On the Solstice Maxima and Azimuth‐Dependent Characteristics of the 150‐km Echoes Observed Using the Equatorial Atmosphere Radar

Abstract

AbstractWe present long overdue statistical analysis of the 150‐km echoes based on 10 years of observations made using the Equatorial Atmosphere Radar located at Kototabang, Indonesia. Analysis shows that while the basic features of the echoes are very similar to those observed from other equatorial/low‐latitude stations, occurrence and power/signal‐to‐noise ratio of the echoes are much higher in the solstices than in the equinoxes. Furthermore, both occurrence rate and power/signal‐to‐noise ratio of the echoes in the December solstice are marginally lower than those of the June solstice. The observed solstice‐equinox asymmetry has important implications with regard to the generation mechanism of the 150‐km echoes since this seasonal behavior cannot be accounted for by the recently proposed photoelectron‐induced enhanced plasma wave process alone. Equatorial Atmosphere Radar observations also display remarkable azimuthal variations of the echo characteristics, which indicate magnetic aspect angle dependence of the echoes. The implications of these results are discussed in terms of the origin of the 150‐km echoes.