Cluster observations in the magnetosheath – Part 2: Intensity of the turbulence at electron scales, Ann

Abstract. We analyse the power spectral density δB2 and δE2 of the magnetic and electric fluctuations measured by Cluster 1 (Rumba) in the magnetosheath during 23 h, on four different days. The frequency range of the STAFF Spectral Analyser (f =8 Hz to 4 kHz) extends from about the lower hybrid frequency, i.e. the electromagnetic (e.m.) range, up to about 10 times the proton plasma frequency, i.e. the electrostatic (e.s.) range. In the e.m. range, we do not con-sider the whistler waves, which are not always observed, but rather the underlying, more permanent fluctuations. In this e.m. range, δB2 (at 10 Hz) increases strongly while the lo-cal angle 2BV between the magnetic field B and the flow velocity V increases from 0 ◦ to 90◦. This behaviour, also observed in the solar wind at lower frequencies, is due to the Doppler effect. It can be modelled if we assume that, for th