A rocket-borne investigation of auroral electrodynamics within the auroral-ionosphere

This dissertation focuses on data analyzed from the Auroral Current and Electrodynamics Structure (ACES) sounding rocket mission. ACES consisted of two payloads launched nearly simultaneously in 2009 into a dynamic multiple-arc aurora. The mission was designed to observe the three-dimensional current system of an auroral arc system. To constrain the spatial-temporal ambiguity, the payloads were flown along nearly conjugate magnetic field footpoints, at various altitudes with small temporal separation. The high altitude payload took in situ measurements of the plasma parameters above the current closure region to measure the input signature into the lower ionosphere. The low-altitude payload took similar observations within the current closure region, where perpendicular cross-field currents can flow.

A detailed description of the experimental configuration is presented, including operational details of the fields and plasma instruments flown on both payloads. The methods used to process data from the electrostatic particle detectors and the fluxgate magnetometer on both payloads are presented.

Data from the all-sky imager details the auroral configuration at the time of launch. In situ data are presented detailing observations of the electric fields, magnetic fields, and the electron differential energy flux, as the payloads crossed nearly conjugate magnetic field lines.

Field-aligned currents were calculated from magnetometer observations on the high altitude payload. These data were combined with electron flux data to show that the high altitude payload traversed regions of upward and downward field-aligned current. The low altitude payload observed signatures in the residual magnetic field components consistent with perpendicular closure current. Ionospheric collisionality is investigated to determine if it is a significant mechanism to explain observed differences in the low energy electron flux between the high altitude and low altitude payload. As a result of increased ionospheric collisionality, the ionospheric conductivity is investigated to interpret the in situ electric field observations.

A model of auroral electrodynamics, that is under development, is discussed in the context of interpreting magnetometer data from the low altitude payload. The evolution of precipitating electron flux into the ionosphere and the effect this precipitation has on generating ionization is presented. The electron spectrum produced by the model were fit to the electron flux data observed by the low altitude payload. The height ionization profile, equilibrium electron density, and Hall and Pedersen conductivities were determined from the model electron spectrum incident to the ionosphere. It was shown that the low altitude payload flew just above the peak Hall and Pedersen conductivities, suggesting that the low altitude payload flew directly in the region where perpendicular closure currents were most significant.