On the effect of directional medium‐scale interplanetary variations on the diffusion of galactic cosmic rays and their solar cycle variation
On the effect of directional medium‐scale interplanetary variations on the diffusion of galactic cosmic rays and their solar cycle variation
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定向中尺度行星际变化对银河系宇宙线扩散及其太阳周期变化的影响
DOI：
10.1029/ja081i034p05841
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发表时间：
1976
期刊：
影响因子：
--
通讯作者：
Martin A. Lee
中科院分区：
文献类型：
--
作者：
G. Morfill;H. Völk;Martin A. Lee
本文认为，如果要计算银河系宇宙射线的平均输运性质，就不能简单地把行星际磁场看作是叠加在长期平均螺旋场上的小的短尺度共振波动。兴趣集中在俯仰角扩散上，其中相关的平均场在超过磁相关长度的中等尺度上变化强烈。这导致了平均星系强度的平均福克-普朗克方程。直接反射和可能在同一尺度上起作用的大尺度漂移效应未被考虑。假设行星际介质在统计上是轴对称的，由上述Fokker-Planck方程推导出平均空间扩散系数，并与芝加哥小组得到的先锋10号和11号径向强度梯度进行比较。中等尺度的变化也引入了扩散系数的太阳周期变化，由此估计了相应的星系强度变化。从数量上说，由此产生的太阳周期变化似乎只是勉强足够的强度。这可能并不太令人惊讶，因为磁场拓扑结构的变化、漂移效应和直接粒子反射都没有被考虑在内。
It is argued that the interplanetary magnetic field cannot be simply considered as consisting of small short-scale resonant fluctuations superposed on the long-term average spiral field if one wants to calculate the average transport properties of galactic cosmic rays. The interest is focused on pitch angle diffusion, where the relevant average field varies strongly on a medium scale exceeding the magnetic correlation length. This leads to an average Fokker-Planck equation for the average galactic intensity. Direct reflections and large-scale drift effects that may play a role on the same scale are not considered. When the interplanetary medium is assumed to be statistically axisymmetric, an average spatial diffusion coefficient is derived from the above Fokker-Planck equation and compared with the Pioneer 10 and 11 radial intensity gradients as obtained by the Chicago group. The medium-scale variations also introduce a solar cycle variation of the diffusion coefficient from which a corresponding variation of the galactic intensity is estimated. Quantitatively, the resulting solar cycle variation appears to be only of marginally sufficient strength. This may not be too surprising, since changes in magnetic field topology, drift effects, and direct particle reflections have not been considered.