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.

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.

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 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 Reconstructing solar magnetic fields from historical observations

2018 ◽  
Vol 616 ◽  
pp. A134 ◽  
Author(s):  
I. O. I. Virtanen ◽  
I. I. Virtanen ◽  
A. A. Pevtsov ◽  
K. Mursula
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Active Regions ◽  
Surface Flux ◽  
Magnetic Activity ◽  
Maunder Minimum ◽  
Photospheric Magnetic Field ◽  
Sunspot Activity

Aims. Sunspot activity is often hemispherically asymmetric, and during the Maunder minimum, activity was almost completely limited to one hemisphere. In this work, we use surface flux simulation to study how magnetic activity limited only to the southern hemisphere affects the long-term evolution of the photospheric magnetic field in both hemispheres. The key question is whether sunspot activity in one hemisphere is enough to reverse the polarity of polar fields in both hemispheres. Methods. We simulated the evolution of the photospheric magnetic field from 1978 to 2016 using the observed active regions of the southern hemisphere as input. We studied the flow of magnetic flux across the equator and its subsequent motion towards the northern pole. We also tested how the simulated magnetic field is changed when the activity of the southern hemisphere is reduced. Results. We find that activity in the southern hemisphere is enough to reverse the polarity of polar fields in both hemispheres by the cross-equatorial transport of magnetic flux. About 1% of the flux emerging in the southern hemisphere is transported across the equator, but only 0.1%–0.2% reaches high latitudes to reverse and regenerate a weak polar field in the northern hemisphere. The polarity reversals in the northern hemisphere are delayed compared to the southern hemisphere, leading to a quadrupole Sun lasting for several years.

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 Variations in the occurrence of SuperDARN F region echoes

2014 ◽  
Vol 32 (2) ◽  
pp. 147-156 ◽  
Author(s):  
M. Ghezelbash ◽  
R. A. D. Fiori ◽  
A V. Koustov
Keyword(s):  
Solar Cycle ◽  
Southern Hemisphere ◽  
Local Time ◽  
Northern Hemisphere ◽  
Solar Minimum ◽  
Solar Maximum ◽  
Radar Data ◽  
Occurrence Rate ◽  
Major Focus ◽  
F Region

Abstract. The occurrence of F region ionospheric echoes observed by a number of SuperDARN HF radars is analyzed statistically in order to infer solar cycle, seasonal, and diurnal trends. The major focus is on Saskatoon radar data for 1994–2012. The distribution of the echo occurrence rate is presented in terms of month of observation and magnetic local time. Clear repetitive patterns are identified during periods of solar maximum and solar minimum. For years near solar maximum, echoes are most frequent near midnight during winter. For years near solar minimum, echoes occur more frequently near noon during winter, near dusk and dawn during equinoxes and near midnight during summer. Similar features are identified for the Hankasalmi and Prince George radars in the northern hemisphere and the Bruny Island TIGER radar in the southern hemisphere. Echo occurrence for the entire SuperDARN network demonstrates patterns similar to patterns in the echo occurrence for the Saskatoon radar and for other radars considered individually. In terms of the solar cycle, the occurrence rate of nightside echoes is shown to increase by a factor of at least 3 toward solar maximum while occurrence of the near-noon echoes does not significantly change with the exception of a clear depression during the declining phase of the solar cycle.

scholarly journals North-South Distribution and Asymmetry of GOES SXR Flares during Solar Cycle 24

2020 ◽  
Vol 28 (1) ◽  
pp. 228-235
Author(s):  
Anita Joshi ◽  
Ramesh Chandra
Keyword(s):  
Data Analysis ◽  
Solar Cycle ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Solar Maximum ◽  
X Ray ◽  
The North ◽  
Solar Cycle 24 ◽  
Cycle 24 ◽  
Second Peak

AbstractHere we present the results of the study of the north-south (N-S) distribution and asymmetry of GOES soft X-ray (SXR) flares during solar cycle 24. The period of study includes ascending, maximum and descending phases of the cycle. During the cycle double-peaked (2011, 2014) solar maximum has occurred. The cycle peak in the year 2011 is due to B-class flares excess activity in the northern hemisphere (NH) whereas C and M class flares excess activity in the southern hemisphere (SH) supported the second peak of the cycle in 2014. The data analysis shows that the SXR flares are more pronounced in 11 to 20 degree latitudes for each hemisphere. Cumulative values of SXR flare count show northern excess during the ascending phase of the cycle. However, in the descending phase of the cycle, southern excess occurred. In the cycle a significant SH dominated asymmetry exists. Near the maximum of the cycle, the asymmetry enhances pronouncedly and reverses in sign.

scholarly journals Vorticity, Current Helicity and Alpha-effect for Magnetic-driven Turbulence in the Solar Convection Zone

2001 ◽  
Vol 203 ◽  
pp. 152-155
Author(s):  
G. Rüdiger
Keyword(s):  
Numerical Simulation ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Electromotive Force ◽  
Convection Zone ◽  
Solar Convection Zone ◽  
Solar Convection ◽  
Magnetic Buoyancy ◽  
Alpha Effect ◽  
Current Helicity

The turbulent electromotive force as well as the kinetic and current helicities have been computed for a turbulence subject to magnetic buoyancy and global rotation. The dynamo-alpha is found as positive in the northern hemisphere and negative in the southern hemisphere and the kinetic helicity has just the same signs.In agreement with the observations the current helicity is negative in the northern hemisphere and positive in the southern hemisphere. Our current helicities and alpha-effects are thus always out of phase. The signs of alpha-effect and both helicities exactly correspond to a numerical simulation by Brandenburg & Schmitt (1998).

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