Energy Release Site Research Articles

Unraveling the Origins of an Extreme Solar Eruptive Event with Hard X-Ray Imaging Spectroscopy

Hard X-ray (HXR) observations are crucial for understanding the initiation and evolution of solar eruptive events, as they provide a key signature of flare-accelerated electrons and heated plasma. The potential of high-cadence HXR imaging for deciphering the erupting structure, however, has not received adequate attention in an era of extreme ultraviolet (EUV) imaging abundance. An extreme solar eruptive event on 2022 September 5 observed on the solar far side by both Parker Solar Probe and Solar Orbiter provides the opportunity to showcase the power of HXR imaging in the absence of high-cadence EUV imaging. We investigate the evolution of flare energy release through HXR timing, imaging, and spectral analyses using data from the Spectrometer/Telescope for Imaging X-rays (STIX) on board Solar Orbiter. STIX provides the highest cadence imaging of the energy release sites for this far-side event and offers crucial insight into the nature of energy release, timing of flare particle acceleration, and evolution of the acceleration efficiency. We find that this is a two-phase eruptive event, rather than two distinct eruptions, as has been previously suggested. The eruption begins with an initial peak in flare emission on one side of the active region (AR), marking the rise/destabilization of a loop system followed by notable episodes of energy release across the AR and an eruptive phase associated with a very fast coronal mass ejection, type III radio bursts, and solar energetic particles. We demonstrate that high-cadence HXR imaging spectroscopy is indispensable for understanding the formation of powerful, space-weather relevant eruptions.

Properties of magnetic null points associated with X-class flares during solar cycle 24

ABSTRACT Since the launch of the Solar Dynamics Observatory (SDO) in 2010 and throughout the solar cycle 24, the Sun has produced few tens of X-class flares, which are the most energetic solar events. Those flares are produced in regions where the magnetic flux/energy is large and the magnetic configurations are complex. To provide more insights into the flaring process, we investigate the properties of magnetic null points (MNPs) and their correlation with the energy release sites. During solar cycle 24, we identify 17 X-class flares satisfying selection criteria. From SDO/HMI magnetograms, we perform potential extrapolations around the peak time of the flare to access the 3D coronal magnetic field and thus investigate the existence of coronal MNPs. We then correlate the flaring sites with the existing MNPs using SDO/AIA 171 Å; EUV observations, and deduce their properties (sign, spine, and fan). Six active regions out of 10 possess at least one MNP which is stable and with large magnetic field gradients: this implies that 35 per cent of X-class flares are associated with an MNP; of which 87.5 per cent of MNPs are of positive type. The MNPs associated with the flare sites are predominantly located at a height between 0.5 and 2 Mm, and with a vertical/radial spine field line. We also find a slight correlation between the MNPs not associated with a flare and negative-type MNPs (55 per cent) within the active region. Regarding the physics of flares, the association between the enhanced intensity at the flaring site and an MNP represents about a third of the possible scenarios for triggering X-class flares.

Impulse generated from detonation waves in non-premixed and partially premixed reactants

Rotating detonation engines (RDEs) are the subject of research in the combustion community due to the prospects of enhanced thermal efficiency and power density when compared to current deflagrative-based aerospace combustors. Many current simulations presume premixed reactants and therefore miss the important characteristics of transient mixing, wave-induced mixing, and injector design/spacing that are known to play a pivotal role in the system performance. Very ambitious large eddy simulations are being conducted, but necessarily on a limited number of realistic and complex cases, thus limiting their utility in deriving fundamental understanding. For these reasons, a two dimensional parametric study was conducted to assess propagation of a detonation across an idealized array of mixing/injection sites, parametrically characterized by the width and axial mixing profile.Under such non-premixed conditions, discrete energy release and interdependence are observed. The discrete energy release sites frequently create pressures that exceed idealized Chapman-Jouguet (CJ) predictions based on perfect and uniform mixtures. The local higher pressure is shown to be caused by delayed heat release behind the shock, near constant pressure combustion, and additional compression due to the non-uniformities present. The resulting compression and the near constant pressure combustion are accompanied by time scale separation of exothermic and endothermic reactions due to the mixing efficiencies in the non/poorly-premixed cases. In contrast, the better mixed cases show that the detonation wave is sustained but unburnt fuel and oxidizer exist behind the main combustion wave and impulse performance suffers. Results show that for the conditions modeled there exists an optimal injector spacing to maximize the impulse produced and that discrete injection impulses can exceed that of the premixed systems. These somewhat counter-intuitive results imply that the detailed mixing evolution, provoked by the passage of the wave can lead to an extended heat release zone that elevates the pressure over a longer distance along the wavefront. These revelations provide potential for optimizing injector configurations for real non-premixed systems in order to exploit these physics.

Construction of a prognostic model based on genes associated with mitochondrial energy metabolic pathway in colon adenocarcinoma and its clinical significance.

Mitochondria are the main sites of oxidative metabolism and energy release of sugars, fats and amino acids in the body. According to studies, malignant tumor occurrence and development have been linked to abnormal mitochondrial energy metabolism (MEM). However, the feasible role of abnormal MEM in colon adenocarcinoma (COAD) is poorly understood. In this work, we obtained COAD patient data from The Cancer Genome Atlas (TCGA) as the training set, and GSE103479 from Gene Expression Omnibus (GEO) as the validation set. Combined with the mitochondrial energy metabolic pathway (MEMP)-related genes in Kyoto Encyclopedia of Genes and Genomes (KEGG) database, a risk prognostic model was constructed by utilizing Cox regression analysis to identify 6 feature genes (CYP4A11, PGM2, PKLR, PPARGC1A, CPT2 and ACAT2) that were significantly associated with MEMP in COAD. By stratifying the samples based on riskscore, two distinct groups, namely the high- and low-risk groups, were identified. The model demonstrated accurate assessment of the prognosis risk in COAD patients and exhibited independent prognostic capability, as evidenced by the survival curve and receiver operating characteristic (ROC) curve analysis. A nomogram was plotted based on clinical information and riskscore. We proved it could predict the survival time of COAD patients effectively combined with the calibration curve of risk prediction. Subsequently, based on the immune evaluation and mutation frequency analysis performed on COAD patients, patients in high-risk group had observably higher immune scores, immune activity and PDCD1 expression level than low-risk group. In general, the prognostic model developed using MEMP-related genes served as a valuable biomarker for forecasting the prognosis of COAD patients, which offered a reference for the prognosis evaluation and clinical cure of COAD patients.

Identifying the energy release site in a solar microflare with a jet

Context. One of the main science questions of the Solar Orbiter and Parker Solar Probe missions deals with understanding how electrons in the lower solar corona are accelerated and how they subsequently access interplanetary space. Aims. We aim to investigate the electron acceleration and energy release sites as well as the manner in which accelerated electrons access the interplanetary space in the case of the SOL2021-02-18T18:05 event, a GOES A8 class microflare associated with a coronal jet. Methods. This study takes advantage of three different vantage points, Solar Orbiter, STEREO-A, and Earth, with observations drawn from eight different instruments, ranging from radio to X-ray. Multi-wavelength timing analysis combined with UV/EUV imagery and X-ray spectroscopy by Solar Orbiter/STIX (Spectrometer/Telescope for Imaging X-rays) is used to investigate the origin of the observed emission during different flare phases. Results. The event under investigation satisfies the classical picture of the onset time of the acceleration of electrons coinciding with the jet and the radio type III bursts. This microflare features prominent hard X-ray (HXR) nonthermal emission down to at least 10 keV and a spectrum that is much harder than usual for a microflare with γ = 2.9 ± 0.3. From Earth’s vantage point, the microflare is seen near the limb, revealing the coronal energy release site above the flare loop in EUV, which, from STIX spectroscopic analysis, turns out to be hot (i.e., at roughly the same temperature of the flare). Moreover, this region is moving toward higher altitudes over time (∼30 km s−1). During the flare, the same region spatially coincides with the origin of the coronal jet. Three-dimensional (3D) stereoscopic reconstructions of the propagating jet highlight that the ejected plasma moves along a curved trajectory. Conclusions. Within the framework of the interchange reconnection model, we conclude that the energy release site observed above-the-loop corresponds to the electron acceleration site, corroborating that interchange reconnection is a viable candidate for particle acceleration in the low corona on field lines open to interplanetary space.

First detection of metric emission from a solar surge

We report the first detection of metric radio emission from a surge, observed with the Nançay Radioheliograph (NRH), STEREO, and other instruments. The emission was observed during the late phase of the M9 complex event SOL2010-02-012T11:25:00, described in a previous publication. It was associated with a secondary energy release, also observed in STEREO 304 Å images, and there was no detectable soft X-ray emission. The triangulation of the STEREO images allowed for the identification of the surge with NRH sources near the central meridian. The radio emission of the surge occurred in two phases and consisted of two sources, one located near the base of the surge, apparently at or near the site of energy release, and another in the upper part of the surge; these were best visible in the frequency range of 445.0 to about 300 MHz, whereas a spectral component of a different nature was observed at lower frequencies. Sub-second time variations were detected in both sources during both phases, with a 0.2–0.3 s delay of the upper source with respect to the lower, suggesting superluminal velocities. This effect can be explained if the emission of the upper source was due to scattering of radiation from the source at the base of the surge. In addition, the radio emission showed signs of pulsations and spikes. We discuss possible emission mechanisms for the slow time variability component of the lower radio source. Gyrosynchrotron emission reproduced the characteristics of the observed total intensity spectrum at the start of the second phase of the event fairly well, but failed to reproduce the high degree of the observed circular polarization or the spectra at other instances. On the other hand, type IV-like plasma emission from the fundamental could explain the high polarization and the fine structure in the dynamic spectrum; moreover, it gives projected radio source positions on the plane of the sky, as seen from STEREO-A, near the base of the surge. Taking all the properties into consideration, we suggest that type IV-like plasma emission with a low-intensity gyrosynchrotron component is the most plausible mechanism.

The high-energy Sun - probing the origins of particle acceleration on our nearest star

As a frequent and energetic particle accelerator, our Sun provides us with an excellent astrophysical laboratory for understanding the fundamental process of particle acceleration. The exploitation of radiative diagnostics from electrons has shown that acceleration operates on sub-second time scales in a complex magnetic environment, where direct electric fields, wave turbulence, and shock waves all must contribute, although precise details are severely lacking. Ions were assumed to be accelerated in a similar manner to electrons, but γ-ray imaging confirmed that emission sources are spatially separated from X-ray sources, suggesting distinctly different acceleration mechanisms. Current X-ray and γ-ray spectroscopy provides only a basic understanding of accelerated particle spectra and the total energy budgets are therefore poorly constrained. Additionally, the recent detection of relativistic ion signatures lasting many hours, without an electron counterpart, is an enigma. We propose a single platform to directly measure the physical conditions present in the energy release sites and the environment in which the particles propagate and deposit their energy. To address this fundamental issue, we set out a suite of dedicated instruments that will probe both electrons and ions simultaneously to observe; high (seconds) temporal resolution photon spectra (4 keV – 150 MeV) with simultaneous imaging (1 keV – 30 MeV), polarization measurements (5–1000 keV) and high spatial and temporal resolution imaging spectroscopy in the UV/EUV/SXR (soft X-ray) regimes. These instruments will observe the broad range of radiative signatures produced in the solar atmosphere by accelerated particles.

The origin of quasi-periodicities during circular ribbon flares

Context. Solar flares with a fan-spine magnetic topology are able to form circular ribbons. A previous study based on Hα line observations of the solar flares on 5 March 2014 revealed a uniform and continuous rotation of the magnetic fan-spine. A preliminary analysis of the flare time profiles revealed quasi-periodic pulsations (QPPs) with similar properties in hard X-rays, Hα, and microwaves. Aims. In this work, we address the question of whether the observed periodicities are related to periodic acceleration of electrons or plasma heating. Methods. We analysed QPPs in the Hα emission from the centre of the fan (inner ribbon R1), a circular ribbon (R2), a remote source (R3), and an elongated ribbon (R4) located between R2 and R3. We used methods of correlation, Fourier, wavelet, and empirical mode decomposition. We compared the QPPs in Hα emission with those in microwave and X-ray emission. Results. We found multi-wavelength QPPs with periods around 150 s, 125 s, and 190 s. The 150 s period is seen to co-exist in Hα, hard X-rays, and microwave emissions, which allowed us to connect it with flare kernels R1 and R2. These kernels spatially coincide with the site of the primary flare energy release. The 125 s period is found in the Hα emission of the elongated ribbon R4 and the microwave emission at 5.7 GHz during the decay phase. The 190 s period is present in the emission during all flare phases in the Hα emission of both the remote source, R3, and the elongated ribbon, R4, in soft X-rays and in microwaves at 4–8 GHz. Conclusions. We connected the dominant 150 s QPPs with the slipping reconnection mechanism occurring in the fan. We suggested that the period of 125 s in the elongated ribbon can be caused by a kink oscillation of the outer spine, connecting the primary reconnection site with the remote footpoint. The period of 190 s is associated with the three-minute sunspot oscillations.

Morphology of the Flare-Productive Active Region NOAA 9087

Evolution and morphological properties of the active region NOAA 9087 are analyzed based on space and ground observational data. Data on hard X-ray (HXR) and soft X-ray (SXR) were obtained from Yohkoh Telescopes (HXT and SXT) and the Geostationary Operational Environmental Satellite. Magnetograms and images in far ultraviolet were obtained from the Michelson Doppler Imager (MDI) and Extreme ultraviolet Imaging Telescope (EIT) of the Solar and Heliospheric Observatory (SOHO). White light images from the Big Bear Observatory (BBSO) and Hα-filtergrams from the Meudon Observatory were used. Data on the 2.69 GHz radio flux were taken from the World Data Center of the Learmonth Observatory (Australia). The investigated active region (AR) was observed on the solar disk from July 15 to 27, 2000, and showed a complex multipolar magnetic field configuration. A high flare activity and emissions were observed in this AR. According to Solar Geophysical Data (SGD), the 3N/M6.4 two-ribbon flare occurred on July 19, 2000, and lasted 2.5 h. The energy was released sequentially in different locations in the AR. All observational data indicate a continuous change in the structure and power of the flare at different wavelengths. HXR and type III radio bursts were observed at the initial phase of the flare. The HXR coronal source was above the line of magnetic polarity inversion of the AR. Observational evidence of magnetic reconnections during the main phase of the flare is obtained based on the analysis of sequential images of loops in the ultraviolet wavelength band. Postflare loops were observed in the 19.5 nm passband at the gradual phase, which is a manifestation of the EUV late phase. These extended loops connect the primary and secondary energy release sites of the flare. There was an additional energy transfer and heating mechanism during the main phase of the flare.

A White-light Flare Powered by Magnetic Reconnection in the Lower Solar Atmosphere

Abstract White-light flares (WLFs), first observed in 1859, refer to a type of solar flare showing an obvious enhancement of the visible continuum emission. This type of enhancement often occurs in most energetic flares, and is usually interpreted as a consequence of efficient heating in the lower solar atmosphere through nonthermal electrons propagating downward from the energy release site in the corona. However, this coronal-reconnection model has difficulty in explaining the recently discovered small WLFs. Here we report a C2.3 WLF, which is associated with several observational phenomena: a fast decrease in opposite-polarity photospheric magnetic fluxes, the disappearance of two adjacent pores, significant heating of the lower chromosphere, a negligible increase of the hard X-ray flux, and an associated U-shaped magnetic field configuration. All these suggest that this WLF is powered by magnetic reconnection in the lower part of the solar atmosphere rather than by reconnection higher up in the corona.

Scattering of Energetic Electrons by Heat-flux-driven Whistlers in Flares

Abstract The scattering of electrons by heat-flux-driven whistler waves is explored with a particle-in-cell simulation relevant to the transport of energetic electrons in flares. This simulation is initiated with a large heat flux produced by using a kappa distribution of electrons with positive velocity and a cold return current beam. This system represents energetic electrons escaping from a reconnection-driven energy-release site. This heat-flux system drives large-amplitude oblique whistler waves propagating both along and against the heat flux, as well as electron acoustic waves. While the waves are dominantly driven by the low-energy electrons, including the cold return current beam, the energetic electrons resonate with and are scattered by the whistlers on timescales of the order of a hundred electron cyclotron times. Peak whistler amplitudes of and angles of ∼60° with respect to the background magnetic field are observed. Electron perpendicular energy is increased, while the field-aligned electron heat flux is suppressed. The resulting scattering mean-free-paths of energetic electrons are small compared with the typical scale size of energy-release sites in flares, which might lead to the effective confinement of energetic electrons required for the production of very energetic particles.

C-1.4 class flare and an associated peculiar coronal jet

AbstractUsing HINODE/XRT, GOES, SDO/AIA observations, we study a compact C-1.4 class flare outside a major sunspot of AR 12178 on 4 October 2014. This flare is associated with a peculiar coronal jet, which is erupted in two stages in the overlying corona above the compact flaring region. At the time of flare maximum, the first stage of the jet eruption occurs above the flare energy release site, and thereafter in the second stage its magneto-plasma system interacts with the overlying distinct magnetic field domain in its vicinity to build further the typical jet plasma column.

Observational study on the fine structure and dynamics of a solar jet. II. Energy release process revealed by spectral analysis

Abstract We report on a solar jet phenomenon associated with the C5.4 class flare on 2014 November 11. The data of the jet was provided by the Solar Dynamics Observatory, the X-Ray Telescope (XRT) aboard Hinode, and the Interface Region Imaging Spectrograph and Domeless Solar Telescope (DST) at Hida Observatory, Kyoto University. These plentiful data enabled us to present this series of papers to discuss all the processes of the observed phenomena, including energy storage, event trigger, and energy release. In this paper, we focus on the energy release process of the observed jet, and mainly describe our spectral analysis on the Hα data of DST to investigate the internal structure of the Hα jet and its temporal evolution. This analysis reveals that in the physical quantity distributions of the Hα jet, such as line-of-sight velocity and optical thickness, there is a significant gradient in the direction crossing the jet. We interpret this internal structure as the consequence of the migration of the energy release site, based on the idea of ubiquitous reconnection. Moreover, by measuring the horizontal flow of the fine structures in the jet, we succeeded in deriving the three-dimensional velocity field and the line-of-sight acceleration field of the Hα jet. The analysis result indicates that part of the ejecta in the Hα jet experienced additional acceleration after it had been ejected from the lower atmosphere. This secondary acceleration was found to occur in the vicinity of the intersection between the trajectories of the Hα jet and the X-ray jet observed by Hinode/XRT. We propose that a fundamental cause of this phenomenon is magnetic reconnection involving the plasmoid in the observed jet.

Flare Energy Release in the Lower Solar Atmosphere near the Magnetic Field Polarity Inversion Line

Abstract We study flare processes in the solar atmosphere using observational data for an M1-class flare of 2014 June 12, obtained by the New Solar Telescope (NST/BBSO) and Helioseismic Magnetic Imager (HMI/SDO). The main goal is to understand triggers and manifestations of the flare energy release in the photosphere and chromosphere using high-resolution optical observations and magnetic field measurements. We analyze optical images, HMI Dopplergrams, and vector magnetograms, and use nonlinear force-free field (NLFFF) extrapolations for reconstruction of the magnetic topology and electric currents. The NLFFF modeling reveals the interaction of two magnetic flux ropes with oppositely directed magnetic fields in the polarity inversion line (PIL). These flux ropes are observed as a compact sheared arcade along the PIL in the high-resolution broadband continuum images from NST. In the vicinity of the PIL, the NST observations reveal the formation of a thin three-ribbon structure corresponding to a small-scale photospheric magnetic arcade. The observational results are evidence in favor of the primary energy release site located in the chromospheric plasma with strong electric currents concentrated near the PIL. In this case, magnetic reconnection is triggered by the interacting magnetic flux ropes forming a current sheet elongated along the PIL.

ARCADE IMPLOSION CAUSED BY A FILAMENT ERUPTION IN A FLARE

ABSTRACT Coronal implosions—the convergence motion of plasmas and entrained magnetic field in the corona due to a reduction in magnetic pressure—can help to locate and track sites of magnetic energy release or redistribution during solar flares and eruptions. We report here on the analysis of a well-observed implosion in the form of an arcade contraction associated with a filament eruption, during the C3.5 flare SOL2013-06-19T07:29. A sequence of events including the magnetic flux-rope instability and distortion, followed by a filament eruption and arcade implosion, lead us to conclude that the implosion arises from the transfer of magnetic energy from beneath the arcade as part of the global magnetic instability, rather than due to local magnetic energy dissipation in the flare. The observed net contraction of the imploding loops, which is found also in nonlinear force-free field extrapolations, reflects a permanent reduction of magnetic energy underneath the arcade. This event shows that, in addition to resulting in the expansion or eruption of an overlying field, flux-rope instability can also simultaneously implode an unopened field due to magnetic energy transfer. It demonstrates the “partial opening of the field” scenario, which is one of the ways in 3D to produce a magnetic eruption without violating the Aly–Sturrock hypothesis. In the framework of this observation, we also propose a unification of three main concepts for active region magnetic evolution, namely the metastable eruption model, the implosion conjecture, and the standard “CSHKP” flare model.

Diagnosing physical conditions near the flare energy-release sites from observations of solar microwave type III bursts

In the physics of solar flares, it is crucial to diagnose the physical conditions near the flare energy-release sites. However, so far it is unclear how to diagnose these physical conditions. A solar microwave type III burst is believed to be a sensitive signature of primary energy release and electron accelerations in solar flares. This work takes into account the effect of the magnetic field on the plasma density and develops a set of formulas which can be used to estimate the plasma density, temperature, magnetic field near the magnetic reconnection site and particle acceleration region, and the velocity and energy of electron beams. We apply these formulas to three groups of microwave type III pairs in an X-class flare, and obtained some reasonable and interesting results. This method can be applied to other microwave type III bursts to diagnose the physical conditions of source regions, and provide some basic information to understand the intrinsic nature and fundamental processes occurring near the flare energy-release sites.

MICROWAVE TYPE III PAIR BURSTS IN SOLAR FLARES

ABSTRACT A solar microwave type III pair burst is composed of normal and reverse-sloped (RS) burst branches with oppositely fast frequency drifts. It is the most sensitive signature of the primary energy release and electron accelerations in flares. This work reports 11 microwave type III pair events in 9 flares observed by radio spectrometers in China and the Czech Republic at a frequency of 0.80–7.60 GHz during 1994–2014. These type III pairs occurred in flare impulsive and postflare phases with separate frequencies in the range of 1.08–3.42 GHz and a frequency gap of 10–1700 MHz. The frequency drift increases with the separate frequency (f x ), the lifetime of each burst is anti-correlated to f x , while the frequency gap is independent of f x . In most events, the normal branches are drifting obviously faster than the RS branches. The type III pairs occurring in flare impulsive phase have lower separate frequencies, longer lifetimes, wider frequency gaps, and slower frequency drifts than that occurring in postflare phase. Also, the latter always has strong circular polarization. Further analysis indicates that near the flare energy release sites the plasma density is about 10 10 – 10 11 ?> cm−3 and the temperature is higher than 107 K. These results provide new constraints to the acceleration mechanism in solar flares.

Sources of Quasi-periodic Pulses in the Flare of 18 August 2012

We analyzed spatial and spectral characteristics of quasi-periodic pulses (QPP) for the 18 August 2012 limb are, using new data from a complex of spectral and imaging instruments developed by the Siberian Solar Radio Telescope team and the Wind/Konus gamma-ray spectrometer. A sequence of broadband pulses with periods of approximately ten seconds were observed in X-rays at energies between 25 keV and 300 keV, and in microwaves at frequencies from a few GHz up to 34 GHz during an interval of one minute. The QPP X-ray source was located slightly above the limb where the south legs of large and small EUV loop systems were close to each other. Before the QPPs the soft X-ray emission and the Ramaty High Energy Solar Spectroscopic Imager signal from the energy channels below 25 keV were gradually arising for several minutes at the same location. It was found that each X-ray pulse showed the soft-hard-soft behavior. The 17 and 34 GHz microwave source were at footpoints of the small loop system and the source emitting in the 4.2 {7.4 GHz band in the large one. The QPPs were probably generated by modulation of acceleration processes in the energy release site. Analyzing radio spectra we determined the plasma parameters in the radio sources. The microwave pulses could be explained by relatively weak variations of the spectrum hardness of emitting electrons.

A tiny event producing an interplanetary type III burst

We investigate the conditions under which small scale energy release events in the low corona gave rise to strong interplanetary (IP) type III bursts. We analyze observations of three tiny events, detected by the Nan\c cay Radio Heliograph (NRH), two of which produced IP type IIIs. We took advantage of the NRH positioning information and of the high cadence of AIA/SDO data to identify the associated EUV emissions. We measured positions and time profiles of the metric and EUV sources. We found that the EUV events that produced IP type IIIs were located near a coronal hole boundary, while the one that did not was located in a closed magnetic field region. In all three cases tiny flaring loops were involved, without any associated mass eruption. In the best observed case the radio emission at the highest frequency (435 MHz) was displaced by ~55" with respect to the small flaring loop. The metric type III emission shows a complex structure in space and in time, indicative of multiple electron beams, despite the low intensity of the events. From the combined analysis of dynamic spectra and NRH images we derived the electron beam velocity as well as the height, ambient plasma temperature and density at the level of formation of the 160 MHz emission. From the analysis of the differential emission measure derived from the AIA images we found that the first evidence of energy release was at the footpoints and this was followed by the development of flaring loops and subsequent cooling. We conclude that even small energy release events can accelerate enough electrons to give rise to powerful IP type III bursts. The proximity of the electron acceleration site to open magnetic field lines facilitates the escape of the electrons into the interplanetary space. The offset between the site of energy release and the metric type III location warrants further investigation.

Spectroscopic UV observations of M1.0 class solar flare from IRIS satellite

AbstractThis work presents an analysis of UV spectroscopic observations from the IRIS satellite of an M1.0 class flare occurred on 12 June 2014 in active region NOAA 12087. Our analysis of the IRIS spectra and Slit-Jaw images revealed presence of a strongly redshifted chromospheric jet before the flare. We also found strong emission of the chromospheric lines, and studied the C II 1334.5 Å line emission distribution in details. A blueshift of the Fe XXI line across the flaring region corresponds to evaporation flows of the hot chromospheric plasma with a speed of 50 km/s. Although the enhancement of the C II line integrated redshift correlates with the flare X-ray emission, we classify the evaporation as of a “gentle” type because of its long time scale and subsonic velocities. Analysis of X-ray data from the RHESSI satellite showed that both, an injection of accelerated particles and a heat flux from the energy release site can explain the energetics of the observed event.