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On the sheet‐like nature of 150 km ( F 1 ) radar echoes
Author(s) -
Tsunoda Roland T.,
Ecklund Warner L.
Publication year - 2008
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2007gl032152
Subject(s) - geology , radar , geophysics , zenith , tilt (camera) , curvature , doppler effect , geodesy , plasma sheet , scattering , physics , optics , plasma , geometry , magnetosphere , astronomy , telecommunications , mathematics , quantum mechanics , computer science
The so‐called 150 km (or F 1 ) echoes are shown to arise from field‐aligned irregularities (FAI) that are embedded in a sheet‐like region. Using a 49.92 MHz radar on Christmas Island, which has an antenna beam directed toward geographic east at a zenith angle of 29.5°, high‐resolution Doppler‐velocity variations within the radar scattering volume are used to infer that the sheet‐like region could have both tilt and curvature. This finding is used to infer that plasma density ( N ) must be enhanced within the sheet‐like region, and that FAI could be generated by an interchange instability, driven by a vertical electric field or a zonal neutral wind that acts on the horizontal component of the gradient in N . How tilted sheet‐like structures could form in the F 1 region is discussed.