Context. Even if Ellerman bombs have been observed in the Hα line within emerging magnetic flux regions since the early 20th century, their origin and the mechanisms that lead to their formation have been strongly debated. Recently, new arguments in favor of chromospheric magnetic reconnection have been advanced. Ellerman bombs seem to be the signature of reconnections that take place during the emergence of the magnetic field. Aims. We have observed an active region presenting emergence of magnetic flux. We detected and studied Ellerman bombs in two chromospheric lines: Ca ii 8542 Å and Hα. We investigated the link between Ellerman bombs and other structures and phenomena appearing in an emerging active region: UV bright points, arch filament systems, and magnetic topology. Methods. On August 3, 2004, we performed multi-wavelength observations of the active region NOAA 10655. This active region was the target of SoHO Joint Observation Program 157. Both SoHO/MDI and TRACE (195 Å and 1600 Å) were used. Simultaneously, we observed in the Ca ii and Na D1 lines with the spectro-imager MSDP mode of THEMIS. Alternately to the MSDP, we used the MTR spectropolarimeter on THEMIS to observe in Hα and in the Fe i doublet at 6302 Å. We derived the magnetic field vectors around some Ellerman bombs.Results. We present the first images of EBs in the Ca ii line and confirm that Ellerman bombs can indeed be observed in the Ca ii line, presenting the same "moustache" geometry profiles as in the Hα line, but with a narrower central absorption in the Ca ii line, in which the peaks of emission are around ±0.35 Å. We noticed that the Ellerman bombs observed in the wings of Ca ii line have an elongated shape -the length about 50% greater than the width. We derived mean semi-axis lengths of 1.4 × 2.0 . In the UV time profiles of the Ellerman bombs, we noticed successive enhanced emissions. The distribution of lifetimes of these individual impulses presents a strong mode around 210 s. Study of the magnetic topology shows that 9 out of the 13 EBs are located on the inversion line of the longitudinal field and that some typical examples might be associated with a bald patch topology. Conclusions. We provide new arguments in favor of the reconnection origin of Ellerman bombs. The different individual impulses observed in UV may be related to a bursty mode of reconnection. We also show that this Ca ii 8542 Å chromospheric line is a good indicator of Ellerman bombs and can bring new information about these phenomena.

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.

Context. The dynamics of prominence fine structures present a challenge to our understanding of the formation of cool plasma prominence embedded in the hot corona. Aims. Observations performed by the high resolution Hinode/SOT telescope allow us to compute velocities perpendicular to the lineof-sight or transverse velocities. Combining simultaneous observations obtained in Hα with Hinode/SOT and the MSDP spectrograph operating in the Meudon solar tower, we derive the velocity vectors of a quiescent prominence. Methods. The velocities perpendicular to the line-of-sight are measured using a time-slice technique and the Doppler shifts velocity using the bisector method.Results. The Doppler shifts of bright threads derived from the MSDP show counterstreaming of the order of 5 km s −1 in the prominence and reaching 15 km s −1 at the edges of the prominence. Even though they are minimum values because of seeing effects, they are of the same order as the transverse velocities. Conclusions. These measurements are very important because they suggest that the vertical structures detected by SOT may not be true vertical magnetic structures in the sky plane. The vertical structures could be a pile up of dips in more or less horizontal magnetic field lines in a 3D perspective, as proposed by many MHD modelers. In our analysis, we also calibrate the Hinode Hα data using MSDP observations obtained simultaneously.

In this paper we present a further study of the Ml class flare observed on October 22, 2002. We focus on the SOHO Coronal Diagnostic Spectrometer (CDS) spectral observations performed during a multi-wavelength campaign with TRACE and ground-based instruments (VTT, THEMIS). Strong blue-shifts are observed in the CDS coronal lines in flare kernels during the impulsive phase of this flare. From a careful wavelength calibration we deduce upflows of 140 km/s for the Fe XIX flare emission, with a pattern of progressively smaller flows at lower temperatures. Large line-widths were observed, especially for the Fe XIX line, which indicate the existence of turbulent velocities. The strong upflows correspond to full shifts of the line profiles. These flows are observed at the initial phase of the flare, and correspond to the "explosive evaporation". The regions of the blueshifted kernels, a few arc seconds away from the flare onset location, could be explained by the chain reaction of successive magnetic reconnections of growing emerging field line with higher and higher overlying field. This interpretation is evidenced by the analysis of the magnetic topology of the active region using a linear force-free-field extrapolation of THEMIS magnetograms.