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We present a multiwavelength analysis of two flare-related jets on 2014 November 13, using data from the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA), the Reuven High Energy Solar Spectroscopic Imager (RHESSI), the Hinode/X-ray Telescope (XRT), and the Interface Region Imaging Spectrograph (IRIS). Unlike most coronal jets, where hard X-ray (HXR) emissions are usually observed near the jet base, in these events HXR emissions are found at several locations, including in the corona. We carry out the first differential emission measure analysis that combines both AIA (and XRT, when available) bandpass filter data and RHESSI HXR measurements for coronal jets, and obtain self-consistent results across a wide temperature range and into nonthermal energies. In both events, hot plasma first appears at the jet base, but as the base plasma gradually cools, hot plasma also appears near the jet top. Moreover, nonthermal electrons, while only mildly energetic, are found in multiple HXR locations and contain large amounts of total energy. In particular, the energetic electrons that produce the HXR sources at the jet top are accelerated near the top location, rather than traveling from a reconnection site at the jet base. This means that there is more than one particle acceleration site in each event. Jet velocities are consistent with previous studies, including the upward and downward velocities around ∼200 km s ^−1 and ∼100 km s ^−1 , respectively, and fast outflows of 400–700 km s ^−1 . We also examine the energy partition in the later event, and find that the nonthermal energy in the accelerated electrons is most significant compared to the other energy forms considered. We discuss the interpretations and provide constraints on the mechanisms for coronal jet formation.

In this paper we present the differential emission measures (DEMs) of two sub-A class microflares observed in hard X-rays (HXRs) by the FOXSI-2 sounding rocket experiment, on 2014 December 11. The second Focusing Optics X-ray Solar Imager (FOXSI) flight was coordinated with instruments X-ray Telescope (Hinode/XRT) and Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA), which provided observations in soft X-rays and Extreme Ultraviolet. This unique data set offers an unprecedented temperature coverage, useful for characterizing the plasma temperature distribution of microflares. By combining data from FOXSI-2, XRT, and AIA, we determined a well-constrained DEM for the microflares. The resulting DEMs peak around 3 MK and extend beyond 10 MK. The emission measures determined from FOXSI-2 were lower than 1026 cm−5 for temperatures higher than 5 MK; faint emission in this range is best measured in HXRs. The coordinated FOXSI-2 observations produce one of the few definitive measurements of the distribution and the amount of plasma above 5 MK in microflares. We utilize the multi-thermal DEMs to calculate the amount of thermal energy released during both the microflares as ∼5.0 × 1028 erg for Microflare 1 and ∼1.6 × 1028 erg for Microflare 2. We also show the multi-thermal DEMs provide more comprehensive thermal energy estimates than isothermal approximation, which systematically underestimates the amount of thermal energy released. [ABSTRACT FROM AUTHOR]

We present the statistical analysis of 33 flare-related coronal jets, and discuss the link between the jet and the flare properties in these events. We selected jets that were observed between 2010 and 2016 by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO) that are temporally and spatially associated with flares observed by the Reuven Ramaty High Energy Solar Spectrometric Imager (RHESSI). For each jet, we calculated the jet duration and projected velocity in the plane of sky. The jet duration distribution has a median of 18.8 minutes. The projected velocities are between 31 and 456 km s−1 , with a median at 210 km s−1. For each associated flare, we performed X-ray imaging and spectroscopy and identify nonthermal emission. Nonthermal emission was detected in only 1/4 of the events considered. We did not find a clear correlation between the flare thermal energy or soft X-ray (SXR) peak flux and the jet velocity or jet duration. There is no preferential time delay between the flare and the jet. The X-ray emission is generally located at the base of the jet. The analysis presented in this paper suggests that the flare and jet are part of the same explosive event, that the jet is driven by the propagation of an Alfvénic perturbation, and that the energy partition between flare and jets varies substantially from one event to another. [ABSTRACT FROM AUTHOR]

The standard model of flares predicts the existence of a fast-mode magnetohydrodynamic shock above the looptops, also known as termination shock (TS), as the result of the downward-directed outflow reconnection jets colliding with the closed magnetic loops. A crucial spectral signature of a TS is the presence of large Doppler shifts in the spectra of high-temperature lines (≥10 MK), which has been rarely observed so far. Using high-resolution observations of the Fe xxi line with the Interface Region Imaging Spectrograph (IRIS), we detect large redshifts (≈200 km s−1) at the top of the bright looptop arcade of the X1-class flare on 2014 March 29. In some cases, the redshifts are accompanied by faint simultaneous Fe xxi blueshifts of about −250 km s−1. The values of red and blueshifts are in agreement with recent modeling of Fe xxi spectra downflow of the reconnection site and previous spectroscopic observations with higher temperature lines. The locations where we observe the Fe xxi shifts are co-spatial with 30–70 keV hard X-ray sources detected by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), indicating that nonthermal electrons are located above the flare loops. We speculate that our results are consistent with the presence of a TS in flare reconnection models. [ABSTRACT FROM AUTHOR]

Why the tenuous solar outer atmosphere, or corona, is much hotter than the underlying layers remains one of the greatest challenges for solar modeling. Detailed diagnostics of the coronal thermal structure come from extreme ultraviolet (EUV) emission. The EUV emission is produced by heavy ions in various ionization states and depends on the amount of these ions and on plasma temperature and density. Any nonuniformity of the elemental distribution in space or variability in time affects thermal diagnostics of the corona. Here we theoretically predict ionized chemical element concentrations in some areas of the solar atmosphere, where the electric current is directed upward. We then detect these areas observationally, by comparing the electric current density with the EUV brightness in an active region. We found a significant excess in EUV brightness in the areas with positive current density rather than negative. Therefore, we report the observational discovery of substantial concentrations of heavy ions in current-carrying magnetic flux tubes, which might have important implications for the elemental fractionation in the solar corona known as the first ionization potential effect. We call such areas of heavy ion concentration the “ion traps.” These traps hold enhanced ion levels until they are disrupted by a flare, whether large or small. [ABSTRACT FROM AUTHOR]