Relation Between Shock-Related Impulse and Subsequent ULF Wave in the Earth's Magnetosphere

Dianjun Zhang, Wenlong Liu, Xinlin Li, Theodore E. Sarris, Yongfu Wang, Chao Xiao, Zhao Zhang, John R. Wygant

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The generation of Pc4-5 ultralow frequency (ULF) waves after interplanetary shock-induced electric field impulses in the Earth's magnetosphere is studied using Van Allen Probes measurements by investigating the relationship between the first impulses and subsequent resonant ULF waves. In the dayside, the relevant time scales of the first impulse is correlated better with local Alfvén speed than with local eigenfrequency, implying that the temporal scale of the first impulse is more likely related to fast-mode wave propagation rather than local field line resonance. There are only 20 out of 51 events with narrow-band poloidal ULF waves induced after the first impulse, showing a higher chance for ULF wave generation at the locations where the impulse equivalent frequency scale matches the local eigenfrequency. It is suggested that the shock-related ULF wave can be excited in the magnetosphere on condition that shock-induced impulse has large enough amplitude with its frequency matching the local eigenfrequency.

Original languageEnglish (US)
Article numbere2020GL090027
JournalGeophysical Research Letters
Issue number23
StatePublished - Dec 16 2020

Bibliographical note

Funding Information:
This work was supported by the National Natural Science Foundation of China Grants 41974194, 41821003, and 41574154. We thank the EFW and EMFISIS teams of the Van Allen Probes mission for making data available.


  • ULF wave
  • electric field
  • field line resonance
  • interplanetary shock
  • magnetosphere
  • wave excitation


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