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).

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 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.

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.

Three Super Active Regions in the Descending Phase of Solar Cycle 23

2003 ◽  
Vol 3 (6) ◽  
pp. 491-494 ◽  
Author(s):  
Hong-Qi Zhang ◽  
Xing-Ming Bao ◽  
Yin Zhang ◽  
Ji-Hong Liu ◽  
Shu-Dong Bao ◽  
...  
Keyword(s):  
Solar Cycle ◽  
Active Regions ◽  
Solar Cycle 23

scholarly journals The Opening of EUV Loops

2001 ◽  
Vol 203 ◽  
pp. 347-350
Author(s):  
J. Zhang ◽  
J. Wang
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Neutral Line ◽  
Negative Polarity ◽  
The Other ◽  
Line Of Sight ◽  
Active Region Noaa ◽  
Positive Polarity ◽  
Polarity Field ◽  
Magnetic Features

We analyzed simultaneous data from Huairou Solar Observing Station (HSOS) and the Transition Region and Coronal Explorer (TRACE) of November 4, 1998 in the active region NOAA 8375. The magnetic fields in this region had the following properties: a main positive polarity line-of-sight field was surrounded by relatively weak negative polarity fields; many moving magnetic features emerged from the positive magnetic field, and cancelled (merged) with the opposite (the same) polarity fields. There was a filament on the neutral line between the main positive polarity field and its surrounding negative polarity fields. The filament was cut off at a magnetic cancellation site and separated into two segments. One segment erupted and disappeared; the other segment rose from one end, but another end was fixed at an interface of a pair of opposite magnetic polarities, finally the morphology of this segment appeared as an Hα surge. Comparing Hα filtergrams with EUV images, we noticed that the Hα surge was co-spatial with an EUV surge. The EUV surge was whiplike in shape, then sidewards moved. We suggest that the evolution of the EUV surge represent the process of EUV loop opening.

scholarly journals Towards the reconstruction of the EUV irradiance for solar Cycle 23

2011 ◽  
Vol 7 (S286) ◽  
pp. 97-100 ◽  
Author(s):  
Margit Haberreiter
Keyword(s):  
Solar Cycle ◽  
Spectral Synthesis ◽  
Coronal Holes ◽  
Active Regions ◽  
One Dimensional ◽  
Segmentation Analysis ◽  
Solar Cycle 23 ◽  
Temporal And Spatial ◽  
Near Future ◽  
Good Agreement

AbstractWe present preliminary reconstructions of the EUV from 26 to 34 nm from February 1997 to May 2005, covering most of solar cycle 23. The reconstruction is based on synthetic EUV spectra calculated with the spectral synthesis code Solar Modeling in 3D (SolMod3D). These spectra are weighted by the relative area coverage of the coronal features as identified from EIT images. The calculations are based on one-dimensional atmospheric structures that represent a temporal and spatial mean of the chromosphere, transition region, and corona. The employed segmentation analysis considers coronal holes, the quiet corona, and active regions identified on the solar disk. The reconstructed EUV irradiance shows a good agreement with observations taken with the CELIAS/SEM instrument onboard SOHO. Further improvement of the reconstruction including more solar features as well as the off-limb detection of activity features will be addressed in the near future.

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