tokens: This work is supported by the National Science Foundation of China (41731068, 41774175, and 41621063). The authors thank the FGM and CIS instrument teams of Cluster and the FGM and ESA instrument teams of THEMIS for providing data and the NASA/GSFC’s Space Physics Data Facility for the OMNIWeb service. The OMNI data are available at http://cdaweb.gsfc.nasa.gov/cgi-bin/eval1.cgi . The authors are especially grateful to Dr. Khurana K. Krishan of UCLA for his insightful and useful suggestions for this paper.
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