Rossby‐Type Wave–Induced Periodicities in Flare Activities and Sunspot Areas or Groups during Solar Maxima

Lou, Yu‐Qing

doi:10.1086/309387

Cited by 123 publications

(161 citation statements)

References 51 publications

(65 reference statements)

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“…Recently, Lou (2000) has shown that for typical solar parameters, equatorially trapped Rossby waves with n \ 1(2) and m \ 13 have periods around 164 days, while for equatorially trapped mixed waves with n \ 0 and m \ 12, the Rossby-Poincare obtained period is around 151 days, both in good agreement with the period of the above reported periodicity. Also, Lou (2000) suggests that Rossby-type waves could lead to magnetic Ñux eruption through the modulation of the onset of magnetic buoyancy instabilities, leading to the appearance of Ñares in active regions. However, in spite of this plausible scenario, several important points still remain to be explained, for instance : Why does this periodic emergence of magnetic Ñux take place in already formed active regions setting up a complex magnetic conÐguration ideally suited for the occurrence of high-energy Ñares ?…”

Section: Results and Conclusionsupporting

confidence: 79%

“…Later, Bai & Sturrock (1993) modiÐed the earlier period to the value 25.50 days, but that model seems to be very constrained by helioseismological data about the rotation of the SunÏs interior. Recently, Lou (2000) has suggested that such periodicities can be related to large-scale equatorially trapped Rossbytype waves showing that, for typical solar parameters, the periods of these waves are in good agreement with the observed ones. Moreover, Lou has also pointed out that such waves can give rise to detectable features, such as surface elevations in the photosphere.…”

Section: Introductionsupporting

confidence: 65%

“…Why does this emergence only happen around the maximum of some solar cycles ? Assuming the mechanism proposed by Lou (2000), why is there only coherence between the periodicity in magnetic Ñux, sunspot areas, and high-energy Ñares around 160 days, while other possible periods allowed for di †erent values of n and m do not manifest in solar activity ?…”

Section: Results and Conclusionmentioning

confidence: 99%

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The Near 160 Day Periodicity in the Photospheric Magnetic Flux

Ballester

Oliver

Carbonell

2002

ApJ

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A periodicity near 154 days was discovered in the number of high-energy solar Ñares detected by Solar Maximum Mission (SMM) and Geosynchronous Operational Environmental Satellites (GOES) during the time interval 1980È1984 (Rieger et al. ;Dennis). In this paper, we analyze the historical records of photospheric magnetic Ñux to show that during solar cycle 21 the periodicity appeared in the photospheric magnetic Ñux linked to strong magnetic Ðelds, while it was absent during solar cycle 22. We also show that there was a time and frequency coincidence between both periodicities during solar cycle 21, which suggests the existence of a causal link between them. Taking into account that high-energy Ñares are triggered in regions of enhanced magnetic complexity (Kurokawa ; Ishii et al.), we propose that the appearance of the periodicity in the magnetic Ñux materializes through the formation of new sunspots within already formed sunspot groups, setting up a suitable scenario for the occurrence of energetic Ñares. This scenario leads to the occurrence of periodic episodes of magnetic reconnection between old and new emergent magnetic Ñux, able to trigger the periodic occurrence of energetic Ñares recorded by SMM and GOES.

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Section: Results and Conclusionsupporting

confidence: 79%

Section: Introductionsupporting

confidence: 65%

Section: Results and Conclusionmentioning

confidence: 99%

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The Near 160 Day Periodicity in the Photospheric Magnetic Flux

Ballester

Oliver

Carbonell

2002

ApJ

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“…Since the rotation period of CoRoT-2 is only 4.5 days, this would correspond to a wave period of ∼27 days, close to the periodicity of 28.9 days found by Lanza et al (2009) from the modelling of the out-of-transit light modulation. Moreover, other periodicities, ranging from 2 to 6 rotation periods, have been reported from the analysis of different solar data sets (Lou 2000). In the case of CoRoT-2, we found in Sect.…”

Section: Resultssupporting

confidence: 67%

Time evolution and rotation of starspots on CoRoT-2 from the modelling of transit photometry

Válio

Lanza

2011

A&A

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Context. CoRoT-2, the second planet-hosting star discovered by the CoRoT satellite, is a young and active star. A total of 77 transits were observed for this system over a period of 135 days. Aims. Small modulations detected in the optical light curve of the planetary transits are used to study the position, size, intensity, and temporal evolution of the photospheric spots on the surface of the star that are occulted by the planetary disk. Methods. We apply a spot model to these variations and create a spot map of the stellar surface of CoRoT-2 within the transit band for every transit. From these maps, we estimate the stellar rotation period and obtain the longitudes of the spots in a reference frame rotating with the star. Moreover, the spots temporal evolution is determined. This model achieves a spatial resolution of 2 • . Results. Mapping of 392 spots vs. longitude indicates the presence of a region free of spots, close to the equator, which is reminiscent of the coronal holes observed on the Sun during periods of maximum activity. With this interpretation, the stellar rotation period within the transit latitudes of −14.• 6 ± 10 • is obtained from the auto-correlation function of the time-integrated spot flux deficit, which yields a rotation period of 4.48 days. With this period, the temporal evolution of the spot surface coverage in individual 20 • longitude bins has periodicities ranging from 9 to 53 days with an average value of 31 ± 15 days. On the other hand, the longitude integrated spot flux, which is independent of the stellar rotation period, oscillates with a periodicity of 17.7 days, and its false-alarm probability is ∼3%. Conclusions. The rotation period of 4.48 days obtained here is shorter than the 4.54 days derived from the out-of-transit light modulation. Because the transit data sample a region close to the stellar equator while the period determined from out-of-transit data reflects the average rotation of the star, this is taken as an indication of a latitudinal differential rotation of about 3% or 0.042 rad/d.

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“…The periodicity of the spotted area variations is close to 4 times the mean rotation period of the star, while in the Sun it is ≈6 times and in CoRoT-2 is ≈6.5 times the rotation period. Those oscillations of the spotted area may be associated with hydromagnetic Rossby-type waves propagating in the upper part of the convection zone or at the interface between the radiative interior and the convection zone where the dynamo is probably located (Lou 2000;Zaqarashvili et al 2010). Since only a few examples of stars displaying Rieger-type cycles are known (cf., Massi et al 2005;Lanza et al 2009a), the new results on Kepler-17 are particularly interesting for a better understanding of this phenomenon in the framework of the solar-stellar connection.…”

Section: Resultsmentioning

confidence: 99%

Starspot activity and rotation of the planet-hosting star Kepler-17

Bonomo

Lanza

2012

A&A

101

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Context. Kepler-17 is a G2V sun-like star accompanied by a transiting planet with a mass of ≈2.5 Jupiter masses and an orbital period of 1.486 d, recently discovered by the Kepler space telescope. This star is highly interesting as a young solar analogue. It is also a good candidate for a test of the tidal theories for solar-like stars. Aims. We used about 500 days of high-precision, high-duty-cycle optical photometry collected by Kepler to study the rotation of the star and the evolution of its photospheric active regions.Methods. We applied a maximum-entropy light curve inversion technique to model the flux rotational modulation induced by active regions that consist of dark spots and bright solar-like faculae with a fixed area ratio. Their configuration was varied after a fixed time interval to take their evolution into account. Active regions were used as tracers to study stellar differential rotation, and planetary occultations were used to constrain the latitude of some spots. Results. Our modelling approach reproduces the light variations of Kepler-17 with a standard deviation of the residuals comparable with the precision of Kepler photometry. We find several active longitudes where individual active regions appear, evolve, and decay with lifetimes comparable to those observed in the Sun, although the star has a spotted area ≈10−15 times larger than the Sun at the maximum of the 11-yr cycle. Kepler-17 shows a solar-like latitudinal differential rotation, but the fast spot evolution prevents a precise determination of its amplitude. Moveover, the star shows a cyclic variation of the starspot area with a period of 47.1 ± 4.5 d, particularly evident during the last 200 days of the observations, similar to the solar Rieger cycles. Possible effects of the close-in massive planet on stellar photospheric activity cannot be excluded, but require a long-term monitoring to be unambiguously detected.

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Rossby‐Type Wave–Induced Periodicities in Flare Activities and Sunspot Areas or Groups during Solar Maxima

Cited by 123 publications

References 51 publications

The Near 160 Day Periodicity in the Photospheric Magnetic Flux

The Near 160 Day Periodicity in the Photospheric Magnetic Flux

Time evolution and rotation of starspots on CoRoT-2 from the modelling of transit photometry

Starspot activity and rotation of the planet-hosting star Kepler-17

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