Magnetic field strength distributions and spectra in the heliosphere and their significance for cosmic ray modulation: Voyager 1, 1980–1994
Magnetic field strength distributions and spectra in the heliosphere and their significance for cosmic ray modulation: Voyager 1, 1980–1994
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DOI：
10.1029/98ja02682
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发表时间：
1998-12
影响因子：
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通讯作者：
L. Burlaga;N. Ness
中科院分区：
文献类型：
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作者：
L. Burlaga;N. Ness
分析了旅行者1号(V1)观测到的日光层磁场强度B的小时平均值在1980-1994这15年间的年变化。在此期间，V1从径向距离6.9-58.1AU和日纬度−5.4°移动到32.7°。B的年分布函数接近对数正态分布。分布宽度w不随时间、距离、纬度或太阳活动而有系统地变化：<w>=0.61±0.02。由平均值Bav归一化的B的标准差SD(B)也是不变的：<SD(B)/Bav>=0.67±0.03。在一个十年的频率范围内，B(T)的功率谱密度可用S指数的幂函数很好地描述，其范围从1980年太阳活动极大时的−2.0到1987年至1988年太阳活动最低时的−1.5。全球合并相互作用区(GMIR)是一个围绕太阳的壳状区域，远离太阳传播，具有几个AU量级的径向厚度，并包含强烈的扰动磁场。尺度范围的下限对应于≈5天的周期，并且在所研究的15年中是不变的。在这个范围的下限，PSD的相对幅度也是不变的。但是，在太阳自转26天的周期内，波动的相对幅度随距太阳距离的增加而减小，如R−(0-9±0.2)。这些在时间和频率域得出的观测结果需要太阳风扩展到遥远的日光层的理论模型，其中包括物理和统计特征。这样的模型可以基于(1)能量和/或熵原理或(2)传统的MHD以及时间上复杂但统计上简单的输入函数。我们的结果表明，每年的磁场强度和宇宙线强度之间存在反相关关系，就像在这里所讨论的15年期间所观察到的那样。磁场的统计模型可能会为宇宙线调制的新模型提供基础。
Annual variations of the hourly averages of the heliospheric magnetic field strength B observed by Voyager 1 (V1) have been analyzed for the 15-year interval 1980–1994 inclusive. During this period, V1 moved from a radial distance of 6.9–58.1 AU and from a heliolatitude of −5.4 to 32.7°. The annual distribution function of B is nearly lognormal. The width of the distribution, w, does not change systematically with time, distance, latitude or solar activity: 〈w〉 = 0.61 ± 0.02. The standard deviation of B, SD(B), normalized by the average, Bav, is also invariant: 〈SD(B)/Bav〉 = 0.67 ± 0.03. There is a decadal frequency range for which the power spectral density (PSD) of B(t) is well described by a power law with an exponent s that ranges from −2.0 near solar maximum (1980, 1990) when GMIRs were present to −1.5 near solar minimum (1987–1988). A Global Merged Interaction Region (GMIR) is a shell-like region that encircles the Sun, propagates away from the Sun, has a radial thickness of the order of a few AU and contains intense, disturbed magnetic fields. The lower limit of the scaling range corresponds to a period of ≈ 5 days and is invariant in the 15 years studied. The relative amplitude of the PSD at the lower limit of this range is also invariant. However, the relative amplitude of the fluctuations at the solar rotation period of 26 days decreases with increasing distance from the sun as R−(0–9 ± 0.2). These derived observational results in time and frequency domains require theoretical models of the solar wind expansion into the distant heliosphere that include both physical and statistical features. Such models could be based on (1) energy and/or entropy principles or (2) conventional MHD along with temporally complex but statistically simple input functions. Our results suggest an anticorrelation between the annual magnetic field strength and cosmic ray intensity, as is observed during the 15-year period considered here. Statistical models of the magnetic field might provide a basis for new models of cosmic ray modulation.