# Measuring solar active region inflows with local correlation tracking of granulation

## TL;DR

This study uses local correlation tracking of granulation in solar images to measure and validate inflows around active regions, confirming their magnitude and asymmetry, which are important for understanding the solar dynamo.

## Contribution

It provides the first long-term, empirical validation of active region inflows using granulation tracking, complementing helioseismology results.

## Key findings

- Active regions are surrounded by inflows up to 10 degrees from the center.
- Inflows reach magnitudes of 20-30 m/s, locally up to 40 m/s.
- Inflows are predominantly directed towards the trailing polarity.

## Abstract

Context. Local helioseismology has detected spatially extended converging surface flows into solar active regions. These play an important role in flux-transport models of the solar dynamo. Aims. We aim to validate the existence of the inflows by deriving horizontal flow velocities around active regions with local correlation tracking of granulation. Methods. We generate a six-year long-time series of full-disk maps of the horizontal velocity at the solar surface by tracking granules in continuum intensity images provided by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). Results. On average, active regions are surrounded by inflows extending up to 10 deg from the center of the active region of magnitudes of 20-30 m/s, reaching locally up to 40 m/s, which is in agreement with results from local helioseismology. By computing an ensemble average consisting of 243 individual active regions, we show that the inflows are not azimuthally symmetric but converge predominantly towards the trailing polarity of the active region with respect to the longitudinally and temporally averaged flow field.