Temporal evolution of small-scale internetwork magnetic fields in the solar photosphere

Abstract: While the longitudinal field that dominates photospheric network regions has been studied extensively, small scale transverse fields have recently been found to be ubiquitous in the quiet internetwork photosphere. Few observations have captured how this field evolves. We aim to statistically characterise the magnetic properties and observe the temporal evolution of small scale magnetic features. We present two high spatial/temporal resolution observations that reveal the dynamics of two disk centre internetwork regions taken by the new GRIS/IFU (GREGOR Infrared Spectrograph Integral Field Unit) with the highly magnetically sensitive Fe I line pair at 15648.52 {\AA} and 15652.87 {\AA}. With the SIR code, we consider two inversion schemes: scheme 1 (S1), where a magnetic atmosphere is embedded in a field free medium, and scheme 2 (S2), with two magnetic models and a fixed stray light component. S1 inversions returned a median magnetic field strength of 200 and 240 G for the two datasets, respectively. We consider the median transverse (horizontal) component, among pixels with Stokes Q or U, and the median unsigned longitudinal (vertical) component, among pixels with Stokes V, above a noise threshold. We determined the former to be 263 G and 267 G, and the latter to be 131 G and 145 G, for the two datasets, respectively. We present three regions of interest (ROIs), tracking the dynamics of small scale magnetic features. We apply S1 and S2 inversions to specific profiles, and find S2 produces better approximations when there is evidence of mixed polarities. We find patches of linear polarization with magnetic flux density between 130 and 150 G, appearing preferentially at granule/intergranular lane (IGL) boundaries. The weak hG magnetic field appears to be organised in terms of complex loop structures, with transverse fields often flanked by opposite polarity longitudinal fields.

• The paper demonstrates that small-scale internetwork magnetic fields exhibit median strengths of 200–240 G, indicating prevalent weak fields in the solar photosphere.
• The study employs advanced GRIS-IFU spectropolarimetry and SIR inversions to distinguish between higher transverse (~263–267 G) and lower longitudinal (~131–145 G) field components.
• Temporal analysis reveals loop-like magnetic structures at granule boundaries, suggesting dynamic convective interactions and potential magnetic cancellation or emergence phenomena.

Temporal Evolution of Small-Scale Internetwork Magnetic Fields in the Solar Photosphere

The study of small-scale internetwork magnetic fields in the solar photosphere provides crucial insights into solar atmospheric dynamics and magnetism. This paper addresses the nuanced temporal characteristics of these magnetic features using high-resolution observations. Utilizing the GREGOR Infrared Spectrograph Integral Field Unit (GRIS-IFU), the research employs the photospheric Fe I line pair at 15648.52 Å and 15652.87 Å, offering a detailed spectropolarimetric analysis of quiet Sun internetwork regions.

Experimental Methodology and Analysis

To achieve its objectives, the study collects and examines full Stokes vector data, undertaking inversions via the Stokes inversions based on response functions (SIR) code. Two particular inversion schemes were analyzed: scheme 1 (S1), which models a magnetic atmosphere immersed in a non-magnetic medium, and scheme 2 (S2), consisting of two magnetic models with an incorporated stray light component. The essence of these schemes is to unravel the magnetic vector characteristics and quantify the temporal evolution of small-scale features.

Key Findings

1. Median Field Strengths: The inversions returned median magnetic field strengths of 200 and 240 G for the two datasets, which indicate prevalent weak field strengths within the observed internetwork regions.
2. Transverse vs. Longitudinal Components: The median transverse component was found to be slightly higher, with values of 263 G and 267 G, compared to the longitudinal component values of 131 G and 145 G, across the two datasets.
3. Spatial Organization and Dynamics: The investigation reveals complex loop-like structures characterized by transverse fields flanked by longitudinal fields of opposite polarity. These magnetic arrangements are frequently positioned at the boundaries between granules and intergranular lanes, suggesting a dynamic interaction driven by convective processes.
4. Temporal Evolution: The study tracks specific regions of interest (ROIs) demonstrating how small-scale features evolve over temporal scales. These observations suggest potential magnetic cancellation or emergence scenarios, highlighting the importance of these features in broader solar atmospheric processes.

Implications and Future Directions

The findings contribute significantly to our understanding of solar magnetism, particularly in relation to the structure and dynamics of internetwork regions. The implications for solar physics are considerable, offering potential pathways to resolve longstanding questions about the solar atmospheric heating mechanisms. The observations hint at a complex interplay between solar convection and magnetic field dynamics, which could be pivotal in modeling energy distribution in the solar atmosphere.

Future research can leverage advancements in observational technology, such as the deployment of the Daniel K. Inouye Solar Telescope (DKIST), to enhance spatial and temporal resolution. Such enhancements could further elucidate the magnetic topology and the role of small-scale magnetic fields in global solar phenomena.

In conclusion, this paper underscores the integral role played by advanced spectropolarimetric tools in unveiling the intricate nature of solar magnetism. By mapping the evolution of small-scale magnetic features, it paves the way for future explorations that could significantly augment our understanding of solar energetic processes.