Parametric decay of beam-driven Langmuir wave and enhanced ion-acoustic fluctuations in the ionosphere: a weak turbulence approach

Abstract

Abstract. We present a model that describes the decay of beam generated Langmuir waves into ion-acoustic waves in the topside ionosphere. This calculation is done within the frame of the weak turbulence approximation. We study the spectral signature of such a process as seen by a VHF incoherent scatter radar. An incoherent scatter (IS) spectrum is characterized by two maxima at k r d r and Àk r d r , the right and left ion lines respectively. It is shown that, for reasonable beam parameters, the parametric decay of beam-generated Langmuir waves can enhance either the right, the left or both ion lines simultaneously. The shape of the spectrum can change drastically on time scale of about 0.1 to 1 s. The role of the beam parameter as well as the ionospheric parameters is also investigated. For a given beam number density, the beam energy or the background density are important to trigger either the left or the right ion line. A large energy spread of the beam or low electron collision frequencies can explain the simultaneous observations of the left and the right ion line. The importance of the electron collision frequency can explain the altitude distribution of the coherent echoes observed by incoherent scatter radars.

Enhanced EISCAT UHF backscatter during high-energy auroral electron precipitation

“…Rietveld et al, 1991;Forme, 1999;Sedgemore-Schulthess and St. Maurice, 2001;Isham et al, 2012). Another model recently proposed by Ekeberg et al (2010) describes NEIAL observations from limited-altitude regions with almost flat ion line spectra, i.e.…”

Nonlinear beam generated plasma waves as a source for enhanced plasma and ion acoustic lines

“…8,9 An electron beam can enhance electron plasma waves (Langmuir waves) significantly above the thermal level, and then ion acoustic waves can be excited by parametric decay of these waves. This latter model was invoked in other studies 10,11 and has gained confidence by several works. 1,4,12 Consistent with the basic features of these proposed models, observations of simultaneously enhanced levels of ion, and electron plasma waves have been reported.…”

Incoherent scatter ion line enhancements and auroral arc-induced Kelvin–Helmholtz turbulence

“…The three main theories of classical NEIAL generation are the ion-electron ( [Foster et al, 1988;Collis et al, 1991;Rietveld et al, 1991]) and ion-ion ( [Wahlund et al, 1992a]) two-stream instabilities and parametric decay of Langmuir waves ( [Forme, 1993[Forme, , 1999). …”