Evidence of two types of electron density irregularities in the electrojet over Thumba, India

A coherent backscatter radar has been installed in Thumba, India (8°31′N, 76°57′E and dip 0°47′S), for studying the instability mechanisms responsible for the electron density irregularities in the equatorial electrojet. The power spectra of the radar echoes from these irregularities confirm the results of Cohen and Bowles (1963) and the later classification by Balsley (1967) into type 1 and type 2 irregularities. The spectra of the type 1 irregularities are relatively narrow and are Doppler-shifted by an amount corresponding to the ion acoustic velocity. The type 2 spectra are considerably broader, although the Doppler shift is variable and less than that of the type 1. The similarity of the electron drift velocity over Thumba, India, and Jicamarca, Peru, determined by this method and the dissimilarity between the total electrojet current over these two locations raises a question regarding the spatial structure of the electrojet current and/or of the irregularities themselves