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Title: On the factors controlling occurrence of F-region coherent echoes
Authors: Danskin, D. W.
Koustov, A. V.
Ogawa, T.
Nishitani, N.
Nozawa, S.
Milan, S. E.
Lester, M.
Andre, D.
First Published: 30-Sep-2002
Publisher: European Geosciences Union (EGU), Copernicus Publications
Citation: Annales Geophysicae, 20, 1385-1397, 2002
Abstract: Several factors are known to control the HF echo occurrence rate, including electron density distribution in the ionosphere (affecting the propagation path of the radar wave), D-region radio wave absorption, and ionospheric irregularity intensity. In this study, we consider 4 days of CUTLASS Finland radar observations over an area where the EISCAT incoherent scatter radar has continuously monitored ionospheric parameters. We illustrate that for the event under consideration, the D-region absorption was not the major factor affecting the echo appearance. We show that the electron density distribution and the radar frequency selection were much more significant factors. The electron density magnitude affects the echo occurrence in two different ways. For small F-region densities, a minimum value of 1 × 1011 m-3 is required to have sufficient radio wave refraction so that the orthogonality (with the magnetic field lines) condition is met. For too large densities, radio wave strong "over-refraction" leads to the ionospheric echo disappearance. We estimate that the over-refraction is important for densities greater than 4 × 1011 m-3. We also investigated the backscatter power and the electric field magnitude relationship and found no obvious relationship contrary to the expectation that the gradient-drift plasma instability would lead to stronger irregularity intensity/echo power for larger electric fields.
DOI Link: 10.5194/angeo-20-1385-2002
ISSN: 0992-7689
eISSN: 1432-0576
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: © Author(s) 2002. This work is distributed under the Creative Commons Attribution 3.0 License.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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