Аскаплоты советских станций за 1980 год : (оперативно-информационный материал) / Акад. наук СССР, Кол. фил. им. С. М. Кирова, Поляр. геофиз. ин-т. – Апатиты : Кольский филиал АН СССР, 1984.

12 Auroral PA Index. The index of aurora activity calculated with the help of ascaplots was suggested in /11/. It equals to PA = N^(9', У ) where N is the number of blackened squares within the time interval, and К is the coefficient depending on the corrected geomagnetic coordinates. The connection between H and the auroral magnetic index AL for midnight hours was determined in /11/ from ascaplots of 35 stations during IGY /1,2/. Using the same data the dependence of K-coefficient on the latitude was obtained for two longitudinal intervala. This allows to adjust the data of the stations located at different latitudes to a common value. Since K-index was calculated for midnight aurora, PA index is estimated only for a 4-hour interval in the region of the local geomagnetic midnight. AL scales are chosen so that the corresponding values of PA index are linearly proportional to the energy of auroral electrons of the auroral oval /11/. This permits to make any arithmetic operations with PA index, such as averaging without losing the physical content. Table 2 includes PA values for each day in 1980. For a separate station PA can be determined only for a 4-hour interval which may not cpincide with the maximum of auroral activity. That ia why Table 2 presents PA values obtained by averaging the indices of all the stations operated during that day. The numeral in brackets following-every index gives the number of operating stations the data of which were averaged in calculating the index. The trough in the Table denotes the absence of observations on that day at local midnight. Beginning with this issue aurorae registered at cloudy conditions were taken into account in calculation of PA index. This change increases the representatlvity and statistical veracity of the data, but on the other hand, this leads to the rise of the PA averaged value. The correlation coefficient of PA value obtained accord ing to different procedures is 0.7 for 1980. According to the new procedure, on the average, the value of PA index is higher by a factor of 1.3. Auroral activity in 1980. PA index variations during every day in 19Ѳ0 are presented in Figure 3, the dashes link the gaps between the points. The correspond ing Kp index variations (the scale below) are also shown. Good agreement between aurorae and magnetic field variations is observed even at summer time for the northern hemisphere, when due to a small number of operating stations in Antarctic the information about aurorae is less reliable. Active periods in Figure 3 agree rather well, but the amplitude ratio may vary. Seasonal variations of aurorae (PA averaged), as well as that of the magnetic field (£ Kp averaged ) and solar activity (Wolf numerals W) are shown in Figure 4a. In 1980 the relation between aurorae and magnetic field variations is rather bad. The maximum of aurorae in June is on the descending curve of both magnetic activity and Wolf numerals. It shafld be noted that a distinct minimum of all phenomena is observed in March. It was followed by a rapid grow of activity. The maximum of vernal equinox is significantly shifted towards the summer months (it was May for Wolf numerals and magnetic activity and June for aurorae). Correspondingly the second equinox maximum is shifted towards Hovember-December where it manifested itself distinctly only for magnetic activity for which seasonal variations are well defined and it wag two months later the equinox.