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The observation of HF‐enhanced plasma waves with the EISCAT/UHF‐radar in the presence of strong Landau‐damping
Author(s) -
Frey A.
Publication year - 1986
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/gl013i005p00438
Subject(s) - landau damping , physics , plasma , wave vector , ionosphere , computational physics , plasma oscillation , radar , radio wave , reflection (computer programming) , debye length , atomic physics , optics , geophysics , telecommunications , quantum mechanics , computer science , programming language
It is well known that intense HF‐radiowaves of the ordinary mode transmitted from the ground enhance plasma waves near the reflection height in the ionosphere. These enhancements are observed as an increase in the returned power of radars having a wavevector equal to one half the wavevector of the enhanced plasma waves. It is expected that strong Landau‐damping will suppress such enhancements if kλ D ≃ 0.25 ( k and λ D correspond to the wavevector of the Langmuir wave and the Debye‐length) which was the case for Langmuir‐waves detected by the EISCAT/UHF radar during a recent HF‐modification experiment at Tromsø. Enhanced plasma waves were observed unexpectedly at a low heater frequency of f HF = 2.76 MHz. Enhancements at this frequency were not observed during previous attempts and were believed to be damped too strongly to be observable. The observed power threshold can marginally be matched with theory under the assumption of low but not unreal electron and ion temperatures. The observed spectra indicate that the interaction is more intricate than expected under the given conditions.