East-west asymmetries of the equatorial electrojet 8.3 m type-2 echoes observed over Trivandrum and a possible explanation

Abstract

The east-west asymmetries in the spectral parameters of the type-2 echoes from the equatorial electrojet plasma irregularities observed using a 18 MHz radar from Trivandrum are presented. Observations show that the difference in signal strength, velocity, and spectral width of the type-2 echoes observed in the west and east beam are as high as 15 dB, 60 m s^-1, and 70 m s^-1, respectively. Further, the asymmetry in velocity increases with height, while the asymmetries in signal strength and spectral width decrease with height. While the velocity asymmetry is consistent with the past results, the asymmetries in signal strength and spectral width of the type-2 echoes are significant new results, not reported earlier. Finite vertical drift velocities of the irregularities, associated with the primary wave structures, are found to be responsible for the observed east-west velocity asymmetry. The asymmetries in signal strength and spectral width are attributed to the orientation of kilometer-scale plasma waves present in the equatorial electrojet. Finally, a unified picture is presented to show that the properties of the kilometer-scale waves are the ones that are responsible for all three asymmetries observed in the spectral parameters of the type-2 echoes.