A puzzling feature of the Earth’s equatorial upper atmosphere is the occurrence of enhanced VHF radar echoes near 150-km altitude. These so-called 150-km echoes have been observed for over 50-years, and occur nearly every day, making them a persistent feature of the equatorial ionosphere.

(a) JRO observed signal to noise ratio (SNR) during the September 7, 2005 solar flare. White areas indicate time periods without observations.
(b) Electron densities simulated by WACCM-X at the location of Jicamarca, Peru.
(c) Observed GOES x-ray flux for 0.1-0.8 nm.
The results show the close correspondence between the observed 150-km echoes and WACCM-X simulated electron densities during the solar flare.

However, the source of the echoes remains unknown. We present observational and modeling results of the response of the 150-km echoes and ionosphere electron densities to a solar flare that occurred on September 7, 2005. Similar rapid descent during the solar flare, and gradual ascent following the flare is seen in both the observed 150-km echoes and simulated electron densities. This result provides evidence for the connection between structures in the 150-km echoes and background ionosphere electron densities, providing insight into the formation mechanism of the 150-km echoes.

Publication Name: Geophysical Research Letters
First HAO Author's Name: Nick Pedatella