Coordinated measurements of auroral absorption and luminosity using the narrow beam technique

The correlation of ionospheric absorption with aurora has been examined using photometers and riometers with narrow (∼7°) beam widths. The observations are discussed in terms of three broad categories: Category A describes the occurrence of bright aurora and strong auroral absorption; category B illustrates the occurrence of bright aurora accompanied by negligible absorption; and category C events were those of dim aurora and strong absorption. During the auroral substorm, category A events occur at the midnight meridian, while category B and C events occur in the evening and morning sectors, respectively. Category C events occur coincident with eastward drifting patches and pulsating aurora. The ratio of absorption to the square root of λ5577 intensity [db/(kR)1/2] was derived and used to make inferences concerning the energy spectrum of auroral electrons. The ratio gradually increased between 2300 and 0600 hours local time, implying a gradual hardening of the energy spectrum during this time. Observations of the auroral Hβ emission line showed that proton precipitation correlated poorly with ionospheric absorption. The riometer antenna beam was switched alternately between the 6° north and 6° south positions. The absorption recorded in the two directions was highly correlated. The correlation between auroral luminosity in the corresponding directions was less well correlated. It was concluded that the absorbing region was, at times, larger than the region containing the luminous aurora.