Physics
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sh52a05v&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SH52A-05
Physics
7536 Solar Activity Cycle (2162)
Scientific paper
A study of the time evolution of solar (sunspot number-SSN) and geomagnetic (AA index) activity during the period 1868-1998 (annual averages) was made using Wavelet spectral analysis. As expected, wavelet maps have shown that the strongest signal in the SSN is the 11 years periodicity, while in the AA besides a period near 11 years, significant amplitudes are seen in the 2-8 year band. Wavelet decomposition bands were determined and the cross-correlation between SSN and AA was calculated for each one. The results obtained were : 2-4 years band, lag=0, r=0.32; 4-8 years band, lag =0, r=0.6; 8-16 years, lag= 2 years, r=0.76; 16-30 years band, lag = -1 year, r=0.78; >30 years band, lag = -3 years, r=0.75. The correlation is greater for long periods than for the short ones. The short period bands show a variation in phase between SSN-AA, and the longer periods show an out-of-phase variability. A detailed analysis of the 8-16 year band for SSN and AA shows that the lag is increasing with time since 1960. In order to study the time evolution of solar-geomagnetic correlation, 23-year averages of AA and SSN were calculated. The correlations were observed decreasing with time, whereas the time lag is increasing. From the 1868-1890 period to the 1960-1982 period, r varied form 0.76 to 0.35, and the lag from 0 to 3 years. This study confirms the existence of a trend in which solar and geomagnetic activity become apparently less correlated. The physical mechanism could be associated to the general evolution of solar magnetic field, which could be affecting solar wind parameters and the solar spot activity in a different way.
Echer Ezequiel
Nordemann D. J.
Rodolfo Rigozo Nivaor
Vieira L. E.
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