A quiescent prominence was observed by several instruments on 2007 April 25. The temporal evolution was recorded in Hα by Hinode/SOT, in X-rays by Hinode/XRT and in the 195Å channel by TRACE. Moreover, ground-based observatories (GBO) provided calibrated Hα intensities. Simultaneous EUV data were also taken by the Hinode/EIS and SOHO/SUMER-CDS spectrometers. Here we have selected the SOT Hα image taken at 13:19 UT which nicely shows the prominence fine structure. We compare this image with co-temporal ones taken by XRT and TRACE and show the intensity variations along several cuts parallel to the solar limb. EIS spectra were obtained about half an hour later. Dark prominence structure clearly seen in the TRACE and EIS 195Å images is due to the prominence absorption in HI, HeI and HeII resonance continua plus the coronal emissivity blocking due to the prominence void (cavity). The void clearly visible in XRT images is entirely due to X-ray emissivity blocking, since no prominence structure is seen in the XRT images because of negligible absorption at X-ray wavelengths. We use TRACE, EIS and XRT data to estimate the amount of absorption and blocking. Independently, the Hα integrated intensities provide us with an estimate of the Hα opacity and this is related to the opacity of resonance continua as follows from the non-LTE radiative-transfer modeling. Therefore, we have an independent check of the results obtained from TRACE/XRT and EIS/XRT. However, spatial averaging of the Hα and EUV data have quite different natures which must be taken into account when evaluating the true opacities. We demonstrate this important effect here for the first time. Finally, based on this multi-wavelength analysis, we discuss the determination of the column densities and the ionization degree of hydrogen in the prominence.

We report on the SDO /AIA and Hinode/EIS observations of a transient coronal loop. The loop brightens up in the same location after the disappearance of an arcade formed during a B8.9-class microflare three hours earlier. EIS captures this loop during its brightening phase as observed in most of the AIA filters. We use the AIA data to study the evolution of the loop, as well as to perform the DEM diagnostics as a function of κ. Fe XI-Fe XIII lines observed by EIS are used to perform the diagnostics of electron density and subsequently the diagnostics of κ. Using ratios involving the Fe XI 257.772Å selfblend, we diagnose κ 2, i.e., an extremely non-Maxwellian distribution. Using the predicted Fe line intensities derived from the DEMs as a function of κ, we show that, with decreasing κ, all combinations of ratios of line intensities converge to the observed values, confirming the diagnosed κ 2. These results represent the first positive diagnostics of κ-distributions in the solar corona despite the limitations imposed by calibration uncertainties.

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In the paper by Bárta et al. (ApJ, 2010) the authors addressed some open questions of the CSHKP scenario of solar flares by means of high-resolution MHD simulations. They focused, in particular, on the problem of energy transfer from large to small scales in decaying flare current sheet (CS). Their calculations suggest, that magnetic flux-ropes (plasmoids) are formed in full range of scales by a cascade of tearing and coalescence processes. Consequently, the initially thick current layer becomes highly fragmented. Thus, the tearing and coalescence cascade can cause an effective energy transfer across the scales. In the current paper we investigate whether this mechanism actually applies in solar flares. We extend the MHD simulation by deriving model-specific features that can be looked for in observations. The results of the underlying MHD model showed that the plasmoid cascade creates a specific hierarchical distribution of non-ideal/acceleration regions embedded in the CS. We therefore focus on the features associated with the fluxes of energetic particles, in particular on the structure and dynamics of emission regions in flare ribbons. We assume that the structure and dynamics of diffusion regions embedded in the CS imprint themselves into structure and dynamics of flare-ribbon kernels by means of magnetic-field mapping. Using the results of the underlying MHD simulation we derive the expected structure of ribbon emission and we extract selected statistical properties of the modelled bright kernels. Comparing the predicted emission and its properties with the observed ones we obtain a good agreement of the two.