Closure of Field-Aligned Current Associated with a Discrete Auroral Arc

The Auroral Current and Electrodynamics Structure (ACES) mission consisted of two sounding rockets launched nearly simultaneously into a dynamic multiple-arc aurora with the goal of obtaining multi-point observations of the closure of field-aligned current associated with a discrete auroral arc. The payloads were flown along nearly conjugate magnetic field footpoints, separated in altitude with small temporal separation. The high altitude payload (ACES High) took in situ measurements of plasma and electrodynamic parameters that mapped from the magnetosphere that form the input signature into the lower ionosphere. The low-altitude payload (ACES Low) took similar observations within the region where perpendicular cross-field closure current can flow. A case study is presented of a quasi-stable auroral arc crossing, and in situ electron flux, electric field, and magnetic field observations for this event are presented. Poker Flat Incoherent Scatter Radar (PFISR) observations of the electron densities and electric fields are compared with the in-situ observations. A steady-state 2-D model of auroral electrodynamics has been developed to interpret the in-situ data and has been further constrained using PFISR data. A model describing the precipitating auroral electron flux has been developed and the model parameters were adjusted to be consistent with the electron flux observed by the ACES Low payload. The enhanced Hall and Pedersen conductivities resulting from the auroral precipitation are calculated, along with other relevant parameters. For the condition that the divergence of the current is equal to zero within the arc, the perpendicular current structure is determined using in situ electric fields and field-aligned currents as model inputs. The magnetic field perturbations from the modeled currents are compared with the in-situ observations of the residual magnetic field observed by both payloads. Multi-point in-situ data, ground-based data, and modeling are used to investigate the current structure and energy dissipation associated with a discrete auroral arc