Transpolar Arcs Are Not Always Cusp‐Aligned: Evidence of HiLDA‐Aligned Arcs.

Transpolar arcs (TPAs) are often cusp‐aligned. Especially when multiple TPAs appear simultaneously, they join at the auroral signature of the cusp. Here we investigate the dayside connection point of TPAs using Defense Meteorological Satellite Program measurements and identify three cases where the tip of the TPA ends in a localized brightening. One is a typical cusp spot with a TPA attached. The cusp appears just poleward of the oval with a near circular shape. In the second case, multiple cusp spots are observed over a 3 MLT wide region, each connected to a TPA. In the third case, the brightening at the tip of a TPA is identified as high‐latitude dayside aurora (HiLDA). Cusp aurora appears between the HiLDA and the duskside oval. Plasma flows and particle characteristics indicate a lobe origin of the HiLDA. Our results indicate a more complicated connection between TPAs and dayside aurora than previously anticipated. Plain Language Summary: Transpolar arcs are large‐scale auroral structures that span the polar cap, often connecting the nightside with the dayside part of the auroral oval. In case multiple transpolar arcs appear simultaneously in one hemisphere, they typically join at an auroral intensification on the dayside, which is believed to be the auroral signature of the magnetospheric cusp. In this study, we investigate the dayside region where transpolar arcs connect to auroral intensifications with the help of particle data and semi‐global auroral images from the Defense Meteorological Satellite Program's four satellites (F16, F17, F18, F19) in those cases where the satellites pass right through that region. In this study, we focus on three distinctly different cases. The first two differ in shape, but coincide with cusp aurora, as indicated by strong proton precipitation. The third case consists of arcs connected with a HiLDA (High Latitude Dayside Aurora), which by definition consists of a monoenergetic electron population and a lack of ions. We show for the first time a TPA located in the middle of the polar cap, where the tip of the arc connects with a HiLDA. Key Points: We present three distinct cases of bright dayside oval connection points of transpolar arcs, using DMSP particle data and plasma flowsThe arc connection point is in case I a typical cusp spot, in case II two cusp spots each connected to an arc, and in case III a HiLDAWe show that not only oval‐aligned arcs but also transpolar arcs in the middle of the polar cap can be attached to HiLDA [ABSTRACT FROM AUTHOR]