Ulrich Roger K, Riley Pete, Tran T
Department of Physics and Astronomy University of California Los Angeles CA USA.
Predictive Science Incorporated San Diego CA USA.
Space Weather. 2018 Nov;16(11):1668-1685. doi: 10.1029/2018SW001912. Epub 2018 Nov 5.
This study identifies the solar origins of magnetic clouds that are observed at 1 AU and predicts the helical handedness of these clouds from the solar surface magnetic fields. We started with the magnetic clouds listed by the Magnetic Field Investigation (MFI) team supporting NASA's Wind spacecraft in what is known as the MFI table and worked backward in time to identify solar events that produced these clouds. Our methods utilize magnetograms from the Helioseismic and Magnetic Imager instrument on the Solar Dynamics Observatory spacecraft so that we could only analyze MFI entries after the beginning of 2011. This start date and the end date of the MFI table gave us 37 cases to study. Of these we were able to associate only eight surface events with clouds detected by Wind at 1 AU. We developed a simple algorithm for predicting the cloud helicity that gave the correct handedness in all eight cases. The algorithm is based on the conceptual model that an ejected flux tube has two magnetic origination points at the positions of the strongest radial magnetic field regions of opposite polarity near the places where the ejected arches end at the solar surface. We were unable to find events for the remaining 29 cases: lack of a halo or partial halo coronal mass ejection in an appropriate time window, lack of magnetic and/or filament activity in the proper part of the solar disk, or the event was too far from disk center. The occurrence of a flare was not a requirement for making the identification but in fact flares, often weak, did occur for seven of the eight cases.
本研究确定了在1天文单位处观测到的磁云的太阳起源，并根据太阳表面磁场预测了这些磁云的螺旋性。我们从支持美国国家航空航天局“风”号航天器的磁场调查（MFI）团队列出的磁云开始，即所谓的MFI表，并逆向追溯时间以确定产生这些磁云的太阳事件。我们的方法利用了太阳动力学观测卫星上日震和磁成像仪的磁图，因此我们只能分析2011年初之后的MFI记录。MFI表的这个开始日期和结束日期为我们提供了37个案例进行研究。在这些案例中，我们仅能将8个表面事件与“风”号在1天文单位处探测到的磁云联系起来。我们开发了一种简单的算法来预测云的螺旋度，在所有8个案例中该算法都给出了正确的螺旋性。该算法基于这样一个概念模型：一个被抛出的通量管在太阳表面抛出的拱结束处附近具有两个磁起源点，位于相反极性的最强径向磁场区域的位置。对于其余29个案例，我们未能找到相关事件：在合适的时间窗口内缺乏日冕物质抛射的晕或部分晕，在太阳圆盘的适当部分缺乏磁和/或细丝活动，或者该事件离圆盘中心太远。识别过程并不要求有耀斑发生，但实际上在这8个案例中的7个案例中确实发生了耀斑，且通常较弱。
