Examination of the three-cycle quasiperiodicity of geomagnetic indices in relation to prediction of the size of cycle 23

Details Examination of the three-cycle quasiperiodicity of geomagnetic indices in relation to prediction of the size of cycle 23 Examination of the three-cycle quasiperiodicity of geomagnetic indices in relation to prediction of the size of cycle 23

Nov 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001jgr...10625125k&link_type=abstract

Journal of Geophysical Research, Volume 106, Issue A11, p. 25125-25132

Astronomy and Astrophysics

Astrophysics

2

Solar Physics, Astrophysics, And Astronomy

Scientific paper

From the study of the Ap and aa geomagnetic indices for 1932 onward, Ahluwalia [1998] reported a three-cycle quasiperiodicity, with lower Ap(min) and aa(min) values in cycles 17, 20, 23. An examination of aa indices for periods extending back to 1868 (and further back to 1844, using the Helsinki equivalent aa index data set) did not show the three-cycle pattern, though a possible periodicity of ~25-30 years may exist. The more overwhelming variation was an uptrend that had a minimum near cycle 14 (~1900) and may have peaked recently. The long series of sunspot number maxima (cycles 0-22, 1750 onward, but not reliable before cycle 8) showed two long-term swings, one of ~90 years and another of ~100 years, the latter peaking in recent cycles and indicating a probable downtrend in the coming 100 years. The sunspot number maxima series had an excellent correlation with aa(min) series back to 1868 (and even after including the estimated values back to 1844), which is being used for prediction of the size of the present cycle 23. Various predictions for cycle 23, which started in 1996 and seems to have peaked recently at a smoothed sunspot number of ~121, are discussed.

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