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The auroral ovals in the northern and southern hemispheres observed by the optical instruments aboard the DMSP satellites are studied on a statistical basis in terms of the temporal, spatial, and magnetic activity dependence of the equatorward edge of the diffuse (continuous) aurora. In the nightside (18-08 CGT), the equatorward edges of the auroral ovals are located predominantly in the latitude range 61 deg - 69 deg CGL. They show strong dependence on the levels of magnetic activity. Of the indices Kp, AE, Dst, and Q, the Q index is correlated best with the position of the equatorward edge of the diffuse aurora. Assuming that the auroral oval is approximately circular in a CG coordinate system, the dependence of the radius of the auroral oval on magnetic activity is determined. The radius and the center of the auroral circle changes with variation in magnetic activity. The ovals of the northern and southern hemispheres consistently show an asymmetry. On the nightside, the oval in the southern hemisphere is located about 1 deg closer to the equator than the oval in the northern hemisphere.
Due to the systematic diurnal motion of the auroral oval, the Q values of magnetic activity derived from a single station are not directly usable to determine the expected degree of auroral activity. To remove the diurnal effects from a single station data base, which leads in daytime to an under-estimation of the Q index, an empirical set of detrending factors was determined for the Sodankyla Q data base. These factors show that the probability that a given level of magnetic activity will be exceeded for a given duration is underestimated by up to a factor of 2 in the least sensitive daytime sector. The detrended data base has been analyzed to determine the probability that a given Q value is exceeded for a selected duration. This analysis has been done for durations up to 12 hr separately for the night and daytime detrended data bases. The results are very similar and confirm that the detrending has been successfully accomplished. Finally the individual and cumulative probabilities that a given Q is exceeded for a selected duration (periods from 0.25 to 24 hr) have been established for the fully detrended data base. To interpret the results in their effect on the Over-the-Horizon Experimental Radar System, the distribution of probabilities has been modulated with the dynamics of the auroral oval by use of the Starkov equation (1969). This permits the assessments of the probability that a fixed location in the radar coverage area is under the auroral oval.
Astronomy and Astrophysics Abstracts, which has appeared in semi-annual volumes since 1969, is devoted to the recording, summarizing and indexing of astronomical publications throughout the world. It is prepared under the auspices of the International Astronomical Union (according to a resolution adopted at the 14th General Assembly in 1970). Astronomy and Astrophysics Abstracts aims to present a comprehensive documenta tion of literature in all fields of astronomy and astrophysics. Every effort will be made to ensure that the average time interval between the date of receipt of the original literature and publication of the abstracts will not exceed eight months. This time interval is near to that achieved by monthly abstracting journals, compared to which our system of accumu lating abstracts for about six months offers the advantage of greater convenience for the user. Volume 31 contains literature published in 1982 and received before July 15, 1982; some older literature which was received late and which is not recorded in earlier volumes is also included. We acknowledge with thanks contributions to this volume by Dr. J. Bouska, Prague, who surveyed journals and publications in Czech and supplied us with abstracts in English .