Eruptions from solar ephemeral regions as an extension of the size distribution of coronal mass ejections

Observations of the quiet solar corona in the 171A (~1MK) passband of the Transition Region and Coronal Explorer (TRACE) often show disruptions of the coronal part of small-scale ephemeral bipolar regions that resemble the phenomena associated with coronal mass ejections on much larger scales: ephemeral regions exhibit flare-like brightenings, rapidly rising filaments carrying absorbing material at chromospheric temperatures, or the temporary dimming of the surrounding corona. I analyze all available TRACE observing sequences between 1998/04/01 and 2009/09/30 with full-resolution 171A image sequences spanning a day or more within 500 arcsec of disk center, observing essentially quiet Sun with good exposures and relatively low background. Ten such data sets are identified between 2000 and 2008, spanning 570h of observing with a total of 17133 exposures. Eighty small-scale coronal eruptions are identified. Their size distribution forms a smooth extension of the distribution of angular widths of coronal mass ejections, suggesting that the eruption frequency for bipolar magnetic regions is essentially scale free over at least two orders of magnitude, from eruptions near the arcsecond resolution limit of TRACE to the largest coronal mass ejections observed in the inner heliosphere. This scale range may be associated with the properties of the nested set of ranges of connectivity in the magnetic field, in which increasingly large and energetic events can reach higher and higher into the corona until the heliosphere is reached

Transition region fluxes in A-F Dwarfs: Basal fluxes and dynamo activity

The transition region spectra of 87 late A and early F dwarfs and subgiants were analyzed. The emission line fluxes are uniformly strong in the early F stars, and drop off rapidly among the late A stars. The basal flux level in the F stars is consistent with an extrapolation of that observed among the G stars, while the magnetic component displays the same flux-flux relations seen among solar-like stars. Despite the steep decrease in transition region emission flux for B-V less than 0.28, C II emission is detected in alpha Aql (B-V = 0.22). The dropoff in emission is inconsistent with models of the mechanically generated acoustic flux available. It is concluded that, although the nonmagnetic basal heating is an increasingly important source of atmospheric heating among the early F stars, magnetic heating occurs in any star which has a sufficiently thick convective zone to generate acoustic heating

Oscillations in the magnetic field of the solar corona in response to flares near the photosphere

The magnetic field in the outer solar atmosphere is frequently distorted by flares. In some cases, a fraction of the field exhibits a rapidly damped oscillation (Schrijver et al.; Aschwanden et al.). If this is a resonating wave trapped in the field, then the rapid damping requires a viscosity or resistivity that is at least 108 times larger than expected (Nakariakov et al.). We propose instead that some of the field lines are so sensitive to the source positions that rocking motions of the photospheric plasma associated with some solar flares (Kosovichev & Zharkova) cause a few loops to oscillate in (anti)phase in the fundamental mode, with a period and decay rate that are determined largely by the characteristics of the photosphere, saying little about the high atmosphere