Abstract

In this work, we investigate the interhemispheric transpolar arc (TPA) conjugacy using four previously published datasets based on Polar UV images, DMSP particle data, and IMAGE images, and a new TPA list based on DMSP SSUSI images during 1 Sep to 15 Oct 2015. IMF Bₓ and the Earth’s dipole tilt have often been suggested to influence the TPA conjugacy, as both induce a north-south asymmetry on the magnetosphere. However, by comparing these parameters at TPA formation with the background distribution for each dataset, we find that neither the dipole tilt nor Bₓ plays a major role for the TPA conjugacy in four of the five datasets. The well-known correlation between initial TPA location and IMF B_y appears in all datasets with information about the TPA formation. In addition, we find that a minority of dawnside TPAs form during the “wrong” B_y sign. In the northern (southern) hemisphere, dawn TPAs appear also during weakly duskward (dawnward) IMF. Due to the polar orbit of DMSP satellites, TPA conjugacy and location can be examined on a case-by-case basis with the new dataset. The results show that at least 73% of TPAs appear in both hemispheres simultaneously. IMF Bₓ and dipole tilt values for conjugate TPAs do not differ from those for non-conjugate TPAs. Most conjugate (isolated) TPAs appear on opposite oval sides in each hemisphere (57%). Interestingly, in case northern and southern hemisphere TPAs form on the same oval side, they appear typically at dawn during weak IMF B_y.