Ionospheric electric field estimates from radar observations of the equatorial electrojet

Estimates of the zonal ionospheric electric field have been made on the basis of JULIA radar observations of the equatorial electrojet at Jicamarca. Two observing techniques were used and their merits compared. One technique (here referred to as the “oblique” technique) made use of a new, small antenna array with a broad beam in the equatorial plane. Electric fields were estimated from the Doppler shifts of type II radar echoes at low elevation angles as a function of range in the manner of Balsley [1969a]. For the other technique the main Jicamarca antenna array was used, and interferometry was employed to measure altitude profiles of the phase speeds of intermediate-scale primary gradient drift waves in the electrojet directly overhead. Electric fields were inferred from these profiles following a modeling approach similar to the one described by Murthy and Ravindran [1994], Zonal ionospheric electric field measurements comparable to seasonal average incoherent scatter radar measurements were obtained using both methods. However, the interferometric observations reveal the presence of intense waves and jets in the zonal neutral wind similar to what has been seen in recent chemical release sounding rocket experiments. Zonal winds mainly control the zonal phase speeds of the primary gradient drift waves in the late afternoon and evening. Although the prereversal enhancement of the zonal electric field is evident in data from the oblique technique, there is no evidence of it in measurements derived from the interferometric technique.