropolarimetry to recover flare topology and plasma parameters in the flare sources and along the wave propagation paths. The recorded polarization depends on the emission mechanism and emission regime (optically thick or thin), the emitting particle properties, and propagation effects.
A substantial fraction of the flare energy (as observed e.g. in bolometric luminosity) first appears in non-thermal electrons and ions (Emslie et al. 2012). It implies that the particles are efficiently accelerated to a non-Maxwellian velocity distribution. Most of the non-thermal electrons have energies in the 10 – 30 keV range, but some are accelerated beyond 100 keV and radiate gyro-synchrotron radio emission. Nearly all of the flare energy is […]
A novel operational open-access forecasting system that provides reliable forecasting and nowcasting of solar energetic particle (SEP) events, as well as forecasting of solar flares (SFs) based on precursor information, is presented. FORSPEF offers continuous forecasts and nowcasts of SFs and SEP events, up to 70◦ E/W covering practically the entire course of an active-region (AR) toward the limb (up to ~85◦). The prediction window in the forecasting scheme is […]
Particle acceleration during solar flares is a highly efficient process, in terms of both the energy (tens of percent of the released magnetic energy can be transferred to the energetic particles) and the particle number (nearly all electrons in the flaring region are accelerated). So-called stochastic acceleration (e.g., Petrosian 2012 for a review) is one of the most popular mechanisms capable of providing these characteristics. In this scenario, the magnetic […]
Hard X-ray (HXR) and microwave observations of flares show only a few nonthermal sources. They are simple and compact, especially in impulsive flares, suggesting involvement of one to two loops. Hanaoka (1996) and Nishio et al. (1997) interpreted these observations in terms of double-loop flares. This view was later extended up to long-duration flares (Tzatzakis, Nindos, and Alissandrakis, 2008). A concept of a simple flare loop became dominant. However, observations […]
We study the quasi-periodic pulsations (QPPs) of nonthermal emission in an M7.7 class flare on 2012 July 19 with spatially resolved observations at microwave and HXR bands and with spectral observations at decimetric, metric waves. Microwave emission at 17 GHz of two footpoints, HXR emission at 20–50 keV of the north footpoint and loop top, and type III bursts at 0.7–3 GHz show prominent in-phase oscillations at 270$\,$s. Through the […]