How do solar magnetic fields influence the long term changes of some geomagnetic indeces?
Abstract
Lockwood et al. (Nature, June, 1999) and Stamper et al. (JGR, December, 1999) suggested that the increasing trend in geomagnetic activity seen in the aa index could be due to an increase in the Sun's magnetic field. Because this interpretation has implications for solar physics and climate studies, it is important to examine the connections between these indeces and the solar field, which affects geomagnetic activity through the solar wind. We use Mt. Wilson Observatory magnetograph data from 1967 to the present to study the photospheric field variations and the related variations at the source surface of a potential field model. We find that the source surface field behavior is not a straight forward mirror of the photospheric field. In particular, we find that the phase and amplitude of the source surface field strength variation with time, compared to the photospheric field variation, depends on heliolatitude. What is seen in a low latitude band around the ecliptic shows the desired increasing trend over the previous ~3 cycles that Lockwood, Stamper and coworkers require for their aa index simulations. However, this trend is not seen globally in either the photospheric or integrated source surface field. Thus our biased sampling of the solar field through the ecliptic solar wind is not a good measure from which to make conclusions about the global solar field.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2001
- Bibcode:
- 2001AGUSM..SH52A02L
- Keywords:
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- 2134 Interplanetary magnetic fields;
- 2169 Sources of the solar wind;
- 7524 Magnetic fields;
- 7536 Solar activity cycle (2162)