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.

JAN .4 ,1 9 8 4 ; 0 9 . 0 0 UT ДН LATITUDE PROF ILES Figure 6b. H-component disturbance detected at 17 stations (dots) in the dawn to no o n sector of the polar region in the n o rthern hemisphere at 0900 UT on Ja n . 4, 19S4. The coordinate system is magnetic local time (1£LT) a nd geomagnetic latitude. Negative deflection to the tfight of the three ma g netic m eridian lines. The latitudinal location of the cusp aurora observed from Svalbard is also indicated. The IMP conditions (B and B v components) corresponding to the time of the ground observations IB shown i n the upper left corner. large negative disturbance between 0800 and 0840 UT at the southernmost station located close to the latitude of the aurora. After the IMF northward turning at 0818 UT the poleward boundary of the aurora moved towards north. The H-component deflection also shifted northward increasing at H o m s u n d and N y Alesund, while decreasing at B j o m o y a . The IMP turning towards due no r t h at ~ 0925 UT was followed by a rapid poleward expansion i n the equatorward boundary of the cusp aurora (cf.Fig. 6a middle panel). Pr o m 0900 auroral luminosity occurred n e a r the southern edge of the field of view, separated fr o m the aurora farther no r t h and characterized by a r elatively intense green oxygen line (557.7 run). Pig.6b shows H-component magnetic deflections at 17 stations (marked by dots) in the morning-midday sector of the polar re g i o n and the latitudinal location of the cusp aurora observed from Svalbard at 0900 US, corresponding to large positive and negative values of IMP B z an d By, respectively. A zone of magnetic disturbance centered at 73-75° geom.lat. is observed. N e g a tive йН mainly reflects a westward Hall current (cf. Priis-Chrisfcensen, 1985), flowing in the opposite direction relative to the ExB plasma flow in the P-layer an d above. Figure 6c is explained in section 3. 3. DISCUSSION O P DATA SET Ho 1. The December 27. 1984 c a s e . A major oval expansion and enhanced DP2- type magnetic disturbance started appr. 40 min. prior to the subatorm onset at appr. 1210 UT. Also notice the equatorward movement of the ДH=0 line,- separating zones of positive and negative deflections, in this period (Pig.2a). The relation to IMF B 2 is quite clear. F r o m these observations we m a y infer that the dimension of the polar cap increases towards a maximum approxi mately at the time of the substorm onset on the nightslde. The size of the polar cap is considered to be a measure of the open magnetic flux »27