Climatology of equatorial UHF coherent backscatter F-region radar echoes determined from AMISR-14 measurements at the Jicamarca Radio Observatory

Equatorial ionospheric irregularities at meter scale sizes have been extensively studied using Very High Frequency (VHF) radar systems at the Jicamarca Radio Observatory (JRO). The deployment and later repair of the 14-panel version of the Advanced Modular Incoherent Scatter Radar (AMISR-14) at the JRO provided an opportunity for Ultra High Frequency (UHF) coherent backscatter radar studies of equatorial ionospheric irregularities at sub-meter scale sizes.
Repairs of AMISR-14 were completed in July 2021 and semi-routine measurements of the F-region have been made with the system since then. Here, we present results of an analysis of measurements made between July 2021 and January 2023. More specifically, we present occurrence rates of quiet-time F-region echoes as a function of local time and height for different seasons and solar flux conditions. The occurrence rates were generated with AMISR-14 Range-Time-Intensity (RTI) maps.
Our results show seasonal occurrence rates of UHF echoes that are in good agreement with expectations based on equatorial spread-F (ESF) occurrence for the Peruvian sector. Perhaps more importantly, we found that a change of about 50 SFU units produced a drastic change in the height variation of UHF echoes. We also present and discuss occurrence rates generated with RTI maps from the collocated VHF Jicamarca radar (JULIA) for comparison with AMISR-14 occurrence rates.