冕洞射流的一种机制
A Mechanism for Coronal Hole Jets
摘要：
秃斑是一种磁拓扑结构，其中磁场在光球极性反转线的一部分上是凹的。秃斑拓扑被认为是灯丝通道的基本成分，并且经常在观测到的光球场的外推中发现。使用解析源-表面模型来计算嵌入在全球磁偶极子场中的小双极区域的磁拓扑，我们证明了虽然在靠近太阳赤道的封闭场区域中很常见，但在日冕洞的开放场拓扑中不太可能发生秃斑。我们的结果引起了以下问题：当周围的场线打开时，秃斑拓扑会发生什么？当秃斑移动到冕洞中时，或者当冕洞在包含秃斑的区域中形成时，就会出现这种情况。我们的静磁模型表明，在这种情况下，秃补丁拓扑几乎总是变换成一个零点拓扑的脊椎和风扇。我们认为，这种情况下的时间依赖性的演变将是非常动态的，因为从一个光秃秃的补丁到零点拓扑结构的变化不能发生通过一个简单的理想的演变在日冕。我们讨论了这些研究结果的影响，最近的日野XRT观测冕洞射流，并给出了计划的时间依赖的三维MHD模拟的轮廓，以充分评估这种情况。
英文摘要：
Bald patches are magnetic topologies in which the magnetic field is concave up over part of a photospheric polarity inversion line. A bald patch topology is believed to be the essential ingredient for filament channels and is often found in extrapolations of the observed photospheric field. Using an analytic source-surface model to calculate the magnetic topology of a small bipolar region embedded in a global magnetic dipole field, we demonstrate that although common in closed-field regions close to the solar equator, bald patches are unlikely to occur in the open-field topology of a coronal hole. Our results give rise to the following question: What happens to a bald patch topology when the surrounding field lines open up? This would be the case when a bald patch moves into a coronal hole, or when a coronal hole forms in an area that encompasses a bald patch. Our magnetostatic models show that, in this case, the bald patch topology almost invariably transforms into a null point topology with a spine and a fan. We argue that the time-dependent evolution of this scenario will be very dynamic since the change from a bald patch to null point topology cannot occur via a simple ideal evolution in the corona. We discuss the implications of these findings for recent Hinode XRT observations of coronal hole jets and give an outline of planned time-dependent 3D MHD simulations to fully assess this scenario.
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