Details

Autor(en) / Beteiligte

• Jun, C.‐W.
• Miyoshi, Y.
• Nakamura, S.
• Shoji, M.
• Hori, T.
• Bortnik, J.
• Lyons, L.
• Shinohara, I.
• Matsuoka, A.

Titel

A Triggering Process for Nonlinear EMIC Waves Driven by the Compression of the Dayside Magnetosphere

Ist Teil von

• Geophysical research letters, 2024-01, Vol.51 (1), p.n/a

Ort / Verlag

Washington: Blackwell Publishing Ltd

Erscheinungsjahr

2024

Link zum Volltext

Quelle

Wiley Online Journals

Beschreibungen/Notizen

• Using the Arase and Van Allen Probes satellite observations, we investigate the nonlinear electromagnetic ion cyclotron (EMIC) rising‐tone (RT) emissions with an increase of the solar wind dynamic pressure in the dayside magnetosphere. We find that EMIC RT emissions are accompanied by the extended dayside uniform zone (DUZ) over |MLAT| < 25° due to the dayside magnetospheric compression by an increase in Pdyn. Using the observed plasma and magnetic field data, we modeled the threshold amplitude for the nonlinear EMIC waves and compared it with the observation. The small gradient of the ambient magnetic field strongly contributes to the reduction in the threshold amplitude of nonlinear wave growth compared to other parameters. When the threshold amplitude falls to comparable level of pre‐existing EMIC waves, EMIC RT emissions are immediately triggered, suggesting direct evidence that the DUZ is the preferred condition to cause the nonlinear EMIC RT emission in the dayside magnetosphere. Plain Language Summary Electromagnetic ion cyclotron (EMIC) waves play an important role in controlling the dynamics of charged particles in the inner magnetosphere. Especially, nonlinear EMIC rising‐tone (RT) emissions can cause the rapid loss of relativistic electrons and ring current ions. Here, we present direct evidence demonstrating that the distortion of the dayside magnetic field causes nonlinear EMIC RT emission in response to the intensification of the solar wind dynamic pressure. Remarkably, these nonlinear EMIC waves are generated through a reduction in the threshold wave amplitudes by the distortion of the magnetic fields, even in the absence of any significant change in the pre‐existing EMIC wave amplitude. The present result provides new insights into a triggering process of nonlinear plasma waves in the magnetosphere. Key Points Electromagnetic ion cyclotron (EMIC) waves with rising‐tone (RT) elements were observed in the dayside magnetosphere during an increase in the solar wind dynamic pressure Increasing solar wind dynamic pressure extends the dayside uniform zone of the magnetic field to higher magnetic latitudes The uniform zone leads to the reduction of the nonlinear threshold wave amplitude, which triggers nonlinear EMIC RT emissions