East-west asymmetry in type-2 echoes and enhanced electron drift in the equatorial electrojet

Abstract

Simultaneous measurements of type-2 echoes in the equatorial electrojet (EEJ) and the 150 km echoes were made with a tri-beam radar on Pohnpei (Federated States of Micronesia). Using the mean Doppler velocity (〈VD〉) to estimate the line-of-sight component of electron drift velocity (), we show that its vertical component (Vez) increases with altitude and exceeds Vez measured at 150 km, between 96 and 103 km. At 103 km, the ratio of vertical 〈VD〉 to Vez at 150 km was five. This enhancement explains the hitherto puzzling east-west asymmetry in 〈VD〉 of type-2 echoes. More importantly, we show how the enhanced Vez appears to be associated with the discrepancy in the altitude of peak current density of the EEJ, between measurement and model. We discuss roles played by kilometer-scale irregularities and close by describing apparent effects by atmospheric gravity waves.