Illustration of step 1 of the data analysis: azimuthal cut of the 14.31–14.44 September 2015 UT map of HO. The line-integrated intensity for lines averaged in bins of 15° in azimuth (PA scale on the horizontal axis) and 2.5 km in projected radius is plotted for each PA and with a different color for each range of radial distance. The projected directions of the Sun, north pole (blue), and south pole (magenta) are indicated.