scholarly journals Flare Occurrence in the Solar Active Regions with Reversed Helicity Sign

2001 ◽  
Vol 203 ◽  
pp. 247-250
Author(s):  
S. D. Bao ◽  
G. X. Ai ◽  
H. Q. Zhang
Keyword(s):  
Solar Cycle ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Relative Number ◽  
Active Regions ◽  
Flare Activity ◽  
Sunspot Maximum ◽  
Solar Active Regions ◽  
Current Helicity

Based on the Huairou Solar Observing Station dataset, we computed the current helicity for several hundreds of active regions and found that: (1) Active regions that do not follow the hemispheric helicity sign rule show more flare activity than normal active regions. (2) The relative number of active regions with reversed helicity sign is higher near sunspot maximum. (3) It appears that during solar cycle 22 the southern hemisphere has more the reversed-sign active regions and stronger flare activity than the northern hemisphere.

The Hemispheric Sign Rule of Current Helicity during the Rising Phase of Cycle 23

2000 ◽  
Vol 179 ◽  
pp. 303-306
Author(s):  
S. D. Bao ◽  
G. X. Ai ◽  
H. Q. Zhang
Keyword(s):  
Solar Cycle ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Active Regions ◽  
Hemispheric Preference ◽  
Current Helicity

AbstractWe compute the signs of two different current helicity parameters (i.e., αbestandHc) for 87 active regions during the rise of cycle 23. The results indicate that 59% of the active regions in the northern hemisphere have negative αbestand 65% in the southern hemisphere have positive. This is consistent with that of the cycle 22. However, the helicity parameterHcshows a weaker opposite hemispheric preference in the new solar cycle. Possible reasons are discussed.

Twist of Magnetic Fields in Solar Active Regions

2000 ◽  
Vol 179 ◽  
pp. 245-247
Author(s):  
Hongqi Zhang ◽  
Lirong Tian ◽  
Shudong Bao ◽  
Mei Zhang
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Magnetic Fields ◽  
Northern Hemisphere ◽  
General Trend ◽  
Active Regions ◽  
Astronomical Observatory ◽  
Twisted Field ◽  
Current Helicity ◽  
Sunspot Groups

Extended abstractIn the solar atmosphere, the magnetic and current helicity have played an important role in the study of twisted magnetic field. Current helicity parameterh∥=B∥· (∇ ×B)∥and force free factorcan be used to analyze the distribution of twisted field (current helicity) in the photosphere (Seehafer 1990; Pevtsovet al.1995; Bao & Zhang 1998). Bao & Zhang (1998) and Zhang & Bao (1999) computed the photospheric current helicity parameterh∥for 422 active regions, including most of the large ones observed in the period of 1988–1997 at Huairou Solar Observing Station of Beijing Astronomical Observatory.The calculated results (Pevtsovet al.1995; Abramenkoet al.1996; Bao & Zhang 1998) show that most current helicities in sunspot groups in the northern hemisphere show negative sign in the northern hemisphere, while positive in the southern hemisphere, which is consistent with Seehafer’s result (Seehafer 1990). The distribution of current helicity parameterh∥in active regions also shows the butterfly pattern through the solar cycle. And, less than 30% of the active regions do not follow the general trend (Zhang & Bao 1998).

scholarly journals Periodic Variation of Solar Flare Index for the Last Solar Cycle (Cycle 24)

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Atila Ozguc ◽  
Ali Kilcik ◽  
Volkan Sarp ◽  
Hülya Yeşilyaprak ◽  
Rıza Pektaş
Keyword(s):  
Solar Cycle ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Wavelet Transforms ◽  
Data Sets ◽  
Flare Activity ◽  
Data Set ◽  
Analysis Methods ◽  
Flare Index ◽  
Cycle 24

In this study, we used the flare index (FI) data taken from Kandilli Observatory for the period of 2009–2020. The data sets are analyzed in three categories as Northern Hemisphere, Southern Hemisphere, and total FI data sets. Total FI data set is obtained from the sum of Northern and Southern Hemispheric values. In this study, the periodic variations of abovementioned three categories FI data sets were investigated by using the MTM and Morlet wavelet analysis methods. The wavelet coherence (XWT) and cross wavelet (WTC) analysis methods were also performed between these data sets. As a result of our analysis, the following results were found: (1) long- and short-term periodicities ( 2048 ± 512 day and periodicities smaller than 62 days) exist in all data sets without any exception at least with 95 % confidence level; (2) all periodic variations were detected maximum during the solar cycle, while during the minima, no meaningful period is detected; (3) some periodicities have data preference that about 150 days Rieger period appears only in the whole data set and 682-, 204-, and 76.6-day periods appear only in the Northern Hemisphere data sets; (4) During the Solar Cycle 24, more flare activity is seen at the Southern Hemisphere, so the whole disk data periodicities are dominated by this hemisphere; (5) in general, there is a phase mixing between Northern and Southern Hemisphere FI data, except about 1024-day periodicity, and the best phase coherency is obtained between the Southern Hemisphere and total flare index data sets; (6) in case of the Northern and Southern Hemisphere FI data sets, there is no significant correlation between two continuous wavelet transforms, but the strongest correlation is obtained for the total FI and Southern Hemisphere data sets.

scholarly journals The Current Helicity Parameter Hc is More Sensitive than αbest to Faraday Rotation

2005 ◽  
Vol 13 ◽  
pp. 143-143
Author(s):  
Shudong Bao
Keyword(s):  
Solar Cycle ◽  
Northern Hemisphere ◽  
Faraday Rotation ◽  
Active Regions ◽  
Line Of Sight ◽  
Positive Contribution ◽  
Positive Polarity ◽  
Solar Cycle 23 ◽  
Polarity Field ◽  
Current Helicity

Observations have indicated that the net helicity sign of active regions is predominantly negative in the northern hemisphere and positive in the southern (see Table 1). From Table 1, we find that the hemispheric sign rule of helicity parameter αbest does not change with another solar cycle; but the helicity parameter Hc seems to show a weak opposite hemispheric preference for Huairou data in the solar cycle 23 and no preference for Mees data. How to explain such a phenomenon? We think one reason may be from the action of Faraday rotation. Faraday rotation will cause a counterclockwise rotation of the azimuth for a positive polarity field and vice versa. During the cycle 22, the polarity of leading sunspots is dominantly negative in the northern hemisphere and positive in the southern. The effect of Faraday rotation, which is determined mostly by a leading polarity sunspot, has a positive contribution to the percentage of current helicity signs in active regions and leads to the increase of the strength of the hemispheric sign rule. In the cycle 23, the polarity of most leading sunspots is positive in the northern hemisphere and Faraday rotation will decrease the percentage of current helicity signs. Consequently, the strength of the hemispheric rule should be weakened. On the other hand, Hc is more susceptible to Faraday rotation than αbest because it is mainly related to the areas where the line-of-sight field is strong. Therefore, if the effect of Faraday rotation is not completely removed in our observations, the hemispheric sign rule showed is weak in the cycle 23 than in the cycle 22 (for αbest), even opposite (for Hc).

Alpha-Effect, Current and Kinetic Helicities for Magnetically Driven Turbulence, and Solar Dynamo

2000 ◽  
Vol 179 ◽  
pp. 387-388
Author(s):  
Gaetano Belvedere ◽  
V. V. Pipin ◽  
G. Rüdiger
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Convection Zone ◽  
Solar Surface ◽  
Momentum Transport ◽  
Angular Momentum Transport ◽  
Magnetic Buoyancy ◽  
Alpha Effect ◽  
Current Helicity

Extended AbstractRecent numerical simulations lead to the result that turbulence is much more magnetically driven than believed. In particular the role ofmagnetic buoyancyappears quite important for the generation ofα-effect and angular momentum transport (Brandenburg & Schmitt 1998). We present results obtained for a turbulence field driven by a (given) Lorentz force in a non-stratified but rotating convection zone. The main result confirms the numerical findings of Brandenburg & Schmitt that in the northern hemisphere theα-effect and the kinetic helicityℋkin= 〈u′ · rotu′〉 are positive (and negative in the northern hemisphere), this being just opposite to what occurs for the current helicityℋcurr= 〈j′ ·B′〉, which is negative in the northern hemisphere (and positive in the southern hemisphere). There has been an increasing number of papers presenting observations of current helicity at the solar surface, all showing that it isnegativein the northern hemisphere and positive in the southern hemisphere (see Rüdigeret al. 2000, also for a review).

scholarly journals Intermittency spectra of current helicity in solar active regions

2018 ◽  
Vol 480 (3) ◽  
pp. 3780-3787 ◽  
Author(s):  
A S Kutsenko ◽  
V I Abramenko ◽  
K M Kuzanyan ◽  
Haiqing Xu ◽  
Hongqi Zhang
Keyword(s):  
Active Regions ◽  
Solar Active Regions ◽  
Current Helicity

scholarly journals Magnetic Shear and Nonpotential Energy Evolution of Solar Minimum and the Onset of Solar Cycle 23

2001 ◽  
Vol 203 ◽  
pp. 267-269
Author(s):  
J. Dun ◽  
H. Zhang ◽  
B. Zhang ◽  
R. Li
Keyword(s):  
Solar Cycle ◽  
Relative Number ◽  
Transverse Field ◽  
Active Regions ◽  
Shear Angle ◽  
Magnetic Shear ◽  
Data Set ◽  
Solar Cycle 23 ◽  
Sunspot Relative Number ◽  
The Magnetic Field

Using a 1995-1998 data set of vector magnetograms, the magnetic field flux, shear angle of the transverse field and nonpotential energy of active regions were calculated. The evolution of these parameters were analyzed together with time series of the solar monthly sunspot relative number and area to study their relationships in the ascending phase of solar cycle 23. We find the magnetic flux and nonpotential energy have a good correlation with sunspot relative number and area. But the magnetic shear angle does not develop as above indices.

scholarly journals Super-active regions in solar cycle 24

2015 ◽  
Vol 11 (S320) ◽  
pp. 309-314 ◽  
Author(s):  
Anqin Chen ◽  
Jingxiu Wang
Keyword(s):  
Solar Cycle ◽  
Active Regions ◽  
Total Solar Irradiance ◽  
Flare Activity ◽  
Solar Cycles ◽  
Solar Cycle 24 ◽  
Satisfactory Account ◽  
Current Cycle ◽  
Flare Index ◽  
Cycle 24

AbstractComparing with solar cycles 21-23, the level of solar activity in the current cycle is very low. So far, there have been only five SARs and 45 X class flares. The monthly smoothed total solar irradiance decreased sharply by 0.09% from the maximum of cycle 23 to the minima between cycles 23 and 24. In this contribution, we present new studies on SARs in Cycle 24. The SARs in the current cycle have relatively smaller flare index (Iflare) and composite vector field index (Icom) comparing with the SARs in cycles 22 and 23. There is a clearly linear relationship between Iflare and Icom. The emphasis of this contribution is put on the similarity and different behaviors of vector magnetic fields of the SARs in the current solar cycle and the previous ones. We try to get a satisfactory account for the general characteristics and relatively lower level of solar flare activity in Cycle 24.

scholarly journals Current helicity and magnetic field anisotropy in solar active regions

2015 ◽  
Vol 454 (2) ◽  
pp. 1921-1930 ◽  
Author(s):  
H. Xu ◽  
R. Stepanov ◽  
K. Kuzanyan ◽  
D. Sokoloff ◽  
H. Zhang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Active Regions ◽  
Solar Active Regions ◽  
Current Helicity
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