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arXiv 2006.05565astro-ph.SR
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出现的太阳活动区极性的平均运动II:乔伊定律

Average motion of emerging solar active region polarities II: Joy's law

Hannah Schunker, Christian Baumgartner, Aaron C. Birch, Robert H. Cameron, Douglas C. Braun, Laurent Gizon

摘要:

在Babcock-Leighton发电机模型中,由Joy定律描述的太阳活动区的倾斜是将环向场转换为极向场的必要条件。在薄通量管模型中,科里奥利力导致乔伊定律,作用于东西向流,因为它们朝向表面上升。我们的目标是测量数百个活跃区域出现时的平均倾斜角的演变,这样我们就可以限制乔伊定律的起源。我们在太阳动力学观测站日震新兴活动区巡天中测量了153个新兴活动区的主双极倾斜角。我们使用视线磁场测量平均超过6小时,以确定极性和测量倾斜角后,出现长达四天。我们发现,在出现的时候,极性平均是东西向排列的,并且分离和倾斜都不依赖于纬度。然而,我们发现,在较高纬度的AR有一个更快的南北分离速度比那些靠近赤道的出现时。羽化后,倾斜角增大,约两天后乔伊定律明显。在倾斜角的散射是独立的流量,直到约一天后出现,当较高的通量区域有一个较小的散射比低通量区域的倾斜角。我们的发现,活跃的地区出现了东西对齐是令人惊讶的,因为薄通量管模型预测,倾斜角上升通量管产生的表面以下。以前报道的倾斜角松弛的深锚通量管可以在很大程度上解释了东西分离的变化。我们得出结论,乔伊定律是由一个固有的南北分离速度时,流量首先到达表面,并在倾斜角的散射是一致的抖振的极性超颗粒。

英文摘要:

The tilt of solar active regions described by Joy's law is essential for converting a toroidal field to a poloidal field in Babcock-Leighton dynamo models. In thin flux tube models the Coriolis force causes Joy's law, acting on east-west flows as they rise towards the surface. Our goal is to measure the evolution of the average tilt angle of hundreds of active regions as they emerge, so that we can constrain the origins of Joy's law. We measured the tilt angle of the primary bipoles in 153 emerging active regions in the Solar Dynamics Observatory Helioseismic Emerging Active Region survey. We used line-of-sight magnetic field measurements averaged over 6 hours to define the polarities and measure the tilt angle up to four days after emergence. We find that at the time of emergence the polarities are on average aligned east-west, and that neither the separation nor the tilt depends on latitude. We do find, however, that ARs at higher latitudes have a faster north-south separation speed than those closer to the equator at the emergence time. After emergence, the tilt angle increases and Joy's law is evident about two days later. The scatter in the tilt angle is independent of flux until about one day after emergence, when higher-flux regions have a smaller scatter in tilt angle than lower-flux regions. Our finding that active regions emerge with an east-west alignment is surprising since thin flux tube models predict that tilt angles of rising flux tubes are generated below the surface. Previously reported tilt angle relaxation of deeply anchored flux tubes can be largely explained by the change in east-west separation. We conclude that Joy's law is caused by an inherent north-south separation speed present when the flux first reaches the surface, and that the scatter in the tilt angle is consistent with buffeting of the polarities by supergranulation.

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