Excitation of strong Langmuir turbulence in the ionosphere: Comparison of theory and observations*

Abstract

The predictions of models of strong Langmuir turbulence (SLT) are compared with recent space- and time-resolved radar observations of the power spectra of turbulence induced in the ionosphere by powerful high-frequency (HF) waves. Distinct signatures of caviton dynamics, not predicted by the weak turbulence approximation, are seen in the observations. An improved model of the low-frequency fluctuations for equal electron and ion temperatures is presented as well as a discussion of density profile modification by the induced turbulence.

Geometric aspects of HF driven Langmuir turbulence in the ionosphere

“…Theoretically, a picture emerged DuBois et al, 1993aDuBois et al, , 2001 that cascading was to be expected in most of the height range below the O-mode reflection height, but that near the reflection height, Langmuir cavitation was to be expected. Predictions of radar spectral features resulting from the numerical studies (DuBois et al, 1988(DuBois et al, , 1990Hanssen et al, 1992), were confirmed qualitatively in experiments at Arecibo (Fejer et al, 1991;Sulzer and Fejer, 1994;Cheung et al, 1989Cheung et al, , 1992Cheung et al, , 2001 and later also at Tromsø (Kohl and Rietveld, 1996;Isham et al, 1999b;Rietveld et al, 2000;Djuth et al, 2002), thus, strongly supporting the existence of Langmuir cavitation in these experiments.…”

“…The twodimensional studies of DuBois et al (1990DuBois et al ( , 1991DuBois et al ( , 1993aDuBois et al ( , 2001 were confined to the case where the driving electric field is polarized along the ambient magnetic field, which is relevant for the case of the Arecibo experiments; in the EISCAT experiments other polarizations must also be considered.…”

“…Recent theoretical efforts have been based on numerical solutions to full wave models of the Zakharov type with damping and parametric drive included (Nicholson et al, 1984;DuBois et al, 1990DuBois et al, , 1991Hanssen et al, 1992;Hanssen, 1992;Sprague and Fejer, 1995;DuBois et al, 1993aDuBois et al, , 2001). This allows for the inclusion of phenomena not describable in weak turbulence theory (e.g.…”

Cavitating Langmuir Turbulence in the Terrestrial Aurora

“…In its most developed form, this turbulence contains electron Langmuir modes trapped in dynamic density depressions known as cavitons [14][15][16]. Cavitons have been shown to be artificially produced in the earth's ionosphere during high-power radiowave pumping experiments as deduced from radar spectra containing simultaneously-excited up and downshifted Langmuir and ion-acoustic lines plus a central peak due to cavitation [3][4][5], but evidence of naturally occurring cavitation has until now been elusive.…”

“…Lk, 94.05.Pt, 94.05.Fg, 94.20.wj Langmuir turbulence is known to occur in controlled laboratory [1,2] and space plasma experiments [3][4][5] and is thought to occur naturally in a variety of space and astrophysical plasmas, including pulsar magnetospheres [6], the solar corona [7], the interplanetary medium [8], planetary foreshocks [9], the terrestrial magnetosphere [10], and the ionosphere [11][12][13]. In its most developed form, this turbulence contains electron Langmuir modes trapped in dynamic density depressions known as cavitons [14][15][16]. Cavitons have been shown to be artificially produced in the earth's ionosphere during high-power radiowave pumping experiments as deduced from radar spectra containing simultaneously-excited up and downshifted Langmuir and ion-acoustic lines plus a central peak due to cavitation [3][4][5], but evidence of naturally occurring cavitation has until now been elusive.…”