A Morning Discontinuity in the Orientation of Quiet Auroral Arcs

From all-sky camera recordings taken at this Observatory (geographic co-ordinates 67.8° N., 20.4° E.; geomagnetic co-ordinates 65.3° N., 115.5° E.) during the period December 1958 – March 1961 the directions of 366 quiet auroral arcs were measured. Only arcs extending from horizon to horizon, or at least covering an angle of view of about 100° for the most distant arcs and having an elevation angle of more than 15° for the highest point, were used in the analysis.