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Characteristics of recurrent Forbush decreases in Galactic cosmic ray intensity during positive and negative solar magnetic polarities
Astrophysics and Space Science ( IF 1.8 ) Pub Date : 2021-07-09 , DOI: 10.1007/s10509-021-03970-2
O. Kallaya 1 , T. Yeeram 1
Affiliation  

We present a statistical analysis of recurrent Forbush decreases (RFDs) in Galactic cosmic ray intensity in associated with corotating solar wind streams during low solar activity conditions. Selected RFDs recorded at the ground-based neutron monitors with low to high cutoff rigidities (\(P_{c}\)) have been separately investigated for the periods 2008-2011 (\(A < 0\), 70 events) and 2015-2016 (\(A > 0\), 35 events). We found that medians of RFD amplitudes are larger in the \(A > 0\) than in the \(A < 0\) and exhibit solar phase dependence. Correlations of RFD characteristics with magnitude of interplanetary magnetic field (IMF) and with solar wind speed in case of maximum smooth (moving average) values are more relevant than in case of observed maximum values and difference between the maximum and base values, particular in the \(A<0\). Correlation of RFD amplitudes with maximun smooth solar wind speed and IMF magnitude is weak and exist only for \(A < 0\). Slopes of the graph of RFD amplitude - the solar wind speed/IMF strength for the epoch \(A <0\) tend to decrease from low to high \(P_{c}\), suggesting a rigidity dependent relation. These results are discussed in the context of the convection-diffusion process including drift. We suggest that drift is an important process in controlling RFD amplitudes during the \(A<0\) and \(A>0\) epochs.



中文翻译:

正负太阳磁极期间银河宇宙射线强度反复福布什减小的特征

我们对在低太阳活动条件下与同向旋转的太阳风流相关的银河宇宙射线强度的循环福布什衰减 (RFD) 进行了统计分析。在2008-2011 年(\(A < 0\),70 个事件)和 2015 年期间分别研究了在具有低到高截止刚度 ( \(P_{c}\) )的地基中子监测器上记录的选定 RFD -2016 ( \(A > 0\),35 个事件)。我们发现RFD振幅的该中位数是在较大\(A> 0 \)比在\(A <0 \)并表现出太阳相位依赖性。在最大平滑(移动平均值)值的情况下,RFD 特性与行星际磁场 (IMF) 的大小和太阳风速的相关性比观察到的最大值以及最大值和基值之间的差异更相关,特别是在\(A<0\)。RFD 幅度与最大平滑太阳风速和 IMF 幅度的相关性很弱,仅存在于\(A < 0\)。RFD振幅-太阳风速/IMF强度的曲线斜率\(A <0\)从低到高\(P_{c}\),表明存在刚性依赖关系。这些结果在包括漂移的对流扩散过程的背景下进行了讨论。我们认为漂移是控制\(A<0\)\(A>0\)时期RFD 幅度的重要过程。

更新日期:2021-07-09
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