A Combined Study of Photospheric Magnetic and Current Helicities and Subsurface Kinetic Helicities of Solar Active Regions during 2006-2013

TL;DR

This study investigates the relationship between photospheric magnetic helicities and subsurface kinetic helicities in solar active regions, revealing hemispheric biases and correlations over time, enhancing understanding of solar magnetic dynamics.

Contribution

It provides a comprehensive comparison of photospheric and subsurface helicities across multiple active regions, highlighting hemispheric biases and temporal correlations not previously detailed.

Findings

Hemispheric bias in all three helicity parameters.

No significant region-by-region correlation between subsurface and photospheric helicities.

Significant temporal correlations in a subset of regions indicating surface magnetic twist sensitivity.

Abstract

We compare the average photospheric current helicity $H_c$, photospheric twist parameter $\alpha$ (a well-known proxy for the full relative magnetic helicity), and subsurface kinetic helicity $H_k$ for 194 active regions observed between 2006-2013. We use 2440 Hinode photospheric vector magnetograms, and the corresponding subsurface fluid velocity data derived from GONG (2006-2012) and HMI (2010-2013) Dopplergrams. We find a significant hemispheric bias in all three parameters. The subsurface kinetic helicity is preferentially positive in the southern hemisphere and negative in the northern hemisphere. The photospheric current helicity and the $\alpha$ parameter have the same bias for strong fields ($|B|>1000$ G) and no significant bias for weak fields (100 G $<|B|<500$ G). We find no significant region-by-region correlation between the subsurface kinetic helicity and either the strong-field current helicity or $\alpha$. Subsurface fluid motions of a given handedness correspond to photospheric helicities of both signs in approximately equal numbers. However, common variations appear in annual averages of these quantities over all regions. Furthermore, in a subset of 77 regions we find significant correlations between the temporal profiles of the subsurface and photospheric helicities. In these cases, the sign of the linear correlation coefficient matches the sign relationship between the helicities, indicating that the photospheric magnetic field twist is sensitive to the twisting motions below the surface.