The Auroral Current and Electrodynamics Structure (ACES) mission consisted of two sounding rockets launched nearly simultaneously from Poker Flat Research Range, AK on January 29, 2009 into a dynamic multiple-arc aurora. The ACES rocket mission, in conjunction with the PFISR Radar, was designed to observe the three-dimensional current system of a stable auroral arc system. ACES utilized two well-instrumented payloads flown along very similar magnetic field footprints, at various altitudes with small temporal separation between both payloads. ACES High, the higher altitude payload (apogee 360 km), took in-situ measurements of the plasma parameters above the current closure region that provide the input signature into the lower ionosphere. ACES Low, the low-altitude payload (apogee 130 km), took similar observations within the current closure region, where cross-field currents can flow. Results are presented of observations of the electric fields, magnetic fields, electron flux, and currents derived from magnetometer data for times when the payloads were nearly magnetically conjugate. In situ data is compared to ground based all-sky imager data, which recorded the evolution of the auroral event as the payloads traversed through magnetically conjugate regions.
The effects of ionospheric collisionality are examined and presented as a possible explanation for differences in observations of the low energy electron flux between ACES High and ACES Low. ACES Low further observed promising signatures in the magnetometer data that are consistent with cross-field closure current. Results are presented detailing the development of a 2-D current closure model to assist with the interpretation of the magnetometer observations. A model describing the evolution of precipitating magnetospheric electrons into the auroral ionosphere was fit to data from the ACES Low payload. The resulting model electron flux for this event was then used to calculate the height ionization profiles, electron density, and Hall and Pedersen conductivities.