Some Characteristics of Non-Two-Stream Irregularities in the Equatorial Electrojet

Abstract

The analysis of VHF radar echoes from electron density irregularities in the equatorial electrojet indicate that there are two distinct types of irregularities in the region. One of these has previously been shown to be generated by the two-stream instability mechanism and consists of planar irregularities which travel at the ion-acoustic velocity. The other type of irregularity moves at about the electron drift velocity, and can exist when the electron drift velocity is insufficient to produce the two-stream type irregularities. Drift observations of this second type of irregularity show that the electrojet current reverses during nighttime periods, the electron drift velocity being comparable to that during the day. Additional observations show that these irregularities exist in large patches which move with the same approximate velocity and retain their identity for many seconds.