Dayside Polar Cap Aurora and Their Connection to NBZ Currents

Abstract During northward interplanetary magnetic field (IMF) conditions, magnetic reconnection between the Earth's magnetosphere and the IMF takes place on high latitudes, causing the auroral oval to contract. During those times several auroral structures may appear inside the polar cap, such as cusp aurora, high latitude dayside aurora (HiLDA) and transpolar auroral arcs. Concurrently, a field‐aligned current system appears in the dayside polar cap, called Northward B z (NBZ) currents. In this work, we use Defense Meteorological Satellite Program images and particle data, as well as Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) global field‐aligned current maps in order to investigate the connection between dayside polar cap aurora and NBZ currents. We analyze 10 events during northward IMF for different IMF B y and dipole tilts, the majority of which are taken from the companion paper by Kullen et al. (2026, https://doi.org/10.1029/2026JA035276 ). We observe that when cusp aurora occurs in the middle of the polar cap, electron aurora consistently appears dawnward of the cusp aurora. The extent of the dawnside expansion depends on the IMF clock angle. This dawnside electron aurora region overlaps in all cases with the upward NBZ current region measured by AMPERE, but may appear as broadband, discrete arcs or HiLDA. This shows that electron aurora occurring dawnward of the cusp during northward IMF is a signature of the upward NBZ currents.