Diurnal radio aurora variations at 50 Mhz measured by the bistatic auroral radar system radars

Abstract

Mean Doppler velocity and intensity data obtained from the normal operating mode (alternating single pulse/double pulse mode as also used by STARE) of the BARS radars from selected intervals between March 1986 and July 1987 have been used to describe typical morphological characteristics and diurnal variations in the backscatter. Comparisons with the MARIA magnetometers at Gillam and Eskimo Point verify that the BARS drift velocities obtained by “standard” merging (for which one assumes that the radar Doppler shifts depend on the cosine of the angle between the electron Hall drift and the radar look direction) are in qualitative agreement with the equivalent currents. Three basic time intervals could be identified: (1) an evening interval between 2100 and 0200 UT (1500 to 2000 MLT) with westward E×B drift, which occurs only under disturbed conditions, and for which the Nipawin backscatter intensity is very low most of the time; (2) a breakup interval (dominated by eastward drift but including westward turnings) which under disturbed conditions can extend from 0200 to 1000 UT (2000 to 0400 MLT), but which occurs even under relatively quiet conditions when no backscatter precedes or follows it, in which case it lasts about 2 hours around 0600 UT; (3) an interval with oscillations around a mainly eastward drift; backscatter in this interval does not seem to depend on the occurrence of the previous two types and lasts from 1000 up to 1500 UT (0400 to 0900 MLT). No backscatter has yet been measured during the rest of the day (1500 to 2100 UT or 0900 to 1500 MLT). The period from 2130 UT, May 28, to 1430 UT, May 29, 1987, is used as a sample day during which all three backscatter types occurred.