Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsh21a0514t&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #SH21A-0514
Physics
2134 Interplanetary Magnetic Fields, 2162 Solar Cycle Variations (7536), 2164 Solar Wind Plasma, 7524 Magnetic Fields
Scientific paper
Due to a tilt of the ecliptic by about 7.25 degrees to the solar equatorial plane, the Earth appears northward of the Sun's equatorial plane in fall months and southward in spring months that may lead to an annual variation of the interplanetary magnetic field (IMF) near the Earth's orbit. We investigated the behavior of IMF for two minima of solar activity related to 1985-1987 and 1995-1997. The solar magnetic field was sufficiently regular for these two intervals but had opposite polarity: for the first interval the north magnetic pole coincided with the Sun's south pole while for the second interval it moved to the Sun's north pole. We have found clear differences in IMF Bx for fall and spring months: Bx increased from negative (in spring) to positive (in fall) values during the first interval and decreased for the second interval in accordance with the expectations. The amplitude of this variation appears surprisingly high of about 4-5 nT. This dependence is better seen for high solar wind speed. IMF Bz also shows a clear annual variation but differs significantly from that expected from a simple solar magnetic field model with magnetic field lines coming from the Sun and closed through the equatorial plane. Instead, Bz field shows clear correlation with IMF Bx in spring and anti-correlation in fall, which show that magnetic field lines coming from the Sun must have significant divergence from the solar equatorial plane near the Earth's orbit that is especially evident for large IMF Bx. Such behavior of IMF Bz may be important for forecast of geomagnetic activity: it allows us to suggest that Sun's north magnetic polarity is less favorable for increasing geomagnetic activity than Sun's south magnetic field polarity.
Lyatsky Wladislav
Tan Aihong
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