The rather frequent occurrence, and sometimes long duration, ofray events at photon energies above 100 MeV challenges our understanding of particle acceleration processes at the Sun. The emission is ascribed to pion-decay photons due to protons with energies above 300 MeV. We study the X-ray and radio emissions and the solar energetic particles (SEPs) in space for a set of 25 Fermi -ray events. They are accompanied by strong SEP events, including, in most cases where the parent activity is well-connected, protons above 300 MeV. Signatures of energetic electron acceleration in the corona accompany the impulsive and early post-impulsive -ray emission. -ray emission lasting several hours accompanies in general the decay phase of long-lasting soft X-ray bursts and decametric-tokilometric type II bursts. We discuss the impact of these results on the origin of the -ray events. IntroductionThe advent of the Fermi mission showed that the Sun is an occasional, but unexpectedly frequent, emitter of -ray photons above 100 MeV. These are understood to be produced by pion decays in nuclear interactions involving protons or He-nuclei at energies above 300 MeV/nucleon. One did not expect that the Sun was able to accelerate relativistic protons and nuclei even in seemingly modest flares. These particles are rarely detected in space (<1 event per year). Furthermore, the duration, several hours, of some -ray events is much longer than that of hard X-ray signatures of electron acceleration in the impulsive flare phase.The question of how the -ray emission is related to other signatures of particle acceleration and energy release in the corona is crucial to understanding the origin of the high-energy protons. It might also be expected that such high-energy populations interacting at the Sun are accompanied by particularly energetic solar energetic particle (SEP) events. This chapter is based on 25 events. The Fermi/LAT temporal data were made available to the HESPERIA project by G. Share prior to their publication in a comprehensive paper ). The present chapter introduces the relevant process of emission and pre-Fermi observations of piondecay -rays (Sect. 8.2), and gives an overview of the Fermi/LAT observations (Sect. 8.3). Section 8.3 was prepared by Gerald Share and Ron Murphy. Related X-ray and radio observations and associated SEP events are presented in Sects. 8.4 and 8.5, respectively. Preliminary conclusions on the interpretation of the -ray events are in Sect. 8.6. Theory and Early Observations of Gamma-Ray Emission at Photon Energies >60 MeVOn 1982 Jun 3 the gamma-ray spectrometer on the Solar Maximum Mission satellite observed emission from 0.3 to 100 MeV from a X8.0 GOES-class flare (Forrest et al. 1986). The impulsive flare lasted about 1 min and was followed by a distinct harder emission phase that peaked in about 1 min and lasted for over 15 min. The energy spectrum of this sustained emission displayed a characteristic hump at photon energies above 60 MeV (Fig. 8.1a), which appeared to be consistent with th...

We investigate the role of chromospheric fine structures, e.g. mottles (spicules), in the mass balance and heating of the solar atmosphere by studying two-dimensional high-resolution Hα observations. The temporal and spatial variations of the line-of-sight (LOS) velocity, obtained with an inversion technique based on a cloud model, provide strong indications that the mechanism responsible for the driving of the observed flows is magnetic reconnection. Apart from the LOS velocity, application of the cloud model enables the derivation of several other physical parameters, like pressure, temperature, density etc. Mean values of these parameters permit the estimation of the role of these structures in the mass balance of the solar atmosphere. They, furthermore, permit a reasonable estimate of the energy provided by magnetic reconnection which is available for the heating of the solar corona.

Abstract. We have studied spicules observed at the northern solar limb by using simultaneous high resolution image sequences. The images were obtained by Hinode/SOT (in the Ca II H passband) and TRACE (in the 1600Å passband) during a coordinated campaign. Both data sets were reduced and then carefully co-aligned in order to compare the observed patterns in this highly dynamic region of the Sun. The identification of individual structures in both spectral bands allows us to trace their spatial and temporal behaviour. Persistent intensity variations at certain locations, indicate that at least some spicules have a recurrent behavior. Using wavelet analysis we investigate oscillatory phenomena along the axis of off-limb spicules and we construct 2-D maps of the solar limb with the observed oscillations.Keywords. sun:chromosphere, sun:oscillations Observations, data reduction and analysisSimultaneous time series observations of the northern solar limb were obtained by TRACE and Hinode/SOT on October 15, 2007. All necessary corrections were carried out, such as dark current, flat-field corrections and spike removal. The images of each data set were carefully co-aligned using cross-correlation between consecutive images, achieving sub-pixel offsets. The Ca II H data set was rebinned to the spatial resolution of TRACE (0.5 arcsec/pixel) and then the two data sets were cross-aligned in order to identify and compare similar structures, if any. The cadence of the observations is 53 s for TRACE and 60 s for SOT and they cover about 1 hour.The small-scale temporal variation of every pixel on each image was limited by smoothing the time series over 5 consecutive exposures. Then, for every row its minimum value was subtracted from each pixel. Although this last step introduces errors in the form of horizontal lines due to the fact that we did not take into account the curvature of the limb, it helps to increase the contrast of the off-limb structures. To further improve the visibility of the fine-scale off-limb structures we applied the MADMAX operator (Koutchmy & Koutchmy 1988) on all images. This helps discriminate individual spicules (Fig. 1). Morphology and general remarksThe network is visible in both passbands with almost one to one spatial correspondence, while off-limb there are only coarse similarities (Fig. 1). Most spicules are concentrated in groups (bushes), are relatively inclined and show excessive spatio-temporal variations, due to plasma motions and/or ionization. The Ca II H filter has a FWHM of 2.2Å, while TRACE's 1600Å passband is very wide (275Å) and perhaps this is the reason 165 https://www.cambridge.org/core/terms. https://doi

Abstract. We examine oscillatory phenomena in a solar network region from multi-wavelength, observations obtained by the ground-based Dutch Open Telescope (DOT), and by instruments on the spacecraft Solar and Heliospheric Observatory (SoHO). The observations were obtained during a coordinated observing campaign on October 14, 2005. The temporal variations of the intensities and velocities in two distinct regions of the quiet Sun were investigated: one containing several dark mottles and the other several bright points defining the network boundaries (NB). The aim is to find similarities and/or differences in the oscillatory phenomena observed in these two regions and in different spectral lines formed from the chromosphere to the transition region, as well as propagation characteristics of waves.