First ELF wave measurements with the Equator-S magnetometer

The magnetometer onboard the Equator-S satellite is very sensitive and has a high sampling rate of up to 128 Hz. These specifications allow for the first 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 0.2 - 1 sec. They are right-hand circularly polarized shear waves with typical amplitudes of 0.5 - 1 nT at frequencies of 15 - 40 Hz, i.e., around one, tenth of the electron gyrofrequency. (C) 1999 COSPAR. Published by Elsevier Science Ltd.