The coronal convection

We study the hydrogen Lyman emission in various solar features - now including Lyman-alpha observations free from geocoronal absorption - and investigate statistically the imprint of flows and of the magnetic field on the line profile and radiance distribution. As a new result, we found that in Lyman-alpha rasters locations with higher opacity cluster in the cell interior, while the network has a trend to flatter profiles. Even deeper self reversals and larger peak distances were found in coronal hole spectra. We also compare simultaneous Lyman-alpha and Lyman-beta profiles. There is an obvious correspondence between asymmetry and redshift for both lines, but, most surprisingly, the asymmetries of Lyman-alpha and Lyman-beta are opposite. We conclude that in both cases downflows determine the line profile, in case of Lyman-alpha by absorption and in the case of Ly-beta by emission. Our results show that the magnetically structured atmosphere plays a dominating role in the line formation and indicate the presence of a persisting downflow at both footpoints of closed loops. We claim that this is the manifestation of a fundamental mass transportation process, which Foukal back in 1978 introduced as the 'coronal convection'.Comment: 8 pages, 5 figures, accepted for publication in Cent. Eur. Astrophys. Bul

Cool and hot components of a coronal bright point

We performed a systematic study of the Doppler shifts and electron densities measured in an EUV bright point (hereafter BP) observed in more than 10 EUV lines with formation temperatures from log (T/K) p 4.5 to 6.3. Those parts of a BP seen in transition region and coronal lines are defined as its cool and hot components, respectively. We find that the transition from cool to hot occurs at a temperature around log (T/K) p 5.7. The two components of the BP reveal a totally different orientation and Doppler-shift pattern, which might result from a twist of the associated magnetic loop system. The analysis of magnetic field evolution and topology seems to favor a two-stage heating process, in which magnetic cancellation and separator reconnection are powering, respectively, the cool and hot components of the BP. We also found that the electron densities of both components of the BP are higher than those of the surrounding quiet Sun, and comparable to or smaller than active region densities.Comment: 4 pages, 4 figure