Transient Large-Scale Anisotropy in TeV Cosmic Rays due to an Interplanetary Coronal Mass Ejection
Abstract
Large- or medium-scale cosmic ray anisotropy at TeV energies has not previously been confirmed to vary with time. Transient anisotropy changes have been observed below 150 GeV, especially near the passage of an interplanetary shock and coronal mass ejection containing a magnetic flux rope ejected by a solar storm, which can trigger a geomagnetic storm with practical consequences. In such events, cosmic rays provide remote sensing of the magnetic field properties. Here we report the observation of transient large-scale anisotropy in TeV cosmic ray ions using data from the Large High Altitude Air Shower Observatory (LHAASO). We analyze hourly skymaps of the transient cosmic ray intensity excess or deficit, the gradient of which indicates the direction and magnitude of transient large-scale anisotropy across the field of view. We observe enhanced anisotropy above typical hourly fluctuations with 5 significance during some hours of November 4, 2021, in separate data sets for four primary cosmic ray energy ranges of median energy from =0.7 to 3.1 TeV. The gradient varies with energy as , where . At a median energy 1.0 TeV, this gradient corresponds to a dipole anisotropy of at least 1\%, or possibly a weaker anisotropy of higher order. This new type of observation opens the opportunity to study interplanetary magnetic structures using air shower arrays around the world, complementing existing in situ and remote measurements of plasma properties.
Cite
@article{arxiv.2601.02801,
title = {Transient Large-Scale Anisotropy in TeV Cosmic Rays due to an Interplanetary Coronal Mass Ejection},
author = {Zhen Cao and F. Aharonian and Y. X. Bai and Y. W. Bao and D. Bastieri and X. J. Bi and Y. J. Bi and W. Bian and A. V. Bukevich and C. M. Cai and W. Y. Cao and Zhe Cao and J. Chang and J. F. Chang and A. M. Chen and E. S. Chen and G. H. Chen and H. X. Chen and Liang Chen and Long Chen and M. J. Chen and M. L. Chen and Q. H. Chen and S. Chen and S. H. Chen and S. Z. Chen and T. L. Chen and X. B. Chen and X. J. Chen and Y. Chen and N. Cheng and Y. D. Cheng and M. C. Chu and M. Y. Cui and S. W. Cui and X. H. Cui and Y. D. Cui and B. Z. Dai and H. L. Dai and Z. G. Dai and Danzengluobu and Y. X. Diao and X. Q. Dong and K. K. Duan and J. H. Fan and Y. Z. Fan and J. Fang and J. H. Fang and K. Fang and C. F. Feng and H. Feng and L. Feng and S. H. Feng and X. T. Feng and Y. Feng and Y. L. Feng and S. Gabici and B. Gao and C. D. Gao and Q. Gao and W. Gao and W. K. Gao and M. M. Ge and T. T. Ge and L. S. Geng and G. Giacinti and G. H. Gong and Q. B. Gou and M. H. Gu and F. L. Guo and J. Guo and X. L. Guo and Y. Q. Guo and Y. Y. Guo and Y. A. Han and O. A. Hannuksela and M. Hasan and H. H. He and H. N. He and J. Y. He and X. Y. He and Y. He and S. Hernández-Cadena and B. W. Hou and C. Hou and X. Hou and H. B. Hu and S. C. Hu and C. Huang and D. H. Huang and J. J. Huang and T. Q. Huang and W. J. Huang and X. T. Huang and X. Y. Huang and Y. Huang and Y. Y. Huang and X. L. Ji and H. Y. Jia and K. Jia and H. B. Jiang and K. Jiang and X. W. Jiang and Z. J. Jiang and M. Jin and S. Kaci and M. M. Kang and I. Karpikov and D. Khangulyan and D. Kuleshov and K. Kurinov and B. B. Li and Cheng Li and Cong Li and D. Li and F. Li and H. B. Li and H. C. Li and Jian Li and Jie Li and K. Li and L. Li and R. L. Li and S. D. Li and T. Y. Li and W. L. Li and X. R. Li and Xin Li and Y. Li and Y. Z. Li and Zhe Li and Zhuo Li and E. W. Liang and Y. F. Liang and S. J. Lin and B. Liu and C. Liu and D. Liu and D. B. Liu and H. Liu and H. D. Liu and J. Liu and J. L. Liu and J. R. Liu and M. Y. Liu and R. Y. Liu and S. M. Liu and W. Liu and X. Liu and Y. Liu and Y. Liu and Y. N. Liu and Y. Q. Lou and Q. Luo and Y. Luo and H. K. Lv and B. Q. Ma and L. L. Ma and X. H. Ma and J. R. Mao and Z. Min and W. Mitthumsiri and G. B. Mou and H. J. Mu and A. Neronov and K. C. Y. Ng and M. Y. Ni and L. Nie and L. J. Ou and P. Pattarakijwanich and Z. Y. Pei and J. C. Qi and M. Y. Qi and J. J. Qin and A. Raza and C. Y. Ren and D. Ruffolo and A. Sáiz and D. Semikoz and L. Shao and O. Shchegolev and Y. Z. Shen and X. D. Sheng and Z. D. Shi and F. W. Shu and H. C. Song and Yu. V. Stenkin and V. Stepanov and Y. Su and D. X. Sun and H. Sun and Q. N. Sun and X. N. Sun and Z. B. Sun and N. H. Tabasam and J. Takata and P. H. T. Tam and H. B. Tan and Q. W. Tang and R. Tang and Z. B. Tang and W. W. Tian and C. N. Tong and L. H. Wan and C. Wang and G. W. Wang and H. G. Wang and J. C. Wang and K. Wang and Kai Wang and Kai Wang and L. P. Wang and L. Y. Wang and L. Y. Wang and R. Wang and W. Wang and X. G. Wang and X. J. Wang and X. Y. Wang and Y. Wang and Y. D. Wang and Z. H. Wang and Z. X. Wang and Zheng Wang and D. M. Wei and J. J. Wei and Y. J. Wei and T. Wen and S. S. Weng and C. Y. Wu and H. R. Wu and Q. W. Wu and S. Wu and X. F. Wu and Y. S. Wu and S. Q. Xi and J. Xia and J. J. Xia and G. M. Xiang and D. X. Xiao and G. Xiao and Y. L. Xin and Y. Xing and D. R. Xiong and Z. Xiong and D. L. Xu and R. F. Xu and R. X. Xu and W. L. Xu and L. Xue and D. H. Yan and T. Yan and C. W. Yang and C. Y. Yang and F. F. Yang and L. L. Yang and M. J. Yang and R. Z. Yang and W. X. Yang and Z. H. Yang and Z. G. Yao and X. A. Ye and L. Q. Yin and N. Yin and X. H. You and Z. Y. You and Q. Yuan and H. Yue and H. D. Zeng and T. X. Zeng and W. Zeng and X. T. Zeng and M. Zha and B. B. Zhang and B. T. Zhang and C. Zhang and F. Zhang and H. Zhang and H. M. Zhang and H. Y. Zhang and J. L. Zhang and Li Zhang and P. F. Zhang and P. P. Zhang and R. Zhang and S. R. Zhang and S. S. Zhang and W. Y. Zhang and X. Zhang and X. P. Zhang and Yi Zhang and Yong Zhang and Z. P. Zhang and J. Zhao and L. Zhao and L. Z. Zhao and S. P. Zhao and X. H. Zhao and Z. H. Zhao and F. Zheng and W. J. Zhong and B. Zhou and H. Zhou and J. N. Zhou and M. Zhou and P. Zhou and R. Zhou and X. X. Zhou and X. X. Zhou and B. Y. Zhu and C. G. Zhu and F. R. Zhu and H. Zhu and K. J. Zhu and Y. C. Zou and X. Zuo},
journal= {arXiv preprint arXiv:2601.02801},
year = {2026}
}
Comments
14 pages, 11 figures. Submitted to Physical Review Letters, November, 2025