Emerging Active Regions Studied with Ring‐Diagram Analysis

Abstract

We study the temporal variation of subsurface flows associated with emerging active regions, focusing on four regions in detail. Two of them, AR 10314 and AR 10488, emerge near disk center and the other two, AR 10365 and AR 10375, are older regions where new flux emerges during their disk passage. We measure the horizontal subsurface flows from high-resolution Global Oscillation Network Group (GONG) data using ring-diagram analysis and derive the vertical flow component. Before flux emergence, we find upflows in AR 10314, while the other emerging region, AR 10488, shows mainly weak vertical flows. Both aging regions, AR 10365 and AR 10375, initially show downflows, as expected from already established regions. When new flux emerges, the weaker one of the two, AR 10365, shows upflows, while AR 10375 shows an even stronger downflow. In strong active regions, such as AR 10375 and AR 10488, strong downflows are present after the region has been established. In all four regions, the transition occurs on timescales of about one to two days. As a control experiment, we repeat the analysis for the same locations as those of the four active regions in 53 Carrington rotations and find that it is unlikely that the temporal variations of the vertical velocity are caused by systematics such as a projection effect. We then search our data set for emerging regions with similar characteristics to AR 10314 and AR 10488, i.e., emergence near disk center and large flux increase. From an analysis of 13 emerging regions, we conclude that there is a small preference for upflows before the emergence of new flux and for a transition toward downflows after flux emergence.