University of Oulu

P Frick, D Sokoloff, R Stepanov, V Pipin, I Usoskin, Spectral characteristic of mid-term quasi-periodicities in sunspot data, Monthly Notices of the Royal Astronomical Society, Volume 491, Issue 4, February 2020, Pages 5572–5578,

Spectral characteristic of mid-term quasi-periodicities in sunspot data

Saved in:
Author: Frick, P.1,2; Sokoloff, D.1,3,4; Stepanov, R.1,5;
Organizations: 1Institute of Continuous Media Mechanics, Korolyov str. 1, 614013 Perm, Russia
2Perm State University, Bukireva str. 15, 614990 Perm, Russia
3Department of Physics, Moscow University, 119899 Moscow, Russia
4IZMIRAN, Kaluzhskoe shasse, 4, Troitsl, 108840 Moscow, Russia
5Perm National Research Polytechnic University, 614990 Perm, Russia
6Institute of Solar-Terrestrial Physics, 664030 Irkutsk, Russia
7University of Oulu, 90014 Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.4 MB)
Persistent link:
Language: English
Published: Oxford University Press, 2019
Publish Date: 2020-01-17


Numerous analyses suggest the existence of various quasi-periodicities in solar activity. The power spectrum of solar activity recorded in sunspot data is dominated by the ∼11-yr quasi-periodicity, known as the Schwabe cycle. In the mid-term range (1 month–11 yr) a pronounced variability known as a quasi-biennial oscillation is widely discussed. In the shorter time-scale a pronounced peak, corresponding to the synodic solar rotation period (∼27 d), is observed. Here we revisit the mid-term solar variability in terms of statistical dynamics of fully turbulent systems, where solid arguments are required to accept an isolated dominant frequency in a continuous (smooth) spectrum. For this, we first undertook an unbiased analysis of the standard solar data, sunspot numbers and the F10.7 solar radio flux index, by applying a wavelet tool, which allows one to perform a frequency–time analysis of the signal. Considering the spectral dynamics of solar activity cycle by cycle, we showed that no single periodicity can be separated, in a statistically significant manner, in the specified range of periods. We examine whether a model of the solar dynamo can reproduce the mid-term oscillation pattern observed in solar data. We found that a realistically observed spectrum can be explained if small spatial (but not temporal) scales are effectively smoothed. This result is important because solar activity is a global feature, although monitored via small-scale tracers like sunspots.

see all

Series: Monthly notices of the Royal Astronomical Society
ISSN: 0035-8711
ISSN-E: 1365-8711
ISSN-L: 0035-8711
Volume: 491
Issue: 4
Pages: 5572 - 5578
DOI: 10.1093/mnras/stz3238
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: PF, DS and RS are grateful for the support for this work by the project RSF-Helmholtz (contract nos. 18-41-06201 and HRSF-0044). VP conducted the dynamo model simulations as part of FR II.16 of ISTP SB RAS. IU composed miscellaneous observation data under the support from the Academy of Finland (projects 307411 ReSoLVE and 321882 ESPERA).
Academy of Finland Grant Number: 307411
Detailed Information: 307411 (Academy of Finland Funding decision)
321882 (Academy of Finland Funding decision)
Copyright information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.