Derivation of Energy Parameters of Precipitating Auroral Electrons by Using the Intensity Ratios of Auroral Emissions

抄録

A high speed multi-channel photometer was operated at Syowa Station in Antarctica in 1990, to derive the energy spectrum ofprecipitating electrons through an intensity comparison of auroral emission lines and bands. The main purpose of this paper is to describe the instrumentation, the method of data analysis and preliminary results obtained by using the multi-channel photometer. Our observations showed that the intensity ratio of 844.6 nm (OI) line and 427.8 nm (N₂⁺ 1PG) band is an useful indicator for an average energy of precipitating electrons, and a preliminary data analysis revealed the following results depending on the stage of auroral activity. i) An intense precipitation (several tens of erg/cm²/sec) of very low energy (about 100 eV) electrons was observed in association with a red aurora (called type-A red aurora) during a magnetic storm. ii) Switching signatures of the average energy as well as the total energy flux were observed for intense auroral pulsations. An auroral pulsation, observed for 630.0 nm (OI) emission line, was associated with a noticeable fluctuation in the average energy of precipitating electrons. iii) During the auroral break-up stage, individual intense arcs are associated with a significant increase of the precipitating electrons' average energy. The auroral lines of short wavelength (such as the 427.8 nm band used in the present observation) suffer from a scattering by the atmosphere, but we overcame this difficulty by measuring also the 670.5 nm (N₂ 1PG) auroral band emission.