Premium
On the heliographic latitude dependence of the interplanetary magnetic field as deduced from the 22‐year cycle of geomagnetic activity
Author(s) -
Russell C. T.
Publication year - 1974
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl001i001p00011
Subject(s) - earth's magnetic field , latitude , physics , polar , interplanetary magnetic field , interplanetary spaceflight , sunspot , amplitude , solar cycle , polarity (international relations) , solar cycle 24 , atmospheric sciences , variation (astronomy) , solar wind , magnetic field , astrophysics , astronomy , biology , quantum mechanics , genetics , cell
The geomagnetic activity index, Ci, exhibits a double sunspot cycle in which 11‐year periods alternately have more, then less, than average activity. The amplitude of the cycle‐to‐cycle variation has varied markedly since 1885, being large from 1885 to 1907, small from 1908 to 1948 and large again from 1949 to 1970. If we assume that the 22‐year variation is caused by reversals every sunspot cycle of the heliographic latitude dependence of the dominant polarity of the interplanetary magnetic field, the behavior of the Ci index implies that the amplitude of the heliographic latitude dependence varies with time. If, as has been proposed, the heliographic latitude dependence is associated with the magnetic field at the solar poles, then the Ci index variation also implies that the polar magnetic field strength has undergone long‐term changes.