Borut Podlipnik

FIRST STEREOSCOPIC CORONAL LOOP RECONSTRUCTIONS FROM STEREO SECCHI IMAGES

We present the first reconstruction of the three-dimensional shape of magnetic loops in an active region from two different vantage points based on simultaneously recorded images. The images were taken by the two EUVI telescopes of the SECCHI instrument on board the recently launched STEREO spacecraft when the heliocentric separation of the two space probes was 12°. We demonstrate that these data allow us to obtain a reliable three-dimensional reconstruction of sufficiently bright loops. The result is compared with field lines derived from a coronal magnetic field model extrapolated from a photospheric magnetogram recorded nearly simultaneously by SOHO MDI. We attribute discrepancies between reconstructed loops and extrapolated field lines to the inadequacy of the linear force-free field model used for the extrapolation.

STEREOSCOPIC POLAR PLUME RECONSTRUCTIONS FROM STEREO/SECCHI IMAGES

We present stereoscopic reconstructions of the location and inclination of polar plumes of two data sets based on the two simultaneously recorded images taken by the EUVI telescopes in the SECCHI instrument package onboard the Solar TErrestrial RElations Observatory spacecraft. The 10 plumes investigated show a superradial expansion in the coronal hole in three dimensions (3D) which is consistent with the two-dimensional results. Their deviations from the local meridian planes are rather small with an average of 6 degrees..47. By comparing the reconstructed plumes with a dipole field with its axis along the solar rotation axis, it is found that plumes are inclined more horizontally than the dipole field. The lower the latitude is, the larger is the deviation from the dipole field. The relationship between plumes and bright points has been investigated and they are not always associated. For the first data set, based on the 3D height of plumes and the electron density derived from SUMER/SOHO Si VIII line pair, we found that electron densities along the plumes decrease with height above the solar surface. The temperature obtained from the density scale height is 1.6-1.8 times larger than the temperature obtained from Mg IX line ratios. We attribute this discrepancy to a deviation of the electron and the ion temperatures. Finally, we have found that the outflow speeds studied in the O VI line in the plumes corrected by the angle between the line of sight and the plume orientation are quite small with amaximum of 10 km s(-1). It is unlikely that plumes are a dominant contributor to the fast solar wind.

Measurements of flow speeds and acceleration in gradually evolving solar mass ejections as observed by LASCO

We present observations of slowly evolving, balloon-type solar mass ejections observed by the LASCO coronagraphs aboard SOHO. These mass ejections are typically observed to rise gradually in the solar corona for several hours (>20 hours) as large loops or balloons crossing the entire field of view of the coronagraphs. Usually, their angular extent does not change much. Analysis of several such cases of balloon-type mass ejections show that they rise with very slow speeds (less than 50 km s−1) up to a distance of 2 R⊙ and then are accelerated to higher speeds until 5 R⊙. From a distance of about 20 R⊙, the mass ejecta attain almost a constant speed ranging between 300 and 500 km s−1. The speed profiles obtained for individual mass ejections indicate that they trace out the slow solar wind and, thus, provide an insight into the initiation and the propagation of the CMEs into the solar wind.

Acceleration Profile of the Slow Solar Wind as Inferred from Gradual Mass Ejections Observed by LASCO

The slow solar wind (< 400 km s-1) appears to initiate from the regions in the corona where magnetic fields are closed, or from the interface between streamers and other coronal regions. The nature of the acceleration of slow solar wind is not yet well known. LASCO observations of gradually evolving mass ejections offer us a good opportunity to study the speed and acceleration profiles of the slow solar wind from a distance of 1.1 up to 30 R⊙. We present speed and acceleration profiles of slow solar wind, derived on the basis of measurements of mass flows in several cases of gradual mass ejections and present them in perspective of earlier work.