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Role of asymmetric ring current in forbush decrease profiles during geomagnetic storms
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DOI：10.1016/j.asr.2026.09.042.png)
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Abstract
En 中文
Forbush decreases (FDs) and geomagnetic storms (GSs) are major space weather disturbances often driven by interplanetary coronal mass ejections (ICMEs). In this study, we investigate the modulation of cosmic rays (CRs) during ICME-driven geomagnetic storms. We observe a clear rigidity-dependent anisotropy in CR flux, which is further examined in relation to the Asym-H index, a measure of the asymmetric component of the ring current. The results indicate that the asymmetric ring current plays a significant role in shaping the FD profile. We suggest that storm-time asymmetry leads to longitudinal variations in cutoff rigidity, which in turn modify cosmic ray trajectories and produce diverse responses in CR flux across different rigidities. We propose that the development of an asymmetric ring current during the storm main phase introduces longitudinal variations in cutoff rigidity, in addition to the well-known latitudinal dependence caused by global geomagnetic field changes. These variations can alter the asymptotic trajectories of cosmic rays within the magnetosphere, leading to differential access of particles to the atmosphere. As a result, CR flux observed at ground level exhibits a diverse and rigidity-dependent response. The findings highlight the importance of considering ring current asymmetry, along with interplanetary drivers, in understanding cosmic ray modulation during geomagnetic storms
Keywords:
Forbush decrease
Geomagnetic storm
ICME
Galactic cosmic rays
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2.8
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