Studies of the Conductivities in the Auroral Zone Ionosphere

Abstract

A review of some recent studies by EISCAT of the conductivities in the auroral zone ionosphere is presented. The quiet time Hall and Pedersen conductivities appear to vary smoothly with the solar zenith angle in agreement with a photochemical equilibrium state of the ionospheric plasma. During auroral particle precipitation events the conductivities are strongly enhanced at night time with respect to the quiet time conditions. For strongly disturbed conditions large increases in the conductivities due to particle precipitation are also observed at daytime.
A computer code, CARD, has been developed to deconvolve the observed electron density profiles during precipitation events into energy spectra of the precipitating particles. At night time when no solar background ionization is present the characteristic (root mean square) energy of the particles is found to be less than 20keV. At daytime, however, this energy is typically between 20 and 30keV.
The altitude dependence of the Joule heating rate and the Pedersen conductivity are compared. Differences are found which indicate that the effective Joule heating rate per neutral particle is at maximum above the peak in the Pedersen conductivity, i. e. above 130km on the average.