Electric fields in and around an auroral arc and the inferred current system from the BROR sounding rocket experiment

Abstract. Magnetosphere-ionosphere interactions play a crucial role in the dynamics of near-Earth space, and the electric field in the vicinity of the auroral arc is one of the major links in these interactions. The electric field in the auroral ionosphere has been measured using various techniques: coherent and incoherent radars from the ground, and in situ measurements using rockets and satellites. The effective approach to studying the auroral electric field is to determine it from observations of the motion of artificial ion clouds released into the ionosphere by a sounding rocket. On 23 March 2023, the Barium Radio and Optical Rocket (BROR) experiment was conducted at the Esrange rocket range, near Kiruna, Sweden. In the experiment, 8 canisters containing a barium-strontium-thermite mixture were released at altitudes between 130 and 240 km. A novelty of the experiment is multi-station narrow-band optical observations of emissions with ALIS_4D. This allows us to reconstruct the 3D distribution of optical phenomena in the ionosphere using a tomography-like technique with spatial and temporal resolutions of ∼500 m and 0.1 s, respectively. The active auroral arc developed inside the area occupied by the barium clouds and intersected with the one of clouds at an altitude of ≈230 km for quite a long time. During this time, the ion cloud experienced various deformations, which we observed and used to determine the electric field as a function of position relative to the auroral arc.