TM NUMBER 36 This Week’s Citation Classic SEPTEMBER 3, 1979 Akasofu S-I. The development of the auroral substorm. Planet. Space Sci. 12:273-82, 1964. [Geophysical Institute, University of Alaska, Fairbanks, AK]

This paper recognized that the auroral ‘Auroral Activation’ and sent it to Chapman activity undergoes a systematic, quasi- for his comments. However, he refused to cyclic change. This finding has made it read it until the title was changed to ‘Auroral possible to study systematically Substorm.’ It was also soon found that many complicated polar upper atmospheric other polar upper atmospheric phenomena, and magnetospheric phenomena. [The such as polar magnetic and ionospheric SCI® indicates that this paper has been disturbances undergo a similar quasi-cyclic cited over 155 times since 1964.] change in harmony with the auroral substorm. Thus, I believe that the concept of auroral substorms put forth in the article has Syunlchi Akasofu become a useful guide in organizing, Geophysical Institute analyzing, and understanding a variety of University of Alaska complex polar upper atmospheric data. Fairbanks, AK 99701 “I do not believe that this concept was easily accepted by many in those days, June 27, 1978 since there is no simple way for a single “It is gratifying to learn that my 1964 article observer on Earth to conclusively prove or has been included in the list of mostcited disprove it. During this difficult time, a close papers. A little background of the history of friendship had developed with several the work leading to this concept and of the colleagues; among them, Y.I. Feldstein of subsequent development may be of some the USSR. In an effort to prove the validity interest to the readers. of the concept, an extensive airborne “My paper is concerned with the dynamics observation by large jet aircraft was then of the aurora (the northern light). conducted. One of the happiest occasions Characteristics of auroral activity on a global in my research career came rather scale (namely, how auroral displays would unexpectedly in 1972 when photographs appear when one could look down on the taken from US Air Force satellites indicated Earth from above the north polar region) had clearly auroral patterns which are consistent not accurately been known before I began with those proposed in my 1964 article. to work on the subject. It was for this reason “It has also become apparent that many that Sydney Chapman and C.T. Elvey magnetospheric disturbance phenomena included photographic auroral observations undergo a quasi-cyclic change in harmony as one of the major projects of the with the auroral substorm. Thus, the concept International Geophysical Year (IGY) of auroral substorms is now extended to (195758), the greatest enterprise in Earth include a variety of magnetospheric science history. phenomena, and the concept of “After examining IGY auroral photographs magnetospheric substorms has emerged.1,2 taken simultaneously from a large number of The auroral substorm is now viewed as one auroral observatories, a rather simple but of the manifestations of the magnetospheric fascinating pattern of auroral activity over substorm. In fact, it is most gratifying that the entire polar region began to emerge, namely, that auroral activity over the entire major satellite and theoretical research is polar region undergoes a quasicyclic change now being made in an effort to understand over a period of a few hours. With great basic plasma processes associated with the excitement, I drafted an article entitled magnetospheric substorm.”

1. Akasofu S-I. Polar and magnetospheric substorms. New York, NY: Springer-Verlag, 1968. 280 p. 2. Akasofu S-I. Physics of magnetospheric substorms. Boston, MA: D. Retdel Publishing Co., 1977. 599 p. 322