Magnetic fields in the distant heliosphere approaching solar minimum: Voyager 1 and 2 observations during 1994
Magnetic fields in the distant heliosphere approaching solar minimum: Voyager 1 and 2 observations during 1994
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DOI：
10.1029/96ja00523
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发表时间：
1996-06-01
影响因子：
2.8
通讯作者：
Ness, NF
中科院分区：
文献类型：
--
作者：
Burlaga, LF;Ness, NF
1994 年期间，旅行者 2 号 (V2) 的日心距离 [R] = 43.4 天文单位，纬度 [delta(s/c)] = 11.9 度南纬，而旅行者 1 号 (V1) 的日心距离 [R] = 56.3 天文单位，[δ(s/c)] = 32.5 度北纬。1994 年 V1 观测到的平均磁场强度为 0.05 nT，有史以来现场测量的最弱、最远的磁场。 V2观察到方位磁场方向的双峰分布，V1观察到单峰分布。因此，V2 位于“扇区”（包含日光层电流片的纬度范围），而 V1 位于其上方的单极区域，这与通过太阳磁场观测计算的中性线外推获得的日光层电流片的纬度一致。 95% 的 V1 数据和大部分 V2 数据观察到磁场强度（每小时平均值）的对数正态分布。 B 的近似对数正态分布是日光层磁场的一般特性，在 58.1 天文单位和南纬 32.6 度范围内观测到。 1994 年期间，V1 和 V2 均观察到磁场强度分布呈指数尾部，磁场强于平均值。 1983年至1994年期间，V1和V2在南纬11度至北纬33度、距离13至58天文单位处观察到磁场强度分布的指数尾部。因此，磁场强度分布的指数尾部是超过 13 个天文单位的日光层的基本属性。 1994年，V2在扇形区观察到的指数尾部和V1在扇形区上方观察到的指数尾部均不存在明显的纬度梯度。V1在8小时至256小时期间观察到磁场强度大范围波动的多重分形结构，相当于磁场强于平均水平的10.7天。多重分形谱是从 1983 年到 1994 年在 13 个天文单位到 58 个天文单位之间的大规模磁场强度波动的一般属性。仍然需要一种能够解释这些观测结果的太阳风统计理论，以及包括多重分形磁场强度波动影响的宇宙射线模型。
During 1994, Voyager 2 (V2) was at a heliocentric distance [R] = 43.4 AU and latitude [delta(s/c)] = 11.9 degrees S, while Voyager 1 (V1) was at [R] = 56.3 AU and [delta(s/c)] = 32.5 degrees N. The mean magnetic field strength observed by V1 during 1994 was 0.05 nT, the weakest and most distant magnetic field ever measured in situ. A bimodal distribution of azimuthal magnetic field directions was observed by V2, and a single-peaked distribution was observed by V1. Thus V2 was in the ''sector zone'' (the range of latitudes that contains the heliospheric current sheet), and V1 was in the unipolar region above it, consistent with the latitudes of the heliospheric current sheet obtained from an extrapolation of the neutral line computed from solar magnetic field observations. A lognormal distribution of the magnetic field strength (hourly averages) was observed for 95% of the V1 data and most of the V2 data. An approximately lognormal distribution of B is a general property of the heliospheric magnetic field, observed out to 58.1 AU and up to 32.6 degrees S latitude. During 1994 an exponential tail in the distribution of the magnetic field strength was observed by both V1 and V2 for fields stronger than average. An exponential tail in the magnetic field strength distribution was observed by V1 and V2 from 1983 to 1994 at latitudes from 11 degrees S to 33 degrees N and at distances from 13 to 58 AU. Thus an exponential tail of the distribution of magnetic field strengths is a basic property of the heliosphere beyond 13 AU. There was no significant latitudinal gradient in the exponential tail observed by V2 in the sector zone and observed by V1 above the sector zone during 1994. Multifractal structure in the large-scale fluctuations of the magnetic field strength was observed by V1 for periods from 8 hours to 256 hours equaling 10.7 days for the magnetic fields stronger than average. A multifractal spectrum is a general property of the large-scale magnetic field strength fluctuations, from 1983 through 1994 between 13 AU and 58 AU. There remains a need for a statistical theory of the solar wind that can account for these observations and for cosmic ray models that include the effect of multifractal magnetic field strength fluctuations.