Helical Magnetic Fields in Solar Active Regions: Theory vs. Observations
نویسندگان
چکیده
The mean value of the normalized current helicity αp = B · (∇×B)/B 2 in solar active regions is on the order of 10 m, negative in the northern hemisphere, positive in the southern hemisphere. Observations indicate that this helicity has a subsurface origin. Possible mechanisms leading to a twist of this amplitude in magnetic flux tubes include the solar dynamo, convective buffeting of rising flux tubes, and the accretion of weak external poloidal flux by a rising toroidal flux tube. After briefly reviewing the observational and theoretical constraints on the origin of helicity, we present a recently developed detailed model for poloidal flux accretion.
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