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

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. Key Points: The 51 shock‐related impulse events are investigated based on Van Allen Probes measurement with 39% of them followed by poloidal ULF wave while 61% notThe time scale of shock‐induced electric field impulse is more related to fast‐mode wave propagation than field line resonanceThe shock‐related ULF wave is more likely excited when the shock‐induced impulse's equivalent frequency matches the local eigenfrequency [ABSTRACT FROM AUTHOR]