Contribution of flows around active regions to the north-south helioseismic travel-time measurements
Paul-Louis Poulier, Zhi-Chao Liang, Damien Fournier, Laurent Gizon
TL;DR
This study investigates how inflows into solar active regions affect north-south helioseismic travel-time measurements and finds they only partially explain the observed solar-cycle variations.
Contribution
It introduces a forward-modeling approach to quantify the inflows' contribution to helioseismic travel-time shifts, revealing their limited role in solar-cycle variations.
Findings
Active region inflows account for only part of the solar-cycle variation.
Large-scale inflows do not fully explain meridional circulation changes.
Forward modeling helps quantify inflow contributions to helioseismic signals.
Abstract
Context. In local helioseismology, the travel times of acoustic waves propagating in opposite directions along the same meridian inform us about horizontal flows in the north-south direction. The longitudinal averages of the north-south helioseismic travel-time shifts vary with the sunspot cycle. Aims. We aim to study the contribution of inflows into solar active regions to this solar-cycle variation. Methods. To do so, we identify the local flows around active regions in the horizontal flow maps obtained from correlation tracking of granulation in SDO/HMI continuum images. We compute the forward-modeled travel-time perturbations caused by these inflows using 3D sensitivity kernels. In order to compare with the observations, we average these forward-modeled travel-time perturbations over longitude and time in the same way as the measured travel times. Results. The forward-modeling…
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