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High Altitude Echoes From the Equatorial Topside Ionosphere During Solar Minimum
Author(s) -
Derghazarian S.,
Hysell D. L.,
Kuyeng K.,
Milla M. A.
Publication year - 2021
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2020ja028424
Subject(s) - ionosphere , physics , doppler effect , radar , backscatter (email) , f region , altitude (triangle) , optics , lower hybrid oscillation , pulse (music) , computational physics , geophysics , electromagnetic radiation , astronomy , telecommunications , detector , geometry , mathematics , electromagnetic electron wave , computer science , wireless
We 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.