Derghazarian, S.Hysell, D. L.Kuyeng, K.Milla, Marco2021-06-302021-06-302021-02Derghazarian, S., Hysell, D. L., Kuyeng, K., & Milla, M. A. (2021). High altitude echoes from the equatorial topside ionosphere during solar minimum.==$Journal of Geophysical Research: Space Physics, 126$==(2), e2020JA028424. https://doi.org/10.1029/2020JA028424index-oti2018http://hdl.handle.net/20.500.12816/4953We describe a new class of nonthermal plasma density irregularities observed in the postmidnight topside equatorial ionosphere under low solar flux conditions. They are distinct from irregularities associated with equatorial spread F (ESF) in terms of their morphology and because they exhibit strong spectral sidebands at the lower-hybrid frequency. The coherent echoes were observed in a series high-altitude radar experiments performed at Jicamarca utilizing long- and coded double-pulse modes and a dual-beam mode. The coded double-pulse mode was used to measure the low-frequency characteristics of the echoes with fine range resolution. Doppler shifts of the main backscatter line were observed to fall between ±150 m/s. The long-pulse mode was employed for high-frequency spectral analysis which revealed the presence of strong spectral sidelobes at the lower-hybrid frequency. A dual-beam mode was used to investigate the horizontal structure of the echoes. Zonal drift speeds of 50–70 m/s were inferred with this mode, and longitudinal dimensions of approximately 270 km were estimated. The study summarizes with a discussion of different mechanisms that may be responsible for the phenomenon and the lower-hybrid sidebands in particular.application/pdfenginfo:eu-repo/semantics/closedAccessEchoes at low solar fluxHigh altitude echoesLower hybrid wavesPlasmaspheric echoesinfo:eu-repo/semantics/articlehttps://purl.org/pe-repo/ocde/ford#1.05.01Journal of Geophysical Research: Space Physicshttps://doi.org/10.1029/2020JA028424