Date of minimum of the “protracted” solar cycle 23

Nagovitsyn, Yu. A.; Nagovitsyna, E. Yu.; Makarova, V. V.

doi:10.1134/s1063773710080098

Cited by 8 publications

(14 citation statements)

References 4 publications

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“…Also, in solar data analysis, a method for studying a non-stationary weakly nonlinear oscillatory processes, similar to HHT was developed. It is a so-called Krylov-Bogolyubov's "averaging method", based on the expansion of the original signal on a set of harmonic functions with time-dependent amplitude and frequency (Nagovitsyn 1997). This tool was applied for analysing weakly non-linear, non-stationary large timescale solar cyclicity.…”

Section: Introductionmentioning

confidence: 99%

Multi-mode quasi-periodic pulsations in a solar flare

Kolotkov

Nakariakov

Kupriyanova

et al. 2015

A&A

102

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Context. Quasi-periodic pulsations (QPP) of the electromagnetic radiation emitted in solar and stellar flares are often detected in microwave, white light, X-ray, and gamma-ray bands. Mechanisms for QPP are intensively debated in the literature. Previous studies revealed that QPP may manifest non-linear, non-stationary and, perhaps, multi-modal processes operating in flares. Aims. We study QPP of the microwave emission generated in an X3.2-class solar flare on 14 May, 2013, observed with the Nobeyama Radioheliograph (NoRH), aiming to reveal signatures of the non-linear, non-stationary, and multi-modal processes in the signal. Methods. The NoRH correlation signal obtained at the 17 GHz intensity has a clear QPP pattern. The signal was analysed with the Hilbert-Huang transform (HHT) that allows one to determine its instant amplitude and frequency, and their time variation. Results. It was established that the QPP consists of at least three well-defined intrinsic modes, with the mean periods of 15, 45, and 100 s. All the modes have quasi-harmonic behaviour with different modulation patterns. The 100 s intrinsic mode is a decaying oscillation, with the decay time of 250 s. The 15 s intrinsic mode shows a similar behaviour, with the decay time of 90 s. The 45 s mode has a wave-train behaviour. Conclusions. Dynamical properties of detected intrinsic modes indicate that the 100 s and 15 s modes are likely to be associated with fundamental kink and sausage modes of the flaring loop, respectively. The 100 s oscillation could also be caused by the fundamental longitudinal mode, while this interpretation requires the plasma temperature of about 30 million K and hence is not likely. The 45 s mode could be the second standing harmonics of the kink mode.

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Section: Introductionmentioning

confidence: 99%

Multi-mode quasi-periodic pulsations in a solar flare

Kolotkov

Nakariakov

Kupriyanova

et al. 2015

A&A

102

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“…As a possible solution to this problem a so-called KrylovBogolyubov "averaging" method was suggested. It is based on the expansion of the original signal into a set of harmonic functions with time-dependent amplitude and frequency, and was successfully applied to analysis of weakly nonlinear non-stationary Wolf number data by Nagovitsyn (1997). Another method suitable for nonlinear and non-stationary data processing is the proper orthogonal decomposition (POD).…”

Section: Introductionmentioning

confidence: 99%

Hilbert–Huang transform analysis of periodicities in the last two solar activity cycles

Kolotkov

Broomhall

Nakariakov

2015

Mon. Not. R. Astron. Soc.

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We investigated periodicities associated with the last two-and-a-half solar activity cycles with the novel Hilbert-Huang Transform (HHT) method. Raw data signals of five different observational proxies: the 10.7 cm radio flux intensity, the helioseismic frequency shift, and the sunspot area signals recorded from the whole solar disk, and separately from the Northern and Southern hemispheres, were expanded into a set of intrinsic modes with the Ensemble Empirical Mode Decomposition (EEMD) technique. Instant and mean periods of each empirical mode were obtained with the use of the Hilbert transform applied independently to each separate mode. The periodicities were allocated to three distinct groups: short-term variations (with periods shorter than 0.5 yr), quasi-biennial oscillations (with typical periods from 0.5 yr to 3.9 yr), and longer periodicities, e.g. such as the 11 yr cycle. All periodicities detected in the examined solar cycles 22-24 are consistent with the well known results found in the earlier solar epochs. We have demonstrated that the HHT method is an ideal tool for characterising periodicities in the helioseismic data, which are necessarily relatively limited in terms of their time resolution. Periodicities obtained using the helioseismic data are, nevertheless, consistent with those found in other proxies. Since helioseismic oscillations are sensitive to the solar interior, this indicates that the behaviour of surface and atmospheric magnetic activity reflects that of the Sun's internal magnetic field. All identified intrinsic modes are seen to have clear amplitude modulation highly correlated with the 11 yr cycle. This amplitude modulation is most pronounced in the short-period modes. The short-term periodicities were found to be multiples of the shortest period, of 25 d. This ordering of the short-term periodicities is consistent with the previous findings. Signatures of the North-South asymmetry were detected in the individual hemisphere sunspot area indices. Furthermore, evidence of the last "extended" solar minimum was detected too.

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“…1). This last scenario also qualitatively represents other suggestions of high activity (e.g., Nagovitsyn 1997;Ogurtsov et al 2003;Volobuev 2004). After 1749, both scenarios are extended by the international sunspot number 1 .…”

Section: Introductionmentioning

confidence: 99%

“…For example, there have been several suggestions that sunspot activity was moderate or even high during the core MM (1645-1700), being comparable to or even exceeding the current solar cycle #24 (Schove 1955;Gleissberg et al 1979;Cullen 1980;Nagovitsyn 1997;Ogurtsov et al 2003;Nagovitsyn et al 2004;Volobuev 2004;Rek 2013;Zolotova & Ponyavin 2015). Some of these suggestions were based on a mathematical synthesis using empirical rules in a way similar to Schove (1955) and Nagovitsyn (1997) and therefore are not true reconstructions. Some others used a re-analysis of the direct A&A 581, A95 (2015) data series (Rek 2013;Zolotova & Ponyavin 2015) and provide claimed assessments of the solar variability.…”

Section: Introductionmentioning

confidence: 99%

The Maunder minimum (1645–1715) was indeed a grand minimum: A reassessment of multiple datasets

Usoskin

Arlt

Asvestari

et al. 2015

A&A

187

172

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Aims. Although the time of the Maunder minimum (1645-1715) is widely known as a period of extremely low solar activity, it is still being debated whether solar activity during that period might have been moderate or even higher than the current solar cycle #24. We have revisited all existing evidence and datasets, both direct and indirect, to assess the level of solar activity during the Maunder minimum. Methods. We discuss the East Asian naked-eye sunspot observations, the telescopic solar observations, the fraction of sunspot active days, the latitudinal extent of sunspot positions, auroral sightings at high latitudes, cosmogenic radionuclide data as well as solar eclipse observations for that period. We also consider peculiar features of the Sun (very strong hemispheric asymmetry of the sunspot location, unusual differential rotation and the lack of the K-corona) that imply a special mode of solar activity during the Maunder minimum.Results. The level of solar activity during the Maunder minimum is reassessed on the basis of all available datasets. Conclusions. We conclude that solar activity was indeed at an exceptionally low level during the Maunder minimum. Although the exact level is still unclear, it was definitely lower than during the Dalton minimum of around 1800 and significantly below that of the current solar cycle #24. Claims of a moderate-to-high level of solar activity during the Maunder minimum are rejected with a high confidence level.

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Date of minimum of the “protracted” solar cycle 23

Cited by 8 publications

References 4 publications

Multi-mode quasi-periodic pulsations in a solar flare

Multi-mode quasi-periodic pulsations in a solar flare

Hilbert–Huang transform analysis of periodicities in the last two solar activity cycles

The Maunder minimum (1645–1715) was indeed a grand minimum: A reassessment of multiple datasets

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