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Implications of solar cycles 19 and 20 geomagnetic activity for magnetospheric processes
Author(s) -
Feynman Joan
Publication year - 1980
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/gl007i011p00971
Subject(s) - substorm , solar wind , ring current , earth's magnetic field , interplanetary magnetic field , physics , atmospheric sciences , magnetopause , solar cycle , geophysics , magnetosphere , magnetic field , quantum mechanics
The solar cycle variations of geomagnetic indices are compared for the last two solar cycles. It is found that the midlatitude aa index and the ring current index, D st , exhibit a markedly different relationship to one another in the two cycles. During solar cycle 20 the yearly averaged aa has been shown to be linearly related to either the yearly averaged |B z | v² or v², where B z is the north‐south component of the interplanetary field and v is the solar wind velocity. However, the yearly averaged D st is well represented by a linear function of B z v and not by a function v². A combination of regression formulas for D st and aa allows estimates to be made of the annual average v and B z from 1957 until 1965, when in situ measurements of the solar wind became available. Most interesting, however, is the point that the dependence of aa and D st on different functions of solar wind parameters implies that the ring current is not directly produced by substorm injections. This result is in agreement with models of magnetospheric processes in which the increased ring current and substorm activity are two separate aspects of increased magnetospheric convection.