Enhanced ion acoustic fluctuations and ion outflows

[摘要] A number of observations showing enhanced ionacoustic echoes observed by means of incoherent scatter radars have beenreported in the literature. The received power is extremely enhanced by up to 1or 2 orders of magnitude above usual values, and it is mostly contained in oneof the two ion acoustic lines. This spectral asymmetry and the intensity of thereceived signal cannot be resolved by the standard analysis procedure and oftencauses its failure. As a result, and in spite of a very clear spectralsignature, the analysis is unable to fit the plasma parameters inside theregions of ion acoustic turbulence. We present European Incoherent Scatter radar(EISCAT) observations of large ion outflows associated with the simultaneousoccurrence of enhanced ion acoustic echoes. The ion fluxes can reach 10¹⁴m^-2 s^-1 at 800 km altitude. From the very clear spectralsignatures of these echoes, a method is presented to extract estimates of theelectron temperature and the ion drift within the turbulent regions. It is shownthat the electron gas is strongly heated up to 11 000 K. Also electrontemperature gradients of about 0.02 K/m exist. Finally, the estimates of theelectron temperature and of the ion drift are used to study the possibleimplications for the plasma transport inside turbulent regions. It is shown thatstrong electron temperature gradients cause enhancement of the ambipolarelectric field and can account for the observed ion outflows.

Key words. Ionosphere (auroral ionosphere; ionosphere· magnetosphere interactions; plasma waves and instabilities).

[学科分类] 地球科学(综合)