Solar active regions (ARs) are thought to be formed by magnetic fields from the convection zone. Our flux emergence simulations revealed that a strong horizontal divergent flow (HDF) of unmagnetized plasma appears at the photosphere before the flux begins to emerge. In our earlier study, we analyzed HMI data for a single AR and confirmed presence of this precursor plasma flow in the actual Sun. In this paper, as an extension of our earlier study, we conducted a statistical analysis of the HDFs to further investigate their characteristics and better determine the properties. From SDO/HMI data, we picked up 23 flux emergence events over a period of 14?months, the total flux of which ranges from 1020 to 1022 Mx. Out of 23 selected events, 6 clear HDFs were detected by the method we developed in our earlier study, and 7 HDFs detected by visual inspection were added to this statistic analysis. We found that the duration of the HDF is on average 61?minutes and the maximum HDF speed is on average 3.1 km s–1. We also estimated the rising speed of the subsurface magnetic flux to be 0.6-1.4 km s–1. These values are highly consistent with our previous one-event analysis as well as our simulation results. The observation results lead us to the conclusion that the HDF is a rather common feature in the earliest phase of AR emergence. Moreover, our HDF analysis has the capability of determining the subsurface properties of emerging fields that cannot be directly measured.
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机译：太阳活动区域（ARs）被认为是由来自对流区的磁场形成的。我们的通量出现模拟表明，在通量开始出现之前，未磁化等离子体的强大水平发散流（HDF）出现在光球上。在我们的早期研究中，我们分析了单个AR的HMI数据，并确认了实际太阳中这种前体等离子体流的存在。在本文中，作为我们先前研究的扩展，我们对HDF进行了统计分析，以进一步研究其特性并更好地确定其性能。从SDO / HMI数据中，我们在14个月的时间内拾取了23个通量出现事件，总通量范围为1020至1022 Mx。在我们选择的23个事件中，通过我们在较早的研究中开发的方法检测到6个明确的HDF，并且通过视觉检查将7个HDF添加到此统计分析中。我们发现HDF的持续时间平均为61分钟，最大HDF速度平均为3.1 km s-1。我们还估计了地下磁通的上升速度为0.6-1.4 km s-1。这些值与我们先前的单事件分析以及我们的仿真结果高度一致。观察结果使我们得出结论，在AR出现的最早阶段，HDF是一个相当普遍的特征。此外，我们的HDF分析具有确定无法直接测量的新兴场的地下性质的能力。
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