Spatial variation and evolution of heliospheric sector structure
Spatial variation and evolution of heliospheric sector structure
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DOI：
10.1029/ja094ia02p01245
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发表时间：
1989-02
影响因子：
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通讯作者：
K. W. Behannon;L. Burlaga;J. Hoeksema;L. Klein
中科院分区：
文献类型：
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作者：
K. W. Behannon;L. Burlaga;J. Hoeksema;L. Klein
在太阳黑子周期21的大约四分之三期间，利用斯坦福大学威尔科克斯太阳天文台的光球磁场观测，以及旅行者1号和2号、先锋金星轨道器以及较小程度上的太阳神a、IMP 8和ISEE 3的航天器观测，对太阳和行星际空间的磁扇区极性进行了调查。在1977年至1985年的8年多的研究期间，旅行者号在1-25天文单位的日心距离范围内测量了行星际磁场（IMF），日冕纬度范围为- 5°-27°。利用光球数据和势场（PF）模型计算了同一时期太阳附近日球层电流片的位置，其中包括太阳黑子极大期和大部分下降期。大尺度磁极结构在整个研究过程中几乎处于连续的演化过程中。这包括两扇区和四扇区模式之间的交替，每一种情况的平均持续时间约为七次太阳旋转。尽管旅行者号航天器发现IMF的方位角在20%的情况下与理论帕克螺旋角偏离60°以上，但应用平滑技术产生的IMF极性模式可以与在太阳上得到的模式进行比较。这样的比较表明，先锋金星在内日球层观测到的太阳和IMF扇形模式非常吻合（82%），而旅行者1号和2号观测到的太阳和外日球层模式之间的一致性明显较差（61% - 64%）。这可能是太阳风动力学过程的结果，它改变了电流片的位置和形状，超出了几个天文单位。扇形图的稳定性也随日心距离的增加而降低。有证据表明，太阳附近的四扇形结构比外层的日球层更频繁地出现。1985年，当旅行者1号到达日经25°时，它观察到扇形结构的消失，这与从光球磁场测量中推断出的电流片倾斜一致。
The magnetic sector polarity at the Sun and in interplanetary space has been surveyed during approximately three quarters of sunspot cycle 21 using photospheric magnetic field observations from the Wilcox Solar Observatory at Stanford University and spacecraft observations by Voyagers 1 and 2, Pioneer Venus Orbiter, and, to a lesser extent, Helios A, IMP 8, and ISEE 3. During the more than 8-year period of the study, late 1977–1985, the Voyagers measured the interplanetary magnetic field (IMF) over a heliocentric distance range of 1–25 AU and a heliolatitude range of −5°–27°. The photospheric data were used together with a potential field (PF) model to calculate the location of the heliospheric current sheet near the Sun throughout the same period, which included sunspot maximum and much of the declining phase. The large-scale magnetic polarity structure was found to be in almost continuous evolution throughout the period of study. This included an alternation between two-sector and four-sector patterns, with a mean duration in each case of approximately seven solar rotations. Although the azimuth of the IMF was found by the Voyager spacecraft to be oriented more than 60° from the theoretical Parker spiral angle 20% of the time, application of smoothing techniques produced IMF polarity patterns which could be compared with the pattern derived at the Sun. Such comparisons revealed very good agreement (82%) between solar and IMF sector patterns observed by Pioneer Venus in the inner heliosphere and significantly poorer agreement (61–64%) between solar and outer heliosphere patterns observed by Voyagers 1 and 2. This may be the result of dynamical processes in the solar wind which alter the position and shape of the current sheet beyond a few astronomical units. Sector pattern stability was found to decrease with increasing heliocentric distance, also. Evidence was found for the more frequent occurrence of four-sector structure near the Sun than in the outer heliosphere. In 1985, when Voyager 1 reached a heliolatitude of 25°, it observed the disappearance of the sector structure, consistent with the tilt of the current sheet deduced from photospheric magnetic field measurements.