Waveform and packet structure of lion roars

W. Baumjohann (1) , R. A. Treumann (1) , E. Georgescu (1, 2) , G. Haerendel (1) , K.-H. Fornacon (3) , U. Auster (3)

1 MPE - Max-Planck-Institut für Extraterrestrische Physik
2 ISS - Institute of Space Science [Bucharest-Măgurele]
3 Institut für Geophysik und Meteorologie [Braunschweig]

The Equator-S magnetometer is very sensitive and has a sampling rate of normally 128 Hz. The high sampling rate allows for the first time fluxgate magnetometer measurements of ELF waves between the ion cyclotron and the lower hybrid frequencies in the equatorial dayside magnetosheath. The so-called lion roars, typically seen by the Equator-S magnetometer at the bottom of the magnetic troughs of magnetosheath mirror waves, are near-monochromatic packets of electron whistler waves lasting for a few wave cycles only, typically 0.25 s. They are right-hand circularly polarized waves with typical amplitudes of 0.5?1 nT at around one tenth of the electron gyrofrequency. The cone angle between wave vector and ambient field is usually smaller than 1.5^°.

Domaines: Océan, Atmosphère; Sciences de la Terre

W. Baumjohann, R. A. Treumann, E. Georgescu, G. Haerendel, K.-H. Fornacon, et al.. Waveform and packet structure of lion roars. Annales Geophysicae, 1999, 17 (12), pp.1528-1534. ⟨hal-00316721⟩