HR: 10:20h
AN: SM42A-01    [Abstracts]
TI: The geomagnetic seasons in the auroral zone: dayside magnetopause reconnection versus solar illumination
AU: * Weigel, R S
EM: Robert.Weigel@lasp.colorado.edu
AF: University of Colorado/Laboratory for Atmospheric and Space Physics, 1234 Innovation Drive, Boulder, CO 80303 United States
AB: There are three mechanisms that are proposed to explain the geomagnetic seasons. The most widely accepted mechanism is the Russell-McPherron (R-M) effect, which attributes the dependence to seasonal changes in an external driver of geomagnetic activity, the dayside magnetopause reconnection rate. The second mechanism results from a dipole tilt modulation of dayside magnetopause reconnection that depends on season. The third process is based on seasonal changes in solar generated conductivity. Using data from auroral zone magnetometers over a full solar cycle, we show that the R-M effect does not explain any of the seasonal changes in either the amplitude of the auroral zone geomagnetic field or its variability. The seasonal changes are shown to be too large to be caused by the dipole tilt mechanism. The auroral zone magnetometer data in the eastward electrojet region are shown to be consistent with seasonal changes in solar--generated conductivity. In the midnight sector and westward electrojet region, geomagnetic activity variations are consistent with the solar insulation effect except for a hemisphere--dependent Spring--Fall asymmetry.
DE: 2704 Auroral phenomena (2407)
DE: 2724 Magnetopause, cusp, and boundary layers
DE: 2784 Solar wind/magnetosphere interactions
SC: SPA-Magnetospheric Physics [SM]
MN: 2004 AGU Fall Meeting