Resonance region of a PC5 micropulsation examined by a dual auroral radar system

Abstract

SINCE January 1977 a new radar auroral backscatter facility, STARE—Scandinavian Twin Auroral Radar Experiment—has been in operation in northern Scandinavia. It consists of two multibeam radars that are sensitive to electrostatic ion waves (irregularities) produced in association with current in the auroral zone E region. The radars measure the intensity and Doppler velocity of irregularities within a 200,000 km2 common area. The measurements are made with an effective spatial resolution of approximately 20×20 km2 and a temporal resolution of 20 s. From the Doppler velocity data it is possible to determine the mean irregularity drift velocity field within the common area. It has been shown1 that this mean velocity is approximately equal to the electron drift velocity which, in the E region, is given by E×B /B2. Because of the spatial and temporal resolution of the STARE system, it is well suited for the study of ionospheric electric fields associated with PC5 geomagnetic pulsations (period 150–600 s). Here we present the first results of the analysis of such an event which occurred between 1230 and 1300 UT (∼1500–1530 MLT) on 2 February 1977. This event is typical of one class of PC5 events that we are studying. The magnetic data used in the study come from one of a chain of high precision rubidium vapour magnetometers designed for geomagnetic pulsation research. These have been operated in Scandinavia since October 1976 by the Institute of Geological Sciences as part of its participation in the IMS. These instruments have an essentially flat frequency response and a noise level typically⩽0.1 nT. The magnetic variations in three orthogonal directions (magnetic NE, NW, and Z) are sampled at 2.5-s intervals with a daytime resolution of 0.08 nT and digitally recorded on magnetic tape cassettes.