Аскаплоты советских станций за 1975 год : (оперативно-информационный материал) / Акад. наук СССР, Кол. фил. им. С. М. Кирова, Поляр. геофиз. ин-т. – Апатиты : Кольский филиал АН СССР, 1988.

10 the second and third ball, respectively. For several forms occuring simultaneously the index is calculated by the most important form plus 1. For example, if during more than 15 min a weak homogeneous arc (HA) and a weak radiant band (RB) were observed 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 (radiant band) + 1 (its quick motion) + 1 (occurence of other auroral forms)=9. Thus, it is seen that a very bright homogeneous arc observed during the whole interval (half an hour) gives 2 balls whereas a mere fact of appearance of a weak corona corresponds to the same activity. Such estimation of auroral activity in balls is connected with peculiarities of development of the auroral substorm. According to /10/ at the periods of no disturbances or absolutely quiet periods homogeneous arcs (HA) and bands (HB) with brightness almost 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. Separate rays or weak radiant arcs are usually seen on the dayside. A weak substorm causes increasing of brightness, appearance of curves, i.e. transition of arcs into bands and appearance of radiant structure. A strong aubstorm 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 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 13.00 UT. Observations began at 13.30 UT, no auroras were observed, cloudiness 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 observed in the north and in the zenith, cloudiness with rents was in the south; III and IV corresponds to the time intervals of complete cloudiness covering the whole sky; V denotes cloudiness with rents in the south and in the zenith, 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 seen only in the north, local geomagnetic midnight. IX shows shifting of auroras to the zenith and their activity gaining 2 balls, no clouds in the south. X: auroras spread all over the sky, the activity in the zenith equals to 3 balls. XI: auroras were in the north and in the zenith, 3-ball activity, neither auroras nor 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 cloudless, no auroras, moon lightning. XV: the situation is similar but the ascafilms due to technical reasons (bad development of this part of the roll, breaks of automatic work) turned out to be of low quality. The described example presents practically all the situations which may be encountered in ascaplots.