Horizontal Flows in the Photosphere and the Subphotosphere in Two Active Regions Yang Liu, Junwei Zhao, Peter W. Schuck

Methodology and Data The photospheric velocity is derived by applying the algorithm DAVE4VM (Schuck 2008) to the HMI time-series vector magnetic field data (data cadence is 12 minutes); The subphotospheric flow at -0.5 Mm (actually within [-1.0, 0] Mm depth) is inferred by a helioseismology method, the time-distance, that is applied to the HMI Dopplergrams (8- hour data). Average is done over 8 hours (one derived velocity each hour) for the photospheric velocity in order to make a comparison. Two active regions are selected for this study: AR11084 and AR AR11084 is a mature, simple active region with less solar activity; AR11158 is an emerging, complex active region that produced several flares and CMEs.

Case 1: AR11084

AR11084 Flows in the AR11084 at 04:00 July on the photosphere from the DAVE4VM (green) and at -0.5 Mm from the Time-Distance (red).

Another way to look at difference: Asterisks denote the areas where the angle between the two flows in the photosphere and -0.5 Mm is greater than 90 degree.

Height Photosphere NOT SCALED

Scatter plots of velocities in the two layers for AR cc(vx) = 0.89, cc(vy) = 0.76, cc(|v|) = 0.48, cc(theta) = 0.64.

Case 2: AR11158

Vector magnetic field in AR11158

Shear motionSpinningSeparation motion

Red: -0.5 Mm; Green: the photosphere

Cutouts of three areas where the flows in the two layers differ significantly. The flow patterns in the photosphere are well- documented that are commonly seen during flux emergence, i.e. spinning of sunspots, separation motion of leading and following fields, and shear motion along the PIL. The flows at -0.5 Mm are basically convergent in the sunspots.

Asterisks denote the areas where the flows in the two layers differ by an angle greater than 90 degree.

Scatter plots for AR cc(vx) = 0.78, cc(vy) = 0.70, cc(|v|) = 0.56, cc(theta) = 0.43.

Conclusions For the simple, mature active region AR11084: –Similarity: The horizontal flows in the photosphere and at the -0.5 Mm layer are very similar: inward flows in the sunspot umbra and outward flows in the areas surrounding the sunspot; The separation between the inward and outward flows is at the penumbra. –Difference: The boundaries of separation in the two layers are slightly different: The inward-flow area in the sunspot is larger in the -0.5 Mm than that in the photosphere. For the emerging, complex active region AR11158: –Similarity: Flows in both layers show similar outward flows in the areas surrounding the sunspots; –Difference: the well-documented flux-emergence-related flows in the photosphere (sunspot rotation, separation between leading and following fields, shear motion along the PIL) do not have counterparts in the -0.5 Mm layer.

Vertical velocity at the photosphere (left) from DAVE4VM and -0.5 Mm (right) from the time-distance.