Evaluation of energy parameters of auroral electrons by using photometric observations and its application to investigate a generation mechanism

Abstract

The relations between average energy and total energy flux of incident electrons are examined for three types of auroras, namely, type A aurora, pulsating aurora, and discrete aurora in auroral break up. The energy parameters of primary electrons are derived by using measured intensities at 844.6nm (OI) and 670.5nm (N_21PG) from a multi-channel photometer observation at Syowa Station, Antarctica, in 1990. It is shown that each auroral type has its own relationship between energy parameters of precipitating electrons. In a discrete aurora, downward electron energy flux generally varied proportionally with square of average energy. This tendency can be identified as an ohmic-like feature. This special relation is accounted for by a theory in which electrons are accelerated by a field-aligned-potential difference. We also found that in some discrete auroras, precipitating electrons did not show the ohmic-like behavior. These exceptional cases are thought to be caused by two factors. One is a geometric relation between auroral arcs and the field of view of the photometer. The other is the change of the L-E-L constant in the magnetosphere (M. FRIDMAN and J. LEMAIRE; J. Geophys. Res., 85,664,1980) due to temporal variations of plasma parameters, such as electron density and thermal energy in the source region of the auroral particles.