Other
Scientific paper
Jun 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006spd....37.1106c&link_type=abstract
American Astronomical Society, SPD meeting #37, #11.06; Bulletin of the American Astronomical Society, Vol. 38, p.239
Other
Scientific paper
To investigate persistent periodicities, 12-hour averages of the radial component of the interplanetary magnetic field and the solar wind speed, covering 42 years (1963-2005), were analyzed. A Lomb periodogram for the data up to 1998 showed maximum spectral power at a period of 27.03 days, as encountered previously by Neugebauer et al. (2000). Including cycle 23 shifted the peak to 27.06 days. Analysis of solar cycles 20 - 23 separately showed a dominant period of 27.03 days in solar cycle 20, but not in the other cycles.To investigate the degree of persistency and phase coherence of a particular signal, the technique of complex demodulation was applied since it permits the determination of continuous changes in time of the amplitude and frequency of the signal relative to a test signal. It was found that for a reference signal of 27.03 days, the phase was a flat function of time during the intervals 1965-1972 and 1995-1997. The phase decreased in time from 1972-1995 and increased after 1997. This implies that for the intervals 1972-1995 and 1997-2005 other periodicities better characterize the data. A period of 27.6 days gave an overall flat phase function in time, while other periods < 0.5 day shorter and longer, with comparable but lesser amplitude, come and go.To investigate the solar sources of these periods, the methods of principal component analysis (PCA) and independent component analysis (ICA) were applied to 27 years (1976-2003) of synoptic maps obtained with the NSO Kitt Peak Vacuum Telescope. Before the analysis, the original synoptic maps were shifted relative to the previous maps using the particular period under investigation. PCA and ICA identified 3 modes for the 27.03 reference period and 2 modes for the 27.6 period that showed clusters of magnetic activity at preferred longitudes.
Cadavid Ana C.
Lawrence John K.
Ruzmaikin Aleksandr
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