Semiannual Variation of Geomagnetic Activity: Protons or Photons?

Details Semiannual Variation of Geomagnetic Activity: Protons or Photons? Semiannual Variation of Geomagnetic Activity: Protons or Photons?

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsm42a..02s&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #SM42A-02

Physics

7899 General Or Miscellaneous, 2708 Current Systems (2409), 2731 Magnetosphere: Outer, 2740 Magnetospheric Configuration And Dynamics, 1555 Time Variations: Diurnal To Secular

Scientific paper

The cause(s) of the semiannual variation (SAV) of geomagnetic activity is a problem of long standard ( ˜100 years). The various mechanisms put forward can be divided into 'excitations' and 'modulations'. Using 45 years of the am-index, we show that the SAV is a modulation of existing activity. The modulation is a function of the angle between the Earth's dipole moment and either (1) the aberrated solar wind velocity and/or (2) the sun-Earth line, causing both time of year and time of day (UT) variations. Here we examine the correlation of geomagnetic activity with directions (1) and (2). Mechanisms involving interaction between the solar wind and the magnetopause would correlate best with direction (1). Mechanisms involving ionospheric conductance would correlate best with direction (2).

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