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.

I I Auroral PA index. The index of auroral activity calculated on the basis of ascaplots was suggested in /11/. It equals to РА=Н*К(гр,-Л-'), 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 N 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 the K-coefficient on the latitude was obtained for two longitudinal intervals. This allows to adjust the data of the stations located on different latitudes to a common value. Since the К-index was calculated for midnight aurora, PA index is estimated only for a 4-hour interval in the region of the local geomagnetic midnight. The AL scale is chosen so that the corresponding values of the PA index be linearly proportional to the energy of auroral electrons of the auroral oval /11/. This provides arithmetic operations with the PA index, such as averaging without losing the physical content. Table 2 includes PA values for each day in 1975. By a single station PA can be determined only for a 4-hour interval which may not coincide with the maximum of auroral activity. Thus 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 denotes the number of operating stations the data of which were averaged in index calculation. The trough in the Table marks the absence of observations on that day at local midnight. In calculation of PA index auroras registered at cloudy weather were taken into account. This change increases the representativity and statistical veracity of the data but, on the other hand, this causes the rise of the PA averaged value. The correlation coefficient of PA value obtained according to different procedures is 0.7. On the average, according to the new procedure the value of the PA index is higher by a factor of 1.3. Auroral activity in 1975. PA index variations for each day in 1975 are presented in Fig.3. The dashes link the points with absence of observations. Vacancies are more often in summer since only two stations operated in the south ern hemisphere and only their data have been used for PA calculations. The data from the near-polar station Vostok have not been used in this calculation. The same figure contains corresponding changes of the diurnal Kp index sum (the scale directed downward). Likewise in the previous years /5,6/ general similarity between auroral and magnetic activity variation is observed. Fig.4 demonstrates the curves from Fig.3 for the beginning of the year when the gaps are seldom. The curves are smoothed according to the trapezium method. Similarity of temporal variations is evident enough, sometimes even minor details are seen though the amplitude of changes may differ. Seasonal variations of auroral activity, magnetic disturbances and Wolf numbers are assembled in Fig.5a. Reading is taken off from the mean values of these parameters. Magnetic activity variations demonstrate distinct seasonal variations exposing equinoxial maxima which are shifted toward the winter months of the Northern hemisphere (February, December), note that the spring maximum is much higher. During the summer-autumn months a comparatively low maximum is