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.

plasma drift velocities, assuming pure Exff drift. The dash-dotted curves are equipotential contours drawn to fit the electric fields. The numbers at the full contours indicate the potential in kV with respect to the potential at the EISCAT position A. At the equatorward edge of the precipitation region the electric field vectors point to a "negative charge center". A "positive charge center" seems to be located at the poleward edge. The plotted EISCAT results are the averages over the dwelltime of 150 s at each position. Evaluation of the EISCAT data with higher time resolution, however, does not significantly change the results, thus the displayed overall field configuration is steady and is not a cut through a rotating large scale electric field as has been observed during Pi2 events (Glassmeier,1980; Pashin et al.,1982). FLIGHT TIME Isl Pig. 4. Spectral power density variation of the electric field fluctuations parallel Вversus flight time during the active period south of the precipitation region (see Fig.1, bottom panel). South of the precipitation region electrostatic fluctuations are observed between about 200 s and 450 s flight time. Figure 4 gives an impression of the spectral power density of these signals. The traces represent the squared Fourier transforms of the electric field parallel to S’(as in F i g . 1 , bottom panel) during one spin period from consecutive spins and are estimates of the spectral power density. The activity varies as also can be seen in Figure 1 with a m a ximum between 300 s and 350 s and a minimum around 280 s flight time. The signals are short lifing, i.e. they last shorter than one spin period of O .6 5 s because individual spectra vary from one spin period to the other, even during the period of maximum activity. After 380 s flight time there are a few isol ated events. The electric field components perpendicular to 51 show the same frequency dependence and time history but are much smaller. Assuming that these signals are waveforms of electrostatic ion cyclotron (EIC) waves they are predominantly polarized and propagating parallel to S'. The spectral power is concentrated at about 20 Hz which is about the cyclotron frequency of H0+ or Og or half the cyclotron frequency of 0 + the dominant ion at these ionospheric heights. Fig. 5 gives examples of the observed ac electric field component parallel to 5 of five consecutive spin periods out of four intervals. There is no indication that these signals are related to a certain spin phase which would probably be the case if they were due to any interaction of the payload with the ambient plasma. Individual waveforms last for about 0.1 s, this corresponds to a travel distance of the payload of about 60 m transverse to the Earth magnetic field. (The payload transverse velocity at theee altitudes is about 600 m s~^.) 92