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太阳光球磁亮点的识别
Alternative TitleThe Recognition of Magnetic Bright Points in the Solar Photosphere
刘艳霄
Subtype硕士
Thesis Advisor林隽
2013-05
Degree Grantor中国科学院研究生院(云南天文台)
Place of Conferral北京
Degree Discipline天文技术与方法
Keyword太阳光球 磁亮点 小尺度结构 高分辨观测 区域生长
Abstract在太阳光球表面出现的磁亮点是目前的观测手段能够分辨的最小磁结构,也被认为是日冕磁场在光球的足点运动的可靠的示踪者,其运动所耗散的能量 被认为是日冕加热和色球加热的最终能量来源之一。 在其运动过程中,高密度的光球物质带着磁场一起运动,在色球和日冕磁场当中产生波动或者扭绞将光 球物质的动能传送到色球和日冕。 为了解开日冕加热和色球加热等世纪未解之 谜,对磁亮点的研究就显示出了它特殊的重要性。 关于磁亮点的形成原理,很 多科学家都认为是在磁通量管的对流塌缩过程中形成的。 也有很多观测方面 和数值模拟方面的研究结果重现了对流塌缩过程,确认了磁亮点确实是在对 流塌缩过程中形成的。 即对流塌缩的过程是先有强的等离子体流下沉,磁场强 度增强,最后磁亮点出现。 一些数值模拟和观测的结果发现,在对流塌缩过程中,当强的等离子体流下沉到密度较大的磁通量管底部时会发生较强的反弹上升现象。 而这个上升的等离子体流会形成激波上升至日冕形成针状体。 与此同时,在磁通量管底部的等离子体反弹上升的过程中,磁通量管温度上升,磁场 强度减小,最后导致磁通量管破裂。 这是磁通量管的另一种不稳定性。 理论研究发现,当磁环在光球上的足点以 1?2 km s?1运动时,足点所在的磁通量管产生振荡并激发阿尔芬波。 阿尔芬波在光球中被激发,然后向上传播到色球和日冕层,并在色球和日冕层中消耗掉能量以加热色球和日冕。 不过,阿尔芬波还没有在光球层检测出来。 光球上的足点是否有1?2 km s?1大小的运动速度是研究光球磁通量管能否通过振荡产生阿尔芬波的一个关键因素。 磁亮点的尺度 在 100-200 公里之间,磁亮点的亮度是光球平均亮度的 2?4倍。 磁亮点的运动 速度平均在 1?2 公里/秒。 也有少数磁亮点运动速度较快,达到 3?4 公里/秒。 研究发现有一些磁亮点沿着对数螺线方式进行涡旋运动。 磁亮点的寿命从几十 秒到几十分钟不等。 亮度较大,尺度较大的磁亮点的寿命较长。 对磁亮点的研究基于准确的识别方法。 我们运用区域生长法对磁亮点进行识别,并给出了识别的结果。
Other AbstractMagnetic bright points in the photosphere are the smallest structures that the present observational technique could resolve. They are regarded as a reliable tracer of footpoints of the coronal magnetic ?eld in the photosphere. The energy conversion and transportation caused by the motion of these footpoints is considered as one of the most important energy source of heating the chromosphere and the corona by waves or magnetic reconnection through twist magnetic tubes. The studying of magnetic bright points plays an important role in resolving the century puzzle of the chromosphere and the corona heating. Most of the numerical simulations and observations show that the formation mechanism of the bright points is related to the process of the convective collapse. Namely, magnetic bright points evolve as follows: strong plasma down ?ows in the ?ux tube, magnetic ?eld strengthens, and then magnetic bright points appear. Some simulations and observations revealed that strong down?ows bounce back when they reach the bottom of the ?ux tubes and turn into strong up?ows. The up?ow may develop a shock front that could be energetic enough to bring the chromospheric matter into the corona producing spicules. At the same time the ?ow move upward, the ?ux tube undergoes a kind of instability associated with the convective collapse. The up?owing gas leads the magnetic ?eld in the ?ux tube to weakening, the gas density and the temperature to increasing, and the ?ux tube eventually splits. In theory, Alfv′en waves are found to excite by the oscillation of the ?ux tubes in the photosphere if the footpoints of the ?ux tubes move at a velocity of 1?2 km/s. The Alfv′en wave is invoked in the photosphere and travels upward into the chromosphere and the corona, then dissipates its en- ergy heating the chromosphere and the corona. However, as we have known, the Alfv′en wave has not been detected in the photosphere yet. Whether or not the coronal magnetic ?eld footpoints in the photosphere could move at speed of 1?2 km/s is an important criterion for producing the Alfv′en wave by the ?ux tube motions. Currently, we have known some important facts about the elementary.
Subject Area天文学
Pages47
Language中文
Document Type学位论文
Identifierhttp://ir.ynao.ac.cn/handle/114a53/6621
Collection太阳物理研究组
Recommended Citation
GB/T 7714
刘艳霄. 太阳光球磁亮点的识别[D]. 北京. 中国科学院研究生院(云南天文台),2013.
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