The SAPPHIRE‐North radar experiment: Observations of discrete and diffuse echoes

Abstract

Since February 1995, regular observations have been carried out by the University of Saskatchewan radar group using a new 50‐MHz Doppler radar system called SAPPHIRE‐North. The SAPPHIRE‐North radar monitors the ionospheric processes in the transitional region between the auroral oval and the polar cap over Cambridge Bay, Northwest Territories. In this paper, results of the first 2 months of observations are presented. Echoes were registered at about 10% of observational time. Diurnal echo occurrence exhibited two distinct maxima, one close to noon and another prior to midnight. The noon echoes were usually of a diffuse type, while midnight echoes were of a discrete type. Midnight discrete echoes were found to be associated with an arrival of poleward expanding substorm bulges into the SAPPHIRE‐North field of view. Noon diffuse echoes were most likely due to electric field enhancements in the vicinity of the cusp/cleft region. Salient spectral features of both the diffuse and discrete echoes are presented and compared with auroral zone results. The role of ionospheric refraction for observations of these high‐latitude echoes is discussed.