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Erofeev, D. V.

doi:10.1023/a:1005237028902

Cited by 7 publications

(5 citation statements)

References 17 publications

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“…Evidence for biennial oscillations in the photospheric magnetic field has been provided earlier by Stenflo & Vogel (1986), Stenflo & Güdel (1988), Erofeev (2001), Obridko & Shelting (2001), and Knaack et al (2005). In the latter paper we have performed a time series analysis of the longitudinally averaged Kitt Peak synoptic maps for cycles 21-23 and showed that the biennial oscillations occurred predominantly in the southern hemisphere.…”

Section: Discussionmentioning

confidence: 69%

Spherical harmonic decomposition of solar magnetic fields

Knaack¹,

Stenflo²

2005

A&A

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Abstract.We have investigated the temporal evolution of large-scale magnetic fields in the solar photosphere during the time interval 1966-2004 by means of spherical harmonic decomposition and subsequent time series analysis. Two data sets of daily magnetograms recorded at the Mt. Wilson and Kitt Peak observatories were used to calculate the spherical harmonic coefficients of the radial magnetic field for axisymmetric (m = 0) and non-axisymmetric (m 0) modes. Time series analysis was then applied to deduce their temporal variations. A third data set of synoptic Carrington rotation maps from Kitt Peak was also analyzed for completeness. Besides the obvious 22 yr magnetic cycle, we have found evidence for intermittent oscillations with periods of 2.1−2.5 yr, 1.5−1.8 yr and 1.2−1.4 yr. The biennial oscillation occurred during the solar maxima of cycles 20-22 (and likely also during the current cycle 23) and was most pronounced for modes that resemble non-linear dynamo waves (Stix 1972, A&A, 20, 9). The 1.5−1.8 yr period was stronger during the odd cycles 21 and 23 than during the even cycles 20 and 22, whereas the opposite was the case for the 1. (Krivova & Solanki 2002, A&A, 394, 701), and in the large-scale photospheric magnetic field (Knaack et al. 2005, A&A, in press). In agreement with the latter study, we have found additional quasi-periodicities in the range 320−100 d and rotational periods of 29.0 ± 0.1d, 28.2 ± 0.1d, and 26.8 ± 0.1d. Compared to earlier decompositions by Stenflo & Vogel (1986, Nature, 319, 285) and Stenflo & Güdel (1988, A&A, 191, 137), we can confirm the main features of their results, although several modifications need to be considered.

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Section: Discussionmentioning

confidence: 69%

Spherical harmonic decomposition of solar magnetic fields

Knaack¹,

Stenflo²

2005

A&A

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“…Based on magnetic helicity observations (Bao & Zhang, 1998), it was proposed a double-cycle solar magnetic dynamo model, with one dynamo operating at the basis of the convection zone (11-year cycle) due to radial shear and the other at the top of the convection zone (with 2-year periodicity) due to latitudal shear (Benevolenskaya, 1998(Benevolenskaya, , 2000. Also supporting this model, further analysis of the solar magnetic field data showed that the active region magnetic field exhibits an intense, short-scale component varying with 2-year periodicity (Erofeev, 2001). It was also proposed that the sunspot number can be well fitted by a superposition of the usual 11-year cycles and wave trains with periodicity continuously varying from 38 months at solar maximum, to 21 months towards solar minimum (Krasotkin, 2001).…”

Section: Instantly Maximal Wavelet Skeleton Spectrummentioning

confidence: 70%

On signal-noise decomposition of time-series using the continuous wavelet transform: application to sunspot index

Polygiannakis

Preka‐Papadema

Moussas

2003

Monthly Notices of the Royal Astronomical Society

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We show that the continuous wavelet transform can provide a unique decomposition of a time‐series into ‘signal‐like’ and ‘noise‐like’ components. From the overall wavelet spectrum, two mutually independent skeleton spectra can be extracted, allowing the separate detection and monitoring in even non‐stationary time‐series of the evolution of (i) both stable but also transient, evolving periodicities, such as the output of low‐dimensional dynamical systems, and (ii) scale‐invariant structures, such as discontinuities, self‐similar structures or noise. The idea of the method is to keep from the overall wavelet expansion of the time‐series only the wavelet components of locally maximal amplitude at any given time or scale, thus obtaining the instantly maximal and scale maximal wavelet skeleton spectrum, respectively. The scale maximal spectrum was previously proposed for studying possible multifractal scaling properties of time‐series. The instantly maximal spectrum proposed here exhibits clearer spectral peaks and reduced noise, as compared to the overall wavelet spectrum. An indicative application to the monthly‐averaged sunspot index reveals, apart from the well‐known 11‐yr periodicity, three of its harmonics, the 2‐yr periodicity (quasi‐biennial oscillation, QBO) and several more (some of which have been detected previously in various solar, Earth–solar connection and climate indices), here proposed as just harmonics of the QBO, in all supporting the double‐cycle solar magnetic dynamo model. The scale maximal spectrum reveals the presence of 1/f fluctuations with time‐scales up to 1 yr in the sunspot number, indicating that the solar magnetic configurations involved in the transient solar activity phenomena with those characteristic time‐scales are in a self‐organized critical state, as previously proposed for the solar flare occurrence.

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“…This analysis shows that the neutrino flux has been varying with a period of 26 months. Later on, strong evidences about the presence of the QBO in photospheric magnetic flux have been provided, for instance, by Stenflo and Vogel (1986), Stenflo and Guedel (1988), Erofeev (2001), Obridko and Shelting (2001), Knaack et al (2005). All these authors used a similar approach which involved to expand the magnetic field in spherical harmonics and to analyse the harmonic coefficients.…”

Section: The Rieger Periodicitymentioning

confidence: 99%

Rossby Waves in Astrophysics

et al. 2021

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Rossby waves are a pervasive feature of the large-scale motions of the Earth’s atmosphere and oceans. These waves (also known as planetary waves and r-modes) also play an important role in the large-scale dynamics of different astrophysical objects such as the solar atmosphere and interior, astrophysical discs, rapidly rotating stars, planetary and exoplanetary atmospheres. This paper provides a review of theoretical and observational aspects of Rossby waves on different spatial and temporal scales in various astrophysical settings. The physical role played by Rossby-type waves and associated instabilities is discussed in the context of solar and stellar magnetic activity, angular momentum transport in astrophysical discs, planet formation, and other astrophysical processes. Possible directions of future research in theoretical and observational aspects of astrophysical Rossby waves are outlined.

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Untitled

Cited by 7 publications

References 17 publications

Spherical harmonic decomposition of solar magnetic fields

Spherical harmonic decomposition of solar magnetic fields

On signal-noise decomposition of time-series using the continuous wavelet transform: application to sunspot index

Rossby Waves in Astrophysics

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