Observations of the Sun's magnetic field during the recent solar maximum
Observations of the Sun's magnetic field during the recent solar maximum
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DOI：
10.1029/2002ja009388
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发表时间：
2003
影响因子：
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通讯作者：
T. Sanderson;T. Appourchaux;J. Hoeksema;K. Harvey
中科院分区：
文献类型：
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作者：
T. Sanderson;T. Appourchaux;J. Hoeksema;K. Harvey
我们提出了对太阳磁场和日冕洞的新观测和分析。利用Wilcox太阳天文台的磁场观测，我们提出了一种简单的方法，可以计算出电流片的倾斜角。我们使用了覆盖过去26年的数据集，首次显示了在一个完整的22年太阳周期中偶极子成分是如何旋转一次的。我们将展示这是如何影响当前表的。在太阳活动极小期，太阳的日冕磁场基本上是偶极的，并且与自转轴平行。其结果是，日球层的电流片是平坦的，几乎没有弯曲。在太阳极大期前后，偶极子垂直于自转轴，四极子强度与偶极子强度之比在大部分时间都很高。这意味着洋流是倾斜的，高度弯曲的，并延伸到高纬度地区。令人惊讶的是，当四极/偶极比较低时，也有接近太阳极大期的时候，电流片相对平坦，但仍然高度倾斜。本文首次将磁场四极分量的定量分析方法应用于太阳磁场数据。根据观测到的光球磁场的膨胀，我们计算出了磁场极点的位置。我们首次将威尔科克斯太阳天文台的长时间磁场数据与国家太阳天文台/基特峰的日冕洞位置相结合。我们发现，当磁极在太阳表面移动时，日冕洞的位置跟随磁场磁极的运动，当磁极接近中纬度地区时，极地日冕洞分解成一组更小的类似极性的洞，四极变得更加重要。我们讨论了对尤利西斯高能粒子观测的影响。索引项：7509太阳物理学，天体物理学和天文学：日冕；7511太阳物理、天体物理和天文学：日冕洞；7524太阳物理、天体物理和天文学：磁场；7514太阳物理、天体物理和天文学：高能粒子（2114）；关键词：电流片，源面，太阳偶极子，太阳四极子，日冕洞，太阳极大期
[1] We present new observations and analyses of the Sun’s magnetic field and coronal holes. Using magnetic field observations from the Wilcox Solar Observatory, we present a simple means whereby the tilt angle of the current sheet can be calculated. We use a data set covering the last 26 years, which shows for the first time how the dipole component rotated once during a full 22-year solar cycle. We show how this influenced the current sheet. At solar minimum, the Sun’s coronal magnetic field was essentially dipolar and aligned parallel to the spin axis. As a result, the heliospheric current sheet was flat and had very little warp. Around solar maximum, the dipole was perpendicular to the spin axis, and the ratio of quadrupole to dipole strength was high for much of the time. This meant that the current sheet was tilted and highly warped, and reached up to high latitudes. Surprisingly, there were also times close to solar maximum when the quadrupole/dipole ratio was low, and the current sheet was relatively flat, but still highly inclined. We apply for the first time to solar magnetic data a method, which quantitatively analyses the quadrupole component of the magnetic field. From the terms of the expansion of the observed photospheric magnetic field, we compute the position of the poles of the magnetic field. We combine for the first time over an extended period of time magnetic field data from the Wilcox Solar Observatory with coronal hole positions taken from the National Solar Observatory/Kitt Peak. We find that the position of the coronal holes followed the motion of the poles of the magnetic field as the poles moved over the surface of the Sun and that the polar coronal holes broke up into groups of smaller like-polarity holes as the poles approached the midlatitude regions and the quadrupole became more important. We discuss the implications for energetic particle observations at Ulysses. INDEX TERMS: 7509 Solar Physics, Astrophysics, and Astronomy: Corona; 7511 Solar Physics, Astrophysics, and Astronomy: Coronal holes; 7524 Solar Physics, Astrophysics, and Astronomy: Magnetic fields; 7514 Solar Physics, Astrophysics, and Astronomy: Energetic particles (2114); KEYWORDS: current sheet, source surface, Sun’s dipole, Sun’s quadrupole, coronal holes, solar maximum