Структура и динамика полярных токовых систем : материалы международного симпозиума «Полярные геомагнитные явления», 25-31 мая, Суздаль, СССР / Акад. наук СССР, Кол. фил. им. С. М. Кирова, Поляр. геофиз. ин-т. – Апатиты : [б. и.], 1988.

This discrepancy can Ъе explained Ъу field-aligned potential drops in the precipitation region associated with the inverted-V-event. Such field- aligned electric fields are assumed to be essential for the inverted-V acceler ation mechanism, however, these fields are usually thought to exist in much higher altitudes (Akasofu,1981; Mozer et al.,1980). Figure 6 sketches such V-shaped equipotential contours in the precipitation region which would reduce the electric fields in the lower ionosphere. The field-aligned potential drop between the trajectory and the ionospheric E-region could be of the o r d e r of 300 V, which would correspond to a field-aligned electric field of less than 1 mV/m”^. A host of plasma instabilities can be generated in the disturbed polar ionosphere (Bering,1983; Gurnett and Frank,1977). Destabilized electrostatic ion cyclotron (EIC) waves mainly have frequencies slightly above the cyclotron frequency of the dominant ion which is 0 + at the altitude with f^ 38 Hz and propagate primarily perpendicular to (Kindel and Kennel,1971). The observed wave fields have lower frequencies, are polarized predominantly parallel to Б and thus propagate in this direction. Furthermore the signals are very localized as indicated by the isolated events near 400 s flight time (Fig.5). Yamada et al.(1977) have reported on EIC waves destabilized by ion beams injected into a Maxwellian plasma parallel to a confining magnetic field. This "resonant cyclotjm-cyclotron made" has properties like the observed fluctuations* The frequency may be аз low as half the cyclotron frequency of the beam ions depending on the ratio beam velocity u^ to the thermal velocity vth ^ ie ambient ions. The waves are confined to the interior of the beam and have phase velocities slightly below the beam velocity. After Yamada et al. (1977) it would be sufficient to accelerate ionosph eric ions (0+ , N0+ ) to about four timaa their thermal velocity to generate the observed waves. The thei-mal velocity of 0+ ions of 1800 К (as measured by EISCAT) is about 1400 m s-1 and corresponds to an energy of about .1 eV. Thus the required energy of the beam ions is only of the order of 1 eV. Such localized ion beams or field-aligned currents carried by ionospheric ions can be caused by the high electric field perpendicular to IT (Ex ~ 50 m V m ~ 1 ) together with localized gradients in the ionospheric conductivity because of the locally varying flux of precipitating electrons as seen by the particle spectrometer. Thermal ion flow (Bering et al.,1975) and also energetic upstreaming ions (Kintner et al.j1979) have already been observed by satellites. R E F E R E N C E S ! Akasofu S.I. Auroral arcs and auroral potential structure. In: Physics of auroral arc formation. - Geophys.Monogr., 25, 1, 1981. Bering E.A., Kelley M.C., Mozer F.C. Observations of an intense field- aligned thermal ion flow and associated intense narrow band electric field oscillations. - J.Geophys.Res., 180, 4612, 1975. Bering E.A. Apparent electrostatic ion cyclotron waves in the diffuse aurora. - Geophys.Res.Lett., 10, 647 , 1983. Glassmeier K.-H. Magnetometer array observations of a «iant nulsatinn event. - J.Geophys., 48, 127, 1980. ^ “ Gurnett D.A., Frank L.A. A region of intense plasma wave turbulence in auroral field lines. - J.Geophys.Res., 82, 1031, 1977. Kindel J.M., Kennel C.F. Topside current instabilities. - J.GeoDhvs Rea 76, 3055, 1971. •ueopnya.iiee. , 94