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.