A simple model of auroral electrodynamics compared with HILAT measurements

Abstract

Simultaneous measurements of cold plasma drift velocities, magnetic field perturbations, and precipitating electron fluxes with instrumentation on board the HILAT satellite provide an opportunity to correlate Birkeland current densities, electric fields, and ionospheric conductivities in the region of an auroral form. Typical plasma parameters such as ion density, temperature, and composition and electron density and temperature are also available. On July 17, 1983, the satellite crossed the northern auroral zone in the early morning, magnetic local time sector. As the satellite crossed a bright auroral form, recorded by the auroral imager‐mapper, the particle spectrometer detected a 2 orders of magnitude increase in the flux of >10‐keV electrons. The precipitating electrons of this event produced a double inverted‐V structure embedded in the large‐scale, region 2 field‐aligned current sheet. This paper presents calculations of the component of the electric field along the satellite trajectory and perpendicular to the auroral form, given the Birkeland current feeding the auroral form and conductivities derived from particle precipitation data. This electric field component emerges as a solution to the current continuity equation j∥ = −▽ · (Σ · E) in the infinite current sheet approximation with appropriate boundary conditions. Emphasis is placed on accurately representing the Birkeland current density in the region of the bright auroral form. In general, large‐scale features are well represented by the calculations. Although small‐scale features are not well tracked, calculations of the auroral zone potential drop and the height‐integrated Joule heating varied by less than 2% from measured values. During this particular pass the ionospheric Joule heating exceeded the particle energy deposition along the satellite trajectory by a factor of 2.6.