High resolution soundings of equatorial upper E-region echoes at Jicamarca exhibit gravity wave modulated signal intensity distributions and Doppler velocities corresponding to vertical plasma drifts. A gravity wave wind driven interchange instability is suggested as a possible generation mechanism of the field-aligned plasma irregularities responsible for the echoes. The echoes may be utilized in gravity wave studies and in zonal electric field measurements by radars with modest sensitivities. ¿ American Geophysical Union 1993