Аскаплоты советских станций за 1982 год : (оперативно-информационный материал) / Акад. наук СССР, Кол. фил. им. С. М. Кирова, Поляр. геофиз. ин-т. – Апатиты : Кольский филиал АН СССР, 1989.

I I 7-9 correspond to the second and third ball, respectively. For several forms oocuring simultaneously the index is calculated by the most important form plus one. For example, if during more than 15 minutes a weak homogeneous arc (HA) and a weak radiant band (RB) were observed in the sky, the index equals to: 6 (radiant band) + 1 (occurence of another form) = 7 that corresponds to the third ball of auroral activity. One is added for a quick motion of the main auroral form. For example, a bright quickly moving radiant band existing less than 15 min with occurence of other forms gives: 7 (bright radiant band) + 1 ( its quick motion) + 1 (occurence of other auroral forms) = 9. Thus, a very bright homogeneous arc observed during the whole interval (half an hour) gives 2 balls, whereas a mere fact of appear- ence of a corona corresponds to the same activity. Such estimations of auroral activity in balls is connected with peculiarities of development of the auroral substorm. According to /8/ the periods of no disturbance or absolutely quiet periods homogeneous arcs (HA.) and bands (HB) with brightness gaining sometimes 2 balls (these are not the balls of activity but the balls of brightness according to International Classification) may be observed along the compressed oval. On the dayside separate rays or weak radiant arcs are usually seen. A weak eubstorm causes increasing of brightness, appear ance of curves, i.e. transition of arcs into bands and appearance of radiant structures, A strong substorm is characterized by an apparent breakup, i.e. quick motion of auroras, collapse of forms, appearance of coronas and pulsating auroras. Thus, the series of auroral activity used for ascaplotting is connected with the peculiarities of substorm development and,to some extend, characterizes the intensity of the substorm. Figure 2 presents an example of ascaplots. The numerals I-XV show various possible situations. In the given example the camera did not operate until 13.30 UT. Observations began at 13.30 UT, auroras were absent, cloudi ness with rents was in the north and in the zenith (I). During the next half-an-hour interval (II) auroras were also absent, complete cloudiness was in the north and in the zenith, cloudiness with rents was in the south; III and IV correspond to the time interval of complete cloudiness covering all the sky; V denotes cloudiness with rents in the south and in the zenith, and no clouds in the north. Auroras in the north appeared at 16 UT (VI), there were no clouds in the zenith and cloudiness with rents in the south, VII Shows no clouds in the sky, auroras were observed in the north and in the zenith, VIII marks that the sky was clear, auroras were only in the north, local geomagnetic midnight. IX shows that auroraa again shifted to the zenith and their activity gained 2 balls, no clouds in the south. X: auroras spread all over the зку, the activity in the zenith was equal to 3 balls. XI: auroras were in the north and in the zenith, activity of 3 balls neither auroras no clouds in the south. XII: no auroras were observed in the north, probably because of cloudiness with rents, the activity in the zenith reduced to 2 balls. XIII: auroras of not more than 1 ball were observed in the north and in the zenith, no clouds in the south. XIV: the sky is cloud less, no auroras, moon lightning. XV: the situation is similar, but the ascafilms turned out to be of poor quality due to some technical reasons (bad development of this part of the film, breaks of automatic work). The described example presents all the situations one can encounter in ascaplots.