Active Region Moss: Basic physical parameters and their temporal variation

We present a study of the physical plasma parameters such as electron temperature, electron density, column depth and filling factors in the moss regions and their variability over a short (an hour) and a long period (5 consecutive days) of time. Primarily, we have analyzed the spectroscopic observations recorded by the Extreme-ultraviolet Imaging Spectrometer (EIS) aboard Hinode. In addition we have used supplementary observations taken from TRACE and the X-Ray Telescope (XRT). We find that the moss emission is strongest in the Fe xii and Fe xiii lines. Based on analyses using line ratios and emission measure we found that the moss region has a characteristic temperature of log T = 6.2. The electron densities measured at different locations in the moss regions using Fe xii ratios are about 1-3times1010 cm(-3) and about 2-4times10^9 cm^(-3) using Fe xiii and Fe xiv. The electron density substantially increases (by a factor of about 3-4 or even more in some cases) when a background subtraction was performed. The density and temperature show very small variation over time. The filling factor of the moss plasma can vary between 0.1-1 and the path length along which the emission originates is from a few 100 to a few 1000 kms long. By combining the observations recorded by TRACE, EIS and XRT, we find that the moss regions correspond to the foot-points of both hot and warm loops.

A bright coronal downflow seen in multi-wavelength observations: evidence of a bifurcating flux-rope?

Aims: To study the origin and characteristics of a bright coronal downflow seen after a coronal mass ejection associated with erupting prominences on 5 March 2000. Methods: This study extends that of Tripathi et al. (A&A, v. 449, pp. 369) based on the Extreme-ultraviolet Imaging Telescope (EIT), the Soft X-ray Telescope (SXT) and the Large Angle Spectrometric Coronagraph (LASCO) observations. We combined those results with an analysis of the observations taken by the H${alpha}$ and the Mk4 coronagraphs at the Mauna Loa Solar Observatory (MLSO). The combined data-set spans a broad range of temperature as well as continuous observations from the solar surface out to 30 R$_{sun}$. Results: The downflow started at around 1.6R$_{sun}$ and contained both hot and cold gas. The downflow was observed in the H${alpha}$ and the Mk4 coronagraphs as well as the EIT and the SXT and was approximately co-spatial and co-temporal providing evidence of multi-thermal plasma. The H${alpha}$ and Mk4 images show cusp-shaped structures close to the location where the downflow started. Mk4 observations reveal that the speed of the downflow in the early phase was substantially higher than the free-fall speed, implying a strong downward acceleration near the height at which the downflow started. Conclusions: The origin of the downflow was likely to have been magnetic reconnection taking place inside the erupting flux rope that led to its bifurcation.