RADAR OBSERVATIONS OF THE EQUATORIAL ELECTROJET IRREGULARITIES AND THEORY OF TYPE 1 TURBULENCE.

摘要

In this work we have studied the equatorial electrojet irregularities experimentally and theoretically. The important points here considered can be summarized as follows:;(2) Interferometric studies of the nighttime electrojet. Here we have developed the basic ideas underlying the experiments with the interferometer. This technique allowed us to measure vertical profiles of the electron velocity. Moreover, the improved horizontal resolution achieved with this instrument makes possible a more detailed study of the turbulent characteristics of the irregularities. We have observed that the 'usual' spectra (estimated with one antenna only) are the result of the superposition of more elementary spectra within the scattering volume. We have also observed that the irregularities with small Doppler shifts (< 20 Hz) are usually diffuse while the type 1 waves, for example, are localized in space. The complex structure of the nighttime electrojet is also illustrated by the measurement of reverse (i.e., westward) electron movements. Relevant length and time scales of the plasma processes are discussed.;(3) In an attempt to explain the possibility of nonlinear shifts from the linearly predicted modes for the type 1 waves, we have applied the Direct Interaction Approximation method of Kraichnan to the appropriate fluid equations. The method provides two coupled integral equations relating the intensity of density fluctuations and the nonlinear frequency shift and damping of the unstable waves. For long wavelengths we found that the phase velocity of the type 1 waves is weakly dependent on zenith angle for angles between the k vector and the electron drift velocity smaller than about 60(DEGREES). Moreover, this dependence is also a function of the intensity of the density fluctuations. Our results are discussed under the light or recent experimental observations.;(1) Measurements of the dependence of the cross section of the irregularities with zenith angle (magnetic east-west). For 3m irregularities and for the type 1 irregularities we have found that the cross section has an exponential dependence with zenith angle increasing at a rate of about 0.3 db/degree. The type 2 irregularities, on the other hand, have a constant (independent of zenith angle) cross section. We have also measured absolute values of the cross section and we have estimated total density fluctuation levels for both types of irregularities.