SPACE AND TIME DISTRIBUTION OF HF EXCITED LANGMUIR TURBULENCE IN THE IONOSPHERE - COMPARISON OF THEORY AND EXPERIMENT

The predictions of strong Langmuir turbulence (SLT) theory are compare d with radar observations of HF induced turbulence at Arecibo and Trom so. The altitude distribution of turbulence observed in the cold start experiments of Fejer et al. (1991) imply that the ionospheric electro n density profile is modified by the induced turbulence. The precondit ioned observations at Arecibo and the Tromso observations also appear to require a ''disturbed'' profile with several percent density fluctu ations. With such density modifications postulated we conclude that SL T theory is in, at least, qualitative agreement with a large body of o bservations. Specifically SLT theory predicts, as part of a unified th eory, and in distinction to the weak turbulence approximation, at leas t four unique physical signatures which can be compared to observation s: (1.) A caviton continuum plus free mode peak in the plasma line pow er spectrum near reflection altitude for Arecibo conditions. (2.) A tr uncated decay-cascade spectrum at lower altitudes (or densities). (3.) A continuous spectrum underlying the decay-cascade spectrum. (4.) A z ero frequency feature in the ion line power spectrum directly related to caviton dynamics. We find that there is sufficient ponderomotive pr essure due to the Airy-layered, induced Langmuir turbulence, to modify the electron density profile in a manner consistent with the time beh avior of unpreconditioned Arecibo observations.