The Sao Luis 30 MHz coherent scatter ionospheric radar: System description and initial results

[1] A new 30 MHz coherent scatter ionospheric radar has been operating at the equatorial station at Sao Luis (2.33 degreesS, 44 degreesW, dip latitude 1.3 degreesS), Brazil, since December 2000. This VHF radar has a peak power of only 8 kW but uses long coded pulses and a high PRF with coherent integration to achieve good sensitivity. Two side-by-side square antenna arrays composed of 16 5-element Yagi antennas directed vertically are used for transmission and reception. This radar measures the backscattered signals from E and F region ionospheric irregularities. In the standard operational mode, the irregularity intensity, as well as the vertical and zonal velocities using Doppler analysis and interferometry, respectively, are determined. We initially present a brief description of the radar system, signal characteristics and data processing, followed by some of the initial observations. Electrojet echoes ranged from about 94 to 108 km in altitude with the strongest echoes coming from about 104 km and with an uplift to about 110 km occurring in the late afternoon. Echoes from the valley region ( 150 km echoes) were strong, quasiperiodic with periods of about 10 to 15 minutes, and had the necklace shape observed at others sites. F region bottom-type, bottomside, and topside ( plumes) spread F layers were observed at night. The large-scale topside F region plumes, moving eastward and upward, reached altitudes of about 1,400 km and were preceded by bottom-type layers around 400 km altitude that were moving westward. The characteristics of the echoes were similar to those observed by the JULIA radar at Jicamaca, Peru. However, some differences in the behavior of the echoes between the two sites were noted.