First Three‐Dimensional Reconstructions of Coronal Loops with the STEREO A and B Spacecraft. I. Geometry

Abstract

We present one of the first triangulations and 3D reconstructions of coronal loops, using the EUVI telescopes of the two STEREO A and B spacecraft. The first triangulation of coronal loops was performed in an active region, observed with STEREO A and B on 2007 May 9 with a spacecraft separation angle of α sep = 7.3°, at a wavelength of 171 Å. We identify 30 loop structures (7 complete loops and 23 partial segments) and compute their 3D coordinates ( x,y,z ) (the full 3D coordinates are available as an electronic file). We quantify the height range, the stereoscopic height measurement errors, the loop plane inclination angles, and the coplanarity and circularity of the analyzed loops. The knowledge of the exact 3D geometry of a loop with respect to the observer's line of sight has important consequences for determining the correct vertical density scale height (used in hydrostatic models), the aspect angle of loop cross sections (used in inferring electron densities from optically thin emission measures), the absolute flow speeds (used in siphon flow models), the correct loop length (used in loop scaling laws), and the 3D vectors of the coronal magnetic field (used in testing theoretical magnetic field extrapolation models). The hydrodynamic and magnetic modeling of the analyzed loops will be described in subsequent papers.