The Russell-McPherron mechanism and trends in the semiannual amplitude of geomagnetic activity

ANA G. ELIAS; VIRGINIA M. SILBERGLEIT; ALICIA L. CLUA DE GONZALEZ

Puntarenas

Congreso; IX COLAGE; 2011

ALAGE (Asociación LatinoAmericana de Geofísica Espacial)

The well known semiannual variation in geomagnetic activity, with maxima near equinoxes, is not constant in amplitude neither in phase. In particular, the amplitude presents a long-term variation similar to that shown by solar and geomagnetic indices. In a previous study, where we assessed the time series of the semiannual oscillation amplitude through a wavelet analysis of the aa index, we obtained that a maximum occurred around 1947, almost 10 years before it occurs in solar and geomagnetic indices. Among the three principal sources of this oscillation, which are (1) the axial hypothesis caused by the annual variation of the heliographic latitude of the Earth, (2) the equinoctial hypothesis caused by the annual variation of the orientation of the Earth?s magnetic axis relative to the earth-sun line, and (3) the Russell-McPherron mechanism, we analyze the third as a possible cause of trends. In fact, the Russell-McPherron mechanism depends on properties of the solar wind that change with successive solar cycles in ways that could explain the variations in the amplitude of the semiannual oscillation of geomagnetic activity.