3D Coronal structures and their evolutions measured by Stereoscopy,consequences for Space Weather and the STEREO mission

We are discussing methods of stereoscopic 3D reconstruction of coronal loops structures. In our most sophisticated method we fit loops observed with SOHO/EIT to a set of shape parameters including the internal twist of the loops field lines. We define this twist as the number of turns of the field line around a torus axis between the footpoints of the loops. Twist numbers of the order 0–2 are observed. We observe the emergence of an Active Region with twisted loops which detwist as they expand. The same correlation between detwisting and expansion is observed with filaments in relation to CME formations. On longer time scale, loops seem to accumulate twist, perhaps due to differential rotation. Rapid losses of twist temporarily correlate with flares. From our analysis, we expect that the internal twist of coronal structures will play an important role for the space weather forecast. This revised version was published online in August 2006 with corrections to the Cover Date.     

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. This revised version was published online in June 2006 with corrections to the Cover Date.     

Theoretical modeling for the stereo mission

We summarize the theory and modeling efforts for the STEREO mission, which will be used to interpret the data of both the remote-sensing (SECCHI, SWAVES) and in-situ instruments (IMPACT, PLASTIC). The modeling includes the coronal plasma, in both open and closed magnetic structures, and the solar wind and its expansion outwards from the Sun, which defines the heliosphere. Particular emphasis is given to modeling of dynamic phenomena associated with the initiation and propagation of coronal mass ejections (CMEs). The modeling of the CME initiation includes magnetic shearing, kink instability, filament eruption, and magnetic reconnection in the flaring lower corona. The modeling of CME propagation entails interplanetary shocks, interplanetary particle beams, solar energetic particles (SEPs), geoeffective connections, and space weather. This review describes mostly existing models of groups that have committed their work to the STEREO mission, but is by no means exhaustive or comprehensive regarding alternative theoretical approaches.     

MICA: The Mirror Coronagraph for Argentina

As part of the new German-Argentinian Solar Observatory in El Leoncito, San Juan, Argentina, a new ground-based solar telescope (MICA) began to operate in August 1997. MICA is an advanced mirror coronagraph, its design being an almost exact copy of the LASCO-C1 instrument. Since its installation, it has been imaging the inner solar corona (1.05 to 2.0 solar radii) in two spectral ranges corresponding to the emission lines of the Fe XIV and Fe X ions. The instrument can image the corona as fast as every minute. Thus, it is ideally suited to study fast processes in the inner corona. In this way, it is a good complement for the LASCO-C1 instrument. After a brief review of the instrument, we present some recent observations showing the capabilities of the instrument. This revised version was published online in June 2006 with corrections to the Cover Date.     

The Rotation of the Fe XIV Solar Corona During the Recent Solar Activity Minimum

We analyze data observed by the LASCO C1 coronagraph on board the SOHO spacecraft during the solar minimum activity from April 1996 to March 1997. Using the phase dispersion technique, we investigate the periodicity and recurrence of Fe XIV emission structures with heliospheric latitude and distance above the Sun's surface with high spatial resolution. We find no significant deviation from a rigidly rotating Fe XIV corona with latitude or with distance from the Sun even on these small scales. In agreement with earlier work, the coronal rotation period at solar minimum is about 27.5 ± 1 days. This revised version was published online in June 2006 with corrections to the Cover Date.