Observations of lion roars in the magnetosheath by the STAFF/DWP experiment on the Double Star TC-1 spacecraft

Lion roars are intense, short duration packets of whistler mode waves, observed in the magnetosheath. They are typically seen coincident with the magnetic field minima of mirror mode waves. The orbit of the Double Star TC-1 spacecraft (570 km by 78970 km, inclination at 28.5 degrees) is ideal for observations of lion roars as the spacecraft is in the magnetosheath more than 50% of the time when the apogee is on the dayside. The STAFF/DWP experiment provides the spectral matrix of the three magnetic components at 27 frequencies in the range 10 Hz to 4 kHz, with one second time resolution, and also the waveform up to 180 Hz at a low duty cycle. The characteristics of lion roars observed are reported. The maximum lion roar intensities appear higher than reported by most previous studies. The electron temperature anisotropy is estimated from the lion roar frequency ratios, and is in reasonably good agreement with plasma measurements. This indicates the presence of a trapped electron component in the mirror mode.