Электродинамические процессы в высоких широтах: материалы междунарордного симпозиума «Полярные геомагнитные явления», 25-31 мая 1986 г., Суздаль, СССР / Междунар. геодез. и геофиз. союз, Междунар. ассоц. геомагнетизма и аэрономии ; Акад. наук СССР, Кол. фил. им. С. М. Кирова, Поляр. геофиз. ин-т ; [редкол.: О. М. Распопов (отв. ред.). и др.]. - Апатиты : Кольский филиал АН СССР, 1988.

luminosity. Drift characteristics, spatial scale, time of duration and repet ition frequency of these structures are observed to be consistent w i t h expec ted optical signatures of plasma entry f r o m the magnetoaheath, associated wi t h flux transfer events (cf.Sandholt et al.,1986b), The January 04. 1984 ca s e . The observations can be separated into three periods with different IMP orientation. These periods are indicated in Pig.6a. Period 1 . The magnetic signature indicates a southward D P Y current wi t h the amplitude modulated by IMP B z (By is constant near -17 nT). The observed D P Y ■signature is interpreted as associated wi t h the m erging convection cell centered in the dawn sector of the polar ionosphere, with a northeastward flow (southeastward electric field) i n the mi d d a y cusp region (cf.Crooker, 1979; Heelis,1984; Reiff and Burch,1985s Ba n k s et al.,1984). The strong red aurora (visual intensity) around 0800 UT indicated a large contribution from thermal excitation associated w i t h enhanced electron temperature at high P-layer altitudes (cf.Roble and R e e s , 1977, their Pigure 5; W ick war and Kofman,1984). Period 2 . The transition i n I M P B z from negative to positive at 0818 UT (By not changing) was followed b y marked changes in the optical aurora and ,the D P Y signatures. The location of the aurora and the PDY perturbation are illustrated in Pig.6b. At 0900 U T the D P Y equivalent current center is loca ted ne a r the poleward boundary of the cusp aurora. This shows that the DPY current extends well into the polar cap fr o m approximately the center of the optical cusp. This is in agreement wi t h Vennerstrom et al,(1984), who found that the equatorward boundary of the DP Y current is located w i t h the latitude of m aximum ionospheric electron temperature, usually associated w i t h the cen ter of the cusp region. The DPY current observed i n time interval 2 is prob ably related to the polar cap lobe cell convection postulated for B z > 0 (cf. Crooker,1979; Le v i t i n et al.,1982; Reiff and B u r c h , 1985) a n d identified by use of the dense ma gnetometer chain al o n g the westcoast of Greenland (Priis- Christensen 1985). The limited extent i n latitude of the magnetic disturbance shown i n Pig.6b reflects a low level of ionospheric conductivity within the dark polar cap. The diffuse aurora observed to the south of B j o m o y a fr o m 09 UT onwards w i t h spectral characteristics indicating ~ 1 k eV particles (cf.Pig.6a) is clearly separated from the cusp aurora. One possible source is the dayside extension of the plasma sheet (cf.Peldstein a n d G a lperin,1985; Uakita et al., 1985). P r o m 0835 UT the poleward boundary of the cusp aurora moves northward during several tens of minutes while IM P B z is ne a r l y stable after the no r t h ward transition at 0818 UT. This time period is comparable w i t h the time for the IMF signal (0818 UT) to re a c h the magnetotail (cf.Akaaofu,1977, p.2ic). This interpretation is supported b y nightside magnetograme from Alaska, show i ng very quiet conditions from 09 UT onwards. Cusp movements are considered to be the net result of dayside mer g i n g and nightside reconnection, i.e. the whole convection cycle is involved (of.Cowley,1981), Thus, the cusp movement will continue until the convection cycle reaches a n e w equilibrium state. P e riod 3 . During this period from 0940 to 1000 UT as obeerved f r o m the g round the IMP vector is pointing due north. This state should produce a net magnetic f l u x transfer from open lobe tubes to closed dayside tubes (cf. C o w l e y , 1981) with a resulting poleward m o t i o n of the equatorward boundary of the cusp. This expected effect is observed at 0940 UT. A w e a k cusp-like aurora (Fig.6a) is located to the n o r t h of Ну Alesund. I29