Spatial gradients in the heliospheric magnetic field - Pioneer 11 observations between 1 AU and 24 AU, and over solar cycle 21
Spatial gradients in the heliospheric magnetic field - Pioneer 11 observations between 1 AU and 24 AU, and over solar cycle 21
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日光层磁场的空间梯度 - 1 AU 到 24 AU 之间以及太阳周期 21 期间的 Pioneer 11 观测
DOI：
10.1029/ja095ia01p00001
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发表时间：
1990
影响因子：
--
通讯作者：
J. Slavin
中科院分区：
文献类型：
--
作者：
D. Winterhalter;E. Smith;J. Wolfe;J. Slavin
利用先锋11号和ISEE 3/ICE的磁场观测资料，研究了日球磁场的大尺度时间行为和空间梯度。我们扩展和完善以前的分析，扩大数据集，包括观测到的径向距离为24 Au，并在较长的时间间隔，其中包括最近的太阳极小期。空间梯度的研究，通过删除太阳周期的变化与在1 Au在相应的时间获得的数据。对于一阶，磁场强度和方位角分量的梯度与帕克模型一致。此外，对先锋号数据的这种分析证实了以前的报告，即磁场通量亏损约为1%/Au，因此在20 Au时，相对亏损约为20%。分析了在1 Au和先锋11上测得的太阳风速度，但发现两个位置之间观测到的微小变化对这一结果的影响很小。先锋11号在16 Au距离处的平均场强与旅行者2号在几乎相同的径向距离和时间间隔但在显著不同的纬度处获得的平均场强进行了比较。它们非常接近，相对于1-Au基线，两者都表现出20%的亏损。这个协议表明，B并没有随纬度在这个时候（1984-1985年接近太阳活动极小期）显着变化。此外，1-Au的基线已被调整，以考虑到观测到的磁场对太阳活动极大期（1978-1982年）附近纬度的依赖性，该依赖性是通过比较0.7 Au（PVO）和1.0 Au（ISEE 3）的内日光层测量值推断出来的。1-Au基线的这种调整并没有显著影响赤字，再次证实了先锋测量没有强烈的纬度依赖性的影响。因此，我们认为，大部分的磁场赤字是在径向梯度。
Magnetic field observations by Pioneer 11 and ISEE 3/ICE are used to investigate the large scale temporal behavior and spatial gradients in the heliospheric magnetic field. We extend and refine previous analyses by expanding the data set to include observations out to a radial distance of 24 AU and over a longer time interval which includes the recent solar minimum. The spatial gradients are investigated by removing the solar cycle variations with data obtained at 1 AU at the corresponding time. To first order, the gradients in the magnetic field magnitude and in the azimuthal component are found to agree with the Parker model. Furthermore, this analysis of the Pioneer data confirms previous reports of a magnetic field flux deficit of approximately 1%/AU, so that at 20 AU the relative deficit is of the order of 20%. The solar wind speed measured at 1 AU as well as at Pioneer 11 has been analyzed, but it is found that the small variations observed between the two locations affect this result only minimally. The average field strength at Pioneer 11 at a distance of 16 AU has been compared with a Voyager 2 average obtained at nearly the same radial distance and time interval but at a significantly different latitude. They agree very closely and both exhibit a deficit of ≈ 20% relative to the 1-AU baseline. This agreement demonstrates that B did not vary significantly with latitude at this time (1984–1985 near solar minimum). Furthermore, the 1-AU baseline has been adjusted to allow for an observed dependence of the field on latitude near solar maximum (1978–1982) inferred from a comparison of measurements in the inner heliosphere at 0.7 AU (PVO) and 1.0 AU (ISEE 3). This adjustment of the 1-AU baseline did not significantly affect the deficit, again confirming that the Pioneer measurements were not strongly influenced by the latitude dependences. We thus argue that most of the magnetic field deficit is in the radial gradient.