Solar Stereoscopy with STEREO/EUVI A and B Spacecraft from Small (6 ~({ring operator}))to Large(170 ~({ring operator}))Spacecraft Separation Angles

摘要

We performed for the first time stereoscopic triangulation of coronal loops in active regions over the entire range of spacecraft separation angles (α sep≈6 ~({ring operator}),43 ~({ring operator}),89 ~({ring operator}),127 ~({ring operator}),and 170 ~({ring operator})). The accuracy of stereoscopic correlation depends mostly on the viewing angle with respect to the solar surface for each spacecraft, which affects the stereoscopic correspondence identification of loops in image pairs. From a simple theoretical model we predict an optimum range of α _(sep)≈22 ~({ring operator})-125 ~({ring operator}), which is also experimentally confirmed. The best accuracy is generally obtained when an active region passes the central meridian(viewed from Earth), which yields a symmetric view for both STEREO spacecraft and causes minimum horizontal foreshortening. For the extended angular range of α _(sep)≈6 ~({ring operator})-127 ~({ring operator})we find a mean 3D misalignment angle of μ _(PF)≈21 ~({ring operator})-39 ~({ring operator})of stereoscopically triangulated loops with magnetic potential-field models, and μ _(FFF)≈15 ~({ring operator})-21 {ring operator} for a force-free field model, which is partly caused by stereoscopic uncertainties μ _(SE)≈9 ~({ring operator}). We predict optimum conditions for solar stereoscopy during the time intervals of 2012-2014, 2016-2017, and 2021-2023.