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The Solar Flux Dependence of Ionospheric 150 km Radar Echoes and Implications
Author(s) -
Patra A. K.,
Pavan Chaitanya P.,
St.Maurice J.P.,
Otsuka Y.,
Yokoyama T.,
Yamamoto M.
Publication year - 2017
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 - 10.1002/2017gl074678
Subject(s) - ionosphere , flux (metallurgy) , radar , physics , extreme ultraviolet lithography , amplitude , geophysics , plasma , atmospheric sciences , computational physics , daytime , astrophysics , optics , materials science , telecommunications , quantum mechanics , computer science , metallurgy
Radar echoes from the daytime equatorial ionospheric F 1 region, popularly known as “150 km echoes,” have challenged ionospheric plasma physicists for several decades. Recent theoretical simulations showed that enhanced photoelectron fluxes can amplify the amplitude of plasma waves, generating spectra similar to those of the radar echoes, implying that larger solar fluxes should produce more frequent and stronger 150 km echoes. Inspired by this proposal, we studied the occurrence and intensity dependence of the echoes on the EUV flux observed by SOHO over several years. The occurrence and intensity of the echoes were found to have an inverse relationship with this EUV flux measurement. The multiyear trend is independent of the variability often observed over successive days with nearly identical EUV fluxes. These results imply that the relationship between the echoes and EUV flux is more complex. We propose that gravity waves modulate the amplitude of 150 km echoes through changes in the variations in plasma density and photoelectron fluxes associated with the gravity wave‐induced neutral density modulations.