VIPIR and 50 MHz Radar Studies of Gravity Wave Signatures in 150-km Echoes Observed at Jicamarca

Range-time-intensity (RTI) plots of 50 MHz radar backscatter detected at Jicamarca from the 150-km region of the equatorial ionosphere exhibit necklace-shaped multilayered structures first reported by Kudeki and Fawcett (1993, https://doi.org/10.1029/93GL01256). The backscatter layers also exhibit quasi-periodic intensity fluctuations with periods of about 5–15 min and are separated from adjacent layers by thin and undulating regions of no detectible power returns. A study of the fluctuating backscatter layers and undulating gap regions will be presented using VIPIR ionosonde data taken at the Jicamarca Radio Observatory simultaneously with high-resolution 50-MHz radar backscatter data. VIPIR virtual reflection height variations in time are noted to match the RTI gap-region undulations very closely at selected VIPIR frequencies (or, equivalently, electron densities at reflection heights). This matching enables assigning “true heights” to VIPIR virtual height contour maps, and a joint study of the contour maps with the 50-MHz radar RTI maps strongly suggests that correlated fluctuations and undulations observed in VIPIR and 50-MHz radar data are indicative of gravity wave-induced variations in the 150-km region ionosphere. Accordingly, a complete explanation of the 150-km echo phenomenon will need to include gravity wave coupling and forcing effects in the enhancement and suppression processes that can account for the observed fluctuations and gap-region features of necklace-shaped 150-km echo maps.