Asymmetrical Distribution of Sunspot Groups in the Solar Hemispheres

Li, Kejun; Liu, Xiaohua; Yun, Hong Sik; Xiong, S. Y.; Hu, Liang; Zhao, Hai-Juan; Zhan, L. S.; Gu, Xiaoxia

doi:10.1093/pasj/54.4.629

Cited by 16 publications

(6 citation statements)

References 22 publications

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“…The refined consideration reveals, that the expected polarity dominance for cycle 23 is getting more close to the total number of events, but still with a minority of reversed cases in both hemispheres. A hemispheric asymmetry in the distribution of evolving photospheric magnetic flux, as supported by the results of Li et al (2002) who found more sunspot groups appearing in the northern hemisphere of the Sun in the rising to maximum phase of cycle 23, from 1996 until 2000, is not apparent in the PEA frequency distribution.…”

Section: Photospheric Source Regions and Solar Cycle Dependencementioning

confidence: 55%

The basic characteristics of EUV post-eruptive arcades and their role as tracers of coronal mass ejection source regions

Tripathi

Bothmer

Cremades

2004

A&A

114

109

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Abstract. The Extreme ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO) spacecraft provides unique observations of dynamic processes in the low corona. The EIT 195 Å data taken from 1997 to the end of 2002 were investigated to study the basic physical properties of post-eruptive arcades (PEAs) and their relationship with coronal mass ejections (CMEs) as detected by SOHO/LASCO (Large Angle Spectrometric Coronagraph). Over the investigated time period, 236 PEA events have been identified in total. For each PEA, its EUV lifetime as derived from the emission time at 195 Å, its heliographic position and length, and its corresponding photospheric source region inferred from SOHO/MDI (Michelson Doppler Imager) data has been studied, as well as the variation of these parameters over the investigated phase of solar cycle 23. An almost one to one correspondence is found between EUV PEAs and white-light CMEs. Based on this finding, PEAs can be considered as reliable tracers of CME events even without simultaneous coronagraph observations. A detailed comparison of the white-light, soft X-ray and EUV observation for some of the events shows, that PEAs form in the aftermath of CMEs likely in the course of the magnetic restructurings taking place at the coronal source sites. The average EUV emission life-time for the selected events ranged from 2 to 20 h, with an average of 7 h. The heliographic length of the PEAs was in the range of 2 to 40 degrees, with an average of 15 degrees. The length increased by a factor of 3 to 4 in the latitude range of 20 to 40 degrees in the northern and southern hemispheres, with longer PEAs being observed preferentially at higher latitudes. The PEAs were located mainly in the activity belts in both hemispheres, with the southern hemispheric ones being shifted by about 15 degree in latitude further away from the solar equator during 1997−2002. The decrease in latitude of the PEA positions was 10 to 15 degrees in the northern and southern hemispheres over this period. The axes of the PEAs were overlying magnetic polarity inversion lines when traced back to the MDI synoptic charts of the photospheric field. The magnetic polarities on both sides of the inversion lines agreed with the dominant magnetic pattern expected in cycle 23, i.e. being preferentially positive to the West of the PEA axes in the North and negative in the South. One third (31%) of the PEA events showed reversed polarities. The origin of PEAs is found not just in single bipolar regions (BPRs), but also in between pairs of neighboring BPRs.

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Section: Photospheric Source Regions and Solar Cycle Dependencementioning

confidence: 55%

The basic characteristics of EUV post-eruptive arcades and their role as tracers of coronal mass ejection source regions

Tripathi

Bothmer

Cremades

2004

A&A

114

109

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“…This is not the whole story, though. Other researchers (Li et al 2002;Norton & Gallagher, 2010) parsed the solar cycle into distinct periods of minimum, rising, maximum, and declining times, then found the phase relationship between the hemispheres during these times. (Of course, the smaller the time period analyzed, the smaller the statistical sample of data becomes, especially during cycle minimum).…”

Section: Hemispheric Phase Lag Based On Sunspot Datamentioning

confidence: 99%

Hemispheric Coupling: Comparing Dynamo Simulations and Observations

2014

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Numerical simulations that reproduce solar-like magnetic cycles can be used to generate long-term statistics. The variations in north-south hemispheric solar cycle synchronicity and amplitude produced in simulations has not been widely compared to observations. The observed limits on solar cycle amplitude and phase asymmetry show that hemispheric sunspot area production is no more than 20% asymmetric for cycles 12-23 and that phase lags do not exceed 20% (or two years) of the total cycle period, as determined from Royal Greenwich Observatory sunspot data. Several independent studies have found a long-term trend in phase values as one hemisphere leads the other for, on average, four cycles. Such persistence in phase is not indicative of a stochastic phenomenon. We compare these observational findings to the magnetic cycle found in a numerical simulation of solar convection recently produced with the EULAG-MHD model. This long "millennium simulation" spans more than 1600 years and generated 40 regular, sunspot-like cycles. While the simulated cycle length is too long (∼ 40 yrs) and the toroidal bands

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“…Second, the maximum time of solar activity in a normal cycle is usually different in the two hemispheres [ Li et al , 2002a].…”

Section: Fine‐scale Characteristics Of Full‐disk Activity Cyclesmentioning

confidence: 99%

Cyclic behavior of solar full‐disk activity

Gao

et al. 2008

J. Geophys. Res.

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In order to describe the cyclic behavior of solar full‐disk activity (the surface magnetic fields, filaments, the green Fe XIV, 5303Å corona local maxima intensities, and torsional oscillations), we propose a new concept, a “full‐disk activity cycle,” which consists of two successive normal cycles: a high‐latitude activity cycle following a low‐latitude activity cycle. When solar activity begins to progress into a full‐disk activity cycle, it latitudinally rushes to the poles, starting from middle latitudes (about 40°) at about a normal cycle minimum. At the solar poles, magnetic polarity reversal takes place on both the solar hemispheres, and opposite reversals occur on the opposite hemispheres; resultingly, the new appearing magnetic polarity at high latitudes on a hemisphere will become the leading magnetic polarity of regions at low latitudes on the same hemisphere in the following normal cycle. After the latitudinal drift of solar activity reaches the solar poles at about the maximum time of the normal cycle, solar activity begins to latitudinally migrate in a reverse direction; it moves toward the equator continually till almost arriving at the solar equator and lasting for about 1.5 normal cycles. When a full‐disk activity cycle progresses from a high‐latitude activity cycle into a low‐latitude activity cycle, the next full‐disk activity cycle begins. Two successive full‐disk activity cycles have a normal cycle overlapped in time but are spatially separated. The characteristics of full‐disk activity cycles are summarized as well. At present we do not know why a full‐disk activity cycle begins at midlatitudes; it is perhaps related with solar differential rotation. Further work is required to uncover the physical mechanisms behind the concept.

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Asymmetrical Distribution of Sunspot Groups in the Solar Hemispheres

Cited by 16 publications

References 22 publications

The basic characteristics of EUV post-eruptive arcades and their role as tracers of coronal mass ejection source regions

The basic characteristics of EUV post-eruptive arcades and their role as tracers of coronal mass ejection source regions

Hemispheric Coupling: Comparing Dynamo Simulations and Observations

Cyclic behavior of solar full‐disk activity

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