Some ideas concerning the problem of anomalous polar E region heating due to Farley‐Buneman turbulence

Abstract

The energetics of the excitation of the Farley-Buneman instability is considered, which is recently observed in the auroral and equatorial E regions of the Earth's ionosphere at altitudes between 100 km and 120 km. In the magnetic field of the Earth the Farley-Buneman instability is excited under the condition of a strong enough external electric field in the case of ion-neutral collisions with frequencies much larger than the ion gyrofrequency and electron-neutral collisions with frequencies much below the electron gyrofrequency. I t is shown that the linear increase of the wave amplitudes is caused by a small disbalance between the processes of nonlinear energy pumping into the wave from an external electric field and the energy loss because of the collisions of the electrons and ions with the neutral particles. During the nonlinear energy pumping energy of the external electric field is transferred into a nonlinear current of second order, which is connected with the oscillating motion of the electrons in the wave. The oscillating electron motion takes place perpendicular to wave propagation. From the estimations follows that the energy pumped into a Farley-Buneman wave during one period of pulsation is much larger than the wave energy itself. A new and simply to understand derivation of the anomalous diffusion coefficient is presented, related to the study of the behaviour of a test wave with frequency much above the frequencies of the Farley-Buneman wave in the turbulent region. Taking the anomalous diffusion into account, it is shown that the Farley-Buneman turbulence in developed stage can cause an additional macroscopic nonlinear Pedersen current directed along the external electric field. It is found that the nonlinear Pedersen current can reach the order of the usual Pedersen current and should contribute to the effective heating of the ionospheric plasma.Key words: Farley-Buneman turbulence -nonlinear Pedersen current -plasma heating A A A subject classification: 083, 084 IntroductionCoherent very high-frequency scatter radars are widely used in monitoring the ionospheric electric field. However, coherent E region radars do not measure the electric field directly, but rather the spectral properties of plasma waves becoming unstable under the action of the electric field. In order to estimate the electric field inside the radar scattering volume, one has therefore quantitatively to know what kind of waves will develop under the given electric field conditions. The type of the generated waves will also depend on the plasma parameters such as the ion-neutral and electron-neutral collision frequencies and the large-scale electron density gradients. Farley (1963) and Buneman (1963) showed that the plasma is unstable against a specific type of modified twostream instability, later called the Farley-Buneman instability, if the ambient electric Field is strong enough. There are many factors affecting the growth rate of the waves. The main trend is that the larger the mean relative electron-ion velocity -col is...

Effect of electrojet irregularities on DC current flow

“…Through this interaction a mechanism for the saturation of the turbulence in the electrojet is created which is not locally controlled as is usually assumed [St.-Maurice, 1990;Janhunen, 1994;Oppenheim et al, 1996], but which depends on the complete current circuit, including the electrojet part and the field aligned magnetospheric currents and their sources. This view has also been convincingly advocated by Liperovsky et al [1996]. The external power input to the turbulent plasma per unit volume in the ionosphere, E 0 Á hji, is dissipated by normal collisional damping of the marginally stable modes making up the turbulent density and velocity fluctuations.…”