Statistical Analysis of Current Helicity and Twist in Solar Active Regions over the Phases of the Solar Cycle Using the Spectro-Polarimeter Data of Hinode

TL;DR

This study analyzes the current helicity and twist in solar active regions over the solar cycle using Hinode spectro-polarimeter data, revealing how magnetic field strength influences hemispheric sign rules and dynamo mechanisms.

Contribution

It provides a detailed statistical analysis of current helicity variations with magnetic field strength and spatial smoothing, offering new insights into solar dynamo processes.

Findings

Weak fields follow hemispheric sign rule without smoothing.

Strong fields and smoothed data violate the hemispheric sign rule.

Different properties of helicity in strong and weak fields inform solar dynamo understanding.

Abstract

Current helicity and twist of solar magnetic fields are important quantities to characterize the dynamo mechanism working in the convection zone of the Sun. We have carried out a statistical study on the current helicity of solar active regions observed with the Spectro-Polarimeter (SP) of Hinode Solar Optical Telescope (SOT). We used SOT-SP data of 558 vector magnetograms of a total of 80 active regions obtained from 2006 to 2012. We have applied spatial smoothing and division of data points into weak and strong field ranges to compare the contributions from different scales and field strengths. We found that the current helicity follows the so-called hemispheric sign rule when the weak magnetic fields (absolute field strength $< 300$ gauss) are considered and no smoothing is applied. On the other hand, the pattern of current helicity fluctuates and violates the hemispheric sign rule when stronger magnetic fields are considered and the smoothing of 2.0 arcsec (mimicking ground-based observations) is applied. Furthermore, we found a tendency that the weak and inclined fields better conform to and the strong and vertical fields tend to violate the hemispheric sign rule. These different properties of helicity through the strong and weak magnetic field components give important clues to understanding the solar dynamo as well as the mechanism of formation and evolution of solar active regions.