Test of the Hemisphere Rule of Magnetic Twist in Solar Active Regions Using the Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Data
Yang Liu Submitted: 2014-01-25 12:01
Magnetic twist in solar active regions has been found to have a hemispheric preference in
sign (hemisphere rule): negative in the northern hemisphere and positive in the southern.
The preference reported in previous studies ranges greatly, from sim 58% to 82%.
In this study, we examine this hemispheric preference using vector magnetic field data
taken by HMI and find that 75% pm 7% of 151 active regions studied obey the hemisphere rule,
well within the preference range in previous studies. If the sample is divided into two
groups,-,active regions having magnetic twist and writhe of the same sign and having
opposite signs,-,the strength of the hemispheric preference differs substantially: ( 64% pm 11% )
for the former group and ( 87% pm 8% ) for the latter. This difference becomes even more
significant in a sub-sample of 82 active regions having a simple bipole magnetic
configuration: ( 56% pm 16% ) for the active regions having the same signs of twist
and writhe, and 93% with lower and upper confidence bounds of 80% and 98% for the
active regions having the opposite signs. The error reported here is a 95% confidence interval.
This may suggest that, prior to emergence of magnetic tubes, either the sign of twist does
not have a hemispheric preference or the twist is relatively weak.
Authors: Y. Liu, J. T. Hoeksema, X. Sun
Publication Status: ApJL accepted
Last Modified: 2014-01-28 12:39