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Petrovay, K.; Driel‐Gesztelyi, L. van

doi:10.1023/a:1004988123265

Cited by 129 publications

(112 citation statements)

References 11 publications

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“…A lognormal distribution implies that it is the logarithm of the decay rate D that is normally distributed, and thus it is log D that should be used as the dependent variable in least-square fits and other standard statistical procedures. This realization has helped us in the first paper of this series (Petrovay and van Driel-Gesztelyi, 1997, hereafter Paper I; see also Petrovay, 1998) to finally determine, by rigorous statistical methods and at a quite convincing confidence level, the mean law governing sunspot decay. It was found that an "idealized" sunspot following this mean law exactly, with no random deviations, would decay according to the law D ideal = C D r/r 0 C D = 32.0 ± 0.26.…”

Section: Introductionmentioning

confidence: 94%

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1999

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Abstract. In a statistical analysis of Debrecen Photoheliographic Results sunspot area data we find that the logarithmic deviation (log D) ′ of the area decay rate D from the parabolic mean decay law (derived in the first paper in this series) follows a Gaussian probability distribution. As a consequence, the actual decay rate D and the time-averaged decay rate D are also characterized by approximately lognormal distributions, as found in an earlier work. The correlation time of (log D) ′ is about 3 days. We find a significant physical anticorrelation between (log D) ′ and the amount of plage magnetic flux of the same polarity in an annulus around the spot on Kitt Peak magnetograms. The anticorrelation is interpreted in terms of a generalization of the turbulent erosion model of sunspot decay to the case when the flux tube is embedded in a preexisting homogeneous "plage" field. The decay rate is found to depend inversely on the value of this plage field, the relation being very close to logarithmic, i.e. the plage field acts as multiplicative noise in the decay process. A Gaussian probability distribution of the field strength in the surrounding plage will then naturally lead to a lognormal distribution of the decay rates, as observed. It is thus suggested that, beside other multiplicative noise sources, the environmental effect of surrounding plage fields is a major factor in the origin of lognormally distributed large random deviations from the mean law in the sunspot decay rates.

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Section: Introductionmentioning

confidence: 94%

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1999

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“…It is generally believed that large sunspot groups also live long. In fact, there is a rule of proportionality between the maximum area (A M ) of a sunspot group and its life time (T ) (first noticed by Gnevyshev (1938) and formulated by Waldmeier (1955); see also Petrovay and Van Driel-Gesztelyi, 1997): AM T ≈ 10 msh day −1 . However, the relationship between the area and the life time of sunspot groups may be exponential rather than linear (Javaraiah, 2003a).…”

Section: Introductionmentioning

confidence: 99%

“…Studies on variations in solar activity are important for understanding the mechanism behind the solar activity and solar cycle, and also for predicting the level of activity (Hathaway, 2009;Petrovay, 2010). The properties of solar cycle are generally described by the Zürich or international sunspot number, R Z = k(10g +f ), where k is a correction factor for the observer, g is the number of identified sunspot groups, and f is the number of individual sunspots.…”

Section: Introductionmentioning

confidence: 99%

The G–O Rule and Waldmeier Effect in the Variations of the Numbers of Large and Small Sunspot Groups

Javaraiah

2012

Sol Phys

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We have analysed the combined Greenwich and Solar Optical Observing Network (SOON) sunspot group data during the period of 1874 -2011 and determined variations in the annual numbers (counts) of the small (maximum area A M < 100 millionth of solar hemisphere, msh), large (100 ≤ A M < 300 msh), and big (A M ≥ 300 msh) spot groups. We found that the amplitude of an even-numbered cycle of the number of large groups is smaller than that of its immediately following odd-numbered cycle. This is consistent with the well known Gnevyshev and Ohl rule or G-O rule of solar cycles, generally described by using the Zürich sunspot number (R Z ). During cycles 12 -21 the G-O rule holds good for the variation in the number of small groups also, but it is violated by cycle pair (22, 23) as in the case of R Z . This behavior of the variations in the small groups is largely responsible for the anomalous behavior of R Z in cycle pair (22, 23). It is also found that the amplitude of an odd-numbered cycle of the number of small groups is larger than that of its immediately following even-numbered cycle. This can be called as 'reverse G-O rule'. In the case of the number of the big groups, both cycle pairs (12, 13) and (22, 23) violated the G-O rule. In many cycles the positions of the peaks of the small, large, and big groups are different and considerably differ with respect to the corresponding positions of the R Z peaks. In the case of cycle 23, the corresponding cycles of the small and large groups are largely symmetric/less asymmetric (Waldmeier effect is weak/absent) with their maxima taking place two years later than that of R Z . The corresponding cycle of the big groups is more asymmetric (strong Waldmeier effect) with its maximum epoch taking place at the same time as that of R Z .

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“…Sunspots decay as a result of fragmentation (Petrovay & van Driel-Gesztelyi 1997;Martínez Pillet 2002). The decay rate, which in turn determines the sunspot lifetime, is a function of anchoring depth and the corresponding convection timescales in such depths (Moradi et al 2010).…”

Section: Introductionmentioning

confidence: 99%

Properties of sunspot umbrae observed in cycle 24

Kiess

Rezaei

Schmidt

2014

A&A

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Aims. There is an ongoing debate whether the solar activity cycle is overlaid with a long-term decline that may lead to another grand minimum in the near future. We used the size, intensity, and magnetic field strength of sunspot umbrae to compare the present cycle 24 with the previous one. Methods. We used data of the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory and selected all sunspots between May 2010 and October 2012, using one image per day. We created two subsets of this dataset with a manual tracking algorithm, both without duplication. One contains each sunspot (910 umbrae within 488 spots) and was used to analyze the distribution of umbral areas, selected with an automated thresholding method. The other subset contains 205 fully evolved sunspots. We estimated their magnetic field and the total magnetic flux and discuss the relations between umbral size, minimum continuum intensity, maximum field strength, and total magnetic flux. Results. We find non-linear relations between umbral minimum intensity and size and between maximum magnetic field strength and size. The field strength scales linearly with the intensity and the umbral size scales roughly linearly with the total magnetic flux, while the size and field strength level off with stronger flux. When separated into hemispheres and averaged temporally, the southern umbrae show a temporal increase in size and the northern umbrae remain constant. We detected no temporal variation in the umbral mean intensity. The probability density function of the umbral area in the ascending phase of the current solar cycle is similar to that of the last solar cycle. Conclusions. From our investigation of umbral area, magnetic field, magnetic flux, and umbral intensity of the sunspots of the rising phase of cycle 24, we do not find a significant difference to the previous cycle, and hence no indication for a long-term decline of solar activity.

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Cited by 129 publications

References 11 publications

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The G–O Rule and Waldmeier Effect in the Variations of the Numbers of Large and Small Sunspot Groups

Properties of sunspot umbrae observed in cycle 24

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