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The global geomagnetic secular variation in the l960s and l970s was characterized by a rather rapid intensification which was shown to be of internal origin (Nevanlinna, 1980). An external 11-year wave could also be identified (Nevanlinna, 1980; Yukutake and Cain, 1979). In studying the global secular variation for the last few years, an even more rapid global change can be identified, namely a sudden enhancement followed by a deficit, lasting roughly two years from the end of 1977 to 1979. Here we demonstrate that the pulse is of external origin and that it resembles an intensification of the magnetospheric ring-current system lasting for about two years.
Pushkov, A.N., Ivchenko, M.P. (1979) The summary of the annual mean values of magnetic elements at the world magnetic observatories. Vol 14, Izmiran, Acad. of Sci. of the USSR
Yukutake, T., Cain, J.C. (I 979) Solar cycle variations of the first degree spherical harmonic components of the geomagnetic field. J. Geomagn. Geoelectr. 31:509-544