Cross-layer coupling in active-region upflows: Statistical connections between photospheric magnetic field, chromospheric activity, and coronal blueshifts

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Abstract
Context. Investigating the characteristics and formation mechanisms of plasma upflows at the edges of active regions (ARs) is essential for understanding the coupling between different layers of the solar atmosphere and the origin of the slow solar wind. Aims. The present study aims to statistically characterize AR upflows and investigate their properties and interrelation with the underlying photospheric magnetic field and chromospheric emission. Methods. We performed a statistical analysis of 30 ARs observed with the Extreme ultraviolet Imaging Spectrometer (EIS) on board the Hinode satellite using the Fe XII 195.12 Å line. We also analyzed the corresponding chromospheric 1600 Å intensity from the Atmospheric Imaging Assembly (AIA), the photospheric magnetic field measured by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO), and the associated coronal magnetic field derived from the Potential-field Source-surface (PFSS) model. Results. Regions with blueshifted Fe XII 195.12 Å emission are present in all selected ARs. The blueshift speeds are strongly correlated with the corresponding nonthermal velocities. Compared with the AR same-polarity magnetic field concentration areas, blueshifted regions exhibit significantly weaker coronal intensity, comparable chromospheric intensity, and a weaker photospheric magnetic field. In the upflow regions, the Fe XII line intensity, blueshift speed, and nonthermal velocity are all positively correlated with the corresponding chromospheric intensity and photospheric magnetic field strength. For the ARs with unbalanced magnetic flux, regions with PFSS open magnetic field lines account for 78.6% and 35.7% of the majority- and minority-polarity areas, respectively. The corresponding fraction is 37.5% for ARs with relatively balanced magnetic flux. Blueshift regions with speeds exceeding 7 km s −1 occur at nearly identical rates in areas with (71.4%) and without (71.9%) PFSS open magnetic field lines. However, their area coverage is approximately 24% larger in regions with open magnetic field lines. Conclusions. The occurrence of AR upflow shows no clear association with PFSS open magnetic field lines, although blueshifted regions associated with open fields are approximately one-quarter larger. This suggests that a substantial fraction of AR boundary upflows may be associated with large-scale closed magnetic structures. The coronal upflow properties are positively correlated with the photospheric magnetic field strength and chromospheric intensity. This result suggests that stronger magnetic fields and enhanced chromospheric activity at the loop footpoints may drive greater upward transport of mass and energy. These findings support a cross-layer coupling scenario in which AR upflows are jointly regulated by the footpoint magnetic field, lower-atmosphere activity, and coronal open magnetic field topology.

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