Determination of the True Shape of Coronal Loops

Abstract

Using line of sight velocity measurements from the SUMER and CDS instruments aboard SOHO, in conjunction with a simple geometrical model, we reconstructed the true, 3D shape and the velocity of plasma flow along coronal loops. The projection of the loop on the sky and the position of the footpoints define a family of curves. Assuming that the loop is located on a plane, the line of sight velocity can be used to select the most plausible solution. For two loops, observed in the Ne viii  770 Å and O v  630 Å spectral lines, we find asymmetric, subsonic uni-directional flows, with velocity maxima of ≈ 80 km s⁻¹ near the footpoints. The loops are highly inclined with respect to the vertical, by 55^○ and 70^○, respectively; thus the true height of the loop tops from the photospheric level is ≈ 20^′′, comparable to the isothermal scale height.