Determination of solar cycle length variations using the continuous wavelet transform

Citation
M. Fligge et al., Determination of solar cycle length variations using the continuous wavelet transform, ASTRON ASTR, 346(1), 1999, pp. 313-321
Citations number
28
Categorie Soggetti
Space Sciences
Journal title
ASTRONOMY AND ASTROPHYSICS
ISSN journal
00046361 → ACNP
Volume
346
Issue
1
Year of publication
1999
Pages
313 - 321
Database
ISI
SICI code
0004-6361(199906)346:1<313:DOSCLV>2.0.ZU;2-O
Abstract
The length of the sunspot cycle determined by Friis-Christensen & Lassen (1 991) correlates well with indicators of terrestrial climate, but has been c riticized as being subjective. In the present paper we present a more objec tive and general cycle-length determination. Objectivity is achieved by usi ng the continuous wavelet transform based on Morlet wavelets and carrying o ut a careful error analysis. Greater generality comes from the application of this technique to different records of solar activity, e.g. sunspot numb er, sunspot area, plage area or Be-10 records. The use of different indicat ors allows us to track cycle length variations back to the 15th century. Al l activity indicators give cycle length records which agree with each other within the error bars, whereby the signal due to the solar cycle is weaker within Be-10 than in the other indicators. In addition, all records exhibit cycle length variations which are, within the error bars, in accordance with the record originally proposed by Friis- Christensen & Lassen (1991). In the 16th century, however, the Be-10 record suggests a much longer cycle than the auroral record used by Friis-Christe nsen & Lassen. Also, the presence of a distinct 11-year cycle in the Be-10 record during the Maunder Minimum is confirmed. By combining the results fr om all the indicators a composite of the solar cycle length is constructed, which we expect to be more reliable than the length derived from individua l records.