Solar activity cycle and rotation of the corona

Mouradian, Z.; Bocchia, R.; Botton, Christian

doi:10.1051/0004-6361:20021244

Cited by 24 publications

(15 citation statements)

References 39 publications

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“…Mouradian et al (2002) show that the number of peaks of the power spectrum grows in accordance with cycle evolution. The changes of RR during the cycle are not systematic, as the differential rotation rule can suggest.…”

Section: Discussionmentioning

confidence: 82%

“…To reveal the fluctuations the smooth function is subtracted from the recordings in order to point out an alternate function around a straight line. This is the clear slow varying component of solar activity, that will be treated by harmonic analysis (Mouradian et al 2002). For each considered time interval, the position of the straight line was corrected to obtain the sum of alternate functions equal to zero.…”

Section: Methods Of Analysismentioning

confidence: 99%

“…Radio flux at 10.7 cm concerns full disk radiation flux, out side of any transient event and it is the most characteristic physical index of solar active regions. The effective height for the generation of 10.7 cm radio emission is between 15 000 and 60 000 km above the photosphere (Mouradian et al 2002), therefore in the low corona. In a few cases of gaps in the data, we interpolated between the closest values.…”

Section: The Datamentioning

confidence: 99%

“…Of course this method, as with the two aforementioned methods, has its limit, but each one partially contributes to solar physics. The global method was proposed by Mouradian et al (2000Mouradian et al ( , 2002 and Mouradian & Heristchi (2005).…”

Section: Introductionmentioning

confidence: 99%

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The global rotation of solar activity structures

Heristchi

Mouradian

2009

A&A

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Aims. This paper investigates the rotation rate of solar activity from a global point of view, considering daily index or flux, instead of individual structures. It determines the rotation rate variations inside the cycle by two-year sequences and the comprehensive study of the cycle. Methods. The method consists of harmonic analysis of series of daily monitoring of solar activity. One is the sunspot number covering cycles 9 to 23 (over 157 years) and the second the flux of the corona at 2800 MHz from cycle 19 to 25 (over 53 years). These long series were analysed by the maximum entropy method for the measurement of rotation frequency. Results. The findings displayed in this paper are: i) sunspots and coronal flux show the same global rotation rates; ii) the solar rotation unfolding during the cycle is complex, without any systematic pattern; iii) the analysis of cyclic solar activity rotation leads to variation of the rotation rate with a period of 52.4 years; iv) the present result supports the existence of high-level cycles made of five eleven-year cycles; the global rotation rate also has this periodicity; v) no asymmetry was found in the northern and southern hemisphere rotation rates.

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Section: Discussionmentioning

confidence: 82%

Section: Methods Of Analysismentioning

confidence: 99%

Section: The Datamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The global rotation of solar activity structures

Heristchi

Mouradian

2009

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“…To compare with the stellar behavior, I prefer to use an integral measure of the solar activity. Such a measure with an extended time base is the radio flux at 10.7 cm which has been investigated by Mouradian et al (2002) who found many peaks in the power spectrum between 25 and 29 days. Another measure that reveals the activity in the photospheric layers of the Sun is the daily sunspot number.…”

Section: Introductionmentioning

confidence: 99%

Rotational periodicities in sunspot relative numbers

Balthasar¹

2007

A&A

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Context. The search for active longitudes on the Sun has a long history, and many controversial results have been published. Recently the question became more important when active longitudes were found on other stars. Aims. The aim of this paper is to investigate an integral measure of solar activity available for a long time interval and which allows enough frequency resolution for the investigation of active longitudes. Such a measure is given by the daily sunspot relative numbers. Methods. A search for periodicities is performed with a classical Fast Fourier Transform (FFT), with a wavelet analysis and with the tool of superimposed epochs. Results. The FFT yields a hump of power peaks near the synodic rotation period of 27 days, but only a very weak and insignificant enhancement around 13.5 days, indicating that the mean rotational variation of the sunspot numbers typically has one maximum and one minimum (overlaid by minor fluctuations). The wavelet analysis shows that spectral power for single periods varies for certain time intervals. A systematic drift during the solar activity cycle is not detected. Similar results are obtained from the superimposed epochs. Periodic "flip-flops" with time scales of a few years as for some stars are not found for the Sun in this investigation. Conclusions. Sunspots are not distributed equally over the longitudes; there is a more active and a less active hemisphere. The rotation period derived from the pattern varies over long time scales. The results found in this work are not in favor of an explanation of the variations due to a differential rotation law. The rotation of the sunspot distribution pattern might reflect the internal rotation of the Sun, but it better fits the range of highest rotation rates in the upper convection zone than the rotation near the tachocline.

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The rotation signal in daily sunspot areas

Wen

et al. 2010

Astrophys Space Sci

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The continuous complex Morlet wavelet transform is used to investigate temporal rotation cycle length of daily sunspot areas from May 9, 1874 to February 28, 2010, from a global point of view. The rotation cycle length of the Sun is found to have a secular trend: it decreased from the year of 1874 to 1950s, and since then the Sun is rotating more and more speedily in the long run. The rotation period appears around the maximum times of the Schwabe cycles with statistical significance, but in the minimum times it is always statistically insignificant, although it is found to have no relation with the Schwabe cycle. The period length of the rotation cycle displays the significant periods of 2.61 and 5.77 years.

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Solar activity cycle and rotation of the corona

Cited by 24 publications

References 39 publications

The global rotation of solar activity structures

The global rotation of solar activity structures

Rotational periodicities in sunspot relative numbers

The rotation signal in daily sunspot areas

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