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Abstract: Observations from the two STEREO-spacecraft give us for the first time thepossibility to use stereoscopic methods to reconstruct the 3D solar corona.Classical stereoscopy works best for solid objects with clear edges.Consequently an application of classical stereoscopic methods to the faintstructures visible in the optically thin coronal plasma is by no means straightforward and several problems have to be treated adequately: 1.First there isthe problem of identifying one dimensional structures -e.g. active regioncoronal loops or polar plumes- from the two individual EUV-images observed withSTEREO-EUVI. 2. As a next step one has the association problem to findcorresponding structures in both images. 3. Within the reconstruction problemstereoscopic methods are used to compute the 3D-geometry of the identifiedstructures. Without any prior assumptions, e.g., regarding the footpoints ofcoronal loops, the reconstruction problem has not one unique solution. 4. Onehas to estimate the reconstruction error or accuracy of the reconstructed3D-structure, which depends on the accuracy of the identified structures in 2D,the separation angle between the spacecraft, but also on the location, e.g.,for east-west directed coronal loops the reconstruction error is highest closeto the loop top. 5. Eventually we are not only interested in the 3D-geometryof loops or plumes, but also in physical parameters like density, temperature,plasma flow, magnetic field strength etc. Helpful for treating some of theseproblems are coronal magnetic field models extrapolated from photosphericmeasurements, because observed EUV-loops outline the magnetic field. Thisfeature has been used for a new method dubbed -magnetic stereoscopy-. Asexamples we show recent application to active region loops.



Author: T.Wiegelmann, B. Inhester, L. Feng

Source: https://arxiv.org/



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